Fourth National
Climate Assessment

Volume II

Impacts, Risks, and Adaptation in the United States
Report-in-Brief

Full report available online at: nca2018.globalchange.gov

Image credit
Front cover: National Park Service; back cover: NASA Earth Observatory image by Joshua Stevens, using Landsat
data from the U.S. Geological Survey.

In August 2018, temperatures soared across the northwestern United States. The heat, combined with dry
conditions, contributed to wildfire activity in several states and Canada. The cover shows the Howe Ridge Fire
from across Lake McDonald in Montana’s Glacier National Park on the night of August 12, roughly 24 hours after
it was ignited by lightning. The fire spread rapidly, fueled by record-high temperatures and high winds, leading
to evacuations and closures of parts of the park. The satellite image on the back cover, acquired on August 15,
shows plumes of smoke from wildfires on the northwestern edge of Lake McDonald.

Wildfires impact communities throughout the United States each year. In addition to threatening individual safety and property, wildfire can worsen air quality locally and, in many cases, throughout the surrounding
region, with substantial public health impacts including increased incidence of respiratory illness (Ch. 13: Air
Quality, KM 2; Ch. 14: Health, KM 1; Ch. 26: Alaska, KM 3). As the climate warms, projected increases in wildfire
frequency and area burned are expected to drive up costs associated with health effects, loss of homes andinfrastructure, and fire suppression (Ch. 6: Forests, KM 1; Ch. 17: Complex Systems, Box 17.4). Increased wildfire
activity is also expected to reduce the opportunity for and enjoyment of outdoor recreation activities, affecting
quality of life as well as tourist economies (Ch. 7: Ecosystems, KM 3; Ch. 13: Air Quality, KM 2; Ch. 14: Tribal, KM 1;
Ch. 19: Southeast, KM 3; Ch. 24: Northwest, KM 4).

Human-caused climate change, land use, and forest management influence wildfires in complex ways (Ch. 17:
Complex Systems, KM 2). Over the last century, fire exclusion policies have resulted in higher fuel availability
in most U.S. forests (CSSR, Ch. 8.3, KF 6). Warmer and drier conditions have contributed to an increase in theincidence of large forest fires in the western United States and Interior Alaska since the early 1980s, a trend thatis expected to continue as the climate warms and the fire season lengthens (Ch. 1: Overview, Figure 1.2k; CSSR,
Ch. 8.3, KF 6). The expansion of human activity into forests and other wildland areas has also increased over the
past few decades. As the footprint of human settlement expands, fire risk exposure to people and property is
expected to increase further (Ch. 5: Land Changes, KM 2).

Fourth National
Climate Assessment

Volume II
Impacts, Risks, and Adaptationin the United States
Repor t-in-Brief

Full report available online at: nca2018.globalchange.gov
This report is in the public domain. Some materials used herein are copyrighted and permission
was granted for their publication in this report. For subsequent uses that include such copyrighted materials, permission for reproduction must be sought from the copyright holder. In all cases,
credit must be given for copyrighted materials. All other materials are free to use with credit tothis report.
First published 2018. Revised June 2019—see errata for details:
https://nca2018.globalchange.gov/downloads/.
Printed in the United States of America

Recommended citation

USGCRP, 2018: Impacts, Risks, and Adaptation in the United States: Fourth National Climate
Assessment, Volume II: Report-in-Brief [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel,
K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program,
Washington, DC, USA, 186 pp. doi: 10.7930/NCA4.2018.RiB

Published by U.S. Government Publishing OfficeInternet: bookstore.gpo.gov; Phone: toll free (866) 512-1800; DC area (202) 512-1800
Fax: (202) 512-2104 Mail: Stop IDCC, Washington, DC 20402-0001
Printed copies of the Report-in-Brief can be ordered online at:https://www.globalchange.gov/browse/reportsii

Federal Steering Committee
David Reidmiller, Chair, U.S. Global Change
Research Program

Daniel Dodgen, Department of Health andHuman Services

Benjamin DeAngelo, Vice Chair, Departmentof Commerce

Noel Gurwick, U.S. Agency for International
Development

Farhan Akhtar, Department of StatePat Jacobberger-Jellison, National Aeronautics andSpace Administration

Daniel Barrie, Department of Commerce
Virginia Burkett, Department of the Interior

Rawlings Miller, Department of Transportation(May – August 2018)

Jennifer Carroll, National Science Foundation

Kurt Preston, Department of Defense

Lia Cattaneo, Department of Transportation(through December 2017)

Margaret Walsh, Department of Agriculture
Tristram West, Department of Energy

Pierre Comizzoli, Smithsonian Institution

Darrell Winner, Environmental Protection Agency

Subcommittee on Global Change Research
Scott Harper, Department of Defense

Virginia Burkett, Acting Chair, Department of
the Interior

William Hohenstein, Department of Agriculture

Gerald Geernaert, Vice Chair,
Department of Energy

Jack Kaye, National Aeronautics and Space
Administration

John Balbus, Department of Health andHuman Services

Dorothy Koch, Department of Energy

Bill Breed, U.S. Agency for International
Development (through February 2018)

Barbara McCann, Department of Transportation

Pierre Comizzoli, Smithsonian Institution

James Reilly, Department of the Interior

Noel Gurwick, U.S. Agency for International
Development (since February 2018)

Trigg Talley, Department of State

Andrew Miller, Environmental Protection Agency

Maria Uhle, National Science Foundation

Wayne Higgins, Department of Commerceiii

Executive Leadership and White House LiaisonsMichael Kuperberg, U.S. Global Change
Research Program

Chloe Kontos, Executive Director, National Scienceand Technology Council

David Reidmiller, U.S. Global Change
Research Program

Kimberly Miller, Office of Management and Budget

Administrative Lead Agency
Department of Commerce / National Oceanic and Atmospheric Administration

iv

NCA4

TABLE OF CONTENTS
FOURTH NATIONAL CLIMATE ASSESSMENTREPORT‑IN-BRIEF

Front Matter
About this Report...............................................................................................1
Guide to the Report............................................................................................4

Summary Findings................................................................................................11
1. Overview...............................................................................................................21
What Has Happened Since the Last National Climate Assessment?..... 56

National Topics ......................................................................................................63
2. Our Changing Climate.................................................................................... 64
3. Water.................................................................................................................. 67
4. Energy Supply, Delivery, and Demand......................................................... 70
5. Land Cover and Land-Use Change.............................................................. 73
6. Forests............................................................................................................... 76
7. Ecosystems, Ecosystem Services, and Biodiversity................................ 79
8. Coastal Effects................................................................................................ 82
9. Oceans and Marine Resources.................................................................... 85
10. Agriculture and Rural Communities............................................................ 88
11. Built Environment, Urban Systems, and Cities.......................................... 92
12. Transportation................................................................................................. 95v

13. Air Quality.......................................................................................................... 98
14. Human Health................................................................................................ 101
15. Tribes and Indigenous Peoples.................................................................. 104
16. Climate Effects on U.S. International Interests....................................... 107
17. Sector Interactions, Multiple Stressors, and Complex Systems......... 110

Regions ................................................................................................................... 115
18. Northeast........................................................................................................ 116
19. Southeast........................................................................................................ 121
20. U.S. Caribbean............................................................................................... 126
21. Midwest........................................................................................................... 131
22. Northern Great Plains................................................................................... 136
23. Southern Great Plains.................................................................................. 141
24. Northwest....................................................................................................... 144
25. Southwest....................................................................................................... 148
26. Alaska.............................................................................................................. 153
27. Hawai‘i and U.S.-Affiliated Pacific Islands................................................ 157

Responses ............................................................................................................. 163
28. Reducing Risks Through Adaptation Actions......................................... 164
29. Reducing Risks Through Emissions Mitigation...................................... 168

Authors and Contributors............................................................................... 173

vi

Report-in-Brief | About This Report

About This Report
The National Climate Assessment

Climate Science Special Report:
NCA4 Volume I

The Global Change Research Act of 1990 mandates that the U.S. Global Change Research
Program (USGCRP) deliver a report to Congress
and the President no less than every four years
that “1) integrates, evaluates, and interprets
the findings of the Program . . .; 2) analyzes theeffects of global change on the natural environment, agriculture, energy production and use,land and water resources, transportation, human health and welfare, human social systems,
and biological diversity; and 3) analyzes current
trends in global change, both human-induced
and natural, and projects major trends for thesubsequent 25 to 100 years.”1

The Climate Science Special Report (CSSR),
published in 2017, serves as the first volume ofNCA4. It provides a detailed analysis of how climate change is affecting the physical earth system across the United States and provides thefoundational physical science upon which muchof the assessment of impacts in this report isbased. The CSSR integrates and evaluates current findings on climate science and discusses
the uncertainties associated with these findings. It analyzes trends in climate change, bothhuman-induced and natural, and projects major
trends to the end of this century. Projectedchanges in temperature, precipitation patterns,
sea level rise, and other climate outcomes are
based on a range of scenarios widely used in
the climate research community, referred to as
Representative Concentration Pathways (RCPs).
As an assessment and analysis of the physicalscience, the CSSR provides important input tothe development of other parts of NCA4 andtheir primary focus on the human welfare, societal, economic, and environmental elementsof climate change. A summary of the CSSR isprovided in Chapter 2 (Our Changing Climate)of this report; the full report can be accessed atscience2017.globalchange.gov.

The Fourth National Climate Assessment(NCA4) fulfills that mandate in two volumes.
This report, Volume II, draws on the foundational science described in Volume I, the Climate Science Special Report (CSSR).2 Volume
II focuses on the human welfare, societal, andenvironmental elements of climate change andvariability for 10 regions and 18 national topics, with particular attention paid to observed
and projected risks, impacts, considerationof risk reduction, and implications under different mitigation pathways. Where possible,
NCA4 Volume II provides examples of actions
underway in communities across the UnitedStates to reduce the risks associated with climate change, increase resilience, and improve
livelihoods.

About the Report-in-Brief

The NCA4 Volume II Report-in-Brief presents
overall Summary Findings, an Overview thatsynthesizes material from the underlying chapters, and Executive Summaries for each chapterof this volume.

This assessment was written to help inform
decision-makers, utility and natural resource
managers, public health officials, emergency
planners, and other stakeholders by providing athorough examination of the effects of climatechange on the United States.

The 186-page Report-in-Brief is available
as a downloadable PDF at https://nca2018.
globalchange.gov/downloads.

1

Fourth National Climate Assessment

Report-in-Brief | About this Report
Report Development, Review,
and Approval Process

Sources Used in This Report

The findings in this report are based on an assessment of the peer-reviewed scientific literature, complemented by other sources (such asgray literature) where appropriate. In addition,authors used well-established and carefully
evaluated observational and modeling datasets,technical input reports, USGCRP’s sustained
assessment products, and a suite of scenario
products. Each source was determined to meetthe standards of the Information Quality Act(see Appendix 2: Information in the Fourth National Climate Assessment).

The National Oceanic and Atmospheric Administration (NOAA) served as the administrative
lead agency for the preparation of this report. A
Federal Steering Committee, composed of representatives from USGCRP agencies, oversaw
the report’s development.
A team of more than 300 federal and nonfederal experts—including individuals fromfederal, state, and local governments, tribes andIndigenous communities, national laboratories,
universities, and the private sector—volunteered their time to produce the assessment,with input from external stakeholders at eachstage of the process. A series of regional engagement workshops reached more than 1,000
individuals in over 40 cities, while listening sessions, webinars, and public comment periods
provided valuable input to the authors. Participants included decision-makers from the public
and private sectors, resource and environmental managers, scientists, educators, representatives from businesses and nongovernmentalorganizations, and the interested public.

Sustained Assessment Products
The USGCRP’s sustained assessment processfacilitates and draws upon the ongoing participation of scientists and stakeholders, enabling
the assessment of new information and insights
as they emerge. The USGCRP led the development of two major sustained assessment
products as inputs to NCA4: The Impacts of
Climate Change on Human Health in the UnitedStates: A Scientific Assessment4 and the Second
State of the Carbon Cycle Report.5 In addition,
USGCRP agencies contributed products that
improve the thoroughness of this assessment,
including the U.S. Department of Agriculture’s
scientific assessment Climate Change, Global
Food Security, and the U.S. Food System;6 NOAA’s
Climate Resilience Tool Kit, Climate Explorer,and State Climate Summaries; the U.S. Environmental Protection Agency’s updated economic
impacts of climate change report;7 and a variety
of USGCRP indicators and scenario productsthat support the evaluation of climate-relatedrisks (see Appendix 3: Data Tools and Scenario
Products).

NCA4 Volume II was thoroughly reviewed byexternal experts and the general public, as wellas the Federal Government (that is, the NCA4
Federal Steering Committee and several roundsof technical and policy review by the 13 federal
agencies of the USGCRP). An expert external
peer review of the whole report was performedby an ad hoc committee of the National Academies of Sciences, Engineering, and Medicine(NASEM).3 Additional information on the development of this assessment can be found in
Appendix 1: Report Development Process.

U.S. Global Change Research Program2

Report-in-Brief | About This Report
USGCRP Scenario Products
As part of the sustained assessment process,federal interagency groups developed a suiteof high-resolution scenario products that spana range of plausible future changes (through at
least 2100) in key environmental parameters.
This new generation of USGCRP scenario products (hosted at https://scenarios.globalchange.
gov) includes•

changes in average and extreme statistics
of key climate variables (for example,
temperature and precipitation),•changes in local sea level rise along theentire U.S. coastline,•

changes in population as a function ofdemographic shifts and migration, and•changes in land use driven by
population changes.

compare and synthesize results across chapters. Where possible, authors have used therange of these scenario products to frame
uncertainty in future climate and associatedeffects as it relates to the risks that are thefocus of their chapters. As discussed briefly
elsewhere in this Front Matter and in moredetail in Appendix 3 (Data Tools and Scenario
Products), future scenarios referred to as RCPs
provide the global framing for NCA4 Volumes
I and II. RCPs focus on outputs (such as emissions and concentrations of greenhouse gases
and particulate matter) that are in turn fed into
climate models. As such, a wide range of future socioeconomic assumptions, at the global
and national scale (such as population growth,
technological innovation, and carbon intensityof energy mix), could be consistent with the
RCPs used throughout NCA4. For this reason,
further guidance on U.S. population and landuse assumptions was provided to authors. See
Appendix 3: Data Tools and Scenario Products,
including Table A3.1, for additional detail on
these scenario products.

USGCRP scenario products help ensure consistency in underlying assumptions across thereport and therefore improve the ability to3

Fourth National Climate Assessment

Report-in-Brief | Guide to the Report

Guide to the Report
Summary Findings

The 12 Summary Findings represent a very
high-level synthesis of the material in the underlying report. They consolidate Key Messages
and supporting evidence from 16 underlying
national-level topic chapters, 10 regional chapters, and 2 response chapters.

Overview

The Overview presents the major findings
alongside selected highlights from NCA4 Volume II, providing a synthesis of material fromthe underlying report chapters.

Key Messages and Traceable Accounts
Chapters are centered around Key Messages,
which are based on the authors’ expert judgment of the synthesis of the assessed literature.
With a view to presenting technical information
in a manner more accessible to a broad audience, this report aims to present findings in thecontext of risks to natural and/or human systems. Assessing the risks to the Nation posed byclimate change and the measures that can betaken to minimize those risks helps users weighthe consequences of complex decisions.

•

What do we expect to happen in the absenceof adaptive action and/or mitigation?

•

How bad could things plausibly get? Are
there important thresholds or tipping points
in the unique context of a given region, sector, and so on?

Each Key Message is accompanied by a Traceable Account that restates the Key Message
found in the chapter text with calibrated confidence and likelihood language (see Table 1).
These Traceable Accounts also document the
supporting evidence and rationale the authors
used in reaching their conclusions, while also
providing information on sources of uncertainty. More information on Traceable Accounts isprovided below.

Since risk can most meaningfully be definedin relation to objectives or societal values, Key
Messages in each chapter of this report aim toprovide answers to specific questions about
what is at risk in a particular region or sector
and in what way. The text supporting each Key
Message provides evidence, discusses implications, identifies intersections between systems
or cascading hazards, and points out paths togreater resilience. Where a Key Message focuses on managing risk, authors considered thefollowing questions:

Our Changing Climate
USGCRP oversaw the production of the Climate
Science Special Report (CSSR): NCA4 Volume
I,2 which assesses the current state of science
relating to climate change and its physicalimpacts. The CSSR is a detailed analysis of
how climate change affects the physical earthsystem across the United States. It presents
foundational information and projections forclimate change that improve consistency acrossWhat do we value? What is at risk?

U.S. Global Change Research Program

What outcomes do we wish to avoid with respect to these valued things?

These considerations are encapsulated in asingle question: What keeps you up at night?
Importantly, climate is only one of many driversof change and risk. Where possible, chaptersprovide information about the dominant sources of uncertainty (such as scientific uncertainty
or socioeconomic factors), as well as information regarding other relevant non-climate
stressors.

Chapter Text

•

•

4

Report-in-Brief | Guide to the Reportanalyses in NCA4 Volume II. The CSSR is thebasis for the physical climate science summary
presented in Chapter 2 (Our Changing Climate)of this report.

Regional Chapters
Responding to public demand for more localized information—and because impacts andadaptation tend to be realized at a more local
level—NCA4 provides greater detail in the regional chapters compared to the national topic
chapters. The regional chapters assess current
and future risks posed by climate change toeach of NCA4’s 10 regions (see Figure 1) andwhat can be done to minimize risk. Challenges,
opportunities, and success stories for managing
risk are illustrated through case studies.

National Topic Chapters
The national topic chapters summarize current
and future climate change related risks andwhat can be done to reduce those risks. Thesenational chapters also synthesize relevant content from the regional chapters. New national
topic chapters for NCA4 include Chapter 13:
Air Quality; Chapter 16: Climate Effects on U.S.
International Interests; and Chapter 17: Sector
Interactions, Multiple Stressors, and Complex Systems.

National Climate Assessment Regions

Figure 1: Map of the ten regions used throughout NCA4.

5

Fourth National Climate Assessment

Report-in-Brief | Guide to the Report
The regions defined in NCA4 are similar to
those used in the Third National Climate Assessment (NCA3),8 with these exceptions: theGreat Plains region, formerly stretching fromthe border of Canada to the border of Mexico,
is now divided into the Northern Great Plains
and Southern Great Plains along the Nebraska–
Kansas border; and content related to the U.S.
Caribbean islands is now found in its own chapter, distinct from the Southeast region.

GHG emissions. The resulting range of projections reflects, in part, the uncertainty thatcomes with quantifying future human activities
and their influence on climate.
The most recent set of climate projections
developed by the international scientific community is classified under four Representative Concentration Pathways, or RCPs.9 A
wide range of future socioeconomic assumptions could be consistent with the RCPs usedthroughout NCA4.

Response Chapters
The response chapters assess the science ofadaptation and mitigation, including benefits,
tradeoffs, and best practices of ongoing adaptation measures and quantification of economic damages that can be avoided by reducing
greenhouse gas emissions. The National Climate Assessment does not evaluate or recommend specific policies.

NCA4 focuses on RCP8.5 as a “higher” scenario,
associated with more warming, and RCP4.5 as a“lower” scenario with less warming. Other RCP
scenarios (e.g., RCP2.6, a “very low” scenario)
are used where instructive, such as in analysesof mitigation science issues. To promote understanding while capturing the context of the
RCPs, authors use the phrases “a higher scenario (RCP8.5)” and “a lower scenario (RCP4.5).”
RCP8.5 is generally associated with higher
population growth, less technological innovation, and higher carbon intensity of the global
energy mix. RCP4.5 is generally associated withlower population growth, more technologicalinnovation, and lower carbon intensity of the
global energy mix. NCA4 does not evaluate thefeasibility of the socioeconomic assumptions
within the RCPs. Future socioeconomic conditions—and especially the relationship between economic growth, population growth,and innovation—will have a significant impact
on which climate change scenario is realized.
The use of RCP8.5 and RCP4.5 as core scenarios is broadly consistent with the range used inNCA3.8 For additional detail on these scenarios
and what they represent, please see Appendix 3 (Data Tools and Scenario Products), as
well as Chapter 4 of the Climate Science Special Report.10

Economic Estimates

To the extent possible, economic estimates inthis report have been converted to 2015 dollars
using the U.S. Bureau of Economic Affairs’ Implicit Price Deflators for Gross Domestic Product, Table 1.1.9. For more information, please
visit: https://bea.gov/national/index.htm.
Where documented in the underlying literature, discount rates in specific estimates in thisassessment are noted next to those projections.

Use of Scenarios

Climate modeling experts develop climate projections for a range of plausible futures. These
projections capture variables such as the relationship between human choices, greenhousegas (GHG) and particulate matter emissions,
GHG concentrations in our atmosphere, andthe resulting impacts, including temperaturechange and sea level rise. Some projections are
consistent with continued dependence on fossil
fuels, while others are achieved by reducing

U.S. Global Change Research Program

6

Report-in-Brief | Guide to the Report
Treatment of Uncertainties: Risk Framing,
Confidence, and Likelihood
Risk Framing
In March 2016, NASEM convened a workshop, Characterizing Risk in Climate Change
Assessments, to assist NCA4 authors in theiranalyses of climate-related risks across theUnited States.11 To help ensure consistency andreadability across chapters, USGCRP developed guidance on communicating the risks andopportunities that climate change presents,
including the treatment of scientific uncertainties. Where supported by the underlying literature, authors were encouraged toTraceable Accounts: Confidence and Likelihood
Throughout NCA4’s assessment of climaterelated risks and impacts, authors evaluated therange of information in the scientific literature
to the fullest extent possible, arriving at a seriesof Key Messages for each chapter. Drawing on
guidance developed by the Intergovernmental Panel on Climate Change (IPCC),12 chapter
authors further described the overall reliability
in their conclusions using these metrics in theirchapter’s Traceable Accounts:•

Confidence in the validity of a finding basedon the type, amount, quality, strength, andconsistency of evidence (such as mechanistic
understanding, theory, data, models, and expert judgment); the skill, range, and consistency of model projections; and the degreeof agreement within the body of literature.

describe the likelihood of the consequences
associated with the range of potential impacts, the character and quality of the consequences, both negative and positive, andthe strength of available evidence;•

Likelihood, which is based on measures of
uncertainty expressed probabilistically (inother words, based on statistical analysis ofobservations or model results or on the authors’ expert judgment).

•

communicate cascading effects among andwithin complex systems; and•quantify risks that could be avoided by taking action.

The author team’s expert assessment of confidence for each Key Message is presented in thechapter’s Traceable Accounts. Where the authors consider it is scientifically justified to report the likelihood of a particular impact within
the range of possible outcomes, Key Messages
in the Traceable Accounts also include a likelihood designation. Traceable Accounts describe
the process and rationale the authors usedin reaching their conclusions, as well as theirconfidence in these conclusions. They provide
additional information about the quality of
information used and allow traceability to data
and resources.

•

describe the full scope of potential climatechange impacts, both negative and positive,
including more extreme impacts that are lesslikely but would have severe consequences,and communicate the range of potential impacts and their probabilities of occurrence;•

Additional detail on how risk is defined for thisreport, as well as how risk-based framing wasused, is available in Chapter 1: Overview (seeBox 1.2: Evaluating Risks to Inform Decisions).

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Fourth National Climate Assessment

Report-in-Brief | Guide to the Report
Confidence Level
Very High
Strong evidence (established theory, multiple sources, confident results, well-documented andaccepted methods, etc.), high consesus
High
Moderate evidence (several sources, some consistency, methods vary and/or documentation
limited, etc.), medium consensus
MediumSuggestive evidence (a few sources, limited consistency, models incomplete, methods emerging,etc.), competing schools of thought
Low
Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation
and/or methods not tested, etc.), disagreement or lack of opinions among experts

Likelihood
Very Likely

LikelyAs Likely as Not

Unlikely

Very Unlikely≥ 9 in 10≥ 2 in 3= 1 in 2≤ 1 in 3≤ 1 in 10

Table 1: This table describes the meaning of the various categories of confidence level and likelihood assessment used inNCA4. The levels of confidence are the same as they appear in the CSSR (NCA4 Volume I). And while the likelihood scale isconsistent with the CSSR, there are fewer categories, as that report relies more heavily on quantitative methods and statistics.
This “binning” of likelihood is consistent with other USGCRP sustained assessment products, such as the Climate and Health
Assessment4 and NCA3.8

Glossary of Terms

NCA4 uses the glossary available on the USGCRP
website (http://www.globalchange.gov/
climate-change/glossary). It was developed forNCA3 and largely draws from the IPCC glossaryof terms. Over time, it has been updated withselected new terms from more recent USGCRP

U.S. Global Change Research Programassessments, including The Impacts of Climate
Change on Human Health in the United States(https://health2016.globalchange.gov/
glossary-and-acronyms) and the Climate
Science Special Report (https://science2017.
globalchange.gov/chapter/appendix-e/).

8

Report-in-Brief | Guide to the Report

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Assessments: Proceedings of a Workshop. Beatty, A., Ed.
The National Academies Press, Washington, DC, 100
pp. http://dx.doi.org/10.17226/23569

12. Mastrandrea, M.D., C.B. Field, T.F. Stocker, O. Edenhofer,
K.L. Ebi, D.J. Frame, H. Held, E. Kriegler, K.J. Mach, P.R.
Matschoss, G.-K. Plattner, G.W. Yohe, and F.W. Zwiers,
2010: Guidance Note for Lead Authors of the IPCC
Fifth Assessment Report on Consistent Treatment ofUncertainties. Intergovernmental Panel on Climate
Change (IPCC), 7 pp. https://www.ipcc.ch/pdf/
supporting-material/uncertainty-guidance-note.pdf

9Fourth National Climate Assessment

Summary Findings

Report-in-Brief | Summary Findings

NCA4 Summary Findings
These Summary Findings represent a high-level synthesis of the material in the underlying
report. The findings consolidate Key Messages and supporting evidence from 16 national-level
topic chapters, 10 regional chapters, and 2 chapters that focus on societal response strategies(mitigation and adaptation). Unless otherwise noted, qualitative statements regarding future
conditions in these Summary Findings are broadly applicable across the range of different
levels of future climate change and associated impacts considered in this report.

