U.S. Climate Change Science Program

Synthesis and Assessment Product 4.6

September 2008

Analyses of the Effects 

of Global Change on 

Human Health and Welfare 

and Human Systems
FEDERAL EXECUTIVE TEAM

Director, Climate Change Science Program.......................................................William J. Brennan

Director, Climate Change Science Program Office ................................................ Peter A. Schultz

Lead Agency Principal Representative to Climate Change Science Program, 

National Program Director for the Global Change Research Program, 

U.S. Environmental Protection Agency...................................................................Joel D. Scheraga

Product Lead, Global Ecosystem Research and Assessment Coordinator, 

Global Change Research Program, U.S. Environmental Protection Agency..........Janet L. Gamble

Chair, Synthesis and Assessment Product Advisory Group 

Associate Director, National Center for Environmental 

Assessment, U.S. Environmental Protection Agency......................................... Michael W. Slimak

Synthesis and Assessment Product Coordinator, 

Climate Change Science Program Office............................................................Fabien J.G. Laurier

Special Advisor, National Oceanic and 

Atmospheric Administration ........................................................................................Chad McNutt

EDITORIAL AND PRODUCTION TEAM

Editor, U.S. Environmental Protection Agency.......................................................Janet L. Gamble

Technical Advisor, Climate Change Science Program Office ................................David J. Dokken

Technical Editor, ICF International...........................................................................Melinda Harris

Technical Editor, ICF International.............................................................................Toby Krasney

Reference Coordinator, ICF International .....................................................................Paul Stewart

Reference Coordinator, ICF International .......................................................Dylan Harrison-Atlas

Reference Coordinator, ICF International ...................................................................Sarah Shapiro

Logistical and Technical Support, ICF International .................................................. Lauren Smith

Disclaimer: This document, part of the Synthesis and Assessment Products described in the U.S. Climate 

Change Science Program (CCSP) Strategic Plan, was prepared in accordance with Section 515 of the Treasury 

and General Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554) and the information 

quality act guidelines issued by the U.S. Environmental Protection Agency pursuant to Section 515. The CCSP 

Interagency Committee relies on U.S. Environmental Protection Agency certifications regarding compliance 

with Section 515 and Agency guidelines as the basis for determining that this product conforms with Section 

515. For purposes of compliance with Section 515, this CCSP Synthesis and Assessment Product is an 

“interpreted product” as that term is used in U.S. Environmental Protection Agency guidelines and is classified 

as “highly influential.” This document does not express any regulatory policies of the United States or any of its 

agencies, or provide recommendations for regulatory action.
Final Report, Synthesis and Assessment Product 4.6 

 Report by the U.S. Climate Change Science Program 

and the Subcommittee on Global Change Research

Convening Lead Author

Janet L. Gamble, Ph.D., U.S. Environmental Protection Agency

Lead Authors1

Kristie L. Ebi, Ph.D., ESS LLC

Anne E. Grambsch, U.S. Environmental Protection Agency

Frances G. Sussman, Ph.D., Environmental Economics Consulting

Thomas J. Wilbanks, Ph.D., Oak Ridge National Laboratory

1 Contributing authors are acknowledged in individual chapters.

Analyses of the Effects 

of Global Change on 

Human Health and Welfare 

and Human Systems
July 2008 

Members of Congress: 

On behalf of the National Science and Technology Council, the U.S. Climate Change Science Program 

(CCSP) is pleased to transmit to the President and the Congress this Synthesis and Assessment Product 

(SAP), Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems. 

This is part of a series of 21 SAPs produced by the CCSP aimed at providing current assessments of 

climate change science to inform public debate, policy, and operational decisions. These SAPs are also 

intended to help the CCSP develop future program research priorities. This SAP is issued pursuant to 

Section 106 of the Global Change Research Act of 1990 (Public Law 101-606). 

The CCSP’s guiding vision is to provide the Nation and the global community with the science-based 

knowledge needed to manage the risks and capture the opportunities associated with climate and related 

environmental changes. The SAPs are important steps toward achieving that vision and help to translate 

the CCSP’s extensive observational and research database into informational tools that directly address 

key questions being asked of the research community. 

This SAP focuses on the effects of global change on human health and welfare and human systems. It 

was developed with broad scientific input and in accordance with the Guidelines for Producing CCSP 

SAPs, the Federal Advisory Committee Act, the Information Quality Act, Section 515 of the Treasury 

and General Government Appropriations Act for fiscal year 2001 (Public Law 106-554), and the 

guidelines issued by the Environmental Protection Agency pursuant to Section 515. 

We commend the report’s authors for both the thorough nature of their work and their adherence to an 

inclusive review process. 

Sincerely, 

Carlos M. Gutierrez Samuel W. Bodman John H. Marburger III 

Secretary of Commerce Secretary of Energy Director, Office of Science 

and Technology Policy 

Chair, Committee on Vice Chair, Committee on Executive Director, Committee 

Climate Change Science Climate Change Science on Climate Change Science and 

and Technology Integration and Technology Integration Technology Integration 

iv 
ACKNOWLEDGMENTS

This report has been peer reviewed in draft form by individuals identified for their diverse 

perspectives and technical expertise. The expert review and selection of reviewers followed the Office 

of Management and Budget’s Information Quality Bulletin for Peer Review. The purpose of this 

independent review is to provide candid and critical comments that will assist the Climate Change 

Science Program in making this published report as sound as possible and to ensure that the report meets 

institutional standards. The peer review comments, draft manuscript, and response to the peer review 

comments are publicly available at: www.climatescience.gov/Library/sap/sap4-6/default.php.

Environmental Protection Agency Internal Reviewers

We wish to thank the following individuals from the U.S. Environmental Protection Agency for their 

review of the first and, in some cases, later drafts of the report. Reviewers from within EPA included:

Lisa Conner Adam Daigneault Benjamin De Angelo

Barbara Glenn Doug Grano Matthew Heberling

Ju-Chin Huang Stephen Newbold Jason Samenow

Sara Terry

National Center for Environmental Assessment, 

Global Change Research Program 

We extend our thanks to our colleagues in the Global Change Research Program who contributed 

thoughtful insights, reviewed numerous drafts, and helped with the production of the report.

John Thomas Christopher Weaver

Federal Agency Reviewers

Likewise, we thank the reviewers from within the federal “family.” Reviewers from across the federal 

agencies provided their comments during the public comment period. 

Brigid DeCoursey Department of Transportation

Mary Gant National Institutes of Environmental Health Sciences/NIH

Indur M. Goklany Department of Interior

Charlotte Skidmore Office of Management and Budget

Samuel P. Williamson Office of the Federal Coordinator for Meteorology

Public Reviewers

We also extend our thanks to the reviewers who provided their comments during the public comment 

period, included individuals from the public. 

William Fang Edison Electric Institute

Katherine Farrell AACDH

Hans Martin Fuessel PICIR

Eric Holdsworth Edison Electric Institute

John Kinsman Edison Electric Institute

Kim Knowlton Natural Resources Defense Council

Sabrina McCormick Michigan State University

J. Alan Roberson American Water Works Association

Gina Solomon Natural Resources Defense Council
Human Impacts of Climate Change Advisory Committee (HICCAC)

Finally, we are indebted to the thoughtful review provided by a Federal Advisory Committee convened by the 

U.S. Environmental Protection Agency to provide an independent expert review of the SAP 4.6. The HICCAC 

panel met in October 2007 to discuss their findings and recommendations for the report. Following extensive 

revisions to the report, the HICCAC reconvened by teleconference in January 2008 to review the authors’ 

response to comments. The panel’s review of the report has contributed to a markedly improved document.

Chair Tom Dietz Michigan State University

Co-chair Barbara Entwisle University of North Carolina

Members Howard Frumkin Centers for Disease Control and Prevention

Peter Gleick Pacific Institute

Jonathan Patz University of Wisconsin

Roger Pulwarty NOAA

Eugene Rosa Washington State University

Susan Stonich University of California at Santa Barbara

Thanks are also in order to Joanna Foellmer, the Designated Federal Official from within the National Center 

for Environmental Assessment who organized and managed the HICCAC. 

ICF International

We thank our colleagues at ICF International for their support—logistical and technical—in preparing the 

report. We wish to extend special thanks to Melinda Harris and Randy Freed. 

Summary

It has been an honor and a pleasure to work with all of the people named above as well as the many colleagues 

we have encountered in the process of preparing this report. We hope that this document will be a positive step 

forward in our efforts to assess the impacts of climate change on human systems and to evaluate opportunities 

for adaptation. 
AUTHOR TEAM FOR THIS REPORT

Executive Summary Convening Lead Author: Janet L. Gamble, U.S. EPA 

Lead Authors: Kristie L. Ebi, ESS LLC; Frances G. Sussman, Environmental 

Economics Consulting; Thomas J. Wilbanks, Oak Ridge National Laboratory

Contributing Authors: Colleen Reid, ASPH Fellow; John V. Thomas, U.S. EPA; 

Christopher P. Weaver, U.S. EPA; Melinda Harris, ICF International; Randy Freed, ICF 

International 

Chapter 1 Convening Lead Author: Janet L. Gamble, U.S. EPA

Lead Authors: Kristie L. Ebi, ESS LLC; Anne Grambsch, U.S. EPA; Frances G. 

Sussman, Environmental Economics Consulting; Thomas J. Wilbanks, Oak Ridge 

National Laboratory

Contributing Authors: Colleen E. Reid, ASPH Fellow; Katharine Hayhoe, Texas Tech 

University; John V. Thomas, U.S. EPA; Christopher P. Weaver, U.S. EPA

Chapter 2 Lead Author: Kristie L. Ebi, ESS LLC

Contributing Authors: John Balbus, Environmental Defense; Patrick L. Kinney, 

Columbia University; Erin Lipp, University of Georgia; David Mills, Stratus Consulting; 

Marie S. O’Neill, University of Michigan; Mark Wilson, University of Michigan

Chapter 3 Lead Author: Thomas J. Wilbanks, Oak Ridge National Laboratory

Contributing Authors: Paul Kirshen, Tufts University; Dale Quattrochi, NASA/

Marshall Space Flight Center; Patricia Romero-Lankao, NCAR; Cynthia Rosenzweig, 

NASA/Goddard; Matthias Ruth, University of Maryland; William Solecki, Hunter 

College; Joel Tarr, Carnegie Mellon University

Contributors: Peter Larsen, University of Alaska-Anchorage; Brian Stone, Georgia Tech

Chapter 4 Lead Author: Frances G. Sussman, Environmental Economics Consulting 

Contributing Authors: Maureen L. Cropper, University of Maryland at College Park; 

Hector Galbraith, Galbraith Environmental Sciences LLC.; David Godschalk, University 

of North Carolina at Chapel Hill; John Loomis, Colorado State University; George Luber, 

Centers for Disease Control and Prevention; Michael McGeehin, Centers for Disease 

Control and Prevention; James E. Neumann, Industrial Economics, Inc.; W. Douglass 

Shaw, Texas A&M University; Arnold Vedlitz, Texas A&M University; Sammy Zahran, 

Colorado State University

Chapter 5 Convening Lead Author: Janet L. Gamble, U.S. EPA

Lead Authors: Kristie L. Ebi, ESS LLC; Frances G. Sussman, Environmental 

Economics Consulting; Thomas J. Wilbanks, Oak Ridge National Laboratory

Contributing Authors: Colleen E. Reid, ASPH Fellow; John V. Thomas, U.S. EPA; 

Christopher P. Weaver, U.S. EPA
vi

For the Report as a Whole:

CCSP, 2008: Analyses of the effects of global change on human health and welfare and human systems. A Report by the U.S. 

Climate Change Science Program and the Subcommittee on Global Change Research. [Gamble, J.L. (ed.), K.L. Ebi, F.G. Sussman, 

T.J. Wilbanks, (Authors)]. U.S. Environmental Protection Agency, Washington, DC, USA.

For Executive Summary:

Gamble, J.L., K.L. Ebi, F.G. Sussman, T.J. Wilbanks, C. Reid, J.V. Thomas, C.P. Weaver, M. Harris, and R. Freed, 2008: Executive 

Summary. In: Analyses of the effects of global change on human health and welfare and human systems. A Report by the U.S. 

Climate Change Science Program and the Subcommittee on Global Change Research. [Gamble, J.L. (ed.), K.L. Ebi, F.G. Sussman, 

T.J. Wilbanks, (Authors)]. U.S. Environmental Protection Agency, Washington, DC, USA, p. 1–11.

For Chapter 1:

Gamble, J.L., K.L. Ebi, A. Grambsch, F.G. Sussman, T.J. Wilbanks, C.E. Reid, K. Hayhoe, J.V. Thomas, and C.P. Weaver, 2008: 

Introduction. In: Analyses of the effects of global change on human health and welfare and human systems. A Report by the U.S. 

Climate Change Science Program and the Subcommittee on Global Change Research. [Gamble, J.L. (ed.), K.L. Ebi, F.G. Sussman, 

T.J. Wilbanks, (Authors)]. U.S. Environmental Protection Agency, Washington, DC, USA, p. 13–37.

For Chapter 2:

Ebi, K.L., J. Balbus, P.L. Kinney, E. Lipp, D. Mills, M.S. O’Neill, and M. Wilson, 2008: Effects of Global Change on Human 

Health. In: Analyses of the effects of global change on human health and welfare and human systems. A Report by the U.S. Climate 

Change Science Program and the Subcommittee on Global Change Research. [Gamble, J.L. (ed.), K.L. Ebi, F.G. Sussman, T.J. 

Wilbanks, (Authors)]. U.S. Environmental Protection Agency, Washington, DC, USA, p. 39–87.

For Chapter 3:

Wilbanks, T.J., P. Kirshen, D. Quattrochi, P. Romero-Lankao, C. Rosenzweig, M. Ruth, W. Solecki, and J. Tarr, 2008: Effects of 

Global Change on Human Settlements. In: Analyses of the effects of global change on human health and welfare and human systems. 

A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [Gamble, J.L. (ed.), 

K.L. Ebi, F.G. Sussman, T.J. Wilbanks, (Authors)]. U.S. Environmental Protection Agency, Washington, DC, USA, p. 89–109.

For Chapter 4:

Sussman, F.G., M.L. Cropper, H. Galbraith, D. Godschalk, J. Loomis, G. Luber, M. McGeehin, J.E. Neumann, W.D. Shaw, A. 

Vedlitz, and S. Zahran, 2008: Effects of Global Change on Human Welfare. In: Analyses of the effects of global change on human 

health and welfare and human systems. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global 

Change Research. [Gamble, J.L. (ed.), K.L. Ebi, F.G. Sussman, T.J. Wilbanks, (Authors)]. U.S. Environmental Protection Agency, 

Washington, DC, USA, p. 111–168.

For Chapter 5: 

Gamble, J.L., K.L. Ebi, F.G. Sussman, T.J. Wilbanks, C. Reid, J.V. Thomas, and C.P. Weaver, 2008: Common Themes and Research 

Recommendations. In: Analyses of the effects of global change on human health and welfare and human systems. A Report by 

the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [Gamble, J.L. (ed.), K.L. Ebi, F.G. 

Sussman, T.J. Wilbanks, (Authors)]. U.S. Environmental Protection Agency, Washington, DC, USA, p. 169–176.

RECOMMENDED CITATIONS
TABLE OF CONTENTS

Executive Summary

Abstract ..................................................................................................................1

ES.1 Climate Change and Vulnerability ...............................................................1

ES.2 Climate Change and Human Health...........................................................3

ES.3 Climate Change and Human Settlements..................................................8

ES.4 Climate Change and Human Welfare .......................................................10

CHAPTER

1 Introduction....................................................................................................13

1.1 Scope and Approach of SAP 4.6 ...................................................................13

1.2 Climate Change in the United States: 

Context for an Assessment of Impacts on Human Systems ..............16

1.2.1 Rising Temperatures ......................................................................17

1.2.2 Trends in Precipitation ..................................................................18

1.2.3 Rising Sea Levels and Erosion of Coastal Zones.........................19

1.2.4 Changes in Extreme Conditions ..................................................20

1.3 Population Trends and Migration Patterns: 

A Context for Assessing Climate-related Impacts ..............................22

1.3.1 Trends in Total U.S. Population .....................................................22

1.3.2 Migration Patterns.........................................................................24

1.4 Complex Linkages: The Role of Non-climate Factors ................................26

1.4.1 Economic Status ............................................................................26

1.4.2 Technology ......................................................................................27

1.4.3 Infrastructure.................................................................................27

1.4.4 Human and Social Capital and Behaviors ...................................28

1.4.5 Institutions......................................................................................29

1.4.6 Interacting Effects..........................................................................29

1.5 Reporting Uncertainty in SAP 4.6................................................................30

1.6 References.......................................................................................................32

2 Effects of Global Change on Human Health ...............................................39

2.1 Introduction....................................................................................................39

2.2 Observed Climate-sensitive Health Outcomes in the United States ......40

2.2.1 Thermal Extremes: Heat Waves...................................................40

2.2.2 Thermal Extremes: Cold Waves ...................................................42

	 2.2.3 Extreme Events: Hurricanes, Floods, andWildfires....................42

2.2.4 Indirect Health Impacts of Climate Change...............................44

2.3 Projected Health Impacts of Climate Change in the United States ........50

2.3.1 Heat-related Mortality ..................................................................50

	 2.3.2 Hurricanes, Floods,Wildfires and Health Impacts .....................52

2.3.3 Vector-borne and Zoonotic Diseases ...........................................53

2.3.4 Water- and Food-borne Diseases .................................................53

2.3.5 Air Quality Morbidity and Mortality ............................................53

2.4 Vulnerable Regions and Subpopulations ......................................................61

2.4.1 Vulnerable Regions.........................................................................61

	 2.4.2 Specific Subpopulations at Risk....................................................62

2.5 Adaptation ......................................................................................................65

2.5.1 Actors and Their Roles and Responsibilities for Adaptation......66

2.5.2 Adaptation Measures to Manage 

Climate Change-Related Health Risks .................................................68

2.6 Conclusions.....................................................................................................68

2.7 Expanding the Knowledge Base....................................................................73

2.8 References.......................................................................................................75
3 Effects of Global Change on Human Settlements......................................89

3.1 Introduction....................................................................................................89

3.1.1 Purpose...........................................................................................89

3.1.2 Background ....................................................................................89

3.1.3 Current State of Knowledge.........................................................90

3.2 Climate Change Impacts and the 

Vulnerabilities of Human Settlements .................................................90

3.2.1 Determinants of Vulnerability ......................................................90

3.2.2 Impacts of Climate Change on Human Settlements.................92

3.2.3 The Interaction of Climate Impacts 

with Non-climate Factors ......................................................................96

3.2.4 Realizing Opportunities from 

Climate Change in the United States...................................................98

3.2.5 Examples of Impacts on 

Metropolitan Areas in the United States .............................................98

3.3 Opportunities for Adaptation of 

Human Settlements to Climate Change............................................100

3.3.1 Perspectives on Adaptation by Settlements .............................101

3.3.2 Major Categories of Adaptation Strategies ..............................102

3.3.3 Examples of Current Adaptation Strategies.............................103

3.3.4 Strategies to Enhance Adaptive Capacity .................................104

3.4 Conclusions...................................................................................................104

3.5 Expanding the Knowledge Base..................................................................105

3.6 References.....................................................................................................106

4 Effects of Global Change on Human Welfare............................................111

4.1 Introduction..................................................................................................111

4.2 Human Welfare, Well-being, and Quality of Life .......................................112

4.2.1 Individual Measures of Well-being..............................................114

4.2.2 The Social Indicators Approach..................................................115

4.2.3 A Closer Look at Communities..................................................120

4.2.4 Vulnerable Populations, Communities, and Adaptation...........123

4.3 An Economic Approach to Human Welfare ..............................................124

4.3.1 Economic Valuation .....................................................................126

4.3.2 Impacts Assessment and Monetary Valuation ..........................127

4.3.3 Human Health..............................................................................128

4.3.4 Ecosystems ...................................................................................133

4.3.5 Recreational Activities and Opportunities................................140

4.3.6 Amenity Value of Climate ...........................................................147

4.4 Conclusions...................................................................................................151

4.5 Expanding the Knowledge Base..................................................................153

4.6 References.....................................................................................................154

4.7 Appendix .......................................................................................................163

TABLE OF CONTENTS

viii
5 Common Themes and Research Recommendations ...............................169

5.1 Synthesis and Assessment Product 4.6: Advances in the Science ...........169

5.1.1 Complex Linkages and a Cascading 

Chain of Impacts Across Global Changes...........................................169

5.1.2 Changes in Climate Extremes and Climate Averages .............170

5.1.3 Vulnerable Populations and Vulnerable Locations ....................171

5.1.4 The Cost of and Capacity for Adaptation..................................172

5.1.5 An Integrative Framework..........................................................172

5.2 Expanding the Knowledge Base..................................................................173

5.2.1 Human Health Research Gaps ...................................................174

5.2.2 Human Settlements Research Gaps..........................................175

5.2.3 Human Welfare Research Gaps..................................................176

6 Glossary and Acronyms ...............................................................................177

TABLE OF CONTENTS

ix

EXECUTIVE 

SUMMARY

1

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Executive Summary

Convening Lead Author: Janet L. Gamble, U.S. Environmental 

Protection Agency

Lead Authors: Kristie L. Ebi, ESS, LLC; Frances G. Sussman, 

Environmental Economics Consulting; Thomas J. Wilbanks, Oak Ridge 

National Laboratory

Contributing Authors: Colleen Reid, ASPH Fellow; John V. Thomas, 

U.S. Environmental Protection Agency; Christopher P. Weaver, U.S. 

Environmental Protection Agency; Melinda Harris, ICF International; 

Randy Freed, ICF International 

ES.1 CLIMATE CHANGE

AND VULNERABILITy

Climate variability and change challenge even 

the world’s most advanced societies. At a very 

basic level, climate affects the costs of providing 

comfort in our homes and work places. A 

favorable climate can provide inputs for a good 

life: adequate fresh water supplies; products 

from the ranch, the farm, the forests, the rivers, 

and the coasts; pleasure derived from tourist 

destinations and from nature, biodiversity, and 

outdoor recreation. Climate not only supports 

the provision of many goods and services, but 

also affects the spread of some diseases and 

the prevalence of other health problems. It 

is also associated with threats from extreme 

events and natural disasters such as tropical 

storms, riverine and coastal flooding, wildfires, 

droughts, wind, hail, ice, heat, and cold. 

This report examines the impacts on human 

society of global change, especially those 

associated with climate change. The impact 

assessments in this report do not rely on 

specific emissions or climate change scenarios 

but, instead, rely on the existing scientific 

literature with respect to our understanding 

of climate change and its impacts on human 

health, settlements, and well-being in the United 

States. Because climate change forecasts are 

generally not specific enough for the scale of 

Climate change, interacting with changes in land use and demographics, will affect important 

human dimensions in the United States, especially those related to human health, settlements, and 

welfare. The challenges presented by population growth, an aging population, migration patterns, 

and urban and coastal development will be affected by changes in temperature, precipitation, and 

extreme climate-related events. In the future, with continued global warming, heat waves and heavy 

downpours are very likely to further increase in frequency and intensity. Cold days and cold nights 

are very likely to become much less frequent over North America. Substantial areas of North 

America are likely to have more frequent droughts of greater severity. Hurricane wind speeds, 

rainfall intensity, and storm surge levels are likely to increase. Other changes include measurable 

sea level rise and increases in the occurrence of coastal and riverine flooding. The United States 

is certainly capable of adapting to the collective impacts of climate change. However, there will 

still be certain individuals and locations where the adaptive capacity is less and these individuals 

and their communities will be disproportionally impacted by climate change. 

This report— Synthesis and Assessment Product 4.6 (SAP 4.6)—focuses on impacts of global 

climate change, especially impacts on three broad dimensions of the human condition: human 

health, human settlements, and human welfare. SAP 4.6 has been prepared by a team of experts 

from academia, government, and the private sector in response to the mandate of the U.S. 

Climate Change Science Program’s Strategic Plan (2003). The assessment examines potential 

impacts of climate change on human society, opportunities for adaptation, and associated 

recommendations for addressing data gaps and near- and long-term research goals.
The U.S. Climate Change Science Program Executive Summary

2

local decision-making, this report adopts a 

vulnerability perspective in assessing impacts 

on human society. 

A vulnerability approach focuses on estimating 

risks or opportunities associated with possible 

impacts of climate change, rather than on 

estimating (quantitatively) the impacts 

themselves, which would require far more 

detailed information about future conditions. 

Vulnerabilities are shaped not only by existing 

exposures, sensitivities, and adaptive capacities 

but also by responses to risks. For example, 

Boston is generally more vulnerable to heat 

waves than Dallas because there are fewer airconditioned homes in Boston than in Dallas. 

At the same time, human responses (e.g., the 

elderly not using air-conditioning) also are an 

important determinant of impacts. This leads to 

our conclusion that climate change will result 

in regional differences in impacts in the United 

States not only due to a regional pattern of 

changes in climate but the regional nature of our 

communities in adapting to these changes. 

In the United States, we are observing the 

evidence of long-term changes in temperature 

and precipitation consistent with global 

warming. Changes in average conditions are 

being realized through rising temperatures, 

changes in annual and seasonal precipitation, 

and rising sea levels. Observations also indicate 

there are changes in extreme conditions, such 

as an increased frequency of heavy rainfall 

(with some increase in flooding), more heat 

waves, fewer very cold days, and an increase 

in areas affected by drought. There have been 

large fluctuations in the number of hurricanes 

from year to year, which make it difficult to 

discern trends. Evidence suggests that the 

intensity of Atlantic hurricanes and tropical 

storms has increased over the past few decades. 

However, changes in frequency are currently 

too uncertain for confident projection. 

Changes in the size of the population, including 

especially sensitive sub-populations, and their 

geographic distribution across the landscape 

need to be accounted for when assessing climate 

variability and change impacts. According to 

the Census Bureau’s middle series projection, 

by 2100 the U.S. population will increase to 

some 570 million people. Moreover, the elderly 

population is increasing rapidly and many 

health assessments identify them as more 

vulnerable than younger age groups to a range of 

health impacts associated with climate change. 

Although numbers produced by population 

projections are important, nearly all trends point 

to more Americans living in areas that may be 

especially vulnerable to the effects of climate 

change. Many rapidly growing cities and towns 

in the Mountain West may also experience 

decreased snow pack during winter and earlier 

spring melting, leading to lower stream flows, 

particularly during the high-demand period of 

summer. Similarly, coastal areas are projected 

to continue to increase in population, with 

associated increases in population at risk over 

the next several decades. 

Climate is only one of a number of global 

changes that affect human well-being. Nonclimate processes and stresses interact with 

climate change, determining the overall severity 

of climate impacts. Socioeconomic factors that 

can influence exposures, vulnerability, and 

impacts include population, economic status, 

technology, infrastructure, human capital and 

social context and behaviors, and institutions. 

Trends in these factors alter anticipated impacts 
3

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

from climate because they fundamentally shape 

the nature and scope of human vulnerability. 

Understanding the impacts of climate change 

and variability on the quality of life in the 

United States implies knowledge of how 

these factors vary by location, time, and 

socioeconomic group. 

Climate change will seldom be the sole or 

primary factor determining a population’s or a 

location’s well-being. Ongoing adaptation also 

can significantly influence climate impacts. 

For example, emergency warning systems 

have generally reduced deaths and death rates 

from extreme events, while greater access to 

insurance and broader, government-funded 

safety nets for people struck by natural disasters 

have ameliorated the hardships they face. 

While this assessment focuses on how climate 

change could affect future health, well-being, 

and settlements in the United States, the extent 

of any impacts will depend on an array of nonclimate factors and adaptive measures. Finally, 

the effects of climate change very often spread 

from directly impacted areas and sectors to 

other areas and sectors through extensive and 

complex linkages. In summary, the importance 

of climate change depends on the directness of 

the climate impact coupled with demographic, 

social, economic, institutional, and political 

factors, including, the degree of preparedness.

Consistent with all of the Synthesis and 

Assessment Products being prepared by 

the CCSP, this report includes statements 

regarding uncertainty. Each author team 

assigned likelihood judgments that reflect 

their assessment of the current consensus of 

the science and the quality and amount of 

evidence. The likelihood terminology and 

the corresponding values that are used in this 

report are consistent with the latest IPCC 

Fourth Assessment and are further explained 

in Chapter 1 of this report. As the focus of this 

report is on impacts, it is important to note 

that these likelihood statements refer to the 

statement of the impact, not statements related 

to underlying climatic changes. 

Table ES.1 provides examples of climate change 

impacts that are identified in the chapters for 

human health, settlements, and human welfare 

and includes potential adaptation strategies. 

The list of impacts is not comprehensive, but 

rather includes those that the available evidence 

suggests may occur. It is important to note that 

not all effects have been equally well-studied. 

The effects identified for welfare, in particular, 

should be taken as examples of effects about 

which we have some knowledge, rather than a 

complete listing of all welfare effects.

ES.2 Climate Change 

and Human Health

The United States is a highly developed country 

with a wide range of climates. While there may 

be fewer cases of illness and death associated 

with climate change in the United States than in 

the developing world, we nevertheless anticipate 

increased costs to human health and well being. 

Greater wealth and a more developed public 

health system and infrastructure (e.g., water 

treatment plants, sewers, and drinking water 

systems; roads, rails, and bridges; and flood 

control structures) will continue to enhance 

our capacity to respond to climate change. 

Similarly, governments’ capacities for disaster 

planning and emergency response are key assets 

that should allow the United States to adapt 

to many of the health effects associated with 

climate change. 

It is very likely that heat-related morbidity 

and mortality will increase over the coming 

decades. According to the U.S. Census, the U.S. 

population is aging; the percent of the population 

over age 65 is projected to be 13 percent by 2010 

and 20 percent by 2030 (more than 50 million 
The U.S. Climate Change Science Program Executive Summary

4

Table ES.1 Examples of Possible Impacts (present to 2050) of Climate Variability and Change on Human Health, Settlements, and Welfare in the United States and Potential Adaptation Strategies

Focus Area Climate Event Examples of Possible Impacts Likelihood of Impact Given Climate 

Event Occursa

Potential Adaptation Strategies

HUMAN HEALTH

Extreme temperaturesMore heat waves and higher maximum temperaturesFewer cold waves and higher minimum temperatures

Heat stress/stroke or hyperthermiaUncertain impacts on mortalityb

Very likely in Midwest and Northeast urban centers

Early watch and warning systems and installation of cooling systems in residential and commercial buildings

Changes in precipitation, especially extreme precipitation 

Contaminated water and food supplies with associated gastrointestinal illnesses, including salmonella and giardia

Likely in areas with outdated or oversubscribed water treatment plants Improve infrastructure to guard against combined sewer overflow; 

public health response to include “boil water” advisories

Hurricane and storm surge Injuries from flying debris and 

drowning/exposure to contaminated flood waters and to mold and mildew/exposure to carbon monoxide poisoning from portable generators 

Likely in coastal zones of the southeast Atlantic and the Gulf Coast

Increase knowledge and awareness of vulnerability to climate change (e.g., maps showing areas vulnerable to storm surges); public health advisories in immediate aftermath of storms; coordinate storm relief efforts to insure that people receive necessary information for safeguarding their health

Temperature-related effects on ozonec Ozone concentrations more likely 

to increase than decrease; possible contribution to cardiovascular and pulmonary illnesses, including exacerbation of asthma and chronic obstructive pulmonary disorder (COPD) if current regulatory standards are not attained

Likely in urban centers in the midAtlantic and the Northeast Public warning via air quality action days; encourage public transit, 

walking, and bicycling to decrease emissions

Wildfires Degraded air quality, contributing to 

asthma and COPD aggravated

Likely in California, the intermountain West, the Southwest and the Southeast

Public health air quality advisories
5

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Focus Area Climate Event Examples of Possible Impacts Likelihood of Impact Given Climate 

Event Occursa

Potential Adaptation Strategies

HUMAN SETTLEMENTS

Extreme temperaturesMore heat waves and higher maximum temperaturesFewer cold waves and higher minimum temperatures

Increased net energy demand for peak coolingReduced cold-related stresses and costs

Very likely Expand capacity for cooling through 

public utilities; invest in alternative energy sources 

Drought Strain on municipal and agricultural 

water supplies 

Very likely in intermountain West, desert Southwest, and Southeast

Reallocate water among current users; develop water markets to encourage more efficient allocation; identify new sources; encourage conservation of water for personal and public use; develop drought resistant crops 

Hurricane and storm surge

Disruption of infrastructure, including levee systems, river channels, bridges, and highway systems; disruption of residential neighborhoods

Very likely in southern Atlantic Coast and Gulf Coast

Increase knowledge and awareness of climate impacts (e.g., maps showing areas vulnerable to storm surges); harden coastal zones or retreat or relocate; insure against catastrophic loss due to flooding and high winds

Wildfires Disruption of communities and 

property destruction

Very likely in intermountain West, desert Southwest, and Southeast

Clear vegetation away from buildings; issue emergency evacuation orders, prescribed burns, thinning of combustible matter

Late snow fall and early snow melt Disruption of water supplies for 

municipal and agricultural use

Very likely in intermountain West Build reservoirs; conserve water 

supplies; divert supply from agricultural to municipal use; modify operation of existing infrastructure to account for changes in hydrology; develop drought resistant crops, water prices at replacement cost, enable trading by working with states to develop property rights
The U.S. Climate Change Science Program Executive Summary

6

Focus Area Climate Event Examples of Possible Impacts Likelihood of Impact Given Climate 

Event Occursa

Potential Adaptation Strategies

HUMAN WELFARE

Extreme temperaturesMore heat waves and higher maximum temperaturesFewer cold waves and higher minimum temperatures

Discomfort; limit some outdoor activities/recreationLimit some snow- and cold-related recreational opportunities; substantial economic disruption to recreation industry 

Very likely in more northern latitudes of the United States and in AlaskaVery likely in intermountain West, northern New England and the Upper Great Lakes

Public health watch/warning advisoriesEngage in alternative recreation activities

Late autumn snow fall and early spring snow melt 

Limit some snow-related recreational opportunities; substantial economic disruption to recreation industry 

Very likely in intermountain West, northern New England and the Upper Great Lakes 

Engage in alternative recreation activities 

Extreme precipitation events Local flooding and contamination of 

water supplies

Very likely nationwide Issue flood advisories/warnings

Hurricane and coastal storms At-risk properties experience 

flood and wind damage; individuals experience disruption to daily life

Very likely in coastal zone of the Gulf Coast and the southern Atlantic

Relocate dwellings and business, and reinforce structures and infrastructure to reduce disruptions

a Based on impacts identified in the published, peer-reviewed literature and expert opinion. Does not include an evaluation of likelihood of the climate event. May include some adaptation (e.g., 

in the baseline estimate) but generally does not account for additional changes or developments in adaptive capacity.

b Many factors contribute to winter mortality, making highly uncertain how climate change could affect mortality. No projections have been published for the United States that incorporates 

critical factors, such as the influence of influenza outbreaks.

c If areas remain in compliance with National Ambient Air Quality Standards, people will not be exposed to unhealthy air (i.e., cardiovascular and pulmonary illnesses will not occur). More 

stringent emissions controls may be required to remain in compliance although this is uncertain and additional study is needed. 
7

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

people). Older adults, very young children, and 

persons with compromised immune systems 

are vulnerable to temperature extremes. This 

suggests that temperature-related morbidity 

and mortality are likely to increase. Similarly, 

heat-related mortality affects poor and minority 

populations disproportionately, in part due to 

lack of air conditioning. The concentration of 

poverty in inner city neighborhoods leads to 

disproportionate adverse effects associated with 

urban heat islands.

There is considerable speculation concerning 

the balance of climate change-related decreases 

in winter mortality compared with increases 

in summer mortality. Net changes in mortality 

are difficult to estimate because, in part, much 

depends on complexities in the relationship 

between mortality and the changes associated with 

global change. Few studies have attempted to link 

the epidemiological findings to climate scenarios 

for the United States, and studies that have done so 

have focused on the effects of changes in average 

temperature, with results dependent on climate 

scenarios and assumptions of future adaptation. 

Moreover, many factors contribute to winter 

mortality, making highly uncertain how climate 

change could affect mortality. No projections 

have been published for the United States that 

incorporate critical factors, such as the influence 

of influenza outbreaks.

The impacts of higher temperatures in 

urban areas and likely associated increases 

in tropospheric ozone concentrations can 

contribute to or exacerbate cardiovascular 

and pulmonary illness if current regulatory 

standards are not attained. In addition, 

stagnant air masses related to climate change 

are likely to degrade air quality in some densely 

populated areas. It is important to recognize 

that the United States has a well-developed 

and successful national regulatory program for 

ozone, PM2.5, and other criteria pollutants. That 

is, the influence of climate change on air quality 

will play out against a backdrop of ongoing 

regulatory control that will shift the baseline 

concentrations of air pollutants. Studies to 

date have typically held air pollutant emissions 

constant over future decades (i.e., have examined 

the sensitivity of ozone concentrations to 

climate change rather than projecting actual 

future ozone concentrations). Physical features 

of communities, including housing quality 

and green space, social programs that affect 

access to health care, aspects of population 

composition (level of education, racial/ethnic 

composition), and social and cultural factors are 

all likely to affect vulnerability to air quality.

Hurricanes, extreme precipitation resulting 

in floods, and wildfires all have the potential 

to affect public health through direct and 

indirect health risks. SAP 3.3 indicates that 

there is evidence for increased sea surface 

temperatures in the tropical Atlantic and there 

is a strong correlation to Atlantic tropical storm 

frequency, duration, and intensity. However, a 

valid assessment will require further studies. 

The health risks associated with such extreme 

events are thus likely to increase with the size 

of the population and the degree to which it is 

physically, mentally, or financially constrained 

in its ability to prepare for and respond to 

extreme weather events. For example, coastal 

evacuations prompted by imminent hurricane 

landfall are only moderately successful. Many 

of those who are advised to flee to higher ground 

stay behind in inadequate shelter. Surveys 

find that the public is either not aware of the 

appropriate preventive actions or incorrectly 

assesses the extent of their personal risk.

There will likely be an increase in the spread 

of several food and water-borne pathogens 

among susceptible populations depending on 

the pathogens’ survival, persistence, habitat 

range, and transmission under changing 

climate and environmental conditions. While 

the United States has successful programs to 

protect water quality under the Safe Drinking 

Water Act and the Clean Water Act, some 

contamination pathways and routes of exposure 

do not fall under regulatory programs (e.g., 

dermal absorption from floodwaters, swimming 

in lakes and ponds with elevated pathogen 

levels, etc.). The primary climate-related factors 

that affect these pathogens include temperature, 

precipitation, extreme weather events, and 

shifts in their ecological regimes. Consistent 

with our understanding of climate change on 

human health, the impact of climate on food 

and water-borne pathogens will seldom be the 

only factor determining the burden of human 

injuries, illness, and death.
The U.S. Climate Change Science Program Executive Summary

8

Health burdens related to climate change 

will vary by region. For the continental United 

States, the northern latitudes are likely to 

experience the largest increases in average 

temperatures; they will also bear the brunt 

of increases in ground-level ozone and other 

air-borne pollutants. Because Midwestern and 

Northeastern cities are generally not as well 

adapted to the heat as Southern cities, their 

populations are likely to be disproportionately 

affected by heat related illnesses as heat waves 

increase in frequency, severity, and duration. 

The range of many vectors is likely to extend 

northward and to higher elevations. For some 

vectors, such as rodents associated with 

Hantavirus, ranges are likely to expand, as the 

precipitation patterns under a warmer climate 

enhance the vegetation that controls the rodent 

population. Forest fires, with their associated 

decrements to air quality and pulmonary effects, 

are likely to increase in frequency, severity, 

distribution, and duration in the Southeast, the 

Intermountain West and the West. Table ES.2 

summarizes regional vulnerabilities to a range 

of climate impacts.

Finally, climate change is very likely to 

accentuate the disparities already evident 

in the American health care system. Many 

of the expected health effects are likely to fall 

disproportionately on the poor, the elderly, the 

disabled, and the uninsured. The most important 

adaptation to ameliorate health effects from 

climate change is to support and maintain the 

United States’ public health infrastructure. 

ES.3 Climate Change and

Human Settlements

Effects of climate change on human settlements 

are likely to vary considerably according to 

location-specific vulnerabilities, with the 

most vulnerable areas likely to include Alaska 

with increased permafrost melt, flood-risk 

in coastal zones and river basins, and arid 

areas with associated water scarcity. The main 

climate impacts have to do with changes in the 

intensity, frequency, and location of extreme 

weather events and, in some cases, water 

availability rather than temperature change.

Changes in precipitation patterns will affect 

water supplies nationwide, with precipitation 

varying across regions and over time. Likely 

reductions in snow melt, river flows, and 

groundwater levels, along with increases 

in saline intrusion into coastal rivers and 

groundwater will reduce fresh water supplies. 

All things held constant, population growth 

will increase the demand for drinking water 

even as changes in precipitation will change the 

availability of water supplies. Moreover, storms, 

floods, and other severe weather events are 

likely to affect infrastructure such as sanitation, 

transportation, supply lines for food and energy, 

and communication. Some of the nation’s most 

expensive infrastructure, such as exposed 

structures like bridges and utility networks, 

are especially vulnerable. In many cases, water 

supply networks and stressed reservoir capacity 

interact with growing populations (especially in 

coastal cities and in the Mountain and Pacific 

West). The complex interactions of land use, 

population growth, and dynamics of settlement 

patterns further challenge supplies of water 

for municipal, industrial, and agricultural 

uses. In the Pacific Northwest the electricity 

base dominated by hydropower is directly 

dependent upon water flows from snow melt. 

Reduced hydropower would mean the need 

for supplemental electricity sources, resulting 

in a wide variety of negative ripple effects to 

the economy and to human welfare. Similarly, 

along the West Coast, communities are likely to 

experience greater demands on water supplies 

even as regional precipitation declines and 

average snow packs decrease. 

Communities in risk-prone regions, such as 

coastal zones, have reason to be concerned 

about potential increases in severe weather 

events. The combined effects of severe storms 

and sea level rise in coastal areas or increased 

risks of fire in more arid areas are examples of 

how climate change may increase the magnitude 

of challenges already facing risk-prone regions. 

Vulnerabilities may be especially pronounced 

for rapidly growing and/or larger metropolitan 

areas, where the potential magnitude of both 

impacts and coping requirements are likely to 

be very large. On the other hand, such regions 

have greater opportunity to adapt infrastructure 

and to make decisions that limit vulnerability.
9

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Table ES.2 Summary of Regional Vulnerabilities to Climate-Related Impactsa

United States

Census Regions

Climate-Related Impacts

Early

Snow Melt

Degraded Air 

Quality

Urban Heat 

Island Wildfires Heat Waves Drought Tropical Storms Extreme Rainfall with Flooding Sea Level Rise

New EnglandME VT NH MA RI CT ● ● ● ● ● ● ●

Middle AtlanticNY PA NJ DE ● ● ● ● ● ● ● ●

East North CentralWI MI IL IN OH ● ● ● ● ● ●West North CentralND MN SD IA NE KS MO ● ● ● ● ●

South AtlanticWV VA MD NC SC GA FL DC ● ● ● ● ● ● ● ●

East South CentralKY TN MS AL ● ● ● ●

West South CentralTX OK AR LA ● ● ● ● ● ● ● ●

MountainMT ID WY NV UT CO AZ NM ● ● ● ● ● ●

PacificAK CA WA OR HI ● ● ● ● ● ● ● ● ●

a Based on impacts identified in the published, peer-reviewed literature and expert opinion. 
The U.S. Climate Change Science Program Executive Summary

10

Warming is virtually certain to increase 

energy demand in U.S. cities for cooling in 

buildings while it reduces demands for heating 

in buildings (see SAP 4.5 Effects of Climate 

Change on Energy Production and Use in the 

United States). Demands for cooling during 

warm periods could jeopardize the reliability 

of service in some regions by exceeding the 

supply, especially during periods of unusually 

high temperatures. Higher temperatures also 

affect costs of living and business operation by 

increasing costs of climate control in buildings.

Climate change has the potential not only to 

affect communities directly but also indirectly 

through impacts on other areas linked to 

their economies. Regional economies that 

depend on sectors highly sensitive to climate 

such as agriculture, forestry, water resources, 

or recreation and tourism could be affected 

either positively or negatively by climate 

change. Climate change can add to stress on 

social and political structures by increasing 

management and budget requirements for public 

services such as public health care, disaster risk 

reduction, and even public safety. As sources 

of stress grow and combine, the resilience of 

social and political structures is expected to be 

challenged, especially in locales with relatively 

limited social and political capital. 

Finally, population growth and economic 

development are occurring in those areas 

that are likely to be vulnerable to the effects 

of climate change. Approximately half of the 

U.S. population, 160 million people, live in 

one of 673 coastal counties. Coastal areas—

particularly those on gently sloping coasts and 

zones with gradual land subsidence—will be at 

risk from sea level rise, impacts especially those 

related to severe storms and storm surges. 

ES.4 Climate Change and

Human Welfare

The terms human welfare, quality of life, and 

well-being are often used interchangeably, 

and by a number of disciplines as diverse 

as psychology, economics, health science, 

geography, urban planning, and sociology.

There is a shared understanding that all three 

terms refer to aspects of individual and group 

life that involve living conditions and chances 

of injury, stress, and loss.

Human well-being is typically defined and 

measured as a multi-dimensional concept.

Taxonomies of place-specific well-being or quality 

of life typically converge on six dimensions: 1) 

economic conditions, 2) natural resources and 

amenities, 3) human health, 4) public and private 

infrastructure, including transportation systems, 

5) government and public safety and 6) social 

and cultural resources. Climate change will likely 

have impacts across all of these dimensions—both 

positive and negative. In addition, the positive 

and negative effects of climate change will affect 

broader communities, as networks of households, 

businesses, physical structures, and institutions 

are located together across space and time. 

Quantifying impacts of climate change on 

human well-being requires linking effects in 

quality of life to the projected1 physical effects 

of climate change and the consequent effects 

on human and natural systems. Economic 

analyses provide a means of quantifying and, 

in some cases, placing dollar values on welfare 

effects. However, even in cases where welfare 

effects have been quantified, it is difficult to 

compare and aggregate a range of effects across 

a number of sectors. 

This report examines four types of effects on 

economic welfare: those on ecosystems, human 

health, recreation, and amenities associated 

with climate. Many of the goods and services 

affected by climate are not traded in markets; 

as a result, they can be difficult to value. For 

example, ecologists have already identified a 

number of ecological impacts of climate change, 

including the shifting, break up, and loss of 

certain ecological communities; plant and 

animal extinctions and a loss in biodiversity; 

shifting ranges of plant and animal populations; 

and changes in ecosystem processes, such as 

1 A climate projection is the calculated response of 

the climate system to emissions or concentration 

scenarios of greenhouse gases and aerosols, or radiative forcing scenarios, often based on simulations 

by climate models. Climate projections are distinguished from climate predictions, in that the former 

critically depend on the emissions/concentration/radiative forcing scenario used, and therefore on highly 

uncertain assumptions of future socioeconomic and 

technological development.
11

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

nutrient cycling and decomposition. 

While ecosystems provide a variety 

of services to humans, including 

food and fiber, regulating air and 

water quality, support services such 

as photosynthesis, and cultural 

services such as recreation and 

aesthetic or spiritual values, these 

typically are not traded in markets. 

Little research has been done 

linking these ecological changes 

to changes in services, and still less 

has been done to quantify, or place 

dollar values on, these changes.

Ecosystem impacts also extend 

beyond the obvious direct effects 

within the natural environment to 

indirect effects on human systems. 

For instance, nearly 90 percent of 

Americans take part in outdoor 

recreation. The length of season 

of some of these activities, such as 

hiking, boating, or golfing, may 

be favorably affected by slightly 

increased temperatures. However, 

snow and ice sport seasons are 

likely to be shortened, resulting in 

lost recreation opportunities. The 

net effect is unclear as decrements 

associated with snow-based recreation 

may be more than outweighed by 

increases in other outdoor activities. 

An agenda for understanding 

the impacts of climate change on 

human welfare may require taking 

steps both to develop a framework 

for addressing welfare, and to address the 

data and methodological gaps inherent in 

the estimation and quantification of effects. 

To that end, the study of climate change on 

human welfare is still developing, and, to our 

knowledge, no study has made a systematic 

survey of the full range of welfare impacts 

associated with climate change, much less 

attempted to quantify them. 

CHAPTER

1

13

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Introduction

Convening Lead Author: Janet L. Gamble, U.S. Environmental 

Protection Agency

Lead Authors: Kristie L. Ebi, ESS, LLC; Anne Grambsch, 

U.S. Environmental Protection Agency; Frances G. Sussman, 

Environmental Economics Consulting; Thomas J. Wilbanks, 

Oak Ridge National Laboratory

Contributing Authors: Colleen E. Reid, ASPH Fellow; Katharine 

Hayhoe, Texas Tech University; John V. Thomas, U.S. Environmental 

Protection Agency; Christopher P. Weaver, U.S. Environmental 

Protection Agency

1.1 SCOPE AND APPROACH

OF SAP 4.6

The Global Change Research Act of 1990 (Public 

Law 101-606) calls for the periodic assessment 

of the impacts of global environmental change 

for the United States. In 2001, a series of sector 

and regional assessments were conducted by 

the U.S. Global Change Research Program as 

part of the First National Assessment of the 

Potential Consequences of Climate Variability 

and Change on the United States. Subsequently, 

the U.S. Climate Change Science Program 

developed a Strategic Plan (CCSP, 2003) 

calling for the preparation of 21 synthesis and 

assessment products (SAPs) to inform policy 

making and adaptive management across a 

range of climate-sensitive issues. Synthesis and 

Assessment Product 4.6 examines the effects 

of global change on human systems. This 

product addresses Goal 4 of the five strategic 

goals set forth in the CCSP Strategic Plan to 

“understand the sensitivity and adaptability of 

different natural and managed ecosystems and 

human systems to climate and related global 

changes” (CCSP, 2003). The “global changes” 

assessed in this report include: climate 

variability and change, evolving patterns of 

land use within the United States, and changes 

in the nation’s population. 

While the mandate for the preparation of 

this report calls for evaluating the impacts 

of global change, the emphasis is on those 

impacts associated with climate change. 

Collectively, global changes are human 

problems, not simply problems for the natural 

or the physical world. Hence, this SAP 

examines the vulnerability of human health 

and socioeconomic systems to climate change 

across three foci, including: human health, 

human settlements, and human welfare. The 

three topics are fundamentally linked but 

unique dimensions of global change. 

Human health is one of the most basic and 

direct measures of human welfare. Following 

past assessments of climate change impacts 

on human health, SAP 4.6 focuses on human 

morbidity and mortality associated with 

extreme weather, vector-, water- and foodborne diseases, and changes in air quality in the 

United States. However, it should be noted that 

climate change in other parts of the world could 

impact human health in the United States. (e.g.,

by affecting migration into the U.S., the safety 

of food imported into the U.S., etc.). Adaptation 

is a key component to evaluating human health 

vulnerabilities, including consideration of 

public health interventions (such as prevention, 

response, and treatment strategies) that could 

be revised, supplemented, or implemented to 

protect human health and determine how much 

adaptation could be achieved. 

Settlements are where people live. Humans live 

in a wide variety of settlements in the United 

States, ranging from small villages and towns 

with a handful of people to metropolitan regions 

with millions of inhabitants. In particular, 
The U.S. Climate Change Science Program Chapter 1

14

SAP 4.6 focuses on urban and highly developed 

population centers in the United States. 

Because of their high population density, 

urban areas multiply human health risks, and 

this is compounded by their relatively high 

proportions of the very old, the very young, 

and the poor. In addition, the components of 

infrastructure that support settlements, such as 

energy, water supply, transportation, and waste 

disposal, have varying degrees of vulnerability 

to climate change. 

Welfare is an economic term used to describe 

the state of well-being of humans on an 

individual or collective basis. Human welfare 

is an elusive concept, and there is no single, 

commonly accepted definition or approach to 

thinking about welfare. There is, however, a 

shared understanding that increases in human 

welfare are associated with improvements in 

individual and communal conditions in areas 

such as political power, individual freedom, 

economic power, social contacts, health and 

opportunities for leisure and recreation, 

along with reductions in injury, stress, and 

loss. The physical environment, with climate 

as one aspect, is among many factors that 

can affect human welfare via economic, 

physical, psychological, and social pathways 

that influence individual perceptions of quality 

of life. Some core aspects of quality of life are 

expressed directly in markets (e.g., income, 

consumption, personal wealth, etc.). The focus 

in SAP 4.6 is on non-market effects, although, 

these aspects of human welfare are often 

difficult to measure and value (Mendelsohn et 

al., 1999; EPA, 2000).

The other Synthesis and Assessment Products 

related to CCSP’s Goal 4 include reports on 

climate impacts on sea level rise (SAP 4.1), 

ecosystem changes (SAP 4.2), agricultural 

production (SAP 4.3), adaptive options for 

climate sensitive ecosystems (SAP 4.4), energy 

use (SAP 4.5), and transportation system 

impacts along the Gulf Coast (SAP 4.7). 

Collectively, these reports provide an overview 

of climate change impacts and adaptations 

related to a range of human conditions in the 

United States. 

The audience for this report includes research 

scientists, public health practitioners, resource 

managers, urban planners, transportation 

planners, elected officials and other policy 

makers, and concerned citizens. A recent 

National Research Council analysis of global 

change assessments argues that the best 

assessments have an audience asking for them 

and a broad range of stakeholders (U.S. National 

Research Council, 2007). This report clearly 

identifies the pertinent audience and what 

decisions it will inform.

Chapters 2–4 describe the impacts of climate 

change on human systems and outline 

opportunities for adaptation. SAP 4.6 addresses 

the questions of how and where climate 

change may impact U.S. socio-economic 

systems. The challenge for this project is to 

derive an assessment of risks associated with 

health, welfare, and settlements and to develop 

timely adaptive strategies to address a range 

of vulnerabilities. Risk assessments evaluate 

impacts of climate change across an array of 

characteristics, including: the magnitude of 

risk (both baseline and incremental risks); 

the distribution of risks across populations 

(including minimally impacted individuals as 

compared to maximally exposed individuals); 

and the availability, difficulty, irreversibility, 

and cost of adaptation strategies. While the 

state of science limits the ability to conduct 

formal, quantitative risk assessments, it is 

possible to develop information that is useful 

for formulating adaptation strategies. Primary 

goals for adaptation to climate variability and 

change include the following: 

•	 Avoid maladaptive responses; 

•	 Establish protocols to detect and measure 

risks and to manage risks proactively 

when possible; 
15

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

•	 Leverage technical and institutional 

capacity; 

•	 Re duce cu r re nt v u l ne r abi l it ie s t o 

climate change; 

•	 Develop adaptive capacity to address new 

climate risks that exceed conventional 

adaptive responses; and,

•	 Recognize and respond to impacts that play 

out across time. (Scheraga and Grambsch, 

1998; WHO, 2003; IPCC, 2007b).

The issue of co-benefits is central in the 

consideration of adaptation to climate change. 

Many potential adaptive strategies have cobenefits. Along with helping human populations 

cope with climate change, adaptive strategies 

produce additional benefits. For example:

•	 Creating and implementing early warning 

systems and emergency response plans 

for heat waves can also improve those 

services for other emergency responses 

while improving all-hazards preparedness; 

(Glantz, 2004)

•	 Improving the infrastructure and capacity 

of combined sewer systems to avoid 

overflows due to changes in precipitation 

patterns also has the added benefit of 

decreasing contaminant flows that cause 

beach closings and impact the local 

ecology; (Rose et al., 2001)

•	 A key adaptation technique for settlements 

in coastal zones is to promote maintenance 

or reconstruction of coastal wetlands 

ecosystems, which has the added benefit 

of creation or protection of coastal habitats 

(Rose et al., 2001); and,

•	 Promotion of green building practices 

has added health and welfare benefits as 

improving natural light in office space 

and schools has been shown to increase 

productivity and mental health (Edwards 

and Torcellini, 2002). 

Chapter 2 assesses the potential impacts 

of climate change on human health in the 

United States. Timely knowledge of human 

health impacts may support our public health 

infrastructure in devising and implementing 

strategies to prevent, compensate, or respond 

to these effects. For each of the health 

endpoints, the assessment addresses a number 

of topics, including: 

•	 Reviewing evidence of the cur rent 

burden associated with the identified 

health outcome;

•	 Characterizing the human health impacts 

of current climate variability and projected 

climate change (to the extent that the current 

literature allows);

•	 Discussing adaptation opportunities and 

support for effective decision making; and,

•	 Outlining key knowledge gaps.

Each topic chapter includes research published 

from 2001 through early 2007 in the United 

States, or in Canada, Europe, and Australia 

where results may provide insights for U.S. 

populations. As such, the health chapter 

serves as an update to the Health Sector 

Assessment conducted as part of the First 

National Assessment in 2001. 

Chapter 3 focuses on the climate change 

impacts and adaptations associated with human 

settlements in the United States. The IPCC 

Third and Fourth Assessment Reports (IPCC, 

2001; IPCC, 2007c) conclude that settlements 

are among the human systems that are the 

most sensitive to climate change. For example, 

if there are changes in climate extremes there 

could be serious consequences for human 

settlements that are vulnerable to droughts and 

wildfires, coastal and river floods, sea level 

rise and storm surge, heat waves, land slides, 

and windstorms. However, specific changes in 

these conditions in specific places cannot yet 

be projected with great confidence. Chapter 3 

focuses on the interactions between settlement 

characteristics, climate, and other global 

stressors with a particular focus on urban areas 

and other densely developed population centers 

in the United States. 
The U.S. Climate Change Science Program Chapter 1

16

The scale and complexity of these built 

environments, transportation networks, energy 

and resource demands, and the interdependence 

of these systems and their populaces, suggest 

that urban areas are especially vulnerable to 

multiplying impacts in response to externally 

imposed environmental stresses. The collective 

vulnerability of American urban centers may 

also be determined by the disproportionate 

share of urban growth in areas like the 

Intermountain West or the Gulf Coast. The 

focus of Chapter 3 is on high density or 

rapidly growing settlements and the potential 

for changes over time in the vulnerabilities 

associated with place-based characteristics 

(such as their climate regime, elevation, and 

proximity to coasts and rivers) and spatial 

characteristics (such as whether development 

patterns are sprawling or compact).

Chapter 4 focuses on the impacts of climate 

change on human welfare. To examine the 

impacts of climate change on human welfare, 

this chapter reports on two relevant bodies of 

literature: approaches to welfare that rely on 

both qualitative assessment and quantitative 

measures, and economic approaches that 

monetize, or place money values, on quantitative 

impacts.

Finally, Chapter 5 revisits the research 

recommendations and data gaps of previous 

assessment activities and describes the progress 

to date and the opportunities going forward. In 

addition, Chapter 5 reviews the overarching 

themes derived from Chapters 2–4. 

The remainder of this chapter is designed to 

provide the reader with an overview of the 

current state of knowledge regarding: 

•	 Changes in climate in the united states; 

•	 Population trends, migration patterns, and the 

distribution of people across settlements; 

•	 Non-climate stressors and their interactions 

with climate change to realize complex 

impacts; and,

•	 A discussion of the handling of uncertainty 

in reporting scientific results.

1.2 Climate Change

in the United States: 

Context for an

Assessment of Impacts

on Human Systems

In the following chapters, the authors examine 

the impacts on human society of global change, 

especially those associated with climate 

change. The impact assessments in Chapters 

2–4 do not rely on specific emissions or 

climate change scenarios, but instead rely on 

the existing scientific literature with respect 

to our understanding of climate change and 

its impacts on human health, settlements, and 

human well-being in the United States. This 

report does not make quantitative projections 

of specific impacts in specific locations based 

on specific projections of climate drivers of 

these impacts. Instead the report adopts a 

vulnerability perspective. 

A v ul nerabilit y approach focuses on 

estimating risks or opportunities associated 

with possible impacts of climate change, 

rather than on estimating quantitatively the 

impacts themselves which would require 

far more detailed information about future 

conditions. Vulnerabilities are shaped not 

only by existing exposures, sensitivities, and 

adaptive capacities but also by responses to 

risks. In addition, climate change is not the 

only change confronting human societies: from 

a vulnerability perspective projected changes 

in populations, the economy, technology, 

institutions, infrastructure, and human and 

social capital are among the factors that also 

affect vulnerability to climate change. The 

report reviews historical trends and variability 

to point to vulnerabilities and then, where 

possible, determines the likely direction and 

range of potential climate-related impacts.
17

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

In the United States, we are observing the 

evidence of long-term changes in temperature 

and precipitation consistent with global 

warming. Changes in average conditions are 

being realized through rising temperatures, 

changes in annual and seasonal precipitation, 

and rising sea levels. Observations also indicate 

there are changes in extreme conditions, such as 

an increased frequency of heavy rainfall (with 

some increase in flooding), more heat waves, 

fewer very cold days, and an increase in areas 

affected by drought. Frequencies of tropical 

storms and hurricanes vary considerably from 

year to year and there are limitations in the 

quality of the data, which make it difficult to 

discern trends, but evidence suggests some 

increase in their intensity and duration since 

the 1970s (Christensen et al., 2007).

The following sections provide a brief 

introduction to climate change as a context for the 

following chapters on impacts and adaptation. 

SAP 4.6 does not evaluate climate change 

projections as they are not used quantitatively in 

this assessment. The Intergovernmental Panel 

on Climate Change provides a comprehensive 

evaluation of climate change science. In their 

Summary for Policy Makers (IPCC, 2007a), the 

IPCC reports the following observed changes 

in global climate:

•	 “War ming of the climate system is 

unequivocal, as is now evident from 

observations of increases in global average 

air and ocean temperature, widespread 

melting of snow and ice, and rising global 

average sea level.” 

•	 “Eleven of the last twelve years rank among 

the 12 warmest years in the instrumental 

record of global surface temperatures (since 

1850).”

•	 “Average temperature of the global ocean 

has increased to depths of at least 3000 m and 

that the ocean has been absorbing more than 

80 percent of the heat added to the climate 

system. Such warming causes sea water to 

expand, contributing to sea level rise.”

•	 “Mountain glaciers and snow cover have 

declined on average in both hemispheres.” 

•	 “The frequency of heavy precipitation 

events has increased over most land areas, 

consistent with warming and observed 

increases of atmospheric water vapor.”

•	 “ Wid e s p r e a d ch a n ge s i n e x t r e m e 

temperatures have been observed over the 

last 50 years... Hot days, hot nights, and heat 

waves have become more frequent.”

•	 “There is observational evidence for an 

increase of intense tropical cyclone activity 

in the North Atlantic since about 1970.” 

(IPCC, 2007a)

Note that these changes are for the entire 

globe: changes in the United States may 

be similar or different from these global 

changes. The following sections examine 

U.S. climate trends and historical records 

related to temperature, precipitation, sea 

level rise, and changes in hurricanes and 

other catastrophic events. Information is also 

drawn from the North American Chapter of 

the IPCC Fourth Assessment Report and the 

Climate Change Science Programs Synthesis 

and Assessment Product 3.3: Weather and 

Climate Extremes in a Changing Climate. 

Taken together, this discussion provides 

a context from which to assess impacts of 

climate change on human health, human 

welfare, and human settlements. 

1.2.1 Rising Temperatures 

Climate change is already affecting the United 

States. According to long-term station-based 

observational records such as the Historical 

Climatology Network (Karl et al., 1990; 

Easterling et al., 1999; Williams et al., 2007), 

temperatures across the continental United 

States have been rising at a rate of 0.1°F per 

decade since the early 1900s. Increases in 

average annual temperatures over the last 

century now exceed 1°F (Figure 1.1a). The 

degree of warming has varied by region across 

the United States, with the West and Alaska 
The U.S. Climate Change Science Program Chapter 1

18

experiencing the greatest degree of warming 

(U.S. Environmental Protection Agency, 

2007). These changes in temperature have 

led to an increase in the number of frost-free 

days, with the greatest increases occurring in 

the West and Southwest (Tebaldi et al., 2006). 

The Intergovernmental Panel on Climate 

Change, in its most recent assessment report 

concluded that “Warming of the climate system 

is unequivocal...” (IPCC, 2007a). 

The current generation of global climate models, 

run with IPCC SRES scenarios of future 

greenhouse gas emissions, simulates future 

changes in the earth’s climate system that are 

greater in magnitude and scope than those 

already observed. According to the IPCC, by 

the end of the 21st century, annual surface 

temperature increases are projected to range 

from 2–3°C near the coasts in the conterminous 

United States to more than 5°C in northern 

Alaska. Nationally, annual warming in the United 

States is projected to exceed 2°C, with projected 

increases in summertime temperatures ranging 

between 3 and 5°C (greatest in the Southwest). 

The largest warming is projected to reach 10°C 

for winter temperatures in the northernmost 

parts of Alaska. (IPCC, 2007c). For additional 

information about the modeling results, see 

the IPCC Fourth Assessment Working Group I 

Report, especially Chapter 11: Regional Climate 

Projections (Christensen et al., 2007) 

1.2.2 Trends in Precipitation 

Shifting precipitation patterns have also 

been observed. Over the last century, annual 

precipitation across the continental United 

States has been increasing by an average of 

0.18 inches per decade (Figure 1.1b). Broken 

down by season, winter precipitation around 

the coastal areas, including the West, Gulf, and 

Atlantic coasts, has been increasing by up to 30 

percent while precipitation in the central part of 

the country (the Midwest and the Great Plains) 

has been decreasing by up to 20 percent. Largescale spatial patterns in summer precipitation 

trends are more difficult to identify, as much 

of summer rainfall comes in the form of smallscale convective precipitation. However, it 

appears that there have been increases of 20-80 

percent in summer rainfall over California and 

the Pacific Northwest, and decreases on the 

order of 20 to 40 percent across much of the 

south. The IPCC reports that rainfall is arriving 

in more intense events. (IPCC, 2007a).