1. Communities
Climate change creates new risks and exacerbates existing vulnerabilities in communities acrossthe United States, presenting growing challenges to human health and safety, quality of life, andthe rate of economic growth.
The impacts of climate change are alreadybeing felt in communities across the country.
More frequent and intense extreme weather
and climate-related events, as well as changes
in average climate conditions, are expected tocontinue to damage infrastructure, ecosystems,
and social systems that provide essential benefits to communities. Future climate change
is expected to further disrupt many areas oflife, exacerbating existing challenges to prosperity posed by aging and deteriorating infrastructure, stressed ecosystems, and economic
inequality. Impacts within and across regions

will not be distributed equally. People who are
already vulnerable, including lower-income andother marginalized communities, have lower
capacity to prepare for and cope with extreme
weather and climate-related events and are expected to experience greater impacts. Prioritizing adaptation actions for the most vulnerable
populations would contribute to a more equitable future within and across communities.
Global action to significantly cut greenhousegas emissions can substantially reduce climate-related risks and increase opportunities
for these populations in the longer term.

2. Economy
Without substantial and sustained global mitigation and regional adaptation efforts, climatechange is expected to cause growing losses to American infrastructure and property and impede
the rate of economic growth over this century.
In the absence of significant global mitigation
action and regional adaptation efforts, risingtemperatures, sea level rise, and changes inextreme events are expected to increasingly
disrupt and damage critical infrastructure andproperty, labor productivity, and the vitalityof our communities. Regional economies andindustries that depend on natural resources and favorable climate conditions, such as

U.S. Global Change Research Program

agriculture, tourism, and fisheries, are vulnerable to the growing impacts of climate change.
Rising temperatures are projected to reduce
the efficiency of power generation while increasing energy demands, resulting in higher
electricity costs. The impacts of climate change
beyond our borders are expected to increasingly affect our trade and economy, including
import and export prices and U.S. businesses

12Report-in-Brief | Summary Findings
with overseas operations and supply chains.
Some aspects of our economy may see slightnear-term improvements in a modestly warmer
world. However, the continued warming thatis projected to occur without substantial andsustained reductions in global greenhouse gas
emissions is expected to cause substantial net
damage to the U.S. economy throughout thiscentury, especially in the absence of increased
adaptation efforts. With continued growth inemissions at historic rates, annual losses insome economic sectors are projected to reachhundreds of billions of dollars by the end of the
century—more than the current gross domestic
product (GDP) of many U.S. states.

3. Interconnected Impacts
Climate change affects the natural, built, and social systems we rely on individually and throughtheir connections to one another. These interconnected systems are increasingly vulnerable tocascading impacts that are often difficult to predict, threatening essential services within andbeyond the Nation’s borders.
Climate change presents added risks to interconnected systems that are already exposed
to a range of stressors such as aging and deteriorating infrastructure, land-use changes,
and population growth. Extreme weather andclimate-related impacts on one system can result in increased risks or failures in other critical systems, including water resources, foodproduction and distribution, energy and transportation, public health, international trade,and national security. The full extent of climatechange risks to interconnected systems, manyof which span regional and national boundaries,
is often greater than the sum of risks to individual sectors. Failure to anticipate interconnected
impacts can lead to missed opportunities for
effectively managing the risks of climate change
and can also lead to management responses
that increase risks to other sectors and regions.
Joint planning with stakeholders across sectors, regions, and jurisdictions can help identify
critical risks arising from interaction amongsystems ahead of time.

4. Actions to Reduce Risks
Communities, governments, and businesses are working to reduce risks from and costs associated with climate change by taking action to lower greenhouse gas emissions and implement
adaptation strategies. While mitigation and adaptation efforts have expanded substantially inthe last four years, they do not yet approach the scale considered necessary to avoid substantial
damages to the economy, environment, and human health over the coming decades.
Future risks from climate change depend
primarily on decisions made today. The integration of climate risk into decision-making
and the implementation of adaptation activities
have significantly increased since the Third
National Climate Assessment in 2014, including

in areas of financial risk reporting, capital investment planning, development of engineering
standards, military planning, and disaster risk
management. Transformations in the energy sector—including the displacement of coalby natural gas and increased deployment of13

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Report-in-Brief | Summary Findings
renewable energy—along with policy actions
at the national, regional, state, and local levels are reducing greenhouse gas emissions in
the United States. While these adaptation andmitigation measures can help reduce damages
in a number of sectors, this assessment showsthat more immediate and substantial global
greenhouse gas emissions reductions, as well as
regional adaptation efforts, would be needed to

avoid the most severe consequences in the longterm. Mitigation and adaptation actions alsopresent opportunities for additional benefits
that are often more immediate and localized,
such as improving local air quality and economies through investments in infrastructure.
Some benefits, such as restoring ecosystems
and increasing community vitality, may beharder to quantify.

5. Water
The quality and quantity of water available for use by people and ecosystems across the country
are being affected by climate change, increasing risks and costs to agriculture, energy production,industry, recreation, and the environment.
Rising air and water temperatures and changes in precipitation are intensifying droughts,
increasing heavy downpours, reducing snowpack, and causing declines in surface water
quality, with varying impacts across regions.
Future warming will add to the stress on watersupplies and adversely impact the availabilityof water in parts of the United States. Changes
in the relative amounts and timing of snow andrainfall are leading to mismatches between water availability and needs in some regions, posing threats to, for example, the future reliabilityof hydropower production in the Southwest
and the Northwest. Groundwater depletion isexacerbating drought risk in many parts of theUnited States, particularly in the Southwest andSouthern Great Plains. Dependable and safe
water supplies for U.S. Caribbean, Hawai‘i, andU.S.-Affiliated Pacific Island communities are
threatened by drought, flooding, and saltwatercontamination due to sea level rise. Most U.S.
power plants rely on a steady supply of waterfor cooling, and operations are expected to beaffected by changes in water availability andtemperature increases. Aging and deterioratingwater infrastructure, typically designed for pastenvironmental conditions, compounds the climate risk faced by society. Water management
strategies that account for changing climate
conditions can help reduce present and futurerisks to water security, but implementation ofsuch practices remains limited.

6. Health
Impacts from climate change on extreme weather and climate-related events, air quality, and thetransmission of disease through insects and pests, food, and water increasingly threaten thehealth and well-being of the American people, particularly populations that are already vulnerable.
Changes in temperature and precipitation are
increasing air quality and health risks fromwildfire and ground-level ozone pollution.
Rising air and water temperatures and more

U.S. Global Change Research Program

intense extreme events are expected to increase exposure to waterborne and foodborne
diseases, affecting food and water safety. With
continued warming, cold-related deaths are

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Report-in-Brief | Summary Findings
projected to decrease and heat-related deaths
are projected to increase; in most regions,increases in heat-related deaths are expected
to outpace reductions in cold-related deaths.
The frequency and severity of allergic illnesses, including asthma and hay fever, areexpected to increase as a result of a changing
climate. Climate change is also projected toalter the geographic range and distribution of
disease-carrying insects and pests, exposing
more people to ticks that carry Lyme disease
and mosquitoes that transmit viruses such
as Zika, West Nile, and dengue, with varying
impacts across regions. Communities in theSoutheast, for example, are particularly vulnerable to the combined health impacts from

vector-borne disease, heat, and flooding. Extreme weather and climate-related events canhave lasting mental health consequences in affected communities, particularly if they result
in degradation of livelihoods or community
relocation. Populations including older adults,
children, low-income communities, and somecommunities of color are often disproportionately affected by, and less resilient to, thehealth impacts of climate change. Adaptationand mitigation policies and programs that help
individuals, communities, and states prepare
for the risks of a changing climate reduce thenumber of injuries, illnesses, and deaths fromclimate-related health outcomes.

7. Indigenous Peoples
Climate change increasingly threatens Indigenous communities’ livelihoods, economies, health,and cultural identities by disrupting interconnected social, physical, and ecological systems.
Many Indigenous peoples are reliant on natural resources for their economic, cultural,and physical well-being and are often uniquely affected by climate change. The impacts ofclimate change on water, land, coastal areas,
and other natural resources, as well as infrastructure and related services, are expected toincreasingly disrupt Indigenous peoples’ livelihoods and economies, including agriculture andagroforestry, fishing, recreation, and tourism.
Adverse impacts on subsistence activities havealready been observed. As climate changes continue, adverse impacts on culturally significant
species and resources are expected to resultin negative physical and mental health effects.
Throughout the United States, climate-related

impacts are causing some Indigenous peoples
to consider or actively pursue community relocation as an adaptation strategy, presenting
challenges associated with maintaining culturaland community continuity. While economic,
political, and infrastructure limitations may
affect these communities’ ability to adapt,tightly knit social and cultural networks present
opportunities to build community capacity andincrease resilience. Many Indigenous peoples
are taking steps to adapt to climate change
impacts structured around self-determinationand traditional knowledge, and some tribes are
pursuing mitigation actions through development of renewable energy on tribal lands.

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Report-in-Brief | Summary Findings
8. Ecosystems and Ecosystem Services
Ecosystems and the benefits they provide to society are being altered by climate change, andthese impacts are projected to continue. Without substantial and sustained reductions in global
greenhouse gas emissions, transformative impacts on some ecosystems will occur; some coral
reef and sea ice ecosystems are already experiencing such transformational changes.
Many benefits provided by ecosystems and theenvironment, such as clean air and water, protection from coastal flooding, wood and fiber,crop pollination, hunting and fishing, tourism,
cultural identities, and more will continue tobe degraded by the impacts of climate change.
Increasing wildfire frequency, changes in insect
and disease outbreaks, and other stressors are
expected to decrease the ability of U.S. forests to support economic activity, recreation,and subsistence activities. Climate change has
already had observable impacts on biodiversity,
ecosystems, and the benefits they provide tosociety. These impacts include the migrationof native species to new areas and the spreadof invasive species. Such changes are projected to continue, and without substantial andsustained reductions in global greenhousegas emissions, extinctions and transformative

impacts on some ecosystems cannot be avoided in the long term. Valued aspects of regional
heritage and quality of life tied to ecosystems,
wildlife, and outdoor recreation will changewith the climate, and as a result, future generations can expect to experience and interact
with the natural environment in ways that are
different from today. Adaptation strategies,
including prescribed burning to reduce fuel for
wildfire, creation of safe havens for important
species, and control of invasive species, arebeing implemented to address emerging impacts of climate change. While some targeted
response actions are underway, many impacts,
including losses of unique coral reef and sea ice
ecosystems, can only be avoided by significantly reducing global emissions of carbon dioxide
and other greenhouse gases.

9. Agriculture and Food
Rising temperatures, extreme heat, drought, wildfire on rangelands, and heavy downpours are
expected to increasingly disrupt agricultural productivity in the United States. Expected increases in challenges to livestock health, declines in crop yields and quality, and changes in extreme
events in the United States and abroad threaten rural livelihoods, sustainable food security, andprice stability.
Climate change presents numerous challenges
to sustaining and enhancing crop productivity,
livestock health, and the economic vitality ofrural communities. While some regions (suchas the Northern Great Plains) may see conditions conducive to expanded or alternative
crop productivity over the next few decades,
overall, yields from major U.S. crops are expected to decline as a consequence of increases in

U.S. Global Change Research Program

temperatures and possibly changes in water
availability, soil erosion, and disease and pest
outbreaks. Increases in temperatures during
the growing season in the Midwest are projected to be the largest contributing factor to
declines in the productivity of U.S. agriculture.
Projected increases in extreme heat conditions
are expected to lead to further heat stress forlivestock, which can result in large economic

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losses for producers. Climate change is also expected to lead to large-scale shifts in the availability and prices of many agricultural products
across the world, with corresponding impacts
on U.S. agricultural producers and the U.S.
economy. These changes threaten future gains
in commodity crop production and put rural
livelihoods at risk. Numerous adaptation strategies are available to cope with adverse impactsof climate variability and change on agricultural
production. These include altering what is produced, modifying the inputs used for production, adopting new technologies, and adjusting
management strategies. However, these strategies have limits under severe climate change
impacts and would require sufficient long- andshort-term investment in changing practices.

10. Infrastructure
Our Nation’s aging and deteriorating infrastructure is further stressed by increases in heavy precipitation events, coastal flooding, heat, wildfires, and other extreme events, as well as changes
to average precipitation and temperature. Without adaptation, climate change will continue to degrade infrastructure performance over the rest of the century, with the potential for cascading impacts that threaten our economy, national security, essential services, and health and well-being.
Climate change and extreme weather eventsare expected to increasingly disrupt our Nation’s energy and transportation systems,
threatening more frequent and longer-lasting
power outages, fuel shortages, and service
disruptions, with cascading impacts on other critical sectors. Infrastructure currently
designed for historical climate conditions ismore vulnerable to future weather extremes
and climate change. The continued increase in
the frequency and extent of high-tide flooding
due to sea level rise threatens America’s trillion-dollar coastal property market and public
infrastructure, with cascading impacts to thelarger economy. In Alaska, rising temperaturesand erosion are causing damage to buildings
and coastal infrastructure that will be costly
to repair or replace, particularly in rural areas;
these impacts are expected to grow without

adaptation. Expected increases in the severity
and frequency of heavy precipitation events
will affect inland infrastructure in every region,
including access to roads, the viability of bridges, and the safety of pipelines. Flooding fromheavy rainfall, storm surge, and rising high tides
is expected to compound existing issues withaging infrastructure in the Northeast. Increased
drought risk will threaten oil and gas drilling
and refining, as well as electricity generationfrom power plants that rely on surface waterfor cooling. Forward-looking infrastructure
design, planning, and operational measures andstandards can reduce exposure and vulnerability to the impacts of climate change and reduceenergy use while providing additional nearterm benefits, including reductions in greenhouse gas emissions.

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11. Oceans and Coasts
Coastal communities and the ecosystems that support them are increasingly threatened by the
impacts of climate change. Without significant reductions in global greenhouse gas emissions
and regional adaptation measures, many coastal regions will be transformed by the latter part ofthis century, with impacts affecting other regions and sectors. Even in a future with lower greenhouse gas emissions, many communities are expected to suffer financial impacts as chronic
high-tide flooding leads to higher costs and lower property values.
Rising water temperatures, ocean acidification,
retreating arctic sea ice, sea level rise, high-tide
flooding, coastal erosion, higher storm surge,
and heavier precipitation events threaten our
oceans and coasts. These effects are projected
to continue, putting ocean and marine species
at risk, decreasing the productivity of certain
fisheries, and threatening communities that
rely on marine ecosystems for livelihoods andrecreation, with particular impacts on fishingcommunities in Hawai‘i and the U.S.-AffiliatedPacific Islands, the U.S. Caribbean, and the Gulf
of Mexico. Lasting damage to coastal property
and infrastructure driven by sea level rise andstorm surge is expected to lead to financial
losses for individuals, businesses, and communities, with the Atlantic and Gulf Coasts facing
above-average risks. Impacts on coastal energy
and transportation infrastructure driven by sea
level rise and storm surge have the potential

for cascading costs and disruptions across thecountry. Even if significant emissions reductions occur, many of the effects from sea level
rise over this century—and particularly throughmid-century—are already locked in due to historical emissions, and many communities are
already dealing with the consequences. Actions
to plan for and adapt to more frequent, widespread, and severe coastal flooding, such as
shoreline protection and conservation of coastal ecosystems, would decrease direct losses andcascading impacts on other sectors and partsof the country. More than half of the damages
to coastal property are estimated to be avoidable through well-timed adaptation measures.
Substantial and sustained reductions in global
greenhouse gas emissions would also significantly reduce projected risks to fisheries andcommunities that rely on them.

12. Tourism and Recreation
Outdoor recreation, tourist economies, and quality of life are reliant on benefits provided by our
natural environment that will be degraded by the impacts of climate change in many ways.
Climate change poses risks to seasonal andoutdoor economies in communities across theUnited States, including impacts on economies
centered around coral reef-based recreation,
winter recreation, and inland water-based
recreation. In turn, this affects the well-beingof the people who make their living supportingthese economies, including rural, coastal, andIndigenous communities. Projected increases

U.S. Global Change Research Programin wildfire smoke events are expected to impair
outdoor recreational activities and visibility
in wilderness areas. Declines in snow and ice
cover caused by warmer winter temperatures
are expected to negatively impact the winterrecreation industry in the Northwest, Northern Great Plains, and the Northeast. Somefish, birds, and mammals are expected to shift
where they live as a result of climate change,

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Report-in-Brief | Summary Findings
with implications for hunting, fishing, and otherwildlife-related activities. These and other climate-related impacts are expected to result in
decreased tourism revenue in some places and,for some communities, loss of identity. Whilesome new opportunities may emerge fromthese ecosystem changes, cultural identities
and economic and recreational opportunities

based around historical use of and interaction
with species or natural resources in many areas
are at risk. Proactive management strategies,
such as the use of projected stream temperatures to set priorities for fish conservation, canhelp reduce disruptions to tourist economies
and recreation.

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U.S. Global Change Research Program

20

Overview

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U.S. Global Change Research Program22

1 Overview

Howe Ridge Fire in Montana’s Glacier National Park on August 12, 2018. Photo credit: National Park Service.

Federal Coordinating Lead Author
David Reidmiller, U.S. Global Change Research Program
Chapter Lead
Alexa Jay, U.S. Global Change Research Program
Chapter Authors
Christopher W. Avery, U.S. Global Change Research Program
Daniel Barrie, National Oceanic and Atmospheric Administration
Apurva Dave, U.S. Global Change Research Program
Benjamin DeAngelo, National Oceanic and Atmospheric Administration
Matthew Dzaugis, U.S. Global Change Research Program
Michael Kolian, U.S. Environmental Protection Agency
Kristin Lewis, U.S. Global Change Research Program
Katie Reeves, U.S. Global Change Research Program
Darrell Winner, U.S. Environmental Protection Agency

Recommended Citation for Chapter
Jay, A., D.R. Reidmiller, C.W. Avery, D. Barrie, B.J. DeAngelo, A. Dave, M. Dzaugis, M. Kolian, K.L.M. Lewis,
K. Reeves, and D. Winner, 2018: Overview. In Impacts, Risks, and Adaptation in the United States: Fourth
National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M.
Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC,
USA. doi: 10.7930/NCA4.2018.CH1

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IntroductionE

address physical and mental health challenges driven by climate change and otherenvironmental changes. As Midwestern
farmers adopt new management strategies to reduce erosion and nutrient losses
caused by heavier rains, forest managers
in the Northwest are developing adaptation strategies in response to wildfire
increases that affect human health, water
resources, timber production, fish and wildlife, and recreation. After extensive hurricane damage fueled in part by a warmer
atmosphere and warmer, higher seas, communities in Texas are considering ways torebuild more resilient infrastructure. In the
U.S. Caribbean, governments are developing new frameworks for storm recovery
based on lessons learned from the 2017
hurricane season.

arth’s climate is now changing faster than at any point in the historyof modern civilization, primarily as aresult of human activities. The impactsof global climate change are alreadybeing felt in the United States and areprojected to intensify in the future—but
the severity of future impacts will depend largely on actions taken to reducegreenhouse gas emissions and to adapt
to the changes that will occur. Americans increasingly recognize the risks
climate change poses to their everyday
lives and livelihoods and are beginning to
respond (Figure 1.1). Water managers in
the Colorado River Basin have mobilized
users to conserve water in response toongoing drought intensified by higher
temperatures, and an extension programin Nebraska is helping ranchers reduce
drought and heat risks to their operations. The state of Hawai‘i is developing
management options to promote coral
reef recovery from widespread bleaching
events caused by warmer waters thatthreaten tourism, fisheries, and coastal
protection from wind and waves. To address higher risks of flooding from heavy
rainfall, local governments in southernLouisiana are pooling hazard reduction
funds, and cities and states in the Northeast are investing in more resilient water,energy, and transportation infrastructure.
In Alaska, a tribal health organization
is developing adaptation strategies to

U.S. Global Change Research Program

Climate-related risks will continue to growwithout additional action. Decisions madetoday determine risk exposure for current
and future generations and will either
broaden or limit options to reduce thenegative consequences of climate change.
While Americans are responding in waysthat can bolster resilience and improve
livelihoods, neither global efforts to mitigate the causes of climate change nor
regional efforts to adapt to the impacts
currently approach the scales needed to
avoid substantial damages to the U.S.
economy, environment, and human healthand well-being over the coming decades.

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Americans Respond to the Impacts of Climate Change

Figure 1.1: This map shows climate-related impacts that have occurred in each region since the Third National Climate
Assessment in 2014 and response actions that are helping the region address related risks and costs. These examples areillustrative; they are not indicative of which impact is most significant in each region or which response action might be mosteffective. Source: NCA4 Regional Chapters.

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Report-in-Brief | Overview
Climate shapes where and how we live and theenvironment around us. Natural ecosystems,
agricultural systems, water resources, and thebenefits they provide to society are adapted
to past climate conditions and their naturalrange of variability. A water manager may use
past or current streamflow records to design
a dam, a city could issue permits for coastal
development based on current flood maps,
and an electric utility or a farmer may invest
in equipment suited to the current climate, allwith the expectation that their investments andmanagement practices will meet future needs.

often highest for those that are already vulnerable, including low-income communities, somecommunities of color, children, and the elderly(Ch. 14: Human Health, KM 2; Ch. 15: Tribes, KM
1–3; Ch. 28: Adaptation, Introduction). Climatechange threatens to exacerbate existing socialand economic inequalities that result in higher
exposure and sensitivity to extreme weather
and climate-related events and other changes(Ch. 11: Urban, KM 1). Marginalized populations
may also be affected disproportionately byactions to address the underlying causes andimpacts of climate change, if they are not
implemented under policies that consider
existing inequalities (Ch. 11: Urban, KM 4; Ch.
28: Adaptation, KM 4).

However, the assumption that current andfuture climate conditions will resemble therecent past is no longer valid (Ch. 28: Adaptation, KM 2). Observations collected around theworld provide significant, clear, and compelling
evidence that global average temperature ismuch higher, and is rising more rapidly, thananything modern civilization has experienced,
with widespread and growing impacts (Figure1.2) (CSSR, Ch. 1.9). The warming trend observed
over the past century can only be explainedby the effects that human activities, especiallyemissions of greenhouse gases, have had on the
climate (Ch. 2: Climate, KM 1 and Figure 2.1).

This report draws a direct connection between
the warming atmosphere and the resulting
changes that affect Americans’ lives, communities, and livelihoods, now and in the future. It
documents vulnerabilities, risks, and impacts
associated with natural climate variability andhuman-caused climate change across the United States and provides examples of response
actions underway in many communities. It
concludes that the evidence of human-caused
climate change is overwhelming and continues
to strengthen, that the impacts of climate change
are intensifying across the country, and thatclimate-related threats to Americans’ physical,
social, and economic well-being are rising.
These impacts are projected to intensify—but
how much they intensify will depend on actions
taken to reduce global greenhouse gas emissions and to adapt to the risks from climatechange now and in the coming decades (Ch.
28: Adaptation, Introduction; Ch. 29: Mitigation, KM 3 and 4).

Climate change is transforming where and how
we live and presents growing challenges tohuman health and quality of life, the economy,
and the natural systems that support us. Risks
posed by climate variability and change vary byregion and sector and by the vulnerability ofpeople experiencing impacts. Social, economic,
and geographic factors shape the exposure ofpeople and communities to climate-related
impacts and their capacity to respond. Risks are

U.S. Global Change Research Program

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Report-in-Brief | Overview

Our Changing Climate:
Observations, Causes, andFuture Change

warming, rising, and becoming more acidic, andmarine species are moving to new locations
toward cooler waters. Flooding is becoming
more frequent along the U.S. coastline. Growing
seasons are lengthening, and wildfires are
increasing. These and many other changes areclear signs of a warming world (Figure 1.2) (Ch.
2: Climate, Box 2.2; App. 3: Data & Scenarios,
see also the USGCRP Indicators and EPA Indicators websites).

Observed Change
Observations from around the world show the
widespread effects of increasing greenhousegas concentrations on Earth’s climate. Hightemperature extremes and heavy precipitation
events are increasing. Glaciers and snow cover
are shrinking, and sea ice is retreating. Seas are

California Drought Affects Mountain Snowpack
California’s recent multiyear drought left Tioga Pass in the Sierra Nevada mountain range nearly snowless at the height of winterin January 2015. Photo credit: Bartshé Miller.

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Climate Change Indicators

Figure 1.2: Long-term observations demonstrate the warming trend in the climate system and the effects of increasing
atmospheric greenhouse gas concentrations (Ch. 2: Climate, Box 2.2). This figure shows climate-relevant indicators of change

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Report-in-Brief | Overview

based on data collected across the United States. Upward-pointing arrows indicate an increasing trend; downward-pointing
arrows indicate a decreasing trend. Bidirectional arrows (e.g., for drought conditions) indicate a lack of a definitive national trend.
(Figure caption continued on next page)

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Atmosphere (a–c): (a) Annual average temperatures have increased by 1.8°F across the contiguous United States since thebeginning of the 20th century; this figure shows observed change for 1986–2016 (relative to 1901–1960 for the contiguousUnited States and 1925–1960 for Alaska, Hawai‘i, Puerto Rico, and the U.S. Virgin Islands). Alaska is warming faster than any
other state and has warmed twice as fast as the global average since the mid-20th century (Ch. 2: Climate, KM 5; Ch. 26: Alaska,
Background). (b) The season length of heat waves in many U.S. cities has increased by over 40 days since the 1960s. Hatchedbars indicate partially complete decadal data. (c) The relative amount of annual rainfall that comes from large, single-day
precipitation events has changed over the past century; since 1910, a larger percentage of land area in the contiguous UnitedStates receives precipitation in the form of these intense single-day events.
Ice, snow, and water (d–f): (d) Large declines in snowpack in the western United States occurred from 1955 to 2016. (e) While
there are a number of ways to measure drought, there is currently no detectable change in long-term U.S. drought statistics
using the Palmer Drought Severity Index. (f) Since the early 1980s, the annual minimum sea ice extent (observed in September
each year) in the Arctic Ocean has decreased at a rate of 11%–16% per decade (Ch. 2: Climate, KM 7).
Oceans and coasts (g–i): (g) Annual median sea level along the U.S. coast (with land motion removed) has increased by about
9 inches since the early 20th century as oceans have warmed and land ice has melted (Ch. 2: Climate, KM 4). (h) Fish, shellfish,
and other marine species along the Northeast coast and in the eastern Bering Sea have, on average, moved northward and to
greater depths toward cooler waters since the early 1980s (records start in 1982). (i) Oceans are also currently absorbing morethan a quarter of the carbon dioxide emitted to the atmosphere annually by human activities, increasing their acidity (measured
by lower pH values; Ch. 2: Climate, KM 3).
Land and ecosystems (j–l): (j) The average length of the growing season has increased across the contiguous United Statessince the early 20th century, meaning that, on average, the last spring frost occurs earlier and the first fall frost arrives later;
this map shows changes in growing season length at the state level from 1895 to 2016. (k) Warmer and drier conditions havecontributed to an increase in large forest fires in the western United States and Interior Alaska over the past several decades(CSSR, Ch. 8.3). (l) Degree days are defined as the number of degrees by which the average daily temperature is higher than
65°F (cooling degree days) or lower than 65°F (heating degree days) and are used as a proxy for energy demands for coolingor heating buildings. Changes in temperatures indicate that heating needs have decreased and cooling needs have increasedin the contiguous United States over the past century.
Sources: (a) adapted from Vose et al. 2017, (b) EPA, (c–f and h–l) adapted from EPA 2016, (g and center infographic) EPA
and NOAA.

Causes of Change
Scientists have understood the fundamental
physics of climate change for almost 200 years.
In the 1850s, researchers demonstrated thatcarbon dioxide and other naturally occurringgreenhouse gases in the atmosphere prevent
some of the heat radiating from Earth’s surface
from escaping to space: this is known as thegreenhouse effect. This natural greenhouseeffect warms the planet’s surface about 60°F
above what it would be otherwise, creatinga habitat suitable for life. Since the late 19th
century, however, humans have released anincreasing amount of greenhouse gases into theatmosphere through burning fossil fuels and,to a lesser extent, deforestation and land-use
change. As a result, the atmospheric concentration of carbon dioxide, the largest contributor
to human-caused warming, has increased by

U.S. Global Change Research Program

about 40% over the industrial era. This change
has intensified the natural greenhouse effect,
driving an increase in global surface temperatures and other widespread changes in Earth’s
climate that are unprecedented in the historyof modern civilization.
Global climate is also influenced by natural
factors that determine how much of the sun’senergy enters and leaves Earth’s atmosphereand by natural climate cycles that affecttemperatures and weather patterns in the
short term, especially regionally (see Ch. 2:
Climate, Box 2.1). However, the unambiguous
long-term warming trend in global averagetemperature over the last century cannot be
explained by natural factors alone. Greenhousegas emissions from human activities are the30

Report-in-Brief | Overview
only factors that can account for the observed
warming over the last century; there are no
credible alternative human or natural explanations supported by the observational evidence.
Without human activities, the influence of
natural factors alone would actually have had aslight cooling effect on global climate over thelast 50 years (Ch. 2: Climate, KM 1, Figure 2.1).

to changes in greenhouse gas levels over thiscentury. Scientists test climate models bycomparing them to current observations andhistorical changes. Confidence in these models
is based, in part, on how well they reproduce
these observed changes. Climate models have
proven remarkably accurate in simulating theclimate change we have experienced to date,particularly in the past 60 years or so when
we have greater confidence in observations(see CSSR, Ch. 4.3.1). The observed signalsof a changing climate continue to become
stronger and clearer over time, giving scientists
increased confidence in their findings evensince the Third National Climate Assessment
was released in 2014.

Future Change
Greenhouse gas emissions from humanactivities will continue to affect Earth’s climate
for decades and even centuries. Humans areadding carbon dioxide to the atmosphere at a
rate far greater than it is removed by naturalprocesses, creating a long-lived reservoir of
the gas in the atmosphere and oceans that is
driving the climate to a warmer and warmer
state. Some of the other greenhouse gases
released by human activities, such as methane,are removed from the atmosphere by naturalprocesses more quickly than carbon dioxide; asa result, efforts to cut emissions of these gases
could help reduce the rate of global temperature increases over the next few decades.
However, longer-term changes in climate
will largely be determined by emissions andatmospheric concentrations of carbon dioxide
and other longer-lived greenhouse gases (Ch. 2:
Climate, KM 2).

Today, the largest uncertainty in projecting
future climate conditions is the level ofgreenhouse gas emissions going forward.
Future global greenhouse gas emissions levels
and resulting impacts depend on economic,
political, and demographic factors that can bedifficult to predict with confidence far into
the future. Like previous climate assessments,
NCA4 relies on a suite of possible scenarios toevaluate the implications of different climate
outcomes and associated impacts throughout
the 21st century. These “Representative Concentration Pathways” (RCPs) capture a range ofpotential greenhouse gas emissions pathways
and associated atmospheric concentrationlevels through 2100.

Climate models representing our understanding of historical and current climate conditions
are often used to project how our world willchange under future conditions (see Ch. 2: Climate, Box 2.7). “Climate” is defined as weather
conditions over multiple decades, and climate
model projections are generally not designed
to capture annual or even decadal variationin climate conditions. Instead, projections are
typically used to capture long-term changes,
such as how the climate system will respond

RCPs drive climate model projections fortemperature, precipitation, sea level, and othervariables under futures that have either lower
or higher greenhouse gas emissions. RCPs arenumbered according to changes in radiative
forcing by 2100 relative to preindustrial conditions: +2.6, +4.5, +6.0, or +8.5 watts per square
meter (W/m2). Each RCP leads to a different

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Box 1.1: Confidence and Uncertainty in Climate Science
Many of the decisions we make every day are based on less-than-perfect knowledge. For example, while
GPS-based applications on smartphones can provide a travel-time estimate for our daily drive to work, an
unexpected factor like a sudden downpour or fender bender might mean a ride originally estimated to be 20
minutes could actually take longer. Fortunately, even with this uncertainty we are confident that our trip isunlikely to take less than 20 minutes or more than half an hour—and we know where we are headed. We haveenough information to plan our commute.
Uncertainty is also a part of science. A key goal of scientific research is to increase our confidence andreduce the uncertainty in our understanding of the world around us. Even so, there is no expectation that
uncertainty can be fully eliminated, just as we do not expect a perfectly accurate estimate for our drive timeeach day. Studying Earth’s climate system is particularly challenging because it integrates many aspects ofa complex natural system as well as many human-made systems. Climate scientists find varying ranges of
uncertainty in many areas, including observations of climate variables, the analysis and interpretation of thosemeasurements, the development of new observational instruments, and the use of computer-based models of
the processes governing Earth’s climate system. While there is inherent uncertainty in climate science, there
is high confidence in our understanding of the greenhouse effect and the knowledge that human activities arechanging the climate in unprecedented ways. There is enough information to make decisions based on that
understanding.
Where important uncertainties do exist, efforts to quantify and report those uncertainties can help decisionmakers plan for a range of possible future outcomes. These efforts also help scientists advance understanding and ultimately increase confidence in and the usefulness of model projections. Assessments
like this one explicitly address scientific uncertainty associated with findings and use specific language toexpress it to improve relevance to risk analysis and decision-making (see Front Matter and Box 1.2).

level of projected global temperature change;higher numbers indicate greater projected
temperature change and associated impacts.
The higher scenario (RCP8.5) represents afuture where annual greenhouse gas emissions
increase significantly throughout the 21st
century before leveling off by 2100, whereas
the other RCPs represent more rapid andsubstantial mitigation by mid-century, withgreater reductions thereafter. Current trends inannual greenhouse gas emissions, globally, areconsistent with RCP8.5.

gas emissions than the higher scenario (RCP8.5)
by the end of the 21st century (see Ch. 2:
Climate, Figure 2.2). In some cases, throughout
this report, a very low scenario (RCP2.6) that
represents more immediate, substantial, andsustained emissions reductions is considered.
Each RCP could be consistent with a range ofunderlying socioeconomic conditions or policy
choices. See the Scenario Products sectionof Appendix 3 in this report, as well as CSSR
Chapters 4.2.1 and 10.2.1 for more detail.
The effects of different future greenhouse gas
emissions levels on global climate become mostevident around 2050, when temperature (Figure1.3) (Ch. 2: Climate, Figure 2.2), precipitation,

Of the two RCPs predominantly referenced
throughout this report, the lower scenario(RCP4.5) envisions about 85% lower greenhouse

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Report-in-Brief | Overview

Projected Changes in U.S. Annual Average Temperatures

Figure 1.3: Annual average temperatures across the United States are projected to increase over this century, with greaterchanges at higher latitudes as compared to lower latitudes, and under a higher scenario (RCP8.5; right) than under a lower one(RCP4.5; left). This figure shows projected differences in annual average temperatures for mid-century (2036–2065; top) andend of century (2071–2100; bottom) relative to the near present (1986–2015). From Figure 2.4, Ch. 2: Climate (Source: adaptedfrom Vose et al. 2017).

and sea level rise (Figure 1.4) (Ch. 2: Climate,
Figure 2.3) projections based on each scenario
begin to diverge significantly. With substantial
and sustained reductions in greenhouse gas
emissions (e.g., consistent with the very low
scenario [RCP2.6]), the increase in global annual
average temperature relative to preindustrial
times could be limited to less than 3.6°F (2°C)(Ch. 2: Climate, Box 2.4; CSSR, Ch. 4.2.1). Without significant greenhouse gas mitigation, theincrease in global annual average temperature
could reach 9°F or more by the end of thiscentury (Ch. 2: Climate, KM 2). For some
aspects of Earth’s climate system that takelonger to respond to changes in atmosphericgreenhouse gas concentrations, such as global
sea level, some degree of long-term change will

be locked in for centuries to come, regardlessof the future scenario (see CSSR, Ch. 12.5.3).
Early greenhouse gas emissions mitigation
can reduce climate impacts in the nearer term(such as reducing the loss of arctic sea ice andthe effects on species that use it) and in thelonger term by avoiding critical thresholds(such as marine ice sheet instability and theresulting consequences for global sea level andcoastal development; Ch. 29: Mitigation, Timing
and Magnitude of Action).
Annual average temperatures in the UnitedStates are projected to continue to increasein the coming decades. Regardless of futurescenario, additional increases in temperatures
across the contiguous United States of at least

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Projected Relative Sea Level Change in the United States by 2100

Figure 1.4: The maps show projections of change in relative sea level along the U.S. coast by 2100 (as compared to 2000)
under the lower (RCP4.5) and higher (RCP8.5) scenarios (see CSSR, Ch. 12.5). Globally, sea levels will continue to rise fromthermal expansion of the ocean and melting of land-based ice masses (such as Greenland, Antarctica, and mountain glaciers).
Regionally, however, the amount of sea level rise will not be the same everywhere. Where land is sinking (as along the Gulf of
Mexico coastline), relative sea level rise will be higher, and where land is rising (as in parts of Alaska), relative sea level rise will
be lower. Changes in ocean circulation (such as the Gulf Stream) and gravity effects due to ice melt will also alter the heightsof the ocean regionally. Sea levels are expected to continue to rise along almost all U.S. coastlines, and by 2100, under thehigher scenario, coastal flood heights that today cause major damages to infrastructure would become common during high tides
nationwide (Ch. 8: Coastal; Scenario Products section in Appendix 3). Source: adapted from CSSR, Figure 12.4.

2.3°F relative to 1986–2015 are expected by
the middle of this century. As a result, recent
record-setting hot years are expected to
become common in the near future. By late thiscentury, increases of 2.3°–6.7°F are expectedunder a lower scenario (RCP4.5) and 5.4°–11.0°F
under a higher scenario (RCP8.5) relative to
1986–2015 (Figure 1.3) (Ch. 2: Climate, KM 5,
Figure 2.4). Alaska has warmed twice as fast as
the global average since the mid-20th century;
this trend is expected to continue (Ch. 26:
Alaska, Background).

Alaska are all projected to continue to increase,
while land and sea ice cover, snowpack, andsurface soil moisture are expected to continue
to decline in the coming decades. These andother changes are expected to increasingly
impact water resources, air quality, humanhealth, agriculture, natural ecosystems, energy
and transportation infrastructure, and manyother natural and human systems that support
communities across the country. The severityof these projected impacts, and the risks theypresent to society, is greater under futureswith higher greenhouse gas emissions, especially if limited or no adaptation occurs (Ch. 29:
Mitigation, KM 2).

High temperature extremes, heavy precipitation
events, high tide flooding events along the U.S.
coastline, ocean acidification and warming, andforest fires in the western United States andU.S. Global Change Research Program34

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Box 1.2: Evaluating Risks to Inform Decisions
In this report, risks are often defined in a qualitative sense as threats to life, health and safety, the environment, economic well-being, and other things of value to society (Ch. 28: Adaptation, Introduction). In somecases, risks are described in quantitative terms: estimates of how likely a given threat is to occur (probability)
and the damages that would result if it did happen (consequences). Climate change is a risk management
challenge for society; it presents uncertain—and potentially severe—consequences for natural and humansystems across generations. It is characterized by multiple intersecting and uncertain future hazards and,
therefore, acts as a risk multiplier that interacts with other stressors to create new risks or to alter existingones (see Ch. 17: Complex Systems, KM 1).
Current and future greenhouse gas emissions, and thus mitigation actions to reduce emissions, will largely
determine future climate change impacts and risks to society. Mitigation and adaptation activities can beconsidered complementary strategies—mitigation efforts can reduce future risks, while adaptation can minimize the consequences of changes that are already happening as a result of past and present greenhousegas emissions. Adaptation entails proactive decision-making and investments by individuals, businesses, andgovernments to counter specific risks from climate change that vary from place to place. Climate risk management includes some familiar attributes and tactics for most businesses and local governments, which
often manage or design for a variety of weather-related risks, including coastal and inland storms, heat waves,threats to water availability, droughts, and floods.
Measuring risk encompasses both likelihoods and consequences of specific outcomes and involves judgments about what is of value, ranking of priorities, and cost–benefit analyses that incorporate the tradeoffs
among climate and non-climate related options. This report characterizes specific risks across regions andsectors in an effort to help people assess the risks they face, create and implement a response plan, andmonitor and evaluate the efficacy of a given action (see Ch. 28: Adaptation, KM 1, Figure 28.1).

Climate Change in the UnitedStates: Current and Future Risks

physical climate impacts and by factors that
influence its ability to respond to changing
conditions and to recover from adverse weather and climate-related events such as extreme
storms or wildfires (Ch. 14: Human Health, KM
2; Ch. 15: Tribes, State of the Sector, KM 1 and 2;
Ch. 28: Adaptation, KM 4).

Some climate-related impacts, such asincreasing health risks from extreme heat, arecommon to many regions of the United States(Ch. 14: Human Health, KM 1). Others represent
more localized risks, such as infrastructuredamage caused by thawing of permafrost(long-frozen ground) in Alaska or threats tocoral reef ecosystems from warmer and more
acidic seas in the U.S. Caribbean, as well as
Hawai‘i and the U.S.-Affiliated Pacific Islands(Ch. 26: Alaska, KM 2; Ch. 20: U.S. Caribbean,
KM 2; Ch. 27: Hawai‘i & Pacific Islands, KM 4).
Risks vary by both a community’s exposure to

Many places are subject to more than one
climate-related impact, such as extreme rainfall
combined with coastal flooding, or drought
coupled with extreme heat, wildfire, andflooding. The compounding effects of these
impacts result in increased risks to people,
infrastructure, and interconnected economic
sectors (Ch. 11: Urban, KM 1). Impacts affecting

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Report-in-Brief | Overview
Economy and Infrastructureinterconnected systems can cascade acrosssectors and regions, creating complex risks andmanagement challenges. For example, changes
in the frequency, intensity, extent, and durationof wildfires can result in a higher instance oflandslides that disrupt transportation systems
and the flow of goods and services within or
across regions (Box 1.3). Many observed impacts
reveal vulnerabilities in these interconnected
systems that are expected to be exacerbated asclimate-related risks intensify. Under a higher
scenario (RCP8.5), it is very likely that some
impacts, such as the effects of ice sheet disintegration on sea level rise and coastal development, will be irreversible for many thousandsof years, and others, such as species extinction,
will be permanent (Ch. 7: Ecosystems, KM 1; Ch.
9: Oceans, KM 1; Ch. 29: Mitigation, KM 2).

Without more significant global greenhousegas mitigation and regional adaptation efforts,
climate change is expected to cause substantial
losses to infrastructure and property and
impede the rate of economic growth over thiscentury (Ch. 4: Energy, KM 1; Ch. 8: Coastal, KM
1; Ch. 11: Urban, KM 2; Ch. 12: Transportation,
KM 1; Regional Chapters 18–27). Regional economies and industries that depend on natural
resources and favorable climate conditions,such as agriculture, tourism, and fisheries, areincreasingly vulnerable to impacts driven byclimate change (Ch. 7: Ecosystems, KM 3; Ch.
10: Agriculture, KM 1). Reliable and affordable
energy supplies, which underpin virtually every
sector of the economy, are increasingly at risk
from climate change and weather extremes(Ch. 4: Energy, KM 1). The impacts of climate

Box 1.3: Interconnected Impacts of Climate Change
The impacts of climate change and extreme weather on natural and built systems are often considered fromthe perspective of individual sectors: how does a changing climate impact water resources, the electric grid,or the food system? None of these sectors, however, exists in isolation. The natural, built, and social systems
we rely on are all interconnected, and impacts and management choices within one sector may have cascading effects on the others (Ch. 17: Complex Systems, KM 1).
For example, wildfire trends in the western United States are influenced by rising temperatures and changing
precipitation patterns, pest populations, and land management practices. As humans have moved closer toforestlands, increased fire suppression practices have reduced natural fires and led to denser vegetation,
resulting in fires that are larger and more damaging when they do occur (Figures 1.5 and 1.2k) (Ch. 6: Forests,
KM 1). Warmer winters have led to increased pest outbreaks and significant tree kills, with varying feedbacks
on wildfire. Increased wildfire driven by climate change is projected to increase costs associated with healtheffects, loss of homes and other property, wildfire response, and fuel management. Failure to anticipate theseinterconnected impacts can lead to missed opportunities for effectively managing risks within a single sector
and may actually increase risks to other sectors. Planning around wildfire risk and other risks affected byclimate change entails the challenge of accounting for all of these influences and how they interact with one
another (see Ch. 17: Complex Systems, Box 17.4).

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Box 1.3: Interconnected Impacts of Climate Change, continued
New to this edition of the NCA, Chapter 17 (Complex Systems) highlights several examples of interconnected impacts and documents how a multisector perspective and joint management of systems can enhance
resilience to a changing climate. It is often difficult or impossible to quantify and predict how all relevant processes and interactions in interconnected systems will respond to climate change. Non-climate influences,such as population changes, add to the challenges of projecting future outcomes (Ch. 17: Complex Systems,
KM 2). Despite these challenges, there are opportunities to learn from experience to guide future risk management decisions. Valuable lessons can be learned retrospectively: after Superstorm Sandy in 2012, forexample, the mayor of New York City initiated a Climate Change Adaptation Task Force that brought together
stakeholders from several sectors such as water, transportation, energy, and communications to address theinterdependencies among them (Ch. 17: Complex Systems, Box 17.1, KM 3).

Wildfire at the Wildland–Urban Interface
Figure 1.5: Wildfires are increasingly encroaching on American communities, posing threats to lives, critical infrastructure,and property. In October 2017, more than a dozen fires burned through northern California, killing dozens of people andleaving thousands more homeless. Communities distant from the fires were affected by poor air quality as smoke plumes
darkened skies and caused the cancellation of school and other activities across the region. (left) A NASA satellite image
shows active fires on October 9, 2017. (right) The Tubbs Fire, which burned parts of Napa, Sonoma, and Lake counties,
was the most destructive in California’s history. It caused an estimated $1.2 billion in damages and destroyed over 5,000
structures, including 5% of the housing stock in the city of Santa Rosa. Image credits: (left) NASA; (right) Master Sgt.
David Loeffler, U.S. Air National Guard.

change beyond our borders are expected toincreasingly affect our trade and economy,
including import and export prices and U.S.
businesses with overseas operation and supply
chains (Box 1.4) (Ch. 16: International, KM 1; Ch.
17: Complex Systems, KM 1). Some aspects ofour economy may see slight improvements in amodestly warmer world. However, the continued warming that is projected to occur without
significant reductions in global greenhouse gas
emissions is expected to cause substantial net

damage to the U.S. economy, especially in theabsence of increased adaptation efforts. The
potential for losses in some sectors could reachhundreds of billions of dollars per year by theend of this century (Ch. 29: Mitigation, KM 2).
Existing water, transportation, and energy
infrastructure already face challenges fromheavy rainfall, inland and coastal flooding, landslides, drought, wildfire, heat waves, and other
weather and climate events (Figures 1.5–1.9)

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Report-in-Brief | Overview(Ch. 11: Urban, KM 2; Ch. 12: Transportation, KM
1). Many extreme weather and climate-related
events are expected to become more frequentand more intense in a warmer world, creating
greater risks of infrastructure disruption andfailure that can cascade across economic
sectors (Ch. 3: Water, KM 2; Ch. 4: Energy, KM 1;
Ch. 11: Urban, KM 3; Ch. 12: Transportation, KM
2). For example, more frequent and severe heatwaves and other extreme events in many partsof the United States are expected to increasestresses on the energy system, amplifying
the risk of more frequent and longer-lasting
power outages and fuel shortages that could
affect other critical sectors and systems, suchas access to medical care (Ch. 17: Complex
Systems, Box 17.5; Ch. 4: Energy, KM 1; Ch.
8: Coastal, KM 1; Ch. 11: Urban, KM 3; Ch. 12:
Transportation, KM 3). Current infrastructure
is typically designed for historical climate
conditions (Ch. 12: Transportation, KM 1) anddevelopment patterns—for instance, coastal
land use—generally do not account for a changing climate (Ch. 5: Land Changes, State of the
Sector), resulting in increasing vulnerability tofuture risks from weather extremes and climatechange (Ch. 11: Urban, KM 2). Infrastructure age
and deterioration make failure or interrupted
service from extreme weather even more
likely (Ch. 11: Urban, KM 2). Climate change is
expected to increase the costs of maintaining,
repairing, and replacing infrastructure, withdifferences across regions (Ch. 12: Transportation, Regional Summary).

(Ch. 2: Climate, Box 2.5). Resulting power
outages had cascading effects on critical infrastructure facilities such as hospitals and water
and wastewater treatment plants. Reduced oil
production and refining capacity in the Gulf
of Mexico caused price spikes regionally andnationally from actual and anticipated gasoline
shortages (Figure 1.6) (Ch. 17: Complex Systems,
KM 1). In the U.S. Caribbean, Hurricanes Irma
and Maria caused catastrophic damage toinfrastructure, including the complete failure of
Puerto Rico’s power grid and the loss of power
throughout the U.S. Virgin Islands, as well as
extensive damage to the region’s agriculturalindustry. The death toll in Puerto Rico grew inthe three months following Maria’s landfall on
the island due in part to the lack of electricity
and potable water as well as access to medical
facilities and medical care (Ch. 20: U.S. Caribbean, Box 20.1, KM 5).
Climate-related risks to infrastructure, property, and the economy vary across regions.
Along the U.S. coastline, public infrastructureand $1 trillion in national wealth held in coastal
real estate are threatened by rising sea levels,
higher storm surges, and the ongoing increasein high tide flooding (Figures 1.4 and 1.8) (Ch. 8:
Coastal, KM 1). Coastal infrastructure provides
critical lifelines to the rest of the country,
including energy supplies and access to goods
and services from overseas trade; increased
damage to coastal facilities is expected to resultin cascading costs and national impacts (Ch.
8: Coastal, KM 1; Ch. 4: Energy, State of the
Sector, KM 1). High tide flooding is projected
to become more disruptive and costlier as
its frequency, depth, and inland extent growin the coming decades. Without significant
adaptation measures, many coastal cities in theSoutheast are expected to experience daily hightide flooding by the end of the century (Ch. 8:

Recent extreme events demonstrate thevulnerabilities of interconnected economic
sectors to increasing risks from climate change(see Box 1.3). In 2017, Hurricane Harvey dumped
an unprecedented amount of rainfall over thegreater Houston area, some of which has been
attributed to human-induced climate change

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Widespread Impacts from Hurricane Harvey
Figure 1.6: Hurricane Harvey led to widespread flooding and knocked out power to 300,000 customers in Texas in 2017, withcascading effects on critical infrastructure facilities such as hospitals, water and wastewater treatment plants, and refineries. The
photo shows Port Arthur, Texas, on August 31, 2017—six days after Hurricane Harvey made landfall along the Gulf Coast. From
Figure 17.2, Ch. 17: Complex Systems (Photo credit: Staff Sgt. Daniel J. Martinez, U.S. Air National Guard).

Flooding at Fort Calhoun Nuclear Power Plant

Norfolk Naval Base at Risk from Rising Seas

Figure 1.7: Floodwaters from the Missouri River surround the
Omaha Public Power District’s Fort Calhoun Station, a nuclear
power plant just north of Omaha, Nebraska, on June 20, 2011.
The flooding was the result of runoff from near-record snowfall
totals and record-setting rains in late May and early June. A
protective berm holding back the floodwaters from the plantfailed, which prompted plant operators to transfer offsite power
to onsite emergency diesel generators. Cooling for the reactor
temporarily shut down, but spent fuel pools were unaffected.
From Figure 22.5, Ch. 22: N. Great Plains (Photo credit: Harry
Weddington, U.S. Army Corps of Engineers).

Figure 1.8: Low-lying Norfolk, Virginia, houses the world’s
largest naval base, which supports multiple aircraft carriergroups and is the duty station for thousands of employees.
Most of the area around the base lies less than 10 feet above
sea level, and local relative sea level is projected to rise
between about 2.5 and 11.5 feet by the year 2100 under the
Lower and Upper Bound USGCRP sea level rise scenarios,
respectively (see Scenario Products section of Appendix 3 formore details on these sea level rise scenarios; see also Ch.
8: Coastal, Case Study “Key Messages in Action—Norfolk,
Virginia”). Photo credit: Mass Communication Specialist 1st
Class Christopher B. Stoltz, U.S. Navy.