El Niño events (a periodic warming of the 

tropical Pacific Ocean between South America 

and the International Date Line) are associated 

with increased precipitation and severe storms 

in some regions, such as the southeast United 

States and the Great Basin region of the western 

United States. El Niño events have also been 

characterized by warmer temperatures and 

decreased precipitation in other areas, such 

as the Pacific Northwest, and parts of Alaska. 

Historically, El Niño events occur about every 

3 to 7 years and alternate with the opposite 

phases of below-average temperatures in the 

eastern tropical Pacific (La Niña). Since 1976-

1977, there has been a tendency toward more 

prolonged and stronger El Niños (IPCC, 2007a). 

However, recent analyses of climate simulations 

indicate no consistent trends in future El Niño 

amplitude or frequency (Meehl et al., 2007).

50.5

51.0

51.5

52.0

52.5

53.0

53.5

54.0

54.5

55.0

55.5

1896 1916 1936 1956 1976 1996

Annual Avg Temperature (degF)

Source: NCDC, 2007

(a)

24

25

26

27

28

29

30

31

32

33

34

1896 1916 1936 1956 1976 1996

Annual Avg Precipitation (inches)

Source: NCDC, 2007

(b)

Figure 1. Observed trends in annual average (a) temperature (oF) and (b) precipitation (inches) across the continental United States 

from 1896 to 2006 (Source: NCDC, 2007) 

Figure 1.1 Observed trends in annual average (a) temperature (°F) 

and (b) precipitation (inches) across the continental United States from 

1896 to 2006 (Source: NCDC, 2007)
19

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Global model simulations summarized in the 

North American Chapter of the IPCC Fourth 

Assessment Report show moderate increases 

in precipitation (10 percent or less) over much 

of the United States over the next 100 years, 

except for the southwest. However, projected 

increases in these simulations are partially 

offset by increases in evaporation, resulting in 

greater drying in the central part of the United 

States. Projections for the central, eastern, 

and western regions of the United States show 

similar seasonal characteristics (i.e., winter 

increases, summer decreases), although there 

is greater consensus for winter increases in 

the north and summer decreases in the south. 

However, uncertainty around the projected 

changes is large (IPCC, 2007b). 

1.2.2.1 Changes in Snow Melt 

and Glacial Retreat 

Warmer temperatures are melting mountain 

glaciers and more winter precipitation in 

northern states is falling as rain instead of snow 

(Huntington et al., 2004). Snow pack is also 

melting faster, affecting stream flow in rivers. 

Over the past 50 years, changes in the timing of 

snow melt has shifted the schedule of snow-fed 

stream flow in the western part of the country 

earlier by 1 to 4 weeks. (Stewart et al., 2005). 

The seasonal “center of stream flow volume” 

(i.e., the date at which half of the expected 

winter-spring stream flow has occurred) also 

appears to be advancing by, on average, one 

day per decade for streams in the Northeast 

(Huntington et al., 2003). 

This trend is projected to continue, with more 

precipitation falling as rain rather than snow, 

and snow season length and snow depth are 

generally projected to decrease in most of the 

country. Such changes tend to favor increased 

risk of winter flooding and lower summer soil 

moisture and streamflows (IPCC, 2007a). 

1.2.3 Rising Sea Levels and 

Erosion of Coastal Zones 

Sea levels are rising and the IPCC concluded 

with high confidence that the rate of sea 

level rise increased from the 19th to the 20th 

centuries (IPCC, 2007a). The causes for 

observed sea level rise over the past century 

include thermal expansion of seawater as it 

warms and changes in land ice (e.g., melting 

of glaciers and snow caps). Over the 20th 

century, sea level was rising at a rate of about 

0.7 inches per decade (1.7 mm/yr ± 0.5 mm). 

For the period 1993 to 2003, the rate was nearly 

twice as fast, at 1.2 inches per decade (3.1 mm/

yr ± 0.7 mm). However, there is considerably 

decadal variability in the tide gauge record, 

so it is unknown whether the higher rate in 

1993 to 2003 is due to decadal variability or an 

increase in the longer-term trend. (Bindoff et 

al., 2007). In the past century, global sea level 

rose 5–8 inches. 

Spatially sea level change varies considerably: 

in some regions, rates are up to several times 

the global mean rise, while in other regions 

sea level is falling. For example, for the midAtlantic coast (i.e., from New York to North 

Carolina), the “effective” or relative sea level 

rise rates have exceeded the global rate due to 

a combination of land subsidence and global 

sea level rise. In this region, relative sea level 

rise rates ranged between 3 to 4 mm per year 

(~1ft per century) over the 20th century. In 

other cases, local sea level rise is less than the 

global average because the land is still rising 

(rebounding) from when ice sheets covered 

the area, depressing the Earth’s crust. Local 

sea levels can actually be falling in some cases 

(for example, the Pacific Northwest coast) if 

the land is rising more than the sea is falling 

(for additional details about sea level rise and 

its effects on U.S. coasts see Synthesis and 

Assessment Product 4.1 Coastal elevations and 

sensitivity to sea level rise). 

Rising global temperatures are projected to 

accelerate the rate of sea level rise by further 

expanding ocean water, melting mountain 

glaciers, and increasing the rate at which 

Greenland and Antarctic ice sheets melt or 

discharge ice into the oceans. Estimates of sea 

level rise for a global temperature increase 

between 1.1 and 6.4°C (the IPCC estimate of 

likely temperature increases by 2100) are about 

7 to 23 inches (0.18m to 0.59m), excluding the 

contribution from accelerated ice discharges 

from the Greenland and Antarctica ice sheets. 

Extrapolating the recent acceleration of ice 

discharges from the polar ice sheets would 

imply an additional contribution up to 8 inches 

(20cm). If melting of these ice caps increases, 

larger values of sea level rise cannot be excluded 

(IPCC, 2007a).
The U.S. Climate Change Science Program Chapter 1

20

1.2.4 Changes in Extreme 

Conditions 

The climatic changes described above are often 

referred to as changes in “average” conditions. 

Most observations of temperature will tend 

to be close to the average: days with very hot 

temperatures happen infrequently. Similarly, 

only rarely will there be days with extremely 

heavy precipitation. Climate change could 

result in a shift of the entire distribution of 

a meteorological variable so that a relatively 

small shift in the mean could be accompanied 

by a relatively large change in the number of 

relatively rare (according to today’s perspective) 

events. For example, with an increase in average 

temperatures, it would be expected there would 

be an increase in the number of very hot days 

and a decrease in the number of very cold days. 

Other, relatively rare, extreme events of concern 

for human health, welfare, and settlements 

include hurricanes, floods and droughts. 

In general, it is difficult to attribute any 

individual extreme event to a changing climate. 

Because extreme events occur infrequently, 

there is typically limited information to 

characterize these events and their trends. In 

addition, extreme events usually require several 

conditions to exist for the event to occur, so 

that linking a particular extreme event to 

a single, specific cause is problematic. For 

some extreme events, such as extremely hot/

cold days or rainfall extremes, there is more 

of an observational basis for analyzing trends, 

increasing our understanding and ability to 

project future changes.

Finally, there are many different aspects 

to extremes. Frequency is perhaps the 

most often discussed but changes in other 

aspects of extremes such as intensity (e.g.,

warmer hot days), time of occurrence (e.g.,

earlier snowmelt), duration (e.g., longer 

droughts), spatial extent, and location are 

also important when determining impacts on 

human systems. 

Synthesis and Assessment Product 3.3 Weather 

and Climate Extremes in a Changing Climate

(CCSP, 2008) has a much more detailed discussion 

of climate extremes that are only very briefly 

described here. The interested reader is referred 

to that report for additional details.

1.2.4.1 Heat and Cold Waves 

Extreme temperatures (e.g., temperatures 

in the upper 90th or 95th percentile of the 

distribution) often change in parallel with 

average temperatures. Since 1950, there are 

more 3-day warm spells (exceeding the 90th 

percentile) when averaged over all of North 

America (Peterson et al., 2008). While the 

number of heat waves has increased, the heat 

waves of the 1930s remain the most severe in 

the U.S. historical record. Mirroring this shift 

toward more hot days is a decrease in unusually 

cold days during the past few decades. There 

has been a corresponding decrease in frost 

days and a lengthening of the frost-free season 

over the past century. The number of frost days 

decreased by four days per year in the United 

States during the 1948-1999 period, with the 

largest decreases, as many as 13 days per 

year, occurring in the western United States 

(Easterling, 2002). For the United States, the 

average length of the frost-free season over the 

20th century increased by almost two weeks 

(Kunkel et al., 2004).

Recent studies have found that there is an 

increased likelihood of more intense, longerlasting, and more frequent heat waves (Meehl 

and Tebaldi, 2004, Schar et al., 2004, Clark et 

al., 2006). As the climate warms, the number 

of frost days is expected to decrease (Cubasch 

et al., 2001) particularly along the northwest 

coast of North America (Meehl et al., 2004). 

SAP 3.3, using a range of greenhouse gas 

emission scenarios and model simulations, found 

that hot days, hot nights, and heat waves are 

very likely to become more frequent, that cold 

days and cold nights are very likely to become 
21

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

much less frequent, and that the number of days 

with frost is very likely to decrease (CCSP, 

2008). Growing season length is related to frost 

days, which is projected to increase in a warmer 

climate in most areas (Tebaldi et al., 2006). 

1.2.4.2 Heavy Precipitation Events 

Over the 20th century, periods of heavy 

downpours became more frequent and more 

intense and accounted for a larger percentage 

of total precipitation (Karl and Knight, 1997; 

Groisman et al., 1999, 2001, 2004, 2005; 

Kunkel et al., 1999; Easterling et al., 2000; 

Kunkel, 2003). These heavy rainfall events 

have increased in frequency by as much as 

100 percent across much of the Midwest and 

Northeast over the past century (Kunkel et 

al., 1999). These findings are consistent with 

observed warming and associated increases in 

atmospheric water vapor. 

The intensity of precipitation events is projected 

to increase, particularly in high latitude areas 

that experience increases in mean precipitation 

(Meehl et al., 2007). In areas where mean 

precipitation decreases (most subtropical and 

mid-latitude regions), precipitation intensity is 

projected to increase but there would be longer 

periods between rainfall events. Precipitation 

extremes increase more than does the mean in 

most tropical and mid- and high-latitude areas. 

Some studies project widespread increases in 

extreme precipitation (Christensen et al., 2007), 

with greater risks of not only flooding from 

intense precipitation, but also droughts from 

greater temporal variability in precipitation. 

SAP 3.3 concluded that, over most regions, 

future precipitation is likely to be less frequent 

but more intense, and precipitation extremes are 

very likely to increase (CCSP, 2008). 

1.2.4.3 Changes in Flooding

Heavy rainfall clearly can lead to flooding, 

but assessing whether observed changes in 

precipitation have lead to similar trends in 

flooding is difficult for a number of reasons. 

In particular, there are many human influences 

on streamflow (e.g., dams, land-use changes, 

etc.) that confound climatic influences. In 

some cases, researchers using the same data 

came to opposite assessments about trends 

in high streamflows (Lins and Slack, 1999, 

2005; Groisman et al., 2001, 2004). Short 

duration extreme precipitation events can lead 

to localized flash flooding, but for large river 

basins, significant flooding will not occur 

from these types of episodes alone; excessive 

precipitation must be sustained for weeks to 

months for flooding to occur. 

1.2.4.4 Changes in Droughts 

An extended period with little precipitation is 

the main cause of drought, but the intensity 

of a drought can be exacerbated by high 

temperatures and winds as well as a lack of 

cloudiness/low humidity, which result in high 

evaporation rates. Droughts occur on a range 

of geographic scales and can vary in their 

duration, in some cases lasting years. The 1930s 

and the 1950s experienced the most widespread 

and severe drought conditions (Andreadis et 

al., 2005), although the early 2000s also saw 

severe droughts in some areas, especially in the 

western United States (Piechota et al., 2004). 

Based on observations averaged over the United 

States, there is no clear overall national trend in 

droughts (CCSP, 2008). Over the past century, 

the area affected by severe and extreme drought 

in the United States each year averaged about 

14 percent: by comparison, in 1934 the area 

affected by drought was as high as 65 percent 

(CCSP, 2008). In recent years, the droughtaffected area ranged between 35 and 40 percent 

(CCSP, 2008). These trends at the national 

level however mask important differences 

in drought conditions at regional scales: one 

area may be very dry while another is wet. 

For example, in the Southwest and parts of the 

interior of the West increased temperatures 

have led to rising drought trends (Groisman et 

al., 2004; Andreadis and Lettenmaier, 2006). 
The U.S. Climate Change Science Program Chapter 1

22

In the Southwest, the 1950s were the driest 

period, though droughts in the past 10 years 

are approaching the 1950s drought (CCSP, 

2008). There are also recent regional tendencies 

toward more severe droughts in parts of Alaska 

(CCSP, 2008).

Several generations of global climate models, 

including the most recent, find an increase 

in summer drying in the mid latitudes in 

a future, warmer climate (Meehl et al., 

2007). This tendency for drying of the midcontinental areas during summer indicates 

a greater risk of droughts in those regions 

(CCSP, 2008). Analyses using several coupled 

global circulation models project an increased 

frequency of droughts lasting a month or longer 

in the Northeast (Hayhoe et al., 2007) and 

greatly reduced annual water availability over 

the Southwest (Milly et al., 2005). SAP 3.3 

concluded that droughts are likely to become 

more frequent and severe in some regions of the 

country as higher air temperatures increase the 

potential for evaporation. 

1.2.4.5 Changes in Hurricanes 

Assessing changes in hurricanes is difficult: 

there have been large fluctuations in the number 

of hurricanes from year to year and from decade 

to decade. Furthermore, it is only since the 

1960s that reliable data can be assembled for 

assessing trends. In general, there is increasing 

uncertainty in the data record the further back 

in time one goes but significant increases in 

tropical cyclone frequency are likely since 1900 

(CCSP, 2008). However, the existing data and 

an adjusted record of tropical storms indicate 

no significant linear trends beginning from 

the mid- to late 1800s to 2005 (CCSP, 2008). 

Moreover, SAP 3.3 concluded that there is no 

evidence for a long-term increase in North 

American mainland land-falling hurricanes.

Evidence suggests that the intensity of Atlantic 

hurricanes and tropical storms has increased over 

the past few decades. SAP 3.3 indicates that there 

is evidence for a human contribution to increased 

sea surface temperatures in the tropical Atlantic 

and there is a strong correlation to Atlantic 

tropical storm frequency, duration, and intensity. 

However, a confident assessment will require 

further studies. An increase in extreme wave 

heights in the Atlantic since the 1970s has been 

observed that is consistent with more frequent 

and intense hurricanes (CCSP, 2008).

For North Atlantic hurricanes, SAP 3.3 

concludes that it is likely that wind speeds and 

core rainfall rates will increase (HendersonSellers et al., 1998; Knutson and Tuleya, 

2004, 2008; Emanuel, 2005). However, SAP 

3.3 concluded that “frequency changes are 

currently too uncertain for confident projection 

(CCSP, 2008).” SAP 3.3 also found that the 

spatial distribution of hurricanes will likely 

change. Storm surge is likely to increase due to 

projected sea level rise, although the degree to 

which this will increase has not been adequately 

studied (CCSP, 2008). 

1.3 Population

Trends and Migration

Patterns: A Context

for Assessing Climaterelated Impacts

Assessments of climate-related risk must 

account for the size of the population, including 

especially sensitive sub-populations and their 

geographic distribution across the landscape. 

The following discussion provides a basis for 

assessing the interactions of global change 

within the larger context of demographic 

trends. In particular, the social characteristics 

of a populace may interact with its spatial 

distribution to produce a non-linear risk. In 

such instances, risk assessments are shaped by 

questions such as: 

•	 Which counties, states, and regions will 

grow most rapidly? 

•	 How many people will live in at-risk areas, 

such as coastal zones, flood plains, and 

arid areas?

•	 What share of retirees will migrate and 

where will they move? 

1.3.1 Trends in Total 

U.S. Population

The U.S. population numbered some 280 

million individuals in 2000.1 In 1900, the U.S. 

population numbered about 76 million people; 

fifty years later the population had roughly 

doubled to 151 million people. 

1 Information on historical U.S population data and 

current population estimates and projections can be 

found at http://www.census.gov/.
23

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Population projections are estimates of 

the population at future dates. They are 

based on assumptions about future births, 

deaths, international migration, and domestic 

migration and represent plausible scenarios of 

future population. 

In 2000 the IPCC published a set of emission 

scenarios for use in the Third Assessment Report 

(Nakicenovic et al., 2000). The SRES scenarios 

were constructed to explore future developments 

in the global environment with special reference 

to the production of greenhouse gases and 

aerosol precursor emissions. The SRES team 

defined four narrative storylines labeled A1, 

A2, B1, and B2, describing the relationships 

between the forces driving greenhouse gas and 

aerosol emissions and their evolution during 

the 21st century for large world regions and 

globally. Each storyline represents different 

demographic, social, economic, technological, 

and environmental developments that diverge 

in increasingly irreversible ways. (Nakicenovic 

et al., 2000)

The U.S. Census Bureau periodically releases 

projections for the resident population of the 

United States based on Census data. The 

cohort-component methodology2 is used in 

these projections. Alternative assumptions of 

fertility, life expectancy, and net immigration 

yield low, middle, and high projections.

2 See Census website for additional details on the 

projection methodology.

Figure 1.2 displays the SRES and Census 

population projections3 for the United States. 

The Census projections span a greater range 

than the SRES scenarios: by 2100 the low 

series projection of 282 million is below the 

current population while the high projection 

is about 1.2 billion, or about four times the 

current population. The Census middle series 

projection is relatively close to the SRES A2 

scenario (570 million vs. 628 million in 2100), 

while the SRES A1/B1 and B2 scenarios fall 

below the Census middle projection. 

1.3.1.1 Aging of the Population

The U.S. population has not only increased 

by 300 percent over the past century, it has 

also shifted in its demographic structure. For 

example, in 1900 less than 4 percent of the 

U.S. population was 65 years or older; currently 

about 12 percent of Americans are 65 or older 

(He et al., 2005). By 2050, the US population 

aged 65 and older is projected to be about 

86 million, or about 21 percent of the total 

population. Nearly 5 percent of the projected 

population in 2050, over 20 million people, will 

be 85 years or older (He et al., 2005). Figure 1.3 

displays the projected age distribution for the 

total resident population of the United States by 

sex for the middle projection series. 

The projected increase in the elderly population 

is an important variable in projections of 

3 The Census projections are based on the 1990 

Census. Preliminary projections based on the 2000 

Census for 2000-2050 are available.

0

100

200

300

400

500

600

700

800

900

1000

2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

In millions

Census 1990 low

Census 1990 mid

Census 1990 high

SRES A1, B1

SRES A2

SRES B2

Figure 1.2 U.S. Population Projections 2000–2100

Data source: Census Population Projections http://www.census.gov/population/www/projections/natsum-T1.html 

SRES Population Projections: http://sres.ciesin.columbia.edu/tgcia/
The U.S. Climate Change Science Program Chapter 1

24

the effects of climate change. The elderly 

are identified in many health assessments as 

more vulnerable than younger age groups to 

a range of health outcomes associated with 

climate change, including injury resulting from 

weather extremes such as heat waves, storms, 

and floods (WHO, 2003; IPCC, 2007b; NAST, 

2001). Aging also can be expected to be 

accompanied by multiple, chronic illnesses 

that may result in increased vulnerability to 

infectious disease (NAST, 2001). Chapter two 

in this report also identifies the elderly as a 

vulnerable subpopulation. 

1.3.2 Migration Patterns

Although numbers produced by population 

projections are important, the striking 

relationship between potential future settlement 

patterns and the areas that may experience 

significant impacts of climate change is the 

critical insight. In particular, nearly all trends 

point to more Americans living in areas that 

may be especially vulnerable to the effects of 

climate change (see Figure 1.4). For example, 

many rapidly growing places in the Mountain 

West may also experience decreased snow 

pack during winter and earlier spring melting, 

leading to lower stream flows, particularly 

during the high-demand period of summer. 

The continued growth of arid states in the West 

is therefore a critical crossroads for human 

settlements and climate change. These states 

are expected to account for one-third of all U.S. 

population growth over the next 25 years (U.S. 

Census Bureau, 2005). The combined effects 

of growing demand for water due to a growing 

population and changes in water supplies 

associated with climatic change pose important 

challenges for these states. For example, a 

study commissioned by the California Energy 

Commission estimated that the Sierra Mountain 

snow pack could be reduced by 12 percent to 

47 percent by 2050 (Cayan et al., 2006). At 

the same time, state projections anticipate an 

additional 20 million Californians by that date 

(California Department of Finance, 2007).

Growth in coastal population has kept pace 

with population growth in other parts of the 

country, but given the small land area of the 

coasts, the density of coastal communities has 

been increasing (Crossett et al., 2004). More 

than 50 percent of the U.S. population now 

lives in the coastal zone, and coastal areas are 

projected to continue to increase in population, 

with associated increases in population density, 

over the next several decades. The overlay of 

this migration pattern with climate change 

projections has several implications. Perhaps 

the most obvious is the increased exposure of 

people and property to the effects of sea level 

rise and hurricanes (Kunkel et al., 1999). With 

rapidly growing communities near coastlines, 

property damages can be expected to increase 

even without any changes in storm frequency 

or intensity (Changnon et al., 2003). 

1.3.2.1 How Climate Impacts 

Migration Patterns

It is often said that America is a nation of 

movers and data collected for both the 1990 

and 2000 Census support this notion. While 

roughly half of the U.S. population had lived 

in the same house for the previous five years, 

nearly 10 percent had recently moved from out 

-5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 2 3 4 5

 0 - 4

 5 - 9

 10-14

15 - 19

20 - 24

25 - 29

30 - 34

35 - 39

40 - 44

45 - 49

50 - 54

55 - 59

60 - 64

65 - 69

70 - 74

75 - 79

80 - 84

 85+

Male

Female

Figure 1.3 Population Pyramids of the U.S. 2000 and 2050 (Interim Projections based on 2000 Census)

Data source: Census Population Projections http://www.census.gov/ipc/www/usinterimproj/
25

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

of state.4 In other words, during the five year 

period preceding each Census, over 20 million 

Americans had moved across state lines and 

half of those moved to different regions.

Although many forces shape domestic migration, 

climate is a key element of perceived quality of 

life. In turn, quality of life can be an important 

factor driving the relocation decisions of 

households and businesses. The popularity 

of the Places Rated Almanac and other 

publications ranking cities’ livability illustrates 

the concept’s importance. Additionally, many 

of the indicators in these reports are based 

directly on climatic conditions (average winter 

and summer temperature, precipitation, days of 

sunshine, humidity, etc.). 

A range of studies have attempted to quantify 

how natural amenities, including a favorable 

climate, affect migration. While the methods 

vary5 the conclusions are similar. In general:

4 http://www.census.gov/Press-Release/www/2002/

sumfile3.html

5 Study methodologies include: aggregate studies of 

population changes alongside regional characteristics, explanatory models developed from individual 

migration data and individual surveys.

•	 People move for a variety of reasons other 

than climate, such as: proximity to family 

and friends, employment opportunities, 

lower cost of living, and aesthetics; 

•	 Areas with natural amenities that are close 

to urban centers have attracted the largest 

numbers of in-migrants (Serow, 2001);

•	 Climate’s impact on migration varies by 

income with lower income groups also 

moving to colder areas in which their wages 

are likely to compare more favorably to the 

cost of living (Rebhun and Raveh, 2006);

•	 For retirees, weather is a far more important 

rationale cited for moving out of an area than 

moving to an area (AARP, 2006); and,

•	 Population growth in rural counties 

is strongly related to a more favorable 

climate and other key natural amenities 

(McGranahan, 1999). In addition, new 

information technologies may make it 

possible for some urban dwellers to move to 

and work from rural regions.

Figure 1.4: U.S. Population and Growth Trends with evidence of more pronounced growth projected along 

the coasts, in urban centers, and in cities in the South and West (NAST, 2001)

U.S. Population and Growth Trends

Change in county population, 1970-2030

Each block on map illustrations on county in the U.S. The height of each 

block is proportional to that county’s population density in the year 2000, 

so the volume of the block is proportioned to the county’s total population. 

The color of each block shows the county’s projected change in population 

between 1970 and 2030, with shades of orange denoting increases and blue 

denoting decreases. The patterns of recent population change, with growth 

concentrated along the coasts, in cities, and in the South and West, are 

projected to continue.

Projected change in county 

population (percent), 1970 to 2030

>+250% (highest +3,877%)

+50% ti 250%

+5% to 50%

-5% to +5%

-20% to -5%

-40% to -20%

<-40% (lowest -60%)
The U.S. Climate Change Science Program Chapter 1

26

1.4. Complex Linkages: 

The Role of Non-climate

Factors

Climate is only one of a number of global 

changes that affect human well-being. These 

non-climate processes and stresses interact with 

climate change, determining the overall severity 

of climate impacts. Moreover, climate change 

impacts can spread from directly impacted 

areas and sectors to other areas and sectors 

through extensive and complex linkages (IPCC, 

2007b). Evaluating future climate change 

impacts therefore requires assumptions, explicit 

and implicit, about how future socioeconomic 

conditions will develop. The IPCC (1994) 

recommends the use of socioeconomic scenarios 

in impacts assessments to capture these factors 

in a consistent way.

Socioeconomic scenarios have tended to focus 

on variables such as population and measures 

of economic activity (e.g., Gross Domestic 

Product) that can be quantified using wellestablished models or methods (for examples of 

economic models that have been used for long 

run projections, see Nakicenovic et al., 2000; 

NAST, 2001; Yohe et al., 2007). While useful 

as a starting point, some key socioeconomic 

factors may not allow this type of quantification: 

they could however be incorporated through a 

qualitative, “storyline” approach and thus yield 

a more fully developed socioeconomic scenario. 

The UNEP country study program guidance 

(Tol, 1998) notes the role of formal modeling 

in filling in (but not defining) socioeconomic 

scenarios but also emphasizes the role of expert 

judgment in blending disparate elements into 

coherent and plausible scenarios. Generally, 

socioeconomic scenarios have been developed 

in situations where it is not possible to assign 

levels of probability to any particular future 

state of the world and therefore it usually is not 

appropriate to make confidence statements with 

respect to a specific socioeconomic scenario 

(Moss and Schneider, 2000). 

Socioeconomic scenarios include nonenvironmental factors that influence exposures, 

vulnerability, and impacts. Factors that may be 

incorporated into a scenario include:

•	 Population (e.g., demographics, immigration, 

domestic migration patterns);

•	 Economic status (income, prices);

•	 Technology (e.g., pesticides, vaccines, 

t r a n s p o r t a t i o n m o d e s , w i r e l e s s 

communications);

•	 Infrastructure (e.g., water treatment plants, 

sewers, and drinking water systems; public 

health systems; roads, rails and bridges; 

flood control structures);

•	 Human capital and social context and 

behaviors (e.g., skills and knowledge, social 

networks, lifestyles, diet); and,

•	 I n s t i t u t i o n s ( l e g i s l a t i v e , s o c i a l , 

managerial).

These factors are impor tant both for 

characterizing potential effects of a changing 

climate on human health, settlements, and 

welfare, and for evaluating the ability of the 

United States to adapt to climate change. 

1.4.1 Economic Status

The United States is a developed economy 

with GDP approaching $14 trillion and a per 

capita income of $38,611 in 2007 (US BEA, 

2008). The U.S. economy has large private 

and public sectors, with strong emphasis on 

market mechanisms and private ownership 

(Christensen et al., 2007). A nation’s economic 

status clearly is important for determining 

vulnerability to climate change: wealthy 

nations have the economic resources to invest 

in adaptive measures and bear the costs of 

impacts and adaptation thereby reducing 

their vulnerability (WHO, 2003; IPCC, 2001). 

However, with the aging of the population 

(described in Section 1.3.1.1) the costs of health 

care are likely to rise over the coming decades 

(Christensen et al., 2007). Moreover, if the trend 

toward globalization continues through the 21st 
27

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

century, markets, primary factors of production, 

ownership of assets, and policies and governance 

will become more international in outlook 

(Stiglitz, 2002). Unfortunately, there has been little 

research to understand how these economic trends 

interact with climate change to affect vulnerability 

(i.e., whether they facilitate or hinder adaptation 

to climate change).

1.4.2 Technology

The past half-century has seen stunning levels 

of technological advancement in the United 

States, which has done much to improve 

American standards of living. The availability 

and access to technology at varying levels, in 

key sectors such as energy, agriculture, water, 

transportation, and health is a key component 

to understanding vulnerability to climate 

change. Many technological changes, both 

large and small, have reduced Americans’ 

vulnerability to climate change (NAST, 2001). 

Improved roads and automobiles, better weather 

and climate forecasting systems, computers 

and wireless communication, new drugs and 

vaccines, better building materials, more 

efficient energy production–the list is very 

long–have contributed to America’s material 

well being while reducing vulnerability to 

climate. Many of the currently deployed 

adaptive strategies that protect human beings 

from climate involve technology (e.g., warning 

systems, air conditioning and heating, pollution 

controls, building design, storm shelters, vector 

control, water treatment and sanitation) (WHO, 

2003). Continued advances in technology in 

the 21st century can increase substantially our 

ability to cope with climate change (IPCC, 

2007a; USGCRP, 2001).

However, it will be important to assess risks from 

proposed technological adaptations to avoid or 

mitigate adverse effects (i.e., maladaptation) 

(Patz, 1996; Klein and Tol, 1997). For example, if 

new pesticides are used to control disease vectors 

their effects on human populations, insect 

predators, and insect resistance to pesticides 

need to be considered (Scheraga and Grambsch, 

1998; Gubler et al., 2001). 

In addition, technological change can interact 

in complex ways with other socioeconomic 

factors (e.g., migration patterns) and affect 

vulnerability to climate change. For example, 

advances in transportation technology–electric 

streetcars, freight trucks, personal automobiles, 

and the interstate highway system–have fueled 

the decentralization of urban regions (Hanson 

and Giuliano 2004; Garreau 1991; Lang 2003). 

More recently, the rapid development of new 

information technologies, such as the internet, 

have made previously remote locations more 

accessible for work, recreation, or retirement. 

Whether these developments increase or 

decrease vulnerability is unknown, but they do 

indicate the need for socioeconomic scenarios 

to better characterize the complex linkages 

between climate and non-climate factors in 

order to evaluate vulnerability. 

1.4.3 Infrastructure

Communities have reduced, and can further 

reduce, their vulnerability to adverse climate 

effects through investments in infrastructure. 

United States have been modified and intensively 

managed over the years, partly in response to 

climate variability (Cohan and Miller, 2001). 

These investments range from small, privately 

constructed impoundments, water diversions, 

and levees to major projects constructed by 

federal and state governments. Public health 

infrastructure, such as sanitation facilities, 

waste water treatment, and laboratory buildings 

reduce climate change health risks (Grambsch 

and Menne, 2003). Coastal communities have 

developed an array of systems to manage 

erosion and protect against flooding (see SAP 

4.1 for an extensive discussion). More generally, 

infrastructure such as roads, rails, and bridges; 

water supply systems and drainage; mass 

transit; and buildings can reduce vulnerability 

(Grambsch and Menne, 2003). 

However, inf rast r uct u re can increase 

vulnerability if its presence encourages 

people to locate in more vulnerable areas. 
The U.S. Climate Change Science Program Chapter 1

28

For example, increasing the density of people 

in coastal metropolitan areas, dependent on 

extensive fixed infrastructure, can increase 

vulnerability to extreme events such as floods, 

storm surges, and heat waves (NAST, 2001). 

In assessments of severe storms, measures of 

property damage are consistently higher and 

loss of life lower in the United States when 

compared with less-developed countries (Cohan 

and Miller, 2001). This reflects both the high 

level of development in coastal zones and 

the effectiveness of warnings and emergency 

preparedness (Pielke and Pielke, 1997). 

Fixed infrastructure itself has the potential 

to be adversely impacted by climate change, 

which can increase vulnerability to climate 

change. For example, flooding can overwhelm 

sanitation infrastructure and lead to waterrelated illnesses (Grambsch and Menne, 2003). 

Much of the transportation infrastructure in 

the Gulf Coast has been constructed on land 

at elevations below 16.4 feet. Storm surge, 

therefore, poses risks of immediate flooding 

of infrastructure and damage caused by the 

force of floodwaters (see SAP 4.7 for additional 

information on the vulnerability of Gulf Coast 

transportation infrastructure to climate change). 

Damage to transportation infrastructure 

can make it more difficult to assist affected 

populations (Grambsch and Menne, 2003).

1.4.4 Human and Social Capital 

and Behaviors

While these factors are extremely difficult to 

quantify, much less project into the future, 

they are widely perceived to be important 

in determining vulnerability in a number 

of different ways. In general, countries 

with higher levels of human capital (i.e., the 

knowledge, experience, and expertise of its 

citizens), are considered to be less vulnerable 

to climate change. Effective adaptation will 

require individuals skilled at recognizing, 

reporting, and responding to climate change 

effects. Moreover, a number of the adaptive 

measures described in the literature require 

knowledgeable, trained, and skilled personnel 

to implement them. For example, skilled 

public health managers who understand 

surveillance and diagnostic information will 

be needed to mobilize appropriate responses. 

People trained in the operation, quality 

control, and maintenance of laboratories; 

communications equipment; and sanitation, 

wastewater, and water supply systems are 

also key (Grambsch and Menne, 2003). 

Researchers and scientists spanning a broad 

range of disciplines will be needed to provide 

a sound basis for adaptive responses.

In addition to a country’s human capital, 

the relationships, exchange of resources, 

and knowledge, and the levels of trust and 

conflicts between individuals (i.e., “social 

capital”) are also important for understanding 

future vulnerability to climate change (Adger, 

2003; Lehtonen, 2004; Pelling and High, 

2005). Social networks can play an important 

role in coping and recovery from extreme 

weather events (Adger, 2003). For example, 

individuals who were socially isolated were 

found to be a greater risk of dying from 

extreme heat (Semenza et al., 1996), as well 

as people living in neighborhoods without 

public gathering places and active street life 

(Klinenberg, 2002). 

Individual behaviors and responses to changing 

conditions also determine vulnerability. For 

example, fitness, body composition, and level 

of activity are among the factors that determine 

the impact extremely hot weather will have on 

the human body (see Chapter 2 for additional 

information). Whether this trend continues 

or not could have important implications for 

determining vulnerability to climate change. 

Individual responses and actions to reduce 

exposures to extreme heat can also substantially 
29

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

ameliorate adverse health impacts (McGeehin 

and Mirabelli, 2001). Successfully motivating 

individuals to respond appropriately can 

therefore decrease vulnerability and reduce 

health impacts-a key goal of public health 

efforts (McGeehin and Mirabelli, 2001).

1.4.5 Institutions

The ability to respond to climate change and 

reduce vulnerability is influenced by social 

institutions as well as the social factors noted 

above. Institutions are viewed broadly in the 

climate change context and include a wide 

diversity of things such as regulations, rules, and 

norms that guide behavior. Examples include 

past development and land use patterns, existing 

environmental and coastal laws, building codes, 

and legal rights. Institutions also can determine 

a decision-maker’s access to information and 

the ways in which the information can be used 

(Moser et al., 2007). 

Well-functioning institutions are essential to a 

modern society and provide a mechanism for 

stability in otherwise volatile environments 

(Moser et al., 2007). Future options for 

responding to future climate impacts are thus 

shaped by our past and present institutions and 

how they evolve over time. In addition, the 

complex interaction of issues expected with 

climate change may require new arrangements 

and collaborations between institutions to 

address risks effectively, thereby enhancing 

adaptive capacity (Grambsch and Menne, 

2003). A number of institutional changes have 

been identified that improve adaptive capacity 

and reduce vulnerability (see Chapter 3 for 

additional details). While the importance of 

institutions is clear, there are few scenarios that 

incorporate an explicit representation of them.

1.4.6 Interacting Effects

The same social and economic systems that 

bear the stress of climate change also bear the 

stress of non-climate factors, including: air 

and water pollution, the influx of immigrants, 

and an aging and over-burdened infrastructure 

in rapidly growing metropolitan centers and 

coastal zones. While non-climate stressors 

are currently more pronounced than climate 

impacts, one cannot assume that this trend will 

persist. Understanding the impacts of climate 

change and variability on health and quality of 

life assumes knowledge of how these dynamics 

might vary by location and across time and 

socioeconomic group. The effects of climate 

change often spread from directly affected areas 

and sectors to other areas and sectors through 

complex linkages. The relative importance 

of climate change depends on the directness 

of each climate impact and on demographic, 

social, economic, institutional, and political 

factors, including the degree of emergency 

preparedness. 

Consider the damage left by Hurricanes Katrina 

and Rita in 2005. Damage was measured not only 

in terms of lives and property lost, but also in 

terms of the devastating impacts on infrastructure, 

neighborhoods, businesses, schools, and hospitals 

as well as in the disruption to families and friends 

in established communities, with lost lives and 

lost livelihoods, challenges to psychological 

well-being, and exacerbation of chronic illnesses. 

While the aftermath of a single hurricane is not 

the measure of climate change, such an event 

demonstrates the disruptive power of climate 

impacts and the resulting tangle of climate and 

non-climate stressors that complicate efforts to 

respond and to adapt. The impacts following 

these hurricanes reveal that socioeconomic 

factors and failures in human systems may be 

as damaging as the storms themselves.

Another trend of significance for climate 

change is the suburbanization of poverty. A 

recent study noted that by 2005 the number 

of low income households living in suburban 

communities had for the first time surpassed 

the number living in central cities (Berube and 

Kneebone, 2006). Although the poverty rate in 
The U.S. Climate Change Science Program Chapter 1

30

cities was still double the suburban rate, there 

were 1 million more people living in poverty in 

America’s suburbs. Many of these people live in 

older inner-ring suburbs developed in the 1950’s 

and 60’s. The climate adaptation challenge for 

these places is captured succinctly by a recent 

study: “Neither fully urban nor completely 

suburban, America’s older, inner-ring, “first” 

suburbs have a unique set of challenges—such 

as concentrations of elderly and immigrant 

populations as well as outmoded housing and 

commercial buildings—very different from 

those of the center city and fast growing newer 

places. Yet first suburbs exist in a policy blind 

spot with little in the way of state or federal 

tools to help them adapt to their new realities” 

(Puentes and Warren, 2006). 

1.5 Reporting

Uncertainty in SAP 4.6 

Uncertainty can be traced to a variety of 

sources: (1) a misspecification of the cause(s), 

such as the omission of a causal factor resulting 

in spurious correlations; (2) mischaracterization 

of the effect(s), such as a model that predicts 

cooling rather than warming; (3) absence of or 

imprecise measurement or calibration (such as 

devices that fail to detect minute causal agents); 

(4) fundamental stochastic (chance) processes; 

(5) ambiguity over the temporal ordering of 

cause and effect; (6) time delays in cause and 

effect; and, (7) complexity where cause and 

effect between certain factors are camouflaged 

by a context with multiple causes and effects, 

feedback loops, and considerable noise.

A new perspective on the treatment of 

uncertainty has emerged from the IPCC Third 

and Fourth Assessment processes.6 This new 

perspective suggests that uncertainties about 

projections of climate changes, impacts, and 

responses include two fundamentally different 

dimensions. One dimension recognizes that 

most processes and systems being observed 

are characterized by inherent variability in 

outcomes: the more variable the process or 

system, the greater the uncertainty associated 

with any attempt to project an outcome. A 

second dimension recognizes limitations in our 

knowledge about processes and systems. 

This report is a summary of the state of the 

science on the impacts of climate change on 

human health, human settlements, and human 

welfare. With this focus, the assessment of 

uncertainty in this report is based on the 

literature and the author team’s expert judgment. 

The considerations in determining confidence 

include the degree of belief within the scientific 

community that available understanding, 

models, and analyses are accurate, expressed by 

6 SAP 4.6 follows the Guidance Notes for Lead 

Authors of the IPCC Fourth Assessment Report 

on Addressing Uncertainties, produced by the 

IPCC in July 2005. See http://www.ipcc.ch/pdf/

supporting-material/uncertainty-guidance-note.

pdf for more details.

Figure 1.5 Considerations in determining confidence

Source: IPCC Guidance Notes on risk and uncertainty (2005)

Amount of evidence (number and quality of independent sources) 

High agreement,

limited evidence

High agreement,

medium evidence

High agreement,

much evidence

Medium agreement,

limited evidence

Medium agreement,

medium evidence

Medium agreement,

much evidence

Low agreement,

limited evidence

Low agreement,

medium evidence

Low agreement,

much evidence

Level of agreement 

(on a particular finding)
31

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

the degree of consensus in the available evidence 

and its interpretation. This can be thought 

of using two different dimensions related to 

consensus. Figure 1.5 represents the qualitatively 

defined levels of understanding. It considers both 

the amount of evidence available in support of 

findings and the degree of consensus among 

experts on its interpretation. 

In this report, each chapter author team 

assigned likelihood judgments that reflect their 

assessments of the current consensus of the 

science and the quality and amount of evidence. 

This represents their expert judgment that the 

given likelihood impact statement is true given 

a specified climatic change. The likelihood 

terminology and corresponding values used in 

this report are shown in Table 1.1. As the focus 

of this report is on impacts, it is important to 

note that these likelihood statements refer to the 

impact, not the underlying climatic changes (i.e.,

the report does not address whether the specific 

climatic change is likely to occur). Moreover, 

Table 1.1 Description of likelihood: probabilistic assessment of 

outcome having occurred or occurring in the future based on quantitative analysis or elicitation of expert views. 

Likelihood Terminology Likelihood of the 

Occurrence/Outcome

Virtually certain > 99 percent probability

Very likely > 90 percent probability

Likely > 66 percent probability

About as likely as not 33 - 66 percent 

probability

Unlikely < 33 percent probability

Very unlikely < 10 percent probability

Exceptionally unlikely < 1 percent probability

the authors do not attempt an assessment that 

takes into account a probabilistic accounting 

of both the likelihood of the climatic change 

and the impact. The terms defined in Table 

1.1 are intended to be used in a relative sense 

to summarize judgments of the scientific 

understanding relevant to an issue, or to express 

uncertainty in a finding where there is no basis 

for making more quantitative statements. 

The application of this approach to likelihood 

estimates demonstrates some variability across 

each of the three core chapters (Chapters 2–4). 

This variability in reporting uncertainty is based 

on the degree of richness of their respective 

knowledge bases. A relatively more extensive 

and specific application of likelihood and state 

of the knowledge estimates is possible for 

health impacts, only a more general approach 

is warranted for conclusions about human 

settlements, and uncertainty statements about 

human welfare conclusions are necessarily the 

least explicit.
The U.S. Climate Change Science Program Chapter 1

32

1.6 References

AARP, 2006: Aging, Migration, and Local 

Communities: The Views of 60+ Residents and 

Community Leaders. Washington, DC.

Adger, W. N., 2003: Social capital, collective action 

and adaptation to climate change. Journal of 

Economic Geography, 79(4), 387-404.

Andreadis, K.M., E.A. Clark, A.W. Wood, A.F. 

Hamlet, and D.P. Lettenmaier, 2005: 20th century 

drought in the conterminous United States. Journal 

of Hydrometeorology, 6(6), 985-1001.

Andreadis, K.M. and D.P. Lettenmaier. 2006: Trends 

in 20th century drought over the continental 

United States. Geophysical Research Letters, 33, 

DOI:10.1029/2006GL025711. 

Arctic Climate Impact Assessment, 2004: Impacts 

of a Warming Arctic. Cambridge U n i v e r s i t y 

Press, Cambridge, UK.

Bernard, S.M. and M.A. McGeehin, 2004: 

Municipal heat wave response plans. American 

Journal of Public Health, 94(9), 1520-1522.

Bernard, S.M., J.M. Samet, A. Grambsch, K.L. Ebi, 

I. Romieu, 2001: The potential impacts of climate 

variability and change on air pollution-related 

health effects in the United States. Environmental 

Health Perspectives 109, Supplement 2, 199-209.

Berube, A. and E. Kneebone, 2006: Two Steps 

Back: City and Suburban Poverty Trends 1999–

2005. Metropolitan Policy Program, Brookings 

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Bindoff, N.L., J. Willebrand, V. Artale, A. Cazenave, 

J. Gregory, S. Gulev, K. Hanawa, C. Le Quéré, S. 

Levitus, Y. Nojiri, C.K. Shum, L.D. Talley and 

A. Unnikrishnan, 2007: Observations: Oceanic 

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Borrell, C., M. Marí-Dell’Olmo, M. RodríguezSanz, P. Garcia-Olalla, J. Caylà, J. Benach, and 

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W.L. Murray (eds.)]. Department of Commerce 

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Centers for Disease Control and Prevention, 

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Chagnon, S., 2003: Shifting economic impacts from 

weather extremes in the United States: result of 

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Chen, X. Gao, I. Held, R. Jones, R.K. Kolli, 

W.-T. Kwon, R. Laprise, V. Magaña Rueda, L. 

Mearns, C.G. Menéndez, J. Räisänen, A. Rinke, 

A. Sarr and P. Whetton, 2007: Regional climate 

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CHAPTER

2

39

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Effects of Global Change 

on Human Health

Lead Author: Kristie L. Ebi, ESS, LLC

Contributing Authors: John Balbus, Environmental Defense; Patrick L. 

Kinney, Columbia University; Erin Lipp, University of Georgia; David 

Mills, Stratus Consulting; Marie S. O’Neill, University of Michigan; 

Mark Wilson, University of Michigan

2.1 INTRODUCTION

Climate change can affect health directly and 

indirectly. Directly, extreme weather events 

(floods, droughts, windstorms, fires, and heat 

waves) can affect the health of Americans and 

cause significant economic impacts. Indirectly, 

climate change can alter or disrupt natural 

systems, making it possible for vector-, water-, 

and food-borne diseases to spread or emerge 

in areas where they had been limited or not 

existed, or for such diseases to disappear by 

making areas less hospitable to the vector or 

pathogen (NRC, 2001). Climate change can also 

affect the incidence of diseases associated with 

air pollutants and aeroallergens (Bernard et al., 

2001).1 The cause-and-effect chain from climate 

change to changing patterns of health outcomes 

is complex and includes factors such as initial 

health status, financial resources, effectiveness 

of public health programs, and access to medical 

care. Therefore, the severity of future impacts 

will be determined by changes in climate as 

well as by concurrent changes in nonclimatic 

factors and by adaptations implemented to 

reduce negative impacts. 

A comprehensive assessment of the potential 

impacts of climate change on human health in 

the United States was published in 2000. This 

First National Assessment was undertaken by 

the U.S. Global Change Research Program. 

The Health Sector Assessment examined 

potential impacts and identified research and 

data gaps to be addressed in future research. 

1 Any of various air-borne substances, such as pollen 

or spores, that can cause an allergic response.

The results appeared in a special issue of 

Environmental Health Perspectives (May 2001). 

The Health Sector Assessment’s conclusions on 

the potential health impacts of climate change 

in the United States included:

•	 Populations in northeastern and midwestern 

U.S. cities are likely to experience the 

greatest number of illnesses and deaths in 

response to changes in summer temperatures 

(McGeehin and Mirabelli, 2001).

•	 The health impacts of extreme weather 

events hinge on the vulnerabilities and 

recover y capabilities of the natural 

environment and the local population 

(Greenough et al., 2001).

•	 If the climate becomes warmer and more 

variable, air quality is likely to be affected 

(Bernard et al., 2001). However, uncertainties 

in climate models make the direction and 

degree of change speculative (Bernard and 

Ebi, 2001).

•	 Federal and state laws and regulatory 

programs protect much of the U.S. 

population from water-borne disease. 

However, if climate variability increases, 

current and future deficiencies in areas 

such as watershed protection, infrastructure, 

and storm drainage systems will probably 

increase the risk of contamination events 

(Rose et al., 2000). 

•	 It is unlikely that vector- and rodent-borne 

diseases will cause major epidemics in 

the United States if the public health 

infrastructure is maintained and improved 

(Gubler et al., 2001).
The U.S. Climate Change Science Program Chapter 2

40

•	 Multiple uncertainties preclude any definitive 

statement on the direction of potential future 

change for each of the health outcomes 

assessed (Patz et al., 2000).

The assessment further concluded that much of 

the U.S. population is protected against adverse 

health outcomes associated with weather and/or 

climate by existing public health and medical 

care systems, although certain populations are 

at increased risk.

This chapter of SAP 4.6 updates the 2000 Health 

Sector Assessment. It also examines adaptation 

strategies that have been or are expected to be 

developed by the public health community in 

response to the challenges and opportunities 

posed by climate change. The first section 

of this chapter focuses on climate-related 

impacts on human morbidity and mortality 

from extreme weather, vector-, water- and foodborne diseases, and changes in air quality. For 

each health endpoint, the assessment addresses 

the potential impacts, populations that are 

particularly vulnerable, and research and data 

gaps that, if bridged, would allow significant 

advances in future assessments of the health 

impacts of global change. The assessment 

includes research published from 2001 through 

early 2007 in the United States or in Canada, 

Europe, and Australia, where results may 

provide insights for U.S. populations.

This chapter summarizes the current burden 

of climate-sensitive health determinants and 

outcomes for the United States before assessing 

the potential health impacts of climate change. 

Two types of studies are assessed: (1) studies that 

increase our understanding of the associations 

between weather variables and health outcomes 

raise possible concerns about the impacts of a 

changing climate, and (2) studies that project 

the burden of health outcomes using scenarios 

of socioeconomic and climate change. 

It is important to note that this assessment 

focuses on how climate change could affect 

the future health of Americans. However, 

the net impact of any changes will depend on 

many other factors, including demographics; 

population and regional vulnerabilities; the 

future social, economic, and cultural context; 

availability of resources and technological 

options; built and natural environments; public 

health infrastructure; and the availability and 

quality of health and social services. 

The chapter then turns to adaptation to the 

potential health impacts of environmental 

change in the United States. It also considers 

public health interventions (including prevention, 

response, and treatment strategies) that could be 

revised, supplemented, or implemented to protect 

human health in response to the challenges 

and opportunities posed by global change, and 

considers how much adaptation could achieve. 

2.2 Observed ClimateSensitive Health

Outcomes in the 

United States

2.2.1 Thermal Extremes: 

Heat Waves

Excess deaths occur during heat waves, on days 

with higher-than-average temperatures, and in 

places where summer temperatures vary more 

or where extreme heat is rare (Braga et al.,

2001). Figure 2.1 illustrates that the relation 

between temperature and mortality is nonlinear, 

typically J- or U-shaped, and that increases 

in mortality occur even below temperatures 

considered to be extremely hot. This figure 

was created using log-linear regression to 

analyze 22 years of data on daily mortality and 

outdoor temperature in 11 U.S. cities (Curriero 

et al., 2002). Exposure to excessive natural heat 

caused a reported 4,780 deaths during the period 

1979 to 2002, and an additional 1,203 deaths had 
41

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

hyperthermia reported as a contributing factor 

(CDC, 2005). These numbers are underestimates 

of the total mortality associated with heat 

waves because the person filling out the death 

certificate may not always list heat as a cause. 

Furthermore, heat can exacerbate chronic health 

conditions, and several analyses have reported 

associations with cause-specific mortality, 

including cardiovascular, renal, and respiratory 

diseases; diabetes; nervous system disorders; and 

other causes not specifically described as heatrelated (Conti et al., 2007; Fouillet et al., 2006; 

Medina-Ramon et al., 2006). Among the most 

well-documented heat waves in the United States 

are those that occurred in 1980 (St. Louis and 

Kansas City, Missouri), 1995 (Chicago, Illinois), 

and 1999 (Cincinnati, Ohio; Philadelphia, 

Pennsylvania; and Chicago, Illinois). The highest 

death rates in these heat waves occurred in 

people over 65 years of age. 

Less information exists on temperature-related 

morbidity, and those studies that have examined 

hospital admissions and temperature have not 

seen consistent effects, either by cause or by 

demonstrated coherence with mortality effects 

where both deaths and hospitalizations were 

examined simultaneously (Kovats et al., 2004; 

Michelozzi et al., 2006; Schwartz et al., 2004; 

Semenza et al., 1999). 

Age, fitness, body composition, and level of 

activity are important determinants of how the 

human body responds to exposure to thermal 

extremes (DeGroot et al., 2006; Havenith et 

al., 1995; Havenith et al., 1998; Havenith, 

2001). Groups particularly vulnerable to 

heat-related mortality include the elderly, 

very young, city-dwellers, those with less 

education, people on medications such as 

diuretics, the socially isolated, the mentally 

ill, those lacking access to air conditioning, 

and outdoor laborers (Diaz et al., 2002; 

Klinenberg, 2002; McGeehin and Mirabelli, 

2001; Semenza et al., 1996; Whitman et al.,

1997; Basu et al., 2005; Gouveia et al., 2003; 

Greenberg et al., 1983; O’Neill et al., 2003; 

Schwartz, 2005; Jones et al., 1982; Kovats et 

al., 2004; Schwartz et al., 2004; Semenza et 

al., 1999; Watkins et al., 2001). A sociological 

analysis of the 1995 Chicago heat wave found 

that people living in neighborhoods without 

public gathering places and active street 

life were at higher risk, highlighting the 

important role that community and societal 

characteristics can play in determining 

vulnerability (Klinenberg, 2002).

Urban heat islands may increase heat-related 

health impacts by raising air temperatures in 

cities 2-10°F over the surrounding suburban 

and rural areas due to absorption of heat 

by dark paved surfaces and buildings; lack 

of vegetation and trees; heat emitted from 

buildings, vehicles, and air conditioners; and 

reduced air flow around buildings (EPA, 2005; 

Pinho and Orgaz, 2000; Vose et al., 2004; Xu 

and Chen, 2004). However, in some regions, 

urban areas may not experience greater heatrelated mortality than in rural areas (Sheridan 

and Dolney, 2003); few comparisons of this 

nature have been published. 

The health impacts of high temperatures and 

high air pollution can interact, with the extent 

of interaction varying by location (Bates, 2005; 

Goodman et al., 2004; Goodman et al., 2004; 

Keatinge and Donaldson, 2001; O’Neill et al.,

2005; Ren et al., 2006). 

Figure 2.1 Temperature-mortality relative risk functions for 11 U.S. cities, 

1973–1994. Northern cities: Boston, Massachusetts; Chicago, Illinois; New 

York, New York; Philadelphia, Pennsylvania; Baltimore, Maryland; and Washington, DC. Southern cities: Charlotte, North Carolina; Atlanta, Georgia; 

Jacksonville, Florida; Tampa, Florida; and Miami, Florida. Relative risk is defined 

as the risk of an event such as mortality relative to exposure, such that the 

relative risk is a ratio of the probability of the event occurring in the exposed 

group versus the probability of occurrence in the control (non-exposed) group. 

(Curriero et al., 2002)

Temperature-Mortality Association in 11 US Cities 83

Am J Epidemiol Vol. 155, No. 1, 2002

FIGURE 1. Temperature-mortality relative risk functions for 11 US cities, 1973–1994. Northern cities: Boston, Massachusetts; Chicago, Illinois;

New York, New York; Philadelphia, Pennsylvania; Baltimore, Maryland; and Washington, DC. Southern cities: Charlotte, North Carolina; Atlanta,

Georgia; Jacksonville, Florida; Tampa, Florida; and Miami, Florida.  ̊C = 5/9 � ( ̊F – 32).

We first regressed each of the summary scores (MMT,

cold slope, and hot slope) on each predictor alone and then

on latitude with each of the city-specific variables. We used

this approach to estimate the effect modification by these

city-specific variables over and above the apparent effect

modification due to latitude. S-PLUS statistical software

(18) was used for all analyses.

RESULTS

Table 1 provides summary characteristics of those cities

included in the analysis, listed from the northernmost to the

southernmost. Figure 1 shows the temperature (T0)-

mortality relative risk function S(T0,6) estimated for each of

the 11 cities by using log-linear regression model 1. We

focused on T0 because it was by far the strongest term in the

regression model: it was stronger than D0 because temperature is a much stronger predictor than either dew point or adj

T1–3 and adj D1–3, the variables constructed to be approximately uncorrelated with T0 and D0.

We found that the effect of temperature on mortality varied among cities. For all cities, mortality risk decreased as

temperature increased from the coldest temperatures. For

the northern cities, mortality risk began to rise as the temperature increased from a certain temperature, producing a

J-shaped relation. For the southern cities, the temperaturerisk relations did not have a hooklike shape but tended to

flatten at warmer temperatures, indicating little increase in

mortality risk for the hottest days. With colder temperatures,

the curves for the southern cities had steeper slopes than

those for the northern cities. These findings were similar

when the analysis was limited to winter. During the spring

and fall, a slight increase in mortality risk occurred with

colder temperatures, especially in the southernmost cities. In

the summer, the effect of extreme heat on mortality was evident, increasing almost 40 percent over the baseline average

in the northernmost cities. The results shown in figure 1 are

from a model in which we controlled for trends by using a

smooth function of time with 176 df over the 22 years. The

findings were qualitatively similar when we used 44 or 88

df.

We next explored the association between weather and

mortality for four different time periods—1973–1979,

1980–1984, 1985–1989, and 1990–1994—fitting model 1 to

each period. Fits for each period were similar to those

described earlier for the entire period (figure 1). Thus, it
The U.S. Climate Change Science Program Chapter 2

42

2.2.2 Thermal Extremes: 

Cold Waves

From 1979 to 2002, an average of 689 reported 

deaths per year (range 417-1,021), totaling 

16,555 over the period, were attributed to 

exposure to excessive cold temperatures 

(Fallico et al., 2005). Cold also contributes to 

deaths caused by respiratory and cardiovascular 

diseases, so the overall mortality burden is 

likely underestimated. Factors associated 

with increased vulnerability to cold include 

African American race (Fallico et al., 2005); 

living in Alaska, New Mexico, North Dakota, 

and Montana, or living in milder states that 

experience rapid temperature changes (North 

and South Carolina) and western states with 

greater ranges in nighttime temperatures (e.g., 

Arizona) (Fallico et al., 2005); having less 

education (O’Neill et al., 2003); being female 

or having pre-existing respiratory illness 

(Wilkinson et al., 2004); lack of protective 

clothing (Donaldson et al., 2001); income 

inequality, fuel poverty, and low residential 

thermal standards (Healy, 2003); and living in 

nursing homes (Hajat et al., 2007). 

Because climate change is projected to reduce 

the severity and length of the winter season 

(IPCC, 2007a), there is considerable speculation 

concerning the balance of climate changerelated decreases in winter mortality compared 

with increases in summer mortality. Net changes 

in mortality are difficult to estimate because, 

in part, much depends on complexities in the 

relationship between mortality and the changes 

associated with climate change. Few studies 

have attempted to link the epidemiological 

findings to climate scenarios for the United 

States, and studies that have done so have 

focused on the effects of changes in average 

temperature, with results dependent on climate 

scenarios and assumptions of future adaptation. 

Moreover, many factors contribute to winter 

mortality, making the question of how climate 

change could affect mortality highly uncertain. 

No projections have been published for the 

United States that incorporate critical factors 

such as the influence of influenza outbreaks.

2.2.3 Extreme Events: Hurricanes, 

Floods, and Wildfires

The United States experiences a wide range of 

extreme weather events, including hurricanes, 

floods, tornadoes, blizzards, windstorms, and 

drought. Other extreme events, such as wildfires, 

are strongly influenced by meteorological 

conditions. Direct morbidity and mortality 

due to an event increase with the intensity and 

duration of the event, and can decrease with 

advance warning and preparation. Health also 

can be affected indirectly. Examples include 

carbon monoxide poisonings from portable 

electric generator use following hurricanes 

(CDC, 2006b) and an increase in gastroenteritis 

cases among hurricane evacuees (CDC, 2005a). 

The mental health impacts (e.g., post-traumatic 

stress disorder [PTSD], depression) of these 

events are likely to be especially important but 

are difficult to assess (Middleton et al., 2002; 

Russoniello et al., 2002; Verger et al., 2003; 

North et al., 2004; Fried et al., 2005; Weisler 

et al., 2006). However, failure to fully account 

for direct and indirect health impacts may result 

in inadequate preparation for and response to 

future extreme weather events. 

Figure 2.2 shows the annual number of deaths 

attributable to hurricanes in the United States 

from the 1900 Galveston storm, (NOAA, 

2006), records for the years 1940-2004 (NOAA, 

2005a), and a summary of a subset of the 2005 

hurricanes (NOAA, 2007). The data shown are 

dominated by the 1900 Galveston storm and a 

subset of 2005 hurricanes, particularly Katrina 

and Rita, which together accounted for 1,833 

of the 2,002 lives lost to hurricanes in 2005 

(NOAA, 2007b). While Katrina was a Category 
43

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

3 hurricane and its path was forecast well in 

advance, there was a secondary failure of the 

levee system in Louisianna. This illustrates that 

multiple factors contribute to making a disaster 

and that adaptation measures may not fully 

avert adverse consequences.

From 1940 through 2005 roughly 4,300 lives 

were lost in the United States to hurricanes. 

The impact of the 2005 hurricane season is 

especially notable as it doubled the estimate of 

the average number of lives lost to hurricanes in 

the United States over the previous 65 years.

Figure 2.3 shows the annual number of deaths 

attributed to flooding in the United States from 

1940-2005 (NOAA, 2007a). Over this period 

roughly 7,000 lives were lost.

A wildfire’s health risk is largely a function of 

the population in the affected area and the speed 

and intensity with which the wildfire moves 

through those areas. Wildfires can increase eye 

and respiratory illnesses due to fire-related air 

pollution. Climate conditions affect wildfire 

incidence and severity in the West (Westerling 

et al., 2003; Gedalof et al., 2005; Sibold and 

Veblen, 2006). Between 1987-2003 and 1970-

1986, there was a nearly fourfold increase in the 

incidence of large Western wildfires (i.e., fires 

that burned at least 400 hectares) (Westerling et 

al., 2006). The key driver of this increase was 

an average increase in springtime temperature 

of 0.87°C that affected spring snowmelt, 

subsequent potential for evapotranspiration, 

loss of soil moisture, and drying of fuels 

(Running, 2006; Westerling et al., 2006). Data 

providing a time-series summary of deaths 

similar to the data in Figures 2.2 and 2.3 were 

not identified. 

There is a rich body of literature detailing 

the mental health impacts of extreme weather 

events. Anxiety and depression, the most 

common mental health disorders, can be 

directly attributable to the experience of the 

event (i.e., being flooded) or indirectly during 

the recovery process (e.g., Gerrity and Flynn, 

1997). These psychological effects tend to be 

much longer lasting and can be worse than the 

physical effects experienced during an event 

and its immediate aftermath.

Extreme events are often multi-strike stressors, 

with stress associated with the event itself; 

the disruption and problems of the recovery 

period; and the worry or anxiety about the 

risk of recurrence of the event (Tapsell et al., 

2002). During the recovery period, mental 

health problems can arise from the challenges 

associated with geographic displacement, 

damage to the home or loss of familiar 

possessions, and stress involved with the 

process of repairing. The full impact often is 

not appreciated until after people’s homes have 

been put back in order. For instance, in the 

aftermath of Hurricane Katrina in 2005, mental 

health services in New Orleans were challenged 

by an increased incidence of serious mental 

illness, including anxiety, major depression, 

and PTSD. Shortly after Katrina, a Centers for 

Disease Control and Prevention poll found that 

Figure 2.2 Annual Deaths Attributed to Hurricanes in the United States, 

1900 and 1940-2005 

Source: NOAA, 2007

Figure 2.3 Annual Deaths Attributed to Flooding in the United States, 

1940-2005

Source: NOAA, 2007a
The U.S. Climate Change Science Program Chapter 2

44

nearly half of all survey respondents indicated 

a need for mental health care, yet less than 2 

percent were receiving professional attention 

(Weisler et al., 2006). 

2.2.4 Indirect Health Impacts of 

Climate Change

The observation that most vector-, water- or 

food-borne and/or animal-associated diseases 

exhibit a distinct seasonal pattern suggests a 

priori that weather and/or climate influence 

their distribution and incidence. The following 

sections differentiate between zoonotic and 

water- and food-borne diseases, although many 

water- and food-borne diseases are zoonotic.

2.2.4.1 Vector-borne and 

Zoonotic (VBZ) Diseases

Transmission of infectious agents by bloodfeeding arthropods (particular insect or tick 

species) and/or by non-human vertebrates 

(certain rodents, canids, and other mammals) 

has changed significantly in the United States 

during the past century. Diseases such as rabies 

and cholera have become less widespread and 

diseases such as typhus, malaria, yellow fever, 

and dengue fever have largely disappeared, 

primarily because of environmental modification 

and/or socioeconomic development (Philip 

and Bozeboom, 1973; Beneson, 1995; Reiter, 

1996). While increasing average temperatures 

may allow the permissive range for Aedes 

aegypti, the mosquito vector of dengue virus, 

to move further north in the United States, it is 

unlikely that more cases of dengue fever will 

be observed because most people are protected 

living indoors due to quality housing. Indeed, 

a recent epidemic of dengue in southern Texas 

and northern Mexico produced many cases 

among the relatively poor Mexicans, and very 

few cases among Texans (Reiter et al., 1999). 

At the same time, the distubution of other 

diseases changed either because of suitable 

environmental conditions (including climate) 

or enhanced detection (examples include 

Lyme disease, ehrlichioses, and Hantavirus 

pulmonary syndrome), or have been introduced 

and are expanding their range due to appropriate 

climatic and ecosystem conditions (West Nile 

Virus; e.g., Reisen et al., 2006). Still others 

are associated with non-human vertebrates 

that have complex associations with climate 

variability and human disease (e.g., plague, 

influenza). The burden of VBZ diseases in the 

United States is not negligible and may grow 

in the future because the forces underlying 

VBZ disease risk involve weather/climate, 

ecosystem change, social and behavioral factors 

simultaneously, and larger political-economic 

forces that are part of globalization. In addition, 

introduction of pathogens from other regions of 

the world is a very real threat. 