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Coastal, KM 1; Ch. 19: Southeast, KM 2). Higher
sea levels will also cause storm surge fromtropical storms to travel farther inland than in
the past, impacting more coastal properties
and infrastructure (Ch. 8: Coastal: KM 1; Ch. 19:
Southeast, KM 2). Oil, natural gas, and electricalinfrastructure located along the coasts of
the Atlantic Ocean and Gulf of Mexico are atincreased risk of damage from rising sea levels
and stronger hurricanes; regional disruptions
are expected to have national implications(Ch. 4: Energy, State of the Sector, KM 1; Ch.

Weather and Climate-Related Impacts on
U.S. Military Assets

Figure 1.9: The Department of Defense (DoD) has significant experience in planning for and managing risk anduncertainty. The effects of climate and extreme weather represent additional risks to incorporate into the Department’s
various planning and risk management processes. To identify DoD installations with vulnerabilities to climate-related
impacts, a preliminary Screening Level Vulnerability Assessment Survey (SLVAS) of DoD sites worldwide was conducted
in 2015. The SLVAS responses (shown for the United States; orange dots) yielded a wide range of qualitative information.
The highest number of reported effects resulted from drought (782), followed closely by wind (763) and non-storm surge
related flooding (706). About 10% of sites indicated being affected by extreme temperatures (351), while flooding
due to storm surge (225) and wildfire (210) affected about 6% of the sites reporting. The survey responses provide apreliminary qualitative picture of DoD assets currently affected by severe weather events as well as an indication ofassets that may be affected by sea level rise in the future. Source: adapted from Department of Defense 2018 (http://www.
oea.gov/resource/2018-climate-related-risk-dod-infrastructure-initial-vulnerability-assessment-survey-slvas).

U.S. Global Change Research Program40Report-in-Brief | Overview
18: Northeast, KM 3; Ch. 19: Southeast, KM 2).
Hawai‘i and the U.S.-Affiliated Pacific Islands
and the U.S. Caribbean also face high risks tocritical infrastructure from coastal flooding,erosion, and storm surge (Ch. 4: Energy, Stateof the Sector; Ch. 20: U.S. Caribbean, KM 3; Ch.
27: Hawai‘i & Pacific Islands, KM 3).
In the western United States, increasing wildfire is damaging ranches and rangelands as wellas property in cities near the wildland–urban
interface. Drier conditions are projected toincrease the risk of wildfires and damage toproperty and infrastructure, including energy
production and generation assets and thepower grid (Ch. 4: Energy, KM 1; Ch. 11: Urban,
Regional Summary; Ch. 24: Northwest, KM 3).
In Alaska, thawing of permafrost is responsible for severe damage to roads, buildings,
and pipelines that will be costly to replace,especially in remote parts of Alaska. Alaska oil
and gas operations are vulnerable to thawing
permafrost, sea level rise, and increased coastal
exposure due to declining sea ice; however, alonger ice-free season may enhance offshore
energy operations and transport (Ch. 4: Energy,
State of the Sector; Ch. 26: Alaska, KM 2 and
5). These impacts are expected to grow with
continued warming.

Conservation Practices Reduce Impact of
Heavy Rains
Figure 1.10: Increasing heavy rains are leading to more soil
erosion and nutrient loss on midwestern cropland. Integrating
strips of native prairie vegetation into row crops has beenshown to reduce soil and nutrient loss while improving
biodiversity. The inset shows a close-up example of a prairie
vegetation strip. From Figure 21.2, Ch. 21: Midwest (Photo
credits: [main photo] Lynn Betts; [inset] Farnaz Kordbacheh).

availability and disease and pest outbreaks(Ch. 10: Ag & Rural, KM 1). Increases in growing
season temperatures in the Midwest are projected to be the largest contributing factor to
declines in U.S. agricultural productivity (Ch. 21:
Midwest, KM 1). Climate change is also expected to lead to large-scale shifts in the availability
and prices of many agricultural products acrossthe world, with corresponding impacts on U.S.
agricultural producers and the U.S. economy(Ch. 16: International, KM 1).

U.S. agriculture and the communities it
supports are threatened by increases intemperatures, drought, heavy precipitation
events, and wildfire on rangelands (Figure 1.10)(Ch. 10: Ag & Rural, KM 1 and 2, Case Study“Groundwater Depletion in the Ogallala Aquifer
Region”; Ch. 23: S. Great Plains, KM 1, Case
Study “The Edwards Aquifer”). Yields of major
U.S. crops (such as corn, soybeans, wheat, rice,sorghum, and cotton) are expected to decline
over this century as a consequence of increases
in temperatures and possibly changes in water

Extreme heat poses a significant risk to humanhealth and labor productivity in the agricultural, construction, and other outdoor sectors (Ch.
10: Ag & Rural, KM 3). Under a higher scenario(RCP8.5), almost two billion labor hours areprojected to be lost annually by 2090 from theimpacts of temperature extremes, costing an
estimated $160 billion in lost wages (Ch. 14:
Human Health, KM 4). States within the Southeast (Ch. 19: Southeast, KM 4) and Southern
Great Plains (Ch. 23: S. Great Plains, KM 4)

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Report-in-Brief | Overview
regions are projected to experience some of thegreatest impacts (see Figure 1.21).

Intensifying droughts, heavier downpours, andreduced snowpack are combining with otherstressors such as groundwater depletion to
reduce the future reliability of water supplies in
the region, with cascading impacts on energy
production and other water-dependent sectors(Ch. 3: Water, Regional Summary; Ch. 4: Energy,
State of the Sector; Ch. 25: Southwest, KM 5).
In the Southern Great Plains, current drought
and projected increases in drought length andseverity threaten the availability of water for
agriculture (Figures 1.11 and 1.12) (Ch. 23: S.
Great Plains, KM 1). Reductions in mountainsnowpack and shifts in snowmelt timing areexpected to reduce hydropower productionin the Southwest and the Northwest (Ch. 24:
Northwest, KM 3; Ch. 25: Southwest, KM 5).
Drought is expected to threaten oil and gas
drilling and refining as well as thermoelectric
power plants that rely on a steady supplyof water for cooling (Ch. 4: Energy, Stateof the Sector, KM 1; Ch. 22: N. Great Plains,
KM 4; Ch. 23: S. Great Plains, KM 2; Ch. 25:
Southwest, KM 5).

Natural Environment andEcosystem Services
Climate change threatens many benefits thatthe natural environment provides to society:safe and reliable water supplies, clean air, protection from flooding and erosion, and the useof natural resources for economic, recreational,
and subsistence activities. Valued aspects ofregional heritage and quality of life tied to thenatural environment, wildlife, and outdoor recreation will change with the climate, and as aresult, future generations can expect to experience and interact with natural systems in waysthat are much different than today. Without
significant reductions in greenhouse gas emissions, extinctions and transformative impacts
on some ecosystems cannot be avoided, withvarying impacts on the economic, recreational,
and subsistence activities they support.
Changes affecting the quality, quantity, andavailability of water resources, driven in part by
climate change, impact people and the environment (Ch. 3: Water, KM 1). Dependable and safe
water supplies for U.S. Caribbean, Hawai‘i, andU.S.-Affiliated Pacific Island communities andecosystems are threatened by rising temperatures, sea level rise, saltwater intrusion, andincreased risks of drought and flooding (Ch. 3:
Water, Regional Summary; Ch. 20: U.S. Caribbean, KM 1; Ch. 27: Hawai‘i & Pacific Islands, KM
1). In the Midwest, the occurrence of conditions
that contribute to harmful algal blooms,
which can result in restrictions to water usage
for drinking and recreation, is expected toincrease (Ch. 3: Water, Regional Summary; Ch.
21: Midwest, KM 3). In the Southwest, watersupplies for people and nature are decreasing
during droughts due in part to climate change.

U.S. Global Change Research Program

Impacts of Drought on Texas Agriculture
Figure 1.11: Soybeans in Texas experience the effects ofdrought in August 2013. During 2010–2015, a multiyear
regional drought severely affected agriculture in the Southern
Great Plains. One prominent impact was the reduction ofirrigation water released for farmers on the Texas coastal
plains. Photo credit: Bob Nichols, USDA.

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Desalination Plants Can Reduce Impacts from Drought in Texas

Figure 1.12: Desalination activities in Texas are an important contributor to the state’s efforts to meet current and projected waterneeds for communities, industry, and agriculture. The state’s 2017 Water Plan recommended an expansion of desalination to
help reduce longer-term risks to water supplies from drought, higher temperatures, and other stressors. There are currently 44
public water supply desalination plants in Texas. From Figure 23.8, Ch. 23: S. Great Plains (Source: adapted from Texas Water
Development Board 2017).

Tourism, outdoor recreation, and subsistence
activities are threatened by reduced snowpack,increases in wildfire activity, and other stressors affecting ecosystems and natural resources(Figures 1.2d, 1.2k, and 1.13) (Ch. 7: Ecosystems,
KM 3). Increasing wildfire frequency (Ch. 19:
Southeast, Case Study “Prescribed Fire”), pest
and disease outbreaks (Ch. 21: Midwest, Case
Study “Adaptation in Forestry”), and otherstressors are projected to reduce the abilityof U.S. forests to support recreation as wellas economic and subsistence activities (Ch. 6:
Forests, KM 1 and 2; Ch. 19: Southeast, KM 3;
Ch. 21: Midwest, KM 2). Increases in wildfire

smoke events driven by climate change are
expected to reduce the amount and qualityof time spent in outdoor activities (Ch. 13:
Air Quality, KM 2; Ch. 24: Northwest, KM 4).
Projected declines in snowpack in the western
United States and shifts to more precipitation
falling as rain than snow in the cold season in
many parts of the central and eastern UnitedStates are expected to adversely impact the
winter recreation industry (Ch. 18: Northeast,
KM 1; Ch. 22: N. Great Plains, KM 3; Ch. 24:
Northwest, KM 1, Box 24.7). In the Northeast,
activities that rely on natural snow and ice
cover may not be economically viable by the43

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change further, mismatches between species
and the availability of the resources they needto survive are expected to occur (Ch. 7: Ecosystems, KM 2). Without significant reductions in
global greenhouse gas emissions, extinctions
and transformative impacts on some ecosystems cannot be avoided in the long term (Ch. 9:
Oceans, KM 1). While some new opportunities
may emerge from ecosystem changes, economic and recreational opportunities and cultural
heritage based around historical use of species
or natural resources in many areas are at risk
(Ch. 7: Ecosystems, KM 3; Ch. 18: Northeast, KM
1 and 2, Box 18.6).

Razor Clamming on the Washington Coast
Figure 1.13: Razor clamming draws crowds on the coast of
Washington State. This popular recreation activity is expected
to decline due to ocean acidification, harmful algal blooms,
warmer temperatures, and habitat degradation. From Figure
24.7, Ch. 24: Northwest (Photo courtesy of Vera Trainer,
NOAA).

Ocean warming and acidification pose highand growing risks for many marine organisms,
and the impacts of climate change on ocean
ecosystems are expected to lead to reductionsin important ecosystem services such as aquaculture, fishery productivity, and recreational
opportunities (Ch 9: Oceans, KM 2). While
climate change impacts on ocean ecosystems
are widespread, the scope of ecosystem
impacts occurring in tropical and polar areas isgreater than anywhere else in the world. Ocean
warming is already leading to reductions invulnerable coral reef and sea ice habitats that
support the livelihoods of many communities(Ch. 9: Oceans, KM 1). Decreasing sea ice
extent in the Arctic represents a direct loss ofimportant habitat for marine mammals, causing
declines in their populations (Figure 1.2f) (Ch.
26: Alaska, Box 26.1). Changes in spring ice melt
have affected the ability of coastal communities
in Alaska to meet their walrus harvest needs
in recent years (Ch. 26: Alaska, KM 1). Thesechanges are expected to continue as sea ice
declines further (Ch. 2: Climate, KM 7). In thetropics, ocean warming has already led to widespread coral reef bleaching and/or outbreaksof coral diseases off the coastlines of Puerto

end of the century without significant reductions in global greenhouse gas emissions (Ch.
18: Northeast, KM 1). Diminished snowpack,increased wildfire, pervasive drought, flooding,ocean acidification, and sea level rise directly
threaten the viability of agriculture, fisheries,
and forestry enterprises on tribal lands acrossthe United States and impact tribal tourism andrecreation sectors (Ch. 15: Tribes, KM 1).
Climate change has already had observable
impacts on biodiversity and ecosystems
throughout the United States that are expected
to continue. Many species are shifting theirranges (Figure 1.2h), and changes in thetiming of important biological events (such as
migration and reproduction) are occurring in
response to climate change (Ch. 7: Ecosystems,
KM 1). Climate change is also aiding the spreadof invasive species (Ch. 21: Midwest, Case Study“Adaptation in Forestry”; Ch. 22: N. Great Plains,
Case Study “Crow Nation and the Spread ofInvasive Species”), recognized as a major driverof biodiversity loss and substantial ecologicaland economic costs globally (Ch. 7: Ecosystems,
Invasive Species). As environmental conditions

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Severe Coral Bleaching Projected for Hawai‘i andthe U.S.-Affiliated Pacific Islands

Figure 1.14: The figure shows the years when severe coral bleaching is projected to occur annually in the Hawaiʻi and U.S.Affiliated Pacific Islands region under a higher scenario (RCP8.5). Darker colors indicate earlier projected onset of coralbleaching. Under projected warming of approximately 0.5°F per decade, all nearshore coral reefs in the region will experienceannual bleaching before 2050. From Figure 27.10, Ch. 27: Hawai‘i & Pacific Islands (Source: NOAA).

Rico, the U.S. Virgin Islands, Florida, and Hawai‘iand the U.S.-Affiliated Pacific Islands (Ch. 20:
U.S. Caribbean, KM 2; Ch. 27: Hawai‘i & PacificIslands, KM 4). By mid-century, widespreadcoral bleaching is projected to occur annuallyin Hawai‘i and the U.S.-Affiliated Pacific Islands(Figure 1.14). Bleaching and ocean acidification
are expected to result in loss of reef structure,
leading to lower fisheries yields and loss ofcoastal protection and habitat, with impacts on

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tourism and livelihoods in both regions (Ch. 20:
U.S. Caribbean, KM 2; Ch. 27: Hawai‘i & PacificIslands, KM 4). While some targeted response
actions are underway (Figure 1.15), many
impacts, including losses of unique coral reefand sea ice ecosystems, can only be avoided bysignificantly reducing global greenhouse gas
emissions, particularly carbon dioxide (Ch. 9:
Oceans, KM 1).

services, and other changes increasingly
threaten the health and well-being of theAmerican people, particularly populations thatare already vulnerable. Future climate change is
expected to further disrupt many areas of life,
exacerbating existing challenges and revealing
new risks to health and prosperity.
Rising temperatures pose a number of threats
to human health and quality of life (Figure1.16). High temperatures in the summer are
linked directly to an increased risk of illness
and death, particularly among older adults,
pregnant women, and children (Ch. 18:
Northeast, Box 18.3). With continued warming,

Human Health and Well-Being
Higher temperatures, increasing air quality
risks, more frequent and intense extreme
weather and climate-related events, increases
in coastal flooding, disruption of ecosystem

Promoting Coral Reef Recovery
Figure 1.15: Examples of coral farming in the U.S. Caribbean and Florida demonstrate different types of structures used for
growing fragments from branching corals. Coral farming is a strategy meant to improve the reef community and ecosystem
function, including for fish species. The U.S. Caribbean Islands, Florida, Hawai‘i, and the U.S.-Affiliated Pacific Islands facesimilar threats from coral bleaching and mortality due to warming ocean surface waters and ocean acidification. Degradation ofcoral reefs is expected to negatively affect fisheries and the economies that depend on them as habitat is lost in both regions.
While coral farming may provide some targeted recovery, current knowledge and efforts are not nearly advanced enough tocompensate for projected losses from bleaching and acidification. From Figure 20.11, Ch. 20: U.S. Caribbean (Photo credits:[top left] Carlos Pacheco, U.S. Fish and Wildlife Service; [bottom left] NOAA; [right] Florida Fish and Wildlife).

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Projected Change in Very Hot Days by 2100 in Phoenix, ArizonaFigure 1.16: (left) The chart shows the average annual number of days above 100°F in Phoenix, Arizona, for 1976–2005, andprojections of the average number of days per year above 100°F through the end of the 21st century (2070–2099) under the
lower (RCP4.5) and higher (RCP8.5) scenarios. Dashed lines represent the 5th–95th percentile range of annual observed
values. Solid lines represent the 5th–95th percentile range of projected model values. (right) The map shows hydration stations
and cooling refuges (cooled indoor locations that provide water and refuge from the heat during the day) in Phoenix in August
2017. Such response measures for high heat events are expected to be needed at greater scales in the coming years if theadverse health effects of more frequent and severe heat waves are to be minimized. Sources: (left) NOAA NCEI, CICS-NC, and
LMI; (right) adapted from Southwest Cities Heat Refuges (a project by Arizona State University’s Resilient Infrastructure Lab),available at http://www.coolme.today/#phoenix. Data provided by Andrew Fraser and Mikhail Chester, Arizona State University.

cold-related deaths are projected to decreaseand heat-related deaths are projected toincrease. In most regions, the increases inheat-related deaths are expected to outpace
the reductions in cold-related deaths (Ch. 14:
Human Health, KM 1). Rising temperatures
are expected to reduce electricity generation
capacity while increasing energy demands andcosts, which can in turn lead to power outages
and blackouts (Ch. 4: Energy, KM 1; Ch. 11:
Urban, Regional Summary, Figure 11.2). Thesechanges strain household budgets, increase
people’s exposure to heat, and limit deliveryof medical and social services. Risks from heatstress are higher for people without access tohousing with sufficient insulation or air conditioning (Ch. 11: Urban, KM 1).

in wildfire activity due to climate change
would further degrade air quality, resulting inincreased health risks and impacts on qualityof life (Ch. 13: Air Quality, KM 2; Ch. 14: Human
Health, KM 1). Unless counteracting efforts toimprove air quality are implemented, climatechange is expected to worsen ozone pollution
across much of the country, with adverse
impacts on human health (Figure 1.21) (Ch. 13:
Air Quality, KM 1). Earlier spring arrival, warmer
temperatures, changes in precipitation, andhigher carbon dioxide concentrations can also
increase exposure to airborne pollen allergens.
The frequency and severity of allergic illnesses,
including asthma and hay fever, are expected toincrease as a result of a changing climate (Ch.
13: Air Quality, KM 3).

Changes in temperature and precipitation can
increase air quality risks from wildfire andground-level ozone (smog). Projected increases

Rising air and water temperatures and changes
in extreme weather and climate-related
events are expected to increase exposure to47

Fourth National Climate Assessment

Report-in-Brief | Overview
waterborne and foodborne diseases, affecting
food and water safety. The geographic range
and distribution of disease-carrying insects
and pests are projected to shift as climatechanges, which could expose more people inNorth America to ticks that carry Lyme disease
and mosquitoes that transmit viruses suchas West Nile, chikungunya, dengue, and Zika
(Ch. 14: Human Health, KM 1; Ch. 16: International, KM 4).

Indigenous peoples have historical and cultural
relationships with ancestral lands, ecosystems,
and culturally important species that are
threatened by climate change (Ch. 15: Tribes,
KM 1; Ch. 19: Southeast, KM 4, Case Study“Mountain Ramps”; Ch. 24: Northwest, KM
5). Climate change is expected to compound
existing physical health issues in Indigenous
communities, in part due to the loss of traditional foods and practices, and in some cases,
the mental stress from permanent community
displacement (Ch. 14: Human Health, KM 2; Ch.
15: Tribes, KM 2). Throughout the United States,
Indigenous peoples are considering or actively
pursuing relocation as an adaptation strategy inresponse to climate-related disasters, more frequent flooding, loss of land due to erosion, or
as livelihoods are compromised by ecosystemshifts linked to climate change (Ch. 15: Tribes,
KM 3). In Louisiana, a federal grant is being
used to relocate the tribal community of Islede Jean Charles in response to severe land loss,
sea level rise, and coastal flooding (Figure 1.17)(Ch. 19: Southeast, KM 2, Case Study “A Lesson
Learned for Community Resettlement”). In
Alaska, coastal Native communities are already

Mental health consequences can result fromexposure to climate- or extreme weatherrelated events, some of which are projected
to intensify as warming continues (Ch. 14:
Human Health, KM 1). Coastal city flooding
as a result of sea level rise and hurricanes,
for example, can result in forced evacuation,with adverse effects on family and community stability as well as mental and physicalhealth (Ch. 11: Urban, KM 1). In urban areas,
disruptions in food supply or safety related to
extreme weather or climate-related events are
expected to disproportionately impact those
who already experience food insecurity (Ch.
11: Urban, KM 3).

Community Relocation—Isle de Jean Charles, Louisiana
Figure 1.17: (left) A federal grant is being used to relocate the tribal community of Isle de Jean Charles, Louisiana, in response
to severe land loss, sea level rise, and coastal flooding. From Figure 15.3, Ch. 15: Tribes (Photo credit: Ronald Stine). (right) As
part of the resettlement of the tribal community of Isle de Jean Charles, residents are working with the Lowlander Center and theState of Louisiana to finalize a plan that reflects the desires of the community. From Figure 15.4, Ch. 15: Tribes (Photo provided
by Louisiana Office of Community Development).

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Adaptation Measures in Kivalina, Alaska
Figure 1.18: A rock revetment was installed in the Alaska Native Village of Kivalina in 2010 to reduce increasing risks from
erosion. A new rock revetment wall has a projected lifespan of 15 to 20 years. From Figure 15.3, Ch. 15: Tribes (Photo credit:
ShoreZone. Creative Commons License CC BY 3.0: https://creativecommons.org/licenses/by/3.0/legalcode). The inset shows aclose-up of the rock wall in 2011. Photo credit: U.S. Army Corps of Engineers–Alaska District.

experiencing heightened erosion driven by
declining sea ice, rising sea levels, and warmer
waters (Figure 1.18). Coastal and river erosion
and flooding in some cases will require parts ofcommunities, or even entire communities, torelocate to safer terrain (Ch. 26: Alaska, KM 2).
Combined with other stressors, sea level rise,coastal storms, and the deterioration of coral
reef and mangrove ecosystems put the longterm habitability of coral atolls in the Hawai‘iand U.S.-Affiliated Pacific Islands region at risk,
introducing issues of sovereignty, human andnational security, and equity (Ch. 27: Hawai‘i &Pacific Islands, KM 6).

environment in the United States, particularly
in futures with high greenhouse gas emissions
and limited or no adaptation. Recent findings
reinforce the fact that without substantial andsustained reductions in greenhouse gas emissions and regional adaptation efforts, there will
be substantial and far-reaching changes overthe course of the 21st century with negative
consequences for a large majority of sectors,
particularly towards the end of the century.
The impacts and costs of climate change are
already being felt in the United States, andchanges in the likelihood or severity of somerecent extreme weather events can now be
attributed with increasingly higher confidence
to human-caused warming (see CSSR, Ch. 3).
Impacts associated with human health, such aspremature deaths due to extreme temperaturesand poor air quality, are some of the most

Reducing the Risks of
Climate Change
Climate change is projected to significantly
affect human health, the economy, and the49

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Box 1.4: How Climate Change Around the World Affects the United States
The impacts of changing weather and climate patterns beyond U.S. international borders affect those livingin the United States, often in complex ways that can generate both challenges and opportunities. The International chapter (Ch. 16), new to this edition of the NCA, assesses our current understanding of how global
climate change, natural variability, and associated extremes are expected to impact—and in some cases are
already impacting—U.S. interests both within and outside of our borders.
Current and projected climate-related impacts on our economy include increased risks to overseas operationsof U.S. businesses, disruption of international supply chains, and shifts in the availability and prices of commodities. For example, severe flooding in Thailand in 2011 disrupted the supply chains for U.S. electronics
manufacturers (Ch. 16: International, Figure 16.1). U.S. firms are increasingly responding to climate-relatedrisks, including through their financial disclosures and partnerships with environmental groups (Ch. 16: International, KM 1).
Impacts from climate-related events can also undermine U.S. investments in international development byslowing or reversing social and economic progress in developing countries, weakening foreign markets for
U.S. exports, and increasing the need for humanitarian assistance and disaster relief efforts. Predictive tools
can help vulnerable countries anticipate natural disasters, such as drought, and manage their impacts. For
example, the United States and international partners created the Famine Early Warning Systems Network(FEWS NET), which helped avoid severe food shortages in Ethiopia during a historic drought in 2015 (Ch. 16:
International, KM 2).
Natural variability and changes in climate increase risks to our national security by affecting factors that can
exacerbate conflict and displacement outside of U.S. borders, such as food and water insecurity and commodity price shocks. More directly, our national security is impacted by damage to U.S. military assets suchas roads, runways, and waterfront infrastructure from extreme weather and climate-related events (Figures
1.8 and 1.9). The U.S. military is working to both fully understand these threats and incorporate projectedclimate changes into long-term planning. For example, the Department of Defense has performed a comprehensive scenario-driven examination of climate risks from sea level rise to all of its coastal military sites,
including atolls in the Pacific Ocean (Ch. 16: International, KM 3).
Finally, the impacts of climate change are already affecting the ecosystems that span our Nation’s borders
and the communities that rely on them. International frameworks for the management of our shared resources continue to be restructured to incorporate risks from these impacts. For example, a joint commission that
implements water treaties between the United States and Mexico is exploring adaptive water management
strategies that account for the effects of climate change and natural variability on Colorado River water (Ch.
16: International, KM 4).

substantial (Ch. 13: Air Quality, KM 1; Ch. 14:
Human Health, KM 1 and 4; Ch 29: Mitigation,
KM 2). While many sectors face large economic
risks from climate change, other impacts canhave significant implications for societal orcultural resources. Further, some impacts

U.S. Global Change Research Program

will very likely be irreversible for thousandsof years, including those to species, such ascorals (Ch. 9: Oceans, KM 1; Ch. 27: Hawai‘i& Pacific Islands, KM 4), or that involve thecrossing of thresholds, such as the effects ofice sheet disintegration on accelerated sea level

50Report-in-Brief | Overview
rise, leading to widespread effects on coastal
development lasting thousands of years (Ch. 29:
Mitigation, KM 2).

yet approach the scale needed to avoid substantial damages to the economy, environment,
and human health expected over the coming
decades (Ch. 28: Adaptation, KM 1; Ch. 29:
Mitigation, KM 1 and 2).