Few original research articles on climate and 

VBZ diseases have been published in the 

United States and in other developed temperate 

countries since the First National Assessment. 

Overall, these studies provide evidence that 

climate affects the abundance and distributions 

of vectors that may carry West Nile virus, 

Western Equine encephalitis, Eastern Equine 

encephalitis, Bluetongue virus, and Lyme 

disease. Climate also may affect disease risk, 

but sometimes in counterintuitive ways that do 

not necessarily translate to increased disease 

incidence (Wegbreit and Reisen, 2000; Subak, 

2003; McCabe and Bunnell, 2004; DeGaetano, 

2005; Purse et al., 2005; Kunkel et al., 2006; 

Ostfeld et al., 2006; Shone et al., 2006). 

Changes in other factors such as hosts, habitats, 

and human behavior also are important.
45

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

2.2.4.2 Water-borne and 

Food-borne Diseases 

Water- and food-borne diseases continue to 

cause significant morbidity in the United 

States. In 2002, there were 1,330 food-related 

disease outbreaks (Lynch et al., 2006), 34 

outbreaks from recreational water (2004), 

and 30 outbreaks from drinking water (2004) 

(Dziuban et al., 2006; Liang et al., 2006). For 

outbreaks of food-borne disease with known 

etiology, bacteria (Salmonella) accounted for 

55 percent and viruses accounted for 33 percent 

(Lynch et al., 2006). Viral associated outbreaks 

rose from 16 percent in 1998 to 42 percent in 

2002, primarily due to increases in norovirus 

(Lynch et al., 2006). In recreational water, 

bacteria accounted for 32 percent of outbreaks, 

parasites (primarily Cryptosporidium) for 

24 percent, and viruses 10 percent (Dziuban 

et al., 2006). Similarly in drinking water 

outbreaks of known etiology, bacteria were 

the most commonly identified agent (29 

percent, primarily Campylobacter), followed 

by parasites and viruses (each identified 5 

percent of the time) (2003—2004; Liang et 

al., 2006). Gastroenteritis continues to be the 

primary disease associated with food and water 

exposure. In 2003 and 2004, gastroenteritis was 

noted in 48 percent and 68 percent of reported 

recreational and drinking water outbreaks, 

respectively (Dziuban et al., 2006; Liang et 

al., 2006). 

Water- and food-borne disease remain highly 

underreported (e.g., Mead et al., 1999). Few 

people seek medical attention and of those that 

do, few cases are diagnosed (many pathogens 

are difficult to detect and identify in stool 

samples) or reported. Using a combination of 

underreporting estimates, passive and active 

surveillance data, and hospital discharge data, 

Mead et al. (1999) estimated that more than 210 

million cases of gastroenteritis occur annually in 

the United States, including more than 900,000 

hospitalizations and more than 6,000 deaths. 

More recently, Herikstad et al. (2002) estimated 

as many as 375 million episodes of diarrhea 

occur annually in the United States, based on a 

self-reporting study. These numbers far exceed 

previous estimates. Of the total estimated annual 

cases, just over 39 million can be attributed to 

a specific pathogen and approximately 14 

million are transmitted by food (Mead et al., 

1999). While bacteria continue to cause the 

majority of documented food- and water-borne 

outbreaks (Lynch et al., 2006; Liang et al.,

2006), the majority of sporadic (non-outbreak) 

cases of disease are caused by viruses (67 

percent; primarily noroviruses), followed by 

bacteria (30 percent, primarily Campylobacter

and Salmonella) and parasites (3 percent, 

primarily Giardia and Cryptosporidium). 

While the outcome of many gastrointestinal 

diseases is mild and self-limiting, they can 

be fatal or significantly decrease fitness in 

vulnerable populations, including young 

children, the immunocompromised, and the 

elderly. Children ages 1-4 and older adults (>80 

years) each make up more than 25 percent of 

hospitalizations involving gastroenteritis, but 

older adults contributed to 85 percent of the 

associated deaths (Gangarosa et al., 1992). As 

the U.S. population ages, the economic and 

public health burden of diarrheal disease will 

increase proportionally without appropriate 

interventions.

Most pathogens of concern for food- and waterborne exposure are enteric and transmitted 

by the fecal-oral route. Climate may affect 

the pathogen directly by inf luencing its 

growth, survival, persistence, transmission, or 

virulence. In addition, there may be important 

interactions between land-use practices and 

climate variability. For example, incidence 

of food-borne disease associated with fresh 

produce is growing (FDA, 2001; Powell and 

Chapman, 2007). Storm events and flooding 
The U.S. Climate Change Science Program Chapter 2

may result in the contamination of food crops 

(especially produce such as leafy greens and 

tomatoes) with feces from nearby livestock or 

feral animals. Therefore, changing climate or 

environments may alter the transmission of 

pathogens or affect the ecology and/or habitat 

of zoonotic reservoirs (NAS, 2001).

Studies in North America (United States and 

Canada) (Fleury et al., 2006; Naumova et 

al., 2006), Australia (D’Souza et al., 2004), 

and several countries across Europe (Kovats 

et al., 2004a) report striking similarities 

in cor relations between peak ambient 

temperatures (controlled for season) and 

peak in clinical cases of salmonellosis. Over 

this broad geographic range, yearly peaks in 

salmonellosis cases occur within 1 to 6 weeks 

of the highest reported ambient temperatures. 

Mechanisms suggested include replication in 

food products at various stages of processing 

(D’Souza et al., 2004; Naumova et al., 2006) 

and changes in eating habits during warm 

summer months (i.e., outdoor eating) (Fleury 

et al., 2006). Additionally, because Salmonella

are well adapted to both host conditions and the 

environment, they can grow readily even under 

low nutrient conditions at warm temperatures 

(e.g., in water and associated with fruits and 

vegetables) (Zhuang et al., 1995; Mouslim 

et al., 2002). Evidence supports the notion 

that increasing global temperatures will 

likely increase rates of salmonellosis. 

However, additional research is needed 

to determine the critical drivers behind 

this trend (i.e., intrinsic properties of 

the pathogen or extrinsic factors 

related to human behavior).

The possible effects of 

increasing temperatures 

on Campylobacter

infection rates and 

patterns cannot be 

reliably projected. 

The apparent 

seasonality of 

campylobacteriosis incidence is more variable 

than salmonellosis, and temperature models 

are less consistent in their ability to account 

for the observed infection patterns. In the 

northeastern United States, Canada, and 

the U.K., Camplyobacter infection peaks 

coincide with high annual daily or weekly 

temperatures (Louis et al., 2005; Fleury et 

al., 2006; Naumova et al., 2006). However, 

in several other European countries, 

campylobacteriosis rates peak earlier, before 

high annual temperatures, and in those cases 

temperature accounts for only 4 percent of 

the interannual variability (Kovats, et al., 

2005). Pathogenic species of Campylobacter

cannot replicate in the environment and will 

not persist long under non-microaerophilic 

conditions, suggesting that high ambient 

temperatures would not contribute to 

increased replication in water or in food 

products. 

Leptospirosis is a re-emerging disease in 

the United States and, given its wide case 

distribution, high number of pathogenic strains, 

and wide array of hosts, it is often cited as one 

of the most widespread zoonotic disease in the 

world (Meites et al., 2004; WHO, 1999). While 

it has not been a reportable disease nationally 

since 1995, several states continue to collect 

passive surveillance data and cases continue 

to be reported (Katz et al., 2002; Meites et 

al., 2004). Because increased disease rates are 

linked to warm temperatures, epidemiological 

evidence suggest that climate change may 

increase the number of cases.

Pathogenic species of Vibrio (primarily V. 

vulnificus) account for 20 percent of sporadic 

shellfish-related illnesses and over 95 percent 

of deaths (Lipp and Rose 1997; Morris, 2003). 

While the overall incidence of illness from 

Vibrio infections remains low, the rate of 

infection increased 41 percent since 1996 (Vugia 

et al., 2006). Vibrio species are more frequently 

associated with warm climates (e.g., Janda et 

al., 1988; Lipp et al., 2002). Coincident with 

proliferation in the environment, human cases 

also occur during warm temperatures. In the 

United States, the highest case rates occur in the 

summer months (Dziuban et al., 2006). Given 

the close association between temperature, the 

pathogen, and disease, increasing temperatures 

46
Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

may increase the geographic range and disease 

burdens of Vibrio pathogens (e.g., Lipp et al., 

2002). For example, increasing prevalence and 

diversity of Vibrio species has been noted in 

northern Atlantic waters of the United States 

coincident with warm water (Thompson et al., 

2004). Additionally, although most cases of V. 

vulnificus infection are attributed to Gulf Coast 

states, this species recently has been isolated 

from northern waters in the United States 

(Pfeffer et al., 2003; Randa et al., 2004). 

The most striking example of an increased 

range in pathogen distribution and incidence 

was documented in 2004, when an outbreak of 

shellfish-associated V. parahaemolyticus was 

reported from Prince William Sound in Alaska 

(McLaughlin et al., 2005). V. parahaemolyticus

had never been isolated from Alaskan shellfish 

before and it was thought that Alaskan waters 

were too cold to support the species (McLaughlin 

et al., 2005). In the period preceding the July 

2004 outbreak, water temperatures in the 

harvesting area consistently exceeded 15° C 

and the mean daily water temperatures were 

significantly higher than in the prior six years 

(McLaughlin et al., 2005). This outbreak 

extended the northern range of oysters known to 

contain V. parahaemolyticus and cause illness 

by 1,000 km. Given the well-documented 

association between increasing sea surface 

temperatures and proliferation of many Vibrio 

species, evidence suggests that increasing 

global temperatures will lead to an increased 

burden of disease associated with certain 

Vibrio species in the United States, especially 

V. vulnificus and V. parahaemolyticus. 

P r o t o z o a n p a r a s i t e s , p a r t i c u l a r l y 

Cryptosporidium and Giardia, contribute 

significantly to water-borne and to a lesser 

extent food-borne disease burdens in the United 

States. Both parasites are zoonotic and form 

environmentally resistant infective stages, with 

only 10-12 oocysts or cysts required to cause 

disease. In 1998, 1.2 cases of cryptosporidiosis 

per 100,000 people were reported in the 

United States (Dietz and Roberts, 2000); the 

immunocompromised are at particularly high 

risk (Casman et al., 2001; King and Monis, 

2006). Between 2003 and 2004, of the 30 

reported outbreaks of gastroenteritis from 

recreational water, 78.6 percent were due to 

Cryptosporidium and 14.3 percent were due 

to Giardia (Dzuiban et al., 2006). Giardia has 

historically been the most commonly diagnosed 

parasite in the United States. Between 1992 

and 1997 there were 9.5 cases of Giardia per 

100,000 people (Furness et al., 2000). Both 

Cryptosporidium and Giardia case reports 

peak in late summer and early fall, particularly 

among younger age groups (Dietz and Roberts, 

2000; Furness et al., 2000). For both parasites, 

peak rates of reported infection in Massachusetts 

occurred approximately one month after the 

annual temperature peak (Naumova et al., 2006). 

The lagged association between peak annual 

temperatures and peaks in reported cases in 

late summer has been attributed to increased 

exposure during the summer bathing season, 

especially in the younger age groups, and to a 

slight lag in reporting (Dietz and Roberts, 2000; 

Furness et al., 2000; Casman et al., 2001). With 

increasing global temperatures, an increase 

in recreational use of water can be reasonably 

expected and could lead to increased exposure 

among certain groups, especially children. 

Naegleria fowleri i s a f r e e - l i v i n g 

amboeboflagellate found in lakes and ponds 

at warm temperatures, either naturally or in 

thermally polluted bodies of water. While 

relatively rare, infections are almost always 

fatal (Lee et al., 2002). N. fowleri can be 

detected in environmental waters at rates 

up to 50 percent (Wellings et al., 1977) at 

water temperatures above 25°C (Cabanes et 

al., 2001). Cases are consistently reported in 

the United States. Between 1999 and 2000, 

four cases (all fatal) were reported. While 

N. fowleri continues to be a rare disease, it 

remains more common in the United States 

than elsewhere in the world (Marciano-Cabral 

et al., 2003). Given its association with warm 

water, elevated temperatures could increase 

this pathogen’s range.

Epidemiologically significant viruses for food 

and water exposure include enteroviruses, 

rotaviruses, hepatitis A virus, and norovirus. 

Viruses account for 67 percent of food-borne 

disease, and the vast majority of these are due 

to norovirus (Mead et al., 1999). Rotavirus 

accounts for a much smaller fraction of viral 

food-borne disease (Mead et al., 1999), but is 

a significant cause of diarrheal disease among 

47
The U.S. Climate Change Science Program Chapter 2

48

infants and young children (Charles et al., 

2006). Enteroviruses are not reportable and 

therefore incidence rates are poorly reflected 

in surveillance summaries (Khetsuriani et 

al., 2006). With the exception of hepatitis A 

(Naumova et al., 2006), enteric viral infection 

patterns follow consistent year to year trends. 

Enteroviruses are characterized by peaks in 

cases in the early to late summer (Khetsuriani 

et al., 2006), while rotavirus and norovirus 

infections typically peak in the winter (Cook et 

al., 1990; Lynch et al., 2006). No studies have 

been able to identify a clear role for temperature 

in viral infection patterns.

An analysis of water-borne outbreaks associated 

with drinking water in the United States between 

1948 and 1994 found that 51 percent of outbreaks 

occurred following a daily precipitation event 

in the 90th percentile and 68 percent occurred 

when precipitation levels reached the 80th 

percentile (Curriero et al., 2001) (Figure 2.4). 

Similarly, Thomas et al. (2006) found that 

the risk of water-borne disease doubled when 

rainfall amounts surpassed the 93rd percentile. 

Rose et al. (2000) found that the relationship 

between rainfall and disease was stronger for 

surface water outbreaks, but the association was 

significant for both surface and groundwater 

sources. In 2000, groundwater used for drinking 

water in Walkerton, Ontario was contaminated 

with E. coli O157:H7 and Campylobacter during 

rains that surpassed the 60-year event mark 

for the region and the 100-year event mark in 

local areas (Auld et al., 2004). In combination 

with preceding record high temperatures, 2,300 

people in a community of 4,800 residents became 

ill (Hrudey et al., 2003; Auld et al., 2004). 

Floodwaters may increase the likelihood of 

contaminated drinking water and lead to 

incidental exposure to standing floodwaters. 

In 1999, Hurricane Floyd hit North Carolina 

and resulted in severe flooding of much of the 

eastern portion of the state, including extensive 

hog farming operations. Residents in the affected 

areas experienced more than twice the rate of 

gastrointestinal illness following the flood as 

before it (Setzer and Domino, 2004). Following 

the severe floods of 2001 in the Midwest, contact 

with floodwater was shown to increase the rate 

and risk of gastrointestinal illness, especially 

among children (Wade et al., 2004); however, 

consumption of tap water was not a risk factor as 

drinking water continued to meet all regulatory 

standards (Wade et al., 2004).

2.2.4.3 Influenza

Influenza may be considered a zoonosis in that 

pigs, ducks, etc. serve as non-human hosts to 

the influenza viruses (e.g., H3N2, H1N1) that 

normally infect humans (not H5N1). A number 

of recent studies evaluated the influence of 

weather and climate variability on the timing 

and intensity of the annual influenza season 

in the United States and Europe. Results 

indicated that cold winters alone do not predict 

pneumonia and influenza (P&I)-related winter 

deaths, even though cold spells may serve as 

a short-term trigger (Dushoff et al., 2005), 

and that regional differences in P&I mortality 

burden may be attributed to climate patterns 

and to the dominant circulating virus subtype 

(Greene et al., 2006). Studies in France and the 

United States demonstrated that the magnitude 

of seasonal transmission (whether measured as 

mortality or morbidity) during winter seasons 

is significantly higher during years with cold El 

Niño Southern Oscillation (ENSO) conditions 

than during warm ENSO years (Flahault et al., 

2004; Viboud et al., 2004), whereas a study in 

California concluded that higher temperatures 

and El Niño years increased hospital admissions 

for viral pneumonia (Ebi et al., 2001). In an 

attempt to better understand the spatio-temporal 

patterns of ENSO and influenza, Choi et al.,

Figure 2.4. Drinking Water-borne Disease Outbreaks and 90th percentile 

Precipitation Events (a two month lag precedes outbreaks); 1948–1994.

Source: Curriero et al., 2001

 RESEARCH 

Note. Outbreak locations represent the centroid of the affected watershed.

FIGURE 1—Waterborne disease outbreaks and associated extreme levels of precipitation (precipitation in the highest 10% [90th percentile])

within a 2-month lag preceding the outbreak month: United States, 1948–1994.

dental fecal releases associated with recreational outbreaks and infrastructure problems

in the distribution system.

The conterminous United States is subdivided into 2105 hydrologic cataloging units

called watersheds, which are geographic areas

representing part or all of a surface drainage

largest subdivision in this hierarchy (watersheds are the smallest), which divides the

United States into 18 distinct hydrologic regions, each containing the drainage area of a

major river or the combined drainage areas

of a series of rivers.

Total monthly precipitation readings for the

1997. We considered there to be sufficient information to compute z scores only if the corresponding distributions contained at least 20

years of recorded data. The z score thresholds

were chosen to indicate extreme levels of precipitation. For example, z scores greater than

0.84, 1.28, and 1.65 correspond, respectively,
49

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

(2006) used stochastic models (mathematical 

models that take into account the presence of 

randomness) to analyze California countyspecific influenza mortality and produced maps 

that showed different risks during the warm 

and cool phases. In general, these studies of 

influenza further support the importance of 

climate drivers at a global and regional scale, 

but have not advanced our understanding of 

underlying mechanisms.

2.2.4.4 Valley Fever 

Valley fever (Coccidioidomycosis) is an 

infectious disease caused by inhalation of the 

spores of a soil-inhabiting fungus that thrives 

during wet periods following droughts. The 

disease is of public health importance in the 

Desert Southwest. In the early 1990s, California 

experienced an epidemic of Valley Fever 

following five years of drought (Kolivras and 

Comrie, 2003). Its incidence varies seasonally 

and annually, which may be due partly to 

climatic variations (Kolivras and Comrie, 

2003; Zender and Talamantes, 2006). If so, 

climate change could affect its incidence and 

geographic range.

2.2.4.5 Morbidity and Mortality Due to 

Changes in Air Quality

Millions of Americans continue to live in areas 

that do not meet the health-based National 

Ambient Air Quality Standards for ozone and 

fine particulate matter (PM2.5). Both ozone and 

PM2.5 have well-documented health effects, 

and levels of these two pollutants have the 

potential to be influenced by climate change 

in a variety of ways.

Ground-level ozone is formed mainly by 

reactions that occur in polluted air in the 

presence of sunlight. Nitrogen oxides (emitted 

mainly by burning of fossil fuels) and volatile 

organic compounds (VOCs) (emitted both by 

burning of fossil fuels and by evaporation from 

vegetation and stored fuels, solvents, and other 

chemicals) are the key precursor pollutants for 

ozone formation. Ozone formation increases 

with greater sunlight and higher temperatures; 

it reaches peak concentrations during the warm 

half of the year, and then mostly in the late 

afternoon and early evening. Cloud cover and 

mixing height are two additional meteorological 

factors that influence ozone concentrations. 

It has been firmly established that breathing 

ozone results in short-term, reversible decreases 

in lung function (Folinsbee et al., 1988) 

as well as inflammation deep in the lungs 

(Devlin et al., 1991). In addition, epidemiologic 

studies of people living in polluted areas have 

suggested that ozone may increase the risk 

of asthma-related hospital visits (Schwartz, 

1995), premature mortality (Kinney and 

Ozkaynak, 1991; Bell et al., 2004), and possibly 

the development of asthma (McConnell et 

al., 2002). Vulnerability to ozone health 

effects is greater for persons who spend time 

outdoors during episode periods, especially 

with physical exertion, because this results in 

a higher cumulative dose to the lung. Thus, 

children, outdoor laborers, and athletes may be 

at greater risk than people who spend more time 

indoors and who are less active. At a given lung 

dose, little has been firmly established about 

vulnerability as a function of age, race, and/or 

existing health status. However, because their 

lungs are inflamed, asthmatics are potentially 

more vulnerable than non-asthmatics.

PM2.5 is a far more complex pollutant than 

ozone, consisting of all air-borne solid or liquid 

particles that share the property of being less 

than 2.5 micrometers in aerodynamic diameter.2

All such particles are included, regardless of 

their size, composition, and biological reactivity. 

PM2.5 has complex origins, including primary 

particles directly emitted from sources and 

secondary particles that form via atmospheric 

reactions of precursor gases. Most of the 

particles captured as PM2.5 arise from burning 

of fuels, including primary particles such as 

diesel soot and secondary particles such as 

sulfates and nitrates. Epidemiologic studies 

have demonstrated associations between both 

short-term and long-term average ambient 

concentrations and a variety of adverse health 

outcomes including respiratory symptoms 

such as coughing and difficulty breathing, 

decreased lung function, aggravated asthma, 

2 Aerodynamic diameter is defined in a complex 

way to adjust for variations in shape and density 

of various particles, and is based on the physical 

diameter of a water droplet that would settle to the 

ground at the same rate as the particle in question. 

For a spherical water particle, the aerodynamic and 

physical diameters are identical.
The U.S. Climate Change Science Program Chapter 2

50

development of chronic bronchitis, heart attack, 

and arrhythmias (Dockery et al., 1993; Samet 

et al., 2000; Pope et al., 1995, 2002, 2004; 

Pope and Dockery, 2006; Dominici et al, 2006; 

Laden et al., 2006). Associations have also been 

reported for increased school absences, hospital 

admissions, emergency room visits, and 

premature mortality. Susceptible individuals 

include people with existing heart and lung 

disease, and diabetics, children, and older 

adults. Because the mortality risks of PM2.5 

appear to be mediated through narrowing of 

arteries and resultant heart impacts (Künzli 

et al., 2005), persons or populations with 

high blood pressure and/or pre-existing heart 

conditions may be at increased risk. In a study 

of mortality in relation to long-term PM2.5 

concentrations in 50 U.S. cities, individuals 

without a high school education demonstrated 

higher concentration/response functions than 

those with more education (Pope et al., 2002). 

This result suggests that low education was a 

proxy for increased likelihood of engaging in 

outdoor labor with an associated increase in 

exposure to ambient air.

Using a coupled climate-air pollution threedimensional model, Jacobson (2008) compared 

the health effects of pre-industrial vs. present 

day atmospheric concentrations of CO2. The 

results suggest that increasing concentrations 

of CO2 increased tropospheric ozone and 

PM2.5, which increased mortality by about 1.1 

percent per degree temperature increase over 

the baseline rate. Jacobson estimated that about 

40 percent of the increase was due to ozone and 

the rest to particulate matter. The estimated 

mortality increase was higher in locations with 

poorer air quality.

2.2.4.6 Aeroallergens and 

Allergenic Diseases

Climate change has caused an earlier onset of the 

spring pollen season for several species in North 

America (Casassa et al., 2007). Although data 

are limited, it is reasonable to infer that allergenic 

diseases caused by pollen, such as allergic rhinitis, 

also have experienced concomitant changes in 

seasonality (Emberlin et al., 2002; Burr et al., 

2003). Several laboratory studies suggest that 

increasing CO2 concentrations and temperatures 

could increase ragweed pollen production and 

prolong the ragweed pollen season (Wan et al., 

2002; Wayne et al., 2002; Singer et al., 2005; 

Ziska et al., 2005; Rogers et al., 2006) and 

increase some plant metabolites that can affect 

human health (Ziska et al., 2005; Mohan et al., 

2006). Although there are suggestions that the 

abundance of a few species of air-borne pollens 

has increased due to climate change, it is unclear 

whether the allergenic content of these pollen 

types has changed (Huynen and Menne, 2003; 

Beggs and Bambrick, 2005). The introduction of 

regionally new invasive species associated with 

climatic and other changes, such as ragweed and 

poison ivy, may increase current health risks. 

There are no projections of the possible impacts 

of climate change on allergenic diseases. 

2.3 Projected Health

Impacts of Climate

Change in the United

States

2.3.1 Heat-Related Mortality 

Determinants of how climate change could alter 

heat-related mortality include actual changes in 

the mean and variance of future temperatures; 

factors affecting temperature variability 

at the local scale; demographic and health 

characteristics of the population; and policies 

that affect the social and economic structure of 

communities, including urban design, energy 

policy, water use, and transportation planning. 

Barring an unexpected and catastrophic 

economic decline, residential and industrial 

development will increase over the coming 
51

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

decades, which could increase urban heat 

islands in the absence of urban design and new 

technologies to reduce heat loads. 

The U.S. population is aging. The portion 

of the population over age 65 is projected 

to be 13 percent by 2010 and 20 percent by 

2030 (over 50 million people) (Day, 1996). 

Older adults are physiologically and socially 

vulnerable (Khosla and Guntupalli, 1999; 

Klinenberg, 2002) to hot weather and heat 

waves, suggesting that heat-related mortality 

could increase. Evidence that diabetics are at 

greater risk of heat-related mortality (Schwartz 

2005), along with the increasing prevalence of 

obesity and diabetes (Seidell, 2000; Visscher 

and Seidell, 2001), suggests that reduced 

fitness and higher-fat body composition may 

contribute to increased mortality.

Table 2.1 summarizes projections of temperaturerelated mortality either in the United States or 

in temperate countries whose experience is 

relevant to the United States (Dessai, 2003) 

(Woodruff et al., 2005) (Knowlton et al., 2007) 

(CLIMB, 2004; Hayhoe et al., 2004). Similar 

studies are underway in Europe (Kosatsky 

et al., 2006; Lachowsky and Kovats, 2006). 

All studies used downscaled projections 

of future temperature distributions in the 

geographic region of interest. The studies used 

different approaches to incorporate likely future 

adaptation, addressing such issues as increased 

availability of air conditioning, heat wave early 

warning systems, demographic changes, and 

enhanced services such as cooling shelters and 

physiological adaptation. 

Time-series studies also can shed light on 

potential future mortality during temperature 

extremes. Heat-related mortality has declined 

over the past decades (Davis et al., 2002; Davis 

et al., 2003a; Davis et al., 2003b). A similar 

trend, for cold- and heat-related mortality, 

was observed in London over the past century 

(Carson et al., 2006). The authors speculate 

that these declines are due to increasing 

prevalence of air-conditioning (in the United 

States), improved health care, and other 

factors. These results do not necessarily mean 

that future increases in heat-related mortality 

may not occur in the United States, as some 

have claimed (Davis et al., 2004), because 

the percentage of the population with access 

to air conditioning is high in most regions 

(thus with limited possibilities for increasing 

access). Further, population level declines 

may obscure persistent mortality impacts in 

vulnerable groups.

The impacts projected for Lisbon were more sensitive to the choice of regional climate model than the method used 

to calculate excess deaths, and the author described the challenge of extrapolating health effects at the high end of the 

temperature distribution, for which data are sparse or nonexistent (Dessai, 2003).

Table 2.1. Projections of Impacts of Climate Change on Heat-Related Mortality

Location Period Adaptation 

considered

Projected Impact on Heat- Related Deaths

Lisbon, 

Portugal3

2020s, 2050s compared to 

1980–1998

yes Increase of 57 percent–113 percent in 2020s, 

97 percent–255 percent in 2050s, depending on 

adaption

8 Australian 

cites4

2100 compared to 1900s no Increase of 1700 to 3200 deaths, depending on 

policy approach followed and age structure of 

population

New York, NY5 2050s compared to 1990s yes Increase 47 percent to 95 percent; reduced by 25 

percent with adaptation

California6 2090s compared to 1990s yes Depending on emissions, mortality increases 

2–7fold from 1990 levels, reduced 20–25 percent 

with adaption

Boston, MA7 projections to 2100 

compared to 1970–92

yes Decrease after 2010 due to adaptation

3 Dessai, 2003

4 Woodruff, 2005

5 Knowton, in press

6 Hayhoe, 2004

7 CLIMB, 2004
The U.S. Climate Change Science Program Chapter 2

52

In summary, given the projections of increases 

in the frequency, intensity, and duration of heat 

waves and projected demographic changes, the 

at-risk population will increase (highly likely). 

The extent to which mortality increases will 

depend on the effective implementation of a 

range of adaptation options, including heat 

wave early warning systems, urban design 

to reduce heat loads, and enhanced services 

during heat waves.

2.3.2 Hurricanes, Floods, 

Wildfires, and Health Impacts

No studies have projected the future health 

burdens of extreme weather events. There is 

concern that climate change could increase the 

frequency and/or severity of extreme events, 

including hurricanes, floods, and wildfires. 

Theoretically, climate change could increase 

the frequency and severity of hurricanes by 

warming tropical seas where hurricanes first 

emerge and gain most of their energy (Pielke 

et al., 2005; Trenberth, 2005; Halverson, 

2006). Controversy over whether hurricane 

intensity increased over recent decades stems 

less from the conceptual arguments than from 

the limitations of available hurricane incidence 

data (Halverson, 2006; Landsea, 2005; Pielke 

et al., 2005; Trenberth, 2005). Even if climate 

change increases the frequency and severity of 

hurricanes, it will be difficult to definitively 

identify this trend for some time because 

of the relatively short and highly variable 

historical data available as a baseline for 

comparison. Adding to the uncertainty, some 

research has projected that climate change could 

produce future conditions that might hinder the 

development of Atlantic hurricanes despite the 

warming of tropical seas (NOAA, 2007c). 

Evidence suggests that the intensity of Atlantic 

hurricanes and tropical storms has increased 

over the past few decades. SAP 3.3 indicates 

that there is evidence for a human contribution 

to increased sea surface temperatures in the 

tropical Atlantic and there is a strong correlation 

to Atlantic tropical storm frequency, duration, 

and intensity. However, a confident assessment 

will require further studies. An increase in 

extreme wave heights in the Atlantic since the 

1970s has been observed, consistent with more 

frequent and intense hurricanes (CCSP, 2008).

For North Atlantic hurricanes, SAP 3.3 

concludes that it is likely that wind speeds and 

core rainfall rates will increase (HendersonSellers et al., 1998; Knutson and Tuleya, 2004, 

2008; Emanuel, 2005). However, SAP 3.3 

concludes that “frequency changes are currently 

too uncertain for confident projection” (CCSP, 

2008). SAP 3.3 also found that the spatial 

distribution of hurricanes will likely change. 

Storm surge is likely to increase due to projected 

sea level rise, though the degree to which storm 

surges will increase has not been adequately 

studied (CCSP, 2008).

Theoretical arguments for increases in extreme 

precipitation and flooding are based on the 

principles of the hydrological cycle where 

increasing average temperature will intensify 

evaporation and subsequently increase 

precipitation (Bronstert, 2003; Kunkel, 2003, 

Senior et al., 2002). Looking at the available 

data for evidence of a climate change signal, 

evidence suggests that the number of extreme 

precipitation events in the United States has 

increased (Balling Jr. and Cerveny, 2003; 

Groisman et al., 2004; Kunkel, 2003). However, 

these results are not as consistent when evaluated 

by season or region (Groisman et al., 2004). 

Projections of changes in the future incidence of 

extreme precipitation and flooding rely on the 

results from general circulation models (GCMs). 

These models project increases in mean 

precipitation with a disproportionate increase 

in the frequency of extreme precipitation events 
53

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

(Senior et al., 2002). Kim (2003) used a regional 

climate model to project that a doubling of 

CO2 concentrations in roughly 70 years could 

increase the number of days with at least 0.5 

mm of precipitation by roughly 33 percent 

across the study’s defined elevation gradients 

in the western United States. Furthermore, 

the IPCC concluded that it is very likely (>90 

percent certainty) that trends in extreme 

precipitation will continue in the 21st century 

(IPCC, 2007a). 

Studies modeling future wildfire incidence in 

the western United States using GCM outputs 

project increasingly severe wildfires, measured 

both in terms of energy released and the number 

of fires that avoid initial containment in areas 

that GCMs project will be increasingly dry 

(Brown et al., 2004; Fried et al., 2004). In 

general, these results suggest much of the 

western United States could face an increasing 

wildfire risk from climate change. The apparent 

exception could be the Pacific Northwest, 

including northern California, where GCMs 

generally project a wetter future. 

Factors independent of the impacts of and 

responses to climate change will affect 

vulnerability to extreme events, including 

population growth, continued urban sprawl, 

population shifts to coastal areas, and differences 

in the degree of community preparation for 

extreme events (U.S. Census Bureau, 2004). 

All else equal, the anticipated demographic 

changes will increase the size of the U.S. 

population at risk for future extreme weather 

events (very likely). This raises the potential 

for increasing total numbers of adverse health 

impacts from these events, even if the rate at 

which these impacts are experienced decreases 

(where the rate reflects the number of impacts 

per some standard population size among those 

actually experiencing the events). 

2.3.3 Vector-borne and 

Zoonotic Diseases

Modeling the possible impacts of climate 

change on VBZ diseases is complex, and few 

studies have made projections for diseases of 

concern in the United States. Studies suggest 

that temperature influences the distributions of 

Ixodes spp. ticks that transmit pathogens causing 

Lyme disease in the United States (Brownstein 

et al., 2003) and Canada (Ogden et al., 2006), 

and tick-borne encephalitis (TBE) in Sweden 

(Lindgren et al., 2000). Higher minimum 

temperatures generally were favorable to 

the potential of expanding tick distributions 

and greater local abundance of these vectors. 

However, changing patterns of tick-borne 

encephalitis in Europe are not consistently 

related to changing climate (Randolph, 2004a). 

Climate change is projected to decrease the 

geographic range of TBE in areas of lower 

latitude and elevation as transmission expands 

northward (Randolph and Rogers, 2000).

2.3.4 Water- and 

Food-borne Diseases

Several important pathogens that are commonly 

transmitted by food or water may be susceptible 

to changes in replication, survival, persistence, 

habitat range, and transmission under changing 

climatic and environmental conditions (Table 

2.2). Many of these agents show seasonal infection 

patterns (indicating potential underlying 

environmental or weather control), are capable 

of survival or growth in the environment, or 

are capable of water-borne transport. Factors 

that may affect these pathogens include changes 

in temperature, precipitation, extreme weather 

events (i.e., storms), and ecological shifts. While 

the United States has successful programs to 

protect water quality under the Safe Drinking 

Water Act and the Clean Water Act, some 

contamination pathways and routes of exposure 

do not fall under regulatory programs (e.g., 

dermal absorption from floodwaters, swimming 

in lakes and ponds with elevated pathogen 

levels, etc.). 

2.3.5 Air Quality Morbidity 

and Mortality

The sources and conditions that give rise to 

elevated ozone and PM2.5 in outdoor air in the 

United States have been and will continue to 

be affected by global environmental changes 

related to land use, economic development, 

and climate change. Conversions of farmland 

and forests into housing developments and 

the infrastructure of schools and businesses 

that support them change the spatial patterns 
The U.S. Climate Change Science Program Chapter 2

54

Pathogen Climate-Related Driver Possible Influence of Climate Change Likelihood of 

Changea

Basis for Assessment References

BacteriaSalmonella Rising Temperature Increasing temperature associated with 

increasing clinical cases

Likely Likelihood of climate event is high 

and published research supports disease trend

D’Souza et al., 2004; Kovats et al., 2004a; Fleury et al., 2006; Naumova et al., 2006

Changes in Precipitation

Precipitation and runoff associated with increased likelihood of contamination of surface waters used for recreation, drinking, or irrigation 

Likely Likelihood of climate event is 

probable but more research is needed to confirm disease trend

Haley 2006;Holley et al., 2006

Shifts in Reservoir Host Ranges

Shifts in habitat and range of reservoir hosts may influence exposure routes and/or rate of contact with humans

More likely than not

Likelihood of climate event is probable but there is insufficient research on this relationship

Srikantiah et al., 2003

Campylobacter Rising Temperature Increasing temperatures may expand typical 

peak season of clinical infection, or result in earlier peak (commonly spring and summer)

More likely than not

Likelihood of climate event is high and published research supports disease trend, but mechnisms are not understood

Skelly & Weinstein, 2003; Louis et al., 2005; Kovats et al., 2005

Increasing temperatures may result in shorter developmental times for flies, contributing to increased transmission by this proposed vector 

About as likely as not

Likelihood of climate event and fly development trend is high but additional research is needed to confirm disease association

Nichols, 2005

Changes in Precipitation

Increasing precipitation and runoff associated with increased likelihood of contamination of surface waters used for recreation or drinking

More likely than not

Likelihood of climate event is probable but more research is needed to confirm disease trend

Auld et al., 2004; Vereen et al., 2007

Table 2.2. Possible Influence of Climate Change on Climate-Susceptible Pathogens and/or Disease, Based on Observational Models or Empirical Evidence 
55

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Pathogen Climate-Related Driver Possible Influence of Climate Change Likelihood of 

Changea

Basis for Assessment References

Shifts in Reservoir Host Ranges or Behavoir

Shifts in habitat and range of reservoir hosts (geographically or temporally) may influence exposure routes and/or rate of contact with humans

More likely than not

Likelihood of climate event is probable but there is insufficient research on this relationship

Stanley et al., 1998; Lacey, 1993; Southern et al., 1990

Vibrio species Rising Temperature Increasing ambient temperatures associated 

with growth in pre-harvest and post-harvest shellfish (in absence of appropriate post-harvest controls) and increasing disease 

Very likely Likelihood of climate event is high 

and evidence supports growth trend in ambient waters; adaptive (control) measures (refrigeration) would reduce this effect for postharvest oysters

Cook, 1994

Increasing temperature associated with higher environmental prevalence and disease

Extremely likely

Likelihood of climate event is high and evidence supports environmental growth trend

Janda et al., 1988; Lipp et al., 2002; McLaughlin et al., 2005; Dziuban et al., 2006 

Increasing temperature associated with range expansion

Very likely Likelihood of climate event is high 

and evidence collected to date supports trend; more data needed to confirm

McLaughlin et al., 2005

Changes in Precipitation

Increasing precipitation and fresh water runoff leads to depressed estuarine salinities and increase in some Vibrio species

About as likely as not

Likelihood of climate event is probable but additional research is needed to confirm pathogen distribution patterns

Lipp et al., 2001b; Louis et al., 2003 

Sea Level Changes Rising sea level and or storm surge increase 

range and human exposure

Likely Likelihood of climate event 

is probable but confirmatory research is needed on disease patterns

Lobitz et al., 2000

Leptospira Rising Temperature Increasing temperatures may increase range of 

pathogen (temporally and geographically)

Likely Likelihood of climate event is high 

but additional research is needed to confirm pathogen distribution patterns

Bharti et al., 2003; Howell and Cole, 2006 

Changes in Precipitation

Increasing precipitation and run off precedes outbreaks

Likely Likelihood of climate event in 

probable and research supports this pattern

Meites et al., 2004

VirusesEnteroviruses Rising Temperature Increasing temperature associated with 

increased or expanded peak clinical season (summer)

Unlikely Likelihood of climate event is high 

but no mechanistic studies are available to explain the underlying cause of this seasonality

Khetsuriani et al., 2006
The U.S. Climate Change Science Program Chapter 2

56

Pathogen Climate-Related Driver Possible Influence of Climate Change Likelihood of 

Changea

Basis for Assessment References

Increasing temperature associated with increased decay and inactivation of viruses in the environment

About as likely as not

Likelihood of climate event is high and research demonstrates decreased persistence under increasing temperatures but little data are available to relate this with disease

Gantzer et al., 1998; Wetz et al., 2004

Changes in Precipitation

Increasing precipitation associated with increased loading of viruses to water and increased exposure or disease

Likely Likelihood of climate is probable 

and research supports this pattern

Lipp et al., 2001a; Frost et al., 2002; Fong et al., 2005

Norovirus Rising Temperature Increasing temperature leads to decreased 

retention of virus in shellfish

Unlikely Likelihood of climate event is high 

and research indicates seasonally high shellfish loading in winter but there is no evidence for direct control of temperature on seasonality of infection

Burkhardt and Calci, 2000

Increasing temperature associated with shorter peak clinical season (winter)

Unlikely Likelihood of climate event is high 

and research indicates seasonal disease peak in winter but there is no evidence for direct control of temperature on seasonality of infection

Mounts et al., 2000

Increasing temperature associated with increased decay and inactivation of viruses in the environment

About as likely as not

Likelihood of climate event is high and research demonstrates decreased persistence under increasing temperatures but little data are available to relate this with disease

Griffin et al., 2003

Changes in Precipitation

Increasing precipitation associated with increased loading of viruses to crops and fresh produce

More likely than not

Likelihood of climate event is probable but there is insufficient research on this relationship

Miossec et al., 2000

Increasing precipitation associated with increased loading of viruses to water and increased exposure or disease

Likely Likelihood of climate is probable 

and research supports this pattern

Goodman et al., 1982

Rotavirus Rising Temperature Increasing temperature associated with 

increased decay and inactivation of viruses in the environment

About as likely as not

Likelihood of climate event is high and research demonstrates decreased persistence under increasing temperatures but little data are available to relate this with disease

Rzezutka and Cook, 2004
57

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Pathogen Climate-Related Driver Possible Influence of Climate Change Likelihood of 

Changea

Basis for Assessment References

Dampening of winter seasonal peak in temperate latitudes

About as likely as not

Likelihood of climate event is high and research indicates seasonal disease peak in winter but there is no evidence for direct control of temperature on seasonality of infection; note that tropical countries do not exhibit a seasonal peak

Cook et al., 1990

ParasitesNaegleria fowleri Rising Temperature Increasing temperature associated with 

expanded range and conversion to flagellated form (infective)

More likely than not

Likelihood of climate event is high but more research is needed to confirm disease trend

Cabanes et al., 2001

Cryptosporidium Rising Temperature Expanding recreational (swimming) season may 

increase likelihood of exposure and disease

About as likely as not

Likelihood of climate event is high but there is insufficient research on this relationship

Naumova et al., 2006

Changes in Precipitation

Increasing precipitation associated with increased loading of parasite to water and increased exposure and disease

Very likely Likelihood of climate event is 

probable and research supports this pattern but adaptive measures (water treatment and infrastructure) would reduce this effect

Curriero et al., 2001; Davies et al., 2004

Giardia Rising Temperature Expanding recreational (swimming) season may 

increase likelihood of exposure and disease

About as likely as not

Likelihood of climate event is high but there is insufficient research on this relationship

Naumova et al., 2006

Changes in Precipitation

Increasing precipitation associated with increased loading of parasite to water and increased disease

Very likely Likelihood of climate event is 

probable and research supports this pattern but adaptive measures (water treatment and infrastructure) would reduce this effect

Kistemann et al., 2002

Shifts in Reservoir Host Ranges or Behavoir

Increasing temperature associated with shifting range in reservoir species (carriers) and expanded disease range

About as likely as not

Likelihood of climate event is probable but there is insufficient research on this relationship

Parkinson and Butler, 2005

a Likelihood was based on expert judgment of the strength of the research and the likelihood of the event. See Chapter 1 for a discussion of likelihood (section 1.5).
The U.S. Climate Change Science Program Chapter 2

58

and absolute amounts of emissions from 

fuel combustion related to transportation, 

space heating, energy production, and other 

activities. Resulting vegetation patterns affect 

biogenic (VOC) emissions that influence ozone 

production. Conversion of land cover from 

natural to man-made also changes the degree to 

which surfaces absorb solar energy (mostly in 

the form of light) and later re-radiate that energy 

as heat, which contributes to urban heat islands. 

In addition to their potential for increasing 

heat-related health effects, heat islands also can 

influence local production and dispersion of air 

pollutants such as ozone and PM2.5. 

It is impor tant to recognize that U.S. 

Environmental Protection Agency administers 

a well-developed and successful national 

regulatory program for ozone, PM2.5, and other 

criteria pollutants. Although many areas of the 

United States remain out of compliance with the 

ozone and PM2.5 standards, there is evidence 

for gradual improvements in recent years, and 

this progress can be expected to continue with 

more stringent emissions controls going forward 

in time. Thus, the influence of climate change 

on air quality will play out against a backdrop 

of ongoing regulatory control of both ozone and 

PM2.5 that will shift the baseline concentrations 

of these two important air pollutants. On 

the other hand, most of the studies that have 

examined potential future climate impacts 

on air quality reviewed below have tried to 

isolate the climate effect by holding precursor 

emissions constant over future decades. Thus, 

the focus has been on examining the sensitivity 

of ozone concentrations to alternative future 

climates rather than on attempting to project 

actual future ozone concentrations. 

The influence of meteorology on air quality 

is substantial and well-established (EPRI, 

2005), raising the possibility that changes in 

climate could alter patterns of air pollution 

concentrations. Temperature and cloud cover 

affect the chemical reactions that lead to ozone 

and secondary particle formation. Winds, 

vertical mixing, and rainfall patterns influence 

the movement and dispersion of anthropogenic 

pollutant emissions in the atmosphere, with 

generally improved air quality at higher 

winds, mixing heights, and rainfall. The most 

severe U.S. air pollution episodes occur with 

atmospheric conditions that limit both vertical 

and horizontal dispersion over multi-day 

periods. Methods used to study the influence 

of climatic factors on air quality range from 

statistical analyses of empirical relationships 

to integrated modeling of future air quality 

resulting from climate change. To date, most 

studies have been limited to climatic effects 

on ozone. Additional research is needed on the 

impacts of climate change on anthropogenic 

particulate matter concentrations.

Leung and Gustafson (2005) used regional 

climate simulations for temperature, solar 

radiation, precipitation, and stagnation/

ventilation, and projected worse air quality in 

Texas and better air quality in the Midwest in 

2045-2055 compared with 1995-2005. Aw and 

Kleeman (2003) simulated an episode of high 

air pollution in southern California in 1996 with 

observed meteorology and then with higher 

temperatures. Ozone concentrations increased 

up to 16 percent with higher temperatures, while 

the PM2.5 response was more variable due to 

opposing forces of increased secondary particle 

formation and more evaporative losses from 

nitrate particles. Bell and Ellis (2004) showed 

greater sensitivity of ozone concentrations in 

the Mid-Atlantic to changes in biogenic than to 

changes in anthropogenic emissions. Ozone’s 

sensitivity to changing temperatures, absolute 

humidity, biogenic VOC emissions, and 

pollution boundary conditions on a fine-scale 

(4 km grid resolution) varied in different regions 

of California (Steiner et al., 2006). 

Several studies explored the impacts of climate 

change alone on future ozone projections. 

In a coarse-scale analysis of pollution over 

the continental United States, Mickley et al.,

(2004) used the GISS (NASA Goddard Institute 

for Space Studies) 4x5o model to project that, 

due to climate change alone (A1b emission 

scenario), air pollution could increase in the 

upper Midwest due to decreases between 

2000 and 2052 in the frequency of Canadian 

frontal passages that clear away stagnating air 

pollution episodes. The 2.8x2.8o Mozart global 

chemistry/climate model was used to explore 

global background and urban ozone changes 

over the 21st century in response to climate 

change, with ozone precursor emissions kept 

constant at 1990s levels (Murazaki and Hess, 
59

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

2006). While global background decreased 

slightly, the urban concentrations due to U.S. 

emissions increased. 

As part of the New York Climate and Health 

Study, Hogrefe and colleagues conducted localscale analyses of air pollution impacts of future 

climate changes using integrated modeling 

(Hogrefe et al., 2004a,b,c; 2005a,b) to examine 

the impacts of climate and land use changes on 

heat- and ozone-related health impacts in the 

NYC metropolitan area (Knowlton et al., 2004; 

Kinney et al., 2006; Bell et al., 2007; Civerolo 

et al., 2006). The GISS 4x5o model was used to 

simulate hourly meteorological data from the 

1990s through the 2080s based on the A2 and 

B2 SRES scenarios. The A2 scenario assumes 

roughly double the CO2 emissions of B2. The 

global climate outputs were downscaled to a 36 

km grid over the eastern United States using the 

MM5 regional climate model. The MM5 results 

were used in turn as inputs to the Congestion 

Mitigation and Air Quality Improvement 

Program regional-scale air quality model. Five 

summers (June, July, and August) in each of four 

decades (1990s, 2020s, 2050s, and 2080s) were 

simulated at the 36 km scale. Pollution precursor 

emissions over the eastern United States were 

based on U.S. EPA estimates at the county level 

for 1996. Compared with observations from 

ozone monitoring stations, initial projections 

were consistent with ozone spatial and temporal 

patterns over the eastern United States in the 

1990s (Hogrefe et al., 2004a). Average daily 

maximum 8-hour concentrations were projected 

to increase by 2.7, 4.2, and 5.0 ppb in the 2020s, 

2050s, and 2080s, respectively, due to climate 

change (Figure 2.5) (Hogrefe et al., 2004c). 

The influence of climate on mean ozone values 

was similar in magnitude to the influence of 

rising global background concentrations by the 

2050s, but climate had a much greater impact on 

extreme values than did the global background. 

When biogenic VOC emissions were allowed to 

increase in response to warming, an additional 

increase in ozone concentrations was projected 

that was similar in magnitude to that of climate 

alone (Hogrefe et al., 2004b). Climate change 

shifted the distribution of ozone concentrations 

toward higher values, with larger relative 

increases in future decades (Figure 2.6). 

Projections in Germany also found larger 

climate impacts on extreme ozone values 

(Forkel and Knoche, 2006). Using the IS92a 

business-as-usual scenario, the ECHAM4 

GCM projected changes for the 2030s compared 

with the 1990s; the output was downscaled to 

a 20 km grid using a modification of the MM5 

regional model, which was in turn linked to the 

RADM2 ozone chemistry model. Both biogenic 

VOC emissions and soil nitric oxide emissions 

were projected to increase as temperatures rose. 

Daily maximum ozone concentrations increased 

by between 2 and 6 ppb (6-10 percent) across the 

study region. The number of cases where daily 

maximum ozone exceeded 90 ppb increased by 

nearly four-fold, from 99 to 384.

Using the New York Climate & Health 

Project (NYCHP) integrated model, PM2.5 

concentrations were projected to increase with 

climate change, with the effects differing by 

component species, with sulfates and primary 

PM increasing markedly and with organic and 

nitrated components decreasing, mainly due 

to movement of these volatile species from the 

particulate to the gaseous phase (Hogrefe et al., 

2005b; 2006). 

Hogrefe et al., (2005b) noted that “the 

simulated changes in pollutant concentrations 

stemming from climate change are the result 

of a complex interaction between changes 

in transport, mixing, and chemistry that 

cannot be parameterized by spatially uniform 

linear regression relationships.” Additional 

u ncer tainties include how population 
The U.S. Climate Change Science Program Chapter 2

60

vulnerability, mix of pollutants, housing 

characteristics, and activity patterns may 

differ in the future. For example, in a warmer 

world, more people may stay indoors with 

air conditioners in the summer when ozone 

levels are highest, decreasing personal 

exposures (albeit with potential increases 

in pollution emissions from power plants). 

Baseline mortality rates may change due 

to medical advances, changes in other risk 

factors such as smoking and diet, and aging 

of the population. 

The NYCHP examined the marginal sensitivity 

of health to changes in climate to project the 

potential health impacts of ozone in the eastern 

United States (Knowlton et al., 2004; Bell et 

al., 2007). Knowlton and colleagues computed 

absolute and percentage increases in ozonerelated daily summer-season deaths in the NYC 

metropolitan region in the 2050s compared with 

the 1990s using a downscaled GCM/RCM/air 

quality model (Knowlton et al., 2004; Kinney 

et al., 2006). The availability of county-scale 

ozone projections made it possible to compare 

impacts in the urban core with those in outlying 

areas. Projected increases in ozone-related 

mortality due to climate change ranged from 

0.4 to 7.0 percent across 31 counties. Bell and 

colleagues expanded the analysis to 50 eastern 

cities and examined both mortality and hospital 

admissions (Bell et al., 2007). Average ozone 

hat this approach neglects the effect of climate change

de the domain on the chemical composition of the

al atmosphere (e.g., through changes in reaction rates,

r vapor, transport, and biogenic emissions). To consider

e effects, it would be necessary to apply a coupled

al/regional climate and chemistry model.

Results and Discussion

Changes in O3 Due to Regional Climate Change

Figure 2 depicts spatial maps of the average daily

mum 8-hour O3 concentrations for the 1990s and the

ase from these concentrations for the simulations with

A2 climate for the 2020s, 2050s, and 2080s. In these

lations, anthropogenic emissions and boundary condi

were fixed at the levels used for the 1990s, while the

ulation of biogenic emissions took into account the

O3 increases exceed 7 ppb for the entire urban corridor from

Washington, D. C., to New York City and for the Ohio

River Valley. However, summertime average 8-hour daily

maximum O3 concentrations are predicted to decrease fo

the southern and northern thirds of the modeling domain

Analysis of model results suggests that this O3 decrease is

caused by a sharp increase in convective activity along with

increased mixed layer heights predicted by the regiona

climate model for these regions (B. Lynn, personal com

munication, 2004). When the increases of summertime

average daily maximum 8-hour O3 concentrations are

spatially averaged over the locations of the population

oriented O3 monitors depicted in Figure 1, the increases

are 2.7, 4.2, and 5.0 ppb for the 2020s, 2050s, and 2080s

respectively.

[12] In all decades the largest increases of summertime

average daily maximum 8-hour O3 concentrations typi

Figure 2. (a) Summertime average daily maximum 8-hour O3 concentrations for the 1990s and changes

in summertime average daily maximum 8-hour O3 concentrations for the (b) 2020s, (c) 2050s, and

(d) 2080s A2 scenario simulations relative to the 1990s, in parts per billion. Five consecutive summer

seasons were simulated in each decade.

01 HOGREFE ET AL.: SIMULATING REGIONAL AIR POLLUTION CHANGED22301

Figure 2.5 (a) Summertime Average Daily Maximum 8-hour Ozone Concentrations (ppb) for the 1990s 

and Changes for the (b) 2020s relative to the 1990s, (c) 2050s relative to the 1990s, and (d) 2080s relative 

to the 1990s. All are based on the A2 Scenario relative to the 1990s. Five consecutive summer seasons 

were simulated in each decade. 

Source: Hogrefe et al., 2004c.
61

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

concentrations were projected to increase by 

4.4 ppb (7.4 percent) in the 2050s; the range 

was 0.8 percent to 13.7 percent. In addition, 

ozone red alert days could increase by 68 

percent. Changes in health impacts were of 

corresponding magnitude. 

Based on the new research findings published 

since the previous assessment, the following 

summary statements can be made:

•	 There is an established but incomplete level 

of knowledge suggesting that both ozone and 

fine particle concentrations may be affected 

by climate change. 

•	 A substantial body of new evidence on 

ozone supports the interpretation that 

ozone concentrations would be more likely 

to increase than decrease in the United 

States as a result of climate change, holding 

precursor emissions constant. 

•	 Too few data yet exist for PM to draw firm 

conclusions about the direction or magnitude 

of climate impacts

2.4 Vulnerable Regions

and Subpopulations

In adapting the IPCC (1996) definitions to 

public health, “vulnerability” can be defined as 

the summation of all risk and protective factors 

that ultimately determine whether an individual 

or subpopulation experiences adverse health 

outcomes, and “sensitivity” can be defined as 

an individual’s or subpopulation’s increased 

responsiveness, primarily for biological 

reasons, to a given exposure. Thus, specific 

subpopulations may experience heightened 

vulnerability for climate-related health effects 

for a wide variety of reasons. Biological 

sensitivity may be related to the developmental 

stage, presence of pre-existing chronic medical 

conditions (such as the sensitivity of people 

with chronic heart conditions to heat-related 

illness), acquired factors (such as immunity), 

and genetic factors (such as metabolic enzyme 

subtypes that play a role in sensitivity to air 

pollution effects). Socioeconomic factors also 

play a critical role in altering vulnerability and 

sensitivity to environmentally mediated factors. 

They may alter the likelihood of exposure to 

Figure 2.6 Frequency Distributions of Summertime Daily Maximum 8-hr 

Ozone Concentrations over the eastern United States in the 1990s, 2020s, 

and 2050s based on the A2 Scenario.

Source: From Hogrefe et al., 2005a

ONAL AIR QUALITY MODELING

Impact of Climate Change on Air Quality

global and regional climate modeling studies noted

 have presented evidence that key dynamical features

n to affect ambient pollution concentrations are likely

ange in a future climate. In addition, higher tempera

alone may raise ozone concentrations through in

es in chemical reaction rates and emissions. Simulating

complex interactions of climate and chemically active

llutants requires modeling studies that link the regional

te fields to regional-scale photochemical models such

 Community Multiscale Air Quality (CMAQ) model.11

e models are routinely used for air quality planning

oses by simulating ambient pollutant concentrations

nput of emissions, meteorology, boundary condi

 and land-use parameters. For typical air quality plan

applications, models are run repeatedly with different

ions scenarios, while holding all other inputs (e.g.,

orology, boundary conditions, land use) constant.

ersely, to investigate the effects of climate change,

ions are held constant, while varying meteorological

s based on regional climate simulations such as those

ibed above.

 one recent study, Hogrefe et al.11 applied CMAQ with

izontal grid spacing of 36 km to simulate O3 concen

ns over the eastern United States under current cli

conditions and scenarios of future climate conditions

 on the A2 IPCC scenario.10 Figure 2 displays the fre

cy distributions of model-predicted daily maximum 8-

 concentrations calculated for five summers each in

990s and 20-yr and 50-yr future conditions. These distri

ns show an increase in spatially and temporally aver

summertime daily maximum 8-hr O3 concentrations

 parts per billion (ppb) and 4.2 ppb for the 20-yr and

year future cases, respectively, in the absence of changes

hropogenic emissions and chemical boundary condi

 Even larger effects are simulated for peak values (the

percentile), with increases of 5 ppb and 6.5 ppb, re

vely, for the two future decades. In addition, this work

ed that there was an increase in both the frequency

uration of extreme O3 events over the eastern United

 in the future-year simulations compared to current

tions.

cause atmospheric PM2.5 is a complex mixture of

ical species that are both directly emitted and formed

 atmosphere, emissions sources and atmospheric pro

 have only recently been successfully simulated. Un

anding the effects of the changing climate on these

ons sources and processes is a significant research chal

 at the very early stage of results. Even the effects of

erature changes alone are not clear. For example,

spheric PM2.5 concentrations could increase during

ds of higher ambient temperature because of greater

ions of volatile organic compounds and faster chemi

action rates, resulting in the production of more sec

ry PM

Converselythere are several atmospheric

higher temperatures may alter boundary layer inversions, reducing the concentration of airborne pollutants close to the

Earth’s surface on very hot days. Furthermore, higher temperatures favor the partitioning of semi-volatile particulate

matter into the gas phase, reducing PM2.5 concentrations.

Simulations using a regional air quality model demonstrate higher temperatures may decrease PM2.5 concentrations during a peak episode in the San Joaquin Valley, CA.12

However, this result may indicate a shift in the peak episode

to later in the year, creating a longer season for elevated O3

and PM2.5 episodes. As noted above, the changing climate

involves more than temperature changes alone. Regional

climate simulations indicate that this area may experience

increased stagnation during fall, which would also exacerbate peak PM2.5 events.7

Other Factors Affecting Future Air Quality

The projected growth in global emissions will alter the chemical composition of the troposphere.9

 Changes in U.S. anthropogenic emissions and intercontinental transport of

pollutants both influence regional air quality.13-14 In the absence of more detailed projections, Hogrefe et al.11 approximated these two effects with values based on IPCC literature

in their CMAQ simulations and found that changes in chemical boundary conditions

regional climateand anthropo

Figure 2. Frequency distributions of summertime daily maximum

8-hr O3 concentrations over the eastern United States simulated

by CMAQ for five summers under climate conditions for the

1990s, 20 yr future (2020s), and 50 yr future (2050s).

harmful agents, interact with biological factors 

that mediate risk (such as nutritional status), 

and/or lead to differences in the ability to adapt 

or respond to exposures or early phases of 

illness and injury. For public health planning, 

it is critical to recognize populations that may 

experience synergistic effects of multiple risk 

factors for health problems related to climate 

change and to other temporal trends.

2.4.1 Vulnerable Regions

Populations living in certain regions of the 

United States may experience altered risks for 

specific climate-sensitive health outcomes due 

to their regions’ baseline climate, abundance 

of natural resources such as fertile soil and 

fresh water supplies, elevation, dependence on 

private wells for drinking water, or vulnerability 

to coastal surges or riverine flooding. Some 

regions’ populations may in fact experience 
The U.S. Climate Change Science Program Chapter 2

62

Figure 2.7 a-d U.S. maps indicating counties with existing vulnerability to climate sensitive health 

outcomes: (a) location of hurricane landfalls; (b) EHEs, defined by CDC as temperatures 10 or more 

degrees Fahrenheit above the average high temperature for the region and lasting for several weeks; (c) 

percentage of population over age 65; (d) West Nile Virus cases reported in 2004. Historical disease 

activity, especially in the case of WNV, is not necessarily predictive of future vulnerability. Maps were 

generated using NationalAtlas.govTM Map Maker (2008).

Geographic Vulnerability of US Residents to Selected Climate Health Impacts

multiple climate-sensitive health problems 

simultaneously. One approach to identifying such 

areas is to map regions currently experiencing 

increased rates of climate-sensitive health 

outcomes or other indicators of increased climate 

risk, as illustrated in Figure 2.7a-2.7d.

Residents of low-lying coastal regions, which 

are common locations for hurricane landfalls 

and flooding, are particularly vulnerable to 

the health impacts of climate change. Those 

who live in the Gulf Coast region, for example, 

are likely to experience increased human 

health burdens due to the constellation of 

more intense storms, greater sea level rise, 

coastal erosion, and damage to freshwater 

resources and infrastructure. Other coastal 

areas may also experience the combination 

of sea level rise chronically threatening water 

supplies and periodic infrastructure damage 

from more intense storms. Populations in 

the Southwest and Great Lakes regions may 

experience increased strain on water resources 

and availability due to climate change. More 

intense heat waves and heat-related illnesses 

may take place in regions where extreme heat 

events (EHE) already occur, such as interior 

continental zones of the United States. Highdensity urban populations will experience 

heightened health risks, in part due to the heatisland effect. In addition, increased demand for 

electricity during summers may lead to greater 

air pollution levels (IPCC, 2007b).

2.4.2 Specific Subpopulations at Risk

Vulnerable subpopulations may be categorized 

according to specific health endpoints. (Table 

2.3). While this is typically the way the scientific 

literature reports risk factors for adverse health 
63

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

effects, this section discusses vulnerability for 

a variety of climate-sensitive health endpoints 

one subpopulation at a time. 

2.4.2.1 Children

Children’s small body mass to surface area ratio 

and other factors make them more vulnerable 

to heat-related morbidity and mortality (AAP, 

2000), while their increased breathing rates 

relative to body size, time spent outdoors, and 

developing respiratory tracts heighten their 

sensitivity to harm from ozone air pollution 

(AAP, 2004). In addition, children’s relatively 

naive immune systems increase the risk of 

serious consequences from water- and foodborne diseases. Specific developmental factors 

make them more vulnerable to complications 

from specific severe infections such as E coli

O157:H7. Children’s lack of immunity also plays 

a role in higher risk of mortality from malaria 

(CDC, 2004b). Conversely, maternal antibodies 

to dengue in infants convey increased risk of 

developing dengue hemorrhagic syndromes. 

A second peak of greater risk of complications 

from dengue appears in children between the 

ages of 3 and 5 (Guzman and Khouri, 2002). 

Children may also be more vulnerable to 

psychological complications of extreme 

weather events related to climate change. 

Following two floods in Europe in the 1990s, 

children demonstrated moderate to severe stress 

symptoms (Becht et al., 1998; cited in Hajat et 

al., 2003) and long-term PTSD, depression, and 

dissatisfaction with ongoing life (Bokszanin, 

2000; cited in Hajat et al., 2003). 

2.4.2.2 Older Adults

Health effects associated with climate change 

pose significant risks for the elderly, who 

often have frail health and limited mobility. 

Older adults are more sensitive to temperature 

extremes, particularly heat (Semenza et al., 

1996; Medina-Ramon et al., 2006); individuals 

65 years of age and older comprised 72 percent 

of the heat-related deaths in the 1995 Chicago 

heat wave (Whitman et al., 1997). The elderly 

are also more likely to have preexisting 

medical conditions, including cardiovascular 

and respiratory illnesses, which may put 

them at greater risk of exacerbated illness 

by climate-related events or conditions. For 

example, a 2004 rapid needs assessment of 

older adults in Florida found that Hurricane 

Charley exacerbated preexisting, physiciandiagnosed medical conditions in 24-32 percent 

of elderly households (CDC, 2004a). Also, 

effects of ambient particulate matter on daily 

mortality tend to be greatest in older age groups 

(Schwartz, 1995).

Table 2.3. Climate-Sensitive Health Outcomes and Particularly Vulnerable Groups 

Climate-Sensitive Health Outcome Particularly Vulnerable Groups 

Heat-Related Illnesses and Deaths Elderly, chronic medical conditions, infants and 

children, pregnant women, urban and rural poor, 

outdoor workers

Diseases and Deaths Related to Air Quality Children, pre-existing heart or lung disease, diabetes, 

athletes, outdoor workers

Illnesses and Deaths Due to Extreme 

Weather Events

Poor, pregnant women, chronic medical conditions, 

mobility and cognitive constraints

Water- and Food-borne Illness Immunocompromised, elderly, infants; specific risks 

for specific consequences (e.g., Campylobacter and 

Guillain-Barre syndrome, E. coli O157:H7)

Vector-borne Illnesses

Lyme Disease Children, outdoor workers

Hantavirus Rural poor, occupational groups

Dengue Infants, elderly

Malaria Children, immunocompromised, pregnant women, 

genetic (e.g., G6PD status)
The U.S. Climate Change Science Program Chapter 2

64

2.4.2.3 Impoverished Populations

Even in the United States, the greatest health 

burdens related to climate change are likely 

to fall on those with the lowest socioeconomic 

status (O’Neill et al., 2003a). Most affected are 

individuals with inadequate shelter or resources 

to find alternative shelter in the event their 

community is disrupted. While quantitative 

methods to assess the increase in risk related to 

these social and economic factors are not welldeveloped, qualitative insights can be gained 

by examining risk factors for mortality and 

morbidity from recent weather-related extreme 

events such as the 1995 heat wave in Chicago 

and Hurricane Katrina in 2005 (Box 2.1). 