Future impacts and risks from climatechange are directly tied to decisions madein the present, both in terms of mitigation
to reduce emissions of greenhouse gases (orremove carbon dioxide from the atmosphere)
and adaptation to reduce risks from today’schanged climate conditions and prepare for
future impacts. Mitigation and adaptation
activities can be considered complementarystrategies—mitigation efforts can reduce futurerisks, while adaptation actions can minimize
the consequences of changes that are alreadyhappening as a result of past and present
greenhouse gas emissions.

Mitigation
Many activities within the public and private
sectors aim for or have the effect of reducing
greenhouse gas emissions, such as the increasing use of natural gas in place of coal or the
expansion of wind and solar energy to generate
electricity. Fossil fuel combustion accounts forapproximately 85% of total U.S. greenhouse gas
emissions, with agriculture, land-cover change,
industrial processes, and methane from fossil
fuel extraction and processing as well as fromwaste (including landfills, wastewater treatment, and composting) accounting for most of
the remainder. A number of efforts exist at thefederal level to promote low-carbon energy
technologies and to increase soil and forest
carbon storage.

Many climate change impacts and economic
damages in the United States can be substantially reduced through global-scale reductions
in greenhouse gas emissions complemented
by regional and local adaptation efforts (Ch29: Mitigation, KM 4). Our understanding of
the magnitude and timing of risks that can be
avoided varies by sector, region, and assumptions about how adaptation measures change
the exposure and vulnerability of people, livelihoods, ecosystems, and infrastructure. Acting
sooner rather than later generally results inlower costs overall for both adaptation andmitigation efforts and can offer other benefits
in the near term (Ch. 29: Mitigation, KM 3).

State, local, and tribal government approaches
to mitigating greenhouse gas emissions include
comprehensive emissions reduction strategies
as well as sector- and technology-specificpolicies (see Figure 1.19). Since NCA3, privatecompanies have increasingly reported theirgreenhouse gas emissions, announced
emissions reductions targets, implemented
actions to achieve those targets, and, in somecases, even put an internal price on carbon.
Individuals and other organizations are also
making choices every day to reduce theircarbon footprints.

Since the Third National Climate Assessment(NCA3) in 2014, a growing number of states,
cities, and businesses have pursued or
expanded upon initiatives aimed at reducing
greenhouse gas emissions, and the scale ofadaptation implementation across the country
has increased. However, these efforts do notMarket forces and technological change, particularly within the electric power sector, havecontributed to a decline in U.S. greenhouse gas
emissions over the past decade. In 2016, U.S.

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Mitigation-Related Activities at State and Local Levels

Figure 1.19: (a) The map shows the number of mitigation-related activities at the state level (out of 30 illustrative activities) as
well as cities supporting emissions reductions; (b) the chart depicts the type and number of activities by state. Several territories
also have a variety of mitigation-related activities, including American Sāmoa, the Federated States of Micronesia, Guam,
Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. From Figure 29.1, Ch. 29: Mitigation (Sources: [a] EPA and
ERT, Inc. [b] adapted from America’s Pledge 2017).

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Report-in-Brief | Overview
emissions were at their lowest levels since 1994.
Power sector emissions were 25% below 2005
levels in 2016, the largest emissions reduction
for a sector of the American economy overthis time. This decline was in large part due toincreases in natural gas and renewable energy
generation, as well as enhanced energy efficiency standards and programs (Ch. 4: Energy,
KM 2). Given these advances in electricity
generation, transmission, and distribution, thelargest annual sectoral emissions in the UnitedStates now come from transportation. As of
the writing of this report, business-as-usual (asin, no new policies) projections of U.S. carbon
dioxide and other greenhouse gas emissions
show flat or declining trajectories over the next
decade with a central estimate of about 15% to
20% reduction below 2005 levels by 2025 (Ch.
29: Mitigation, KM 1).

stakeholder interests and values, and planningunder uncertainty. In many sectors, adaptation
can reduce the cost of climate impacts by morethan half (Ch. 28: Adaptation, KM 4; Ch. 29:
Mitigation, KM 4).
At the time of NCA3’s release in 2014, its
authors found that risk assessment and planning were underway throughout the UnitedStates but that on-the-ground implementation
was limited. Since then, the scale and scopeof adaptation implementation has increased,
including by federal, state, tribal, and local
agencies as well as business, academic, andnonprofit organizations (Figure 1.20). While thelevel of implementation is now higher, it is not
yet common nor uniform across the UnitedStates, and the scale of implementation forsome effects and locations is often consideredinadequate to deal with the projected scale ofclimate change risks. Communities have generally focused on actions that address risks fromcurrent climate variability and recent extreme
events, such as making buildings and otherassets incrementally less sensitive to climate
impacts. Fewer communities have focusedon actions to address the anticipated scale offuture change and emergent threats, such as
reducing exposure by preventing building in
high-risk locations or retreating from at-riskcoastal areas (Ch. 28: Adaptation, KM 1).

Recent studies suggest that some of the indirect effects of mitigation actions could significantly reduce—or possibly even completely offset—the potential costs associated with cutting
greenhouse gas emissions. Beyond reductionof climate pollutants, there are many benefits,often immediate, associated with greenhousegas emissions reductions, such as improving
air quality and public health, reducing crop
damages from ozone, and increasing energy
independence and security through increased
reliance on domestic sources of energy (Ch. 13:
Air Quality, KM 4; Ch. 29: Mitigation, KM 4).

Many adaptation initiatives can generate
economic and social benefits in excess of theircosts in both the near and long term (Ch. 28:
Adaptation, KM 4). Damages to infrastructure,such as road and rail networks, are particularly
sensitive to adaptation assumptions, withproactive measures that account for futureclimate risks estimated to be capable of reducing damages by large fractions. More than halfof damages to coastal property are estimated to

Adaptation
Many types of adaptation actions exist, including changes to business operations, hardening
infrastructure against extreme weather, andadjustments to natural resource management
strategies. Achieving the benefits of adaptation
can require upfront investments to achieve
longer-term savings, engaging with different

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Five Adaptation Stages and Progress

Figure 1.20: Adaptation entails a continuing risk management process. With this approach, individuals and organizations
become aware of and assess risks and vulnerabilities from climate and other drivers of change, take actions to reduce thoserisks, and learn over time. The gray arced lines compare the current status of implementing this process with the status reportedby the Third National Climate Assessment in 2014; darker color indicates more activity. From Figure 28.1, Ch. 28: Adaptation(Source: adapted from National Research Council, 2010. Used with permission from the National Academies Press, © 2010,
National Academy of Sciences. Image credits, clockwise from top: National Weather Service; USGS; Armando Rodriguez,
Miami-Dade County; Dr. Neil Berg, MARISA; Bill Ingalls, NASA).

be avoidable through adaptation measures suchas shoreline protection and beach replenishment (Ch. 29: Mitigation, KM 4). Considerable
guidance is available on actions whose benefits
exceed their costs in some sectors (such as
adaptation responses to storms and rising seasin coastal zones, to riverine and extreme precipitation flooding, and for agriculture at thefarm level), but less so on other actions (suchas those aimed at addressing risks to health,biodiversity, and ecosystems services) that may

U.S. Global Change Research Programprovide significant benefits but are not as wellunderstood (Ch. 28: Adaptation, KM 4).
Effective adaptation can also enhance social
welfare in many ways that can be difficult
to quantify, including improving economic
opportunity, health, equity, national security,
education, social connectivity, and sense ofplace, while safeguarding cultural resourcesand enhancing environmental quality. Aggregating these benefits into a single monetary54

Report-in-Brief | Overview
value is not always the best approach, andmore fundamentally, communities may value
benefits differently. Considering various
outcomes separately in risk management
processes can facilitate participatory planning
processes and allow for a specific focus onequity. Prioritizing adaptation actions for
populations that face higher risks from climatechange, including low-income and marginalized
communities, may prove more equitable andlead, for instance, to improved infrastructurein their communities and increased focus onefforts to promote community resilience that
can improve their capacity to prepare for,respond to, and recover from disasters (Ch. 28:
Adaptation, KM 4).

induced changes in the future, including newinvasive species and shifting ranges for native
species, ecosystem managers have alreadybegun to adopt new approaches such as
assisted migration and development of wildlife
corridors (Ch. 7: Ecosystems, KM 2). Many millions of Americans live in coastal areas threatened by sea level rise; in all but the very lowest
sea level rise projections, retreat will become
an unavoidable option in some areas along
the U.S. coastline (Ch. 8: Coastal, KM 1). The
Federal Government has granted funds for the
relocation of some communities, including the
Biloxi-Chitimacha-Choctaw Tribe from Isle deJean Charles in Louisiana (Figure 1.17). However,the potential need for millions of people andbillions of dollars of coastal infrastructure to
be relocated in the future creates challenging
legal, financial, and equity issues that have notyet been addressed (Ch. 28: Adaptation, KM 5).

A significant portion of climate risk can beaddressed by integrating climate adaptation
into existing investments, policies, and practices. Integration of climate adaptation into decision processes has begun in many areas including financial risk reporting, capital investment
planning, engineering standards, militaryplanning, and disaster risk management. A
growing number of jurisdictions address climate risk in their land-use, hazard mitigation,
capital improvement, and transportation plans,
and a small number of cities explicitly link
their coastal and hazard mitigation plans using
analysis of future climate risks. However, overthe course of this century and especially undera higher scenario (RCP8.5), reducing the risksof climate change may require more significant
changes to policy and regulations at all scales,
community planning, economic and financial
systems, technology applications, and ecosystems (Ch. 28: Adaptation, KM 5).

In some areas, lack of historical or current data
to inform policy decisions can be a limitation toassessments of vulnerabilities and/or effective
adaptation planning. For this National Climate
Assessment, this was particularly the case forsome aspects of the Alaska, U.S. Caribbean,and Hawai‘i and U.S.-Affiliated Pacific Islands
regions. In many instances, relying on Indigenous knowledges is among the only current
means of reconstructing what has happenedin the past. To help communities across theUnited States learn from one another in theirefforts to build resilience to a changing climate,this report highlights common climate-relatedrisks and possible response actions across all
regions and sectors.

Some sectors are already taking actions that
go beyond integrating climate risk into current
practices. Faced with substantial climate-

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What Has Happened Since the Last National Climate Assessment?
Our understanding of and experience with climate
science, impacts, risks, and adaptation in the UnitedStates have grown significantly since the Third National Climate Assessment (NCA3), advancing our knowledge of key processes in the earth system, how humanand natural forces are changing them, what the implications are for society, and how we can respond.

Key Scientific Advances
Detection and Attribution: Significant advances havebeen made in the attribution of the human influence forindividual climate and weather extreme events (see CSSR, Chs. 3, 6, 7, and 8).
Extreme Events and Atmospheric Circulation: How climate change may affect specifictypes of extreme events in the United States and the extent to which atmospheric circulation in the midlatitudes is changing or is projected to change, possibly in ways not captured
by current climate models, are important areas of research where scientific understanding
has advanced (see CSSR, Chs. 5, 6, 7, and 9).
Localized Information: As computing resources have grown, projections of future climate
from global models are now being conducted at finer scales (with resolution on the orderof 15 miles), providing more realistic characterization of intense weather systems, including
hurricanes. For the first time in the NCA process, sea level rise projections incorporate
geographic variation based on factors such as local land subsidence, ocean currents, andchanges in Earth’s gravitational field (see CSSR, Chs. 9 and 12).
Ocean and Coastal Waters: Ocean acidification, warming, and oxygen loss are all increasing, and scientific understanding of the severity of their impacts is growing. Both oxygen
loss and acidification may be magnified in some U.S. coastal waters relative to the global
average, raising the risk of serious ecological and economic consequences (see CSSR,
Chs. 2 and 13).
Rapid Changes for Ice on Earth: New observations from many different sources confirm
that ice loss across the globe is continuing and, in many cases, accelerating. Since NCA3,
Antarctica and Greenland have continued to lose ice mass, with mounting evidence
that mass loss is accelerating. Observations continue to show declines in the volume of

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mountain glaciers around the world. Annual September minimum sea ice extent in the
Arctic Ocean has decreased at a rate of 11%–16% per decade since the early 1980s, withaccelerating ice loss since 2000. The annual sea ice extent minimum for 2016 was thesecond lowest on record; the sea ice minimums in 2014 and 2015 were also among thelowest on record (see CSSR, Chs. 1, 11, and 12).
Potential Surprises: Both large-scale shifts in the climate system (sometimes called “tipping points”) and compound extremes have the potential to generate outcomes that are
difficult to anticipate and may have high consequences. The more the climate changes, thegreater the potential for these surprises (see CSSR, Ch. 15).

Extreme Events
Climate change is altering the characteristics of many extreme weather and climate-related
events. Some extreme events have already become more frequent, intense, widespread, orof longer duration, and many are expected to continue to increase or worsen, presenting
substantial challenges for built, agricultural, and natural systems. Some storm types such as
hurricanes, tornadoes, and winter storms are also exhibiting changes that have been linked
to climate change, although the current state of the science does not yet permit detailed
understanding (see CSSR, Executive Summary). Individual extreme weather and climaterelated events—even those that have not been clearly attributed to climate change byscientific analyses—reveal risks to society and vulnerabilities that mirror those we expect ina warmer world. Non-climate stressors (such as land-use changes and shifting demographics) can also amplify the damages associated with extreme events. The National Oceanicand Atmospheric Administration estimates that the United States has experienced 44
billion-dollar weather and climate disasters since 2015 (through April 6, 2018), incurringcosts of nearly $400 billion (https://www.ncdc.noaa.gov/billions/).
Hurricanes: The 2017 Atlantic Hurricane season alone is estimated to have caused
more than $250 billion in damages and over 250 deaths throughout the U.S. Caribbean,
Southeast, and Southern Great Plains. More than 30 inches of rain fell during Hurricane
Harvey, affecting 6.9 million people. Hurricane Maria’s high winds caused widespreaddevastation to Puerto Rico’s transportation, agriculture, communication, and energy infrastructure. Extreme rainfall of up to 37 inches caused widespread flooding and mudslides
across the island. The interruption to commerce and standard living conditions will besustained for a long period while much of Puerto Rico’s infrastructure is rebuilt. Hurricane
Irma destroyed 25% of buildings in the Florida Keys.

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Damage from Hurricane Maria in San Juan, Puerto Rico
Photo taken during a reconnaissance flight of the island on September 23, 2017. Photo credit: Sgt. Jose Ahiram DiazRamos, Puerto Rico National Guard.

Floods: In August 2016, a historic flood resulting from 20 to 30 inches of rainfall over several days devastated a large area of southern Louisiana, causing over $10 billion in damages
and 13 deaths. More than 30,000 people were rescued from floodwaters that damaged
or destroyed more than 50,000 homes, 100,000 vehicles, and 20,000 businesses. In June
2016, torrential rainfall caused destructive flooding throughout many West Virginia towns,
damaging thousands of homes and businesses and causing considerable loss of life. Morethan 1,500 roads and bridges were damaged or destroyed. The 2015–2016 El Niño poured 11days of record-setting rainfall on Hawai‘i, causing severe urban flooding.
Drought: In 2015, drought conditions caused about $5 billion in damages across the Southwest and Northwest, as well as parts of the Northern Great Plains. California experienced
the most severe drought conditions. Hundreds of thousands of acres of farmland remained
fallow, and excess groundwater pumping was required to irrigate existing agriculturalinterests. Two years later, in 2017, extreme drought caused $2.5 billion in agricultural
damages across the Northern Great Plains. Field crops, including wheat, were severely
damaged, and the lack of feed for cattle forced ranchers to sell off livestock.
Wildfires: During the summer of 2015, over 10.1 million acres—an area larger than theentire state of Maryland—burned across the United States, surpassing 2006 for the highest

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The Deadly Carr Fire
The Carr Fire (as seen over Shasta County, California, on August 4, 2018) damaged or destroyed more than 1,500
structures and resulted in several fatalities. Photo credit: Sgt. Lani O. Pascual, U.S. Army National Guard.

annual total of U.S. acreage burned since record keeping began in 1960. These wildfire
conditions were exacerbated by the preceding drought conditions in several states. The
most extensive wildfires occurred in Alaska, where 5 million acres burned within the state.
In Montana, wildfires burned in excess of 1 million acres. The costliest wildfires occurred in
California, where more than 2,500 structures were destroyed by the Valley and Butte Fires;
insured losses alone exceeded $1 billion. In October 2017, a historic firestorm damaged or
destroyed more than 15,000 homes, businesses, and other structures across California (seeFigure 1.5). The Tubbs, Atlas, Nuns, and Redwood Valley Fires caused a total of 44 deaths,
and their combined destruction represents the costliest wildfire event on record.
Tornadoes: In March 2017, a severe tornado outbreak caused damage across much of theMidwest and into the Northeast. Nearly 1 million customers lost power in Michigan alone
due to sustained high winds, which affected several states from Illinois to New York.
Heat Waves: Honolulu experienced 24 days of record-setting heat during the 2015–2016 El
Niño event. As a result, the local energy utility issued emergency public service announcements to curtail escalating air conditioning use that threatened the electrical grid.

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New Aspects of This Report
Hundreds of states, counties, cities, businesses, universities, and other entities are
implementing actions that build resilience to climate-related impacts and risks, while also
aiming to reduce greenhouse gas emissions. Many of these actions have been informedby new climate-related tools and products developed through the U.S. Global Change
Research Program (USGCRP) since NCA3 (see Appendix 3: Scenario Products and Data
Tools); we briefly highlight a few of them here. In addition, several structural changes havebeen introduced to the report and new methods used in response to stakeholder needs formore localized information and to address key gaps identified in NCA3. The Third National
Climate Assessment remains a valuable and relevant resource—this report expands upon
our knowledge and experience as presented four years ago.
Climate Science Special Report: Early in the development of NCA4, experts and Administration officials recognized that conducting a comprehensive physical science assessment(Volume I) in advance of an impacts assessment (Volume II) would allow one to informthe other. The Climate Science Special Report, released in
November 2017, is Volume I of NCA4 and represents themost thorough and up-to-date assessment of climate
science in the United States and underpins the findingsof this report; its findings are summarized in Chapter 2(Our Changing Climate). See the “Key Scientific Advances”
section in this box and Box 2.3 in Chapter 2 for more detail.
Scenario Products: As described in more detail in Appendix 3 (Data Tools & Scenario Products), federal interagencygroups developed a suite of high-resolution scenario
products that span a range of plausible future changes inkey environmental variables through at least 2100. These
USGCRP scenario products help ensure consistency acrossthe report and improve the ability to synthesize across chapters. Where possible, authors
have used these scenario products to frame uncertainty in future climate as it relates tothe risks that are the focus of their chapters. In addition, the Indicators Interagency Working Group has developed an Indicators platform that uses observations or calculations tomonitor conditions or trends in the earth system, just as businesses might use the unemployment index as an indicator of economic conditions (see Figure 1.2 and https://www.
globalchange.gov/browse/indicators).

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Localized Information: With the increased focus on local and regional information in
NCA4, USGCRP agencies developed two additional products that not only inform thisassessment but can serve as valuable decision-support tools. The first are the State Climate Summaries—a peer-reviewed collection of climate change information covering all
ten NCA4 regions at the state level. In addition to standard data on observed and projectedclimate change, each State Climate Summary contains state-specific changes and theirrelated impacts as well as a suite of complementary graphics (stateclimatesummaries.
globalchange.gov). The second product is the U.S. Climate Resilience Toolkit (https://
toolkit.climate.gov/), which offers data-driven tools, information, and subject-matter
expertise from across the Federal Government in one easy-to-use location, so Americans
are better able to understand the climate-related risks and opportunities impacting theircommunities and can make more informed decisions on how to respond. In particular, thecase studies showcase examples of climate change impacts and accompanying response
actions that complement those presented in Figure 1.1 and allow communities to learn how
to build resilience from one another.
New Chapters: In response to public feedback on NCA3 and input solicited in the earlystages of this assessment, a number of significant structural changes have been made.
Most fundamentally, the balance of the report’s focus has shifted from national-level
chapters to regional chapters in response to a growing desire for more localized information on impacts. Building on this theme, the Great Plains chapter has been split into
Northern and Southern chapters (Chapters 22 and 23) along the Kansas–Nebraska border.
In addition, the U.S. Caribbean is now featured as a separate region in this report (Chapter20), focusing on the unique impacts, risks, and response capabilities in Puerto Rico and the
U.S. Virgin Islands.
Public input also requested greater international context in the report, which has beenaddressed through two new additions. A new chapter focuses on topics including theeffects of climate change on U.S. trade and businesses, national security, and U.S. humanitarian assistance and disaster relief (Chapter 16). A new international appendix (Appendix 4)presents a number of illustrative examples of how other countries have conducted national
climate assessments, putting our own effort into a global context.
Given recent scientific advances, some emerging topics warranted a more visible platform
in NCA4. A new chapter on Air Quality (Chapter 13) examines how traditional air pollutants
are affected by climate change. A new chapter on Sector Interactions, Multiple Stressors,
and Complex Systems (Chapter 17) evaluates climate-related risks to interconnected
human and natural systems that are increasingly vulnerable to cascading impacts andhighlights advances in analyzing how these systems will interact with and respond to achanging environment (see Box 1.3).

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Integrating Economics: This report, to a much greater degree than previous National
Climate Assessments, includes broader and more systematic quantification of climatechange impacts in economic terms. While this is an emerging body of literature that is not
yet reflected in each of the 10 NCA regions, it represents a valuable advancement in our
understanding of the financial costs and benefits of climate change impacts. Figure 1.21
provides an illustration of the type of economic information that is integrated throughout
this report. It shows the financial damages avoided under a lower scenario (RCP4.5) versus
a higher scenario (RCP8.5).

New Economic Impact Studies

Figure 1.21: Annual economic impact estimates are shown for labor and air quality. The bar graph on the left shows
national annual damages in 2090 (in billions of 2015 dollars) for a higher scenario (RCP8.5) and lower scenario (RCP4.5);
the difference between the height of the RCP8.5 and RCP4.5 bars for a given category represents an estimate of theeconomic benefit to the United States from global mitigation action. For these two categories, damage estimates do notconsider costs or benefits of new adaptation actions to reduce impacts, and they do not include Alaska, Hawaiʻi and
U.S.-Affiliated Pacific Islands, or the U.S. Caribbean. The maps on the right show regional variation in annual impacts
projected under the higher scenario (RCP8.5) in 2090. The map on the top shows the percent change in hours worked
in high-risk industries as compared to the period 2003–2007. The hours lost result in economic damages: for example,$28 billion per year in the Southern Great Plains. The map on the bottom is the change in summer-average maximum
daily 8-hour ozone concentrations (ppb) at ground-level as compared to the period 1995–2005. These changes inozone concentrations result in premature deaths: for example, an additional 910 premature deaths each year in the
Midwest. Source: EPA, 2017. Multi-Model Framework for Quantitative Sectoral Impacts Analysis: A Technical Report for
the Fourth National Climate Assessment. U.S. Environmental Protection Agency, EPA 430-R-17-001.

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Executive Summaries

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2

Our Changing Climate

Key Message 1

An atmospheric river pours moisture into the western United States in February 2017.

Observed Changes in Global Climate
Global climate is changing rapidly compared to the pace of natural variations in climatethat have occurred throughout Earth’s history. Global average temperature has increased byabout 1.8°F from 1901 to 2016, and observational evidence does not support any credible
natural explanations for this amount of warming; instead, the evidence consistently points
to human activities, especially emissions of greenhouse or heat-trapping gases, as thedominant cause.

Key Message 2
Future Changes in Global Climate
Earth’s climate will continue to change over this century and beyond. Past mid-century, howmuch the climate changes will depend primarily on global emissions of greenhouse gases
and on the response of Earth’s climate system to human-induced warming. With significant
reductions in emissions, global temperature increase could be limited to 3.6°F (2°C) or lesscompared to preindustrial temperatures. Without significant reductions, annual average
global temperatures could increase by 9°F (5°C) or more by the end of this century compared
to preindustrial temperatures.

Key Message 3
Warming and Acidifying Oceans
The world’s oceans have absorbed 93% of the excess heat from human-induced warming
since the mid-20th century and are currently absorbing more than a quarter of the carbon
dioxide emitted to the atmosphere annually from human activities, making the oceans
warmer and more acidic. Increasing sea surface temperatures, rising sea levels, andchanging patterns of precipitation, winds, nutrients, and ocean circulation are contributing tooverall declining oxygen concentrations in many locations.
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Key Message 4
Rising Global Sea Levels
Global average sea level has risen by about 7–8 inches (about 16–21 cm) since 1900,
with almost half this rise occurring since 1993 as oceans have warmed and land-based
ice has melted. Relative to the year 2000, sea level is very likely to rise 1 to 4 feet (0.3
to 1.3 m) by the end of the century. Emerging science regarding Antarctic ice sheet
stability suggests that, for higher scenarios, a rise exceeding 8 feet (2.4 m) by 2100
is physically possible, although the probability of such an extreme outcome cannot
currently be assessed.

Key Message 5
Increasing U.S. Temperatures
Annual average temperature over the contiguous United States has increased by 1.2ºF(0.7°C) over the last few decades and by 1.8°F (1°C) relative to the beginning of thelast century. Additional increases in annual average temperature of about 2.5°F (1.4°C)
are expected over the next few decades regardless of future emissions, and increases
ranging from 3°F to 12°F (1.6°–6.6°C) are expected by the end of century, depending onwhether the world follows a higher or lower future scenario, with proportionally greaterchanges in high temperature extremes.