Studies of heat waves identify poor housing 

conditions, including lack of access to air 

conditioning and living spaces with fewer 

rooms, as significant risk factors for heatrelated mortality (Kalkstein, 1993; Semeza 

et al., 1996). Higher heat-related mortality 

has been associated with socioeconomic 

indicators, such as lacking a high school 

education and living in poverty (Curriero et 

al., 2002). Financial stress plays a role, as one 

study of the 1995 Chicago heat wave found that 

concern about the affordability of utility bills 

influenced individuals to limit air conditioning 

use (Klinenberg, 2002). The risk for exposure 

and sensitivity to air pollution is also elevated 

among groups in a lower socioeconomic 

position (O’Neill et al., 2003a).

Air conditioning is an important short-term method 

for protecting health, but is not a sustainable longterm adaptation technology because the electricity 

use is often associated with greenhouse gas 

emissions and during heat waves can overload the 

grid and contribute to outages (O’Neill, 2003c). 

Furthermore, the elderly with limited budgets and 

racial minorities are less likely to have access to 

air conditioning or to use it during hot weather 

(O’Neill et al., 2005b, Sheridan, 2006). Incentives 

for and availability of high-efficiency, low energydemand residential cooling systems, especially 

among disadvantaged populations, can advance 

health equity and minimize some of the negative 

aspects of air conditioning.

Another area of concern for impoverished 

populations is the impact that climate change 

may have on food systems and food supply. In 

the United States, food insecurity is a prevalent 

health risk among the poor, particularly poor 

children (Cook et al., 2007). On a global scale, 

studies suggest that climate change is likely to 

contribute to food insecurity by reducing crop 

yield, most significantly at lower latitudes, due 

to shortened growing periods and decreases 

in water availability (Parry et al., 2005). In 

Box 2.1 Vulnerable Populations and Hurricane Katrina

In 2005, Hurricane Katrina caused more than 1,500 deaths along the Gulf Coast. Many of these victims 

were members of vulnerable subpopulations, such as hospital and nursing-home patients, older adults who 

required care within their homes, and individuals with disabilities (U.S. CHSGA, 2006). The hurricane was 

complicated by a catastrophic failure of the levee system that was intended to shield those areas in New 

Orleans that lie at or below sea level. According to the Louisiana Department of Health and Hospitals, 

more than 45 percent of the state’s identified victims were 75 years of age or older; 69 percent were above 

age 60 (LDHH, 2006). In Mississippi, 67 percent of the victims whose deaths were directly, indirectly, or 

possibly related to Katrina were 55 years of age or older (MSDH, 2005). 

At hurricane evacuation centers in Louisiana, Mississippi, Arkansas, and Texas, chronic illness was the most 

commonly reported health problem, accounting for 33 percent or 4,786 of 14,531 visits (CDC, 2006a). 

Six of the fifteen deaths indirectly related to the hurricane and its immediate aftermath in Alabama were 

associated with preexisting cardiovascular disease (CDC, 2006c), and the storm disrupted an estimated 

100,000 diabetic evacuees across the region from obtaining appropriate care and medication (Cefalu et 

al., 2006). One study suggested that the hurricane had a negative effect on reproductive outcomes among 

pregnant women and infants, who experienced exposure to environmental toxins, limited access to safe 

food and water, psychological stress, and disrupted health care (Callaghan et al., 2007). Other vulnerable 

individuals included those without personal means of transportation and poor residents in Louisiana and 

Mississippi who were unable to evacuate in time (U.S. CHSGA, 2006). 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

the United States, changes in the price of food 

would likely contribute to food insecurity to a 

greater degree than overall scarcity.

The tragic loss of life that occurred after 

Hurricane Katrina underscores the increased 

vulnerability of special populations and 

demonstrates that, in the wake of extreme 

weather events, particularly those that disrupt 

medical infrastructure and require largescale evacuation, treating individuals with 

chronic diseases is of critical concern (Ford 

et al., 2006). 

2.4.2.4 People with Chronic Conditions 

and Mobility and Cognitive Constraints 

People with chronic medical conditions have 

an especially heightened vulnerability for the 

health impacts of climate change. Extreme heat 

poses a great risk for individuals with diabetes 

(Schwartz, 2005), and extreme cold has an 

increased effect on individuals with chronic 

obstructive pulmonary disease (Schwartz, 

2005). People with mobility and cognitive 

constraints may be at particular risk during heat 

waves and other extreme weather events (EPA, 

2006). As noted above, those with chronic 

medical conditions are also at risk of worsened 

status as the result of climate-related stressors 

and limited access to medical care during 

extreme events.

2.4.2.5 Occupational Groups

Certain occupational groups, primarily by virtue 

of spending their working hours outdoors, are at 

greater risk of climate-related health outcomes. 

Outdoor workers in rural or suburban areas, 

such as electricity and pipeline utility workers, 

are at increased risk of infection with Lyme 

Disease, although evidence is lacking for 

greater risk of clinical illness (Schwartz and 

Goldstein, 1990; Piacentino and Schwartz, 

2002). They and other outdoor workers have 

increased exposures to ozone air pollution and 

heat stress, especially if work tasks involve 

heavy exertion.

2.4.2.6 Recent Migrants and Immigrants

Residential mobility, migration, and immigration 

may increase vulnerability. For example, new 

residents in an area may not be acclimated to 

the weather patterns, have lower awareness 

of risks posed by local vector-borne diseases, 

and have fewer social networks to provide 

support during an extreme weather event. U.S. 

immigrants returning to their countries of 

origin to visit friends and relatives have also 

been shown to suffer increased risks of severe 

travel-associated diseases (Bacaner et al., 2004, 

Angell and Cetron, 2005). This vulnerability 

may become more significant if such diseases, 

which include malaria, viral hepatitis, and 

typhoid fever, become more prevalent in 

immigrants’ countries of origin because of 

climate change. 

2.5 Adaptation

Realistically assessing the potential health effects 

of climate change must include consideration 

of the capacity to manage new and changing 

climatic conditions. Individuals, communities, 

governments, and other organizations currently 

engage in a wide range of actions to identify 

and prevent adverse health outcomes associated 

with weather and climate. Although these 

actions have been largely successful, recent 

extreme events and outbreaks of vector-borne 

diseases highlight areas for improvement 

(Confalonieri et al., 2007). Climate change is 

likely to further challenge the ability of current 

programs and activities to control climatesensitive health determinants and outcomes. 

Preventing additional morbidity and mortality 

requires consideration of all upstream drivers of 

adverse health outcomes, including developing 

and deploying adaptation policies and measures 

that consider the full range of health risks that 

are likely to arise with climate change. 

In public health, prevention is the term analogous 

to adaptation, acknowledging that adaptation 

implies a set of continuous or evolving practices 

and not just upfront investments. Public health 

prevention is classified as primary, secondary, 

or tertiary. Primary prevention aims to prevent 

the onset of disease in an otherwise unaffected 

population (such as regulations to reduce 

harmful exposures to ozone). Secondary 

prevention entails preventive action in response 

to early evidence of health effects (including 

strengthening disease surveillance programs 

to provide early intelligence on the emergence 
The U.S. Climate Change Science Program Chapter 2

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or re-emergence of health risks at specific 

locations, and responding effectively to disease 

outbreaks, such as West Nile virus). Tertiary 

prevention consists of measures (often treatment) 

to reduce long-term impairment and disability 

and to minimize suffering caused by existing 

disease. In general, primary prevention is more 

effective and less expensive than secondary and 

tertiary prevention. For every health outcome, 

there are multiple possible primary, secondary, 

and tertiary preventions. 

The degree to which programs and measures will 

need to be modified to address the additional 

pressures due to climate change will depend on 

factors such as the current burden of climatesensitive health outcomes, the effectiveness 

of current interventions, projections of where, 

when, and how quickly the health burdens could 

change with changes in climate and climate 

variability (which depends on the rate and 

magnitude of climate change), the feasibility 

of implementing additional cost-effective 

interventions, other stressors that could increase 

or decrease resilience to impacts, and the social, 

economic, and political context within which 

interventions are implemented (Ebi et al., 

2006a). Failure to invest in adaptation may leave 

communities poorly prepared and increase the 

probability of severe adverse consequences 

(Haines et al., 2006a,b). 

Adaptation to climate change is basically a risk 

management issue. Adaptation and mitigation 

are the primary responses to manage current and 

projected risks. Mitigation and adaptation are not 

mutually exclusive. Co-benefits to human health 

can result concurrently with implementation of 

mitigation and adaptation actions. A dialogue 

is needed on prioritizing the costs of mitigation 

actions designed to limit future climate change 

and the potential costs of continually trying 

to adapt to its impacts. This dialogue should 

explicitly recognize that there is no guarantee 

that future changes in climate will not present 

a threshold that poses technological or physical 

limits to which adaptation is not possible.

Adaptation policies and measures should 

address both projected risks and the regions 

and populations that currently are not well 

adapted to climate-related health risks. Because 

the degree and rate of climate change are 

projected to increase over time, adaptation 

will be a continual process of designing and 

implementing policies and programs to prevent 

adverse impacts from changing exposures and 

vulnerabilities (Ebi et al., 2006). Clearly, the 

extent to which effective proactive adaptations 

are developed and deployed will be a key 

determinant of future morbidity and mortality 

attributable to climate change.

Regional vulnerabilities to the health impacts 

of climate change are influenced by physical, 

social, demographic, economic, and other 

factors. Adaptation activities take place within 

the context of slowly changing factors that are 

specific to a region or population, including 

specific population and regional vulnerabilities, 

social and cultural factors, the built and natural 

environment, the status of the public health 

infrastructure, and health and social services. 

Because these factors vary across geographic 

and temporal scales, adaptation policies and 

measures generally are more successful when 

focused on a specific population and location. 

Additional important factors include the degree 

of risk perceived, the human and financial 

resources available for adaptation, the available 

technological options, and the political will to 

undertake adaptation. 

2.5.1 Actors and Their Roles and 

Responsibilities for Adaptation

Responsibility for the prevention of climatesensitive health risks rests with individuals, 

c o m m u n it y a n d s t a t e gove r n m e nt s , 

national agencies, and others. The roles and 

responsibilities vary by health outcome. 

For example, individuals are responsible 

for taking appropriate action on days with 

declared poor air quality, with health care 

providers and others responsible for providing 

the relevant information, and government 

agencies providing the regulatory framework. 

Community governments play a central role in 

preparedness and response for extreme events 

because of their jurisdiction over police, fire, 

and emergency medical services. Early warning 

systems for extreme events such as heat waves 

(Box 2.2) and outbreaks of infectious diseases 

may be developed at the community or state 

level. The federal government funds research 

and development to increase the range of 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

decision support planning and response tools. 

Medical and nursing schools are responsible for 

ensuring that health professionals are trained 

in the identification and treatment of climatesensitive diseases. The Red Cross and other 

nongovernmental organizations (NGOs) often 

play critical roles in disaster response. 

Ensuring that surveillance systems account 

for and anticipate the potential effects of 

climate change will be beneficial. For example, 

surveillance systems in locations where changes 

in weather and climate may foster the spread 

of climate-sensitive pathogens and vectors 

into new regions would help advance our 

understanding of the associations between 

disease patterns and environmental variables. 

This knowledge could be used to develop 

early warning systems that warn of outbreaks 

before most cases have occurred. Increased 

understanding is needed of how to design these 

systems where there is limited knowledge of 

the interactions of climate, ecosystems, and 

infectious diseases (NAS, 2001).

There are no inventories in the United 

States of the various actors taking action 

to cope with climate change-related health 

impacts. However, the growing numbers 

of city and state actions on climate change 

show increasing awareness of the potential 

risks. As of 1 November 2007, more than 700 

cities have signed the U.S. Mayors’ Climate 

Protection Agreement (http://www.seattle.

gov/mayor/climate/cpaText.htm). Although 

this agreement focuses on mitigation through 

increased energy efficiency, one strategy, 

planting trees, can both sequester CO2 and 

reduce urban heat islands. The New England 

Governors and Eastern Canadian Premiers 

developed a Climate Change Action Plan 

because of concerns about public health 

associated with degradation in air quality, 

public health risks, the magnitude and 

frequency of extreme climatic phenomena, 

and availability of water. (NEG/ECP, 2001). 

One action item focuses on the reduction and/

or adaptation of negative social, economic, 

and environmental impacts. Activities being 

undertaken include a long-term phenology 

study and studies on temperature increases 

and related potential impacts.

Strategies, policies, and measures implemented 

by community and state governments, federal 

agencies, NGOs, and other actors can change the 

Box 2.2 Heat Wave Early Warning Systems

Projections for increases in the frequency, intensity, and duration of heat waves suggest that more cities 

need heat wave early warning systems, including forecasts coupled with effective response options, to warn 

the public about the risks during such events (Meehl and Tebaldi, 2004). Prevention programs designed to 

reduce the toll of hot weather on the public have been instituted in several cities, and guidance has been 

developed to further aid communities seeking to plan such interventions, including buddy systems, cooling 

centers, and community preparedness (EPA, 2006b). Although these systems appear to reduce the toll of 

hot weather (Ebi et al., 2004; Ebi and Schmier, 2005; Weisskopf et al., 2002), and enhance preparedness 

following events such as the 1995 heat waves in Chicago and elsewhere, a survey of individuals 65 or 

older in four North American cities (Dayton, OH; Philadelphia, PA; Phoenix, AZ; and Toronto, Ontario, 

Canada) found that the public was unaware of appropriate preventive actions to take during heat waves 

(Sheridan, 2006). Although respondents were aware of the heat warnings, the majority did not consider 

they were vulnerable to the heat, or did not consider hot weather to pose a significant danger to their 

health. Only 46 percent modified their behavior on the heat advisory days. Although many individuals 

surveyed had access to home air conditioning, their use of it was influenced by concerns about energy 

costs. Precautionary steps recommended during hot weather, such as increasing intake of liquids, were 

taken by very few respondents (Sheridan, 2006). Some respondents reported using a fan indoors with 

windows closed and no air conditioning, a situation that can increase heat exposure and be potentially 

deadly. Further, simultaneous heat warnings and ozone alerts were a source of confusion, because 

recommendations not to drive conflicted with the suggestion to seek cooler locations if the residence was 

too warm. Critical evaluation of heat wave early warning systems is needed, including a determination of 

which components are effective and why (Kovats and Ebi, 2006; NOAA, 2005). 
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context for adaptation by conducting research to 

assess vulnerability and to identify technological 

options available for adaptation, implementing 

programs and activities to reduce vulnerability, 

and shifting human and financial resources to 

address the health impacts of climate change. 

State and federal governments also can provide 

guidance for vulnerability assessments that 

consider a range of plausible future scenarios. 

The results of these assessments can be used 

to identify priority health risks (over time), 

particularly vulnerable populations and regions, 

effectiveness of current adaptation activities, 

and modifications to current activities or new 

activities to address current and future climate 

change-related risks. 

Table 2.4 summarizes the roles and responsibilities 

of various actors for adapting to climate change. 

Note that viewing adaptation from a public 

health perspective results in similar activities 

being classified as primary rather than secondary 

prevention under different health outcomes. 

It is not possible to prevent the occurrence of 

a heat wave, so primary prevention focuses 

on actions such as developing and enforcing 

appropriate infrastructure standards, while 

secondary prevention focuses on implementing 

early warning systems and other activities. For 

vector-borne diseases, primary prevention refers 

to preventing exposure to infected vectors. In this 

case, early warning systems can be considered 

primary prevention. For most vector-borne 

diseases, there are few options for preventing 

disease onset once an individual has been bitten. 

A key activity not included in this framework 

is research on the associations between 

weather / climate and various health outcomes, 

taking into consideration other drivers of 

those outcomes (e.g., taking a systems-based 

approach), and projecting how those risks 

may change with changing weather patterns. 

Increased understanding of the human health 

risks posed by climate change is needed for 

the design of effective, efficient, and timely 

adaptation options. 

2.5.2 Adaptation Measures to 

Manage Climate Change-Related 

Health Risks

Determining where populations are not 

effectively coping with current climate 

variability and extremes facilitates identification 

of the additional interventions that are needed 

now. However, given uncertainties in climate 

change projections, identifying current 

adaptation deficits is not sufficient to protect 

against projected health risks. 

Adaptation measures can be categorized into 

legislative policies, decision support tools, 

technology development, surveillance and 

monitoring of health data, infrastructure 

development, and other measures. Table 2.5 

lists some adaptation measures for health 

impacts from heat waves, extreme weather 

events, vector-borne diseases, water-borne 

diseases, and air quality. These measures are 

generic because the local context, including 

vulnerabilities and adaptive capacity, needs to 

be considered in the design of programs and 

activities to be implemented.

An additional category of measures includes 

public education and outreach to provide 

information to the general public and specific 

vulnerable groups on climate risks to which 

they may be exposed and appropriate actions to 

take. Messages need to be specific to the region 

and group. For example, warnings to senior 

citizens of an impending heat wave should focus 

on keeping cool and drinking lots of water. Box 

2.3 provides tips for dealing with extreme heat 

waves developed by U.S. EPA with assistance 

from federal, state, local, and academic partners 

(U.S. EPA, 2006).

2.6 Conclusions

The conclusions from this assessment are 

consistent with those of the First National 

Assessment: climate change poses a risk for 

U.S. populations, with uncertainties limiting 

quantitative projections of the number of 

increased injuries, illnesses, and deaths 

attributable to climate change. However, the 

strength and consistency of projections for 

climatic changes for some exposures of concern 

to human health suggest that implementation 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Actor Reduce Exposures Prevent Onset of Adverse Health Outcomes Reduce Morbidity and Mortality

Extreme Temperature and Weather EventsIndividuals Stay informed about impending weather events

Follow guidance for emergency preparedness

Follow guidance for conduct during and following an extreme weather event (such as seeking cooling centers during a heat wave or evacuation during a hurricane)

Seek treatment when needed

Community, State, and National Agencies

Provide scientific and technical guidance for building and infrastructure standardsEnforce building and infrastructure standards, including identification of restricted building zones where necessary

Develop scientific and technical guidance and decisions support tools for development of early warning systems and emergency response plans, including appropriate individual behaviorImplement early warning systems and emergency response plansConduct tests of early warning systems and response plans before eventsConduct education and outreach on emergency preparedness

Ensure that emergency preparedness plans include medical servicesImprove programs to monitor the air, water, and soil for hazardous exposuresImprove surveillance programs to collect, analyze, and disseminate data on the health consequences of extreme events and heat waves Monitor and evaluate the effectiveness of systems

NGOs and Other Actors

NGOs and other actors play critical roles in emergency preparedness and disaster relief

Educate and train health professionals on risks from extreme weather events

Vector-borne and Zoonotic DiseasesIndividuals Take appropriate actions to reduce exposure 

to infected vectors, including eliminating vector breeding sites around residence

Vaccinate for diseases to which one would likely be exposed

Seek treatment when needed

Community, State, and National Agencies

Provide scientific and technical guidance and decision support tools for development of early warning systemsConduct effective vector (and pathogen) surveillance and control programs (including consideration of land use policies that affect vector distribution and habitats)Develop early warning systems for disease outbreaks, such as West Nile virusDevelop and disseminate information on appropriate individual behavior to avoid exposure to vectors

Conduct research on vaccines and other preventive measuresConduct research and development on rapid diagnostic toolsProvide vaccinations to those likely to be exposed

Conduct research on treatment optionsDevelop and disseminate information on signs and symptoms of disease to guide individuals on when to seek treatment

Table 2.4: Actors and Their Roles and Responsibilities for Adaptation to Climate Change Health Risks
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Actor Reduce Exposures Prevent Onset of Adverse Health Outcomes Reduce Morbidity and Mortality

Water-borne and Food-borne DiseasesIndividuals Follow proper food-handling guidelines

Follow guidelines on drinking water from outdoor sources

Seek treatment when needed

Community, State, and National Agencies

Improve surveillance and control programs for early detection of disease outbreaksDevelop methods to ensure watershed protection and safe water and food handling (e.g., Clean Water Act)

Sponsor research and development on rapid diagnostic tools for food- and water-borne pathogens

Sponsor research and development on treatment optionsDevelop and disseminate information on signs and symptoms of disease to guide individuals on when to seek treatment

Diseases Related to Air QualityIndividuals Follow advice on appropriate behavior on high 

ozone days

For individuals with certain respiratory diseases, follow medical advice during periods of high air pollution

Seek treatment when needed

Community, State, and National Agencies

Develop and enforce regulations of air pollutants (e.g., Clean Air Act)

Develop decision support tools for early warning systemsConduct education and outreach on the risks of exposure to air pollutants

Conduct research on treatment options

Table 2.4. Actors and Their Roles and Responsibilities for Adaptation to Climate Change Health Risks
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Heat waves Extreme Weather Events Vector-borne Diseases Waterborne Diseases Air Quality

Decision Support Tools Enhance early warning 

systems

Enhance early warning systems and emergency response plans

Enhance early warning systems based on climate and environmental data for selected diseases

Develop early warning systems based on climate and environmental data for conditions that may increase selected diseases

Enhance alert systems for high air pollution days

Technology Development Improve building design to 

reduce heat loads during summer months

Develop vaccines for West Nile virus and other vector-borne diseasesDevelop more rapid diagnostic tests

Develop more rapid diagnostic tests

Surveillance and Monitoring

Alter health data collection systems to monitor for increased morbidity and mortality during a heat wave 

Alter health data collection systems to monitor for disease outbreaks during and after an extreme event

Enhance vector surveillance and control programsMonitor disease occurrence

Enhance surveillance and monitoring programs for water-borne diseases

Enhance health data collection systems to monitor for health outcomes due to air pollution

Infrastructure Development

Improve urban design to reduce urban heat islands by planting trees, increasing green spaces, etc.

Design infrastructure to withstand projected extreme events

Consider possible impacts of infrastructure development, such as water storage tanks, on vector-borne diseases

Consider possible impacts of placement of sources of water- and food-borne pathogens (e.g., cattle near drinking water sources)

Improve public transit systems to reduce traffic emissions

Other Conduct research on 

effective approaches to encourage appropriate behavior during a heat wave

Conduct research on effective approaches to encourage appropriate behavior during an extreme event
The U.S. Climate Change Science Program Chapter 2

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Box 2.3: Quick Tips for Responding to Excessive Heat Waves

For the Public

Do

•	 Use air conditioners or spend time in airconditioned locations such as malls and libraries 

•	 Use portable electric fans to exhaust hot air

from rooms or draw in cooler air 

•	 Take a cool bath or shower

•	 Minimize direct exposure to the sun

•	 Stay hydrated: regularly drink water or other

nonalcoholic fluids 

•	 Eat light, cool, easy-to-digest foods such as fruit

or salads 

•	 Wear loose-fitting, light-colored clothes

•	 Check on older, sick, or frail people who may

need help responding to the heat 

•	 Know the symptoms of excessive heat exposure

and the appropriate responses. 

Don’t 

•	 Direct the flow of portable electric fans toward

yourself when room temperature is hotter than 

90°F 

•	 Leave children and pets alone in cars for any

amount of time 

•	 Drink alcohol to try to stay cool

•	 Eat heavy, hot, or hard-to-digest foods

•	 Wear heavy, dark clothing.

Useful Community Interventions

For Public Officials

Send a clear public message

•	 Communicate that EHEs are dangerous and

conditions can be life-threatening. In the event of 

conflicting environmental safety recommendations, 

emphasize that health protection should be the 

first priority. 

Inform the public of anticipated EHE conditions 

•	 When will EHE conditions be dangerous?

•	 How long will EHE conditions last?

•	 How hot will it feel at specific times during the

day (e.g., 8 a.m., 12 p.m., 4 p.m., 8 p.m.)?

Assist those at greatest risk

•	 Assess locations with vulnerable populations,

such as nursing homes and public housing

•	 Staff additional emergency medical personnel to

address the anticipated increase in demand

•	 Shift/expand homeless intervention services to

cover daytime hours

•	 Open cooling centers to offer relief for people

without air conditioning and urge the public to 

use them.

Provide access to additional sources of information 

•	 Provide toll-free numbers and Website

addresses for heat exposure symptoms 

and responses

•	 Open hotlines to report concerns about

individuals who may be at risk

•	 Coordinate broadcasts of EHE response

information in newspapers and on television 

and radio. 

Source: U.S. EPA, 2006

of adaptation actions should commence now 

(Confalonieri et al., 2007). Further, trends 

in factors that affect vulnerability, such as a 

larger and older U.S. population, will increase 

overall vulnerability to health risks. At the 

same time, the capacity of the United States 

to implement effective and timely adaptation 

measures is assumed to remain high throughout 

this century, thus reducing the likelihood of 

severe health impacts if appropriate programs 

and activities are implemented. However, the 

nature of the risks posed by climate change 

means that some adverse health outcomes 

might not be avoidable, even with attempts 

at adaptation. Severe health impacts will not 

be evenly distributed across populations and 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

regions, but will be concentrated in the most 

vulnerable groups.

Proactive policies and measures should 

be identified that improve the context for 

adaptation, reduce exposures related to climate 

variability and change, prevent the onset 

of climate-sensitive health outcomes, and 

increase treatment options. Future community, 

state, and national assessments of the health 

impacts of climate variability and change 

should identify gaps in adaptive capacity, 

including where barriers and constraints 

to implementation, such as governance 

mechanisms, need to be addressed. 

Because of regional variability in the types of 

health stressors attributable to climate change 

and their associated responses, it is difficult 

to summarize adaptation at the national level. 

Planning for adaptation is hindered by the 

fact that downscaled climate projections, 

as well as other climate information and 

tools, are generally not available to local 

governments. Such data and tools are essential 

for sectors potentially affected by climate 

change to assess their vulnerability and possible 

adaptation options, and to catalogue, evaluate, 

and disseminate adaptation measures. Explicit 

consideration of climate change is needed in 

the many programs and research activities 

within federal, state, and local agencies that 

are relevant to adaptation to ensure that they 

have maximum effectiveness and timeliness 

in reducing future vulnerability. In addition, 

collaboration and coordination are needed 

across agencies and sectors to ensure protection 

of the American population from the current 

and projected impacts of climate change.

2.7 Expanding the

Knowledge Base

Few research and data gaps have been filled 

since the First National Assessment. An 

important shift in perspective that occurred 

since the First National Assessment is a 

greater appreciation of the complex pathways 

and relationships through which weather and 

climate affect health, and the understanding 

that many social and behavioral factors will 

influence disease risks and patterns (NRC, 

2001). Several research gaps identified in the 

First National Assessment have been partially 

filled by studies that address the differential 

effects of temperature extremes by community, 

demographic, and biological characteristics; 

that improve our understanding of exposureresponse relationships for extreme heat; and 

that project the public health burden posed by 

climate-related changes in heat waves and air 

quality. Despite these advances, the body of 

literature remains small, limiting quantitative 

projections of future impacts. 

Improving our understanding of the linkages 

between climate change and health in the 

United States, may require a wide range of 

activities. 

•	 Improve characterization of exposureresponse relationships, par ticularly 

at regional and local levels, including 

identifying thresholds and particularly 

vulnerable groups. 

•	 Collect data on the early effects of changing 

weather patterns on climate-sensitive health 

outcomes. 

•	 Collect and enhance long-term surveillance 

data on health issues of potential concern, 

including VBZ diseases, air quality, pollen 

and mold counts, reporting of food- and 

water-borne diseases, morbidity due to 

temperature extremes, and mental health 

impacts from extreme weather events. 

•	 Develop quantitative models of possible 

health impacts of climate change that can be 

used to explore the consequences of a range 

of socioeconomic and climate scenarios. 

•	 Increase understanding of the processes of 

adaptation, including social and behavioral 

dimensions, as well as the costs and benefits 

of interventions. 

•	 Evaluate the implementation of adaptation 

measures. For example, evaluation of heat 

wave warning systems, especially as they 

become implemented on a wider scale 

(NOAA, 2005), is needed to understand how 

to motivate appropriate behavior. 

•	 Understand local- and regional-scale 

vulnerability and adaptive capacity to 

characterize the potential risks and the 

time horizon over which climate risks 
The U.S. Climate Change Science Program Chapter 2

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might arise. These assessments should 

include stakeholders to ensure their needs 

are identified and addressed in subsequent 

research and adaptation activities.

•	 Improve comprehensive estimates of the cobenefits of adaptation and mitigation policies 

in order to clarify trade-offs and synergies. 

•	 Improve collaboration across the multiple 

agencies and organizations with responsibility 

and research related to climate change-related 

health impacts, such as weather forecasting, 

air and water quality regulations, vector 

control programs, and disaster preparation 

and response.

•	 Anticipate infrastructure requirements that 

will be needed to protect against extreme 

events such as heat waves, and food- and 

water-borne diseases, or to alter urban 

design to decrease heat islands, and to 

maintain drinking and wastewater treatment 

standards and source water and watershed 

protection. 

•	 Develop downscaled climate projections 

at the local and regional scale in order to 

conduct the types of vulnerability and 

adaptation assessments that will enable 

adequate response to climate change and 

to determine the potential for interactions 

between climate and other risk factors, 

including societal, environmental, and 

economic. The growing concern over 

impacts from extreme events demonstrates 

the importance of climate models that allow 

for stochastic generation of possible future 

events, assessing not only how disease 

and pathogen population dynamics might 

respond, but also to assess whether levels of 

preparedness are likely to be adequate.
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2.8 References

American Academy of Pediatrics (AAP)

Committee on Sports Medicine and Fitness,

2000: Climatic heat stress and the exercising child 

and adolescent. Pediatrics, 106(1), 158-159.

American Academy of Pediatrics (AAP), 2004: 

Ambient air pollution: health hazards to children. 

Pediatrics, 114(6), 1699-1707. 

Angell, S.Y., and M.S. Cetron, 2005: Health 

disparities among travelers visiting friends and 

relatives abroad. Annals of Internal Medicine,

142, 67-72.

Auld, H., D. MacIver, and J. Klaassen, 2004: Heavy 

rainfall and waterborne disease outbreaks: the 

Walkerton example. Journal of Toxicology and 

Environmental Health, Part A, 67, 1879-1887.

Aw, J. and M.J. Kleeman, 2003: Evaluating the 

first-order effect of inter-annual temperature

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CHAPTER

3

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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Effects of Global Change 

on Human Settlements

Lead Author: Thomas J. Wilbanks, Oak Ridge National Laboratory

Contributing Authors: Paul Kirshen, Tufts University; Dale Quattrochi, 

NASA/Marshall Space Flight Center; Patricia Romero-Lankao, 

NCAR; Cynthia Rosenzweig, NASA/Goddard; Matthias Ruth, 

University of Maryland; William Solecki, Hunter College; Joel Tarr, 

Carnegie Mellon University

Contributors: Peter Larsen, University of Alaska-Anchorage; 

Brian Stone, Georgia Tech

3.1 INTRODUCTION

3.1.1 Purpose

Human settlements are where people live and 

work, including all population centers ranging 

from small rural communities to densely 

developed metropolitan areas. This chapter 

addresses climate change impacts, both positive 

and negative, on human settlements in the 

United States. First, the chapter summarizes 

current knowledge about the vulnerability 

of human settlements to climate change, in a 

context of concurrent changes in other nonclimate factors. Next, the chapter summarizes 

opportunities within settlements for adaptation 

to climate change. Finally, the chapter provides 

an overview of recommendations for expanding 

the current knowledge base with respect to 

climate change and human settlements.

3.1.2 Background

Events such as Hurricane Katrina in 2005 

and electric power outages during the hot 

summer of 2006 have demonstrated how 

climate-related events can dramatically impact 

U.S. settlements. Climate affects the costs of 

assuring comfort at home and work. Climate 

affects inputs for a good life: water; products 

and services from agriculture and forestry; 

pleasures and tourist potentials from nature, 

biodiversity, and outdoor recreation. Climate 

also affects the presence and spread of diseases 

and other health problems, and it is associated 

with threats from natural disasters, including 

floods, fires, droughts, wind, hail, ice, and heat 

and cold waves.

Some U.S. settlements may find opportunities 

in climate change. Warmer winters are not 

necessarily undesirable. Periods of change tend 

to reward forward-looking, effectively governed 

communities. Considering climate change 

effects may help to focus attention on other 

important issues for the long-term sustainable 

development of settlements and communities. 

Furthermore, planning for the future is an 

essential part of public policy decision-making 

in urban areas. 

Since infrastructure investments in urban areas 

are often both large and difficult to reverse, 

climate considerations are increasingly perceived 

as one of a number of relevant issues to consider 

when planning for the future (Ruth, 2006a). If 

U.S. settlements, especially larger cities, respond 

effectively to climate change concerns, their 

actions could have far-reaching implications 

for human well-being, because these areas are 

where most of the U.S. population lives, large 

financial decisions are made, political influence 

is often centered, and technological and social 

innovations take place.

Meanwhile, the pattern of human settlements 

in the United States is changing. In addition 

to shifts of population from frost-belt to sunbelt settlements, patterns are changing in 

other ways as well. For instance, the trend 

of households moving from urban centers to 

peripheries is reversing as many city centers 

renew and metropolitan areas continue to 
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expand across multiple jurisdictions (Solecki 

and Leichenko, 2006). Modern information 

technologies are enabling people to perform 

what were historically urban functions from 

relatively remote locations (Riebsame, 1997). 

3.1.3 Current State of Knowledge

The current knowledge base provides limited 

grounds for developing conclusions and 

recommendations related to climate impacts 

on human settlements. In many cases, the 

best that can be done is to sketch out the issue 

“landscape” that should be considered by both 

policy-makers and the research community 

as a basis for further discussions and offer 

illustrations from the relatively limited research 

literature that is now available.

The fact is that little research has been done 

to date specifically on the effects of climate 

change in U.S. cities and towns. Reasons appear 

to include (i) limitations in capacities to project 

climate change impacts at the geographic scale 

of a metropolitan area (or smaller) and (ii) the 

fact that none of the federal agencies currently 

active in climate science research has a clear 

responsibility for settlement impact issues. 

Improvements are required in our understanding 

of the impacts of and adaptation to climate change 

across different sectors and geographic regions, 

differential vulnerabilities, and interventions to 

build resilience. (NRC, 2007).

To some degree, gaps can be filled by referring 

to several comprehensive analyses that do 

exist, including literature on effects of climate 

variation on settlements and their responses, 

research on climate change impacts on cities in 

other parts of the world, and historical analogs 

of responses of urban areas to significant 

environmental changes. Box 3.1 presents a 

historical perspective of U.S. urban responses 

to environmental change. This perspective 

examines how American cities have been 

affected by environmental change over the 

past two centuries. But this is little more than 

a place to start.

At the current state of knowledge, vulnerabilities

to possible impacts are easier to project than 

actual impacts because they estimate risks 

or opportunities associated with possible 

consequences rather than estimating the 

consequences themselves, which requires 

far more detailed information about future 

conditions. Vulnerabilities are shaped not 

only by existing exposures, sensitivities, and 

adaptive capacities but also by the ability of 

settlements to develop responses to risks.

3.2 Climate Change

Impacts and the

Vulnerabilities of

Human Settlements

This section examines possible impacts 

of climate change on settlements in the 

United States including the determinants of 

vulnerability to such impacts and how those 

impacts could affect settlement patterns and 

various systems related to those patterns.

3.2.1 Determinants of 

Vulnerability

It has been difficult to project impacts of 

climate change on human settlements in the 

United States, in part because climate change 

forecasts are not specific enough for the scale of 

decision-making, but more so because climate 

change is not the only change being confronted 

by settlements. More often, attention is paid 

to vulnerabilities to climate change, if those 

changes should occur.

Vulnerabilities to or opportunities from climate 

change are related to three factors, both in 

absolute terms and in comparison to other 

elements (Clark et al., 2000):

1. Exposure to climate change. To what 

climate changes are settlements likely to 

be exposed: Changes in temperature or 

precipitation? Changes in storm exposures 

and/or intensities? Changes in sea level?
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

BOX 3.1. U.S. Urban Responses to Environmental Change:

An Historical Perspective

Over time, American cities have been affected by environmental change. City founders often showed 

an important disregard with respect to siting of settlements, focusing on aspects of location such as 

commercial or recreational opportunities rather than on risks such as flood potential, limited water, 

food or fuel supplies, or the presence of health threats. Oftentimes settlers severely exploited their 

environments, polluting ground water and adjacent water bodies, building in unsafe and fragile locations, 

changing landforms, and filling in wetlands. Construction of the urban built environment involved vast 

alterations in the landscape, as forests and vegetation and wildlife species were eliminated and replaced 

by highways, suburbs, and commercial buildings. The building of wastewater and water supply systems 

had the effect of altering regional hydrology and creating large vulnerabilities. In other cases settlers 

concluded that the weather was changing for the good, that technology would solve problems, or that 

new resources could be discovered.

Technological fixes were pursued to seek ways to modify or control environmental change. Cities 

exposed to flooding built levees and seawalls and channelized rivers. When urbanites depleted and 

polluted local water supplies, cities went outside their boundaries to seek new supplies: building 

reservoirs, aqueducts, and creating protected watersheds. When urban consumption exhausted local 

fuel sources, cities adapted to new fuels, embraced new technologies, or searched far beyond city 

boundaries for new supplies. Many of these actions resulted in the extension of the urban ecological 

footprint, so that urban growth and development affected not only the urban site but also increasingly 

the urban hinterland and beyond.

There are few examples of environmental disasters or climate change actually resulting in the 

abandonment of an urban site. One case appears to be that of the Hohokam Indians of the Southwest, 

who built extensive irrigation systems, farmed land, and built large and dense settlements over a 

period of approximately 1,500 years (Krech, 1999: 45-72). Yet, they abandoned their settlements and 

disappeared into history. The most prominent explanation for their disappearance is an ecological 

one—that the Hohokam irrigation systems suffered from salinization and water logging, eventually 

making them unusable. Other factors besides ecological ones may have also entered into the demise 

of their civilization and abandonment of their cities, but the ecological explanation appears to have the 

most supporters. 

In the case of America in the 19th and 20th centuries, however, no city has been abandoned because of 

environmental or climatic factors. Galveston, Texas suffered from a catastrophic tidal wave but still exists 

as a human settlement, now protected by an extensive sea wall. Johnstown, Pennsylvania has undergone 

major and destructive flooding since the late 19th century, but continues to survive as a small city. Los 

Angeles and San Francisco are extremely vulnerable to earthquakes, but still continue to increase in 

population. And, in coming years New Orleans almost certainly will experience a hurricane as or more 

severe than Katrina, and yet rebuilding goes on, encouraged by the belief that technology will protect 

it in the future. Whether or not ecological disaster or extreme risk will eventually convince Americans 

to abandon some of their settlements, as the Hohokam did, has yet to be determined (Colten, 2005; 

Steinberg, 2006; Vale and Campanella, 2005). 

2. Sensitivity to climate change. If primary 

climate changes occur, how sensitive are the 

activities and populations of a settlement to 

those changes? For instance, a city dependent 

substantially on a regional agricultural 

or forestry economy, or the availability 

of abundant water resources, might be 

considered more sensitive than a city whose 

economy is based mainly on an industrial 

sector less sensitive to climate variation.

3. Adaptive capacity. Finally, if effects are 

experienced due to a combination of exposure 

and sensitivity, how able is a settlement to 

handle those impacts without disabling 

damages, perhaps even while realizing new 

opportunities? 
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3.2.2 Impacts of Climate Change 

on Human Settlements

Impacts of climate change on hu man 

settlements vary regionally (see Boxes 3.2 

and 3.3), and generally relate to some of the 

following issues:

1. Effects on health. It is well-established that 

higher temperatures in urban areas are 

related to higher levels of ozone, which cause 

respiratory and cardiovascular problems. 

There is also some evidence that combined 

effects of heat stress and air pollution may 

be greater than simple additive effects (Patz 

and Balbus, 2001). Moreover, historical 

data show relationships between mortality 

and temperature extremes (Rozenzweig 

and Solecki, 2001a). Other health concerns 

include changes in exposure to water and 

food-borne diseases, vector-borne diseases, 

concentrations of plant species associated 

with allergies, and exposures to extreme 

weather events such as storms, floods, and 

fires (see Chapter 2).

2. Effects on water and other urban infrastructures.

Changes in precipitation patterns may lead to 

reductions in meltwater, river flows, groundwater 

levels, and in coastal areas may lead to saline 

intrusion in rivers and groundwater, affecting 

water supply. Meanwhile, warming may 

increase water demands (Gleick et al., 2000; 

Kirshen, 2002; Ruth et al., 2007). Moreover, 

storms, floods, and other severe weather events 

may affect other infrastructure, including 

sanitation systems, transportation, supply 

lines for food and energy, and communication. 

Exposed structures such as bridges and 

electricity transmission networks are especially 

vulnerable. In many cases, infrastructures are 

interconnected; an impact on one can also affect 

others (Kirshen, et al., 2007). An example is an 

interruption in energy supply, which increases 

heat stress for vulnerable populations (Ruth et 

al., 2006a). Many of the infrastructures in older 

cities are aging and are already under stress 

from increasing demands.

3. Effects on energy requirements. Warming is 

virtually certain to increase energy demand 

in U.S. cities for cooling in buildings while 

reducing demand for heating in buildings 

(see SAP 4.5). Demands for cooling during 

warm periods could jeopardize the reliability 

of service in some regions by exceeding the 

supply capacity, especially during periods of 

unusually high temperatures (see Vignettes 

in Boxes 3.2 and 3.3). Higher temperatures 

also affect costs of living and business 

operation by increasing costs of climate 

control in buildings (Amato et al., 2005; 

Ruth and Lin, 2006c; Kirshen et al., 2007).

4. Effects on the urban metabolism.An urban area 

is a living complex mega-organism, associated 

with a host of inputs, transformations, and 

outputs: heat, energy, materials, and others 

(Decker et al., 2000). An example is the Urban 

Heat Index, which measures the degree to 

which built/paved areas are associated with 

higher temperatures relative to surrounding 

areas (see Box 3.4: Climate Change Impacts 

on the Urban Heat Island Effect (UHI)). 

Imbalances in the urban metabolism can 

aggravate climate change impacts, such as 

roles of UHI in the formation of smog in 

cities. The maps in this box demonstrate how 

the built environment creates and retains heat 

in metropolitan settings.

5. Effects on economic competitiveness, 

opportunities, and risks. Climate change has 

the potential not only to affect settlements 

directly but also to affect them through impacts 

on other areas linked to their economies at 

regional, national, and international scales 

(Rosenzweig and Solecki, 2006). In addition, 

it can affect a settlement’s economic base if 

it is sensitive to climate, as in areas where 

settlements are based on agriculture, forestry, 

water resources, or tourism (IPCC, 2001a).

6. Effects on social and political structures. 

Climate change can add to stress on social 

and political structures by increasing 

management and budget requirements 

for public services such as public health 

care, disaster risk reduction, and even 

public security. As sources of stress grow 

and combine, the resilience of social 

and political structures that are already 

somewhat unstable is likely to suffer, 

especially in areas with relatively limited 

resources (Sherbinin et al., 2006).
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

BOX 3.2. Vignettes of Vulnerability—I

Alaskan Settlements

No other region in the United States is likely to be as profoundly changed by climate change as Alaska, 

our nation’s part of the polar region of Earth (ACIA, 2004). Because warming is more pronounced 

closer to the poles, and because settlement and economic activities in Alaska have been shaped and 

often constrained by Arctic conditions, in this region warming is especially likely to reshape patterns of 

human settlement.

Human settlements in Alaska are already being exposed to impacts from global warming (ACIA, 2004), 

and these impacts are expected to increase. Many coastal communities see increasing exposure to 

storms, with significant coastal erosion, and in some cases facilities are being forced either to relocate 

or to face increasing risks and costs. Thawing ground is beginning to destabilize transportation, buildings, 

and other facilities, posing needs for rebuilding, with ongoing warming adding to construction and 

maintenance costs. And indigenous communities are facing major economic and cultural impacts. One 

recent estimate of the value of Alaska’s public infrastructure at risk from climate change set the value 

at tens of billions of today’s dollars by 2080, with the replacement of buildings, bridges, and other 

structures with long lifetimes having the largest public costs (Larsen et al., 2007).

Besides impacts on built infrastructures designed for permafrost foundations and effects on indigenous 

societies, many observers expect warming in Alaska to stimulate more active oil and gas development 

(and perhaps other natural resource exploitation), and if thawing of Arctic ice permits the opening 

of a year-round Northwest sea passage it is virtually certain that Alaska’s coast will see a boom in 

settlements and port facilities (ACIA, 2004).

Coastal Southeast Settlements

While there is currently no evidence for a long-term increase in North American mainland land-falling 

hurricanes, concerns remain that certain aspects of hurricanes, such as wind speed and rainfall rates 

may increase (CCSP, 2008). In addition, sea level rise is expected to increase storm surge levels (CCSP, 

2008). Recent hurricanes striking the coast of the U.S. Southeast cannot be attributed clearly to climate 

change, but they suggest a range of possible impacts. As an extreme case, consider the example of 

Hurricane Katrina. In 2005, the city of New Orleans had a population of about half a million, located on 

the delta of the Mississippi River along the U.S. Gulf Coast. Urban development throughout the 20th 

Century has significantly increased land use and settlement in areas vulnerable to flooding, and a number 

of studies had indicated growing vulnerabilities to storms and flooding. In late August 2005, Hurricane 

Katrina moved onto the Louisiana and Mississippi coast with a storm surge, supplemented by waves, 

reaching up to 8.5 m above sea level. In New Orleans, the surge reached around 5 m, overtopping and 

breaching sections of the city’s 4.5 m defenses, flooding 70 to 80 percent of New Orleans, with 55 

percent of the city’s properties inundated by more than 1.2 m and maximum flood depths up to 6 m. 

Approximately 1,101 people died in Louisiana, nearly all related to flooding, concentrated among the 

poor and elderly. 

Across the whole region, there were 1.75 million private insurance claims, costing in excess of $40 

billion (Hartwig, 2006), while total economic costs are projected to be significantly in excess of $100 

billion. Katrina also exhausted the federally backed National Flood Insurance Program (Hunter, 2006), 

which had to borrow $20.8 billion from the Government to fund the Katrina residential flood claims. In 

New Orleans alone, while flooding of residential structures caused $8-$10 billion in losses, $3-6 billion 

was uninsured. 34,000-35,000 of the flooded homes carried no flood insurance, including many that 

were not in a designated flood risk zone (Hartwig, 2006). Six months after Katrina, it was estimated 

that the population of New Orleans was 155,000, with the number projected to rise to 272,000 by 

September 2008 – 56 percent of its pre-Katrina level (McCarthy et al., 2006).
The U.S. Climate Change Science Program Chapter 3

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BOX 3.3. Vignettes of Vulnerability—II

Arid Western Settlements

Human settlements in the arid West are affected by climate in a variety of ways, but perhaps most 

of all by water scarcity and risks of fire. Clearly, access to water for urban populations is sensitive to 

climate, although the region has developed a vast system of engineered water storage and transport 

facilities, associated with a very complex set of water rights laws (NACC, 2001). It is very likely that 

climate change will reduce winter snowfall in the West, reducing total runoff – increasing spring runoff 

while decreasing summer water flows. Meanwhile, water demands for urban populations, agriculture, 

and power supply are expected to increase, and conflicts over water rights are likely to increase. If total 

precipitation decreases or becomes more variable, extending the kinds of drought that have affected 

much of the interior West in recent years, water scarcity will be exacerbated, and increased water 

withdrawals from wells could affect aquifer levels and pumping costs. Moreover, drying increases risks of 

fire, which has threatened urban areas in California and other Western areas in recent years. The fiveyear average of acres burned in the West is more than 5 million, and urban expansion is increasing the 

length of the urban-wild lands interface (Morehouse et al., 2006). Drying would lengthen the fire season, 

and pest outbreaks such as the pine beetle could affect the scale of fires.

Summer 2006 Heat Wave

In July and August 2006, a severe heat wave spread across the United States, with most parts of 

the country recording temperatures well above the average for that time of the year. For example, 

temperatures in California were extraordinarily high, setting records as high as 130°. As many as 225 

deaths were reported by press sources, many of them in major cities such as New York and Chicago. 

Electric power transformers failed in several areas, such as St. Louis and Queens, New York, causing 

interruptions of electric power supply, and some cities reported heat-related damages to water lines 

and roads. In many cities, citizens without home air-conditioning sought shelter in public and office 

buildings, and city/county health departments expressed particular concern for the elderly, the young, 

pregnant women, and individuals in poor health. Although this heat wave cannot be attributed directly 

to climate change, it suggests a number of issues for human settlements in the United States as they 

contemplate a prospect of temperature extremes in the future that are higher and/or longer-lasting 

than historical experience.

7. Effects on vulnerable populations (see 

Chapter 1). Where climate change stresses 

settlements, it is likely to be especially 

problematic for vulnerable parts of the 

population: the poor, the elderly, those 

already in poor health, the disabled, those 

living alone, those with limited rights 

and power (e.g., recent in-migrants with 

limited English skills), and/or indigenous 

populations dependent on one or a few 

resources. As one example, warmer 

temperatures in urban summers have a more 

direct impact on populations who live and 

work without air-conditioning. Implications 

for environmental justice are clear; see, 

for instance, Congressional Black Caucus 

Foundation, 2004.

8. Effects on vulnerable regions. Approximately 

half of the U.S. population, 160 million 

people, will live in one of 673 coastal counties 

by 2008 (Crossett et al., 2004). Obviously, 

settlements in coastal areas—particularly on 

gently sloping coasts—should be concerned 

about sea level rise in the longer term, 

especially if they are subject to severe 

storms and storm surges and/or if their 

regions are showing gradual land subsidence 

(Neumann et al., 2000; Kirshen et al., 2004). 

Settlements in risk-prone regions have reason 

to be concerned about severe weather events, 

ranging from severe storms combined with 

sea level rise in coastal areas to increased 

risks of fire in drier arid areas. Vulnerabilities 

may be especially great for rapidly growing 

and/or larger metropolitan areas, where the 

potential magnitude of both impacts and 

coping requirements could be very large 

(IPCC, 2001a; Wilbanks et al., 2007b).
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

BOx 3.4. Climate Change Impacts on the Urban Heat Island Effect (UHI) 

(Lo and Quattrochi, 2003; Brazel and Quattrochi, 2006; Ridd, 2006; Stone, 2006)

Climate change impacts on the UHI will primarily depend upon the geographic location of a specific city, 

its urban morphology (i.e., landscape and built-up characteristics), and areal extent (i.e., overall spatial 

“footprint”). These factors will mitigate or exacerbate how the UHI phenomenon (Figure 3.1) is affected 

by climate change, but overall, climate change is likely to impact the UHI in the following ways:

•	 Exacerbation	of the intensity and	areal	extent of the UHI as	a	result of warmer surface and air

temperatures along with the overall growth of urban areas around the world. Additionally, as urban 

areas grow and expand, there is a propensity for lower albedos, which forces a more intense UHI 

effect. (There is also some indication that sustained or prolonged higher nighttime air temperatures 

over cities that may result from warmer global temperatures will have a more significant impact on 

humans than higher daytime temperatures.)

•	 As	the UHI intensifies and increases, there could be	a	subsequent impact on deterioration of air quality,

particularly on ground level ozone caused by higher overall air temperatures and an increased background 

effect produced by the UHI as an additive air temperature factor that helps to elevate ground level ozone 

production. Additionally, particulate matter (PM2.5) could increase due to a number of human induced and 

natural factors (e.g., more energy production to support higher usage of air conditioning).

•	 The	UHI has an impact on local meteorological conditions by	forcing	rainfall production either over,

or downwind, of cities. As the UHI intensifies, there will be a higher probability for urban-induced 

rainfall production (dependent upon geographic location) with a subsequent increase in urban runoff 

and flash flooding.

•	 Exacerbation	and intensification of the UHI would have the following impacts on human	health:

- increased incidence of heat stress

- impact on respiratory illnesses such as asthma due to increases in particulate matter caused by 

deterioration in air quality as well as increased pollination production because of earlier pollen 

production from vegetation in response to warmer overall temperatures

The image on the left illustrates daytime surface heating for urban surfaces across the Georgia 

Central Business District (CBD). White and red colors indicate very warm surfaces (~40-50°C). 

Green relates to surfaces 

of moderately warm 

temperatures (~25-

30°C). Blue indicates cool 

surfaces (e.g., vegetation, 

shadows) (~15-20°C). 

Surface temperatures are 

reflected in the albedo 

image on the right where 

warm surfaces are dark 

(i.e., low reflectivity) and 

cooler surfaces are in 

red and green (i.e., higher 

reflectivity). The images 

exemplify how urban 

surface characteristics 

influence temperature and 

albedo as drivers of the 

UHI (Quattrochi et al., 

2000). Figure 3.1. Example of urban surface temperatures and albedo for the Atlanta, 

Georgia Central Business District area derived from high spatial resolution (10m) 

aircraft thermal remote sensing data. 
The U.S. Climate Change Science Program Chapter 3

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Different combinations of circumstances are 

likely to cause particular concerns for cities 

and towns in the United States as they consider 

possible implications of climate change. 

3.2.3 The Interaction of Climate 

Impacts with Non-Climate 

Factors

In general, climate change effects on human 

settlements in the United States are imbedded in 

a variety of complexities that make projections 

of quantitative impacts over long periods of time 

very difficult. For instance, looking out over a 

period of many decades, it seems likely that 

other kinds of change—such as technological, 

economic, and institutional—will have more 

impact on the sustainability of most settlements 

rather than climate change per se (Wilbanks, et 

al., 2007b). Climate change will interact with 

other processes, driving forces, and stresses; 

and its significance, positive or negative, will 

largely be determined by these interactions. It 

is therefore difficult to assess effects of climate 

change without a reasonably clear picture of 

future scenarios for these other processes.

In many cases, these interactions involve 

not only direct impacts such as warming or 

more or less precipitation but, sometimes 

more important, second, third, or higher order 

impacts, as direct impacts cascade through 

urban systems and other settlement-determined 

processes (e.g., warming which affects urban 

air pollution which affects health which affects 

public service requirements which affect 

social harmony: Kirshen et al., 2007). Some of 

these higher order impacts, in turn, may feed 

back to create ripple effects of their own. For 

example, a heat wave may trigger increased 

energy demands for cooling, which may cause 

more air conditioners and power generators to 

be operated, which could lead to higher UHI 

effects, inducing even higher cooling needs.

Besides this “multi-stress” perspective, it is 

highly likely that effects of climate change on 

settlements are shaped by certain “thresholds,” 

below which effects are incidental but beyond 

where effects quickly become major when 

a limiting or inflection point is reached. An 

example might be a city’s capacity to cope with 

sustained heat stress combined with a natural 

disaster. In general, these climate-related 

thresholds for human settlements in the United 

States are not well-understood. For multi-stress 

assessments of thresholds, changes in climate 

extremes are very often of more concern than 

changes in climate averages. Besides extreme 

weather events, such as hurricanes or tornadoes, 

ice storms, winds, heat waves, drought, or fire, 

settlements may be affected by changes in daily 

or seasonal high or low levels of temperature 

or precipitation, which have not always been 

projected by climate change models.

Finally, human settlements may be affected by 

climate change mitigation initiatives as well 

as by climate change itself. Examples include 

effects on policies related to energy sources 

and uses, environmental emissions, and land 

use. The most direct and short-term effects 

would likely be on settlements in regions 

whose economies are closely related to the 

production and consumption of large quantities 

of fossil fuels. Indirect and longer term effects 

are less predictable. 

As climate change affects settlements in the 

United States, impacts are realized at the 

intersection of climate change with underlying 

forces. Most of the possible effects are linked 

with changes in regional comparative advantage, 

with consequent migration of population and 

economic activities (Ruth and Coelho, in press). 

Examples of these complex interactions and 

issues include: 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

1. Regional risks and availability of insurance.

It is possible that regions exposed to risks 

from climate change will see movement of 

population and economic activity to other 

locations. One reason is public perceptions 

of risk, but a more powerful driving force 

may be the availability of insurance. The 

insurance sector is one of the most adaptable 

of all economic sectors, and its exposure to 

costs from severe storms and other extreme 

weather events is likely to lead it to withdraw 

(or to make much more expensive) private 

insurance coverage from areas vulnerable 

to climate change impacts (Wilbanks, 

et al., 2007b), which would encourage 

both businesses and individual citizens to 

consider other locations over a period of 

several decades.

2. Areas whose economies are linked with 

climate-sensitive resources or assets.

Settlements whose economic bases are 

related to such sectors as agriculture, 

forestry, tourism, water availability, or other 

climate-related activities could be affected 

either positively or negatively by climate 

change, depending partly on the adaptability 

of those sectors (i.e., their ability to adapt 

to changes without shifting to different 

locations).

3. Shifts in comparative living costs, risks, and 

amenities. Related to a range of possible 

climate change effects—higher costs for 

space cooling in warmer areas, higher costs 

of water availability in drier areas, more or 

less exposure to storm impacts in some areas, 

and sea level rise—regions of the United 

States and their associated settlements are 

likely to see gradual changes over the long 

term in their relative attractiveness for a 

variety of human activities. One example, 

although its likelihood is highly uncertain, 

would be a gradual migration of the “Sun 

Belt” northward, as retirees and businesses 

attracted by environmental amenities find 

that regions less exposed to very high 

temperatures and seasonal major storms are 

more attractive as places to locate. 

4. Changes in regional comparative advantage 

related to shifts in energy resource use. 

If climate mitigation policies result in 

shifts from coal and other fossil resources 

toward non-fossil energy sources, or if 

climate changes affect the prospects of 

renewable energy sources (especially 

hydropower), regional economies related 

to the production and/or use of energy from 

these sources could be affected, along with 

regional economies more closely linked with 

alternatives (Wilbanks, 2007c)

5. Urban “ footprints” on other areas.Resource 

requirements for urban areas involve larger 

areas than their own bounded territories 

alone. Ecologists have sought to estimate the 

land area required to supply the consumption 

of resources and compensate for emissions 

and other wastes from urban areas (e.g., 

Folke et al., 1997). By possibly affecting 

settlements, along with their resource 

capacities for their inputs and destinations 

of their outputs, climate change could affect 

the nature, size, and geographic distribution 

of these footprints.

Human settlements are foci for many 

economic, social, and governmental processes, 

and historical experience has shown that 

catastrophes in cities can have significant 

economic, financial, and political effects much 

more broadly. The case that has received the 

most attention to date is insurance and finance 

(Wilbanks, et al., 2007b). 
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3.2.5 Examples of Impacts 

on Metropolitan Areas in the 

United States

Possible impacts of climate change on settlements 

in the United States are usually assessed by 

projecting climate changes at a regional scale: 

temperature, precipitation, severe weather 

events, and sea level rise (see Table 3.2 and Boxes 

3.2 and 3.3). Ideally, these regional projections 

are at a relatively detailed scale, and ideally they 

consider seasonal as well as annual changes and 

changes in extremes as well as in averages; but 

these conditions cannot always be met.

The most comprehensive assessments of 

possible climate change impacts on settlements 

in the United States have been two studies of 

major metropolitan areas:

1. New York: This assessment concluded 

that impacts of climate change on this 

metropolitan area are likely to be primarily 

negative over the long term, with potentially 

significant costs increasing as the magnitude 

of climate change increases, although there 

are substantial uncertainties (Rosenzweig 

and Solecki, 2001a; Rosenzweig and Solecki, 

2001b; Solecki and Rosenzweig, 2006). 

2. Boston: This assessment concluded that longterm impacts of climate change are likely 

to depend at least as much on behavioral 

and policy changes over this period as on 

temperature and other climate changes 

(Kirshen et al., 2004; Kirshen et al., 2006; 

Kirshen et al., 2007).

Other U.S. studies include Seattle (Hoo and 

Sumitani, 2005) and Los Angeles (Koteen et 

al., 2001) (Table 3.1). Internationally, studies 

have included several major metropolitan areas, 

such as London (London Climate Change 

Partnership, 2004) and Mexico City (Molina 

et al., 2005) as well as possible impacts on 

smaller settlements (e.g., AIACC: see www.

aiaccproject.org). A relevant historical study 

of effects of an urban heat wave in the United 

States is reported by Klinenberg (2003).

3.2.4 Realizing Opportunities 

from Climate Change in the 

United States 

Climate change can have positive as well as 

negative implications for settlements. Examples 

of potential positive effects include:

1. Reduced winter weather costs and stresses.

Warmer temperatures in periods of the year 

that are normally cold are not necessarily 

undesirable. They reduce cold-related 

stresses and costs (e.g., costs of warming 

buildings and costs of clearing ice and 

snow from roads and streets), particularly 

for cold-vulnerable populations. They 

expand opportunities for warmer-weather 

recreational opportunities over larger parts 

of the year, and they expand growing seasons 

for crops, parks, and gardens.

2. In c r e a s e d a t t e n t i o n t o lo n g - t e r m 

sustainability. One of the most positive 

aspects of climate change can be its 

capacity to stimulate a broader discussion 

of what sustainability means for settlements 

(Wilbanks, 2003; Ruth, 2006). Even if 

climate change itself may not be the most 

serious threat to sustainability, considering 

climate change impacts in a multi-change, 

multi-stage context can encourage and 

facilitate processes that lead to progress in 

dealing with other sources of stress.

3. Improved competitiveness compared with 

settlements subject to more serious adverse 

impacts. While some settlements may turn 

out to be “losers” due to climate change 

impacts, others may be “winners,” as 

changes in temperature or precipitation 

result in added economic opportunities (see 

the following section), at least if climate 

change is not severe. In addition, for many 

settlements climate change can be an 

opportunity not only to compare their net 

impacts with others, seeking advantages 

as a result, but to present a progressive 

image by taking climate change (and related 

sustainability issues) seriously.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Table 3.1. Overview of Integrated Assessments of Climate Impacts and Adaptation in U.S. Cities. “X” Indicates that the 

Reference Addresses a Category of Interest. 

Bloomfield

et al., 1999

Kooten

et al., 2001

Rosenzweig 

et al., 2000

Kirshen 

et al., 2004 

Hoo and 

Sumitani, 2005

Location: Greater Los 

Angeles

New York Metropolitan 

New York 

Metropolitan 

Boston

Metropolitan

Seattle

Coverage:

Water Supply ✗ ✗ ✗ ✗

Water Quality ✗

Water Demand ✗

Sea level rise ✗ ✗ ✗ ✗

Transportation ✗ ✗

Communication

Energy ✗ ✗

Public Health

Vector-borne Diseases

Food-borne Diseases ✗

Temperature-related Mortality ✗

Temperature-related Morbidity ✗ ✗

Air-quality Related Mortality

Air-quality Related Morbidity ✗

Other Health Issues ✗ ✗ ✗

Ecosystems

Wetlands

Other Ecol. (Wildfires) ✗ ✗

Urban Forests (Trees and 

Vegetation) ✗

Air Quality ✗ ✗

Extent of:

Quantitative Analysis Low Medium Medium High Low

Computer-based Modeling None Low Low High None

Scenario Analysis None None Medium High Medium

Explicit Risk Analysis None None None Medium None

Involvement of:

Local Planning Agencies None None High High High

Local Government Agencies None None High High High

Private Industry None None None Low None

Non-profits None None Low High None

Citizens None None None Medium None

Identification of:

Adaptation Options ✗ ✗ ✗ ✗ ✗

Adaptation Cost ✗ ✗

Extent of Integration Across 

Systems None None Low Medium Low

Attention to Differential 

Impacts (e.g., on individual 

types of businesses, 

populations)

None None Low Low Low
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3.3 Opportunities for 

Adaptation of Human

Settlements to Climate

Change

Settlements are important in considering 

prospects for adaptation to climate change, both 

because they represent concentrations of people 

and because buildings and other infrastructures 

offer ways to manage risk and monitor/control 

threats associated with climate extremes and 

other non-climate stressors.

Where climate change presents risks of 

adverse impacts for U.S. settlements and their 

populations, there are two basic options to 

respond to such concerns (a third is combining 

the two). One response is to contribute to 

climate change mitigation strategies, i.e., 

by taking actions to reduce greenhouse gas 

emissions and by showing leadership in 

encouraging others to support such actions 

(see Box 3.5: Roles of Settlements in Climate 

Change Mitigation). The second response is to 

consider strategies for adaptation, i.e., finding 

ways either to reduce sensitivity to projected 

changes or to increase the settlement’s coping 

capacities. Adaptation can rely mainly on 

anticipatory actions to avoid damages and 

costs, such as “hardening” coastal structures 

to sea level rise; or adaptation can rely mainly 

on response potentials, such as emergency 

preparedness; or it can include a mix of the 

two approaches. Research to date suggests 

that anticipatory adaptation may be more 

cost-effective than reactive adaptation 

(Kirshen et al., 2004).

Adaptation strategies will be important to 

the well-being of U.S. settlements as climate 

change evolves over the next century. As just 

one example, the New York climate impact 

assessment (Rosenzweig and Solecki, 2001a) 

projects significant increases in heat-related 

deaths based on historical relationships between 

Table 3.2. Regional Vulnerabilities of Settlements to Impacts of Climate Change in the United States 

Region Vulnerabilities Major Uncertainties

Metro NE Flooding, infrastructures, health, water supply, 

sea level rise

Storm behavior, precipitation

Larger NE Changes in local landscapes, tourism, water, 

energy needs

Ecosystem impacts

Mid-Atlantic Multiple stresses; e.g., interactions between 

climate change and aging infrastructures

Ecosystem impacts

Coastal SE More intense storms, sea level rise, flooding, 

heat stress

Storm behavior, coastal land use, sea level rise

Inland SE Water shortages, heat stress, UH1, 

economic impacts

Precipitation change, development paths

Upper Midwest Lake and river levels, extreme weather 

events, health

Precipitation change, storm behavior

Inner Midwest Extreme weather events, health Storm behavior

Appalachians Ecological change, reduced demand for coal Ecosystem impacts, energy policy impacts

Great Plains Water supply, extreme events, stresses on 

communities

Precipitation changes, weather extremes

Mountain West Reduced snow, water shortages, fire, tourism Precipitation changes, effects on 

winter snowpack

Arid Southwest Water shortages, fire Development paths, precipitation changes

California Water shortages, heat stress, sea level rise Temperature and precipitation changes, 

infrastructure impacts

Northwest Water shortages, ecosystem stresses, coastal 

effects

Precipitation changes, sea level rise

Alaska Effects of warming, vulnerable populations Warming, sea level rise

Hawaii Storms and other weather extremes, 

freshwater supplies, health, sea level rise

Storm characteristics, precipitation change
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

BOX 3.5. Roles of Settlements in Climate Change Mitigation

Although U.S. government commitments to climate change mitigation policies at the national level have 

emerged only recently, an increasing number of state and local authorities are involved in strategies 

to mitigate greenhouse gas emissions (GHG) (Selin and Vandeveer, 2005; Rabe, 2006; Selin, 2006). 

U.S. states and cities are joining such initiatives as the International Council for Local Environmental 

Initiatives (ICLEI) (ICLEI, 2006), the U.S. Mayor Climate Protection Agreement, the Climate Change 

Action Plan, the Regional Greenhouse Gas Initiative (RGGI) (Selin, 2006), and the Large Cities 

Climate Leadership Group.a These initiatives focus on emissions inventories; on such actions aimed at 

reducing GHG emissions as switching to more energy efficient vehicles, using more efficient furnaces 

and conditioning systems, and introducing renewable portfolio standards. These strategies, which 

mandate an increase in the amount of electricity generated from renewable resources also adapt to 

negative social, economic, and environmental impacts; and on actions to promote public awareness (see 

references in footnotea).

Different drivers lie behind these mitigation efforts. Public and private entities have begun to 

“perceive” such possible impacts of climate change as rising sea level, extreme shifts in weather, and 

losses of key resources. They have realized that a reduction of GHG emissions opens opportunities 

for longer economic development (e.g., investment in renewable energy: Rabe, 2006). In addition, 

climate change can become a political priority if it is reframed in terms of local issues (i.e., air quality, 

energy conservation) already on the policy agenda (Betsill, 2001; Bulkeley and Betsill, 2003; Romero 

Lankao, 2007) 

The promoters of these initiatives face challenges related partly to inertia (e.g., the time it takes to 

replace energy facilities and equipment with a relatively long life of 5 to 50 years: Haites et al., 2007). 

They can also face opposition from organizations who do not favor actions to reduce GHG emissions, 

some of whom are prepared to bring legal challenges against state and local initiatives (Rabe, 2006:17). 

But the number of bottom-up grassroots activities currently under way in the United States is 

considerable, and that number appears to be growing. 

a Local governments participating in ICLEI’s Cities for Climate Protection Campaign commit to a) conduct an energy- and 

emissions-inventory and fore-cast, b) establish an emissions target, c) develop and obtain approval for the Local Action 

Plan, d) implement policies and measures, and e) monitor and verify results (ICLEI, 2006: April 20 2006 www.iclei.org). 

The Large Cities Climate Leadership Group is a group of cities committed to the reduction of urban carbon emissions and 

adapting to climate change. It was founded following the World Cities Leadership Climate Change Summit organized by 

the Mayor of London in October 2005. For more information on the US Mayor Climate Protection Agreement see http://

www.seattle.gov/mayor/climate/.

heat stress and mortality, unchanged by 

adaptation. The Climate’s Long Term Impacts 

on Metro Boston (CLIMB) assessment (Kirshen 

et al., 2004) projects that, despite similar 

projections of warming, heat-related deaths 

will decline over the coming century because 

of adaptation. Whether or not adaptation 

to climate change occurs in U.S. cities is 

therefore a potentially serious issue. The 

CLIMB assessment includes analyses showing 

that in many cases adaptation actions taken now 

are better than adaptation actions delayed until 

a later time (Kirshen et al., 2006).

3.3.1 Perspectives on 

Adaptation by Settlements

For decision-makers in U.S. settlements, climate 

change is yet one more source of possible risks 

that need to be addressed. Climate change is 

different as an issue because it is relatively 

long-term in its implications, future impacts 

are uncertain, and public awareness is growing 

from a relatively low level to a higher level of 

concern. Because climate change is different in 

these ways, it is seldom attractive to consider 

allocating massive amounts of funding or 

management attention to current climate change 

actions. What generally makes more sense is to 

consider actions that reduce vulnerabilities to 

climate change impacts (or increase prospects 
The U.S. Climate Change Science Program Chapter 3

102

for realizing benefits from climate change 

impacts) and have other desirable aspects, often 

referred to as “co-benefits.” Examples include 

actions that reduce vulnerabilities to current 

climate variability regardless of long-term 

climate change, actions that add resilience to 

water supply and other urban infrastructures 

that are already stressed, and actions that 

make metropolitan areas more attractive for 

their citizens in terms of their overall quality 

of life.

Cities and towns have used both “hard” 

approaches such as developing infrastructure 

and “soft” approaches such as regulations to 

address impacts of climate variability. Examples 

include water supply and waste water systems, 

drainage networks, buildings, transportation 

systems, land use and zoning controls, water 

quality standards, and emission caps and tax 

incentives. All of these are designed in part with 

climate and environmental conditions in mind. 

The setting of regulations has always been in 

a context of benefit-cost analysis and political 

realities; and infrastructure is also designed 

in a benefit-cost framework, subject to local 

design codes. The fact that both regulations 

and infrastructures vary considerably across 

the United States reflects cultural, economic, 

and environmental factors. This suggests that 

mechanisms exist to respond to concerns about 

climate change. Urban designers and managers 

deal routinely with uncertainties because they 

must consider uncertain demographic and 

other socioeconomic changes. Thus if climate 

change is properly institutionalized into the 

urban planning process, it can be handled as 

yet another uncertainty. 

3.3.2 Major Categories of 

Adaptation Strategies

Adaptation strategies for human settlements, 

large and small, include a wide range of 

possibilities such as:

1. Changing the location of people or activities 

(within or between settlements)—especially 

addressing the costs of sustaining built 

environments in vulnerable areas: e.g., siting 

and land-use policies and practices to shift 

from more vulnerable areas to less, adding 

resilience to new construction in vulnerable 

areas, increased awareness of changing 

hazards and associated risks, and assistance 

for the less-advantaged (including actions 

by the private insurance sector as a likely 

driving force).

2. Changing the spatial form of a settlement—

managing growth and change over decades 

without excluding critical functions (e.g., 

architectural innovations improving the 

sustainability of structures, reducing 

transportation emissions by reducing 

the length of journeys to work, seeking 

efficiencies in resource use through 

integration of functions, and moving from 

brown spaces to green spaces). Among the 

alternatives receiving the most attention 

are encouraging “green buildings” (e.g., 

green roofs: Parris, 2007; see Rosenzweig 

et al., 2006a; Rosenzweig et al., 2006b) and 

increasing “green spaces” within urban areas 

(e.g., Bonsignore, 2003).

3. Technological change to reduce sensitivity of 

physical and linkage infrastructures—e.g., 

more efficient and affordable interior climate 

control, surface materials that reduce heat 

island effects (Quattrochi et al., 2000), waste 

reduction and advanced waste treatment, 

and better warning systems and controls. 

Physical design changes for long-lived 

infrastructure may also be appropriate, such 

as building water-treatment or storm-water 

runoff outflow structures based on projected 

sea level rather than the historical level.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

4. Institutional change to improve adaptive 

capacity, including assuring effective 

governance, providing financial mechanisms 

for increasing resiliency, improving 

structures for coordinating among multiple 

jurisdictions, targeting assistance programs 

for especially impacted segments of the 

population, adopting sustainable community 

development practices, and monitoring 

changes in physical infrastructures at an 

early stage (Wilbanks et al., 2007a). Policy 

instruments include zoning, building and 

design codes, terms for financing, and early 

warning systems (Kirshen et al., 2005).

5. “No regrets” or low net cost policy initiatives 

that add resilience to the settlement and its 

physical capital—e.g., in coastal areas 

changing building codes for new construction 

to require coping with projected amounts of 

sea level rise over the expected lifetimes of 

the structures.

The choice of strategies from among the options 

is likely to depend on co-benefits in terms of 

other social, economic, and ecological driving 

forces; the availability of fiscal and human 

resources; and political aspects of “who wins” 

and “who loses.”

3.3.3 Examples of Current 

Adaptation Strategies

In most cases in the United States, settlements 

have been more active in climate change 

mitigation than climate change adaptation (see 

Box 3.5), but there are some indications that 

adaptation is growing as a subject of interest 

(Solecki and Rosenzweig, 2005; Ruth, 2006). 

Bottom-up grassroots activities currently under 

way in the United States are considerable, and 

that number appears to be growing. For example, 

Boston has built a new wastewater treatment 

plant at least one-half meter higher than currently 

necessary to cope with sea level rise, and in a 

coastal flood protection plan for a site north of 

Boston the U.S. Corps of Engineers incorporated 

sea level rise into their analysis (Easterling et 

al., 2004). California is considering climate 

change adaptation strategies as a part of its 

more comprehensive attention to climate change 

policies (Franco, 2005), and Alaska is already 

pursuing ways to adapt to permafrost melting 

and other climate change effects.

Meanwhile, in some cases, settlements are 

taking actions for other reasons that add 

resilience to climate change effects. An example 

is the promotion of water conservation, which is 

reducing per capita water consumption in cities 

that could be subject to increased water scarcity 

(City of New York, 2005).

It seems very likely that local governments 

will play an important role in climate change 

responses in the United States. Many adaptation 

options must be evaluated at a relatively local scale 

in terms of their relative costs and benefits and 

their relationships with other urban sustainability 

issues, and local governments are important as 

guardians of public services, able to mobilize a 

wide range of stakeholders to contribute to broad 

community-based initiatives (as in the case of 

the London Climate Change Partnership, 2004). 

Because climate change impact concerns and 

adaptation potentials tend to cross jurisdictional 

boundaries in highly fragmented metropolitan 

areas, local actions might encourage crossboundary interactions that would have value for 

other reasons as well.

While no U.S. communities have developed 

comprehensive programs to ameliorate the 

effects of heat islands, some localities are 

recognizing the need to address these effects. 

In Chicago, for example, several municipal 

buildings have been designed to accommodate 

“green” rooftops. Atlanta has had a Cool 

Communities “grass roots” effort to educate 

local and state officials and developers on 

strategies that can be used to mitigate the UHI. 
The U.S. Climate Change Science Program Chapter 3

104

This Cool Communities effort was instrumental 

in getting the State of Georgia to adopt the 

first commercial building code in the country 

emphasizing the benefits of cool roofing 

technology (Young, 2002; Estes, Jr. et al., 

2003). The “Excessive Heat Events Guidebook,” 

developed by the Environmental Protection 

Agency in collaboration with National Oceanic 

and Atmospheric Administration, the Centers 

for Disease Control and Prevention, and the 

Department of Human Services provides 

information for municipal officials in the event 

of an excessive heat event.1

3.3.4 Strategies to 

Enhance Adaptive Capacity

In most cases, the likelihood of effective 

adaptation is related to the capacity to adapt, 

which in turn is related to such variables as 

knowledge and awareness, access to fiscal and 

human resources, and good governance (IPCC, 

2001a). Strategies for enhancing such capacities 

in U.S. settlements are likely to include the 

development and use of local expertise on 

climate change issues (AAG, 2003); attention 

to the emerging experience with climate change 

effects and response strategies globally and in 

other U.S. settlements; information sharing 

about adaptation potentials and constraints 

among settlements and their components (likely 

aided by modern information technology); 

and an emphasis on participatory decisionmaking where local industries, institutions, and 

community groups are drawn into discussions 

of possible responses.

1 For more information please see: http://www.epa.

gov/hiri/about/heatguidebook.html.

3.4 Conclusions

Even from a current knowledge base that is 

very limited, it is possible to conclude several 

things about effects of climate change on human 

settlements in the United States:

1. Climate change takes place in the context 

of a variety of factors driving an area’s 

development: it is likely to be a secondary 

factor in most places, with its importance 

determined mainly by its interactions with 

other factors, except in the case of major 

abrupt climate change (very likely).

2. Effects of climate change will var y 

considerably according to location-specific 

vulnerabilities, and the most vulnerable 

areas are likely to be Alaska, coastal and 

river basins susceptible to flooding, arid 

areas where water scarcity is a pressing 

issue, and areas whose economic bases are 

climate-sensitive (very likely).

3. The main impact concerns, in areas other 

than Alaska, have to do with changes in 

the intensity, frequency, and/or location of 

extreme weather events and, in some cases, 

water availability rather than changes in 

temperature (very likely).

4. Over the time period covered by current 

climate change projections, the potential 

for adaptation through technological 

and institutional development as well 

as behavioral changes are considerable, 

especially where such developments meet 

other sustainable development needs and 

especially considering the initiatives already 

being shown at the local level across the 

United States (extremely likely).

5. While uncertainties are very large about 

specific impacts in specific time periods, 

it is possible to talk with a higher level of 

confidence about vulnerabilities to impacts 

for most settlements in most parts of the 

United States (virtually certain).
105

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

3.5 Expanding the 

Knowledge Base

A number of sources, including NACC, 1998; 

Parson et al., 2003; Ruth, 2006; and Ruth et 

al., 2004, have considered research pathways 

for improving the understanding of effects of 

climate change on human settlements in the 

United States. 

The following list suggests a number of research 

topics that would help expand the knowledge 

base about the linkages between climate change 

and human settlements.

•	 Advance understanding of settlement 

vulnerabilities, impacts, and adaptive 

responses in a variety of different local 

contexts around the country through case 

studies. In addition to identifying vulnerable 

settlements, these studies should also identify 

vulnerable populations (such as the urban 

poor and native populations on rural and/

or tribal lands) that have limited capacities 

for response to climate change within those 

settlements. Better understanding of climate 

change at the community scale would 

provide a basis for adaptation research that 

addresses social justice and environmental 

equity concerns. 

•	 Develop better projections of climate 

change at the scale of U.S. metropolitan 

areas or smaller, including scenarios 

project i ng ext remes a nd scena r ios 

involving abrupt changes. 

•	 Improve abilities to associate projections 

of climate change in U.S. settlements with 

changes in other driving forces related to 

impacts, such as changes in metropolitan/

urban patterns and technological change.

•	 Design practically implementable, socially 

acceptable strategies for shifting human 

populations and activities away from 

vulnerable locations.

•	 Improve the understanding of vulnerabilities 

of urban inflows and outflows to climate 

change impacts, as well as second and thirdorder impacts of climate change in urban 

environments, including interaction effects 

among different aspects of the urban system. 

•	 I mprove t he u nde r st a nd i ng of t he 

relationships between settlement patterns 

(both regional and intra-urban) and 

resilience/adaptive capacity.

•	 Improve understanding of how urban 

decision-making is changing as populations 

become more heterogeneous and decisions 

become more decentralized, especially as 

this affects adaptive responses. 

•	 Review current policies and practices related 

to climate change responses to help inform 

community decision-makers and other 

stakeholders about potentials for relatively 

small changes to make a large difference. 

•	 Evaluate and document experiences with 

urban/settlement climate change responses 

while involving decision-making, research 

and stakeholder communities more actively 

in discussions of climate change impacts and 

response issues. Focus attention on the costs, 

benefits, and possible limits and potentials of 

adaptation to climate change vulnerabilities 

in U.S. cities and smaller settlements.

•	 I mprove tools a nd approa ches for 

infrastructure planning and design to reduce 

exposure and sensitivity to climate change 

effects while increasing adaptive capacity.

•	 Enhance coordination within federal 

g ove r n m e n t a g e n c i e s t o i m p r ove 

understanding about impacts, vulnerabilities, 

and responses to climate change for the 

nation’s cities and smaller settlements. 

Connections with U.S. urban decisionmakers can enable integration of climate 

change considerations into what they do with 

building codes, zoning, lending practices, etc. 

as mainstreamed urban decision processes.
The U.S. Climate Change Science Program Chapter 3

106

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CHAPTER

4

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Effects of Global Change 

on Human Welfare

Lead Author: Frances G. Sussman, Environmental Economics Consulting

Contributing Authors: Maureen L. Cropper, University of Maryland at 

College Park; Hector Galbraith, Galbraith Environmental Sciences LLC; 

David Godschalk, University of North Carolina at Chapel Hill; John 

Loomis, Colorado State University; George Luber, Centers for Disease 

Control and Prevention; Michael McGeehin, Centers for Disease Control 

and Prevention; James E. Neumann, Industrial Economics, Incorporated; 

W. Douglass Shaw, Texas A&M University; Arnold Vedlitz, Texas A&M 

University; Sammy Zahran, Colorado State University

4.1 INTRODUCTION

Human welfare is an elusive concept. There 

is no single, commonly accepted definition or 

approach to thinking about welfare. Clearly 

there is a shared understanding that human 

welfare, well-being, and quality of life (terms 

that are often used interchangeably) refer to 

aspects of individual and group life that improve 

living conditions and reduce chances of injury, 

stress, and loss. The physical environment is 

one factor, among many, that may improve 

or reduce human well-being. Climate is one 

aspect of the physical environment, and 

can affect human well-being via economic, 

physical, psychological, and social pathways 

and influence individual perceptions of quality 

of life. 

Climate change may result in lifestyle changes 

and adaptive behavior with both positive 

and negative implications for well-being. For 

example, warmer temperatures may change the 

amount of time that individuals are comfortable 

spending outdoors in work, recreation, or other 

activities, and temperature combined with 

other climatic changes may alter (or induce) 

changes in intra- and inter-country human 

migration patterns. More generally, studies of 

climate change and the United States identify 

an assortment of impacts on human health, the 

productivity of human and natural systems, and 

human settlements. Many of these impacts—

ranging from changes in livelihoods to changes 

in water quality and supply—are linked to some 

aspect of human well-being. 

Communities are an integral determinant 

of human well-being. Climate change that 

affects public goods—such as damaged 

infrastructure or interruptions in public 

services—or disrupts the production of 

goods and services, will affect economic 

performance including overall health, poverty, 

employment, and other measures. These 

changes may have consequences, such as a 

lost job or a more difficult commute, that 

affect individual well-being directly. In other 

cases, individual well-being may be indirectly 

affected due to concern for the well-being of 

other individuals, or for a lack of cohesion 

within the community. The sustainability or 

resilience of a community (i.e., its ability to 

cope with climate change and other stressors 

over the long term) may be reduced by climate 

change weakening the physical and social 

environment. In the extreme, such changes 

may undermine the individual’s sense of 

security or faith in government’s capacity to 

accommodate change. 

Completely cataloging the effects of global 

change on human well-being or welfare 

would be an immense undertaking. Despite 

its importance, no well-accepted structure 

for doing so has been developed and applied. 

Moreover, little (if any) research focuses 

explicitly on the impact of global change on 

human well-being, per se. The chapter seeks 

to make a review of this topic manageable by 

focusing on several discrete issues: 
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•	 Alternative approaches to defining and 

studying human well-being;

•	 Identifying human well-being and quality 

of life measures and indicators (qualitative 

and quantitative);

•	 Describing economic welfare and monetary 

methods of assigning value to climate 

change’s potential impacts; and, 

•	 Providing examples of climate change 

impacts on selected categories of wellbeing and reporting indicators of economic 

welfare for these categories.

Section 4.2 focuses on valuation and nonmonetary metrics and draws on the literature 

to provide insights into a possible foundation 

for future research into the effects of climate 

change on human well-being. This section 

first discusses the literature defining human 

well-being. Next, it presents an illustrative 

place-based indicators approach (the typical 

approach of planners and policy makers to 

evaluating quality of life in communities, 

cities, and countries). Approaches of this 

type represent a commonly accepted way 

of thinking about well-being that is linked 

to objective (and sometimes subjective) 

measures. While a place-based indicators 

approach has not been applied to climate 

change, it has the potential to provide a 

framework for identifying categories of human 

well-being that might be affected by climate 

change, and for making the identification of 

measures or metrics of well-being a more 

concrete enterprise in the future. To illustrate 

that potential, the section draws links between 

community welfare and some of the negative 

impacts of climate change.

Economics has been at the forefront of efforts 

to quantify the welfare impacts of climate 

change. Economists employ, however, a very 

specific definition of well-being—economic

welfare—for valuing goods and services or, 

in this case, climate impacts. This approach 

is commonly used to support environmental 

policy decision making in many areas. Section 

4.3 very briefly describes the basis of this 

approach, and the techniques that economists 

use (focusing on those that have been applied 

to estimate impacts of climate change). This 

section next summarizes the existing economic 

estimates of the non-market impacts of climate 

change.1 An accompanying appendix provides 

more information on the economic approach 

to valuing changes in welfare, and highlights 

some of the challenges in applying valuation 

techniques to climate impacts. 

The fourth section of the chapter summarizes some 

of the key points of the chapter, and concludes with 

a brief discussion of research gaps.

4.2 Human Welfare, 

Well-being, and Quality 

of Life

No single, widely accepted definition exists for 

the term human welfare, or for related terms 

such as well-being and quality of life. They are 

all often used interchangeably (Veenhoven, 

1988, 1996, 2000; Ng, 2003; Rahman, 2007). 

Economists, epidemiologists, health scientists, 

psychologists, sociologists, geographers, 

political scientists, and urban planners have all 

rendered their own definitions and statistical 

indicators of life quality at both individual and 

1 Because more concrete aspects of welfare, such as 

impacts on prices or income, may be covered by 

other synthesis and assessment products (see, for 

example, discussions of dollar values in SAP 4.3, 

The Effects of Climate Change on Agriculture, Land 

Resources, Water Resources, and Biodiversity), this 

report focuses exclusively on the types of intangible 

amenities that directly impact quality of life, but are 

not traded in markets, including health, recreation, 

ecosystems, and climate amenities.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

community levels.2 For purposes of clarity in 

this chapter, we adopt the convention of the 

Millenium Assessment (MA, 2005) and the 

Intergovernmental Panel on Climate Change 

(IPCC, 2007a), which use “well-being” as an 

umbrella term—referring broadly to the extent 

to which human conditions satisfy the range of 

constituents of well-being, including health, 

social relations, material needs, security, and 

freedom of choice. “Quality of life” is here 

used synonymously with well-being, to reflect 

usage in a wide range of disciplines, including 

medical, sociological, psychological, and urban 

planning literatures. The term “welfare” is 

generally used to refer narrowly to economic 

measures of individual well-being, although it 

is also used in the context of communities in a 

broader sense.

Despite differences in definitions, human 

well-being—in its broadest sense—is typically 

a multi-dimensional concept, addressing 

the availability, distribution, and possession 

of economic assets, and non-economic 

goods such as life expectancy, morbidity 

and mortality, literacy and educational 

attainment, natural resources and ecosystem 

services, and participatory democracy. These 

conceptualizations often also include social and 

community resources (sometimes referred to 

as social capital in social scientific literature), 

such as the presence of voluntary associations, 

arts, entertainment, and shared recreational 

amenities (see Putnam, 1993, 2000). The 

quantity of community resources shared by a 

population is often called social capital.3 These 

components of life quality are interrelated 

and correlate with subjective valuations of 

life satisfaction, happiness, pleasure, and the 

operation of successful democratic political 

systems (Putnam, 2000). 

2 For example, in sociological literature, the terms 

well-being and welfare are used interchangeably 

to refer to objectively measurable life chances and 

experiences, and the term quality of life is used to 

describe subjective assessments and experiences of 

individuals. 

3 The concept of social capital has been defined, in 

different ways, by Putnam (1993, 1995, 2000) and 

by Coleman (1988, 1990, 1993). For Coleman, social 

capital is a store of community value that is embodied in social structures and the relations between 

social actors, from which individuals can draw in 

the pursuit of private interest. Putnam’s definition is 

similar, but places a stronger emphasis on altruism 

and community resources. 

The concepts of well-being, economic welfare, 

and quality of life play important roles not 

only in academic research, but also in practical 

analysis and policy making. Quality of life 

measures may be used, for example, to gauge 

progress in meeting policy or normative goals 

in particular cities by planners. Municipalities 

in New Zealand, England, Canada, and the 

United States have constructed their own 

metrics of quality of life to estimate the 

overall well-being and life chances available 

to citizens. Similarly, health-related quality 

of life measures can indicate progress in 

meeting goals. For example, the U.S. Medicare 

program uses metrics to track quality of life 

for beneficiaries and to monitor and improve 

health care quality (HCFR, 2004). Moreover, 

international agencies from the United Nations 

Human Development Programme (UNDP), 

to the Millenium Ecosystem Assessment on 

Ecosystems and Human Well-Being, and highly 

regarded periodicals like The Economist, have 

built composite measures of human and societal 

well-being to compare and rank nations of the 

world.4

Life quality and human well-being are 

increasingly important objects of theoretical and 

empirical research in diverse disciplines. Two 

analytic approaches characterize the research 

literature: (1) studies that emphasize wellbeing as an individual attribute or possession; 

4 See, for example, the discussion of the sources of 

Table 1 subsequently in this chapter, which include a 

number of country-level quality of life assessments. 

The UNDP Human Development Index, a country 

by country ranking of quality of life indicators, can 

be accessed at http://hdr.undp.org/en/statistics/.
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and (2) studies that treat well-being as a social 

or economic phenomenon associated with a 

geographic place. 

4.2.1 Individual Measures 

of Well-being 

Approaches focusing on individuals are 

generally found in medical, health, cognitive, 

and economic sciences. We turn to these first, 

and then next to place-focused indicators. 

4.2.1.1 Health-focused Approaches 

In medical science, quality of life is used as an 

outcome variable to evaluate the effectiveness of 

medical, therapeutic, and/or policy interventions 

to promote population health. Quality of life is 

an individual’s physiological state constituted 

by body structure, function, and capability 

that enable pursuit of stated and revealed 

preferences. In medical science, the concept of 

life quality is synonymous with good health–a 

life free of disease, illness, physical, and/or 

cognitive impairment (Raphael et al., 1996, 

1999, 2001). 

In addition to objective measures of physical 

and occupational function, disease absence, 

or somatic sensation, life quality scientists 

measure an individual’s perception of life 

satisfaction. The scientific basis of such research 

is that pain and/or discomfort associated with 

a physiological impairment are registered 

and experienced variably. Based on patient 

reports or subjective valuations, psychologists 

and occupational therapists have developed 

valid and reliable instruments to assess 

how mental, developmental, and physical 

disabilities interfere with the performance 

and enjoyment of life activities (Bowling, 

1997; Guyatt et al., 1993). 

4.2.1.2 Economic and Psychological 

Approaches

Individual valuations of life quality also anchor 

economic and psychological investigations 

of happiness and utility. In the new science 

of happiness, scholars use the tools of 

neuroscience, experimental research, and 

modern statistics to discover and quantify the 

underlying psychological and physiological 

sources of happiness (for reviews see Kahneman 

et al., 1999; Frey and Stutzer, 2002; Kahneman 

and Krueger, 2006). Empirical studies 

show, for example, that life satisfaction and 

happiness correlate predictably with marital 

status (married persons are generally happier 

than single people), religiosity (persons that 

practice religion report lower levels of stress 

and higher levels of life satisfaction), and 

individual willingness to donate time, money 

and effort to charitable causes. Similarly, the 

scholarly literature notes interesting statistical 

associations between features of climate (such 

as variations in sunlight, temperature, and 

extreme weather events) and self-reported levels 

of happiness, utility, or life satisfaction. 

Individual valuations of health, psychological, 

and emotional well-being are sometimes summed 

across representative samples of a population or 

country to estimate correspondences between 

life satisfaction and “hard” indicators of living 

standards such as income, life expectancy, 

educational attainment, and environmental 

quality. Cross-national analyses generally find 

that population happiness or life satisfaction 

increases with income levels and material 

standards of living (Ng, 2003) and greater 

personal autonomy (Diener et al., 1995; Diener 

and Diener, 1995).5 In such studies, subjective 

valuations of life satisfaction are embedded in 

5 Some studies suggest that individual utility or happiness is not positively determined by some absolute 

quantity of income, wealth, or items consumed, but 

rather how an individual perceives his or her lot in 

relation to others or to conditions in their past. See, 

for example, Frank 1985. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

broader conceptions of quality of life associated 

with the conditions of a geographic place, 

community, region, or country—the social 

indicators approach.

4.2.2 The Social Indicators 

Approach

In a second strand of research, what some refer 

to as the social indicators approach, scholars 

assemble location-specific measures of social, 

economic, and environmental conditions, such 

as employment rates, consumption flows, 

the availability of affordable housing, rates 

of crime victimization and public safety, 

public monies invested in education and 

transportation infrastructure, and local access 

to environmental, cultural, and recreational 

amenities. These place-specific variables 

are seen as exogenous sources of individual 

life quality. Scholars reason that life quality 

is a bundle of conditions, amenities, and 

lifestyle options that shape stated and revealed 

preferences. In technical terms, the social 

indicators approach treats quality of life as a 

latent variable, jointly determined by several 

causal variables that can be measured with 

reasonable accuracy. 

The indicators approach has several advantages 

in the context of understanding the impacts of 

climate change on human well-being. First, 

social indicators have considerable intuitive 

appeal, and their widespread use has not only 

made it familiar to both researchers and the 

general public, but has subjected them to 

considerable debate and discussion. Second, 

they offer considerable breadth and flexibility 

in terms of categories of human well-being 

that can be included. Third, for many of 

the indicators or dimensions of well-being, 

objective metrics exist for measurement. 

In addition, while its strength is in providing 

indicators of progress on individual dimensions 

of quality of life, the indicators approach has also 

been used to support aggregate or composite 

measures, at least for purposes of ranking or 

measuring progress. Various techniques are also 

available, or being developed, that aggregate 

or combine measures of well-being. These 

range from pure data reduction procedures to 

stakeholder input models where variables are 

evaluated on their level of social and economic 

importance. For example, Richard Florida 

(2002a) has constructed a statistical index 

of technology, talent, and social tolerance 

variables to estimate the human capital of 

cities in the United States. Given the analytical 

strengths of the social indicators approach, it 

may be a good starting point for understanding 

the relationships between human well-being and 

climate change. 

4.2.2.1 A Taxonomy of 

Categories of Well-being

Taxonomies of place-specific well-being 

or quality of life typically converge on six 

categories or dimensions: (1) economic 

conditions; (2) natural resources, environment, 

and amenities; (3) human health; (4) public 

and private infrastructure; (5) government 

and public safety; and (6) social and cultural 

resources. These categories represent broad 

aspects of personal and family circumstances, 

social structures, government, environment, and 

the economy that influence well-being. Table 

4.1 illustrates these categories, which are listed 

in Column 1. The third column, “components/

indicators of well-being,” provides examples 

of the way in which these categories are often 

interpreted. These components represent what, 

in an ideal world, researchers would wish to 

measure in order to determine how a specific 

society fares from the perspective of well-being. 

The fourth column provides illustrative metrics, 

i.e., objective or quantifiable measures that 

are often used by researchers as indicators of 
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well-being for each category.6 Finally, the last 

column provides some examples of climate 

impacts that may be linked to that category. 

This column should not be viewed as an attempt 

to create a comprehensive list of impacts, or 

even to list impacts with equal weights, in terms 

of importance or likelihood of occurrence. 

Further, while Table 4.1 focuses on negative 

impacts (as potentially more troubling for 

quality of life), in some categories there are also 

opportunities or potential positive impacts. 

These categories of well-being or life quality 

are interrelated. For example, as economic or 

social conditions in a society improve (e.g.,

as measured by Gross Domestic Product 

(GDP), GDP per capita, and rates of adult 

literacy), improvements occur in human 

health outcomes such as infant mortality, rates 

of morbidity, and life expectancy at birth. 

Thus, while the categories and corresponding 

metrics of well-being presented in Table 4.1 are 

analytically separable, in reality they are highly 

interconnected.7

Economics as a source of quality of life refers 

to a mix of production, consumption, and 

exchange activities that constitute the material 

well-being of a geographic place, community, 

region, or country. Standard components of 

economic well-being include income, wealth, 

poverty, employment opportunities, and 

costs of living. Localities characterized by 

efficient and equitable allocation of economic 

6 Sources that contributed to the development of Table 

4.1 include: MA (2005); Sufian, 1993; Rahman, 2007, 

and Lambiri, et al., 2007. Insights were also derived 

from quality of life studies of individual cities and 

countries, including: http://www.bigcities.govt.nz/

indicators.htm Quality of Life in New Zealand’s Large 

Urban Areas; http://www.asu.edu/copp/morrison/

public/qofl99.htm What Matters in Greater Phoenix 

1999 Edition: Indicators of Our Quality of Life; 

and http://www.jcci.org/statistics/qualityoflife.aspx

Tracking the Quality of Life in Jacksonville. 

7 More recently, scholars (Costanza et al. 2007) and 

government agencies (like NOAA’s Coastal Service 

Center) have moved toward the global concept of 

capital to integrate indicators and assess community 

quality of life. The term capital is divided into four 

types: economic; physical; ecological or natural; 

and socio-cultural. Various metrics constitute these 

types of capital, and are understood to foster community resilience and human needs of subsistence, 

reproduction, security, affection, understanding, 

participation, leisure, spirituality, creativity, identity, and freedom. See also Rothman, Amelung, and 

Poleme (2003). 

rewards and opportunities enable material 

security and subjective happiness of residents 

(Florida, 2002a).

Natural resources, environment, and amenities 

as a source of well-being refers to natural 

features, such as ecosystem services, species 

diversity, air and water quality, natural hazards 

and risks, parks and recreational amenities, 

and resource supplies and reserves. Natural 

resources and amenities directly and indirectly 

affect economic productivity, aesthetic and 

spiritual values, and human health (Blomquist 

et al., 1988; Glaeser et al., 2001; Cheshire and 

Magrini, 2006). 

Human health as a source of well-being 

includes features of a community, locality, 

region, or country that influence risks of 

mortality, morbidity, and the availability of 

health care services. Good health is desirable 

in itself as a driver of life expectancy (and the 

quality of life during those years), and is also 

critical to economic well-being by enabling 

labor force participation (Raphael et al., 1996, 

1999, 2001). 

Public and private infrastructure sources 

of well-being include transportation, energy 

and communication technologies that enable 

commerce, mobility, and social connectivity. 

These technologies provide basic conditions 

for individual pursuits of well-being (Lambiri 

et al., 2007). 

Government and public safety as a source 

of well-being are activities by elected 

representatives and bureaucratic officials 

that secure and maximize the public services, 

rights, liberties, and safety of citizens. 

Individuals derive happiness and utility from 

the employment, educational, civil rights, 

public service, and security efforts of their 

governments (Suffian, 1993).

Finally, social and cultural resources as a 

source of well-being are conditions of life that 

promote social harmony, family and friendship, 

and the availability of arts, entertainment, 

and leisure activities that facilitate human 

happiness. The terms social and creative capital 

have become associated with these factors. 

Communities with greater levels of social and 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Category of 

Well-being Description and Rationale

Components/Indicators of

Well-being

Illustrative Metrics/ 

Measures of Well-being

Examples of Negative 

Climate Linkages*

Economic conditions

The economy supports a mix of activities: opportunities for employment, a strong consumer market, funding for needed public services, and a high standard of living shared by citizens. 

Income and production •	Economic standard of living, e.g., •	wealth and income, cost of living, povertyEconomic development, e.g., •	business and enterprise, employmentAvailability of affordable housing •	Equity in the distribution of income •	

GDP •	Wage rates (e.g., persons at minimum •	wage)Employment rates •	Business startups and job creation •	Housing prices •	Dependence on public assistance •	Families/children living in poverty •	Utility costs, gasoline prices, and •	other prices

Reduced job opportunities and wage rates in areas dependent on natural resources, such as agricultural production in a given region that faces increased drought.Higher electricity prices resulting from increased demand for air conditioning as average temperatures and frequency of heat waves rise. 

Natural resources, environment, and amenities

Resources enhance the quality of life of citizens; pollution and other negative environmental effects are kept below levels harmful to ecosystems, human health, and other quality of life considerations; and natural beauty and aesthetics are enhanced.

Air, water, and land pollution •	Recreational opportunities •	Water supply and quality •	Natural hazards and risks •	Ecosystem condition and services •	Biodiversity •	Direct climate amenity effects •	

Air and water quality indices •	Waste recycling rates •	Acreage, visitation, funding of •	recreational and protected/preserved areasWater consumption and levels •	Deaths, injuries, and property loss •	due to natural hazardsEndangered and threatened species •	

Sea level rise could both inundate coastal wetland habitats (with negative effects on marsh and estuarine environments necessary to purify water cycle systems and support marine hatcheries) and erode recreational beaches.

Human health Health care institutions 

provide medical and preventive health-care services with excellence, citizens have access to services regardless of financial means, and physical and mental health is generally high.

Mortality risks •	Morbidity and risk of illness •	Quality and accessibility of health •	careHealth status of vulnerable •	populationsPrenatal and childhood health •	Psychological and emotional health •	

Deaths from various causes (suicide, •	cancer, accidents, heart disease)Life expectancy at birth •	Health insurance coverage •	Hospital services and costs •	Infant mortality and care of elderly •	Subjective measure of health status •	

Increased frequency of heat waves in a larger geographical area will directly affect health, resulting in higher incidence of heat-related mortality and illness. Climate can also affect human health indirectly via effects on ecosystems and water supplies. 

Table 4.1 Categorization of Well-being 
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Category of 

Well-being Description and Rationale

Components/Indicators of

Well-being

Illustrative Metrics/ 

Measures of Well-being

Examples of Negative 

Climate Linkages*

Public and private infrastructure

Transportation and communication infrastructure enable citizens to move around efficiently and communicate reliably. 

Affordable, and accessible public •	transitAdequate road, air, and rail •	infrastructureReliable communication systems •	Waste management and sewerage •	Maintained and available public and •	private facilitiesPower generation •	

Mass transit use and commute times •	Rail lines, and airport use and •	capacityTelephones, newspapers, and internet •	Waste tonnage and sewerage safety •	Congestion and commute to work •	Transportation accident rates •	Noise pollution •	

Melting permafrost due to warming in the arctic damages road transport, pipeline, and utility infrastructure, which in turn leads to disrupted product and personal movements, increased repair costs, and shorter time periods for capital replacement. 

Government and public safety

Governments are led by competent and responsive officials, who provide public services effectively and equitably, such as order and public safety; citizens are well-informed and participate in civic activities.

Electoral participation •	Civic engagement •	Equity and opportunity •	Municipal budgets and finance •	Public safety •	Emergency services •	

Voter registration, turnout, approval •	Civic organizations membership rates •	Availability of public assistance •	programsDebt, deficits, taxation, and spending •	Crime rates and victimization •	Emergency first-responders per •	capita

Dislocations and pressures created by climate change stressors can place significant new burdens on police, fire and emergency services.

Social and cultural resources

Social institutions provide services to those in need, support philanthropy, volunteerism, patronage of arts and leisure activities, and social interactions characterized by equality of opportunity and social harmony.

Volunteerism •	Culture, arts, entertainment, and •	leisure activitiesEducation and human capital services •	Social harmony •	Family and friendship networks •	

Donations of time, money, and effort •	Sports participation, library •	circulation, and support for the artsGraduation rates and school quality •	Hate, prejudice, and homelessness •	Divorce rates, social supports •	

Disruptions in economic and political life caused by climate change stressors or extreme weather events associated with climate change could create new conflicts and place greater pressure on social differences within communities.

* The focus is on negative impacts as potentially more troubling for quality of life; there are also positive impacts and opportunities in some categories.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

creative capital are expected to have greater 

individual and community quality of life 

(Putnam, 2000; Florida, 2002b). 

In thinking about these indicators, it is 

important to keep two important contextual 

realities about climate change and well-being 

at the forefront. First, while discussions of 

climate change usually have a global context 

to them, the fact is that the effects of any 

specific changes in temperature, rainfall, storm 

frequency/intensity, and sea level rise will be 

felt at the local and regional level by citizens 

and communities living and working in those 

vulnerable areas. Therefore, not all populations 

will be placed under equal amounts of climate 

change-generated stress. Some will experience 

greater impacts, will suffer greater damage, and 

will need more remediation and better plans and 

resource allocations for adaptation and recovery 

efforts to protect and restore quality of life (see, 

for example, Zahran et al., 2008; Liu, Vedlitz 

and Alston, 2008; Vedlitz et al., 2007).

Second, not all citizens in areas more 

vulnerable to climate change effects are 

equally at risk. Some population groupings, 

within the same community, will be more 

vulnerable and at risk than others. Those who 

are poorer, minorities, aged or infirmed, and 

children are at greater risk than others to the 

stresses of climate change events (Lindell and 

Perry, 2004; Peacock, 2003). Recognizing that 

not all citizens of a particular vulnerable area 

share the same level of risk is something that 

planners and decision makers must take into 

account in projecting the likely impacts of 

climate change events on their populations, and 

in dealing with recovery of those populations 

(Murphy and Gardoni, 2008).

Finally, the situation is further complicated 

as climate stressors negatively affect disease 

conditions in other nations with particularly 

vulnerable and mobile populations. Increased 

communicable disease incidence in developing 

nations has the potential, through legal and 

illegal tourism and immigration, to affect 

community welfare and individual well-being 

in the United States.

4.2.2.2 Climate Change and 

Quality of Life Indicators

Social indicators are generally used to evaluate 

progress towards a goal: How is society doing? 

Who is being affected? Tracking performance 

for these indicators—using the types of metrics 

or measures indicated in Table 4.1—could 

provide information to the public on how 

communities and other entities are reacting 

to, and successfully adapting to (or failing to 

adapt to), climate change. The indicators and 

metrics included in Table 4.1 are intended to 

be illustrative of the types of indicators that 

might be used, rather than a comprehensive or 

recommended set. In any category, multiple 

indicators could be used; and any one of the 

indicators could have several measures. For 

example, exposure to natural hazards and 

risks could be measured by the percentage of 

a locality’s tax base located in a high hazard 

zone, the number of people exposed to a 

natural hazard, the funding devoted to hazard 

mitigation, or the costs of hazard insurance, 

among others. Similarly, some indicators are 

more amenable to objective measurement; 

others are more difficult to measure, such 

as measures of social cohesion. The point 

to be taken from Table 4.1 is that social 

indicators provide a diverse and potentially rich 

perspective on human well-being. 

The taxonomy presented in Table 4.1—or a 

similar taxonomy—might also provide a basis 

for analyses of the impacts of climate change on 

human well-being, providing a list of important 

categories for research (the components or 

indicators of life quality), as well as appropriate 

metrics (e.g., employment, mortality or 

morbidity, etc.). The social indicators approach, 

and the specific taxonomy presented here, are 

only one of many that could be developed.8 At 

the least, different conditions and stakeholder 

8 In addition to variants on the social indicators approach, other types of taxonomies are possible—for 

example a taxonomy based on broad systems (atmospheric, aquatic, geologic, biological, and built 

environment), or on forms of capital that make up the 

productive base of society (natural, manufactured, 

human, and social). Well-being can also be viewed 

in terms of its endpoints: necessary material for a 

good life, health and bodily well-being, good social 

relations, security, freedom and choice, and peace of 

mind and spiritual existence (Rothman, Amelung, 

and Poleme, 2003).
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mixes may demand different emphases. All 

taxonomies, however, face a common problem: 

how to interpret and use the diverse indicators, 

in order to compare and contrast alternative 

adaptive or mitigating responses to climate 

change. For some purposes, metrics have been 

developed that aggregate across individuals 

or individual categories of well-being and 

present a composite measure of well-being; or 

otherwise operationalize related concepts, such 

as vulnerability (see, for example the discussion 

of Figure 4.1). 

4.2.3 A Closer Look at 

Communities

Looking beyond well-being of individuals to the 

welfare (broadly speaking) of communities—

networks of households, businesses, physical 

structures, and institutions—provides a broader 

perspective on the impacts of climate change. 

The categories and metrics in Table 4.1 are 

appealing from an analytical perspective in part 

because they represent dimensions of well-being 

that are clearly important to individuals, but 

that also have counterparts and can generally 

be measured objectively at the community 

level. Thus, for example, the counterparts of 

individual income or health status are, at the 

social level, per capita income or mortality/

illness rates. The concept of community welfare 

is linked to human communities, but is not 

confined to communities in urban areas, or even 

in industrialized cultures. Human communities 

in remote areas, or subsistence economies, face 

the same range of quality of life issues—from 

health to spiritual values—although they may 

place different weights on different values; thus, 

the weights placed on different components of 

welfare are not determined a priori, but depend 

on community values and decision making. 

Viewing social indicators and metrics through 

the lens of the community can be instructive in 

several ways. First, communities are dynamic 

entities, with multiple pathways of interactions 

among people, places, institutions, policies, 

structures, and enterprises. Thus, while the social 

indicators described in Table 4.1 have metrics 

that can be measured independently of each 

other, they are not determined independently 

within the complex reality of interdependent 

human systems. Second, in part because of 

this interdependence, the aggregate welfare 

of a community is more than a composite 

of its quality of life metrics; sustainability 

provides one means of approaching a concept 

of aggregate welfare. Third, vulnerability 

and adaptation are typically analyzed at the 

sectoral level: “what should agriculture, or the 

public health system, do to plan for or adapt to 

climate change.” The issue can also, however, 

be addressed at the level of the community. 

Each of these issues is touched on below. 

4.2.3.1 Community Welfare and 

Individual Well-being

Rapid onset extreme weather events, such 

as hurricanes or tornadoes, can do serious 

damage to community infrastructure, public 

facilities and services, the tax base, and overall 

community reputation and quality of life, from 

which recovery may take years and never be 

complete (see additional discussion in Chapter 

3). More gradual changes in temperature 

and precipitation will have both negative and 

positive effects. For example, as discussed 

elsewhere in this chapter, warmer average 

temperatures increase risks from heat-related 

mortality in the summer, but decrease risks 

from cold-related mortality in the winter, 

for susceptible populations. Effects such as 

these will not, however, be confined to a few 

individual sectors, nor are the effects across all 

sectors independent. 

To illustrate the interdependence of impacts and, 

by extension, the analogous social indicators 

and metrics, consider a natural resource that 

faces additional stresses from climate change: 

fish populations in estuaries, such as the 

Chesapeake Bay, that are already stressed by air 

and water pollution from industry, agriculture, 

and cities. In this case, while the direct effects 

of climate will occur to the resource itself, 

indirect effects can alter welfare as measured by 

economic, social, and human health indicators. 

Table 4.2 presents some of the pathways by 

which resource changes could affect diverse 

categories of quality of life; the purpose of 

Table 4.2 is not to assert that all these effects 

will occur or that they will be significant if 

they do occur as a result of climate change, but 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Figure 4.1 Geography of Climate Change Vulnerability at the County Scale

Three measures of climate change risk are used to create the vulnerability index: expected 

temperature change, extreme weather event history, and coastal proximity. Risk measures are 

geo-referenced at the county scale. The expected temperature change variable is measured as the 

expected unit change in average minimum temperature (in degrees Celsius) for a county from 2004 

to 2099. Temperature data are from the Hadley Center. Hadley Center monthly time series data on 

average minimum temperature for the United States are plotted at the 0.5 x 0.5 degree of spatial 

resolution. In cases where climate cells intersect county boundaries, temperature data are averaged 

across intersecting climate cells. To estimate extreme weather event history, we summarize the 

number of reported injuries and fatalities from hydo-meterological hazard events at the county 

level Jan 01, 1960 to Jul 31, 2004. Higher values on our natural hazard casualty variable reflect more 

pronounced histories of injury and death from extreme weather events. Casualty data were collected 

from the Spatial Hazard Events and Losses Database for the United States (SHELDUS). The coastal 

proximity variable is measured dichotomously. A country receives a score of 1 if it is designated by 

the National Oceanic and Atmospheric Administration (NOAA) as an “at-risk-coastal” county, and a 

score of 0 if it is not. NOAA defines a county as at-risk-coastal if at least 15 percent of its total area 

is located in a coastal watershed. The vulnerability index was created by standardizing then summing 

each measure of climate change risk (z-score). The distribution of vulnerability is divided into equal 

quintles, with darker colors reflecting higher vulnerability to climate change. 
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122

rather to illustrate the linkages. These linkages 

underscore the importance of understanding 

interdependencies within the community 

or, from another perspective, across welfare 

indicators. Table 4.2 illustrates the general 

principle of complex linkages in which a 

general equilibrium approach can be used to 

model climate change impacts. 

4.2.3.2 Sustainability of Communities

Understanding how climate change and 

extreme events affect community welfare 

requires a different conceptual framework 

than that for understanding individual level 

impacts, such as quality of life.9 Communities 

9 Measures of quality of life provide a database 

of relevant individual characteristics at various 

points in time, including economic conditions, 

natural resources and amenities, human health, 

public and private infrastructure, government and 

public safety, and social and cultural resources. 

Sustainable development measures are similar, but 

reflect more emphasis on long-term and reciprocal 

effects, as well as a concern for community-wide 

and equitable outcomes. 

are more than the sum of their parts; they 

have unique aggregate identities shaped by 

dynamic social, economic, and environmental 

components. They also have life cycles, 

waxing and waning in response to societal 

and environmental changes (Diamond, 2005; 

Fagan, 2001; Ponting, 1991; Tainter, 1988). 

Sustainability is a paramount community goal, 

typically expressed in terms of sustainable 

development in order to express the ongoing 

process of adaptation into the long-term 

future. “Climate change involves complex 

interactions between climatic, environmental, 

economic, political, institutional, social, 

and technological processes. It cannot be 

addressed or comprehended in isolation from 

broader societal goals (such as sustainable 

development)...” (Banuri and Weyant, 2001). 

Even for a country as developed as the United 

States, continuing growth and development 

creates both pressures on the natural and built 

environments and opportunities for moving in 

sustainable directions. 

Table 4.2 An illustration of Possible Effects of Climate Change on Fishery Resources

Linkages/Pathways Category of Welfare Effect Possible Metrics

Fishery resource declines as climate 

changes

Natural resources, environment, and 

amenities Fish populations

Recreational opportunities decline Natural resources, environment, and 

amenities Fish catch, visitation days

Related species and habitats are 

affected

Natural resources, environment, and 

amenities Species number and diversity

Employment and wages in resourcebased jobs (including recreation) fall as 

resources decline

Economic conditions Number of jobs, unemployment 

rate, wages

Incomes fall as jobs are lost Economic conditions Per capita income 

More children live in poverty as jobs 

are lost and incomes fall Economic conditions Families, children below poverty level

Access to health care that is tied to 

jobs and income falls Human health Households without health insurance increase

Increased mortality and morbidity as a 

result of reduced health care Human health Disease and death rates increase

Lack of jobs results in out-migration Economic conditions Working age population decreases

Fewer new residents attracted, 

because of reduced jobs and amenities 

(recreation)

Social and cultural resources Population growth rate slows

Less incentive/drive to participate in 

community activities Social and cultural resources

Drop in volunteerism, civic 

participation, completion of high 

school
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

While the term sustainability does not 

have a single, widely accepted definition, 

a central guideline is to balance economic, 

environmental, and social needs and values 

(Campbell, 1996; Berke et al., 2006). It is 

distinguished from quality of life by its 

dynamic linking of economic, environmental, 

and social components, and by its future 

orientation (Campbell, 1996; Porter, 2000). 

Sustainability is seen as living on nature’s 

“interest,” while protecting natural capital. 

Sustainability is a comprehensive social 

goal that transcends individual sector or 

impact measurements, although it can include 

narrower community welfare concepts such 

as the healthy city. Thinking about the 

impacts of climate change on communities 

through the lens of sustainable development 

allows us to envision cross-sector economic, 

environmental, and social dynamics.

4.2.4 Vulnerable Populations, 

Communities, and Adaptation

Responding to climate change at the community 

level requires understanding both vulnerability 

and adaptive responses that the community can 

take. Vulnerability of a community depends 

on its exposure to climate risk, how sensitive 

systems within that community are to climate 

variability and change, and the adaptive capacity 

of the community (i.e., how it is able to respond 

and protect its citizens from climate change). 

Different groups within the community will 

be differentially vulnerable to climate changes 

(such as extreme events), and infrastructure 

and community coping capacity will be more 

or less effective in invoking a resilient response 

to climate change.

4.2.4.1 Vulnerable Populations 

Categor ies of persons suscept ible to 

environmental risks and hazards include racial 

and ethnic groups (Bolin, 1986; Fothergill et al.,

1999; Lindell and Perry, 2004; Cutter, 2006), 

and groups defined by economic variables of 

wealth, income, and poverty (Peacock, 2003; 

Dash et al., 1997; Fothergill and Peek, 2004). 

Overall, research indicates that minorities and 

the poor are differentially harmed by disaster 

events. Economic disadvantage, lower human 

capital, limited access to social and political 

resources, and residential choices are social 

and economic reasons that contribute to 

observed differences in disaster vulnerability 

by race and ethnicity, and by economic 

status. While the literature on climate change 

and vulnerable populations is relatively 

underdeveloped, Chapter 2 on Human Health 

and Chapter 3 on Human Settlements each 

address population vulnerabilities.

Economic, social, and health effects are not 

neatly bounded by geographic or political 

regions, and so the damage and stresses that 

occur in a specific locality are not limited 

in their effects to only that community. As 

Hurricane Katrina made clear, impacts felt in 

one community ripple throughout the region 

and nation. Many of the persons made homeless 

in New Orleans resettled in Baton Rouge, 

Lafayette, and Houston, creating stresses on 

those communities. Vulnerable groups migrate 

from stricken areas to more hospitable ones, 

taking their health, economic, and educational 

needs and problems with them across both 

national and state lines.

4.2.4.2 Vulnerable Communities 

While most analyses of vulnerability tend to 

be conducted at the regional scale, Zahran 

et al. (2008) have brought the analysis closer 

to the community level by mapping the 

geography of climate change vulnerability at 

the county scale. Their study uses measures 

of both physical vulnerability (expected 

temperature change, extreme weather events, 

and coastal proximity) and adaptive capacity 

(as represented by economic, demographic, 

and civic participation variables that constitute 

a locality’s socioeconomic capacity to commit 

to costly climate change policy initiatives). 

Their map identifies the concentrations of 

highly vulnerable counties as lying along the 

east and west coasts and Great Lakes, with 

medium vulnerability counties mostly inland 

in the southeast, southwest, and northeast. (See 

Figure 4.1, in which darker areas represent 

higher vulnerability.)

Many possible dimensions can be used to 

identify and measure vulnerabilities to climate 

change impacts and stressors. The one presented 

in Figure 4.1 illustrates that the concept 
The U.S. Climate Change Science Program Chapter 4

124

of vulnerability is a viable one and can be 

measured and applied to communities in a 

Geographic Information System context. It is 

not the purpose of this chapter to focus in great 

detail on vulnerability measurement issues 

(for those interested in other formulations 

of the vulnerability concept, see Dietz et al., 

In Press). 

4.2.4.3 Adaptation

From the perspective of the community, the goal 

of successful adaptation to climate impacts—

particularly potentially adverse impacts—is 

to maintain the long-term sustainability and 

survival of the community. Thus, a resilient 

community is capable of absorbing climate 

changes and the shocks of extreme events 

without breakdowns in its economy, natural 

resource base, or social systems (Godschalk, 

2003). Given their control over shared resources, 

communities have the capacity to adapt to 

climate change in larger and more coordinated 

ways than individuals, by creating plans and 

strategies to increase resilience in the face of 

future shocks, while at the same time ensuring 

that the negative impacts of climate change 

do not fall disproportionately on their most 

vulnerable populations and demographic 

groups (Smit and Pilifosova, 2001). 

Public policies and programs are in place in 

the United States to enhance the capacity of 

communities to mitigate10 damage and loss 

from natural hazards and extreme events 

(Burby, 1998; Mileti, 1999; Godschalk, 2007). 

A considerable body of research looks at 

responses to natural hazards, and recent 

research has shown that the benefits of natural 

hazard mitigation at the national level outweigh 

its costs by a factor of four to one on average 

(Multihazard Mitigation Council, 2005; Rose et 

al., 2007). Research also has been done on the 

social vulnerability of communities to natural 

hazards (Cutter et al., 2003) and the economic 

resilience of businesses to natural hazards 

(Tierney, 1997; Rose, 2004). However, there 

10 In the natural hazards and disasters field, a single 

term—mitigation—refers both to adaptation to hazards and mitigation of their stresses (see the Disaster 

Mitigation Act of 2000, Public Law 106-390).

is scant research on U.S. policies dealing with 

community adaptation to the broader impacts 

of climate change.

4.3 An Economic

Approach to Human

Welfare

Welfare, well-being, and quality of life are often 

viewed as multi-faceted concepts. In subjective 

assessments of happiness or quality of life (see 

the discussion in Section 4.2), the individual 

makes a net evaluation of his or her current 

state, taking into account (at least implicitly) 

and balancing all the relevant facets or 

dimensions of that state of being. Constructing 

an overall statement regarding welfare from a 

set of objective measures, however, requires a 

means of weighting or ranking, or otherwise 

aggregating, these measures. The economic 

approach supplies one—although not the only 

possible—approach to aggregation.11

Quantitative measures of welfare that use a 

common metric have two potential advantages. 

First, the ability to compare welfare impacts 

across different welfare categories makes it 

possible to identify and rank categories with 

regard to the magnitude or importance of effects. 

Welfare impacts can then provide a signal about 

the relative importance of different impacts, and 

so help to set priorities with regard to adaptation 

or research. Second, if the concept of welfare 

is (ideally) a net measure, then it should be 

possible to aggregate the effects of climate across 

disparate indicators. Quantitative measures that 

use the same metric can, potentially, be summed 

to generate net measures of welfare, and gauge 

progress over time, or under different policy or 

adaptation scenarios.

11 In part because of the difficulty in compiling the 

information needed for aggregation of economic 

measures, Jacoby (2004) proposes a portfolio approach to benefits estimation, focusing on a limited 

set of indicators of global climate change, of regional 

impact, and one global monetary measure. The set 

of measures would not be the only information generated and made available, but it would represent a 

set of variables continuously maintained and used 

to describe policy choices. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Given the value of welfare both as a multidimensional concept, and as one that facilitates 

comparisons, the economic approach to welfare 

analysis—which monetizes or puts dollar 

values on impacts—is one means of comparing 

disparate impacts. Further—and this is the 

second advantage of the economic approach—

dollar values of impacts can be aggregated, and 

so provide net measures of changes in impacts 

that can be useful to policy makers. This 

section of the chapter discusses the foundation 

of economic valuation, the distinction between 

market and non-market effects (only the latter 

are covered in this paper), and describes some 

of the valuation tools that economists use for 

non-market effects. An appendix covers these 

issues in additional detail, and also describes 

the challenges that economic valuation faces 

when used as a tool for policy analysis in the 

long term context of climate change. 

Fundamental to the economic approach is a 

notion that a key element of support for decisionmaking is an understanding of the magnitude of 

costs and benefits, so that the tradeoffs implicit 

in any decision can be balanced and compared. 

However, the economic approach, when 

interpreted as requiring a strict cost-benefit 

test, is not appropriate in all circumstances, 

and is viewed by some as controversial in 

the context of climate change.12 Cost-benefit 

analysis is one tool available to decision 

makers. In the context of climate change, other 

decision rules and tools, or other definitions 

of welfare, may be equally, or more relevant. 

For example, the recent Synthesis Report of 

the IPCC Fourth Assessment (IPCC, 2007b) 

presents an average social cost (i.e., damages) 

of carbon in 2005 of $12 per ton of CO2, but 

also notes that the range of the roughly 100 

peer-reviewed estimates of this value is -$3 to 

$95/tCO2.13 The IPCC attributes this very broad 

12 See Arrow et al., 1996 - at page 7, “There may be 

factors other than economic benefits and costs that 

agencies will want to weigh in decisions, such as 

equity within and across generations. In addition, 

a decision maker may want to place greater weight 

on particular characteristics of a decision, such as 

potential irreversible consequences.” 

13 See IPCC 2007b, page 23.

range to differences in assumptions on climate 

sensitivity, response lags, the treatment 

of risk and equity, economic and noneconomic impacts, the inclusion of potentially 

catastrophic losses, and discount rates. The 

IPCC therefore suggests consideration of 

an “iterative risk management process” 

to support decision-making.14 Estimated 

benefits and costs therefore can provide 

information relevant to decision makers, 

but some of the methodologies and data 

necessary to provide a relatively complete 

assessment may be unavailable, as discussed 

subsequently in this section.15

14 The IPCC further notes that existing analyses suggest costs and benefits of mitigation are roughly 

comparable in magnitude, “but do not as yet permit 

an unambiguous determination of an emissions 

pathway or stabilization level where benefits exceed 

costs.” (IPCC 2007b page 23). 

15 Other factors that might be considered, in addition to 

economic estimates, include emotions, perceptions, 

cultural values, and other subjective factors, all of 

which can play a role in creating preferences and 

reaching decisions. Those factors are beyond what 

we can evaluate in this chapter. 
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4.3.1 Economic Valuation 

The framework that economists employ reflects 

a specific view of human welfare and how to 

measure it. Economists define the value of 

something—be it a good, service, or state of the 

world—by focusing on the well-being, utility, or 

level of satisfaction that the individual derives. 

The basic economic paradigm assumes that 

individuals allocate their available income and 

time to achieve the greatest level of satisfaction. 

The value of a good—in terms of the utility 

or satisfaction it provides—is revealed by the 

tradeoffs that individuals make between that 

good and other goods, or between that good and 

income.16 The term “willingness to pay” (WTP) 

is used by economists to represent the value of 

something, i.e., the individual’s willingness to 

trade money for that particular good, service, 

or state of the world.

Economists distinguish between market and 

non-market goods. Market goods are those that 

can be bought and sold in the market, and for 

which a price generally exists. Market behavior 

and, in particular, the prices that are paid for 

these goods, is a source of information on the 

economic value or benefit of these goods. The 

economic benefit—the amount that members 

of society would in aggregate be willing to pay 

16 Although economists are careful to distinguish between the metrics of utility and money as distinct, 

valuation metric in dollar units (rather than units of 

utility) may be generally viewed as the outcomes 

of individual preference expressions among goods, 

income, and time.

for these goods—is related to, but frequently 

greater than, market prices. 

Non-market goods are those that are not 

bought and sold in markets. Consequently, 

climate change impacts that involve nonmarket effects—such as health effects, loss 

of endangered species, and other effects—are 

difficult to value in monetary terms. Economists 

have developed techniques for measuring 

non-market values, by inferring economic 

value from behavior (including other market 

behavior), or by asking individuals directly. 

A number of studies have attempted to value 

the range of effects of climate change. For the 

United States, some of the most comprehensive 

studies are the Report to Congress completed 

by U.S. EPA in 1989 (U.S. EPA, 1989), Cline 

(1992), Nordhaus (1994), Fankhauser (1995), 

Mendelsohn and Neumann (1999), Nordhaus 

and Boyer (2000), and a body of work by 

Richard Tol (e.g., Tol, 2002 and Tol, 2005). 

In all of these studies, the focus is largely on 

market impacts, particularly the effects of 

climate change on agriculture, forestry, water 

resource availability, energy demand (mostly 

for air conditioning), coastal property, and in 

some cases, health. 

Non-market effects, however, are less well 

characterized in these studies (Smith et al., 

2003); where comprehensive attempts are made, 

they usually involve either expert judgment 

or very rudimentary calculations, such as 

multiplying the numbers of coastal wetland 

acres at risk of inundation from sea level rise 

by an estimate of the average non-market 

value of a wetland. One such comprehensive 

attempt generated a value for 17 ecosystem 

services from 16 ecosystem types (Costanza et 

al., 1997), but also generated controversy and 

criticism from many economists (Bockstael et 

al., 2000; Toman, 1998; see National Research 

Council 2004 for a summary). Other analysts 

have attempted to define measures to reflect 

non-market ecosystem services in terms similar 

to those used for Gross Domestic Product 

(Boyd, 2006), or indicators of ecosystem health 

that reflect ecological contributions to human 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

welfare (Boyd and Banzhaf, 2006).17 While 

there are several well-done valuation analyses 

for non-market effects of climate change (as 

described later in this chapter), it is fair to 

characterize this literature as opportunistic in 

its focus; where data and methods exist, there 

are high quality studies, but the overall coverage 

of non-market effects remains inadequate.

4.3.2 Impacts Assessment and 

Monetary Valuation 

The process of estimating the welfare effects of 

climate change involves four steps: (1) estimate 

climate changes; (2) estimate physical effects 

of climate change, (3) estimate the impacts on 

human and natural systems that are amenable 

to valuation and (4) value or monetize effects. 

The first step requires estimating the change 

in relevant measures of climate, including 

temperature, precipitation, sea level rise, and 

the frequency and severity of extreme events. 