Key Message 6
Changing U.S. Precipitation
Annual precipitation since the beginning of the last century has increased across mostof the northern and eastern United States and decreased across much of the southern
and western United States. Over the coming century, significant increases are projected
in winter and spring over the Northern Great Plains, the Upper Midwest, and the Northeast. Observed increases in the frequency and intensity of heavy precipitation eventsin most parts of the United States are projected to continue. Surface soil moisture
over most of the United States is likely to decrease, accompanied by large declines insnowpack in the western United States and shifts to more winter precipitation falling as
rain rather than snow.

Key Message 7
Rapid Arctic Change
In the Arctic, annual average temperatures have increased more than twice as fast as
the global average, accompanied by thawing permafrost and loss of sea ice and glaciermass. Arctic-wide glacial and sea ice loss is expected to continue; by mid-century, it
is very likely that the Arctic will be nearly free of sea ice in late summer. Permafrost is
expected to continue to thaw over the coming century as well, and the carbon dioxideand methane released from thawing permafrost has the potential to amplify human-induced warming, possibly significantly.

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Key Message 8
Changes in Severe Storms
Human-induced change is affecting atmospheric dynamics and contributing to thepoleward expansion of the tropics and the northward shift in Northern Hemisphere
winter storm tracks since 1950. Increases in greenhouse gases and decreases in air
pollution have contributed to increases in Atlantic hurricane activity since 1970. In the
future, Atlantic and eastern North Pacific hurricane rainfall and intensity are projected
to increase, as are the frequency and severity of landfalling “atmospheric rivers” on theWest Coast.

Key Message 9
Increases in Coastal Flooding
Regional changes in sea level rise and coastal flooding are not evenly distributed acrossthe United States; ocean circulation changes, sinking land, and Antarctic ice melt will result in greater-than-average sea level rise for the Northeast and western Gulf of Mexico
under lower scenarios and most of the U.S. coastline other than Alaska under higher
scenarios. Since the 1960s, sea level rise has already increased the frequency of hightide flooding by a factor of 5 to 10 for several U.S. coastal communities. The frequency,
depth, and extent of tidal flooding are expected to continue to increase in the future,
as is the more severe flooding associated with coastal storms, such as hurricanes andnor’easters.

Key Message 10
Long-Term Changes
The climate change resulting from human-caused emissions of carbon dioxide will
persist for decades to millennia. Self-reinforcing cycles within the climate system havethe potential to accelerate human-induced change and even shift Earth’s climate system
into new states that are very different from those experienced in the recent past. Futurechanges outside the range projected by climate models cannot be ruled out, and dueto their systematic tendency to underestimate temperature change during past warm
periods, models may be more likely to underestimate than to overestimate long-term
future change.
For full chapter, including references and Traceable Accounts, see https://nca2018.globalchange.
gov/chapter/climate.

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3

Water

Key Message 1

Levee repair along the San Joaquin River in California, February 2017

Changes in Water Quantity and Quality
Significant changes in water quantity and quality are evident across the country.
These changes, which are expected to persist, present an ongoing risk to coupledhuman and natural systems and related ecosystem services. Variable precipitation
and rising temperature are intensifying droughts, increasing heavy downpours, andreducing snowpack. Reduced snow-to-rain ratios are leading to significant differences
between the timing of water supply and demand. Groundwater depletion is exacerbating
drought risk. Surface water quality is declining as water temperature increases andmore frequent high-intensity rainfall events mobilize pollutants such as sediments andnutrients.

Key Message 2
Deteriorating Water Infrastructure at Risk
Deteriorating water infrastructure compounds the climate risk faced by society.
Extreme precipitation events are projected to increase in a warming climate and maylead to more severe floods and greater risk of infrastructure failure in some regions.
Infrastructure design, operation, financing principles, and regulatory standards typicallydo not account for a changing climate. Current risk management does not typicallyconsider the impact of compound extremes (co-occurrence of multiple events) and therisk of cascading infrastructure failure.

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Key Message 3
Water Management in a Changing Future
Water management strategies designed in view of an evolving future we can only
partially anticipate will help prepare the Nation for water- and climate-related risks ofthe future. Current water management and planning principles typically do not address
risk that changes over time, leaving society exposed to more risk than anticipated.
While there are examples of promising approaches to manage climate risk, the gap
between research and implementation, especially in view of regulatory and institutional
constraints, remains a challenge.
Ensuring a reliable supply of clean freshwater
to individuals, communities, and ecosystems,
together with effective management of floods
and droughts, is the foundation of humanand ecological health. The water sector isalso central to the economy and contributes
significantly to the resilience of many othersectors, including agriculture, energy, urban
environments, and industry.

decades. Because such protracted exposures toextreme floods or droughts in different partsof the country are extraordinary comparedto events experienced in the 20th century,
they are not yet incorporated in water management principles and practice. Anticipatedfuture climate change will exacerbate this risk
in many regions.
A central challenge to water planning andmanagement is learning to plan for plausible
future climate conditions that are wider inrange than those experienced in the 20th
century. Doing so requires approaches that
evaluate plans over many possible futuresinstead of just one, incorporate real-timemonitoring and forecast products to better
manage extremes when they occur, and update
policies and engineering principles with thebest available geoscience-based understandingof planetary change. While this represents a
break from historical practice, recent examplesof adaptation responses undertaken by large
water management agencies, including major
metropolitan water utilities and the U.S. Army
Corps of Engineers, are promising.

Water systems face considerable risk, even
without anticipated future climate changes.
Limited surface water storage, as well as a limited ability to make use of long-term drought
forecasts and to trade water across uses andbasins, has led to a significant depletion of
aquifers in many regions in the United States.
Across the Nation, much of the critical water
and wastewater infrastructure is nearing theend of its useful life. To date, no comprehensive
assessment exists of the climate-related vulnerability of U.S. water infrastructure (including
dams, levees, aqueducts, sewers, and water
and wastewater distribution and treatment
systems), the potential resulting damages,
or the cost of reconstruction and recovery.
Paleoclimate information (reconstructions ofpast climate derived from ice cores or treerings) shows that over the last 500 years, North
America has experienced pronounced wet/
dry regime shifts that sometimes persisted for

U.S. Global Change Research Program

For full chapter, including references andTraceable Accounts, see https://nca2018.
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Depletion of Groundwater in Major U.S. Regional Aquifers(left) Groundwater supplies have been decreasing in the major regional aquifers of the United States over the last century(1900–2000). (right) This decline has accelerated recently (2001–2008) due to persistent droughts in many regions and the lackof adequate surface water storage to meet demands. This decline in groundwater compromises the ability to meet water needs
during future droughts and impacts the functioning of groundwater dependent ecosystems (e.g., Kløve et al. 2014).The values
shown are net volumetric rates of groundwater depletion (km3 per year) averaged over each aquifer. Subareas of an aquifer may
deplete at faster rates or may be actually recovering. Hatching in the figure represents where the High Plains Aquifer overlies
the deep, confined Dakota Aquifer. From Figure 3.2 (Source: adapted from Konikow 2015. Reprinted from Groundwater withpermission of the National Groundwater Association. © 2015).

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4Energy Supply, Delivery, and Demand

Key Message 1

Linemen working to restore power in Puerto Rico after Hurricane Maria in 2017

Nationwide Impacts on Energy
The Nation’s energy system is already affected by extreme weather events, and due
to climate change, it is projected to be increasingly threatened by more frequent andlonger-lasting power outages affecting critical energy infrastructure and creating fuelavailability and demand imbalances. The reliability, security, and resilience of the energy
system underpin virtually every sector of the U.S. economy. Cascading impacts on othercritical sectors could affect economic and national security.

Key Message 2
Changes in Energy System Affect Vulnerabilities
Changes in energy technologies, markets, and policies are affecting the energy system’svulnerabilities to climate change and extreme weather. Some of these changes increase
reliability and resilience, while others create additional vulnerabilities. Changes include
the following: natural gas is increasingly used as fuel for power plants; renewable
resources are becoming increasingly cost competitive with an expanding market
share; and a resilient energy supply is increasingly important as telecommunications,transportation, and other critical systems are more interconnected than ever.

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Key Message 3
Improving Energy System Resilience
Actions are being taken to enhance energy security, reliability, and resilience withrespect to the effects of climate change and extreme weather. This progress occurs
through improved data collection, modeling, and analysis to support resilience planning;private and public–private partnerships supporting coordinated action; and bothdevelopment and deployment of new, innovative energy technologies for adaptingenergy assets to extreme weather hazards. Although barriers exist, opportunities remain
to accelerate the pace, scale, and scope of investments in energy systems resilience.

The Nation’s economic security is increasingly
dependent on an affordable and reliable supply of energy. Every sector of the economy
depends on energy, from manufacturing toagriculture, banking, healthcare, telecommunications, and transportation. Increasingly,
climate change and extreme weather events areaffecting the energy system, threatening more
frequent and longer-lasting power outages andfuel shortages. Such events can have cascading
impacts on other critical sectors, potentiallyaffecting the Nation’s economic and national
security. At the same time, the energy sector
is undergoing substantial policy, market, andtechnology-driven changes that are projected
to affect these vulnerabilities.

greater use of air conditioning and increaseelectricity demand, likely resulting in increases inelectricity costs. The increase in annual electricity
demand across the country for cooling is offset
only marginally by the relatively small decline
in electricity demand for heating. Extreme cold
events, including ice and snow events, can damage power lines and impact fuel supplies. Severe
drought, along with changes in evaporation,
reductions in mountain snowpack, and shifting
mountain snowmelt timing, is projected to reducehydropower production and threaten oil and gas
drilling and refining, as well as thermoelectric
power plants that rely on surface water for cooling. Drier conditions are projected to increase therisk of wildfires and damage to energy production
and generation assets and the power grid.

The impacts of extreme weather and climatechange on energy systems will differ across theUnited States. Low-lying energy facilities andsystems located along inland waters or near thecoasts are at elevated risk of flooding from more
intense precipitation, rising sea levels, and more
intense hurricanes. Increases in the severity andfrequency of extreme precipitation are projected
to affect inland energy infrastructure in every
region. Rising temperatures and extreme heat
events are projected to reduce the generation
capacity of thermoelectric power plants anddecrease the efficiency of the transmission grid.
Rising temperatures are projected to also drive

At the same time, the nature of the energy
system itself is changing. Low carbon-emitting
natural gas generation has displaced coal
generation due to the rising production of
low-cost, unconventional natural gas, in part
supported by federal investment in researchand development. In the last 10 years, the shareof generation from natural gas increased from
20% to over 30%, while coal has declined fromnearly 50% to around 30%. Over this sametime, generation from wind and solar has grownfrom less than 1% to over 5% due to a combination of technological progress, dramatic cost
reductions, and federal and state policies.

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It is possible to address the challenges of achanging climate and energy system, and bothindustry and governments at the local, state,regional, federal, and tribal levels are taking
actions to improve the resilience of the Nation’senergy system. These actions include planningand operational measures that seek to anticipate climate impacts and prevent or respond todamages more effectively, as well as hardening
measures to protect assets from damage during
extreme events. Resilience actions can haveco-benefits, such as developing and deploying

new innovative energy technologies that
increase resilience and reduce emissions. While
steps are being taken, an escalation of the pace,scale, and scope of efforts is needed to ensure
the safe and reliable provision of energy andto establish a climate-ready energy system toaddress present and future risks.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/energy.

Potential Impacts from Extreme Weather and Climate Change

Extreme weather and climate change can potentially impact all components of the Nation’s energy system, from fuel (petroleum,coal, and natural gas) production and distribution to electricity generation, transmission, and demand. From Figure 4.1 (Source:
adapted from DOE 2013).

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5Land Cover and Land-Use Change

Agricultural fields near the Ririe Reservoir in Bonneville, Idaho

Key Message 1

Land-Cover Changes Influence Weather and Climate
Changes in land cover continue to impact local- to global-scale weather and climate
by altering the flow of energy, water, and greenhouse gases between the land and theatmosphere. Reforestation can foster localized cooling, while in urban areas, continued
warming is expected to exacerbate urban heat island effects.

Key Message 2
Climate Impacts on Land and Ecosystems
Climate change affects land use and ecosystems. Climate change is expected to directly
and indirectly impact land use and cover by altering disturbance patterns, species
distributions, and the suitability of land for specific uses. The composition of the naturaland human landscapes, and how society uses the land, affects the ability of the Nation’s
ecosystems to provide essential goods and services.

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Climate can affect and be affected by changes
in land cover (the physical features that cover
the land such as trees or pavement) and landuse (human management and activities onland, such as mining or recreation). A forest, forinstance, would likely include tree cover but
could also include areas of recent tree removals
currently covered by open grass areas. Land
cover and use are inherently coupled: changes
in land-use practices can change land cover,and land cover enables specific land uses.
Understanding how land cover, use, condition,and management vary in space and time
is challenging.

Land use is also changed by both human andclimate drivers. Land-use decisions are traditionally based on short-term economic factors.
Land-use changes are increasingly being influenced by distant forces due to the globalizationof many markets. Land use can also change due
to local, state, and national policies, such as
programs designed to remove cultivation fromhighly erodible land to mitigate degradation,
legislation to address sea level rise in local
comprehensive plans, or policies that reduce
the rate of timber harvest on federal lands.
Technological innovation has also influenced
land-use change, with the expansion of cultivated lands from the development of irrigation
technologies and, more recently, decreases indemand for agricultural land due to increases
in crop productivity. The recent expansion ofoil and gas extraction activities throughout
large areas of the United States demonstrates
how policy, economics, and technology cancollectively influence and change land use
and land cover.

Changes in land cover can occur in response toboth human and climate drivers. For example,
demand for new settlements often results inthe permanent loss of natural and working
lands, which can result in localized changes
in weather patterns, temperature, and precipitation. Aggregated over large areas, thesechanges have the potential to influence Earth’s
climate by altering regional and global circulation patterns, changing the albedo (reflectivity)of Earth’s surface, and changing the amount ofcarbon dioxide (CO2) in the atmosphere. Conversely, climate change can also influence land
cover, resulting in a loss of forest cover fromclimate-related increases in disturbances, theexpansion of woody vegetation into grasslands,
and the loss of beaches due to coastal erosion
amplified by rises in sea level.

U.S. Global Change Research Program

Decisions about land use, cover, and management can help determine society’s ability to
mitigate and adapt to climate change.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/land-changes.

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Changes in Land Cover by Region

The figure shows the net change in land cover by class in square miles, from 1973 to 2011. Land-cover change has been highly
dynamic over space, time, and sector, in response to a range of driving forces. Net change in land cover reveals the trajectoryof a class over time. A dramatic example illustrated here is the large decline in agricultural lands in the two Great Plains regions
beginning in the mid-1980s, which resulted in large part from the establishment of the Conservation Reserve Program. Over thesame period, agriculture also declined in the Southwest region; however, the net decline was largely attributable to prolonged
drought conditions, as opposed to changes in federal policy. Data for the period 1973–2000 are from Sleeter et al. (2013) whiledata from 2001–2011 are from the National Land Cover Database (NLCD). Note: the two disturbance categories used for the
1973–2000 data were not included in the NLCD data for 2001–2011 and largely represent conversions associated with harvest
activities (mechanical disturbance) and wildfire (nonmechanical disturbance). Comparable data are unavailable for the U.S.
Caribbean, Alaska, and Hawai‘i & U.S.-Affiliated Pacific Islands regions, precluding their representation in this figure. From
Figure 5.2 (Source: USGS).

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Forests

Key Message 1

California’s multiyear drought killed millions of trees in low-elevation forests

Ecological Disturbances and Forest Health
It is very likely that more frequent extreme weather events will increase the frequency
and magnitude of severe ecological disturbances, driving rapid (months to years) andoften persistent changes in forest structure and function across large landscapes. It isalso likely that other changes, resulting from gradual climate change and less severe
disturbances, will alter forest productivity and health and the distribution and abundanceof species at longer timescales (decades to centuries).

Key Message 2
Ecosystem Services
It is very likely that climate change will decrease the ability of many forest ecosystems
to provide important ecosystem services to society. Tree growth and carbon storage are
expected to decrease in most locations as a result of higher temperatures, more frequent
drought, and increased disturbances. The onset and magnitude of climate change
effects on water resources in forest ecosystems will vary but are already occurring insome regions.

Key Message 3
Adaptation
Forest management activities that increase the resilience of U.S. forests to climate change
are being implemented, with a broad range of adaptation options for different resources,
including applications in planning. The future pace of adaptation will depend on how
effectively social, organizational, and economic conditions support implementation.

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Forests on public and private lands provide
benefits to the natural environment, as well as
economic benefits and ecosystem services topeople in the United States and globally. The
ability of U.S. forests to continue to provide goods
and services is threatened by climate change
and associated increases in extreme events anddisturbances. For example, severe drought andinsect outbreaks have killed hundreds of millions
of trees across the United States over the past 20
years, and wildfires have burned at least 3.7 million
acres annually in all but 3 years from 2000 to 2016.
Recent insect-caused mortality appears to be outside the historical context and is likely related toclimate change; however, it is unclear if the apparent climate-related increase in fire-caused treemortality is outside the range of what has been
observed over centuries of wildfire occurrence.

dry forests in the western United States that havenot experienced wildfire for several decades,
increased fire frequency is expected to facilitate
the persistence of sprouting hardwood species
such as quaking aspen in western mountains andfire tolerant pine and hardwood species in theeastern United States (see regional chapters formore detail on variation across the United States).
Drought, heavy rainfall, altered snowpack, andchanging forest conditions are increasing thefrequency of low summer streamflow, winterand spring flooding, and low water quality insome locations, with potential negative impacts
on aquatic resources and on water supplies forhuman communities.
From 1990 to 2015, U.S. forests sequestered 742
teragrams (Tg) of carbon dioxide (CO2) per year,
offsetting approximately 11% of the Nation’s CO2
emissions. U.S. forests are projected to continue to store carbon but at declining rates, asaffected by both land use and lower CO2 uptake
as forests get older. However, carbon accumulation in surface soils (at depths of 0–4 inches)
can mitigate the declining carbon sink of U.S.
forests if reforestation is routinely implemented
at large spatial scales.

A warmer climate will decrease tree growth inmost forests that are water limited (for example,
low-elevation ponderosa pine forests) but will
likely increase growth in forests that are energy
limited (for example, subalpine forests, wherelong-lasting snowpack and cold temperatures
limit the growing season). Drought and extreme
high temperatures can cause heat-related stressin vegetation and, in turn, reduce forest productivity and increase mortality. The rate of climate
warming is likely to influence forest health (thatis, the extent to which ecosystem processes arefunctioning within their range of historic variation) and competition between trees, which willaffect the distributions of some species.

Implementation of climate-informed resource
planning and management on forestlands has
progressed significantly over the past decade.
The ability of society and resource management
to continue to adapt to climate change will be
determined primarily by socioeconomic factors
and organizational capacity. A viable forest-based
workforce can facilitate timely actions that minimize negative effects of climate change. Ensuring
the continuing health of forest ecosystems and,
where desired and feasible, keeping forestland inforest cover are key challenges for society.

Large-scale disturbances (over thousands tohundreds of thousands of acres) that cause rapidchange (over days to years) and more gradualclimate change effects (over decades) will alter theability of forests to provide ecosystem services,
although alterations will vary greatly dependingon the tree species and local biophysical conditions. For example, whereas crown fires (forest
fires that spread from treetop to treetop) willcause extensive areas of tree mortality in dense,

For full chapter, including references and Traceable Accounts, see https://nca2018.globalchange.
gov/chapter/forests.

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Climate Change Vulnerabilities and Adaptation Options

To increase resilience to future stressors and disturbances, examples of adaptation options (risk management) have beendeveloped in response to climate change vulnerabilities in forest ecosystems (risk assessment) in the Pacific Northwest.
Vulnerabilities and adaptation options vary among different forest ecosystems. From Figure 6.7 (Sources: U.S. Forest Service
and University of Washington).

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7

Ecosystems, Ecosystem Services, and Biodiversity

Kodiak National Wildlife Refuge, Alaska

Key Message 1
Impacts on Species and Populations

Climate change continues to impact species and populations in significant andobservable ways. Terrestrial, freshwater, and marine organisms are responding toclimate change by altering individual characteristics, the timing of biological events, andtheir geographic ranges. Local and global extinctions may occur when climate change
outpaces the capacity of species to adapt.

Key Message 2
Impacts on Ecosystems
Climate change is altering ecosystem productivity, exacerbating the spread of invasive
species, and changing how species interact with each other and with their environment.
These changes are reconfiguring ecosystems in unprecedented ways.

Key Message 3
Ecosystem Services at Risk
The resources and services that people depend on for their livelihoods, sustenance,
protection, and well-being are jeopardized by the impacts of climate change on
ecosystems. Fundamental changes in agricultural and fisheries production, the supply ofclean water, protection from extreme events, and culturally valuable resources are occurring.

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Key Message 4
Challenges for Natural Resource Management
Traditional natural resource management strategies are increasingly challenged by the
impacts of climate change. Adaptation strategies that are flexible, consider interacting
impacts of climate and other stressors, and are coordinated across landscapescales are progressing from theory to application. Significant challenges remain tocomprehensively incorporate climate adaptation planning into mainstream natural
resource management, as well as to evaluate the effectiveness of implemented actions.

Biodiversity—the variety of life on Earth—provides vital services that support and improve
human health and well-being. Ecosystems,
which are composed of living things thatinteract with the physical environment, provide numerous essential benefits to people.
These benefits, termed ecosystem services,encompass four primary functions: provisioning
materials, such as food and fiber; regulating
critical parts of the environment, such as water
quality and erosion control; providing cultural
services, such as recreational opportunities andaesthetic value; and providing supporting services, such as nutrient cycling. Climate change
poses many threats and potential disruptions
to ecosystems and biodiversity, as well as to theecosystem services on which people depend.

new conditions is determined by their adaptive
capacity, which may be inadequate to keep
pace with rapid change. Our understanding ofclimate change impacts and the responses of
biodiversity and ecosystems has improved sinceNCA3. The expected consequences of climatechange will vary by region, species, and ecosystem type. Management responses are evolving
as new tools and approaches are developed andimplemented; however, they may not be able
to overcome the negative impacts of climatechange. Although efforts have been madesince NCA3 to incorporate climate adaptation
strategies into natural resource management,
significant work remains to comprehensively
implement climate-informed planning. This
chapter presents additional evidence forclimate change impacts to biodiversity, ecosystems, and ecosystem services, reflecting
increased confidence in the findings reported
in NCA3. The chapter also illustrates the complex and interrelated nature of climate change
impacts to biodiversity, ecosystems, and theservices they provide.

Building on the findings of the Third National
Climate Assessment (NCA3), this chapter
provides additional evidence that climatechange is significantly impacting ecosystems and biodiversity in the United States.
Mounting evidence also demonstrates thatclimate change is increasingly compromising
the ecosystem services that sustain humancommunities, economies, and well-being. Bothhuman and natural systems respond to change,
but their ability to respond and thrive under

U.S. Global Change Research Program

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/ecosystems.

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Climate Change, Ecosystems, and Ecosystem Services

Climate and non-climate stressors interact synergistically on biological diversity, ecosystems, and the services they provide
for human well-being. The impact of these stressors can be reduced through the ability of organisms to adapt to changes
in their environment, as well as through adaptive management of the resources upon which humans depend. Biodiversity,
ecosystems, ecosystem services, and human well-being are interconnected: biodiversity underpins ecosystems, which in turnprovide ecosystem services; these services contribute to human well-being. Ecosystem structure and function can also influence
the biodiversity in a given area. The use of ecosystem services by humans, and therefore the well-being humans derive fromthese services, can have feedback effects on ecosystem services, ecosystems, and biodiversity. From Figure 7.1 (Sources:
NOAA, USGS, and DOI).

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8

Coastal Effects

Key Message 1

Natural “green barriers” help protect this Florida coastline and infrastructure from severe storms and floods.

Coastal Economies and Property Are Already at Risk
America’s trillion-dollar coastal property market and public infrastructure are threatenedby the ongoing increase in the frequency, depth, and extent of tidal flooding due to sea
level rise, with cascading impacts to the larger economy. Higher storm surges due tosea level rise and the increased probability of heavy precipitation events exacerbate therisk. Under a higher scenario (RCP8.5), many coastal communities will be transformedby the latter part of this century, and even under lower scenarios (RCP4.5 or RCP2.6),
many individuals and communities will suffer financial impacts as chronic high tide
flooding leads to higher costs and lower property values. Actions to plan for and adapt
to more frequent, widespread, and severe coastal flooding would decrease direct losses
and cascading economic impacts.

Key Message 2
Coastal Environments Are Already at Risk
Fisheries, tourism, human health, and public safety depend on healthy coastal
ecosystems that are being transformed, degraded, or lost due in part to climate change
impacts, particularly sea level rise and higher numbers of extreme weather events.
Restoring and conserving coastal ecosystems and adopting natural and nature-based
infrastructure solutions can enhance community and ecosystem resilience to climatechange, help to ensure their health and vitality, and decrease both direct and indirect
impacts of climate change.

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Key Message 3
Social Challenges Intensified
As the pace and extent of coastal flooding and erosion accelerate, climate change
impacts along our coasts are exacerbating preexisting social inequities, as communities
face difficult questions about determining who will pay for current impacts and future
adaptation and mitigation strategies and if, how, or when to relocate. In response toactual or projected climate change losses and damages, coastal communities will be
among the first in the Nation to test existing climate-relevant legal frameworks andpolicies against these impacts and, thus, will establish precedents that will affect bothcoastal and non-coastal regions.

The Coasts chapter of the Third National Climate
Assessment, published in 2014, focused on coastal
lifelines at risk, economic disruption, unevensocial vulnerability, and vulnerable ecosystems.
This Coastal Effects chapter of the Fourth National
Climate Assessment updates those themes, witha focus on integrating the socioeconomic andenvironmental impacts and consequences of achanging climate. Specifically, the chapter builds
on the threat of rising sea levels exacerbating tidal
and storm surge flooding, the state of coastal ecosystems, and the treatment of social vulnerability
by introducing the implications for social equity.