The second step involves estimating the physical 

effects of those changes in climate. Such effects 

might include changes in ecosystem structure 

and function, human exposures to heat stress, 

changes in the geographic range of disease 

vectors, or flooding of coastal areas. In the third 

step, the physical effects of climate change are 

translated into measures that economists can 

value, for example the number and location of 

properties that are vulnerable to floods, or the 

number of individuals exposed to and sensitive 

to heat stress. Many analyses that reach this 

step in the process, but not all, also proceed 

on to the fourth step, valuing the changes in 

dollar terms.

The simplest approach to valuation would be to 

apply a unit valuation approach. For example, 

the cost of treating a nonfatal case of heat stress 

or malaria attributable to climate change is a 

first approximation of the value of avoiding 

that case altogether. In many contexts, however, 

unit values can misrepresent the true marginal 

economic impact of these changes. For example, 

if climate change reduces the length of the ski 

season, individuals could engage in another 

17 Some political economists also emphasize the role of 

explicit recognition of non-market environmental values as an important step in improving the well-being 

of poor populations (Boyce and Shelley, 2003).

recreational activity, such as golf. Whether 

they might prefer skiing to golf at that time 

and location is something economists might 

try to measure.

This step-by-step linear approach to effects 

estimation is sometimes called the “damage 

function” approach. A damage function 

approach might imply that we look at effects 

of climate on human health as separate and 

independent from effects on ecology and 

recreation, an assumption that ignores the 

complex economic interrelationships among 

goods and services and individual decisions 

regarding these. Recent research suggests that 

the damage function approach, under some 

conditions, may be both overly simplistic 

(Freeman, 2003) and sometimes subject to 

serious errors (Strzepek and Smith, 1995; 

Strezpek et al., 1999). 

Economists have a number of techniques 

available for moving from quantified effects 

to dollar values. In some cases, the values 

estimated in one situation—e.g., one ecosystem 

or species—can be transferred and used to 

value another. For example, value or benefits 

transfer is commonly used by federal agencies 

such as the U.S. EPA and U.S. Forest Service to 

value recreation when there is insufficient time 

or budget to conduct original valuation studies 

(Rosenberger and Loomis, 2003). Techniques 

commonly used by economists to value nonmarket goods and services include:
The U.S. Climate Change Science Program Chapter 4

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•	 Revealed preference. Revealed preference, 

sometimes referred to as the indirect 

valuation approach, involves inferring the 

value of a non-market good using data 

from market transactions (U.S. EPA, 2000; 

Freeman, 2003). For example, the value of a 

lake for its ability to provide a good fishing 

experience can be estimated by the time and 

money expended by the angler to fish at that 

particular site, relative to all other possible 

fishing sites. Likewise, the amenity value 

of a coastal property that is protected from 

storm damage (by a dune, perhaps) can be 

estimated by comparing the price of that 

property to other properties similar in every 

way but the enhanced storm protection. 

•	 Stated preference. Stated preference 

methods, sometimes referred to as the direct 

valuation, are survey methods that estimate 

the value individuals place on particular nonmarket goods based on choices they make 

in hypothetical markets. The earliest stated 

preference studies involved simply asking 

individuals what they would be willing to pay 

for a particular non-market good. The best 

studies involve great care in constructing a 

credible, though still hypothetical, trade-off 

between money and the non-market good 

of interest (or bundle of goods) to discern 

individual preferences for that good and 

hence, willingness to pay WTP. 

•	 Replacement or avoided costs. Replacement 

cost studies approach non-market values by 

estimating the cost to replace the services 

provided to individuals by the non-market 

good. For example, healthy coastal wetlands 

may provide a wide range of services to 

individuals who live near them (such as 

filtering pollutants present in water). A 

replacement cost approach would estimate 

the value of these services by estimating 

market costs for replacing the services 

provided by the wetlands. Analogously, the 

cost of health effects can be estimated using 

the cost of treating illness and of the lost 

workdays, etc. associated with illness. 

•	 Value of inputs. This approach calculates 

value based on the contribution of an input into 

some productive process. This approach can 

be used to determine the value of both market 

and non-market inputs, for example, fertilizer, 

water, or soil, in farm output and profits.

In the remainder of this section, we briefly 

discuss the relationship between climate 

change and four non-market effects (human 

health, ecosystems, recreation and tourism, and 

amenities), and discuss economic estimates of 

these effects using these techniques.

4.3.3 Human Health

In the United States, climate change is likely 

to measurably affect health outcomes known 

to be associated with weather and climate, 

including heat-related illnesses and deaths, 

health effects due to storms, floods, and other 

extreme weather events, health effects related to 

poor air quality, water- and food-borne diseases, 

and insect-, tick-, and rodent-borne diseases. In 

addition to changes in mortality and morbidity, 

climate change may affect health in more subtle 

ways. Good health is more than the absence of 

illness; it includes mental health, the ability to 

function physically (to climb stairs or walk a 

mile), socially (to move freely in the world), 

and in a work environment. See Chapter 2 of 

this report, for an overview of health effects that 

have been associated with climate change. 

Despite our understanding of the pathways 

linking climate and health effects, there is 

uncertainty as to the magnitude and geographic 

and temporal variation of possible impacts on 

morbidity and mortality in the United States. 

This is primarily due to a poor understanding 

of many key risk factors and confounding 

issues, such as behavioral adaptation and 

variability in population vulnerability (Patz 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

et al., 2001). Even where our understanding of 

underlying climate and health relationships is 

better, few studies have attempted to explicitly 

link these findings to climate change scenarios 

to quantitatively estimate health impacts. 

Economists have relatively well established 

(although sometimes controversial) techniques 

for valuing mortality and some forms of 

morbidity, which could, in theory, be applied 

to quantified impacts assessments. 

4.3.3.1 Overview of 

Health Effects of Climate Change 

The United States is a developed country with 

a temperate climate. It has a well-developed 

health infrastructure and government and 

non-governmental agencies involved in 

disaster planning and response, both of which 

can help to mitigate potential health effects 

from climate change. Nevertheless, certain 

regions of the United States will face difficult 

challenges arising from some of the following 

health effects. 

•	 Illnesses and deaths due to heat waves. 

A likely impact in the United States is 

an increase in the severity, duration, and 

frequency of heat waves (Kalkstein and 

Greene, 1997; IPCC, 2007c). This, coupled 

with an aging (and therefore more vulnerable) 

population, will increase the likelihood of 

higher mortality from exposure to excessive 

heat (see, for example, Semenza et al., 1996, 

and Knowlton et al., 2007).

•	 Injuries and death from extreme weather 

events. Climate change is projected to 

alter the frequency, timing, intensity, and 

duration of extreme weather events, such 

as hurricanes and f loods (Fowler and 

Hennessey, 1995). The health effects of these 

extreme weather events range from the direct 

effects, such as loss of life and acute trauma, 

to indirect effects, such as loss of shelter, 

large-scale population displacement, damage 

to sanitation infrastructure (drinking water 

and sewage systems), interruption of food 

production, damage to the health care 

infrastructure, and psychological problems 

such as post traumatic stress disorder 

(Curriero et al., 2001).

•	 Illnesses and deaths due to poor air quality. 

Climate change can affect air quality by 

modifying local weather patterns and 

pollutant concentrations (such as ground 

level ozone), by affecting natural sources 

of air pollution, and by changing the 

distribution of air-borne allergens (Morris 

et al., 1989; Sillman and Samson, 1995). 

Many of these effects are localized and, 

for ozone, compounded by assumptions 

of trends in precursor emissions. Despite 

these uncertainties, all else being equal, 

climate change is projected to contribute to 

or exacerbate ozone-related illnesses. 

•	 Water- and food-borne diseases. Altered 

weather patterns, including changes in 

precipitation, temperature, humidity, 

and water salinity, are likely to affect the 

distribution and prevalence of food- and 

water-borne diseases resulting from bacteria, 

overloaded drinking water systems, and 

increases in the frequency and range of 

harmful algal blooms (Weniger et al., 1983; 

MacKenzie et al., 1994; Lipp and Rose, 1997; 

Curriero et al., 2001). 

•	 Insect-, tick-, and rodent-borne diseases. 

Vector-borne diseases, such as plague, 

Lyme’s disease, malaria, hanta virus, and 

dengue fever have distinct seasonal patterns, 

suggesting that they may be sensitive to 

climate-driven changes in rainfall and 

temperature (Githeko and Woodward, 2003). 

Moderating factors, such as housing quality, 

land-use patterns, vector control programs, 

and a robust public health infrastructure, are 

likely to prevent the large-scale spread of 

these diseases in the United States.
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130

4.3.3.2 Quantifying the 

Health Impacts of Climate Change

A large epidemiological literature exists on the 

health effects associated with climate change, 

particularly the mortality effects associated 

with increases in average monthly or seasonal 

temperature, and with changes in the intensity, 

frequency, and duration of heat waves. As 

described in Chapter 2, there is considerable 

speculation concerning the balance of climate 

change-related decreases in winter mortality 

compared with increases in summer mortality, 

although researchers suspect that declines in 

winter mortality associated with climate change 

are unlikely to outweigh increases in summer 

mortality (McMichael et al., 2001; Kalkstein 

and Greene, 1997; Davis, 2004). 

Net changes in mortality are difficult to 

estimate because, in part, much depends 

on complexities in the relationship between 

mortality and the changes associated with 

global change. Using average temperatures to 

estimate cold-related mortality, for example, 

is complicated by the fact that many factors 

contribute to winter mortality (such as spread 

of the influenza virus). Similarly, increased 

summer mortality may be affected not only 

by average temperature, but also by other 

temperature factors, such as variability 

in temperature, or the duration of heat 

waves. Moreover, quantifying projected 

temperature-related mortality requires going 

beyond epidemiology and projecting adaptive 

behaviors, such as the use of air conditioning, 

expanded public programs (such as heat 

warning systems), or migratory patterns. 

Few studies have attempted to link the 

epidemiological findings to climate scenarios 

for the United States, and studies that have 

done so have focused on the effects of changes 

in average temperature, with results dependent 

on climate scenarios and assumptions of future 

adaptation.18 Moreover, many factors contribute 

to winter mortality, making highly uncertain 

how climate change could affect mortality. No 

projections have been published for the United 

States that incorporate critical factors, such as 

the influence of influenza outbreaks. Below, 

we report the results of these studies in order to 

give a sense of the magnitude of mortality that 

might be associated with temperature changes 

due to climate change and, by intimation, the 

magnitude of potential changes in economic 

welfare. The conclusions should be considered 

preliminary, however, in part because of the 

complexities in estimating mortality under 

future climate scenarios. Moreover, none of 

the studies reported below traces through the 

quantitative implications of various climate 

scenarios for mortality in all regions of the 

United States using region-specific data, 

suggesting a clear need for future research.

18 McMichael et al. (2004) estimate the impact of 

climate change on DALYs (Disability-Adjusted Life 

Years) associated with waterborne and vector-borne 

illness for WHO regions. (DALYs represent the sum 

of life-years lost due to premature death and productive life years lost due to chronic illness or injury.) 

For the US, it is not anticipated that climate change 

will lead to loss of life or years of life due to chronic 

illness or injury from waterborne or foodborne illnesses. However, there will likely be an increase 

in the spread of several food- and water-borne 

pathogens among susceptible populations depending on the pathogens’ survival, persistence, habitat 

range and transmission under changing climate and 

environmental conditions.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Quantifying the relationship between climate 

change and cases of injury, illness, or death 

requires an exposure-response function that 

quantifies the relationship between a health 

endpoint (e.g., premature mortality due to 

cardiovascular disease (CVD), cases of diarrheal 

disease) and climate variables (e.g., temperature 

and humidity). The exposure-response function 

can be used to compute the relative risk of 

illness or death due to a specified change in 

climate, e.g., a temperature increase of 2.5°C. 

Applying this relative risk to the baseline 

incidence of the illness or death in a population 

yields an estimated number of cases associated 

with the climate scenario. 

Two studies have attempted to link exposureresponse functions to future climate scenarios 

and thereby develop temperature-related 

mortality estimates.19 McMichael et al. (2004) 

estimate the effects of average temperature 

changes associated with projected climates 

resulting from alternative emissions scenarios, 

by WHO region. For the AMR-A region, which 

includes the United States, Canada, and Cuba, 

they estimate the impact on cardio-vascular 

mortality relative to baseline conditions 

in 1990. Effects are estimated for average 

temperature projections associated with three 

alternative emissions scenarios: (1) no control 

of GHG emissions,20 (2) stabilization at 750 

parts-per-million (ppm) of CO2 equivalent 

by 2210, and (3) stabilization at 550 ppm CO2

equivalent by 2170.21

McMichael et al. (2004) bases the estimates 

of the effects of average temperature changes 

on mortality from CVD for AMR-A on Kunst 

et al. (1993). Kunst et al. (1993) find CVD 

mortality rates to be lowest at 16°C, and to 

increase by 0.5 percent for every degree C 

below 16°C and increase by 1.1 percent for each 

degree above 16°C. In applying these results 

to future climate scenarios, McMichael et al.

19 These studies use climate scenarios that are associated with different emissions scenarios from IPCC 

(2000), the so-called SRES scenarios. 

20 McMichael et al. (2004) represent unmitigated emissions using the IS92a emissions scenario presented 

in IPCC (2000). 

21 Climate scenarios are projected for 2025 and 

2050 using the HadCM2 model at a resolution of 

3.75◦ longitude by 2.5◦ latitude and interpolated 

to other years. 

(2004) assume that people will adjust to higher 

average temperatures; thus, the temperature 

at which mortality rates reach a minimum is 

adjusted by scenario. No adjustment is made 

for attempts to mitigate the effects of higher 

temperatures through (for example) increased 

use of air-conditioning. The effect of the climate 

scenarios for the AMR-A, reported for 2020 

and 2030, is, on net, zero. Reductions in CVD 

mortality due to warmer winter temperatures 

cancel out increases in CVD mortality due to 

warmer summer temperatures. 

Hayhoe et al. (2004) examine the impacts on 

climate and health in California of projected 

climate change associated with two emissions 

scenarios. The emissions scenarios are similar 

to those used in McMichael et al. (2004): 

(1) stabilization at 970 ppm of CO2 and (2) 

stabilization at 550 ppm of CO2.22 In Los 

Angeles, by the end of the century, the number 

of heat wave days (3 or more days with 

temperatures above 32°C) increases fourfold 

under scenario B1 and six to eight times under 

scenario A1fi. From a baseline of 165 excess 

deaths in the 1990s, heat-related deaths in Los 

Angeles are projected to increase two to three 

times under scenario B1 and five to seven times 

under scenario A1fi by 2090. 

These results can be compared with those of an 

earlier study that employed a composite climate 

variable to examine the impact of extreme 

temperatures on daily mortality under future 

climate scenarios. Kalkstein and Greene (1997) 

22 Hayhoe uses two SRES (IPCC 2000) emissions 

scenarios: A1fi (corresponding to 970 ppm of CO2) 

and B1 (corresponding to 550 ppm of CO2).
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132

analyzed the effect of temperature extremes 

(both hot and cold) on mortality for 44 U.S. 

cities in the summer and winter. They then 

applied these results to climate projections from 

two GCMs for 2020 and 2050. In 2020, under a 

no-control scenario, excess summer deaths in 

the 44 cities were estimated to increase from 

1,840 to 1,981-4,100, depending on the GCM 

used. The corresponding figures for 2050 were 

3,190-4,748 excess deaths. 

4.3.3.3 Valuation of Health Effects

In cost-benefit analyses of health and safety 

programs, mortality risks are commonly valued 

using the “value of a statistical life” (VSL)—

defined as the sum of what people would pay 

to reduce their risk of dying by small amounts 

that, together, add up to one statistical life. This 

approach allows valuation economists to focus 

on how people respond to and implicitly value 

mortality risk in their daily decisions, rather 

than attempting to value the lives lost, per se

(U.S. EPA, 2000). This approach also responds 

to the type of data that is typically available; 

the excess deaths associated with a particular 

climate scenario are indeed the number of 

statistical lives that would be lost. 

Willingness to pay for a current reduction in risk 

of death (e.g., over the coming year) is usually 

estimated from compensating wage differentials 

in the labor market (a revealed preference 

method), or from contingent valuation surveys 

(a stated preference method) in which people 

are asked directly what they would pay for 

a reduction in their risk of dying. The basic 

idea behind compensating wage differentials 

is that jobs can be characterized by various 

attributes, including risk of accidental death. If 

workers are well-informed about risks of fatal 

and non-fatal injuries, and if labor markets 

are competitive, riskier jobs should pay 

more, holding worker and other job attributes 

constant (Viscusi, 1993). In theory, the impact 

of a small change in risk of death on the wage 

should equal the amount a worker would have 

to be compensated to accept this risk. For 

small risk changes, this is also what the worker 

should pay for a risk reduction.

For the compensating wage approach to yield 

reliable estimates of the VSL, it is necessary 

that workers be informed about fatal job risks 

and that there be sufficient competition in labor 

markets for compensating wage differentials 

to emerge.23 To measure these differentials 

empirically requires accurate estimates of the 

risk of death on the job—ideally, broken down 

by industry and occupation. The researcher 

must also be able to include enough other 

determinants of wages that fatal job risk does 

not pick up the effects of other worker or job 

characteristics. Empirical estimates of the value 

of a statistical life based on compensating wage 

studies conducted in the United States lie in the 

range of $0.6 million to $13.5 million (1990 

dollars) (Viscusi, 1993; U.S. EPA, 1997), which 

is the rough equivalent of $0.7 million to $16.5 

million in year 2000 dollars.24

The challenge in valuating health effects is 

compounded by the long-term nature of climate 

risks, which suggests that much of the premature 

mortality associated with higher temperatures 

will occur in the future. Indeed, McMichael 

et al. (2004) and Kalkstein and Greene (1997) 

estimate mortality based on climate effects 

around the years 2020 and 2050; Hayhoe et al.

(2004) analyze impacts in 2070-2099. 

It is also the case that the majority of the health 

effects of climate change will be felt by persons 

65 and over. Recent attempts to examine how 

the VSL varies with worker age (Viscusi and 

Aldy, 2007) suggest that the VSL ranges from 

$9.0 million (2000 dollars) for workers aged 

35-44 to $3.7 million for workers aged 55-62. 

Contingent valuation studies (Alberini et al., 

2004) also suggest that the VSL may decline 

with age. Further, economic theory suggests 

that, under some assumptions, persons are 

willing to pay less to reduce a risk they will 

face in the future (say, at age 65) than they 

are willing to pay to reduce a risk they face 

today (Cropper and Sussman, 1990). Both 

these factors may affect the economic value 

23 Estimates of compensating wage differentials are 

often quite sensitive to the exact specification of the 

wage equation. Black et al. (2003), in a reanalysis of 

data from U.S. compensating wage studies requested 

by the USEPA, conclude that the results are too 

unstable to be used for policy.

24 Adjusted using the GDP implicit price deflator 

produced by the Bureau of Economic Analysis US 

Department of Commerce, available at http://www.

bea.gov/national/nipaweb/TableView.asp#Mid.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

that would be attached to excess mortality 

estimates, such as those derived by Kalkstein 

and Greene (1997). 

The potential health effects associated with 

climate change are much broader than the 

changes in excess mortality discussed above. 

The effects of climate on illness have been 

examined in the literature, as indicated in the 

previous section; however, there have been few 

attempts to examine the implications of these 

studies for future climate scenarios. In addition 

to quantified estimates of mortality and 

morbidity, themselves indications of well-being 

and welfare, a range of economic techniques 

that have been developed for use in cost-benefit 

analyses of health and safety regulations could 

be applied to many of the endpoints that may 

be affected by climate change, as suggested 

by Table 4.3. Before these methods could be 

applied, however, the impacts of climate change 

must be translated into physical damages. 

It is also the case that good health is more than 

the absence of illness. All of the dimensions of 

functioning measured in standard questionnaires 

(including various health outcomes surveys) 

(HCFR, 2004) may be affected by changes in 

climate. From a valuation perspective, we would 

expect changes in functional limitations 

(stiffness of joints, difficulty walking) not 

to be linked directly to climate or to weather, 

but rather to be instrumental in people’s 

location decisions and, thus, ref lected in 

wages and property values. The relationship 

between climate and wages and property 

values are discussed below in Section 4.3.6 

on amenity values.

4.3.4 Ecosystems

Human welfare depends, in many ways, on 

the Earth’s ecosystems and the services that 

they provide, where ecosystem services may 

be defined as “the conditions and processes 

through which natural ecosystems, and the 

species that make them up, sustain and fulfill 

human life” (Daily, 1997). These services 

contribute to human well-being and welfare by 

contributing to basic material needs, physical 

and psychological health, security, and economic 

activity, and in other ways (see Table 4.4). For 

example, a variety of ecosystem changes may 

be linked to changes in human health, from 

changes that encourage the expansion of the 

range of vector-borne diseases (discussed in 

Chapter 2) to the frequency and impact of 

floods and fires on human populations due to 

changes in protection afforded by ecosystems. 

Table 4.3 Techniques to Value Health Effects Associated with Climate Change

Health Effect Economic Valuation Tools

Premature mortality (associated 

with temperature changes, 

extreme weather events, and air 

pollution effects)

Use of revealed preference techniques to value changes in risk of death (e.g.,

compensating wage studies).

Use of stated preference studies to value changes in risk of death.

Use of foregone earnings as a lower bound estimate to the value of premature 

mortality.

Exacerbation of cardiovascular 

and respiratory morbidity; 

morbidity associated with waterborne or vector-borne disease

Use of stated preference methods to elicit WTP to avoid illness (e.g., asthma attacks) 

or risk of illness (heart attack risk) or injury.

Estimation of medical costs and productivity losses (known as the cost-of-illness 

(COI)) as a lower bound estimate of the value of avoiding illness.

Injuries associated with extreme 

weather events

Use of stated preference methods to elicit WTP.

Use of compensating wage studies that value risk of injury.

Use of COI as a lower bound estimate.

Impacts of climate change on 

physical functioning; subclinical effects

Use of stated preference methods to estimate WTP to avoid functional limitation. 
The U.S. Climate Change Science Program Chapter 4

134

The ability of the biosphere to continue providing 

these vital goods and services is being strained 

by human activities, such as habitat destruction, 

releases of pollutants, over-harvesting of plants, 

fish, and wildlife, and the introduction of 

invasive species into fragile systems. The recent 

Millennium Ecosystem Assessment reported 

that of 24 vital ecosystem services, 15 were 

being degraded by human activity (MA, 2005). 

Climate change is an additional human stressor 

that threatens to intensify and extend these 

adverse impacts to biodiversity, ecosystems, 

and the services they provide. 

Changes in temperature, precipitation, and 

other effects of climate change will have direct 

effects on ecosystems. Climate change will also 

indirectly affect ecosystems, via, for example, 

effects of sea level rise on coastal ecosystems, 

decision-makers’ responses to climate change 

(in terms of coastline protection or land use), 

or increased demands on water supplies in 

some locations for drinking water, electricity 

generation, and agricultural use. Understanding 

how these changes alter economic welfare 

requires identifying and potentially valuing 

changes in ecosystems resulting from climate 

change. Getting to the point of valuation, 

however, requires establishing a number of 

linkages—from projected changes in climate 

to ecosystem change, to changes in services, 

to changes in the value of those services—

as illustrated in Figure 4.2. The scientific 

community has not, thus far, focused explicitly 

on establishing these linkages in the context of 

climate change. Consequently, the published 

literature is somewhat fragmented, consisting 

of discussions of climate effects on ecosystems 

and of valuation of ecosystems and their 

services (in only a few cases do the latter focus 

on climate change). 

Already observed effects (see reviews in 

Parmesan and Yohe, 2003; Root et al., 2003; 

Parmesan and Galbraith, 2004) and modeling 

results indicate that climate change is very likely 

to have major adverse impacts on ecosystems 

(Peters and Lovejoy, 1992; Bachelet et al., 

2001; Lenihan et al., 2006; Galbraith et al.,

2006). It is also likely that these changes will 

Table 4.4 Examples of Ecosystem Services Important to Human Welfare*

Service Category Components of Service Illustration of Service

Provisioning services Food

Fiber

Fresh water 

Genetic resources 

Pharmaceuticals

Harvestable fish, wildlife, and plants

Timber, hemp, cotton

Water for drinking, hydroelectricity generation, and 

irrigation

Regulating services Air quality regulation 

Erosion regulation 

Water purification 

Pest control 

Crop pollination 

Climate and water supply regulation 

Protection from natural hazards

Local and global amelioration of extremes

Removal of contaminants by wetlands

Removal of timber pests by birds

Pollination of orchards by flying insects

Support services Primary production 

Soil formation 

Photosynthesis

Nutrient and water cycling

Conversion of solar energy to plant material 

Conversion of geological materials to soil by addition 

of organic material and bacterial activity

Cultural services Recreation/tourism

Aesthetic values 

Spiritual/religious values 

Cultural heritage

Natural sites for “green” tourism/recreation/nature 

viewing

Existence value of rainforests and charismatic 

species, “holy” or “spiritual” natural sites

*Based on a classification system developed for the Millennium Ecosystem Assessment (MA, 2005).
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

adversely affect the services that humans and 

human systems derive from ecosystems (MA, 

2005). Climate change may affect ecosystems 

in the United States within this century in the 

following ways.

Shifting, breakup, and loss of ecological 

communities. As climate changes, species 

that are components of communities will be 

forced to shift their ranges to follow cooler 

temperatures either poleward or upward in 

elevation. In at least some cases, this is likely 

to result in the breakup of communities as 

organisms respond to temperature change and 

migrate at different rates. In general, study 

projections include: northern extensions of the 

ranges of southern broadleaf forest types, with 

northward contractions of the ranges of northern 

and boreal conifer forests; elimination of alpine 

tundra from much of its current range in the 

United States; and the replacement of forests 

by grasslands, shrub-dominated communities, 

and savannas, particularly in the south (e.g., 

VEMAP, 1995; Melillo et al., 2001; Lenihan et 

al., 2006). Because of different intrinsic rates 

of migration, ecological communities may not 

move intact into new areas (Box 4.1).

Another potential ecological community 

effect of climate change is the facilitation of 

community penetration and degradation by 

invasive weeds that will replace more sensitive 

native species (Malcolm and Pitelka, 2000).

Extinctions of plants and animals and reduced 

biodiversity. While some species may be able 

to adapt to changing climate conditions, others 

will be adversely affected. It is very likely that 

one result of this will be to accelerate current 

extinction rates, resulting in loss in biodiversity. 

The most vulnerable species within the United 

States may be those that are currently confined 

to small, fragmented habitats that may be 

sensitive to climate change. This is the case with 

Changes in the ability of

ecosystems to provide services

Effects of changes in services on 

human welfare and quality of life

Economic valuation of changes 

in quality of life

Indirect effects on ecosystems

• increased wildfires

• effects of sea level rise on 

coastal ecosystems

• adaptation, e.g., coastline 

protection, changes in land use

Direct effects on ecosystems

• extinctions

• range shifts

• community dissociation

• timing changes

• changes in ecosystem processes

Climate change will result in

• temperature increase

• precipitation change

• changes in extreme events

Figure 4.2 Steps from Climate Change to Economic Valuation of Ecosystem Services
The U.S. Climate Change Science Program Chapter 4

136

Edith’s checkerspot, a western butterfly species 

that is already undergoing local subpopulation 

extinctions due to climate change (Parmesan, 

1996). Other potentially vulnerable organisms 

include those that are restricted to alpine tundra 

habitats (Wang et al., 2002), or to coastal 

habitats that may be inundated by sea level rise 

(Galbraith et al., 2002). 

Range shifts. Faced wit h i ncreasi ng 

temperatures, populations of plants and animals 

will attempt to track their preferred climatic 

conditions by shifting their ranges. Range shifts 

will be limited by factors such as geology (in 

the case of plants that are confined to certain 

soil types), or the presence of cities, agricultural 

land, or other human activities that block 

northward migration. Some individual species 

in North America and the United States are 

already undergoing range shifts (Root et al., 

2003; Parmesan and Galbraith, 2004). The 

red fox in the Canadian arctic shifted its range 

northward by up to 600 miles during the 20th 

century, with the greatest expansion occurring 

where temperature increases have been the 

largest (Hersteinsson and Macdonald, 1992). 

More generally, a number of bird species have 

shifted their ranges northward in the United 

States over the past few decades. While some 

of these changes may be attributable to nonclimatic factors, it is very likely that some 

are due to climate change (Root et al., 2003; 

Parmesan and Galbraith, 2004).

Timing changes. The timing of major ecological 

events is often triggered or modulated by seasonal 

temperature change. Changes in timing may 

already be occurring in the breeding seasons of 

birds, hibernation seasons of amphibians, and 

emergences of butterflies in North America and 

Europe (Bebee, 1995; Crick et al., 1997; Brown 

et al., 1999; Dunn and Winkler, 1999; Root et 

al., 2003; Roy and Sparks, 2000). Disconnects 

in timing of interdependent ecological events 

may be accompanied by adverse effects on 

sensitive organisms in the United States. Such 

effects have already been observed in Europe 

where forest-breeding birds have been unable 

to advance their breeding seasons sufficiently 

to keep up with the earlier emergence of the 

arboreal caterpillars with which they feed 

their young. This has resulted in declining 

productivity and population reductions in at 

least one species (Both et al., 2006). 

Changes in ecosystem processes. Ecosystem 

proce sse s, such a s nut r ie nt cycl i ng, 

decomposition, carbon f low, etc., are 

fundamentally influenced by climate. Climate 

change is likely to disrupt at least some of these 

processes. While these effects are difficult to 

quantify, some types of changes can—and have 

been observed. Increasing temperatures over 

BOX 4.1. Effects of Climate Change on Selected U.S. Ecosystems

At their most extreme, ecological community changes could result in the loss of entire habitats valued by 

the general public. For example, sea level rise puts much of the freshwater wetland that comprises Florida 

Everglades National Park at risk (Glick and Clough, 2006). Even relatively modest sea level rise projections 

could result in the conversion of much of this low-lying area to brackish or intertidal marine and mangrove 

habitats. Another such extreme example is alpine tundra habitat in mountain ranges in the contiguous 

states. Since tundra lies at the highest elevations, there is little or no opportunity for the plants and animals 

that comprise this ecosystem to respond to increasing temperatures by moving upward. Thus, one of the 

probable effects of climate change will be the further fragmentation and loss of this unique habitat (VEMAP, 

1995; Root et al., 2003; Lenihan et al., 2006). 

California already reports an example of how climate change might modify major marine ecological 

communities. Over the final four decades of the 20th century the average annual ocean surface 

temperature off the California coast warmed by approximately 1.5°C (Holbrook et al., 1997). Sagarin et 

al. (1999) found that the intertidal invertebrate community at Monterey has changed since first it was 

characterized in the 1930s. Many of the coolwater species have retracted their ranges northward, to be 

replaced by southern warm water species. The ecological community that exists there now is markedly 

different in its make-up from that which existed prior to warming of the coastal California Current.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

the past few decades on the North Slope of 

Alaska have resulted in a summer breakdown 

of the permanently frozen soil of the Alaskan 

Tundra and increased activity by soil bacteria 

that decompose plant material. This has 

accelerated the rate at which CO2 (a breakdown 

product of the decomposition of the vegetation 

and also a greenhouse gas) is released to the 

atmosphere—changing the Tundra from a net 

sink (absorber) to a net emitter of CO2 (Oechel 

et al., 1993; Oechel et al., 2000).

Indirect effects of climate change. Climate 

change may also result in “indirect” ecological 

effects as it triggers events (the frequency and 

intensity of fires, for example) that, in turn, 

adversely affect ecosystems. In U.S. forest 

habitats, increased temperatures are very likely 

to result in increased frequency and intensity 

of wildfires, especially in the arid west, leading 

to the breakup of contiguous forests into 

smaller patches, separated by shrub and grass 

dominated ecological communities that are 

more resistant to the effects of fire (Lenihan et 

al., 2006). Other major indirect effects are likely 

to include the loss of coastal habitat through 

sea level rise (Warren and Niering, 1993; Ross 

et al., 1994; Galbraith et al., 2002), and the 

loss of coldwater fish communities (and the 

recreational fishing that they support) as water 

temperatures increase (Meyer et al., 1999). 

The linkages between these types of changes 

and the provision of ecosystem services are 

difficult to define. While ecologists have 

developed a number of metrics of ecosystem 

condition and functioning (e.g., species diversity, 

presence/absence of indicator species, primary 

productivity, nutrient cycling rates), these do not 

generally bear an obvious relation to metrics of 

services. In some cases, such as species diversity 

and bird population sizes, direct links might be 

drawn to services (in this case, opportunities for 

bird watching). However, in many, if not most 

cases, the linkages between stressor effects, 

change in ecosystem metrics, and service flows, 

are more obscure. For example, it is known that 

freshwater wetlands can remove contaminants 

from surface water (Daily, 1997) and this is 

an important service. However, the specific 

ways in which wetlands do this—in terms of 

the ecological processes and linkages within 

the system—are not well understood, probably 

vary between different types of wetland (e.g., 

beaver swamps vs. cattail stands), and may vary 

spatially and temporally. 

4.3.4.1 Economic Valuation of 

Effects on Ecosystems

Ecosystems are generally considered nonmarket goods: although land itself can be bought 

and sold, there is no market for ecosystem 

services per se, and so land value is only a 

partial measure of the value of the full range 

of ecosystem services provided. From the 

perspective of human welfare and climate 

change, however, we are concerned less with 

the ecosystems or the land on which they are 

located, than with the diverse services they 

provide, as illustrated in Table 4.4. 

Economic valuation of changes in ecosystem 

services will be easier in cases where there 

are relationships between market goods and 

the ecosystem services being valued. For 

example, ecosystem changes may result in 

changes in the availability of goods and services 

that are traded on markets, as in the case of 

provisioning services, such as food, fisheries, 

pharmaceuticals, etc. In other cases, market 

counterparts to the services may exist, as in 

the case of regulating services; for example, 

insights into the value of water purification 

services can come from looking at the (avoided) 

cost of a water purification plant to substitute 

for the ecosystem service. Services, such as 

water purification, may also have relationships 

with market goods and services (e.g., as an 

input into the production process) that make it 

possible to estimate economic values at least in 

part or approximately. 

Many ecosystem services however, are truly 

non-market, in that there are no market 

counterparts by which to estimate their value. 

Recreational uses of ecosystems fall into this 

category, and so economists have developed 

means of inferring values from behavior (e.g.,

travel cost), as discussed in the next section, 

and in other ways. Most of the support services 

and cultural values of ecosystems are also in 

the “true” non-market category. Value can 

arise even if a good or service is not explicitly 
The U.S. Climate Change Science Program Chapter 4

138

consumed, or an ecosystem even experienced.25

Thus, it can be difficult to define, much less 

to measure the value of changes in these 

non-market services. To value these services, 

economists typically use stated preference 

(direct valuation) methods, a method that can be 

used not only for non-market services, but also 

to value services in other categories, such as the 

value that individuals place on clean drinking 

water or swimming facilities.

Below we report on the relevant literature in 

two categories. First, we report on studies that 

have looked at the non-market value of specific 

ecosystems or species. Since only a few of these 

studies attempt to value the impacts of climate 

change on ecosystems, we also highlight some 

non-market studies from the more general 

literature on ecosystem valuation, which can 

provide insights into the magnitude of potential 

values of services that might be vulnerable to 

climate change. Next we look at a different 

approach to valuation of ecosystems—a more 

“top-down” approach—that has been adopted 

both to look at the effects of climate change and 

more broadly at the total value of ecosystems. 

As the discussions indicate, the treatment of 

climate change, per se has been very sparse. 

Moreover, the lack of studies reflects, in part, 

25 Economists have devoted much effort to defining 

the source of non-market values of ecosystems, 

coining such terms as “use” and “non-use” value, 

consumption value, existence value, and invoking, as reasons why people care about ecosystesm, 

the moral philosophies inherent in terms such as 

stewardship, spiritual values, etc. (see for example, 

Freeman (2003)).

a need to develop analytical linkages between 

the physical effects of climate on ecosystems, 

the services valued by humans, and appropriate 

techniques to value changes of the types, and 

with the breadth, indicated by studies of the 

effects of global change on ecosystems. 

4.3.4.2 Valuation of the Effects of Climate 

Change on Selected Ecosystem and Species

Although climate change appears in a number 

of studies, it is often as a context for the 

scenario presented in the study for valuation, 

and so the study cannot be interpreted as 

valuation of climate change or climate effects 

per se. Only a few studies can be said to value 

the economic impacts of climate change on a 

particular ecosystem. 

Two studies, Layton and Brown (2000) and 

Layton and Levine (2003) estimate total values 

for preventing Colorado (Rocky Mountain) 

forest loss due to climate change, based on 

data from the same stated choice or preference 

survey. The survey was conducted with Denverarea residents, who were expected to be familiar 

with forested regions in their nearby mountains. 

Respondents were given detailed information 

about climate change impacts on these forests, 

including changes in tree line elevation over 

both 60-year and 150-year time horizons, and 

asked to make choices between alternatives, 

allowing recovery of implied WTP. Layton 

and Brown (2000) found WTP in the range 

of $10 to $100 per month, per respondent, to 

prevent forest loss, with the range depending, 

in part, on the amount of forest lost. Layton 

and Levine (2003) reanalyzed the same data 

set, using a different approach that focuses on 

understanding respondents’ least preferred, as 

well as most preferred, choices. They found that 

respondents’ value of forest protection depends 

also on the time horizon—preventing effects 

that occur further into the future are valued less 

than nearer term effects. 

Kinnell et al. (2002) designed and implemented 

several versions of stated preference studies that 

explored the impacts of wild bird (duck) loss due 

to either adverse agricultural practices, climate 

change, or both. The respondents consisted 

of Pennsylvania duck hunters, although the 

hypothetical ecosystem impacts occurred in the 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Prairie Pothole region, which is in the northern 

midwestern states and parts of Canada. The 

authors considered a hypothetical loss in duck 

populations, with a scenario that presented 

some respondents with a 30 percent loss, and 

others with a 74 percent loss, some with a 40 

year time horizon, and others with a 100 year 

time horizon. The study cannot be viewed as 

an estimate of WTP to avoid climate change; 

however, it is interesting because it suggests that 

recreational enthusiasts are willing to pay for 

ecosystem impacts that they do not necessarily 

expect to use. In addition, the study provides 

evidence that the context of climate change or 

other cause of ecosystem harm (in this case 

agricultural practices)—irrespective of the level 

of harm—may affect respondents’ valuation of 

the harm. 

Although very few studies have valued climate 

change impacts on ecosystems, economists 

have conducted numerous studies (primarily 

using direct valuation methods) of ecosystem 

values in particular geographic locations, often 

focusing on charismatic species, or specific 

types of ecosystems, such as wetlands, in a 

particular location. In some cases, the estimated 

values are linked to specific services that the 

species or ecosystem provide, but in many the 

services provided are somewhat ambiguous, 

and it is not always clear what aspect of the 

species, habitat, or ecosystem is driving the 

individual respondent’s economic valuation. 

A number of studies indicate that people value 

the protection of species or ecosystems. Some of 

these studies find potentially significant species 

values, ranging from a few dollars to hundreds 

of dollars per year, per person. For example, 

MacMillan et al. (2001) estimate the value of 

restoring woodlands habitat, and separately 

evaluate the reintroduction of the wolf and the 

beaver to Scottish highlands. In the United 

States, species such as salmon and spotted owls, 

as well as their habitat, have been examined in 

connection to their respective controversies.

Studies have also looked at the value of 

ecosystems or changes in ecosystems. In the 

former case, economists use either the value 

of productive output (harvest) as an indicator 

of value, or respondents value protecting the 

ecosystem. For example, numerous coastal 

wetland and beach protection studies have used 

a variety of non-market valuation approaches. 

A survey of a number of these studies reports 

values ranging from $198 to approximately 

$1500 per acre (Woodward and Wui, 2001). 

Some studies have looked explicitly at the 

services provided by ecosystems. For example, 

Loomis et al. (2000) consider restoration 

of several ecosystem services (dilution of 

wastewater, purification, erosion control, as fish 

and wildlife habitat, and recreation) for a 45-mile 

section of the Platte River, which runs east from 

the State of Colorado into western Nebraska. 

Average values are about $21 per month for 

these additional ecosystem services for the 

in-person interviewees. While these studies 

and their values are generally informative, 

transferring values from studies like the ones 

above to other ecosystems, and using the results 

to estimate values associated with climate 

change impacts, can be problematic. 

4.3.4.3 Top-down Approaches to Valuing 

the Effects of Climate Change and 

Ecosystem Services

From the perspective of deriving values for 

ecosystem changes (or changes in ecosystem 

services) associated with climatic changes, 

one difficulty with the above studies is that the 

focus is on discrete changes to particular species 

or geographic areas. It is therefore difficult to 

know how these studies relate to, or shed light 

on, the types of widespread and far-reaching 

changes to ecosystems (and the services they 
The U.S. Climate Change Science Program Chapter 4

140

provide) that will result from climate change. 

Consequently, some studies have attempted 

to value ecosystems in a more aggregate or 

holistic manner. While these studies do not 

focus specifically on the United States, they 

are indicative of an alternative approach that 

recognizes the interdependence of ecosystems 

and their components, and therefore deserve 

some discussion. 

Several models include values for non-market 

damages, worldwide, resulting from projected 

climate change. These impact studies have 

been conducted at a highly aggregated 

level; most of the models are calibrated 

using studies of the United States that are 

then scaled for application to other regions 

(Warren et al., 2006). 

A study of total ecosystem values, but not 

undertaken in the context of climate change, 

is the highly publicized study by Costanza et 

al. (1997), which offers a controversial look 

at valuing the “entire biosphere.” Because 

their reported estimated average value of 

$33 trillion per year exceeds the global gross 

national product, economists have a difficult 

time reconciling this estimate with the concept 

of economic value. Ehrlich and Ehrlich (1996) 

and Pimental et al. (1997) are studies by natural 

scientists that have attempted to value ecosystems 

or in the case of the latter, biodiversity. These 

are important attempts to indicate the value of 

ecosystems, but the accuracy and reliability 

of the values are questionable. To paraphrase 

a study by several prominent environmental 

economists that is slightly critical of all of 

these studies, economists do not have any 

fundamental difference of opinion with these 

natural scientists about the importance of 

ecosystems and biodiversity, rather it is with the 

correct use of economic value concepts in these 

applications (see Bockstael et al., 2000).

4.3.5 Recreational Activities 

and Opportunities

Ecosystems provide humans with a range 

of services, including outdoor recreational 

opportunities. In turn, outdoor recreation 

contributes to individual well-being by providing 

physical and psychological health benefits. In 

addition, tourism is one of the largest economic 

sectors in the world, and it is also one of the 

fastest growing (Hamilton and Tol, 2004). The 

jobs created by recreational tourism provide 

economic benefits not only to individuals but 

also to communities.26 A number of studies have 

looked at the qualitative effects of climate change 

on recreational opportunities (i.e., resources 

available) and activities in the United States, 

but only a few have taken this literature the 

additional step of estimating the implications of 

climate change for visitation days or economic 

welfare. This section describes the results of 

this research into the impacts on several forms 

of recreation and reports the economic benefits 

and losses associated with these changes at the 

national level.

Slightly more than 90 percent of the U.S. 

population participates in some form of outdoor 

recreation, representing nearly 270 million 

participants (Cordell et al., 1999), and several 

billion person-days spent each year in a 

wide variety of outdoor recreation activities. 

According to Cordell et al. (1999), the number 

of people participating in outdoor recreation is 

highest for walking (67 percent), visiting a beach 

or lakeshore or river (62 percent), sightseeing 

(56 percent), swimming (54 percent) and 

picnicking (49 percent). Most days are spent in 

activities such as walking, biking, sightseeing, 

bird-watching, and wildlife viewing (Cordell et 

al., 1999), but the range of outdoor recreation 

activities in the United States is as diverse as 

its people and environment. While camping, 

hunting, backpacking and horseback riding 

attract a fraction of the people who go biking or 

bird-watching, these other specialized activities 

provide a very high value to their devotees. 

Many of these devotees of specialized outdoor 

recreation activities are people who “work to 

live,” i.e., specialized weekend recreation is one 

of their rewards for the 40+ hour workweek. 

Climate change resulting from increasing 

average temperatures as well as changes in 

precipitation, weather variability (including more 

extreme weather events), and sea level rise, has 

the potential to affect recreation and tourism 

along two pathways. Figure 4.3 illustrates 

these direct and indirect effects of climate 

26 Effects on jobs, income, and similar metrics are considered market impacts, and are not discussed here. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

change on recreation. Since much recreation 

and tourism occurs out of doors, increased 

temperature and precipitation have a direct effect 

on the enjoyment of these activities, and on the 

desired number of visitor days and associated 

level of visitor spending (as well as tourism 

employment). Weather conditions are considered 

one of the four greatest factors influencing 

tourism visitation (Pileus Project, 2007). In 

addition, much outdoor recreation and tourism 

depends on the availability and quality of natural 

resources such as beaches, forests, wetlands, 

snow, and wildlife (Wall, 1998). Consequently, 

climate change can also indirectly affect the 

outdoor recreational experience by affecting the 

quality and availability of natural resources used 

for recreation.

Effects of climate change can be both positive 

and negative. The length of season for and 

desirability of several of the most popular 

activities—walking, visiting a beach, lakeshore, 

or river, sightseeing, swimming, and picnicking 

(Cordell et al., 1999)—will likely be enhanced 

by small near- term increases in temperature. 

However, long-term higher increases in 

temperature may eventually have adverse 

effects on activities like walking, and result 

in sufficient sea level rise to reduce publicly 

accessible beach areas, just at the time when 

demand for beach recreation to escape the heat 

is increasing. In contrast, some activities are 

likely to be unambiguously harmed by even 

small increase in global warming, such as snow 

and ice-dependent activities.

In some ways, one can interpret the direct 

effects of climate change as inf luencing 

the demand for recreation and the indirect 

effects as influencing the supply of recreation 

opp or t u n it ie s. For exa mple, wa r me r 

temperatures make whitewater boating more 

desirable. However, the warmer temperatures 

may reduce river flows since there is less 

snow pack, higher evapot ranspiration, 

and greater water diversions for irrigated 

agriculture. Some studies cited below look 

only at the direct effects, while others 

represent the combined effect of the direct 

and indirect pathways. 

Direct effects. To date, most studies of the 

direct effects of climate change on recreation 

and tourism have been qualitative, although a 

few have been quantitative. Qualitatively, we 

would expect both positive and negative effects 

of climate change on different recreational 

Climate change:

• + temperature

• +/- precipitation

• + climate variability

Effects of climate change:

Changes in:

...vegetation (forests)

...stream flows

...reservoir levels

...recreational fisheries

...wildlife populations

...miles of beaches

...snow, ice

...length of season

Direct

Indirect

Effects on outdoor 

recreaton use and benefits:

• enjoyment and comfort 

while outdoors

• visitor days of outdoor 

recreation

• benefits of outdoor 

recreation

Figure 4.3 Direct and Indirect Effects of Climate Change on Recreation 
The U.S. Climate Change Science Program Chapter 4

142

activities. Many of the qualitative studies rely 

simply on intuition to suggest that increases in 

air and water temperatures will have a positive 

effect on outdoor recreation visitation in two 

ways: (a) more enjoyment from the activity, and 

(b) a longer season in which to enjoy the activity 

(DeFreitas, 2005; Scott and Jones, 2005; Scott, 

Jones and Konopek (2007). Hall and Highman 

(2005) note that climate change may provide 

more days of “ideal” temperatures for waterbased recreation activities and some land 

based recreation activities such as camping, 

picnicking and golf. 

The recreational activities most obviously 

harmed by warmer climate are sports that require 

snow or cold temperatures, such as downhill 

and cross country skiing, snowmobiling, ice 

fishing, and snowshoeing. Reductions in visitor 

use (see, for example, the studies reported in 

Table 4.5) occur primarily from shorter season, 

particularly early in the year at such traditional 

times as Thanksgiving and spring break. But 

with warmer temperatures, there is also less 

precipitation as snow and more as rain on 

snow, which contributes to a much shallower 

snowpack and harder snow. Further, recreating 

in freezing rain or slushy temperatures is 

not a pleasant experience, reducing benefits 

from skiing, snowshoeing, and snowmobiling, 

further reducing use. 

Some recreation areas that are already hot 

during the summer recreation season will see 

decreases in use. For example, the Death Valley 

National Park, Joshua Tree National Park, and 

Mesa Verde National Park are all projected to be 

“intolerably hot,” reducing visitation (Saunders 

and Easley, 2006). 

Most quantitative studies of the effects of climate 

change on recreation evaluate specific projected 

changes in temperature and/or precipitation, 

such as a 2.5°C increase in temperature over the 

next fifty years. Two quantitative studies look 

at effects of temperature change in Canadian 

recreation.27 Scott and Jones (2005) project 

that the golf season in Banff, Canada could 

be extended by at least one week and up to 

27 Scott and Jones (2005) used +1°C to +5°C in their 

scenarios and Scott et al. (2006) used +1.5°C to +3°C 

in their low impact scenario and +2°C to +8°C in 

their high impact scenario. 

Table 4.5 Comparison of Changes in U.S. Visitor Days 

Activity Loomis and Crespi (1999) Mendelsohn and Markowski (1999)

Boating 9.2 percent 36.1 percent

Camping -2.0 percent -12.7 percent

Fishing 3.5 percent 39.0 percent

Golf 13.6 percent 4.0 percent

Hunting -1.2 percent no change

Snow Skiing -52.0 percent -39.0 percent

Wildlife Viewing -0.1 percent -38.4 percent

Beach Recreation 14.1 percent not estimated

Stream Recreation 3.4 percent included in boating

Gain in Visitor 

Benefits (in Billions) $2.74 $2.80 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

eight weeks. The combined effect of warmer 

temperatures lengthening the golfing season, 

and the increasing desirability of golfing 

during the existing season, together result in an 

increase in the rounds of golf played by between 

50 percent and 86 percent. Similar increases 

might be expected for golf in northern states of 

the United States such as Minnesota, Wisconsin, 

New York, etc. with longer golf seasons. Scott 

et al. (2006) and Scott and Jones (2005) suggest 

that some of the previously projected large (30 

percent to 50 percent) reductions in length of ski 

seasons at northern ski areas (e.g., in Canada, 

Michigan, and Vermont) can be reduced (to 

5 percent to 25 percent) through the use of 

advanced snowmaking. While use of advanced 

snowmaking to minimize reductions in ski 

season seems plausible for the studied northern 

ski areas, it is doubtful that snowmaking would 

benefit ski areas in California, New Mexico, 

Oregon, and West Virginia where in some 

years the Thanksgiving and “Spring Break” 

periods are already too warm for successful 

snowmaking or retention of snow made.

Some studies have used natural variations in 

temperature to evaluate the effects of climate 

on recreation (including measures on monthly, 

seasonal, and inter-annual variation). Two of 

these have found that while visitation increases 

with initial increases in temperature, visitation 

actually decreases as temperature increases even 

further (Hamilton and Tol, 2004; Loomis and 

Richardson, 2006). Following the discussion of 

indirect effects two of the quantitative studies, 

which look not only at visitor days but also at 

monetary measures of economic welfare, are 

discussed in more detail below. 

Indirect effects. While increased temperature 

may increase the demand for some outdoor 

recreation activities, in some cases climate 

change may reduce the supply of natural 

resources on which those recreational activities 

depend. As noted above, reduced snowpack 

for winter activities has been projected in the 

Great Lakes (Scott et al., 2005), in northern 

Arizona (Bark-Hodgins and Colby, 2006) and 

at a representative set of ski areas in the United 

States (Loomis and Crespi, 1999).28

For example, lower in-stream flows and lower 

reservoir levels have consistently been shown 

to reduce recreation use and benefits (Shaw, 

2005). Thus, changes associated with climate 

can reduce opportunities for summer boating 

and other water sports. When less precipitation 

falls as snow in the winter, and more falls as 

rain in the spring, early spring season runoff will increase. Summer river flows will be 

correspondingly lower, at times when demand 

for whitewater boating is higher. Human 

responses to the physical changes associated 

with climate change may exacerbate natural 

effects reducing recreational opportunities. 

For example, many current reservoirs are not 

designed to handle huge spring inflows, and 

thus this water may be “spilled,” which lowers 

reservoir levels during the summer season. 

These lower reservoir levels are then drawn 

down more rapidly as higher temperatures 

increase evapotranspiration and increase 

irrigation releases. In turn, the resulting lower 

reservoir may leave boat docks, marinas, and 

boat ramps inaccessible. 

28 Higher temperatures (while they increase snowmelt 

reducing the snow skiing season) may have two subtle 

effects: (a) stimulating demand for snow skiing due 

to warmer temperatures, for those skiers who prefer 

“spring skiing” due to the warmer temperatures even 

if the snow conditions are less than ideal; and (b) 

reduced snowmelt opens up the high mountains for 

hiking, backpacking and mountain biking activities 

somewhat earlier than is the case now, which may lead 

to increases in those visitor use days. 
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144

Ecosystems that provide recreational benefits 

may also be at risk from climate change. 

Wetlands are another recreational environment 

that is at risk from climate change. Wetland 

based recreation include wildlife viewing and 

waterfowl hunting. With sea level rise, many 

existing coastal wetlands will be lost, and 

given existing development inland, these lost 

wetlands may not be naturally replaced (Wall, 

1998). The higher temperatures and reduced 

water availability is also expected to adversely 

affect freshwater wetlands in the interior of 

the country. As such, waterfowl hunting and 

wildlife viewing may be adversely affected. 

Higher water temperatures and lower stream 

flows are projected to reduce coldwater trout 

fisheries (U.S. EPA, 1995; Ahn et al., 2000) as 

well as native and hatchery stocks of Chinook 

salmon in the Pacific Northwest (Anderson et 

al., 1993). Given trout and Chinook salmon 

sensitivity to warm water temperatures, these 

affects are not surprising. However, Anderson 

et al.’s estimated magnitude of 50 percent to 

100 percent reduction in Chinook spawning 

returns is quite large. Reductions of such 

magnitude will have a substantial adverse effect 

on recreational salmon catch rates, and possibly 

whether recreational fishing would even be 

allowed to continue in some areas of the Pacific 

Northwest. However, from a national viewpoint, 

fishing participation for trout, cool water 

species and warm water species dominates 

geographically specialized fishing like Chinook 

salmon. Warmer water temperatures are 

projected to eliminate stream trout fishing in 

8-10 states and result in a 50 percent reduction 

in coldwater stream habitat in another 11-16 

states depending on the GCM model used (U.S. 

EPA, 1995). This could adversely affect up to 

25 percent of U.S. fishing days (Vaughan and 

Russell, 1982). This 25 percent loss may be an 

upper limit as some coldwater stream anglers 

may substitute to less affected coldwater lakes/

reservoirs or switch to cool/warm-water species 

such as bass (U.S. EPA, 1995). Studies that 

better account for substitution effects, such 

as Ahn et al. (2000), indicate a 2-20 percent 

drop in benefits of trout fishing depending on 

the projected degrees of temperature increase 

which ranged from 1°C to 5°C. 

Sea level rise reducing beach area and beach 

erosion are concerns with climate change that 

may make it difficult to accommodate the 

increased demand for beach recreation (Yohe 

et al., 1999). In the near term, recreational 

forests may also be adversely affected by 

climate change. Although forests may slowly 

migrate northward and into higher elevations, 

in the short run there may be dieback of 

forests at the current forest edges (as these 

areas become too hot), resulting in a loss 

of forests for recreation. In the long term, 

however, several analyses suggest forest 

species composition and migration due as well 

as net increases in forest area due to carbon 

dioxide fertilization (Joyce et al., 2001; Iverson 

and Matthews, 2007). Thus, eventually there 

may be resurgence in forest recreation. 

Saunders and Easley (2006) find that natural 

resources of many western National Parks, 

National Recreation Areas, and National 

Monuments resources will be adversely 

affected by climate change. The most common 

adverse effects are reductions in some wildlife 

species, loss of coldwater fishing opportunities 

and increasing park closures due to wildfire 

associated with stressed and dying forest 

stands. Box 4.2 discusses in more detail 

potential effects of climate change on one 

park: Rocky Mountain National Park, which 

has been the subject of both ecological and 

economic analysis.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

4.3.5.1 Economic Studies of 

Effects of Climate on Recreation

Changes in economic welfare due to the effects 

of climate change on non-market resources, such 

as recreation, can be evaluated in several ways. 

First, since decisions regarding recreational 

activities depend on both direct and indirect 

effects of climate, changes in human well-being 

(as a result of these changes) will be reflected 

in changes in visitor use. Social scientists 

believe changes in visitor use are motivated by 

people “voting with their feet” to maintain or 

improve their well-being. In the face of higher 

temperatures, people may seek relief, for 

example, by visiting the beach or water skiing 

at reservoirs more frequently to cool down. 

Similarly, reduced opportunities for recreation 

due to indirect effects of climate change will 

also be reflected in reduced visitation days. 

Thus, one metric of effects on human wellbeing is the change in visitation days. 

Second, recreational trips—for example, 

to reservoirs and beaches—have economic 

implications to the visitor and the economy. 

Visitors allocate more of their scarce time and 

household budgets to the recreational activities 

that are now more preferred in a warmer 

climate. This reflects their WTP for these 

recreational activities, which is a monetary 

measure of the benefits they receive from the 

activity. Numerous economic studies provide 

estimates of the value of changes in diverse 

recreational activities, using various economic 

techniques (such as travel cost29 analysis and 

stated preference methods) (see Section 3 of 

this chapter and the chapter Appendix for more 

information). While these studies typically 

do not focus directly on climate change, they 

can be used to extract values for the types of 

changes that are projected to be associated with 

climate change.

Third, some people who do not currently visit 

unique natural environments may value climate 

stabilization policies that preserve these natural 

29 The travel cost method traces out a demand curve for 

recreation using travel cost as proxies for the price 

of recreation, along with the corresponding number 

of trips individual visitors take at these travel costs. 

From the demand curve, the net willingness to pay 

or consumer surplus is calculated. 

environments for future visitation. These 

people have what economists call a value for 

preserving their option—their ability— to visit 

the environments in the future (Bishop, 1982). 

This option value is much like purchasing trip 

insurance to guarantee that if one wanted to go 

in the future, that conditions would be as they 

are today. 

As discussed below, economists have available 

a number of well-studied techniques to evaluate 

the impacts of climate change on at least 

some of the recreational service provided 

by ecosystems. However, only a few studies 

have looked explicitly at the effects of climate 

change on recreation in the United States. 

More research is needed to understand the 

linkages between weather and recreation, and 

to extrapolate results to the range of recreational 

activities throughout the United States.

Change in visitation days. Two studies 

(Loomis and Crespi, 1999; Mendelsohn and 

Markowski, 1999) have comprehensively 

examined the effects of climate on recreational 

opportunities for the entire United States. These 

studies both examined the effects of 2.5°C and 

5°C increases in temperature, along with a 

7 percent increase in precipitation. The studies 

used similar methodologies to estimate visitor 

days for a range of recreational opportunities. 

Each study looked at slightly different effects, 

but between them examined a mix of direct 

and indirect climate effects, including direct 

effects of higher temperatures on golf and beach 

recreation visitor days, and indirect effects of 
The U.S. Climate Change Science Program Chapter 4

146

snow cover on skiing. Both studies estimate 

changes in visitation days due to climate 

change, and then use the results of a number of 

economic valuation studies to place monetary 

values on the visitation days. The studies find 

that, as expected, near-term climate change 

will increase participation in activities such as 

water-based recreation, and reduce participation 

in snow sports. 

Table 4.5 presents the results of the two 

studies. The results suggest that relatively high 

participation recreation activities such as beach 

and stream recreation gain, and low participation 

activities like snow skiing lose. Although the 

percentage drop in visitor days of snow sports 

is much larger than the percentage increase in 

visitor days in water-based recreation, the larger 

number of water-based sports participants more 

than offsets the loss in the low participation 

snow sports. Thus, on net, there is an overall net 

gain in visitation associated with the assumed 

increases of 2.5°C in temperature and 7 percent 

in precipitation.30

The methods used to forecast visitation were 

slightly different between the two studies. To 

estimate visitor days for all recreation activities, 

30 Geographic regions within the U.S. will experience 

different gains and losses. Currently hot areas with 

less access to water resources (e.g., New Mexico) 

may suffer net overall reductions in recreation use 

to due higher heat that makes walking, sightseeing, 

and picnicking less desirable. States with substantial 

water resources (lakes, seashores) may gain visitor 

days and tourism. Currently cold areas such as the 

Dakotas and New York may see increases in some 

recreation due to longer summer seasons. 

Mendelsohn and Markowski regressed state 

level data on visitation by recreation activity as 

a function of land area, water area, population, 

monthly temperature and monthly precipitation. 

The Loomis and Crespi study used a similar 

approach to Mendelsohhn and Markowski for 

some activities, such as golf. Other forecasting 

techniques were used for other activities. 

For example, for beach recreation, they used 

detailed data on two individual beaches in the 

northeastern, southern, and western United 

States to estimate three regional regression 

equations to project beach use, and the response 

of reservoir recreation to climate change was 

analyzed using visitation at U.S. Army Corps 

of Engineers reservoirs.

For some of the recreational activities, the 

Loomis and Crespi study included indirect, 

as well as direct, effects. For example, in 

addition to temperature and precipitation the 

reservoir models incorporated climate-induced 

reductions in reservoir surface area. Similarly, 

the estimate of visitor days for snow skiing 

used projected changes in the number of days 

of minimum snow cover to adjust skier days 

proportionally. In some cases, only indirect 

(supply) effects were included, as in the case 

of stream recreation, water fowl hunting, bird 

viewing, and forest recreation. Since these 

estimates do not include changes in visitation 

associated with direct effects of climate we have 

less confidence in the accuracy of these results 

than we do for reservoir recreation, which takes 

into account both demand and supply effects on 

recreation use.

Valuation of gains and losses in visitor days. 

Since different activities may have different 

levels of enjoyment provided to the visitor (and, 

therefore, different economic values), adding 

up changes in visitation days to produce a “net 

change” is not an accurate representation of the 

overall change in well-being. The two studies 

discussed above used net WTP as a measure 

of value of each day of recreation (Section 3 of 

this chapter provides a discussion of the concept 

of WTP as a common economic measure of 

changes in welfare). 

To date there have been few original or primary 

valuation studies of climate change per se on 

recreation. The case study on Rocky Mountain 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

National Park presented below provides one 

of the few examples. Other studies include 

Scott and Jones (2005), which focused on 

Banff National Park, Scott et al. (2006), which 

looked at snow skiing, Scott et al. (2007), 

which focused on Waterton National Parks, 

and Pendleton and Mendelsohn (1998), which 

estimated values for fishing in the northeastern 

United States.31 There have, however, been 

hundreds of recreation valuation studies. The 

values from these studies (generally travel 

cost or stated preference) can be applied to 

other applications using a “benefit transfer” 

approach, and applying average values of 

recreation from previous studies to value their 

respective visitor days. 

Loomis and Crespi (1999) and Mendelsohn 

and Markowski (1999) estimate the overall 

net gain in visitor benefits, using the change 

in visitor days reported in Table 4.5 and 

estimated values of a visitation day reported 

in the literature. Loomis and Crespi (1999) 

adopt a disaggregated activity approach, and 

Mendelsohn and Markowski (1999) apply a state 

level approach.32 Both of these studies find that 

temperature increases of 5°C and up result in 

increased benefits. However, as noted below, the 

case study of Rocky Mountain National Park 

suggests that extreme heat is likely (based on 

model results) to cause these visitor benefits to 

decrease at some point. 

Visitors are somewhat adaptable to climate 

change in the recreation activities they choose 

and when they choose them. Thus, recreation 

represents one situation with opportunities to 

reduce the adverse impacts of climate change, or 

31 The three papers by Scott are discussed elsewhere 

in this paper. Pendleton and Mendelsohn use a 

random utility model of recreational fishing in the 

northeastern United States. They find that, while 

catch rates of rainbow trout would decrease, catch 

rates of other trout and pan fish would increase. On 

net, recreational fishing benefits (under a climate 

scenario associated with a doubling of atmospheric 

CO2 concentrations) are reduced in the State of New 

York, but there are offsetting gains in more northern 

states like Maine.

32 As noted above, Mendelsohn and Markowski (1999) 

used state level regression modeling to estimate effects on all activities. In contrast, Loomis and Crespi 

(1999), used different regression models and different 

geographic scales for different recreation activities 

to take advantage of the more micro-level datasets 

available for beach and reservoir recreation.

increase its benefits, via adaptation. As noted by 

Hamilton and Tol (2004), warmer temperatures 

may shift visitors northward, and up into the 

mountains. Thus, currently cool areas (e.g., 

Maine, Minnesota, Washington) may gain, 

and warm areas (e.g., Florida, Arizona) may 

lose, tourism. 

Some adaptive responses can be expensive, 

and may be of limited effectiveness; such as 

snowmaking at night, which is often mentioned 

as an adaptation for downhill skiing (Irland et 

al., 2001). Other adaptive behavior may include 

moving some outdoor recreation activities 

indoors. For example, bouldering is now 

taking place in climbing gyms on artificial 

climbing walls. Running on a treadmill in an 

air-conditioned gym may be a substitute for 

running out of doors for some people, but casual 

observation suggests that many people prefer 

to run out doors when weather permits. Unless 

preferences adjust to increased temperatures, 

there may be a loss in human well-being from 

substituting the treadmill in the air conditioned 

gym for the out of doors. Box 4.2 summarizes 

a case study of the impacts of climate change 

on Rocky Mountain National Park.

4.3.6 Amenity Value of Climate

It is well established that preferences for climate 

affect where people choose to live and work. 

The desire to live in a mild, sunny climate may 

reflect health considerations. For example, 

people with chronic obstructive lung disease or 

angina may wish to avoid cold winters. Warmer 
The U.S. Climate Change Science Program Chapter 4

148

climates may be more pleasant for persons with 

arthritis. Climate preferences may also reflect 

the desire to reduce heating and/or cooling costs. 