The social, economic, and environmental systems
along the coasts are being affected by climatechange. Threats from sea level rise (SLR) areexacerbated by dynamic processes such as hightide and storm surge flooding (Ch. 19: Southeast,
KM 2), erosion (Ch. 26: Alaska, KM 2), waves andtheir effects, saltwater intrusion into coastal
aquifers and elevated groundwater tables (Ch. 27:
Hawai‘i & Pacific Islands, KM 1; Ch. 3: Water, KM1), local rainfall (Ch. 3: Water, KM 1), river runoff(Ch. 3: Water, KM 1), increasing water and surface
air temperatures (Ch. 9: Oceans, KM 3), and ocean
acidification (see Ch. 2: Climate, KM 3 and Ch. 9:
Oceans, KM 1, 2, and 3 for more information on
ocean acidification, hypoxia, and ocean warming).

U.S. coasts are dynamic environments andeconomically vibrant places to live and work. Asof 2013, coastal shoreline counties were home to133.2 million people, or 42% of the population. The
coasts are economic engines that support jobs
in defense, fishing, transportation, and tourism
industries; contribute substantially to the U.S.
gross domestic product; and serve as hubs ofcommerce, with seaports connecting the country
with global trading partners. Coasts are home todiverse ecosystems such as beaches, intertidal
zones, reefs, seagrasses, salt marshes, estuaries,
and deltas that support a range of important
services including fisheries, recreation, and coastal
storm protection. U.S. coasts span three oceans,as well as the Gulf of Mexico, the Great Lakes, andPacific and Caribbean islands.

Although storms, floods, and erosion have always
been hazards, in combination with rising sea levels
they now threaten approximately $1 trillion innational wealth held in coastal real estate and thecontinued viability of coastal communities that
depend on coastal water, land, and other resources for economic health and cultural integrity (Ch.
15: Tribes, KM 1 and 2).
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/coastal.

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Impacts of the 2017 Hurricane Season

Quintana Perez dumps water from a cooler into floodwaters in the aftermath of Hurricane Irma in Immokalee, Florida. From
Figure 8.6 (Photo credit: AP Photo/Gerald Herbert).

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Oceans and Marine Resources

Coral reefs in the U.S. Virgin Islands

Key Message 1
Ocean Ecosystems

The Nation’s valuable ocean ecosystems are being disrupted by increasing global temperatures
through the loss of iconic and highly valued habitats and changes in species composition and foodweb structure. Ecosystem disruption will intensify as ocean warming, acidification, deoxygenation,and other aspects of climate change increase. In the absence of significant reductions in carbon
emissions, transformative impacts on ocean ecosystems cannot be avoided.

Key Message 2
Marine Fisheries
Marine fisheries and fishing communities are at high risk from climate-driven changes in the
distribution, timing, and productivity of fishery-related species. Ocean warming, acidification, anddeoxygenation are projected to increase these changes in fishery-related species, reduce catches
in some areas, and challenge effective management of marine fisheries and protected species.
Fisheries management that incorporates climate knowledge can help reduce impacts, promoteresilience, and increase the value of marine resources in the face of changing ocean conditions.

Key Message 3
Extreme Events
Marine ecosystems and the coastal communities that depend on them are at risk of significant
impacts from extreme events with combinations of very high temperatures, very low oxygen levels,
or very acidified conditions. These unusual events are projected to become more common andmore severe in the future, and they expose vulnerabilities that can motivate change, including
technological innovations to detect, forecast, and mitigate adverse conditions.

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Americans rely on ocean ecosystems forfood, jobs, recreation, energy, and other vital
services. Increased atmospheric carbon dioxidelevels change ocean conditions through threemain factors: warming seas, ocean acidification, and deoxygenation. These factors aretransforming ocean ecosystems, and thesetransformations are already impacting the U.S.
economy and coastal communities, cultures,and businesses.

active movements of species to track theirpreferred temperature conditions, with mostmoving northward or into deeper water withwarming oceans. These changes are impacting
the distribution and availability of many commercially and recreationally valuable fish andinvertebrates. The effects of ocean warming,
acidification, and deoxygenation on marine
species will interact with fishery management
decisions, from seasonal and spatial closures toannual quota setting, allocations, and fish stock
rebuilding plans. Accounting for these factors
is the cornerstone of climate-ready fishery
management. Even without directly accounting
for climate effects, precautionary fishery
management and better incentives can increase
economic benefits and improve resilience.

While climate-driven ecosystem changes arepervasive in the ocean, the most apparent
impacts are occurring in tropical and polar ecosystems, where ocean warming is causing theloss of two vulnerable habitats: coral reef andsea ice ecosystems. The extent of sea ice in the
Arctic is decreasing, which represents a directloss of important habitat for animals like polar
bears and ringed seals that use it for hunting,shelter, migration, and reproduction, causing
their abundances to decline (Ch. 26: Alaska, KM
1). Warming has led to mass bleaching and/or
outbreaks of coral diseases off the coastlinesof Puerto Rico, the U.S. Virgin Islands, Florida,
Hawai‘i, and the U.S.-Affiliated Pacific Islands(Ch. 20: U.S. Caribbean, KM 2; Ch. 27: Hawai‘i &Pacific Islands, KM 4) that threaten reef ecosystems and the people who depend on them.
The loss of the recreational benefits alone fromcoral reefs in the United States is expected toreach $140 billion (discounted at 3% in 2015
dollars) by 2100. Reducing greenhouse gas
emissions (for example, under RCP4.5); (see the
Scenario Products section of Appendix 3 formore on scenarios) could reduce these cumulative losses by as much as $5.4 billion but will not
avoid many ecological and economic impacts.

Short-term changes in weather or ocean
circulation can combine with long-term climate
trends to produce periods of very unusual
ocean conditions that can have significant
impacts on coastal communities. Two such
events have been particularly well documented:
the 2012 marine heat wave in the northwestern
Atlantic Ocean and the sequence of warm
ocean events between 2014 and 2016 in thenortheastern Pacific Ocean, including a large,
persistent area of very warm water referred toas “the Blob.” Ecosystems within these regions
experienced very warm conditions (morethan 3.6°F [2°C] above the normal range) thatpersisted for several months or more. Extreme
events in the oceans other than those related
to temperature, including ocean acidificationand low-oxygen events, can lead to significant
disruptions to ecosystems and people, but they
can also motivate preparedness and adaptation.

Ocean warming, acidification, and deoxygenation are leading to changes in productivity,
recruitment, survivorship, and, in some cases,

U.S. Global Change Research Program

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/oceans.

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Extreme Events in U.S. Waters Since 2012

The 2012 North Atlantic heat wave was concentrated in the Gulf of Maine; however, shorter periods with very warm temperatures
extended from Cape Hatteras to Iceland during the summer of 2012. American lobster and longfin squid and their associatedfisheries were impacted by the event. The North Pacific event began in 2014 and extended toward the shore in 2015 and into
the Gulf of Alaska in 2016, leading to a large bloom of toxic algae that impacted the Dungeness crab fishery and contributed
directly and indirectly to deaths of sea lions and humpback whales. U.S. coral reefs that experienced moderate to severe
bleaching during the 2015–2016 global mass bleaching event are indicated by coral icons. From Figure 9.3 (Source: Gulf ofMaine Research Institute).

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10 Agriculture and Rural Communities

Tyringham, Massachusetts

Key Message 1
Reduced Agricultural Productivity

Food and forage production will decline in regions experiencing increased frequency and durationof drought. Shifting precipitation patterns, when associated with high temperatures, will intensify
wildfires that reduce forage on rangelands, accelerate the depletion of water supplies for irrigation,and expand the distribution and incidence of pests and diseases for crops and livestock. Modern
breeding approaches and the use of novel genes from crop wild relatives are being employed todevelop higher-yielding, stress-tolerant crops.

Key Message 2
Degradation of Soil and Water Resources
The degradation of critical soil and water resources will expand as extreme precipitation events
increase across our agricultural landscape. Sustainable crop production is threatened by excessive
runoff, leaching, and flooding, which results in soil erosion, degraded water quality in lakes andstreams, and damage to rural community infrastructure. Management practices to restore soil
structure and the hydrologic function of landscapes are essential for improving resilience to thesechallenges.

Key Message 3
Health Challenges to Rural Populations and Livestock
Challenges to human and livestock health are growing due to the increased frequency andintensity of high temperature extremes. Extreme heat conditions contribute to heat exhaustion,
heatstroke, and heart attacks in humans. Heat stress in livestock results in large economic losses
for producers. Expanded health services in rural areas, heat-tolerant livestock, and improved designof confined animal housing are all important advances to minimize these challenges.
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Key Message 4
Vulnerability and Adaptive Capacity of Rural Communities
Residents in rural communities often have limited capacity to respond to climate change
impacts, due to poverty and limitations in community resources. Communication,transportation, water, and sanitary infrastructure are vulnerable to disruption fromclimate stressors. Achieving social resilience to these challenges would require
increases in local capacity to make adaptive improvements in shared community
resources.

In 2015, U.S. agricultural producers contributed$136.7 billion to the economy and accounted
for 2.6 million jobs. About half of the revenue
comes from livestock production. Other
agriculture-related sectors in the food supply
chain contributed an additional $855 billionof gross domestic product and accounted for
21 million jobs.

adopting new technologies, and adjusting management strategies.
U.S. agricultural production relies heavily on the
Nation’s land, water, and other natural resources,
and these resources are affected directly by agricultural practices and by climate. Climate change
is expected to increase the frequency of extreme
precipitation events in many regions in the UnitedStates. Because increased precipitation extremes
elevate the risk of surface runoff, soil erosion, andthe loss of soil carbon, additional protective measures are needed to safeguard the progress thathas been made in reducing soil erosion and water
quality degradation through the implementationof grassed waterways, cover crops, conservation
tillage, and waterway protection strips.

In 2013, about 46 million people, or 15% of the
U.S. population, lived in rural counties covering
72% of the Nation’s land area. From 2010 to 2015,a historic number of rural counties experienced
population declines, and recent demographic
trends point to relatively slow employment andpopulation growth in rural areas as well as highrates of poverty. Rural communities, where
livelihoods are more tightly interconnected with
agriculture, are particularly vulnerable to theagricultural volatility related to climate.

Climate change impacts, such as changes inextreme weather conditions, have a complex
influence on human and livestock health. The
consequences of climate change on the incidenceof drought also impact the frequency and intensity of wildfires, and this holds implications for
agriculture and rural communities. Rural populations are the stewards of most of the Nation’s
forests, watersheds, rangelands, agriculturalland, and fisheries. Much of the rural economy
is closely tied to the natural environment. Rural
residents, and the lands they manage, have thepotential to make important economic andconservation contributions to climate change

Climate change has the potential to adversely
impact agricultural productivity at local, regional,
and continental scales through alterations inrainfall patterns, more frequent occurrences ofclimate extremes (including high temperatures ordrought), and altered patterns of pest pressure.
Risks associated with climate change dependon the rate and severity of the change and theability of producers to adapt to changes. These
adaptations include altering what is produced,
modifying the inputs used for production,

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mitigation and adaptation, but their capacity toadapt is impacted by a host of demographic andeconomic concerns.

For full chapter, including references and Traceable Accounts, see https://nca2018.globalchange.
gov/chapter/agriculture-rural.

Agricultural Jobs and Revenue

The figure shows (a) the contribution of agriculture and related sectors to the U.S. economy and (b) employment figures inagriculture and related sectors (as of 2015). Agriculture and other food-related value-added sectors account for 21 million fulland part-time jobs and contribute about $1 trillion annually to the United States economy. From Figure 10.1 (Source: adaptedfrom Kassel et al. 2017).

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Population Changes and Poverty Rates in Rural Counties

The figure shows county-level (a) population changes for 2010–2017 and (b) poverty rates for 2011–2015 in rural U.S.
communities. Rural populations are migrating to urban regions due to relatively slow employment growth and high rates ofpoverty. Data for the U.S. Caribbean region were not available at the time of publication of this report. From Figure 10.2
(Sources: [a] adapted from ERS 2018; [b] redrawn from ERS 2017).

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11 Built Environment, Urban Systems, and Cities

Cleveland, Ohio

Key Message 1
Impacts on Urban Quality of Life

The opportunities and resources in urban areas are critically important to the healthand well-being of people who work, live, and visit there. Climate change can exacerbate
existing challenges to urban quality of life, including social inequality, aging anddeteriorating infrastructure, and stressed ecosystems. Many cities are engaging increative problem solving to improve quality of life while simultaneously addressing
climate change impacts.

Key Message 2
Forward-Looking Design for Urban Infrastructure
Damages from extreme weather events demonstrate current urban infrastructure
vulnerabilities. With its long service life, urban infrastructure must be able to endure
a future climate that is different from the past. Forward-looking design informs
investment in reliable infrastructure that can withstand ongoing and future climate risks.

Key Message 3
Impacts on Urban Goods and Services
Interdependent networks of infrastructure, ecosystems, and social systems provide
essential urban goods and services. Damage to such networks from current weather
extremes and future climate will adversely affect urban life. Coordinated local, state, andfederal efforts can address these interconnected vulnerabilities.

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Key Message 4
Urban Response to Climate Change
Cities across the United States are leading efforts to respond to climate change. Urban
adaptation and mitigation actions can affect current and projected impacts of climatechange and provide near-term benefits. Challenges to implementing these plans remain.
Cities can build on local knowledge and risk management approaches, integrate social
equity concerns, and join multicity networks to begin to address these challenges.

Urban areas, where the vast majority of Americans live, are engines of economic growth andcontain land valued at trillions of dollars. Cities
around the United States face a number ofchallenges to prosperity, such as social inequality, aging and deteriorating infrastructure,and stressed ecosystems. These social, infrastructure, and environmental challenges affecturban exposure and susceptibility to climatechange effects.

respond to such incidents depends on theirunderstanding of risk, their way of life, accessto resources, and the communities to which
they belong. Infrastructure designed forhistorical climate trends is vulnerable to future
weather extremes and climate change. Investing in forward-looking design can help ensurethat infrastructure performs acceptably underchanging climate conditions.
Urban areas are linked to local, regional, andglobal systems. Situations where multiple
climate stressors simultaneously affect multiple
city sectors, either directly or through system
connections, are expected to become morecommon. When climate stressors affect one
sector, cascading effects on other sectors
increase risks to residents’ health and wellbeing. Cities across the Nation are taking action
in response to climate change. U.S. cities areat the forefront of reducing greenhouse gas
emissions and many have begun adaptation
planning. These actions build urban resilience
to climate change.

Urban areas are already experiencing theeffects of climate change. Cities differ acrossregions in the acute and chronic climate
stressors they are exposed to and how thesestressors interact with local geographic characteristics. Cities are already subject to higher
surface temperatures because of the urban heatisland effect, which is projected to get stronger.
Recent extreme weather events reveal thevulnerability of the built environment (infrastructure such as residential and commercial
buildings, transportation, communications,energy, water systems, parks, streets, andlandscaping) and its importance to how people
live, study, recreate, and work. Heat waves
and heavy rainfalls are expected to increase infrequency and intensity. The way city residents

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/built-environment.

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Projected Change in the Number of Very Hot Days

Projected increases in the number of very hot days (comparedto the 1976–2005 average) are shown for each of five U.S.
cities under lower (RCP4.5) and higher (RCP8.5) scenarios.
Here, very hot days are defined as those on which the daily
high temperature exceeds a threshold value specific to each of the five U.S. cities shown. Dots represent the modeled median(50th percentile) values, and the vertical bars show the range of values (5th to 95th percentile) from the models used in theanalysis. Modeled historical values are shown for the same temperature thresholds, for the period 1976–2005, in the lower left
corner of the figure. These and other U.S. cities are projected to see an increase in the number of very hot days over the rest of
this century under both scenarios, affecting people, infrastructure, green spaces, and the economy. Increased air conditioning
and energy demands raise utility bills and can lead to power outages and blackouts. Hot days can degrade air and water quality,
which in turn can harm human health and decrease quality of life. From Figure 11.2 (Sources: NOAA NCEI, CICS-NC, and LMI).

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12 Transportation

St. Louis, Missouri

Key Message 1
Transportation at Risk

A reliable, safe, and efficient U.S. transportation system is at risk from increases inheavy precipitation, coastal flooding, heat, wildfires, and other extreme events, aswell as changes to average temperature. Throughout this century, climate change willcontinue to pose a risk to U.S. transportation infrastructure, with regional differences.

Key Message 2
Impacts to Urban and Rural Transportation
Extreme events that increasingly impact the transportation network are inducing
societal and economic consequences, some of which disproportionately affectvulnerable populations. In the absence of intervention, future changes in climate willlead to increasing transportation challenges, particularly because of system complexity,
aging infrastructure, and dependency across sectors.

Key Message 3
Vulnerability Assessments
Engineers, planners, and researchers in the transportation field are showing increasing
interest and sophistication in understanding the risks that climate hazards pose totransportation assets and services. Transportation practitioner efforts demonstrate
the connection between advanced assessment and the implementation of adaptive
measures, though many communities still face challenges and barriers to action.

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Transportation is the backbone of economic
activity, connecting manufacturers with supply
chains, consumers with products and tourism,
and people with their workplaces, homes,
and communities across both urban andrural landscapes. However, the ability of thetransportation sector to perform reliably, safely,and efficiently is undermined by a changing
climate. Heavy precipitation, coastal flooding,heat, wildfires, freeze–thaw cycles, and changes
in average precipitation and temperature
impact individual assets across all modes.
These impacts threaten the performance ofthe entire network, with critical ramifications
for economic vitality and mobility, particularly for vulnerable populations and urban
infrastructure.

the increasing frequency and intensity of heavy
precipitation events reduce transportation
system efficiency and increase accident risk.
High temperatures can stress bridge integrity
and have caused more frequent and extended
delays to passenger and freight rail systems
and air traffic.
Transportation is not only vulnerable toimpacts of climate change but also contributes
significantly to the causes of climate change. In
2016, the transportation sector became the top
contributor to U.S. greenhouse gas emissions.
The transportation system is rapidly growing
and evolving in response to market demand andinnovation. This growth could make climate
mitigation and adaptation progressively morechallenging to implement and more importantto achieve. However, transportation practitioners are increasingly invested in addressing
climate risks, as evidenced in more numerous
and diverse assessments of transportation
sector vulnerabilities across the United States.

Sea level rise is progressively making coastalroads and bridges more vulnerable and lessfunctional. Many coastal cities across theUnited States have already experienced anincrease in high tide flooding that reduces thefunctionality of low-elevation roadways, rail,and bridges, often causing costly congestionand damage to infrastructure. Inland transportation infrastructure is highly vulnerable tointense rainfall and flooding. In some regions,

U.S. Global Change Research Program

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/transportation.

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U.S. Transportation Assets and Goals at Risk

Heavy precipitation, coastal flooding, heat, and changes in average precipitation and temperature affect assets (such as roads
and bridges) across all modes of transportation. The figure shows major climate-related hazards and the transportation assets
impacted. Photos illustrate national performance goals (listed in 23 U.S.C. § 150) that are at risk due to climate-related hazards.
From Figure 12.1 (Source: USGCRP. Photo credits from left to right: JAXPORT, Meredith Fordham Hughes [CC BY-NC 2.0];
Oregon Department of Transportation [CC BY 2.0]; NPS–Mississippi National River and Recreation Area; Flickr user Tom
Driggers [CC BY 2.0]; Flickr user Mike Mozart [CC BY 2.0]; Flickr user Jeff Turner [CC BY 2.0]; Flickr user William Garrett [CCBY 2.0] — see https://creativecommons.org/licenses/ for specific Creative Commons licenses).

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13 Air Quality

Carr Fire, Shasta County, California, August 2018

Key Message 1
Increasing Risks from Air Pollution

More than 100 million people in the United States live in communities where air pollution
exceeds health-based air quality standards. Unless counteracting efforts to improve
air quality are implemented, climate change will worsen existing air pollution levels.
This worsened air pollution would increase the incidence of adverse respiratory andcardiovascular health effects, including premature death. Increased air pollution would
also have other environmental consequences, including reduced visibility and damage to
agricultural crops and forests.

Key Message 2
Increasing Impacts of Wildfires
Wildfire smoke degrades air quality, increasing the health risks to tens of millions ofpeople in the United States. More frequent and severe wildfires due to climate change
would further diminish air quality, increase incidences of respiratory illness fromexposure to wildfire smoke, impair visibility, and disrupt outdoor recreational activities.

Key Message 3
Increases in Airborne Allergen Exposure
The frequency and severity of allergic illnesses, including asthma and hay fever, arelikely to increase as a result of a changing climate. Earlier spring arrival, warmer
temperatures, changes in precipitation, and higher carbon dioxide concentrations canincrease exposure to airborne pollen allergens.

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Key Message 4
Co-Benefits of Greenhouse Gas Mitigation
Many emission sources of greenhouse gases also emit air pollutants that harm humanhealth. Controlling these common emission sources would both mitigate climate change
and have immediate benefits for air quality and human health. Because methane is botha greenhouse gas and an ozone precursor, reductions of methane emissions have thepotential to simultaneously mitigate climate change and improve air quality.

Unless offset by additional emissions reductions of ozone precursor emissions, there
is high confidence that climate change will
increase ozone levels over most of the UnitedStates, particularly over already polluted areas,
thereby worsening the detrimental healthand environmental effects due to ozone. The
climate penalty results from changes in local
weather conditions, including temperature andatmospheric circulation patterns, as well aschanges in ozone precursor emissions that are
influenced by meteorology. Climate change has
already had an influence on ozone concentrations over the United States, offsetting someof the expected ozone benefit from reduced
precursor emissions. The magnitude of theclimate penalty over the United States could be
reduced by mitigating climate change.

Climate change, specifically rising temperatures and increased carbon dioxide (CO2)concentrations, can influence plant-basedallergens, hay fever, and asthma in three ways:
by increasing the duration of the pollen season,
by increasing the amount of pollen producedby plants, and by altering the degree of allergic
reactions to the pollen.
The energy sector, which includes energy production, conversion, and use, accounts for 84%
of greenhouse gas (GHG) emissions in the United States as well as 80% of emissions of nitrogen oxides (NOx) and 96% of sulfur dioxide, themajor precursor of sulfate aerosol. In addition
to reducing future warming, reductions in GHG
emissions often result in co-benefits (otherpositive effects, such as improved air quality)and possibly some negative effects (disbenefits)(Ch. 29: Mitigation). Specifically, mitigating
GHG emissions can lower emissions of particulate matter (PM), ozone and PM precursors, andother hazardous pollutants, reducing the risks
to human health from air pollution.

Climatic changes, including warmer springs,
longer summer dry seasons, and drier soils
and vegetation, have already lengthened thewildfire season and increased the frequencyof large wildfires. Exposure to wildfire smoke
increases the risk of respiratory disease, resulting in adverse impacts to human health. Longer
fire seasons and increases in the number oflarge fires would impair both human healthand visibility.

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/air-quality.

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Projected Changes in Summer Season Ozone

The maps show projected changes in summer averages of the maximum daily 8-hour ozone concentration (as compared to the
1995–2005 average). Summertime ozone is projected to change non-uniformly across the United States based on multiyear
simulations from the Community Multiscale Air Quality (CMAQ) modeling system. Those changes are amplified under the higher
scenario (RCP8.5) compared with the lower scenario (RCP4.5), as well as at 2090 compared with 2050. Data are not available
for Alaska, Hawai‘i, U.S.-Affiliated Pacific Islands, and the U.S. Caribbean. From Figure 13.2 (Source: adapted from EPA 2017).

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14 Human Health

Algal bloom in Lake Erie in the summer of 2015

Key Message 1

Climate Change Affects the Health of All Americans
The health and well-being of Americans are already affected by climate change, withthe adverse health consequences projected to worsen with additional climate change.
Climate change affects human health by altering exposures to heat waves, floods,
droughts, and other extreme events; vector-, food- and waterborne infectious diseases;changes in the quality and safety of air, food, and water; and stresses to mental healthand well-being.

Key Message 2
Exposure and Resilience Vary Across Populations and Communities
People and communities are differentially exposed to hazards and disproportionately
affected by climate-related health risks. Populations experiencing greater health risks
include children, older adults, low-income communities, and some communities of color.

Key Message 3
Adaptation Reduces Risks and Improves Health
Proactive adaptation policies and programs reduce the risks and impacts fromclimate-sensitive health outcomes and from disruptions in healthcare services.
Additional benefits to health arise from explicitly accounting for climate change risks ininfrastructure planning and urban design.

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Key Message 4
Reducing Greenhouse Gas Emissions Results in Health and Economic Benefits
Reducing greenhouse gas emissions would benefit the health of Americans in the nearand long term. By the end of this century, thousands of American lives could be saved
and hundreds of billions of dollars in health-related economic benefits gained each year
under a pathway of lower greenhouse gas emissions.

Climate-related changes in weather patterns
and associated changes in air, water, food, andthe environment are affecting the health andwell-being of the American people, causing
injuries, illnesses, and death. Increasing
temperatures, increases in the frequency
and intensity of heat waves (since the 1960s),
changes in precipitation patterns (especially
increases in heavy precipitation), and sea level
rise can affect our health through multiple
pathways. Changes in weather and climate
can degrade air and water quality; affect thegeographic range, seasonality, and intensityof transmission of infectious diseases throughfood, water, and disease-carrying vectors (suchas mosquitoes and ticks); and increase stresses
that affect mental health and well-being.
Changing weather patterns also interact withdemographic and socioeconomic factors, aswell as underlying health trends, to influence
the extent of the consequences of climatechange for individuals and communities.
While all Americans are at risk of experiencing
adverse climate-related health outcomes, some
populations are disproportionately vulnerable.

U.S. Global Change Research Program

The risks of climate change for human healthare expected to increase in the future, with theextent of the resulting impacts dependent on
the effectiveness of adaptation efforts and on
the magnitude and pattern of future climatechange. Individuals, communities, public healthdepartments, health-related organizations andfacilities, and others are taking action to reduce
health vulnerability to current climate change
and to increase resilience to the risks projectedin coming decades.
The health benefits of reducing greenhouse gas
emissions could result in economic benefitsof hundreds of billions of dollars each year by
the end of the century. Annual health impacts
and health-related costs are projected to beapproximately 50% lower under a lower scenario (RCP4.5) compared to a higher scenario(RCP8.5). These estimates would be even larger
if they included the benefits of health outcomesthat are difficult to quantify, such as avoided
mental health impacts or long-term physicalhealth impacts.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/health.