Certain climates may be complementary to 

leisure activities. For example, skiers may wish 

to live in colder climates, sunbathers in warmer 

ones. Alternatively, a particular climate may 

simply make life more enjoyable in the course of 

everyday life. Based on the evidence one would 

also expect that, in addition to preferring certain 

temperatures and more sunshine, people would 

prefer to reduce the risk of experiencing abrupt 

climate events such as hurricanes and floods. 

While climate itself is not bought and sold in 

markets, the goods that are integral to location 

decisions—such as housing and jobs—are 

market goods. Consequently, economists look 

at behavior with regard to location choice (the 

prices that are paid for houses and the wages 

that are accepted for jobs) in order to determine 

how large a role climate plays in these decisions 

and, therefore, how valuable different climates 

are to the general public. The remainder of 

this section discusses methods that have been 

used to estimate the amenity values people 

attach to various climate attributes, as well 

as the value they attach to avoiding extreme 

weather events. Unfortunately, few studies 

have rigorously estimated climate amenity 

values (e.g., the value of a 2°C change in mean 

January temperature) for the United States and 

then used these values to estimate the dollar 

value of various climate scenarios. 

4.3.6.1 Valuing Climate Amenities

People’s preferences for climate attributes 

should be reflected in their location decisions. 

BOX 4.2. Study of the Effects of Climate Change on Rocky Mountain 

National Park

One of the national parks most closely studied to determine the net effect of direct and indirect effect 

of climate change on visitation, visitor benefits, and tourism employment in Rocky Mountain National 

Park (RMNP) in Colorado. This alpine national park is located at elevations ranging from 7,000 to 14,000 

feet above sea level. It is known for elk viewing, hiking, tundra flowers, snowcapped peaks, and one of 

Colorado’s most visible and recognizable 14,000 foot peaks, Longs Peak. 

Loomis and Richardson (2006) compared two approaches to estimating the effect of climate change 

on visitation and employment in RMNP. The first approach examined variations in monthly visitation in 

response to historic variations in temperature. The results of this first approach showed a statistically 

significant positive effect of temperature on visitation (see Loomis and Richardson (2006) for more details). 

However, increased visitation slowed as temperatures got hotter and hotter, and visitation even declined 

during one summer of very high temperatures (60 days over 80°F) by 7.5 percent. 

The second approach used a survey that portrayed the direct effects (e.g., temperature) and indirect effects 

(e.g., changes in elk and ptarmigan (an alpine bird), or percent of the park in tundra). Visitors were then 

asked to indicate if they would change their visits to RMNP or length of stay in the park. The surveys used 

three climate change scenarios, one produced by the Canadian Climate Center (CCC) indicating a 4°F 

increase in temperature by 2020, a Hadley climate scenario that forecasted a 2°F temperature increase 

by 2020, and an extreme heat scenario designed to capture very hot future conditions (50 days with 

temperatures above 80°F, as compared to 3 days currently). All climate change scenarios were used with 

wildlife models to estimate the increase in elk populations and decrease in ptarmigan populations. The 

extreme heat survey found similar results to that of the monthly visitation model. 

Table 4.6 shows the results of the CCC, Hadley, and Extreme Heat temperature scenarios on visitation, 

visitor benefits, and tourism employment as compared to current conditions. As indicated in the table, 

applying visitor survey estimates of visitation change yields a 13.6 percent increase with CCC and 9.9 

percent increase with Hadley. Loomis and Richardson also report that applying the historic visitation 

patterns to the same scenarios yields an 11.6 percent increase in visitation with CCC and 6.8 percent with 

Hadley. Not only is there fairly good agreement between the two methods, but the warmer CCC climate 

change scenario produces larger increases in visitation. In the extreme heat scenario, however, visitations 

declines from current conditions.
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Other things equal, homeowners should be 

willing to pay more for housing (and so bid up 

housing prices) in more desirable climates, and 

so property values should be higher in those 

climates. Similarly, workers should be willing 

to accept lower wages to live in more pleasant 

climates. If climate also affects firms’ costs, 

however, actual wages may rise or fall due 

to the interaction between firms and workers 

(Roback, 1982).

Early attempts to estimate how much consumers 

will pay for more desirable climates start from 

the view that a good—such as housing or a 

job—is a bundle of attributes that are valued 

by the homeowner or worker. The price the 

consumer pays for the good (such as a house) 

is actually a composite of the prices that are 

implicitly paid for all the attributes of the 

good. Using a statistical technique (known 

as a hedonic value function), economists can 

estimate the price of a particular attribute, 

such as climate. The hedonic property value 

function, thus, describes how housing prices 

vary across cities as a function of housing 

characteristics and locational amenities, such 

as climate, crime, air quality, or proximity to 

the ocean. Similarly, the hedonic wage function 

relates observed wages to job characteristics 

(such as occupation and industry), worker 

characteristics (such as education and years of 

experience), and locational amenities. 

The value of locational amenities—i.e.,

how much individuals are willing to pay 

for amenities—can be inferred from these 

estimated hedonic wage and property value 

functions. Extracting this value, however, 

assumes that workers and homeowners are 

mobile, i.e., that they can choose where to live 

fairly freely within the United States. Similarly, 

it assumes that, in general, individuals have 

moved to where they would like to live (at 

the moment), so that housing and job markets 

are in what is said to be “equilibrium.” It also 

assumes that workers and homeowners have 

good information about the location to which 

they are moving, and that sufficient options (in 

terms of jobs and houses and amenities) are 

available to them. The estimates of the value 

of a particular amenity—such as climate—

will be more accurate the more nearly these 

assumptions are met. 

A number of hedonic wage and property value 

studies have included climate, among other 

variables, in their analyses. See, for example, 

studies by Hoch and Drake (1974); Cropper 

and Arriaga-Salinas (1980); Cropper (1981); 

Roback (1982); Smith (1983); Blomquist et al.

(1988); and Gyourko and Tracy (1991). The 

first four studies estimate only hedonic wage 

functions, while the last three estimate both 

wage and property value equations. As Moore 

(1998) and Gyourko and Tracy (1991) note, this 

literature suggests that climate amenities are 

reflected to a greater extent in wages than in 

property values.33 Roback (1982), Smith (1983), 

and Blomquist et al. (1988) all find sunshine 

to be capitalized in wages as an amenity, 

while heating degree days are capitalized as a 

33 The effect of weather variables on property values is 

mixed, with Blomquist et al. (1988) finding property 

values to be negatively correlated with precipitation, 

humidity and heating and cooling degree days, but 

Roback (1982) finding property values positively 

correlated with heating degree days. Gyourko and 

Tracy (1991) find heating and cooling degree days 

negatively correlated with housing expenditures, but 

humidity positively correlated.

Table 4.6 Change in Visits, Jobs, and Visitor Benefits with Three Climate Change Scenarios

Climate Scenario Annual Visits Change Tourism Jobs Visitor Benefits 

(Millions)

Current 3,186,323 6,370 $1,004

CCC 3,618,856 13.6 percent 7,351 $1,216

Hadley 3,502,426 9.9 percent 7,095 $1,157

Extreme Heat 2,907,520 -8.7 percent 5,770 $959
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150

disamenity (Roback, 1982, 1988; Gyourko and 

Tracy, 1991). 

More recent studies using the hedonic approach 

include Moore (1998) and Mendelsohn (2001), 

who use their results to estimate the value of 

mean temperature changes in the United States 

associated with future climate scenarios. Moore 

uses aggregate wage data for Metropolitan 

Statistical Areas (MSAs) to estimate the 

responsiveness of wages with respect to climate 

variables for various occupations. Climate is 

captured by annual temperature, precipitation, 

and by the difference between average July 

and average January temperature. Moore 

estimates that a 4.5°C increase in mean annual 

temperature would be worth between $30 

and $100 billion (in 1987 dollars) assuming 

that precipitation and seasonal variation in 

temperature remain unchanged. 

Mendelsohn (2001) uses county-level data on 

wages and rents to estimate hedonic wage and 

property value models. Separate equations 

are estimated for wages in retail, wholesale, 

service, and manufacturing jobs. Climate 

variables, which include average January, 

April, June, and October temperature and 

precipitation, enter each equation in quadratic 

form. Warmer temperatures are generally 

associated with lower wages and lower rents, 

although the former effect is larger in magnitude. 

Mendelsohn uses the results of these models to 

estimate the impact of a uniform increase in 

temperature of 1°C, 2°C, and 3.5°C, paired, 

alternately with an 8 percent and a 15 percent 

increase in precipitation. The results suggest 

that warming produces positive benefits in 

every scenario except the 3.5°C temperature 

change. Averaging across estimates produced 

by the 3 models for each of the 6 scenarios 

suggests annual net benefits (in 1987 dollars) 

of $25 billion.

Unfortunately, hedonic wage and property 

value studies have limitations that have caused 

them to be replaced by alternate approaches 

to analyzing data on location choices. One 

drawback of the hedonic approach is that, as 

mentioned above, it assumes that national 

labor and housing markets exist and are in 

equilibrium. As Graves and Mueser (1993) and 

Greenwood et al. (1991) point out, if national 

markets are not in equilibrium, inferring 

the value of climate amenities from hedonic 

wage and property value studies can lead to 

badly biased results. A second problem is 

that variables that are correlated with climate 

(e.g., the availability of recreational facilities) 

may be difficult to measure. Hence, climate 

variables may pick up their effects. In hedonic 

property value studies, for example, the use of 

heating and cooling degree days to measure 

climate amenities is problematic because 

their coefficients may capture differences in 

construction and energy costs as well as climate 

amenities per se. A related problem in hedonic 

wage equations is that more able workers may 

locate in areas with more desirable climates. If 

ability is not adequately captured in the hedonic 

wage equation, the coefficients of climate 

amenities will reflect worker ability as well as 

the value of climate.

Cragg and Kahn (1997) were the first to relax 

the national land and labor market equilibrium 

assumption by estimating a discrete location 

choice model. Using Census data, they model 

the location decisions of people in the United 

States who moved between 1975 and 1980. 

Movers compare the utility they would receive 

from living in different states—which depends 

on the wage they would earn and on the cost of 

housing, as well as on climate amenities—and 

are assumed to choose the state that yields the 

highest utility. This allows Cragg and Kahn to 

estimate the parameters of individuals’ utility 

functions and thus infer the rate at which they 

will trade income for climate amenities. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

The drawback of this study is that it estimates 

the preferences of movers, who may differ from 

the general population. An alternate approach 

(Bayer et al., 2006; Bayer and Timmins, 2005) 

is to acknowledge that moving is costly and to 

explain the location decisions of all households, 

assuming that all households are in equilibrium, 

given moving costs. Unfortunately, the discrete 

choice literature has yet to provide reliable 

estimates of the value of climate amenities in 

the United States.

4.3.6.2 Valuing Hurricanes, Floods, and 

Extreme Weather Events

It is sometimes suggested that the value people 

place on avoiding extreme weather events can 

be measured by the damages that such events 

cause, or by the premiums that people pay for 

flood or disaster insurance. If people are risk 

averse, ex post losses associated with extreme 

weather events represent a lower bound to the 

value people place on avoiding these events. It is 

also the case that people can purchase insurance 

only against the monetary losses associated 

with floods and hurricanes. Thus, insurance 

premiums will not capture the entire value 

placed on avoiding these events.

Assuming that people are informed about risks, 

the value of avoiding extreme weather events 

should be reflected in property values, and, 

holding other amenities constant, houses in an 

area with high probability of hurricane damage 

should sell for less than comparable houses in an 

area with a lower chance of hurricane damage. 

To estimate the value of avoiding these events 

correctly is, however, tricky. It can be difficult, 

for example, to disentangle hurricane risk (a 

negative effect) from proximity to the coast 

(an amenity). 

Recent studies use natural experiments to 

determine the value of avoiding hurricanes 

and floods. Hallstrom and Smith (2005) use 

property value data before and after hurricane 

Andrew in Lee County, Florida, a county that 

did not suffer damage from the hurricane, to 

determine the impact of people’s perceptions 

of hurricane risk on property values. They find 

that property values in special flood hazard 

areas of Lee County declined by 19 percent 

after hurricane Andrew. The magnitude of 

this decline is significant, and agrees with 

Bin and Polasky (2004). Bin and Polasky find 

that housing values in a flood plain in North 

Carolina declined significantly after hurricane 

Floyd, compared to houses not at risk. For the 

average house, the decline in price exceeded the 

present value of premiums for flood insurance, 

suggesting that the latter are, indeed, a lower 

bound to the value of avoiding floods.

4.4 Conclusions

The study of the impacts of climate change 

on human welfare, well-being, and quality 

of life, is still developing. Many studies 

of impacts on particular sectors—such 

as health or agriculture—discuss, and in 

some cases quantify, effects that have clear 

implications for welfare. Studies also hint 

at changes that are perhaps less obvious, 

but also have welfare implications (such as 

changes in outdoor activity levels and how 

much time is spent indoors) and point also to 

effects with far more dramatic consequences 

(such as the breakdown in public services 

and infrastructure associated with possible 

extreme events of the magnitude of Katrina). 

Adaptation, too, has welfare implications 

that studies do not always point out, such as 

the costs (financial and psychological) to the 

individual of changing behavior. 

To our knowledge, no study has made a systematic 

survey of the myriad welfare implications of 

climate change, much less attempted to quantify, 

nor aggregate them. An almost bewildering 
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152

choice of typologies is available for categorizing 

effects on quality of life, well-being, or human 

welfare. The social science and planning 

literatures provide not only a range of typologies, 

but also an array of metrics that could be used to 

measure life quality. 

This chapter explores one commonly used 

method: the social indicators approach. This 

approach generally divides life quality effects 

into broad categories, such as economic 

conditions or human health, and then identifies 

subcategories of important effects. 

Most of the measures of well-being—including 

the social indicators approach—focus on 

individual measures of well-being, although 

measured at the society level. There is, 

however, another dimension to well-being—

community welfare. Communities represent 

networks of households, businesses, physical 

structures, and institutions and so reflect the 

interdependencies and complex reality of 

human systems. Understanding how climate 

impacts communities, and how communities are 

vulnerable—or can be made more resilient—in 

the face of climate change, is an important 

component of understanding well-being and 

quality of life. 

Economics offers one alternative to address the 

diversity of impacts: valuing welfare impacts in 

monetary terms, which can then be summed. 

Estimating value, however, requires completing 

a series of links—from projected climate 

change to quantitative measures of effects on 

commodities, services, or conditions that are 

linked to well-being, and then valuing those 

effects using economic techniques.

Regardless of the framework, estimating 

impacts on human well-being involves numerous 

and diverse effects. This poses several critical 

difficulties:

•	 The large number of effects makes the task of 

linking impacts to climate change—whether 

qualitatively or quantitatively—difficult.

•	 The interdependence of physical and human 

systems further complicates the process of 

quantification—both for community effects, 

and also for ecosystems, raising doubts about 

a piecemeal approach to estimation.

•	 The diversity of effects raises questions 

of how to aggregate effects in order to 

develop a composite measure of wellbeing or other metrics that can be used 

for policy purposes. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

4.5 Expanding the

Knowledge Base

Despite the potential for impacts on human 

well-being, little research focuses directly 

on understanding the relationship between 

well-being and climate change. Completely 

cataloging the effects of global change on 

human well-being or welfare would be an 

immense undertaking, and no well-accepted 

structure for doing so has been developed and 

applied. Moreover, identifying the potentially 

lengthy list of climate-related changes in 

lifestyle, as well as in other, more tangible, 

features of well-being (such as income), is itself 

a daunting task—and may include changes that 

are not easily captured by objective measures 

of well-being or quality of life.

This chapter has looked at the climate impacts 

and economics literature in four areas of welfare 

effects—human health, ecosystems, recreation, 

and climate amenities. For each of the nonmarket effects analyzed here, significant data 

gaps exist at each of the steps necessary to 

provide monetized values of climate impacts. 

Although the economics literature for only a few 

areas of effects is examined, it is probable that 

similar information gaps exist for the valuation 

of other impacts of climate change, particularly 

those that involve non-market effects (see 

Table 4.1). In addition, economic welfare—as 

with any other aggregative approach—does 

not adequately address the question of how to 

deal with effects that might not be amenable 

to valuation or with interdependencies among 

effects and systems. 

Developing an understanding of the impacts of 

climate change on human welfare may require 

taking the following steps: 

•	 Develop a framework for addressing 

individual and community welfare and 

well-being, including defining welfare/wellbeing for climate analysis and systematically 

categorizing and identifying impacts on 

welfare/well-being.

•	 Identify priority categories for data collection 

and research, in order to establish and 

quantify the linkage from climate to welfare 

effects.

•	 Decide which metrics should be used for 

these categories; more generally, which 

components of welfare/well-being should be 

measured in natural or physical units, and 

which should be monetized.

•	 Investigate methods by which diverse 

metrics can be aggregated into a synthetic 

indicator (e.g., vulnerability to climate 

change impacts, including drought, sea level 

rise, etc.), or at least weighted and compared 

in policy decisions where aggregation is 

impossible.

•	 Develop an approach for addressing those 

welfare effects that are difficult to look at in 

a piecemeal way, such as welfare changes on 

communities or ecosystems.

•	 Identify appropriate top-down and bottomup approaches for estimating impacts and 

value (whether economic or otherwise) of 

the most critical welfare categories.

•	 Identify situations in which evaluation 

following the above steps is likely to be 

prohibitively difficult, and determining 

alternative methods for approaching the 

topic of the impact of global change on 

well-being. 

Together, these steps should enable researchers 

to make progress towards promoting the 

consistency and coordination in analyses 

of welfare/well-being that will facilitate 

developing the body of research necessary to 

analyze impacts on human welfare, well-being, 

and quality of life. 
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154

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geographic range of disease vectors, melting of 

snow on ski slopes, or flooding of coastal areas. 

A wide range of disciplines might be involved 

in carrying out those analyses, deploying an 

equally wide range of tools. Many analyses 

are complete once this step is completed; for 

example, we may be unable to say anything 

more than that increases in precipitation will 

change an ecosystem’s function.

The third step involves translating the physical 

effects of changes in climate into metrics 

indicating quantitative impacts. If the ultimate 

goal is monetization, ideally these measures 

should be amenable to valuation. Examples 

include quantifying the number and location 

of properties that are vulnerable to floods, 

estimating the number of individuals exposed 

to and sensitive to heat stress, or estimating the 

effect of diminished migratory bird populations 

on bird-watching participation rates. Many 

analyses that reach this step in the process, but 

not all, also proceed on to the fourth step.

The fourth step involves valuing or monetizing 

the changes. The simplest approach would be to 

apply a unit valuation approach; for example, 

the cost of treating a nonfatal case of heat stress 

or malaria attributable to climate change is a 

first approximation of the value of avoiding 

that case altogether. In many contexts, however, 

unit values can misrepresent the true marginal 

economic impact of these changes. For example, 

if climate change reduces the length of the ski 

season, individuals could engage in another 

recreational activity, such as golf. Whether 

4.7 Appendix 

Human Welfare Economic 

Valuation: An Introduction to 

Techniques and Challenges

Assessments of the benefits and costs, whether 

explicit or tacit, underlie all discussion and 

debates over alternative actions regarding 

climate change. These assessments are 

frequently used to inform such questions as: 

What actions are justified to ease adaptation to 

changing climate? Or how much are we willing 

to pay to reduce emissions? (Jacoby, 2004). 

Ideally, such analyses would be undertaken with 

complete and reliable information on benefits, 

converted into a common unit, commensurable 

with costs and with each other (Jacoby, 2004). 

In reality, however, while many impacts can be 

valued, some linkages from climate change to 

welfare effects are difficult to quantify, much 

less value. This appendix describes the steps 

in developing a benefits estimate, and the tools 

that economists have available for monetizing 

benefits. It also briefly discusses some of 

the challenges in monetizing benefits, and 

weaknesses in the approach. 

Estimating the Effects 

of Climate Change

The process of estimating the effects of climate 

change, including effects on human welfare, 

involves up to four steps, illustrated in Figure 

4A.1. Moving down from the top of Figure 4A.1, 

the gray area occupies a smaller portion of each 

box, indicating (in rough terms) that at each 

stage it is more and more difficult to develop 

quantified, rather than qualitative, results. The 

first step is to estimate the change in relevant 

measures of climate, including temperature, 

precipitation, sea level rise, and the frequency 

and severity of extreme events. This step is 

usually accomplished by atmospheric scientists; 

some form of global circulation model (GCM) 

is typically deployed. Some analyses stop after 

this step.

The second step involves estimating the 

physical effects of those changes in climate 

in terms of qualitative changes in human 

and natural systems. These might include 

changes in ecosystem structure and function, 

human exposures to heat stress, changes in the 
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164

they might prefer skiing to golf at that time 

and location is something economists might 

try to measure.

This step-by-step linear approach to effects 

estimation is sometimes called the “damage 

function” approach. One practical advantage of 

the damage function approach is the separation 

of disciplines—scientists can complete their 

work in steps 1 and 2, and sometimes in step 

3, and then economists do their work in step 4. 

The linear process can work well in cases where 

individuals respond and change their behavior 

in response to changes in their environment, 

without any “feedback” loop. 

The linear approach is not always appropriate, 

however. A damage function approach might 

imply that we look at effects of climate on 

human health as separate and independent from 

effects on ecology and recreation, but at some 

level they are inter-related, as health care and 

recreation both require resources in the form of 

income. In addition, responding to heat stress 

by installing air conditioning leads to higher 

energy demand, which in turn may increase 

greenhouse gas emissions and therefore 

contribute to further climate change. Recent 

research suggests that the damage function 

approach, under some conditions, may be both 

overly simplistic (Freeman, 2003) and subject 

to serious errors (Strzepek et al., 1999; Strzepek 

and Smith, 1995). 

Monetizing and Valuing 

Non-Market Goods

Economists have developed a suite of methods 

to estimate WTP for non-market goods (see text 

for a discussion of the market vs. non-market 

distinction). These methods can be grouped 

into two broad categories, based largely on 

the source of the data: revealed preference 

and stated preference approaches (Freeman, 

2003; U.S. EPA, 2000). Revealed preference, 

sometimes referred to as the indirect valuation 

approach, involves inferring the value of a 

non-market good using data from market 

transactions. For example, a lake may be 

valued for its ability to provide a good fishing 

experience. This value can be estimated by 

the time and money expended by the angler to 

fish at that particular site, relative to all other 

Step 1: Estimate climate change

(magnitude & timing)

• temperature

• precipitation

• sea-level rise

• extreme weather events

Step 2: Estimate physical effects

(spatial & temporal distribution)

• human exposure to heat stress

• change in ecosystem structure 

and function

• arial extent of flooding

• timing of snow melt

• many more...

Step 3: Estimate 

quantitative impacts

• number of sick individuals

• changes in recreational 

participation rates

• property losses

• change in species populations

• many more...

Step 4: Value or 

“monetize” effects

• lost property value

• cost of illness

• loss in recreational “use 

value”

• loss of human welfare for 

other effects

Non-quantified

physical effects

Impacts that can 

not be quantified

Impacts that can

not be monetized

Figure 4A.1 Estimating the Effects of Climate Change
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

possible fishing sites. Or, the amenity value of 

a coastal property that is protected from storm 

damage (by a dune, perhaps) can be estimated 

by comparing the price of that property to 

other properties similar in every way but the 

enhanced storm protection. 

Stated and Revealed Preference 

Approaches

Accurate measurement of the non-market 

amenity of interest, in a manner that is not 

inconsistent with the way market participants 

perceive the amenity, is critical to a robust 

estimate of value. 

Revealed preference approaches include 

recreational demand models, which estimate 

the value of recreational amenities through time 

and money expenditures to enjoy recreation; 

hedonic wage and hedonic property value 

models, which attempt to isolate the value of 

particular amenities of property and jobs not 

themselves directly traded in the marketplace 

based on their price or wage outcomes; and 

averting behavior models, which estimate the 

value of time or money expended to avert a 

particular bad outcome as a measure of its 

negative effect on welfare.

Stated preference approaches, sometimes 

referred to as direct valuation approaches, 

are survey methods that estimate the value 

individuals place on particular non-market goods 

based on choices they make in hypothetical 

markets.34 The earliest stated preference studies 

involved simply asking individuals what they 

would be willing to pay for a particular nonmarket good. The best studies involve great 

care in constructing a credible, though still 

hypothetical, trade-off between money and 

the non-market good of interest to discern 

individual preferences for that good and hence, 

WTP. For example, economists might construct 

a hypothetical choice between multiple housing 

locations, each of which differs along the 

dimensions of price and health risk. Repeated 

choice experiments of this type ultimately map 

out the individual’s tradeoff between money and 

the non-market good. The major challenges in 

34 The contingent valuation method (CVM), or a modern variants, a stated choice model (SCM), are forms 

of the stated preference methods. 

stated preference methods involve study design, 

particularly the construction of a reasonable and 

credible market for the good, and estimation of a 

valuation function from the response data. 

In theory, if individuals understand the full 

implications of their market choices, in real or 

constructed markets, then both revealed and 

stated preference approaches are capable of 

providing robust estimates of the total value 

of non-market goods. When considering the 

complex and multidimensional implications of 

climate change in the application of revealed 

and stated preference approaches, it can be 

extraordinarily challenging to ensure that 

individuals are sufficiently informed that their 

observed or stated choices truly reflect their 

preferences for a particular outcome. As a 

result, these methods are most often applied to a 

narrowly defined non-market good, rather than 

to a complex bundle of non-market goods that 

might involve multiple tradeoffs and synergistic 

or antagonistic effects that would be difficult 

to disentangle.

In addition to market or non-market goods that 

reflect some use of the environment, value can 

arise even if a good or service is not explicitly 

consumed, or even experienced. For example, 

very few individuals would value a polar bear 

for its ability to provide sustenance; those who 

do might not express that value through a direct 

market for polar bear meat, but by hunting for 

the bear. Whether through a market or in a nonmarket activity, those individuals have value for 

a consumptive use—once enjoyed, that good 

is no longer available to others to enjoy. In 

addition to the consumptive users, a small but 

somewhat larger number of individuals might 

travel to the Arctic to see a polar bear in its 

natural environment. These individuals might 

express a value for polar bears, and their “use” 

of the bear is non-consumptive, but in some 

sense it does nonetheless affect others’ ability 

to view the bear—if too many individuals 

attempt to view the bears, the congestion might 

cause the bears to become frightened or, worse, 

domesticated, diminishing the experience of 

viewing them.

A third, perhaps much larger group of individuals 

will never travel to see a polar bear in the flesh. 

But many individuals in this group would 
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166

experience some diminishment in their overall 

quality of life if they knew that polar bears had 

become extinct. This concept is called “non-use 

value.” Although there are several categories 

of non-use value, some individuals may wish 

to preserve the future option to visit the Arctic 

and see a bear, others to bequeath a world with 

polar bears to future generations, and others 

might value the mere existence of the bears 

out of a sense of environmental stewardship. 

While not all economists agree that non-use 

values ought to be relevant to policy decisions 

(Diamond and Hausman, 1993), there is broad 

agreement that they are difficult to measure, 

because the expression of non-use values does 

not result in measurable economic behavior 

(that is, there is no “use” expressed). Those that 

recognize non-use values acknowledge that they 

are likely to be of greatest consequence where 

a resource has a uniqueness or “specialness” 

and loss or injury is irreversible, for example 

in the global or local extinction of a species, or 

the distribution of a unique ecological resource 

(Freeman, 2003).

Other Methods of Monetizing

Analysts can employ other non-market valuation 

methods: avoided cost or replacement cost, and 

input value estimates. These methods do not 

measure WTP as defined in welfare economic 

terms, but because the methods are relatively 

straightforward to apply and the results often 

have a known relationship to WTP, they provide 

insights into non-market values. This chapter 

focuses on WTP measures, but recognizes that 

alternative methods may provide insights and 

sometimes be more manageable (or appropriate) 

to estimate a particular non-market value, given 

data constraints and the limitations imposed by 

available methods. 

Cost of illness studies estimate the change in 

health expenditures resulting from the change 

in incidence of a given illness. Direct costs of 

illness include costs for hospitalization, doctors’ 

fees, and medicine, among others. Indirect costs 

of illness include effects such as lost work and 

leisure time. Complete cost of illness estimates 

reflect both direct and indirect costs. Even 

the most complete cost of illness estimates, 

however, typically underestimate WTP to avoid 

incidence of illness, because they ignore the loss 

of welfare associated with pain and suffering 

and may not reflect costs of averting behaviors 

the individuals have taken to avoid the illness. 

Some studies suggest that the difference 

between cost of illness and WTP can be large, 

but the difference varies greatly across health 

effects and individuals (U.S. EPA, 2000).

Replacement cost studies approach non-market 

values by estimating the cost to replace the 

services provided to individuals by the nonmarket good. For example, healthy coastal 

wetlands may provide a wide range of services 

to individuals who live near them; they may 

filter pollutants present in water; absorb 

water in times of flood; act as a buffer to 

protect properties from storm surges; provide 

nursery habitat for recreational and commercial 

fish; and provide amenities in the form of 

opportunities to view wildlife. A replacement 

cost approach would estimate the value of these 

services by estimating market costs for treating 

contaminants, containing floods, providing 

fish from hatcheries, or perhaps restoring an 

impaired wetland to health. 

The replacement cost approach is limited in 

three important ways: 1) the cost of replacing a 

resource does not necessarily bear any relation to 

the welfare enhancing effect of the resource; 2) 

as resources grow scarce, we would expect their 

value would be underestimated by an average 

replacement cost; 3) complete replacement of 

ecological systems and services may be highly 

problematic. Replacement cost studies are most 

informative in those conditions where loss 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

of the resource would certainly and without 

exception trigger the incidence of replacement 

costs - in reality, those conditions are not as 

common as they might seem, because in most 

cases there are readily available substitutes for 

those services, even if accessing them involves 

incurring some transition costs.

Finally, value can also be calculated using the 

contribution of the resource as an input into a 

productive process. This approach can be used 

for both market and non-market inputs. For 

example, it can be used to estimate the value of 

fertilizer, as well as water or soil, in farm output 

and profits. An ecosystem’s service input into 

a productive process could, in theory, be used 

in this same way.

Issues in Valuation 

and Aggregation

The topic of issues in valuation is far larger 

than can be covered here. We focus only 

on identifying in a superficial way a few of 

the most important issues, in the context of 

climate change. 

By virtue of the simple process of aggregation, 

the economic approach creates some difficulties. 

These difficulties are not specific to the 

economic approach, however; any method of 

aggregation would face the same limitations.

•	 Aggregation, by balancing out effects to 

produce a “net” effect, masks the positive 

and negative effects that comprise net 

effects, hides inequities in the distribution 

of impacts, or large negative impacts that 

fall on particular regions or vulnerable 

populations.

•	 Any method of aggregation must make 

an explicit assumption about how to 

aggregate over time, i.e., whether to weight 

future benefits the same as current benefits 

(economic analyses generally discount 

the future, i.e., weight it less heavily in 

decision making than the present, for a 

number of reasons).

•	 The method of putting diverse impacts on 

the same yardstick ignores differences in 

how we may wish to treat these impacts 

from a policy perspective, and assumes 

that all impacts are equally certain or 

uncertain, despite differences in estimation 

and valuation methods. These differences 

may be particularly apparent, for example, 

for non-market and market goods.

Several potential criticisms of the economic 

approach in the context of climate change relate 

more directly to how economists approach the 

task of valuation. One issue is the assumption 

of stability of preferences over time. Economic 

studies conducted today, whether revealed 

or stated preference, reflect the actions and 

preferences of individuals today, expressed in 

today’s economic, social, and technological 

context. For an issue such as climate change, 

however, impacts may occur decades or 

centuries hence. The valuation of impacts 

that occur in the future should depend on 

preferences in the future. For the most part, 

however, while there are some rudimentary 

ways in which economists model changes in 

technology or income, there is no satisfactory 

means of modeling changes in preferences 

over time. 

A second issue is the treatment of uncertainty. 

Economic analysis under conditions of imperfect 

information and uncertainty is possible, but 

is one of the most difficult undertakings in 

economics. While some climate change impacts 

may be relatively straight-forward, valuation of 

many climate change impacts requires analysis 

and use of welfare measures that incorporate 

uncertainty. When imperfect information 

prevails, the valuation measure must factor in 

errors that arise because of it, and when risk or 
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168

uncertainty prevail, the most commonly used 

valuation measure is the option price. Two 

related concepts are option value, and expected 

consumer’s surplus. All three concepts are more 

complicated than the discussion here can do 

justice to, but briefly:

•	 Expected consumer’s surplus, E[CS] is 

just consumer’s surplus (CS), or value in 

welfare terms, weighted by the probabilities 

of outcomes that yield CS. For example, if a 

hiker gets $5 of CS per year in a “dry” forest 

and $10 in a wet forest (one that is greener) 

and the probability of the forest being dry 

is 0.40 and of it being wet is 0.60, then the 

E[CS] = 0.40 X $5 + 0.60 X $10. Expected 

consumer’s surplus is really an ex-post 

concept, because we must know CS in each 

state after it occurs.

•	 Option price (OP) is the WTP that balances 

expected utility (utility weighted by the 

probabilities of outcomes) with and without 

some change. It is a measure of WTP the 

individual must express before outcomes 

can be known with certainty, i.e., a true 

ex ante welfare measure. For example, the 

hiker might be willing to pay $8 per year to 

balance her expected utility with conditions 

being wet, versus conditions being dry. 

The $8 might be a payment to support 

a reduction in dryness otherwise due to 

climate change.

•	 Option value (OV) is the difference between 

OP and E[CS]. A related concept is called 

quasi-option value and pertains to the value 

of waiting to get more information.

A third issue concerns behavioral paradoxes. 

Most economic analyses, particularly if they 

involve uncertain or risky outcomes, require 

rationality in the expression of preferences. 

Such basic axioms as treating gains and losses 

equally, reacting to a series of small incremental 

gains with equal strength to a single large gain 

of the same aggregate magnitude, and viewing 

gains and losses from an absolute rather than 

relative or positional scale are particularly 

important to studies that rely on expected utility 

theory—that individuals gain and lose welfare 

in proportion to the product of the likelihood of 

the gain or loss and its magnitude. Several social 

and psychological science studies, however, 

suggest that under many conditions individuals 

do not behave in a manner consistent with this 

definition of rationality. For example, prospect 

theory, often credited as resulting from the 

work of Daniel Kahneman and Amos Tversky, 

suggests that behavior under risk or uncertainty 

is better explained both by reference to a status 

quo reference point and acknowledgement 

of unequal treatment of risk aversion when 

considering losses and gains, even when it 

can be shown that a different behavior would 

certainly make the individual better off. 

Finally, the issue of perspective—“whose 

lens are we looking through”—is critical 

to welfare analysis, particularly economic 

welfare. In health policy, for example, thinking 

about whether it is worthwhile to invest in 

mosquito netting to control malaria depends 

on whether you are at CDC, are a provider 

of health insurance, or are an individual 

in a place where malaria risk is high. In 

general, the perspective of valuation focuses 

on the valuation of individuals who are 

directly affected, and who are living today. 

The perspectives of public decision makers 

may be somewhat different from those of 

individuals, since they will take into account 

social and community consequences, as well 

as individual consequences. 
169

CHAPTER

5

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Common Themes and Research 

Recommendations

Convening Lead Author: Janet L. Gamble, U.S. Environmental 

Protection Agency

Lead Authors: Kristie L. Ebi, ESS, LLC; Frances G. Sussman, 

Environmental Economics Consulting; Thomas J. Wilbanks, Oak 

Ridge National Laboratory

Contributing Authors: Colleen E. Reid, ASPH Fellow; John V. Thomas, 

U.S. Environmental Protection Agency; Christopher P. Weaver, U.S. 

Environmental Protection Agency

5.1 SyNTHESIS AND

ASSESSMENT PRODUCT 4.6: 

ADVANCES IN THE SCIENCE

The Synthesis and Assessment Product 4.6 

assesses the impacts of climate variability and 

change on human systems in the United States. 

Each of the assessment chapters has drawn on 

different bodies of literature, with generally 

more available scientific knowledge on impacts 

and adaptation related to human health, 

somewhat less related to human settlements, 

and still less related to human welfare. 

Several themes recur across these chapters 

and point to advances in the science of climate 

impacts assessment and the development and 

deployment of adaptation responses.

1. The connections between climate change 

and other environmental and social changes 

are complex and dynamic. In some cases, 

climate change compounds the effects of 

other global changes. Socioeconomic factors 

can, in some cases, determine or moderate 

the impacts of climate change (5.1.1).

2. Extreme weather events will play a defining 

role, particularly in the near-term, shaping 

climate-related impacts and adaptive 

capacity. While impacts associated with 

changes in climate averages may be less 

important now, these averages are expected 

to have more pronounced long-run effects 

on sea level rise, permafrost melt, glacial 

retreat, drought patterns and water supplies, 

etc. (5.1.2). 

3. Climate change will have a disproportionate 

impact on disadvantaged groups in 

communities across the United States. 

Some regions and some resources are more 

vulnerable to climate impacts, such as 

coastal zones, drought-prone regions, and 

flood-prone river basins (5.1.3).

4. Adaptation of infrastructure and services 

to climate change may be costly, but 

many communities will have adequate 

resources. However, for places already 

struggling to provide or maintain basic 

public amenities and services, the additional 

costs of adaptation will impose a potentially 

insupportable burden (5.1.4).

5. With such a complex scientific and policy 

landscape, an integrated multi-disciplinary 

framework is needed for climate change 

impacts to be measured in meaningful ways 

and for optimal mitigation and adaptation 

strategies to be identified, developed, and 

deployed (5.1.5).

5.1.1 Complex Linkages and a 

Cascading Chain of Impacts 

Across Global Changes

Climate is only one of a number of global 

changes that impact human well-being. The 

major effects of climate will be shaped by 

interactions with non-climate stressors. As 

such, climate change will seldom be the sole or 

primary factor determining a population’s or 

a location’s well-being. Moreover, the impacts 

of changes in climate will be tied to the effects 
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of socioeconomic variables, such as population 

growth, and how these influence key sectors and 

decisions, such as infrastructure development, 

habitat preservation, and access to health care. 

Consequently, while this assessment focuses 

on the mechanisms by which climate change 

could affect future health, well-being, and 

settlements in the United States, the extent of 

any impacts will depend on an array of nonclimate factors, including:

•	 Demographic changes related to the location, 

size, age, and characteristics of populations; 

•	 Population and regional vulnerabilities;

•	 Future social, economic, and cultural 

contexts; 

•	 Availability of natural resources;

•	 Human, cultural, and social capital;

•	 Advances in science and technology; 

•	 Characteristics of the built environment; 

•	 Land use change; 

•	 P u b l i c h e a l t h a n d p u b l i c u t i l i t y 

infrastructures; and 

•	 The capacity and availability of health and 

social services. 

The effects of climate change very often 

spread from directly affected areas and sectors 

to other areas and sectors through extensive 

and complex linkages. The importance of 

climate change depends on the directness of 

the climate impact coupled with demographic, 

social, economic, institutional, and political 

factors, including the degree of preparedness. 

Consider, for example, the damage caused by 

Hurricanes Katrina and Rita in 2005. Damage 

was measured not only in terms of lives and 

property lost, but also in the devastating 

impacts on infrastructure, neighborhoods, 

businesses, schools, and hospitals. In addition, 

there have been consequences from continuing 

disruptions to established communities, 

livelihoods, psychological well-being, and 

the exacerbation of chronic illnesses. While 

the impacts of a single hurricane are not 

readily linked to climate change, such an 

event demonstrates the disruptive capacity of 

extreme weather events. 

5.1.2 Changes in Climate 

Extremes and Climate Averages

Past and present climates have been, and are, 

variable. This variability in all likelihood 

will continue into the future. Changes in 

climate occur as changes in particular weather 

conditions, including extremes, in specific 

places (unfortunately, projections of climate 

changes at small geographic scales remain 

highly uncertain). The meteorological variables 

of interest from an impacts perspective include 

changes in both average and extreme conditions. 

Gradual changes in average temperature and 

precipitation have the potential to strongly affect, 

both positively and negatively, human systems. 

For example, changes in the average length of the 

growing season can affect agricultural practices, 

and changes in the timing and amount of spring 

runoff can affect water resource management. 

Effects such as these will not be confined to a 

few individual sectors, nor are the effects across 

all sectors independent (e.g., changes in water 

supplies can impact agricultural practices such 

as irrigation).

Changes in climate extremes, both those that 

accompany changes in mean conditions (e.g., a 

shift in the entire temperature distribution) as 

well as changes in variability are very often of 

more concern than changes in climate averages. 

Unfortunately these types of changes (which 

include prolonged and intense heat waves and 

drought or severe storms) are especially difficult 

to project using climate change models. Many 

human systems have evolved to accommodate 

the “average climate” and some variation around 

this average. This evolution takes place in the 

context of a variety of dynamic social, economic, 

technological, biophysical, and political settings, 

which together determine the ability of human 
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systems to cope. Rapid onset extreme weather 

events in particular can do serious damage to 

a settlement’s infrastructure, public health, and 

overall community reputation and quality of life, 

from which recovery might take years. 

Finally, key vulnerabilities are often defined 

by certain “thresholds,” below which effects 

are incidental but beyond which effects quickly 

become major. The severity of impacts is 

therefore not only related to the rate and 

magnitude of climate change, but also to the 

presence or absence of thresholds. In general, 

these climate-related thresholds for human 

systems in the United States are not wellunderstood. Focused research on thresholds 

would substantially improve our understanding 

of climate impacts and our ability to cope with 

extreme events.

5.1.3 Vulnerable Populations and 

Vulnerable Locations

Impacts of climate variability and change on 

human systems are location- and populationspecific. For instance, along densely developed 

coastlines, populations are especially vulnerable 

to tropical storms, storm surge, and flooding. 

Likewise, the very old and the very young 

residing in urban areas are susceptible to 

increases in cardiovascular and pulmonary 

morbidity and mortality caused by extreme 

heat coupled with degraded air quality. Native 

American peoples in Alaska and elsewhere are 

vulnerable because of their limited capacity to 

prepare for and respond to the impacts of climate 

change. Just as there are differences across 

populations, there are important differences in 

vulnerability across geographic regions, such as 

the exposure to extreme events along the Gulf 

Coast and water supply issues in the Southeast, 

the Southwest and the Inter-Mountain West. 

With respect to health impacts from climate 

variability and change, specific subpopulations 

may experience heightened vulnerability for 

climate-related health effects associated with 

any or all of the following: 

1. Biological sensitivity relates to age 

(especially the very young and the very old), 

the presence of pre-existing chronic medical 

conditions (such as the sensitivity of people 

with chronic heart and pulmonary conditions 

to heat-related illness), developmental 

characteristics, acquired factors (such 

as immunizations from vaccines), the 

use of certain medications (e.g., some 

ant i hy per tensive a nd psychot ropic 

medications), and genetic factors (such as 

those that play a role in vulnerability to air 

pollution effects). 

2. Socioeconomic factors also play a 

critical role in determining vulnerability 

to environmental condition factors. The 

distribution of climate-related effects will 

vary among those who live alone, among 

those with limited rights (for instance, some 

in the immigrant communities), by economic 

strata, by housing type, and according to 

other elements that either accentuate or 

limit vulnerability. Socioeconomic factors 

can increase the likelihood of exposure to 

harmful agents, interact with biological 

factors that mediate risk (such as nutritional 

status), and/or lead to differences in the 

ability to adapt or respond to exposures or 

to early phases of illness and injury. 

3. Given their location, the underlying 

vulnerability of some communities is 

inherently high just as their adaptive 

capacity is similarly limited. Populations 

in gently sloping coastal areas are 

particularly vulnerable to sea level rise, and 

settlements along floodplains of large rivers 

are particularly vulnerable to increased 

variability in precipitation. The potential 

for increased frequencies of drought put the 

increasing populations of desert Southwest 

cities at risk. 
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It is essential that public health interventions 

and preventions recognize populations that may 

experience interactive or synergistic effects of 

multiple risk factors for health problems. Poor 

communities and households are already under 

stress from climate variability and climaterelated extreme events such as heat waves, 

hurricanes, and tropical and riverine flooding. 

Since they tend to be concentrated in relatively 

high-risk areas and have limited access to 

services and other resources for coping, they 

can be especially vulnerable to climate change. 

These differential effects raise concerns about 

social inequity and environmental justice and 

increase pressure for adaptive responses from 

local, state, and federal governments. 

5.1.4 The Cost of and Capacity 

for Adaptation

The United States is capable of considerable 

adaptation. The success of adaptation plans 

and/or measures will depend heavily on the 

competence and capacity of individuals; 

communities; federal, state, and local 

governments; and available financial and other 

social resources. While adaptation to climate 

change will come at a cost that will likely reduce 

resources available to cope with other societal 

burdens, the potential for adaptation through 

technological and institutional development and 

behavioral changes is considerable, especially 

where such options meet other sustainable 

development needs. 

With scarce resources, communities should 

also choose adaptation options with co-benefits 

that help ameliorate other issues or where they 

can easily add climate concerns to existing 

response plans. The focus on all-hazards 

response within public health agencies can 

simply add climate impacts to its list of hazards 

for which to prepare. This will likely improve 

their response plans to events in the near term 

such as storms that happen in a variable climate, 

whether or not they increase in frequency or 

intensity with a changing climate. Planting trees 

and creating green roofs can help reduce the 

urban heat island effect. In addition to creating 

more aesthetically pleasing locations, green 

roofs can also help with energy conservation 

in the buildings upon which they are located. 

Thus, some adaptation measures can also be 

considered mitigation measures. 

5.1.5 An Integrative Framework

Human well-being is an emerging concept, 

and in theory could encompass human health 

and settlements—the two key focuses of this 

Product—as well as other critical aspects 

of the effect of climate change on human 

systems and the services provided by natural 

systems. As an organizing principle, human 

well-being could provide a paradigm for 

identifying and categorizing climate impacts, 

and may ultimately provide a framework 

for integrating multiple impacts into an 

internally consistent, coherent framework for 

assessing costs, benefits, and tradeoffs. As an 

integrating concept, human well-being can 

develop insights into the linkages between 

climate change impacts and human happiness. 

Just as health can be considered a component 

of well-being (i.e., physical health is closely 

tied to individual measures of happiness, 

contentment, and quality of life) aspects of 

human settlements also determine well-being 

and could be incorporated into a broader 

framework of well-being or welfare.

The impacts of climate variability and change 

on human health and human settlements 

are fairly well characterized in broad terms, 

although additional research is needed to 

refine impact assessments and provide better 

decision support (particularly with respect to 

deploying adaptation measures). However, the 

potential for utilizing concepts of human well-
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

being to develop an integrating framework 

is not yet mature. Additional conceptual 

work and research will be needed, such as 

developing valuation methodologies (in the case 

of economic welfare), or developing metrics of 

well-being or quality of life (in the case of a 

place-based indicators, or similar, approach). 

An alternative integrating framework could 

revolve around settlements or the more 

expansive concept of communities (see Section 

4.2.3 for an elaborated discussion). There is a 

growing awareness that the built environment 

can have a profound impact on our health and 

quality of life.1 A major goal of community 

design is to create more vibrant and livable 

communities, making sure that they address the 

needs of residents and improve their quality of 

life. More specifically, “green communities,” 

“smart communities,” “smart growth,” and 

“sustainable development” are intended to offer 

alternatives to traditional settlement patterns, 

aiming to meet the goals of creating livable, 

desirable communities while minimizing the 

collective footprint of communities on natural 

resources, ecosystems, and pollution. 

As an integrating framework, communities 

could be evaluated based on how well they 

protect human health and welfare. Put slightly 

differently, adaptation could be realized as 

increasing resilience within communities. 

Resilience is measured by a community’s 

capacity for absorbing climate changes and the 

shocks of extreme events without breakdowns 

in its economy, natural resources, and social 

systems. Resiliency, as a central concept in 

measuring the vulnerability and adaptability of 

communities and individuals, depends not only 

on physical infrastructure, but also on social 

infrastructure and the natural environment. 

As with welfare, these concepts involving 

settlements or communities as an integrating 

framework are not yet mature.

1 See for example, the CDC website on healthy places: 

www.cdc.gov/healthyplaces/.

5.2 EXPANDING THE 

KNOWLEDGE BASE 

The present state of the science suggests that 

opportunities remain for addressing critical 

research areas. SAP 4.6 concludes that climate 

observations and modeling are becoming 

increasingly important for a wide segment 

of public and private sector entities, such 

as water resource managers, public health 

officials, agribusinesses, energy providers, 

forest managers, insurance companies, and 

urban and transportation planners. In order to 

more accurately portray the consequences of 

climate change and support better-informed 

adaptation strategies, research efforts should 

focus on: 

•	 Deriving socioeconomic scenarios that 

describe how the world may evolve in the 

future, including assumptions about changes 

in societal characteristics, governments, 

and public policy, as well as economic and 

technological development; 

•	 Connecting socioeconomic scenarios to 

downscaled climate models in order to 

evaluate future actions that might address 

changes in climate, including the intensity 

and severity of extreme weather events, at 

the regional and local scales; 

•	 Characterizing the costs of climate change, 

both those that relate to impacts and those 

that relate to response strategies (including 

adaptation and mitigation); 

•	 Estimating the damages avoided by 

stabilizing or reducing emissions; 
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•	 Determining the factors that contribute to 

synergies between adaptive capacity and 

sustainable development as well as synergies 

between adaptation and mitigation; 

•	 Pursuing cross-disciplinary efforts that 

focus on the human dimensions of climate 

change in an integrated fashion; 

•	 Improving capacity to incorporate scientific 

knowledge about climate, including 

uncertainty, into existing adaptation 

strategies; 

•	 Conducting research at regional and sectoral 

levels that promotes understanding how 

human and natural systems respond to 

multiple stressors; 

•	 Evaluating the adaptation strategies that 

effectively address challenges presented 

by current non-climate stressors (e.g., land 

use and population dynamics) and develop 

comprehensive estimates of the co-benefits 

of actions to address anticipated climate 

change; 

•	 Investigating adaptation measures to address 

the near- and long-term responses to climate 

change, using regional and local stakeholders 

as key contributors for recommending 

effective, responsive, and timely adaptation 

policies; 

•	 Advancing the concept of human welfare 

as an integrating framework by developing 

methods to achieve comparable and 

comprehensive valuations across diverse 

impacts and sectors; 

•	 Determining which climate impacts exhibit 

thresholds. Threshold-based damage 

functions can be fundamentally different 

in their nature and extent than continuous 

damage functions; and

•	 Supporting the development, implementation, 

and evaluation of adaptive responses, as well 

as expanding our understanding of impacts, 

by collecting high quality time-series 

measurements and other observations of 

both climate and human systems.

This report concludes that periodic assessments 

of the impacts of global change on human 

health, human settlements, and human welfare 

are necessary to support a rapidly developing 

knowledge base, especially related to impacts 

and adaptation. Gaps should be addressed that 

characterize exposure and sensitivity at the 

local or regional level. Research should evaluate 

the adaptive capacity of places and institutions 

to climate-induced risks. Key research and 

development areas should address short-term 

risk assessment and evaluation of the costs and 

effectiveness of near-term adaptive strategies as 

well as longer-term impacts and responses. 

The following sections provide a more 

detailed discussion of research needs and 

recommendations by topic: human health, 

human settlements, and human welfare. 

There is significant overlap across topics 

with opportunities for investigating crossdisciplinary pursuits of research opportunities 

and adaptation responses. 

5.2.1 Human Health Research Gaps

An important shift in perspective has occurred 

since the Health Sector Assessment of the First 

National Assessment in 2001. There is a greater 

appreciation of the complex pathways by which 

weather and climate affect individual and 

societal health and well-being. In the research 

community, there is a more finely honed 

understanding of the interaction of multiple 

non-climate, social, and behavioral factors and 

impacts on risks from injury and disease. While 

significant gaps remain, several gaps identified 

in the First National Assessment have been 

addressed, including: 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

•	 A better understanding of the differential 

effects of temperat ure extremes by 

community, demographic, and biological 

characteristics; 

•	 Improved characterization of the exposureresponse relationships for extreme heat; 

and

•	 Improved understanding of the public health 

burden posed by climate-related changes 

from heat waves and air pollution. 

Despite these advances, the body of literature 

has only limited quantitative projections of 

future impacts. Research related to the human 

health impacts of climate change will lead to a 

better understanding in this area.

Specific suggestions for research on climate 

change and human health include the following. 

•	 Increase the skill with which we characterize 

exposure-response relationships, including 

identifying thresholds and particularly 

vulnerable groups, considering relevant 

factors that affect the geographic range 

and incidence of climate-sensitive health 

outcomes, and including disease ecology 

and transmission dynamics; 

•	 Develop quantitative models of possible 

health impacts of climate change that can 

be used to explore a range of socioeconomic 

and climate scenarios;

•	 Evaluate effectiveness of current adaptation 

projects, including the costs and benefits 

of interventions. For example, heat wave 

and health early warning systems have not 

been effective. Further research is needed to 

understand how public health messages can 

be made more helpful;

•	 Characterize with local stakeholders the 

local and regional scale vulnerability and 

adaptive capacity related to the potential 

risks and the time horizon over which 

climate risks might arise; and,

•	 Anticipate requirements for infrastructure 

such as may be needed to provide protection 

against extreme events, to alter urban design 

to decrease heat islands, and to maintain 

drinking and wastewater treatment standards 

and source water and watershed protection.

5.2.2 Human Settlements 

Research Gaps

Preceding chapters examine the vulnerabilities 

and impacts of climate change and variability 

on human settlements. The following list 

enumerates topics where a better understanding 

of the linkages between climate change and 

human settlements is appropriate. 

•	 Advance the understanding of settlement 

vulnerabilities, impacts, and adaptive 

responses in a variety of different local 

contexts around the country.

•	 Develop plans for out-migration from 

vulnerable locations via realistic, socially 

acceptable strategies for shifting human 

populations away from vulnerable zones.

•	 Improve the understanding of vulnerable 

populations (such as the urban poor and 

native populations on rural, tribal lands) 

that have limited capacities for response to 

climate change in order to provide a basis 

for adaptation research that addresses social 

justice and environmental equity concerns. 

•	 Improve the understanding of how urban 

decision-making is changing as populations 

become more heterogeneous and decisions 

become more decentralized, especially 

in so far as these changes affect adaptive 

responses.
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•	 Improve researchers’ abilities to associate 

projections of climate change in U.S. 

settlements with changes in other driving 

forces related to impacts, such as changes 

in metropolitan/urban patterns, changes 

in transportation infrastructure, and 

technological change. With continued 

growth in vulnerable regions, research 

is needed to consider alternative growth 

futures and to minimize the vulnerability of 

new development, to insure that communities 

adopt measures to manage significant 

changes in sea level, temperature, rainfall, 

and extreme weather events. 

•	 Improve the understanding of relationships 

between settlement patterns (both regional 

and intra-urban) and resilience/adaptation.

•	 Improve the understanding of vulnerabilities 

of urban population inflows and outflows to 

climate change impacts.

•	 Improve the understanding of second- and 

third-order impacts of climate change in 

urban environments, including interactive 

effects among different aspects of the 

urban system.

•	 Review current policies and practices related 

to climate change responses to help inform 

community decision-makers and other 

stakeholders about potentials for relatively 

small changes that make a large difference. 

Meeting these needs is likely to require 

well-developed partnerships across local, 

state, and federal governments; industry; 

non-governmental organizations; foundations; 

stakeholders; resource managers; urban planners; 

public utility and public health authorities; and 

the academic research community. 

5.2.3 Human Welfare 

Research Gaps

Despite the potential for impacts on human 

well-being, little research focuses directly 

on understanding the relationship between 

well-being and climate change. Completely 

cataloging the effects of global change on 

human well-being or welfare would be an 

immense undertaking, and no well-accepted 

structure for doing so has been developed and 

applied. Moreover, identifying the potentially 

lengthy list of climate-related changes in 

lifestyle, as well as in other, more tangible, 

features of well-being (such as income), is itself 

a daunting task—and may include changes that 

are not easily captured by objective measures 

of well-being or quality of life.

Developing an understanding of the impacts 

of climate change on human welfare will 

require steps designed to develop a framework 

for addressing individual and community 

welfare and well-being, as well as to fill the 

data gaps associated with the estimation and 

quantification of effects. 

Regarding climate change and human welfare, 

there is a range of topics associated with 

human welfare impacts and adaptations where 

improved understanding would be useful. 

•	 Desig n a n appropr iate met hod for 

systematically categorizing and identifying 

impacts on welfare/well-being.

•	 Identify priority categories for data collection 

and research in order to establish and 

quantify the linkage from climate to effects 

on welfare/well-being.

•	 Decide which metrics should be used for 

these categories and, more generally, which 

components of welfare/well-being should be 

measured in natural or physical units, and 

which should be monetized.

•	 Investigate methods by which diverse 

metrics can be aggregated, or at least 

weighted and compared in policy decisions 

where aggregation is impossible.

•	 Develop an approach for addressing those 

human welfare effects that are difficult to look 

at in a piecemeal way, such as welfare changes 

on communities or ecosystem services.

•	 Identify appropriate top-down and bottomup approaches for estimating impacts and 

value (whether economic or otherwise) 

of the most critical categories of welfare/

well-being.

Together, these steps should enable researchers 

to make progress towards promoting the 

consistency and coordination in analyses 

of welfare/well-being that will facilitate 

developing the body of research necessary to 

analyze impacts on human welfare, well-being, 

and quality of life.
CHAPTER

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Glossary and Acronyms 6

6.1 GLOSSARy

Sources: Derived from the Intergovernmental 

Panel on Climate Change Third and Fourth 

Assessment Reports, Working Group II and 

other sources as indicated.

Words in italics indicate that the term is also 

contained in this glossary.

A

Acclimatization

The physiological adaptation to climatic 

variations.

Adaptability

See adaptive capacity.

Adaptation

Adjustment in natural or human systems to a 

new or changing environment. Adaptation to 

climate change refers to adjustment in natural 

or human systems in response to actual or 

expected climatic stimuli or their effects, 

which moderates harm or exploits beneficial 

opportunities. Various types of adaptation 

can be distinguished, including anticipatory 

and reactive adaptation, private and public 

adaptation, and autonomous and planned 

adaptation.

Adaptation assessment

The practice of identifying options to adapt to 

climate change and evaluating them in terms 

of criteria such as availability, benefits, costs, 

effectiveness, efficiency, and feasibility.

Adaptation benefits

The avoided damage costs or the accrued benefits 

following the adoption and implementation of 

adaptation measures.

Adaptation costs

Costs of planning, preparing for, facilitating, 

and implementing adaptation measures, 

including transition costs.

Adaptive capacity

The ability of a system to adjust to climate 

change (including climate variability and 

extremes) to moderate potential damages, to 

take advantage of opportunities, or to cope with 

the consequences.

Aeroallergens1

Any of various air-borne substances, such as 

pollen or spores, that can cause an allergic 

response.

1 The American Heritage® Dictionary of the English 

Language, Fourth Edition. Retrieved November 21, 

2007 from http://dictionary.reference.com/browse/

aeroallergen.

Convening Lead Author: Janet L. Gamble, 

U.S. Environmental Protection Agency

Lead Authors: Kristie L. Ebi, ESS, LLC; Anne Grambsch, 

U.S. Environmental Protection Agency; Frances G. Sussman, 

Environmental Economics Consulting; Thomas J. Wilbanks, 

Oak Ridge National Laboratory

Contributing Authors: Colleen E. Reid, ASPH Fellow
The U.S. Climate Change Science Program Glossary and Acronyms 

178

Aerosol

Particulate matter (solid or liquid) that is 

larger than a molecule but small enough to 

remain suspended in the atmosphere. Natural 

sources include dust and clay particles from 

weathered rocks and salt particles from sea 

spray, both of which are carried upward by the 

wind. Aerosols are often considered pollutants 

and can be created through human activities. 

They are important in the both the atmosphere

and the Earth’s climate system as nuclei for 

condensation of water droplets and ice crystals, 

participants in various chemical cycles, and as 

absorbers/scatterers of solar radiation.

Aggregate impacts

Total impacts summed up across sectors and/

or regions. The aggregation of impacts requires 

knowledge of (or assumptions about) the relative 

importance of impacts in different sectors 

and regions. Measures of aggregate impacts 

include, for example, the total number of people 

affected, change in net primary productivity, 

number of systems undergoing change, or total 

economic costs.

Albedo

The fraction of solar radiation ref lected 

by a surface or object, often expressed as a 

percentage. Snow-covered surfaces have a high 

albedo; the albedo of soils ranges from high to 

low; vegetation-covered surfaces and oceans 

have a low albedo. The Earth’s albedo varies 

mainly through varying cloudiness, snow, ice, 

leaf area, and land-cover changes.

Algal bloom 

A reproductive explosion of algae in a lake, 

river, or ocean. 

Ancillary benefits

The ancillary or side effects, of policies aimed 

exclusively at climate change mitigation. 

Such policies have an impact not only on 

greenhouse gas emissions, but also on 

resource use efficiency, like reduction in 

emissions of local and regional air pollutants 

associated with fossil fuel use, and on issues 

such as transportation, agriculture, land-use 

practices, employment, and fuel security. 

Sometimes these benefits are referred to as 

“ancillary impacts” to reflect that in some 

cases the benefits may be negative. From the 

perspective of policies directed at abating 

local air pollution, greenhouse gas mitigation

may also be considered an ancillary benefit, 

but these relationships are not considered in 

this assessment.

Anthropogenic

Resulting from or produced by human beings.

Anthropogenic emissions

Emissions of greenhouse gases, greenhouse gas

precursors, and aerosols associated with human 

activities. These include burning of fossil fuels 

for energy, deforestation, and land use changes 

that result in net increase in emissions.

Aquifer

A stratum of permeable rock that bears water. 

An unconfined aquifer is recharged directly by 

local rainfall, rivers, and lakes, and the rate of 

recharge is influenced by the permeability of 

the overlying rocks and soils. 

Arid regions

Ecosystems with less than 250 mm precipitation 

per year.

Atmosphere

The gaseous envelop surrounding the Earth. 

The dry atmosphere consists almost entirely 

of nitrogen (78.1 percent volume mixing ratio) 

and oxygen (20.9 percent volume mixing ratio), 

together with a number of trace gases, such 

as argon (0.93 percent volume mixing ratio), 

helium, and radiatively active greenhouse 

gases such as carbon dioxide (0.035 percent 

volume mixing ratio) and ozone. In addition, 

the atmosphere contains water vapor, whose 

amount is highly variable but typically 1 percent 

volume mixing ratio. The atmosphere also 

contains clouds and aerosols.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

B

Baseline

The baseline (or reference) is any datum 

against which change is measured. It might be 

a “current baseline,” in which case it represents 

observable, present-day conditions. It might 

also be a “future baseline,” which is a projected 

future set of conditions excluding the driving 

factor of interest. Alternative interpretations 

of the reference conditions can give rise to 

multiple baselines.

Biodiversity

A term that refers to the variety and variability 

among living organisms and the ecological 

systems in which they exist. Diversity can be 

measured by the number of different items 

and their relative frequencies. The items 

are organized at many levels, encompassing 

everything from ecosystems, to species, to 

genes.

Biofuel

A fuel produced from organic matter or 

combustible oils produced by plants. Examples 

of biofuel include alcohol, black liquor from 

the paper-manufacturing process, wood, and 

soybean oil. 

Biogenic2

Produced by living organisms or biological 

processes. 

Biomass

The total dry weight of all living organisms that 

can be sustained at each tropic level in a food 

chain. Also, all biological materials, including 

organic material (dead and living) from above 

and below ground, such as crops, grasses, roots, 

animals, animal waste, etc.

2 The American Heritage Dictionary of the English 

Language, Fourth Edition. Retrieved November 

21, 2007 from http://dictionary.reference.com/

browse/biogenic.

Biosphere

The region of Earth and the atmosphere where 

organisms exist. Also, a part of the global 

carbon cycle that includes living organisms and 

biogenic organic matter.

Bottom-up models

An approach to modeling that includes both 

technological and engineering details in the 

analysis.

C

Carbon cycle

The term to describe the f low of carbon 

through a system by various chemical, physical, 

geological, and biological processes. This 

cycle is usually thought of as a series of four 

main reservoirs of carbon interconnected by 

pathways of exchange. The reservoirs include 

the atmosphere, terrestrial biosphere (including 

freshwater systems), oceans, and sediments 

(including fossil fuels).

Carbon dioxide (CO2)

A naturally occurring gas, and also a byproduct of burning fossil fuels and biomass, as 

well as land-use changes and other industrial 

processes. It is the principal anthropogenic 

greenhouse gas that affects the Earth’s radiative 

balance. It is the reference gas against which 

other greenhouse gases are measured and has 

a Global Warming Potential of 1.

Cholera

An intestinal infection that results in frequent 

watery stools, cramping abdominal pain, and 

eventual collapse from dehydration.

Chronic obstructive pulmonary disease 

(COPD)3

Chronic obstructive pulmonary disease, 

or COPD, refers to a group of diseases that 

cause airflow blockage and breathing-related 

problems. It includes emphysema, chronic 

bronchitis, and in some cases asthma.

3 Centers for Disease Control and Prevention (CDC), 

“Chronic Obstructive Pulmonary Disease.” Retrieved November 21, 2007 from http://www.cdc.

gov/nceh/airpollution/copd/copdfaq.htm.
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180

Climate

Climate in a narrow sense is usually defined 

as the “average weather” or, more rigorously, 

as the statistical description in terms of the 

mean and variability of relevant quantities 

over a period of time ranging from months to 

thousands or millions of years. The classical 

period is 30 years, as defined by the World 

Meteorological Organization (WMO, 2003). 

These relevant quantities are most often surface 

variables such as temperature, precipitation, 

and wind. Climate in a wider sense is the 

state, including a statistical description, of the 

climate system.

Climate change

Climate change refers to any change in climate 

over time, whether due to natural variability or 

as a result of human activity. This usage differs 

from that in the United Nations Framework 

Convention on Climate Change (UNFCCC), 

which defines “climate change” as: “a change 

of climate which is attributed directly or 

indirectly to human activity that alters 

the composition of the global atmosphere 

and which is in addition to natural climate 

variability observed over comparable time 

periods” (IPCC, 2007). See also climate 

variability.

Climate change commitment

Due to the thermal inertia of the ocean and 

slow processes in the biosphere, the cryospere 

and land surfaces, the climate would continue 

to change even if the atmospheric composition 

was held fixed at today’s values. Past changes 

in atmospheric position lead to a “committed” 

climatic change, which continues for as long 

as a radiative imbalance persists and until 

all components of the climate system have 

adjusted to a new state. The further change 

in temperature after the composition of 

the atmosphere is held constant is referred 

to as the committed warming or warming 

commitment. Climate change commitment 

includes other future changes, for example 

in the hydrological cycle, in extreme weather 

events, and in sea level rise.

Climate model (hierarchy)

A numerical representation of the climate 

system based on the physical, chemical, 

and biological properties of its components, 

their interactions and feedback processes, 

and accou nting for all or some of its 

known properties. The climate system

can be represented by models of varying 

complexity—that is, for any one component 

or combination of components a “hierarchy” 

of models can be identified, differing in such 

aspects as the number of spatial dimensions, 

the extent to which physical, chemical, 

or biological processes are explicitly 

represented, or the level at which empirical 

parametrizations are involved. Coupled 

atmosphere/ocean/sea-ice general circulation 

models (AOGCMs) provide a comprehensive 

representation of the climate system. There 

is an evolution towards more complex 

models with active chemistry and biology. 

Climate models are applied, as a research 

tool, to study and simulate the climate, but 

also for operational purposes, including 

monthly, seasonal, and interannual climate 

predictions. 

Climate prediction

A climate prediction or climate forecast is 

the result of an attempt to produce a most 

likely description or estimate of the actual 

evolution of the climate in the future (e.g., 

at seasonal, interannual, or long-term time 

scales). See also climate projection and 

climate (change) scenario.

Climate projection

A projection of the response of the climate 

system to emission or concentration scenarios 

of greenhouse gases and aerosols, or radiative 

forcing scenarios, often based upon simulations 

by climate models. Climate projections are 

distinguished from climate predictions in order 

to emphasize that climate projections depend 

upon the emission/concentration/radiative 

forcing scenario used, which are based on 

assumptions, concerning, for example, future 

socio-economic and technological developments 

that may or may not be realized, and are 

therefore subject to substantial uncertainty.
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Climate scenario

A plausible and often simplified representation 

of the future climate, based on an internally 

consistent set of climatological relationships, 

that has been constructed for explicit use in 

investigating the potential consequences of 

anthropogenic climate change, often serving 

as input to impact models. Climate projections 

often serve as the raw material for constructing 

climate scenarios, but climate scenarios usually 

require additional information such as about the 

observed current climate. A “climate change 

scenario” is the difference between a climate 

scenario and the current climate.

Climate sensitivity

The equilibrium response of the climate to a 

change in radiative forcing, such as a doubling 

of carbon dioxide concentrations.

Climate system

The climate system is the highly complex 

system consisting of five major components: 

the atmosphere, the hydrosphere, the cryospere, 

the land surface and the biosphere, and the 

interactions between them. The climate system 

evolves in time under the influence of its own 

internal dynamics and because of external 

forcings such as volcanic eruptions, solar 

variations, and human-induced forcings such 

as the changing composition of the atmosphere

and land use change.

Climate variability

Climate variability refers to variations in the 

mean state and other statistics (such as standard 

deviations, the occurrence of extremes, etc.) of 

the climate on all spatial and temporal scales 

beyond that of individual weather events. 

Variability may be due to natural internal 

processes within the climate system (internal 

variability), or to variations in natural or 

anthropogenic external forcing (external 

variability). See also climate change.

Co-benefits

The benefits of policies that are implemented 

for various reasons at the same time—including 

climate change mitigation— acknowledging that 

most policies designed to address greenhouse 

gas mitigation also have other, often at least 

equally important, rationales (e.g., related to 

objectives of development, sustainability, and 

equity). The term co-impact is also used in a 

more generic sense to cover both the positive 

and negative sides of the benefits. See also 

ancillary benefits.

Communicable disease

An infectious disease caused by transmission of 

an infective biological agent (virus, bacterium, 

protozoan, or multicellular macroparasite).

Confidence

In this Report, the level of confidence in 

a statement is expressed using a standard 

terminology defined in the Introduction. See 

also uncertainty.

Coping range

The variation in climatic stimuli that a system 

can absorb without producing significant 

impacts.

Cost-effective

A criterion that specifies that a technology or 

measure delivers a good or service at equal or 

lower cost than current practice, or the leastcost alternative for the achievement of a given 

target.

Cryosphere

The component of Earth’s climate system

that includes snow, ice, and permafrost on or 

beneath land and ocean surfaces.
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182

D

DALY (Disability-adjusted life years)4

The sum of years of life lost due to premature 

death and illness, taking into account the age 

of death compared with natural life expectancy 

and the number of years of life lived with a 

disability. The measure of number of years lived 

with the disability considers the duration of the 

disease, weighted by a measure of the severity 

of the disease.

Deforestation

Those processes that result in the conversion 

of forested lands for non-forest land uses. 

This process is often considered to be a major 

cause of enhanced greenhouse effect, because 

the burning/decomposition of wood releases 

carbon dioxide, and also because trees that once 

removed carbon dioxide from the atmosphere

through the process of photosynthesis are no 

longer present. 

Dengue fever

An infectious viral disease spread by mosquitoes 

often called breakbone fever because it is 

characterized by severe pain in joints and back. 

Subsequent infections of the virus may lead to 

dengue hemorrhagic fever and dengue shock 

syndrome, which may be fatal.

Desert

An ecosystem with less than 100 mm 

precipitation per year.

Desertification

According to the United Nations Convention 

to Combat Deser tif ication (U NCCD), 

desertification is “land degradation in arid, semiarid, and dry sub-humid areas resulting from 

various factors, including climatic variations 

and human activities” (United Nations, 2004). 

Further, the UNCCD defines land degradation 

as a reduction or loss in arid, semi-arid, 

and dry sub-humid areas of the biological 

or economic productivity and complexity of 

rain-fed cropland, irrigated cropland, or range, 

pasture, forest, and woodlands resulting from 

4 Millennium Ecosystem Assessment, 2005 glossary. 

land uses or from a process or combination of 

processes, including processes arising from 

human activities and habitation patterns, such 

as: (i) soil erosion caused by wind and/or water; 

(ii) deterioration of the physical, chemical, and 

biological or economic properties of soil; and 

(iii) long-term loss of natural vegetation.

Detection and attribution

Climate varies continually on all time scales. 

Detection of climate change is the process of 

demonstrating that climate has changed in some 

defined statistical sense, without providing a 

reason for that change. Attribution of causes of 

climate change is the process of establishing the 

most likely causes for the detected change with 

some defined level of confidence.

Disturbance regime

Frequency, intensity, and types of disturbances, 

such as fires, insect or pest outbreaks, floods, 

and droughts.

Diurnal temperature range

The difference between the maximum and 

minimum temperature during a day.

Dose-response function5

A mathematical relationship is established 

which relates how much a certain amount 

of exposure impacts production, capital, 

ecosystems, or human health.

Downscaling

A method that derives local- to regional-scale 

(10 to 100 km) information from larger-scale 

models or data analyses.

Drought

The phenomenon that exists when precipitation 

has been significantly below normal recorded 

levels, causing serious hydrological imbalances 

that adversely affect land resource production 

systems.

5 Modified from OECD Glossary of Statistical Terms. 

“Dose-response Function.” Retrieved November 

21, 2007 from http://stats.oecd.org/glossary/detail.

asp?ID=6404.
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E

Economic potential

The portion of technological potential for 

reductions in greenhouse gas emissions

or energy efficiency improvements that 

could be achieved cost-effectively through 

activities like creation of markets, reduction of 

market failures, or increases in financial and 

technological transfers. In order to achieve 

economic potential, additional policies and 

measures must be established to remove market 

barriers.

Ecosystem

A system of interacting living organisms 

together with their physical environment. 

The boundaries of what could be called an 

ecosystem are somewhat arbitrary, depending 

on the focus of interest or study. Thus, the extent 

of an ecosystem may range from very small 

spatial scales to, ultimately, the entire Earth. 

Ecosystem processes 

The processes that underpin the integrity 

and functioning of ecosystems, such as 

decomposition, carbon cycling, or soil 

renewal, etc.

Ecosystem services

Ecological processes or functions that have 

monetary or non-monetary value to individuals 

or society. There are (i) supporting services such 

as productivity or biodiversity maintenance, (ii) 

provisioning services such as food, fibre, or 

fish, (iii) regulating services such as climate 

regulation or carbon sequestration, and (iv) 

cultural services such as tourism or spiritual 

and aesthetic appreciation.

El Niño Southern Oscillation (ENSO)

El Niño, in its original sense, is a warm water 

current that periodically flows along the coast 

of Ecuador and Peru, disrupting the local 

fishery. This oceanic event is associated with a 

fluctuation of the intertropical surface pressure 

pattern and circulation in the Indian and Pacific 

Oceans, called the Southern Oscillation. This 

coupled atmosphere-ocean phenomenon 

is collectively known as El Niño Southern 

Oscillation, or ENSO. During an El Niño event, 

the prevailing trade winds weaken and the 

equatorial countercurrent strengthens, causing 

warm surface waters in the Indonesian area to 

flow eastward to overlie the cold waters of the 

Peru current. This event has great impact on the 

wind, sea surface temperature, and precipitation 

patterns in the tropical Pacific. It has climatic 

effects throughout the Pacific region and in 

many other parts of the world. The opposite of 

an El Niño event is called La Niña.

Emissions

In the climate change context, emissions refer 

to the release of greenhouse gases and/or their 

precursors and aerosols into the atmosphere 

over a specified area and period of time.

Endemic

Restricted or peculiar to a locality or region. 

With regard to human health, endemic can 

refer to a disease or agent present or usually 

prevalent in a population or geographical area 

at all times.

Epidemic

Occurring suddenly in numbers clearly in 

excess of normal expectancy, said especially 

of infectious diseases but applied also to any 

disease, injury, or other health-related event 

occurring in such outbreaks.

Erosion

The wearing away of land surfaces by wind 

or water, which is intensified by land-clearing 

activities related to farming, road building, 

logging, or residential/industrial development.

Eutrophication

The process by which a body of water (often 

shallow) becomes (either naturally or by 

pollution) rich in dissolved nutrients with a 

seasonal deficiency in dissolved oxygen.

Evaporation

The process by which a liquid becomes a gas.
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184

Evapotranspiration

The combined process of evaporation from 

the Earth’s surface and transpiration from 

vegetation.

Exotic species

See introduced species.

Exposure

The nature and degree to which a system is 

exposed to significant climatic variations.

External cost

Used to define the costs arising from any 

human activity, when the agent responsible for 

the activity does not take full account of the 

impacts of his or her actions on others. Equally, 

when the impacts are positive and not accounted 

for in the actions of the agent responsible they 

are referred to as external benefits. Emissions of 

particulate pollution from a power station affect 

the health of people in the vicinity, but this is 

not often considered, or is given inadequate 

weight, in private decision making and there is 

no market for such impacts. Such a phenomenon 

is referred to as an “externality,” and the costs it 

imposes are referred to as the external costs.

Externality

See external cost.

Extinction

The complete disappearance of an entire 

species.

Extirpation

The disappearance of a species from part of its 

range; local extinction.

Extreme weather event

An extreme weather event is an event that is 

rare within its statistical reference distribution 

at a particular place. Definitions of “rare” vary, 

but an extreme weather event would normally 

be as rare as or rarer than the 10th or 90th 

percentile. By definition, the characteristics of 

what is called extreme weather may vary from 

place to place. An extreme climate event is an 

average of a number of weather events over a 

certain period of time, an average which is itself 

extreme (e.g., rainfall over a season).

F

Feedback

In relation to the climate, feedback is an 

interaction mechanism between processes in 

the climate system that occur when the result 

of an initial process triggers a change in a 

second process, which in turn influences the 

initial one again. Positive feedback occurs when 

the original process is intensified, negative 

feedback occurs when it is reduced.

Foodborne illness6

An illness caused by consuming foods 

or beverages contaminated with any of 

many different disease-causing microbes, 

pathogens, poisonous chemicals, or other 

harmful substances.

Food security

A situation that exists when people have 

secure access to sufficient amounts of safe and 

nutritious food for normal growth, development, 

and an active and healthy life. Food insecurity 

may be caused by the unavailability of food, 

insufficient purchasing power, inappropriate 

distribution, or inadequate use of food at the 

household level.

6 Modif ied from CDC. “Foodbor ne Illness.” 

Retrieved November 21, 2007 from http://

www.cdc.gov/ncidod/dbmd/diseaseinfo/

foodborneinfections_g.htm. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Footprint (ecological)7

An index of the area of productive land and 

aquatic ecosystems required to produce the 

resources used and to assimilate the wastes 

produced by a defined population at a specified 

material standard of living, wherever on Earth 

that land may be located.

Forecast

See climate prediction and climate projection.

Fossil fuel

The general term for combustible geologic 

deposits of organic material buried underground. 

Fossil fuels are formed from decayed plant and 

animal matter that have been exposed to heat 

and pressure in the Earth’s crust for hundreds 

of millions of years. Crude oil, coal, and natural 

gas are all fossil fuels.

G

General circulation

The large scale motions of the atmosphere 

and the ocean as a consequence of differential 

heating on a rotating Earth, aiming to restore 

the energy balance of the system through 

transport of heat and momentum.

General Circulation Model (GCM)

See climate model.

GIS (Geographic Information System)8

A computerized system organizing data sets 

through a geographical referencing of all data 

included in its collections.

Glacier

A mass of land ice that flows downhill and is 

constrained by its surrounding topography (i.e. 

sides of a valley or surrounding peaks). Glaciers 

are maintained by accumulation of snow at 

high altitudes and balanced by melting at low 

altitudes or discharge into the sea.

7 Millennium Ecosystem Assessment, 2005 glossary.

8 Millennium Ecosystem Assessment, 2005 glossary. 

Globalization

The growing integration and interdependence 

of c ou nt r ie s worldw ide t h r ou g h t he 

increasing volume and variety of cross 

border transactions in goods and services; 

free international capital flows; and the more 

rapid and widespread diffusion of technology, 

information, and culture.

Global surface temperature

The global surface temperature is the areaweighted global average of (i) the sea surface 

temperature over the oceans (i.e., the subsurface bulk temperature in the first few meters 

of the ocean) and (ii) the surface air temperature 

over land at 1.5 m above the ground.

Global Warming Potential (GWP)

An index used to translate the emission levels 

of various gasses into a common measure so 

that their relative radiative forcing may be 

compared without directly calculated changes 

in atmospheric concentrations. GWPs are 

calculated as the ratio of radiative forcing that 

would result from the emissions of one kilogram 

of a greenhouse gas to that from the emission

of one kilogram of carbon dioxide over a period 

of time (usually 100 years). 

Greenhouse effect

Greenhouse gases effectively absorb infrared 

radiation, emitted by the Earth’s surface, by 

the atmosphere itself due to the same gases, 

and by clouds. Atmospheric radiation is 

emitted to all sides, including downward to the 

Earth’s surface. Thus greenhouse gases trap 

heat within the surface-troposphere system. 

This is called the “natural greenhouse effect.” 

Atmospheric radiation is strongly coupled to the 

temperature of the level at which it is emitted. 

In the troposphere, the temperature generally 

decreases with height. Effectively, infrared 

radiation emitted to space originates from 

an altitude with a temperature of, on average, 

-19°C, in balance with the net incoming solar 

radiation, whereas the Earth’s surface is kept 

at a much higher temperature of, on average, 

+14°C. An increase in the concentration of 

greenhouse gases leads to an increased infrared 

opacity of the atmosphere, and therefore to an 
The U.S. Climate Change Science Program Glossary and Acronyms 

186

effective radiation into space from a higher 

altitude at a lower temperature. This causes 

a radiative forcing, an imbalance that can 

only be compensated for by an increase of the 

temperature of the surface-troposphere system. 

This is the “enhanced greenhouse effect.”

Greenhouse gas

G reen house gases a re t hose gaseous 

constituents of the atmosphere, both natural and 

anthropogenic, that absorb and emit radiation 

at specific wavelengths within the spectrum 

of infrared radiation emitted by the Earth’s 

surface, the atmosphere, and clouds. This 

property causes the greenhouse effect. Water 

vapor (H2O), carbon dioxide (CO2), nitrous 

oxide (N2O), methane (CH4), and ozone (O3) 

are the primary greenhouse gases in the Earth’s 

atmosphere. Moreover there are a number 

of entirely human-made greenhouse gases 

in the atmosphere, such as the halocarbons 

and other chlorine- and bromine-containing 

substances, dealt with under the Montreal 

Protocol. Besides CO2, N2O, and CH4, the 

Kyoto Protocol deals with the greenhouse gases 

sulfur hexafluoride (SF6), hydrofluorocarbons 

(HFCs), and perfluorocarbons (PFCs).

Gross Domestic Product

Gross Domestic Product (GDP) is the monetary 

value of all goods and services produced within 

a nation.

Gross National Product

Gross National Product (GNP) is the monetary 

value of all goods and services produced in a 

nation’s economy, including income generated 

abroad by domestic residents, but without 

income generated by foreigners.

Groundwater recharge

The process by which external water is added 

to the zone of saturation of an aquifer, either 

directly into a formation or indirectly by way 

of another formation.

H

Habitat

The particular environment or place where 

an organism or species tend to live; a more 

locally circumscribed portion of the total 

environment.

Halocarbon

A chemical that consists of carbon, sometimes 

hydrogen, and either chlorine, fluorine, bromine, 

or iodine.

Hantavirus

A virus in the family Bunyaviridae that causes 

a type of hemorrhagic fever. It is thought that 

humans catch the disease mainly from infected 

rodents, either through direct contact with the 

animals or by inhaling or ingesting dust that 

contains aerosolized viral particles from their 

dried urine and other secretions.

Healthy Cities program9

The WHO Healthy Cities program engages local 

governments in health development through a 

process of political commitment, institutional 

change, capacity building, partnership-based 

planning, and innovative projects. It promotes 

comprehensive and systematic policy and 

planning with a special emphasis on health 

inequalities and urban poverty; the needs of 

vulnerable groups; participatory governance; 

and the social, economic, and environmental 

determinants of health. It also strives to include 

health considerations in economic regeneration 

and urban development efforts.

Heat exhaustion10

Heat exhaustion is a phenomenon caused by 

fluid loss, which in turn causes decreased blood 

flow to vital organs. Reduced blood flow from 

heat exhaustion can result in a form of shock. 

9 World Health Organization. “Healthy Cities and 

Urban Governance.” Retrieved November 21, 2007 

from http://www.euro.who.int/healthy-cities.

10 U.S. Environmental Protection Agency. “Heat Island 

Effect Glossary.” Retrieved November 21, 2007 

from http://www.epa.gov/hiri/resources/glossary.

html#h. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Victims of heat exhaustion often complain of 

flu-like symptoms hours after exposure.

Heat index11

The heat index (HI), given in degrees F, is 

a measure of how hot it feels when relative 

humidity (RH) is combined with the actual 

air temperature. 

Heat island

An area within an urban area characterized by 

ambient temperatures higher than those of the 

surrounding area because of the absorption of 

solar energy by materials like asphalt.

Heat stroke12

Heat stroke occurs when the body’s heat 

regulating mechanisms–including convection, 

sweating, and respiration–fail. The likelihood

of heat stroke increases when air temperatures 

are higher than skin temperature, and when 

individuals are low on fluids. Body temperatures 

can be raised to the point at which brain damage 

and death can result unless cooling measures 

are quickly taken.

Human settlement

A place or area occupied by settlers.

Human system

Any system in which human organizations play 

a major role. Often, but not always, the term is 

synonymous with “society” or “social system” 

(e.g., agricultural system, political system, 

technological system, economic system).

Hydrofluorocarbons (HFCs)

Compounds that contain hydrogen, fluorine, 

chlorine, and carbon atoms. They have been 

introduced as temporary replacements for 

chloroflourocarbons (CFCs) as they are less 

potent at destroying stratospheric ozone. 

However, they are considered both ozone

depleting substances and greenhouse gases.

11 Modified from NOAA. “Heat Index.” Retrieved 

November 21, 2007 from http://www.crh.noaa.gov/

jkl/?n=heat_index_calculator.

12 U.S. EPA. “Heat Island Effect Glossary.” 

Hydrological systems

T he syst e m s i nvolve d i n move me nt , 

distribution, and quality of water throughout 

the Earth, including both the hydrologic cycle 

and water resources.

Hydrosphere

All the water present on Earth, including 

liquid water (oceans, fresh water, underground 

aquifers), frozen water (polar ice caps, 

floating ice, frozen upper layer of soil known 

as permafrost), and water vapor in the 

atmosphere.

Hyperthermia13

Unusually high body temperature. 

I

Ice sheet

A mass of land ice that is sufficiently deep 

to cover most of the underlying bedrock 

topography, so that its shape is mainly 

determined by its internal dynamics (the flow 

of the ice as it deforms internally and slides at its 

base). An ice sheet flows outward from a high 

central plateau with a small average surface 

slope. The margins slope steeply, and the ice 

is discharged through fast-flowing ice streams 

or outlet glaciers, in some cases into the sea or 

into ice shelves floating on the sea. There are 

only two large ice sheets in the modern world, 

on Greenland and Antarctica, the Antarctic 

ice sheet being divided into East and West by 

the Transantarctic Mountains; during glacial 

periods there were others.

Ice shelf

A floating ice sheet of considerable thickness 

attached to a coast (usually of great horizontal 

extent with a level or gently undulating surface); 

often a seaward extension of ice sheets.

13 The American Heritage Dictionary of the English 

Language, Fourth Edition. Retrieved November 21, 

2007 from http://dictionary.reference.com/browse/

hyperthermia.
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188

(Climate) Impact assessment

The practice of identifying and evaluating the 

detrimental and beneficial consequences of 

climate change on natural and human systems.

(Climate) Impacts

Consequences of climate change on natural and 

human systems. Depending on the consideration 

of adaptation, one can distinguish between 

potential impacts and residual impacts. 

Potential impacts: All impacts that may occur 

given a projected change in climate, without 

considering adaptation. Residual impacts: The 

impacts of climate change that would occur 

after adaptation. See also aggregate impacts, 

market impacts, and non-market impacts.

Indicator14

Information based on measured data used to 

represent a particular attribute, characteristic, 

or property of a system.

Indigenous peoples

People whose ancestors inhabited a place or 

a country when persons from another culture 

or ethnic background arrived on the scene and 

dominated them through conquest, settlement, 

or other means and who today live more in 

conformity with their own social, economic, 

and cultural customs and traditions than those 

of the country of which they now form a part 

(also referred to as “native,” “aboriginal,” or 

“tribal” peoples). 

Industrial revolution

A period of rapid industrial growth with farreaching social and economic consequences, 

beginning in England during the second half of 

the 18th century and spreading to Europe and 

later to other countries including the United 

States. The invention of the steam engine was 

an important trigger of this development. The 

industrial revolution marks the beginning of 

a strong increase in the use of fossil fuels and 

emission of, in particular, fossil carbon dioxide. 

In this report, the terms “pre-industrial” and 

“industrial” refer, somewhat arbitrarily, to 

14 Millennium Ecosystem Assessment, 2005, Current 

State and Trends Assessment glossary.

the periods before and after the year 1750, 

respectively.

Inertia

Delay, slowness, or resistance in the response 

of the climate, biological, or human systems to 

factors that alter their rate of change, including 

continuation of change in the system after the 

cause of that change has been removed.

Infectious disease

Any disease that can be transmitted from one 

person to another. This may occur by direct 

physical contact, by common handling of an 

object that has picked up infective organisms, 

through a disease carrier, or by spread of infected 

droplets coughed or exhaled into the air.

Infrared radiation

Heat energy emitted by the Earth’s surface 

and its atmosphere, some of which is strongly 

absorbed by greenhouse gases and re-radiated 

back towards the Earth’s surface, creating the 

greenhouse effect. Also describes the heat 

energy emitted from all solids, liquids and 

gases. 

Infrastructure

The basic equipment, utilities, productive 

enterprises, installations, institutions, and 

services essential for the development, 

operation, and growth of an organization, 

city, or nation. For example, roads; schools; 

electric, gas, and water utilities; transportation; 

communication; and legal systems would be all 

considered as infrastructure.

Integrated assessment

A method of analysis that combines results and 

models from the physical, biological, economic, 

and social sciences, and the interactions 

between these components, in a consistent 

framework, to evaluate the status and the 

consequences of environmental change and the 

policy responses to it.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Introduced species

A species occurring in an area outside its 

historically known natural range as a result of 

accidental dispersal by humans (also referred to 

as “exotic species” or “alien species”).

Invasive species

An introduced species that invades natural 

habitats.

IPCC15

A panel set up by the United Nations in 1988 

to review scientific information on climate 

change. This panel involves over 2,000 of the 

world’s climate experts. Many of the climate 

change facts and future predictions we read 

about come from information reviewed by the 

IPCC.

K

Kyoto Protocol

The Kyoto Protocol was adopted at the Third 

Session of the Conference of the Parties to the 

UN Framework Convention on Climate Change 

(UNFCCC) in 1997 in Kyoto, Japan. It contains 

legally binding commitments, in addition to those 

included in the UNFCCC. Countries included in 

Annex B of the Protocol (most member countries 

of the Organization for Economic Cooperation 

and Development (OECD) and those with 

economies in transition) agreed to reduce their 

anthropogenic greenhouse gas emissions (CO2, 

CH4, N2O, HFCs, PFCs, and SF6) by at least 5 

percent below 1990 levels in the commitment 

period 2008 to 2012. The Kyoto Protocol entered 

into force on 16 February 2005.

15 Climate Change North. “Glossary.” Retrieved 

November 21, 2007 from http://www.climatechangenorth.ca/H1_Glossary.html. 

L

Landslide

A mass of material that has slipped downhill 

by gravity, often assisted by water when the 

material is saturated; rapid movement of a mass 

of soil, rock, or debris down a slope. 

Land use

The total of arrangements, activities, and inputs 

undertaken in a certain land cover type (a set 

of human actions). The social and economic 

purposes for which land is managed (e.g., 

grazing, timber extraction, and conservation).

Land-use change

A change in the use or management of land by 

humans, which may lead to a change in land 

cover. Land cover and land-use change may have 

an impact on the albedo, evapotranspiration, 

sources, and sinks of greenhouse gases, or other 

properties of the climate system, and may thus 

have an impact on climate, locally or globally. 

La Niña

See El Niño Southern Oscillation.

Lifetime (atmospheric)

The lifetime of a greenhouse gas refers to the 

approximate amount of time it would take for 

the atmospheric pollutant concentration to 

return to its natural level (assuming emissions

cease), as a result of either being converted to 

another chemical compound or being taken 

out of the atmosphere via a sink. This length of 

time depends on both the pollutant’s sources

and sinks, and its level of reactivity. Average 

lifetimes can vary from a week (e.g., sulfate 

aerosols) to more than a century (e.g., CFCs, 

carbon dioxide). Long lifetimes allow the 

pollutant to mix throughout the atmosphere.

Likelihood

The likelihood of an occurrence, an outcome or a 

result, where this can be estimated probabilistically, 

is expressed in this Report using a standard 

terminology, defined in the Introduction. See also 

uncertainty and confidence.
The U.S. Climate Change Science Program Glossary and Acronyms 

190

Lyme disease

A vector-borne disease caused by the spirochete 

Borrelia burgdorferi and transmitted by Ixodes 

ticks, commonly known as deer ticks. Symptoms 

include skin lesions, fatigue, fever, and chills, 

and if left untreated may later manifest itself in 

cardiac and neurological disorders, joint pain, 

and arthritis. 

M

Maladaptation

Any changes in natural or human systems that 

inadvertently increase vulnerability to climatic 

stimuli; an adaptation that does not succeed in 

reducing vulnerability but increases it instead.

Malaria

Endemic or epidemic parasitic disease caused 

by species of the genus Plasmodium (protozoa) 

and transmitted by mosquitoes of the genus 

Anopheles; produces high fever attacks and 

systemic disorders, and kills approximately 2 

million people every year.

Market barriers

In the context of mitigation of climate change, 

conditions that prevent or impede the diffusion 

of cost-effective technologies or practices that 

would mitigate greenhouse gas emissions.

Market-based incentives

Measures intended to use price mechanisms 

(e.g., taxes and tradable permits) to reduce 

greenhouse gas emissions.

Market impacts

Impacts that are linked to market transactions 

and directly affect Gross Domestic Product 

(a country’s national accounts)—for example, 

changes in the supply and price of agricultural 

goods. See also non-market impacts.

Market potential

The portion of economic potential for reductions 

in greenhouse gas emissions or improvements 

in energy-efficiency that could be achieved 

under forecast market conditions; assuming 

there are no new policies and measures 

Methane (CH4)

A hydrocarbon greenhouse gas produced 

t h roug h a n a e robic (w it hout ox yge n) 

decomposition of waste in landfills, animal 

digestion, decomposition of animal wastes, 

production and distribution of natural gas and 

petroleum, coal production, and incomplete 

fossil fuel combustion. 

Mitigation

An anthropogenic intervention to reduce the 

sources or enhance the sinks of greenhouse 

gases.

Mitigative capacity

The social, political, and economic structures 

and conditions that are required for effective 

mitigation.

Montreal Protocol

Titled Montreal Protocol on Substances that 

Deplete the ozone layer, this international 

agreement addresses the phase-out of ozone

depleting substances production and use. Under 

the Protocol, several international organizations 

report on the science of ozone depletion, 

implement projects to help move away from 

ozone depleting substances, and provide a 

forum for policy discussions. In the United 

States, the Protocol is implemented under the 

Clean Air Act Amendments of 1990.

Morbidity

Rate of occurrence of disease or other health 

disorder within a population, taking account 

of the age-specific morbidity rates. Health 

outcomes include chronic disease incidence/

prevalence, rates of hospitalization, primary 

care consultations, disability-days (i.e., days 

when absent from work), and prevalence of 

symptoms.

Mortality 

Rate of occurrence of death within a population 

within a specified time period; calculation of 

mortality takes account of age-specific death 

rates, and can thus yield measures of life 

expectancy and the extent of premature death.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

N

Net primary production (NPP)

Refers to the increase in plant biomass or carbon 

of a unit of landscape. NPP is equal to the Gross 

Primary Production minus carbon lost through 

autotrophic respiration.

Nitrogen oxides16

Compounds of nitrogen and oxygen produced 

by the burning of fossil fuels. 

Non-linearity

A process is called “non-linear” when there is 

no simple proportional relation between cause 

and effect. The climate system contains many 

such non-linear processes, resulting in a system 

with a potentially very complex behavior. Such 

complexity may lead to rapid climate change.

Non-market impacts

Impacts that affect ecosystems or human 

welfare, but that are not directly linked to market 

transactions—for example, an increased risk of 

premature death. See also market impacts.

Non-point source pollution

A large, non-specific area that discharges 

pollutants into surface and sub-surface water 

flows, for example crop fields and urban 

areas.

No-regrets opportunities

See no-regrets policy.

No-regrets options

See no-regrets policy.

No-regrets policy

One that would generate net social benefits 

whether or not there is climate change. Noregrets opportunities for greenhouse gas 

emissions reduction are defined as those 

options whose benefits such as reduced 

energy costs and reduced emissions of local/

16 Energy Administration Information, “Glossary.” 

Retrieved November 21, 2007 from http://www.eia.

doe.gov/glossary/glossary_n.htm. 

regional pollutants equal or exceed their costs 

to society, excluding the benefits of avoided 

climate change. No-regrets potential is defined 

as the gap between the market potential and 

the socio-economic potential.

North Atlantic Oscillation (NAO)

The North Atlantic Oscillation consists of 

opposing variations of barometric pressure 

near Iceland and near the Azores. On average, 

a westerly current, between the Icelandic low 

pressure area and the Azores high pressure 

area, carries cyclones with their associated 

frontal systems towards Europe. However, the 

pressure difference between Iceland and the 

Azores fluctuates on time scales of days to 

decades, and can be reversed at times. It is the 

dominant mode of winter climate variability in 

the North Atlantic region, ranging from central 

North America to Europe.

O

Ocean conveyor belt

The theoretical route by which water circulates 

around the entire global ocean, driven by wind 

and the thermohaline circulation.

Opportunity

An opportunity is a situation or circumstance 

to decrease the gap between the market 

potential of any technology or practice and the 

economic potential, socio-economic potential, 

or technological potential.

Opportunity cost

The cost of an economic activity forgone by the 

choice of another activity.

Ozone (O3)

Ozone, the triatomic form of oxygen (O3), 

is a gaseous atmospheric constituent. In the 

troposphere, it is created both naturally and 

by photochemical reactions involving gases 

resulting from human activities (photochemical

“smog”). In high concentrations, tropospheric 

ozone can be harmful to a wide-range of 

living organisms. Tropospheric ozone acts as 

a greenhouse gas. In the stratosphere, ozone 

is created by the interaction between solar 
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192

ultraviolet radiation and molecular oxygen 

(O2). Stratospheric ozone plays a decisive 

role in the stratospheric radiative balance. Its 

concentration is highest in the ozone layer. 

Depletion of stratospheric ozone, due to 

chemical reactions that may be enhanced by 

climate change, results in an increased groundlevel flux of ultraviolet-B radiation. See also 

Montreal Protocol and ozone layer.

Ozone layer

A group of human-made chemicals composed 

only of carbon and fluorine, introduced as 

alternatives (like hydroflourocarbons) to ozone

depleting substances. PFCs are emitted as byproducts of industrial processes, and they are 

used in manufacturing. While PFCs do not 

harm the stratospheric ozone layer, they are 

powerful greenhouse gases which high global 

warming potential. Examples of PFCs are CF4 

and C2F6. See Montreal Protocol. 

P

Parameterization

In climate models, this term refers to the 

technique of representing processes-that 

cannot be explicitly resolved at the spatial or 

temporal resolution of the model (sub-grid scale 

processes)-by relationships between the areaor time-averaged effect of such sub-grid-scale 

processes and the larger scale flow.

Pareto criterion/Pareto optimum

A requirement or status that an individual’s 

welfare could not be further improved without 

making others in the society worse off.

Particulates

Very small solid exhaust particles emitted 

during the combustion of fossil and biomass

fuels. Particulates may consist of a wide variety 

of substances. Of greatest concern for health are 

particulates of less than or equal to 10nm and 

2.5 nm in diameter, usually designated as PM10 

and PM2.5, respectively.

Pathogen17

An agent that causes disease, especially a 

living microorganism such as a bacterium 

or fungus.

Perfluorocarbons (PFCs)

A group of human-made chemicals composed 

only of carbon and fluorine, introduced as 

alternatives (like hydroflourocarbons) to ozone

depleting substances. PFCs are emitted as byproducts of industrial processes, and they are 

used in manufacturing. While PFCs do not 

harm the stratosphereic ozone layer, they are 

powerful greenhouse gases which high global 

warming potential. Examples of PFCs are CF4

and C2F6.

Permafrost

Perennially frozen ground that occurs 

wherever the temperature remains below 

0°C for several years.

Photochemical smog

A mix of photochemical oxidant air pollutants 

produced by the reaction of sunlight with primary 

air pollutants, especially hydrocarbons.

Photosynthesis

Complex process that takes place in living green 

plant cells that combines radiant energy from 

the sun with water (H20) and carbon dioxide

(CO2) to produce oxygen (O2) and sugar, such 

as glucose (C6H12O6).

Point-source pollution

Pollution resulting from any confined, discrete 

source, such as a pipe, ditch, tunnel, well, container, 

concentrated animal feeding operation, or floating 

craft. See also non-point source pollution.

Precursors

A term in photochemistry meaning a compound 

antecedent to a pollutant. For example, volatile 

organic compounds (VOCs) and nitric oxides 

of nitrogen react in sunlight to form ozone or 

17 The American Heritage Dictionary, Fourth Edition. 

Retrieved November 21, 2007 from http://dictionary.

reference.com/browse/pathogen.
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

other photochemical oxidants. As such, VOCs 

and oxides of nitrogen are precursors.

Present value cost

The sum of all costs over all time periods, with 

future costs discounted.

Projection (generic)

A projection is a potential future evolution of 

a quantity or set of quantities, often computed 

with the aid of a model. Projections are 

distinguished from “predictions” in order to 

emphasize that projections involve assumptions 

concerning, for example, future socio-economic 

and technological developments that may or 

may not be realized, and are therefore subject 

to substantial uncertainty. See also climate 

projection and climate prediction.

Proxy

A proxy climate indicator is a local record that 

is interpreted, using physical and biophysical 

principles, to represent some combination 

of climate-related variations back in time. 

Climate-related data derived in this way are 

referred to as proxy data. Examples of proxies 

are tree ring records, characteristics of corals, 

and various data derived from ice cores.

Q

QALY (Quality Adjusted Life Year)18

A measure of the outcome of actions (either 

individual or treatment interventions) in terms 

of their health impact. If an action gives a person 

an extra year of healthy life expectancy, that 

counts as one QALY. If an action gives a person 

an extra year of unhealthy life expectancy 

(partly disabled or in some distress), it has a 

value of less than one. Death is rated at zero.

18 Australian Institute of Health and Welfare. “Australia’s Health 1996” glossary. Retrieved November 

21, 2007 from http://www.aihw.gov.au/publications/

health/ah96/ah96-x04.html.

Quality of life19

A scientific measure of personal well-being. 

Categories used to define place-specific quality 

of life include the inter-related categories 

of economic conditions; natural resources, 

environment, and amenities; human health; 

public and private infrastructure; government 

and public safety; and social and cultural 

resources.

R

Radiative forcing

Radiative forcing is the change in the net 

vertical irradiance (expressed in Wm-2) at 

the tropopause due to an internal change 

or a change in the external forcing of the 

climate system, for example, a change in the 

concentration of carbon dioxide or the output of 

the Sun. Usually, radiative forcing is computed 

after allowing for stratospheric temperatures 

to readjust to radiative equilibrium, but with 

all tropospheric properties held fixed at their 

unperturbed values.

Rangelands

Lands (mostly grasslands) that support the 

growth of plants that provide food (i.e., forage) 

for grazing or browsing animals.

Range shifts

Climate change-induced changes in the 

geographical distributions of plants, animals 

and ecosystems

Rapid climate change

The non-linearity of the climate system may 

lead to rapid climate change, sometimes 

called abrupt events or even surprises. Some 

such abrupt events may be imaginable, 

such as a dramatic reorganization of the 

thermohaline circulation, rapid deglaciation, 

or massive melting of permafrost leading to 

fast changes in the carbon cycle. Others may 

be truly unexpected, as a consequence of a 

strong, rapidly changing forcing of a nonlinear system.

19 Modified from text within Chapter 5 of this document.
The U.S. Climate Change Science Program Glossary and Acronyms 

194

Reference scenario

See baseline/reference.

Reinsurance

The transfer of a portion of primary insurance 

risks to a secondary tier of insurers (reinsurers); 

essentially “insurance for insurers.”

Relative sea level

Sea level measured by a tide gauge with respect 

to the land upon which it is situated. See also 

mean sea level.

Reservoir

A component of the climate system, other than 

the atmosphere, that has the capacity to store, 

accumulate, or release a substance of concern 

(e.g., carbon or a greenhouse gas). Oceans, 

soils, and forests are examples of carbon 

reservoirs. The term also means an artificial or 

natural storage place for water, such as a lake, 

pond, or aquifer, from which the water may be 

withdrawn for such purposes as irrigation or 

water supply.

Resilience

Amount of change a system can undergo 

without changing state.

Response time

The response time or adjustment time is the 

time needed for the climate system or its 

components to re-equilibrate to a new state, 

following a forcing resulting from external 

and internal processes or feedbacks. It is very 

different for various components of the climate 

system. The response time of the troposphere 

is relatively short, from days to weeks, whereas 

the stratosphere comes into equilibrium 

on a time scale of typically a few months. 

Due to their large heat capacity, the oceans 

have a much longer response time, typically 

decades, but up to centuries or millennia. 

The response time of the strongly coupled 

surface-troposphere system is, therefore, 

slow compared to that of the stratosphere, 

and mainly determined by the oceans. The 

biosphere may respond fast (e.g., to droughts), 

but also very slowly to imposed changes. 

Revealed preference20

The use of the value of expenditure to “reveal” 

the preference of a consumer or group of 

consumers for the bundle of goods they 

purchase compared to other bundles of equal 

or smaller value.

Rodent-borne disease21

Disease that is transmitted between hosts by a 

rodent (e.g., bubonic plague, hantavirus).

Runoff

That part of precipitation that does not evaporate 

and is not transpired.

S

Salinization

The accumulation of salts in soils.

Salmonella22

There are many different kinds of Salmonella 

bacteria. They pass from the feces of people 

or animals to other people or other animals 

and can cause diarrheal illness in humans. For 

over 100 years, Salmonella have been known 

to cause illness. They were discovered by an 

American scientist named Salmon, for whom 

they are named.

Saltwater intrusion/encroachment

Displacement of fresh surface water or ground 

water by the advance of saltwater due to its greater 

density, usually in coastal and estuarine areas.

Scenario (generic)

A plausible and often simplified description of 

how the future may develop, based on a coherent 

and internally consistent set of assumptions 

about key driving forces (e.g., rate of technology 

20 Deardorff’s Glossary of International Economics. 

Retrieved November 21, 2007 from http://wwwpersonal.umich.edu/~alandear/glossary/r.html.

21 Modified from definition of vector-borne disease. 

22 Modified from information on the CDC’s website 

retrieved November 21, 2007 from http://www.

cdc.gov/nczved/dfbmd/disease_listing/salmonellosis_gi.html. 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

change, prices) and relationships. Scenarios are 

neither predictions nor forecasts and sometimes 

may be based on a “narrative storyline.” 

Scenarios may be derived from projections, but 

are often based on additional information from 

other sources. See also SRES scenarios, climate 

scenario, and emission scenarios.

Sea level rise

An increase in the mean level of the ocean. 

Eustatic sea level rise is a change in global 

average sea level brought about by an alteration 

to the volume of the world ocean. Relative sea 

level rise occurs where there is a net increase 

in the level of the ocean relative to local land 

movements. Climate modelers largely concentrate 

on estimating eustatic sea level change. Impact 

researchers focus on relative sea level change.

Seawall

A human-made wall or embankment along a 

shore to prevent wave erosion.

Semi-arid regions

Ecosystems that have more than 250 mm 

precipitation per year but are not highly 

productive; usually classified as rangelands.

Sensitivity

Sensitivity is the degree to which a system 

is affected, either adversely or beneficially, 

by climate-related stimuli. The effect may be 

direct (e.g., a change in crop yield in response 

to a change in the mean, range, or variability of 

temperature) or indirect (e.g., damages caused 

by an increase in the frequency of coastal 

flooding due to sea level rise). 

Sequential decision making

Stepwise decision making aiming to identify 

short-term strategies in the face of long-term 

uncertainties, by incorporating additional 

information over time and making midcourse corrections.

Sequestration

The process of increasing the carbon content of 

a carbon reservoir other than the atmosphere. 

Biological approaches to sequestration 

include direct removal of carbon dioxide from 

the atmosphere through land-use change, 

afforestation, reforestation, and practices that 

enhance soil carbon in agriculture. Physical 

approaches include separation and disposal 

of carbon dioxide from flue gases or from 

processing fossil fuels to produce hydrogen and 

carbon dioxide-rich fractions, as well as longterm storage in depleted oil and gas reservoirs, 

coal seams, and saline aquifers. 

Sink

Any process, activity or mechanism that 

removes a greenhouse gas, an aerosol, or a 

precursor of a greenhouse gas or aerosol from 

the atmosphere.

Smog23

Air pollution typically associated with 

oxidants.

Snowpacks

A seasonal accumulation of slow-melting 

snow.

Social cost

The social cost of an activity includes the value 

of all the resources used in its provision. Some 

of these are priced and others are not. Nonpriced resources are referred to as externalities. 

It is the sum of the costs of these externalities 

and the priced resources that makes up the 

social cost. See total cost.

23 U.S. EPA. “Terms of Environment Glossary.” Retrieved November 21, 2007 from http://www.epa.

gov/OCEPAterms/sterms.html.
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196

Social indicators24

Broad, standardized measures of the quality 

of life or other socio-economic conditions of 

geographic areas such as nations, metropolitan 

areas, or other areas; used to assess health 

conditions, educational levels, food availability, 

violence, and other conditions.

Socio-economic potential

Represents the level of greenhouse gasmitigation

that would be reached by overcoming social and 

cultural obstacles to using technologies that are 

cost effective. 

Socio-economic scenarios

Scenarios concerning future conditions in 

terms of population, Gross Domestic Product 

and other socio-economic factors relevant 

to understanding the implications of climate 

change. See SRES scenarios.

Solar radiation

Energy from the sun, including ultra-violet 

radiation, visible radiation, and infrared 

radiation; also referred to as short-wave 

radiation.

Source

Any process, activity, or mechanism that 

releases a greenhouse gas, an aerosol, or a 

precursor of a greenhouse gas or aerosol into 

the atmosphere.

Southern Oscillation

See El Niño Southern Oscillation.

Spatial and temporal scales

Climate may vary on a large range of spatial and 

temporal scales. Spatial scales may range from 

local (less than 100,000 km2), through regional 

(100,000 to 10 million km2), to continental (10 

to 100 million km2). Temporal scales may range 

from seasonal to geological (up to hundreds of 

millions of years).

24 Methods for Social Researchers in Developing 

Countries. Glossary. Retrieved November 21, 2007 

from http://srmdc.net/glossary.htm#s.

SRES scenarios

SRES scenarios are emissions scenarios 

developed by Nakicenovic et al. (2000) and 

used, among others, as a basis for the climate 

projections in the IPCC WGI contribution to 

the Third Assessment Report (IPCC, 2001). 

The following terms are relevant for a better 

understanding of the structure and use of the 

set of SRES scenarios:

(Scenario) Family: Scenarios that have a 

similar demographic, societal, economic, and 

technical-change storyline. Four scenario

families comprise the SRES scenario set: 

A1, A2, B1, and B2.

(Scenario) Group: Scenarios within a 

family that reflect a consistent variation 

of the storyline. The A1 scenario family

includes four groups designated as A1T, 

A1C, A1G, and A1B that explore alternative 

structures of future energy systems.

In the Summary for Policymakers of 

Nakicenovic et al. (2000), the A1C and A1G 

groups have been combined into one “FossilIntensive” A1FI scenario group. The other 

three scenario families consist of one group 

each. The SRES scenario set reflected in the 

Summary for Policymakers of Nakicenovic 

et al. (2000) thus consist of six distinct 

scenario groups, all of which are equally 

sound and together capture the range of 

uncertainties associated with driving forces 

and emissions.

(Scenario) Illustrative: A scenario that 

is illustrative for each of the six scenario 

groups ref lected in the Summary for 

Policymakers of Nakicenovic et al. (2000). 

They include four revised scenario markers 

for the scenario groups A1B, A2, B1, B2, 

and two additional scenarios for the A1FI 

and A1T groups. All scenario groups are 

equally sound.

(Scenario) Marker: A scenario that was 

originally posted in draft form on the SRES 

website to represent a given scenario family. 

The choice of markers was based on which of 

the initial quantifications best reflected the 

storyline, and the features of specific models. 

Markers are no more likely than other 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

scenarios, but are considered by the SRES 

writing team as illustrative of a particular 

storyline. They are included in revised 

form in Nakicenovic et al. (2000). These 

scenarios have received the closest scrutiny 

of the entire writing team via the SRES open 

process. Scenarios have also been selected to 

illustrate the other two scenario groups.

(Scenario) Storyline: A na r rat ive 

description of a scenario (or family of 

scenarios) highlighting the main scenario

characteristics, relationships between key 

driving forces, and the dynamics of their 

evolution.

Stabilization

The achievement of stabilization of atmospheric 

concentrations of one or more greenhouse gases 

(e.g., carbon dioxide or a CO2-equivalent basket 

of greenhouse gases).

Stakeholder

A person or an organization that has a legitimate 

interest in a project or entity, or would be 

affected by a particular action or policy.

Stated preference25

Stated preference approaches, sometimes 

referred to as direct valuation approaches, 

are survey methods that estimate the value 

individuals place on particular non-market 

goods based on choices they make in 

hypothetical markets.

Stimuli (climate-related)

All the elements of climate change, including 

mean climate characteristics, climate 

variability, and the frequency and magnitude 

of extremes.

Storm surge

The temporary increase, at a particular 

locality, in the height of the sea due to extreme 

meteorological conditions (low atmospheric 

pressure and/or strong winds). The storm surge 

is defined as being the excess above the level 

expected from the tidal variation alone at that 

time and place.

25 SAP 4.6. 

Storyline

See SRES scenarios.

Stratosphere

The highly stratified region of the atmosphere 

above the troposphere extending from about 10 

km (ranging from 9 km in high latitudes to 16 

km in the tropics on average) to about 50 km.

Streamflow

Water within a river channel, usually expressed 

in m3 sec-1.

Submergence

A rise in the water level in relation to the land, 

so that areas of formerly dry land become 

inundated; it results either from a sinking of the 

land or from a rise of the water level.

Subsidence

The sudden sinking or gradual downward 

settling of the Earth’s surface with little or no 

horizontal motion.

Subsidy

Direct payment from the government to an 

entity, or a tax reduction to that entity, for 

implementing a practice the government wishes 

to encourage. Greenhouse gas emissions can 

be reduced by lowering existing subsidies that 

have the effect of raising emissions, such as 

subsidies for fossil fuel use, or by providing 

subsidies for practices that reduce emissions or 

enhance sinks (e.g., for insulation of buildings 

or planting trees).

Sulfur hexafluoride (SF6)

A colorless gas that is soluble in alcohol and 

ether, and slightly soluble in water. It is a very 

powerful greenhouse gas used primarily in 

electrical transmission and distribution systems, 

and as a dielectric in electronics.

Sustainable development

Development that meets the needs of the present 

without compromising the ability of future 

generations to meet their own needs.
The U.S. Climate Change Science Program Glossary and Acronyms 

198

T

Technological potential

The amount by which it is possible to create 

a reduction in greenhouse gas emissions

or an improvement in energy efficiency by 

implementing a technology or practice that has 

already been demonstrated.

Technology

A piece of equipment or a technique for 

performing a particular activity.

Thermal erosion

The erosion of ice-rich permafrost by the 

combined thermal and mechanical action of 

moving water.

Thermal expansion

In connection with sea level, this refers to the 

increase in volume (and decrease in density) 

that results from warming water. A warming 

of the ocean leads to an expansion of the ocean 

volume and hence an increase in sea level.

Thermohaline circulation

Large-scale, density-driven circulation in the 

ocean, caused by differences in temperature 

and salinity. In the North Atlantic, the 

thermohaline circulation consists of warm 

surface water flowing northward and cold 

deepwater flowing southward, resulting in a 

net poleward transport of heat. The surface 

water sinks in highly restricted sinking regions 

located in high latitudes.

Threshold

The level of magnitude of a system process 

at which sudden or rapid change occurs. A 

point or level at which new properties emerge 

in an ecological, economic or other system, 

invalidating predictions based on mathematical 

relationships that apply at lower levels.

Time scale

The characteristic time it takes for a process to 

be expressed. 

Time-series studies26

Studies done using a set of data that expresses a 

particular variable measured over time.

Top-down models

The terms “top” and “bottom” are shorthand for 

aggregate and disaggregated models. The topdown label derives from how modelers applied 

macro-economic theory and econometric 

techniques to historical data on consumption, 

prices, incomes, and factor costs to model final 

demand for goods and services, and supply 

from main sectors, like the energy sector, 

transportation, agriculture, and industry. 

Therefore, top-down models evaluate the 

system from aggregate economic variables, as 

compared to bottom-up models that consider 

technological options or project specific 

climate change mitigation policies. Some 

technology data were, however, integrated into 

top-down analysis and so the distinction is not 

that clear-cut.

Total cost

All items of cost added together. The total cost 

to society is made up of both the external cost 

and the private cost, which together are defined 

as social cost.

Trade effects

Economic impacts of changes in the purchasing 

power of a bundle of exported goods of a 

country for bundles of goods imported from 

its trade partners. Climate policies change the 

relative production costs and may change terms 

of trade substantially enough to change the 

ultimate economic balance.

Transient climate response

The globally averaged surface air temperature 

increase, averaged over a 20-year period, 

centered at the time of CO2 doubling (i.e., at 

year 70 in a 1 percent per year compound CO2

increase experiment with a global coupled 

climate model).

26 Modified from Millennium Ecosystem Assessment, 

2005. “Time-Series Data.” 
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Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Transpiration

The process by which water vapor is lost to the 

atmosphere from living plants; the term can 

also be used to describe the quantity of water 

dissipated as such. 

Troposphere

The lowest part of the atmosphere from the 

surface to about 10 km in altitude in midlatitudes (ranging from 9 km in high latitudes 

to 16 km in the tropics on average) where 

clouds and “weather” phenomena occur. In the 

troposphere, temperatures generally decrease 

with height. 

Tropopause

The boundary between the troposphere and the 

stratosphere.

Tundra

A treeless, level, or gently undulating plain 

characteristic of arctic and subarctic regions.

U

Uncertainty

An expression of the degree to which a value

(e.g., the future state of the climate system) is 

unknown. Uncertainty can result from lack of 

information or from disagreement about what is 

known or even knowable. It may have many types 

of sources, from quantifiable errors in the data 

to ambiguously defined concepts or terminology, 

or uncertain projections of human behavior. 

Uncertainty can therefore be represented by 

quantitative measures (e.g., a range of values 

calculated by various models) or by qualitative 

statements (e.g., reflecting the judgment of a 

team of experts). See Moss and Schneider (2000). 

See also confidence and likelihood.

Unique and threatened systems

Entities that are confined to a relatively narrow 

geographical range but can affect other, often 

larger entities beyond their range; a narrow 

geographical range points to sensitivity to 

environmental variables, including climate, 

and therefore attests to potential vulnerability 

to climate change.

United Nations Framework Convention on 

Climate Change (UNFCCC)

The Convention was adopted on 9 May 1992, in 

New York, and signed at the 1992 Earth Summit 

in Rio de Janeiro by more than 150 countries 

and the European Community. Its ultimate 

objective is the “stabilization of greenhouse 

gas concentrations in the atmosphere at a level 

that would prevent dangerous anthropogenic 

interference with the climate system.” It 

contains commitments for all Parties. Under the 

Convention, Parties included in Annex I aim to 

return greenhouse gas emissions not controlled 

by the Montreal Protocol to 1990 levels by the 

year 2000. The Convention entered into force in 

March 1994. See also Kyoto Protocol.

Uptake

The addition of a substance into a reservoir. 

For example, the uptake of carboncontaining substances is often called (carbon) 

sequestration.

Urban heat island effect27

The urban heat island effect is a measurable 

increase in ambient urban air temperatures 

resulting primarily from the replacement of 

vegetation with buildings, roads, and other heatabsorbing infrastructure. The heat island effect 

can result in significant temperature differences 

between rural and urban areas.

Urbanization

The conversion of land from a natural state 

or managed natural state (such as agriculture) 

to cities; a process driven by net rural-tourban migration through which an increasing 

percentage of the population in any nation 

or region come to live in settlements that are 

defined as “urban centers.”

27 U.S. EPA. “Heat Island Glossary.” Retrieved November 21, 2007 from http://www.epa.gov/hiri/

resources/glossary.html#h.
The U.S. Climate Change Science Program Glossary and Acronyms 

200

V

Valley fever (Coccidiomycosis)28

An infectious respiratory disease of humans and 

other animals caused by inhaling the fungus 

Coccidioides immitis. It is characterized by 

fever and various respiratory symptoms. Also 

called coccidiomycosis. 

Valuation29

The process of expressing a value for a 

particular good or service in a certain context 

(e.g., of decision-making) usually in terms of 

something that can be counted, often money, 

but also through methods and measures from 

other disciplines (sociology, ecology). See also 

values.

Value added

The net output of a sector after adding up all 

outputs and subtracting intermediate inputs.

Value of a statistical life (VSL)30

The sum of what people would pay to reduce 

their risk of dying by small amounts that, 

together, add up to one statistical life.

Values

Worth, desirability, or utility based on 

individual preferences. The total value of 

any resource, is the sum of the values of the 

different individuals involved in the use of the 

resource. The values, which are the foundation 

of the estimation of costs, are measured in 

terms of the willingness to pay (WTP) by 

individuals to receive the resource, or by the 

willingness of individuals to accept payment 

(WTA) to part with the resource.

28 The American Heritage Dictionary of the English 

Language, Fourth Edition. Retrieved November 21, 

2007 from http://dictionary.reference.com/browse/

valley fever.

29 Millennium Ecosystem Assessment, 2005 glossary. 

30 SAP 4.6. 

Vector

An organism, such as an insect, that transmits 

a pathogen from one host to another. See also 

vector-borne diseases.

Vector-borne diseases

Disease that is transmitted between hosts by a 

vector organism such as a mosquito or tick (e.g., 

malaria, dengue fever, and leishmaniasis).

Volatile organic compounds (VOCs)31

Organic compounds that evaporate readily 

into the air. VOCs include substances such 

as benzene, toluene, methylene chloride, and 

methyl chloroform.

Vulnerability

The degree to which a system is susceptible 

to, or unable to cope with, adverse effects of 

climate change, including climate variability 

and extremes. Vulnerability is a function of 

the character, magnitude, and rate of climate 

variation to which a system is exposed, its 

sensitivity, and its adaptive capacity.

W

Waterborne diseases32

Diseases contracted through contact with water 

that is infected with any of numerous pathogens 

including Vibrio cholerae, Campylobacter, 

Salmonella, Shigella, and the diarrheogenic 

Escherichia coli. 

Water consumption

Amount of extracted water irretrievably lost 

during its use (by evaporation and goods 

production).Water consumption is equal to 

water withdrawal minus return flow.

31 Agency for Toxic Substances & Disease Registry 

(ATSDR). “ATSDR Glossary of Terms.” Retrieved 

November 21, 2007 from http://www.atsdr.cdc.gov/

glossary.html#G-T-. 

32 Modified from CDC. “Preventing Bacterial Waterborne Diseases.” Retrieved November 21, 2007 

from http://www.cdc.gov/ncidod/dbmd/diseaseinfo/

waterbornediseases_t.htm. 
201

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

Watershed33

The land area that drains into a particular 

watercourse or body of water. Sometimes used 

to describe the dividing line of high ground 

between two catchment basins.

Water stress

A country is water-stressed if the available 

freshwater supply relative to water withdrawals

acts as an important constraint on development. 

Withdrawal exceeding 20 percent of renewable 

water supply has been used as an indicator of 

water stress.

Water-use efficiency

Carbon gain in photosynthesis per unit water lost 

in evapotranspiration. It can be expressed on a 

short-term basis as the ratio of photosynthetic 

carbon gain per unit transpirational water loss, 

or on a seasonal basis as the ratio of net primary 

production or agricultural yield to the amount 

of available water.

Water withdrawal

Amount of water extracted from water bodies.

Welfare

An economic term used to describe the state 

of well-being of humans on an individual or 

collective basis. The constituents of well-being

are commonly considered to include materials 

to satisfy basic needs, freedom and choice, 

health, good social relations, and security.

Well-being 34

A context- and situation-dependent state, 

comprising basic material for a good life, 

freedom and choice, health and bodily wellbeing, good social relations, security, peace of 

mind, and spiritual experience.

33 M i l l e n n i u m E c o s y s t e m A s s e s s m e n t , 

2005 glossary.

34 Modified from the Millennium Ecosystem Assessment, Current State and Trends Assessment Glossary, 2005.

West Nile virus35

West Nile virus (WNV) is a single-stranded 

RNA virus of the family Flaviviridae, genus 

Flavivirus. The main lifecycle of WNV is 

between birds and insects. Humans are most 

often infected by a bite from an infected 

mosquito. Most people infected with WNV 

don’t show any symptoms, whereas those that 

do are often diagnosed with West Nile fever 

which can last up to two weeks. 

Z

Zoonoses

Diseases and infections which are naturally 

transmitted between vertebrate animals and 

people. See also zoonotic disease.

Zoonotic disease

A disease that normally exists in other 

vertebrates but also infects humans, such as 

dengue fever, avian flu, West Nile virus and 

bubonic plague.

35 Modified from CDC. “West Nile Virus.” Retrieved 

November 21, 2007 from http://www.cdc.gov/ncidod/dvbid/westnile/index.htm. 
The U.S. Climate Change Science Program Glossary and Acronyms 

202

References

IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the 

Third Assessment Report of the Intergovernmental Panel on Climate Change. J. T. Houghton, 

Y. Ding, D.J. Griggs, M. Noguer, P. J. van der Linden and D. Xiaosu Eds. Cambridge University 

Press, UK. pp 944

IPCC, 2007: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth 

Assessment Report of the IntergovernmentalPanel on Climate Change. B. Metz, O.R. Davidson, 

P.R. Bosch, R. Dave, L.A. Meyer (eds). Cambridge University Press, Cambridge, UK.

Moss, R.H., and S.H. Schneider, 2000: Towards Consistent Assessment and Reporting of 

Uncertainties in the IPCC TAR. In: Pachauri, R., and Taniguchi, T., eds., Cross-Cutting Issues 

in the IPCC Third Assessment Report. Global Industrial and Social Progress Research Institute 

(Tokyo) for IPCC.

Nakićenović, N., J. Alcamo, G. Davis, B. de Vries, J. Fenhann, S. Gaffin, K. Gregory, A. Grübler,

T.Y. Jung, T. Kram, E.L. LaRovere, L. Michaelis, S. Mori, T. Morita, W. Pepper, H. Pitcher, L. 

Price, K. Raihi, A. Roehrl, H.-H. Rogner, A. Sankovski, M. Schlesinger, P. Shukla, S. Smith, R. 

Swart, S. van Rooijen, N. Victor and Z. Dadi, 2000: Emissions Scenarios: A Special Report of 

Working Group III of the Intergovernmental Panel on Climate Change. Cambridge University 

Press, Cambridge, and New York, 599 pp.

United Nations, 1994: United Nations Convention to Combat Desertification (UNCCD). UN 

document number A/AC.241/27, United Nations, New York, NY, USA, 58 pp.

World Meteorological Organization (WMO), 2003: Climate: Into the 21st Century. Burroughs, W. 

ed. Cambridge University Press, Cambridge, UK and New York, NY, USA.
203

Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems

6.2 Acronyms

AAG Association of American Geographers

AAP American Academy of Pediatrics

AIACC Assessment of Impacts and Adaptations to Climate Change

AMR-A North American Region

AR4 IPCC’s Fourth Assessment Report

CCC Canada Climate Center

CCP ICLEI’s Cities for Climate Protection

CCSP Climate Change Science Program

CDC Centers for Disease Control and Prevention

CLIMB Climate’s Long-Term Impacts on Metro Boston

CO2 Carbon Dioxide

CVD Cardiovascular Disease

DHS Department of Homeland Security 

ECHAM4 A model named after the European Centre for Medium Range Weather 

Forecasts (ECMRWF), (giving it the first part of the name—EC), which was 

developed in Hamburg (HAM)

EHE Extreme Heat Event

ENSO El Niño Southern Oscillation

EPA Environmental Protection Agency

FDA Food and Drug Administration 

FEMA Federal Emergency Management Agency

GCM General Circulation Model

GDP Gross Domestic Product

GHG Greenhouse Gas

GIS Geographic Information System

GISS NASA Goddard Institute for Space Studies

ICLEI International Council for Local Environmental Initiatives

IPCC Intergovernmental Panel on Climate Change

MA Millennium Assessment

MM5 Mesoscale Model 

MSA Metropolitan Statistical Area

NAAQS National Ambient Air Quality Standards

NACC U.S. National Assessment of Climate Change
The U.S. Climate Change Science Program Glossary and Acronyms 

204

NAS National Academy of Sciences

NAST National Assessment Synthesis Team

NEG/ECP New England Governors and Eastern Canadian Premiers

NGO Non-gGovernmental Organization

NO Nitric Oxide

NOAA National Oceanic and Atmospheric Administration

NRC National Research Council

NYCHP New York Climate and Health Project

PM Particulate Matter

PM2.5 Particulate Matter (smaller than 2.5 micrometers)

PTSD Post-traumatic Stress Disorder

RADM2 Regional Acid Deposition Model, Version 2

RCM Regional Climate Model

RGGI Regional Greenhouse Gas Initiative

RMNP Rocky Mountain National Park

RPS Renewable Portfolio Standards

SAP Synthesis and Assessment Product

SHELDUS Spatial Hazard Events and Losses Database for the United States

SRES Special Report on Emissions Scenarios

TAR IPCC’s Third Assessment Report

TBE Tick-borne Encephalitis

UHI Urban Heat Island Effect

UNDP United Nations Development Programme

UNEP United Nations Environmental Programme

USBEA United States Bureau of Economic Analysis

USDA U.S. Department of Agriculture

USGCRP United States Global Change Research Program

VBZ Vector-borne and Zoonotic

VEMAP Virtual Earth Map

VOC Volatile Organic Compounds 

VSL Value of Statistical Life

WHO World Health Organization

WTP Willingness to Pay
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