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Vulnerable Populations

Examples of populations at higher risk of exposure to adverse climate-related health threats are shown along with adaptation
measures that can help address disproportionate impacts. When considering the full range of threats from climate change
as well as other environmental exposures, these groups are among the most exposed, most sensitive, and have the least
individual and community resources to prepare for and respond to health threats. White text indicates the risks faced by thosecommunities, while dark text indicates actions that can be taken to reduce those risks. From Figure 14.2 (Source: EPA).

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15 Tribes and Indigenous Peoples

Key Message 1

Wind River Indian Reservation students collect seeds for a land restoration project.

Indigenous Livelihoods and Economies at Risk
Climate change threatens Indigenous peoples’ livelihoods and economies, including
agriculture, hunting and gathering, fishing, forestry, energy, recreation, and tourism
enterprises. Indigenous peoples’ economies rely on, but face institutional barriers
to, their self-determined management of water, land, other natural resources, andinfrastructure that will be impacted increasingly by changes in climate.

Key Message 2
Physical, Mental, and Indigenous Values-Based Health at Risk
Indigenous health is based on interconnected social and ecological systems thatare being disrupted by a changing climate. As these changes continue, the health ofindividuals and communities will be uniquely challenged by climate impacts to lands,
waters, foods, and other plant and animal species. These impacts threaten sites,
practices, and relationships with cultural, spiritual, or ceremonial importance that arefoundational to Indigenous peoples’ cultural heritages, identities, and physical andmental health.

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Key Message 3
Adaptation, Disaster Management, Displacement, and Community-Led Relocations
Many Indigenous peoples have been proactively identifying and addressing climate
impacts; however, institutional barriers exist in the United States that severely limit theiradaptive capacities. These barriers include limited access to traditional territory andresources and the limitations of existing policies, programs, and funding mechanisms
in accounting for the unique conditions of Indigenous communities. Successful
adaptation in Indigenous contexts relies on use of Indigenous knowledge, resilient androbust social systems and protocols, a commitment to principles of self-determination,and proactive efforts on the part of federal, state, and local governments to alleviateinstitutional barriers.
Indigenous peoples in the United States arediverse and distinct political and culturalgroups and populations. Though they may beaffected by climate change in ways that are
similar to others in the United States, Indigenous peoples can also be affected uniquely anddisproportionately. Many Indigenous peoples
have lived in particular areas for hundreds if not
thousands of years. Indigenous peoples’ histories and shared experience engender distinct
knowledge about climate change impacts andstrategies for adaptation. Indigenous peoples’
traditional knowledge systems can play a rolein advancing understanding of climate change
and in developing more comprehensive climate
adaptation strategies.
Observed and projected changes of increased
wildfire, diminished snowpack, pervasive drought,
flooding, ocean acidification, and sea level risethreaten the viability of Indigenous peoples’
traditional subsistence and commercial activities
that include agriculture, hunting and gathering,fisheries, forestry, energy, recreation, and tourism
enterprises. Despite institutional barriers to
tribal self-determination stemming from federal
trust authority over tribal trust lands, a numberof tribes have adaptation plans that include a
focus on subsistence and commercial economic
activities. Some tribes are also pursuing climate

mitigation actions through the development of
renewable energy on tribal lands.
Climate impacts to lands, waters, foods, andother plant and animal species threaten cultural
heritage sites and practices that sustain intraand intergenerational relationships built on
sharing traditional knowledges, food, andceremonial or cultural objects. This weakens
place-based cultural identities, may worsen
historical trauma still experienced by many
Indigenous peoples in the United States, andadversely affects mental health and Indigenous
values-based understandings of health.
Throughout the United States, climate-related
disasters are causing Indigenous communities
to consider or actively pursue relocation as an
adaptation strategy. Challenges to Indigenous
actions to address disaster management andrecovery, displacement, and relocation in theface of climate change include economic,
social, political, and legal considerations thatseverely constrain their abilities to respond to
rapid ecological shifts and complicate action
toward safe and self-determined futures forthese communities.
For full chapter, including references and Traceable Accounts, see https://nca2018.globalchange.
gov/chapter/tribes.

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Indigenous Peoples’ Climate Initiatives and Plans

Many Indigenous peoples are taking steps to adapt to climate change impacts. Search the online version of this map by activity
type, region, and sector to find more information and links to each project: https://biamaps.doi.gov/nca/. To provide feedback
and add new projects for inclusion in the database, see: https://www.bia.gov/bia/ots/tribal-resilience-program/nca/. Thus far,tribal entities in the Northwest have the highest concentration of climate activities (Ch. 24: Northwest). For other case studies of
selected tribal adaptation activities, see both the Institute for Tribal Environmental Professionals’ Tribal Profiles, and Tribal Case
Studies within the U.S. Climate Resilience Toolkit. From Figure 15.1 (Source: Bureau of Indian Affairs).

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16 Climate Effects on U.S. International Interests

Container ship bringing goods to port

Key Message 1
Economics and Trade

The impacts of climate change, variability, and extreme events outside the United States
are affecting and are virtually certain to increasingly affect U.S. trade and economy,
including import and export prices and businesses with overseas operations andsupply chains.

Key Message 2
International Development and Humanitarian Assistance
The impacts of climate change, variability, and extreme events can slow or reverse
social and economic progress in developing countries, thus undermining international
aid and investments made by the United States and increasing the need forhumanitarian assistance and disaster relief. The United States provides technical andfinancial support to help developing countries better anticipate and address the impactsof climate change, variability, and extreme events.

Key Message 3
Climate and National Security
Climate change, variability, and extreme events, in conjunction with other factors, canexacerbate conflict, which has implications for U.S. national security. Climate impacts
already affect U.S. military infrastructure, and the U.S. military is incorporating climate
risks in its planning.

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Key Message 4
Transboundary Resources
Shared resources along U.S. land and maritime borders provide direct benefits to
Americans and are vulnerable to impacts from a changing climate, variability, andextremes. Multinational frameworks that manage shared resources are increasingly
incorporating climate risk in their transboundary decision-making processes.

U.S. international interests, such as economics
and trade, international development andhumanitarian assistance, national security,and transboundary resources, are affectedby impacts from climate change, variability,and extreme events. Long-term changes inclimate could lead to large-scale shifts in the
global availability and prices of a wide arrayof agricultural, energy, and other goods, withcorresponding impacts on the U.S. economy.
Some U.S.-led businesses are already working
to reduce their exposure to risks posed by achanging climate.
U.S. investments in international development
are sensitive to climate-related impacts andwill likely be undermined by more frequentand intense extreme events, such as droughts,
floods, and tropical cyclones. These events
can impede development efforts and result ingreater demand for U.S. humanitarian assistance and disaster relief. In response, the U.S.
government has funded adaptation programs
that seek to reduce vulnerability to climate
impacts in critical sectors.
Climate change, variability, and extreme events
increase risks to national security throughdirect impacts on U.S. military infrastructure
and, more broadly, through the relationshipbetween climate-related stress on societies
and conflict. Direct linkages between climate

U.S. Global Change Research Programand conflict are unclear, but climate variability
has been shown to affect conflict throughintermediate processes, including resourcecompetition, commodity price shocks, andfood insecurity. The U.S. military is working
to fully understand these threats and toincorporate projected climate changes into
long-term planning.
The impacts of changing weather and climate
patterns across U.S. international borders affectthose living in the United States. The changes
pose new challenges for the management ofshared and transboundary resources. Manybilateral agreements and public–private
partnerships are incorporating climate risk
and adaptive management into their near- andlong-term strategies.
U.S. cooperation with international and othernational scientific organizations improves
access to global information and strategic
partnerships, which better positions the Nation
to observe, understand, assess, and respondto the impacts associated with climate change,
variability, and extremes on national interests
both within and outside of U.S. borders.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/international.

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Transboundary Climate-Related Impacts

Shown here are examples of climate-related impacts spanning U.S. national borders. (left) The North American Drought
Monitor map for June 2011 shows drought conditions along the U.S.–Mexico border. Darker colors indicate greater intensity ofdrought (the letters A and H indicate agricultural and hydrological drought, respectively). (right) Smoke from Canadian wildfires
in 2017 was detected by satellite sensors built to detect aerosols in the atmosphere. The darker orange areas indicate higher
concentrations of smoke and hazy conditions moving south from British Columbia to the United States. From Figure 16.4
(Sources: [left] adapted from NOAA 2018, [right] adapted from NOAA 2018).

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17 Sector Interactions, Multiple Stressors, and Complex Systems

Landslide blocking a road in California

Key Message 1
Interactions Among Sectors

The sectors and systems exposed to climate (for example, energy, water, andagriculture) interact with and depend on one another and other systems less directly
exposed to climate (such as the financial sector). In addition, these interacting systems
are not only exposed to climate-related stressors such as floods, droughts, andheat waves, they are also subject to a range of non-climate factors, from population
movements to economic fluctuations to urban expansion. These interactions can leadto complex behaviors and outcomes that are difficult to predict. It is not possible to fully
understand the implications of climate change on the United States without considering
the interactions among sectors and their consequences.

Key Message 2
Multisector Risk Assessment
Climate change risk assessment benefits from a multisector perspective, encompassing
interactions among sectors and both climate and non-climate stressors. Becausesuch interactions and their consequences can be challenging to identify in advance,
effectively assessing multisector risks requires tools and approaches that integrate
diverse evidence and that consider a wide range of possible outcomes.

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Key Message 3
Management of Interacting Systems
The joint management of interacting systems can enhance the resilience ofcommunities, industries, and ecosystems to climate-related stressors. For example,
during drought events, river operations can be managed to balance water demandfor drinking water, navigation, and electricity production. Such integrated approaches
can help avoid missed opportunities or unanticipated tradeoffs associated with theimplementation of management responses to climate-related stressors.

Key Message 4
Advancing Knowledge
Predicting the responses of complex, interdependent systems will depend on developing
meaningful models of multiple, diverse systems, including human systems, andmethods for characterizing uncertainty.

The world we live in is a web of natural, built, andsocial systems—from global and regional climate;to the electric grid; to water management systems
such as dams, rivers, and canals; to managed andunmanaged forests; and to financial and economic
systems. Climate affects many of these systems
individually, but they also affect one another, andoften in ways that are hard to predict. In addition,
while climate-related risks such as heat waves,
floods, and droughts have an important influenceon these interconnected systems, these systems
are also subject to a range of other factors, such as
population growth, economic forces, technological change, and deteriorating infrastructure.
A key factor in assessing risk in this context isthat it is hard to quantify and predict all theways in which climate-related stressors mightlead to severe or widespread consequences fornatural, built, and social systems. A multisector
perspective can help identify such critical risks
ahead of time, but uncertainties will always
remain regarding exactly how consequences

will materialize in the future. Therefore,
effectively assessing multisector risks requires
different tools and approaches than would beapplied to understand a single sector by itself.
In interacting systems, management responses
within one system influence how other systems
respond. Failure to anticipate interdependencies
can lead to missed opportunities for managing
the risks of climate change; it can also lead to
management responses that increase risks toother parts of the system. Despite the challenge ofmanaging system interactions, there are opportunities to learn from experience to guide future risk
management decisions.
There is a large gap in the multisector and multiscale tools and frameworks that are available todescribe how different human systems interact
with one another and with the earth system,and how those interactions affect the total
system response to the many stressors they are
subject to, including climate-related stressors.

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Characterizing the nature of such interactions andbuilding the capacity to model them are importantresearch challenges.

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/complex-systems.

Complex Sectoral Interactions

Sectors are interacting and interdependent through physical, social, institutional, environmental, and economic linkages. These
sectors and the interactions among them are affected by a range of climate-related and non-climate influences. From Figure 17.1
(Sources: Pacific Northwest National Laboratory, Arizona State University, and Cornell University).

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Banner Photo Credits
2. Climate: An atmospheric river pours moisture into thewestern United States in February 2017. NASA Earth
Observatory images by Jesse Allen and Joshua Stevens,using VIIRS data from the Suomi National Polar-orbiting
Partnership and IMERG data provided courtesy of the Global
Precipitation Mission (GPM) Science Team’s Precipitation
Processing System (PPS).

10. Ag & Rural: Tyringham, Massachusetts. © DenisTangneyJr/
E+/Getty Images.
11. Urban: Cleveland, Ohio. © Erik Drost/Flickr. CC BY 2.0,
https://creativecommons.org/licenses/by/2.0/legalcode.
12. Transportation: St. Louis, Missouri. © Cathy Morrison/Missouri Department of Transportation. CC BY-NC-SA 2.0, https://creativecommons.org/licenses/by-nc-sa/2.0/legalcode.

3. Water: Levee repair along the San Joaquin River in
California, February 2017. U.S. Army Corps of Engineers,
Sacramento District.

13. Air Quality: Carr Fire, Shasta County, California, August 2018.
Sgt. Lani O. Pascual/U.S. Army National Guard.

4. Energy: Linemen working to restore power in Puerto Ricoafter Hurricane Maria in 2017. © Jeff Miller/Western Area
Power Administration/Flickr. CC BY 2.0, https://creativecommons.org/licenses/by/2.0/legalcode.

14. Human Health: Algal bloom in Lake Erie in summer 2015.
NOAA Great Lakes Environmental Research Laboratory.
15. Tribes: Wind River Indian Reservation students collectseeds for a land restoration project. U.S. Department of theInterior/Bureau of Land Management Wyoming.

5. Land Changes: Agricultural fields near the Ririe Reservoir in
Bonneville, Idaho. © Sam Beebe/Flickr. CC BY 2.0, https://creativecommons.org/licenses/by/2.0/legalcode.

16: International: Container ship bringing goods to port.
© wissanu01/iStock/Getty Images.

6. Forests: California’s multiyear drought killed millions oftrees in low-elevation forests. Nathan Stephenson/U.S.
Geological Survey.

17. Complex Systems: Landslide blocking a road in California.
© gece33/E+/Getty Images.

7. Ecosystems: Kodiak National Wildlife Refuge, Alaska. Lisa
Hupp/U.S. Fish and Wildlife Service.

Note: Photos have been cropped from their original size in order
to fit the report template.

8. Coastal: Natural “green barriers” help protect thisFlorida coastline and infrastructure from severe storms
and floods. NOAA.
9. Oceans: Coral reefs in the U.S. Virgin Islands. NOAA Coral
Reef Conservation Program.

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U.S. Global Change Research Program114Regions
Executive Summaries

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18 Northeast

Bartram Bridge in Pennsylvania

Key Message 1

Changing Seasons Affect Rural Ecosystems, Environments, and Economies
The seasonality of the Northeast is central to the region’s sense of place and is an
important driver of rural economies. Less distinct seasons with milder winter andearlier spring conditions are already altering ecosystems and environments in waysthat adversely impact tourism, farming, and forestry. The region’s rural industries
and livelihoods are at risk from further changes to forests, wildlife, snowpack, andstreamflow.

Key Message 2
Changing Coastal and Ocean Habitats, Ecosystem Services, and Livelihoods
The Northeast’s coast and ocean support commerce, tourism, and recreation thatare important to the region’s economy and way of life. Warmer ocean temperatures,
sea level rise, and ocean acidification threaten these services. The adaptive capacityof marine ecosystems and coastal communities will influence ecological andsocioeconomic outcomes as climate risks increase.

Key Message 3
Maintaining Urban Areas and Communities and Their Interconnectedness
The Northeast’s urban centers and their interconnections are regional and national hubs
for cultural and economic activity. Major negative impacts on critical infrastructure,urban economies, and nationally significant historic sites are already occurring and will
become more common with a changing climate.

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Key Message 4
Threats to Human Health
Changing climate threatens the health and well-being of people in the Northeast
through more extreme weather, warmer temperatures, degradation of air and water
quality, and sea level rise. These environmental changes are expected to lead to healthrelated impacts and costs, including additional deaths, emergency room visits andhospitalizations, and a lower quality of life. Health impacts are expected to vary bylocation, age, current health, and other characteristics of individuals and communities.

Key Message 5
Adaptation to Climate Change Is Underway
Communities in the Northeast are proactively planning and implementing actions to
reduce risks posed by climate change. Using decision support tools to develop andapply adaptation strategies informs both the value of adopting solutions and theremaining challenges. Experience since the last assessment provides a foundation toadvance future adaptation efforts.

The distinct seasonality of the Northeast’s
climate supports
a diverse naturallandscape adapted
to the extremes ofcold, snowy winters
and warm to hot,humid summers.
This natural landscape provides the
economic and cultural foundation for many ruralcommunities, which are largely supported by adiverse range of agricultural, tourism, and natural
resource-dependent industries (see Ch. 10: Ag &Rural, Key Message 4). The recent dominant trend
in precipitation throughout the Northeast has
been towards increases in rainfall intensity, withincreases in intensity exceeding those in otherregions of the contiguous United States. Further
increases in rainfall intensity are expected, withincreases in total precipitation expected during
the winter and spring but with little change in thesummer. Monthly precipitation in the Northeast

is projected to be about 1 inch greater for December through April by end of century (2070–2100)
under the higher scenario (RCP8.5).
Ocean and coastal ecosystems are being affectedby large changes in a variety of climate-related
environmental conditions. These ecosystems
support fishing and aquaculture, tourism andrecreation, and coastal communities. Observed
and projected increases in temperature, acidification, storm frequency and intensity, and sea
levels are of particular concern for coastal andocean ecosystems, as well as local communities
and their interconnected social and economic
systems. Increasing temperatures and changing
seasonality on the Northeast Continental Shelfhave affected marine organisms and the ecosystem in various ways. The warming trend experienced in the Northeast Continental Shelf has
been associated with many fish and invertebrate
species moving northward and to greater depths.
Because of the diversity of the Northeast’s coastal
landscape, the impacts from storms and sea level
rise will vary at different locations along the coast.

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Northeastern cities, with their abundanceof concrete and asphalt and relative lack ofvegetation, tend to have higher temperatures
than surrounding regions due to the urban
heat island effect. During extreme heat events,nighttime temperatures in the region’s big
cities are generally several degrees higher thansurrounding regions, leading to higher riskof heat-related death. Urban areas are at risk
for large numbers of evacuated and displaced
populations and damaged infrastructure due toboth extreme precipitation events and recurrent flooding, potentially requiring significant
emergency response efforts and considerationof a long-term commitment to rebuilding andadaptation, and/or support for relocation
where needed. Much of the infrastructure in
the Northeast, including drainage and sewer
systems, flood and storm protection assets,transportation systems, and power supply, isnearing the end of its planned life expectancy.
Climate-related disruptions will only exacerbate existing issues with aging infrastructure.
Sea level rise has amplified storm impacts in
the Northeast (Key Message 2), contributing
to higher surges that extend farther inland, as
demonstrated in New York City in the aftermath of Superstorm Sandy in 2012. Service andresource supply infrastructure in the Northeast
is at increasing risk of disruption, resulting
in lower quality of life, economic declines,
and increased social inequality. Loss of public
services affects the capacity of communities
to function as administrative and economic
centers and triggers disruptions of interconnected supply chains (Ch. 16: International,
Key Message 1).
Increases in annual average temperatures
across the Northeast range from less than 1°F(0.6°C) in West Virginia to about 3°F (1.7°C) or
more in New England since 1901. Although therelative risk of death on very hot days is lower
today than it was a few decades ago, heatrelated illness and death remain significant

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public health problems in the Northeast. For
example, a study in New York City estimatedthat in 2013 there were 133 excess deaths due
to extreme heat. These projected increases intemperature are expected to lead to substantially more premature deaths, hospital admissions, and emergency department visits acrossthe Northeast. For example, in the Northeast
we can expect approximately 650 additional
premature deaths per year from extreme heatby the year 2050 under either a lower (RCP4.5)
or higher (RCP8.5) scenario and from 960(under RCP4.5) to 2,300 (under RCP8.5) morepremature deaths per year by 2090.
Communities, towns, cities, counties, states,
and tribes across the Northeast are engagedin efforts to build resilience to environmental
challenges and adapt to a changing climate.
Developing and implementing climate adaptation strategies in daily practice often occur incollaboration with state and federal agencies.
Advances in rural towns, cities, and suburban
areas include low-cost adjustments of existingbuilding codes and standards. In coastal areas,
partnerships among local communities andfederal and state agencies leverage federal
adaptation tools and decision support frameworks. Increasingly, cities and towns acrossthe Northeast are developing or implementing
plans for adaptation and resilience in theface of changing climate. The approaches
are designed to maintain and enhance theeveryday lives of residents and promote economic development. In some cities, adaptation
planning has been used to respond to present
and future challenges in the built environment.
Regional efforts have recommended changes
in design standards when building, replacing,or retrofitting infrastructure to account for achanging climate.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/northeast.

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Lengthening of the Freeze-Free Period

These maps show projected shifts in the date of the last spring freeze (left column) and the date of the first fall freeze (rightcolumn) for the middle of the century (as compared to 1979–2008) under the lower scenario (RCP4.5; top row) and the higher
scenario (RCP8.5; middle row). The bottom row shows the shift in these dates for the end of the century under the higher
scenario. By the middle of the century, the freeze-free period across much of the Northeast is expected to lengthen by as muchas two weeks under the lower scenario and by two to three weeks under the higher scenario. By the end of the century, thefreeze-free period is expected to increase by at least three weeks over most of the region. From Figure 18.3 (Source: adaptedfrom Wolfe et al. 2018).

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Coastal Impacts of Climate Change(top) The northeastern coastal landscape is composed of uplands and forested areas, wetlands and estuarine systems, mainlandand barrier beaches, bluffs, headlands, and rocky shores, as well as developed areas, all of which provide a variety of important
services to people and species. (bottom) Future impacts from intense storm activity and sea level rise will vary across thelandscape, requiring a variety of adaptation strategies if people, habitats, traditions, and livelihoods are to be protected. From
Figure 18.7 (Source: U.S. Geological Survey).

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19 Southeast

Red mangrove in Titusville, Florida

Key Message 1
Urban Infrastructure and Health Risks

Many southeastern cities are particularly vulnerable to climate change compared tocities in other regions, with expected impacts to infrastructure and human health. The
vibrancy and viability of these metropolitan areas, including the people and criticalregional resources located in them, are increasingly at risk due to heat, flooding, andvector-borne disease brought about by a changing climate. Many of these urban areas
are rapidly growing and offer opportunities to adopt effective adaptation efforts toprevent future negative impacts of climate change.

Key Message 2
Increasing Flood Risks in Coastal and Low-Lying Regions
The Southeast’s coastal plain and inland low-lying regions support a rapidly growing
population, a tourism economy, critical industries, and important cultural resources thatare highly vulnerable to climate change impacts. The combined effects of changing
extreme rainfall events and sea level rise are already increasing flood frequencies, which
impacts property values and infrastructure viability, particularly in coastal cities. Without
significant adaptation measures, these regions are projected to experience daily hightide flooding by the end of the century.

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Key Message 3
Natural Ecosystems Will Be Transformed
The Southeast’s diverse natural systems, which provide many benefits to society, willbe transformed by climate change. Changing winter temperature extremes, wildfire
patterns, sea levels, hurricanes, floods, droughts, and warming ocean temperatures
are expected to redistribute species and greatly modify ecosystems. As a result, theecological resources that people depend on for livelihood, protection, and well-being
are increasingly at risk, and future generations can expect to experience and interact
with natural systems that are much different than those that we see today.

Key Message 4
Economic and Health Risks for Rural Communities
Rural communities are integral to the Southeast’s cultural heritage and to the strong
agricultural and forest products industries across the region. More frequent extreme
heat episodes and changing seasonal climates are projected to increase exposurelinked health impacts and economic vulnerabilities in the agricultural, timber, andmanufacturing sectors. By the end of the century, over one-half billion labor hours could
be lost from extreme heat-related impacts. Such changes would negatively impact theregion’s labor-intensive agricultural industry and compound existing social stresses inrural areas related to limited local community capabilities and associated with ruraldemography, occupations, earnings, literacy, and poverty incidence. Reduction ofexisting stresses can increase resilience.

The Southeast
includes vast
expanses ofcoastal andinland low-lying
areas, the southern portion of
the Appalachian
Mountains,numerous highgrowth metropolitan areas, and large rural
expanses. These beaches and bayous, fields
and forests, and cities and small towns are allat risk from a changing climate. While someclimate change impacts, such as sea level riseand extreme downpours, are being acutely
felt now, others, like increasing exposure to

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dangerous high temperatures, humidity, andnew local diseases, are expected to become
more significant in the coming decades. While
all regional residents and communities arepotentially at risk for some impacts, somecommunities or populations are at greater risk
due to their locations, services available tothem, and economic situations.
Observed warming since the mid-20th century
has been uneven in the Southeast region, withaverage daily minimum temperatures increasing
three times faster than average daily maximum
temperatures. The number of extreme rainfall
events is increasing. Climate model simulationsof future conditions project increases in bothtemperature and extreme precipitation.

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Trends towards a more urbanized and denser
Southeast are expected to continue, creating
new climate vulnerabilities. Cities across theSoutheast are experiencing more and longer
summer heat waves. Vector-borne diseases
pose a greater risk in cities than in rural areas
because of higher population densities andother human factors, and the major urban
centers in the Southeast are already impacted
by poor air quality during warmer months.
Increasing precipitation and extreme weather
events will likely impact roads, freight rail, andpassenger rail, which will likely have cascading
effects across the region. Infrastructure related
to drinking water and wastewater treatment
also has the potential to be compromised byclimate-related events. Increases in extreme
rainfall events and high tide coastal floods due
to future climate change will impact the qualityof life of permanent residents as well as tourists
visiting the low-lying and coastal regions of
the Southeast. Sea level rise is contributing toincreased coastal flooding in the Southeast,and high tide flooding already poses daily risks
to businesses, neighborhoods, infrastructure,transportation, and ecosystems in the region.
There have been numerous instances of intense
rainfall events that have had devastating
impacts on inland communities in recent years.
The ecological resources that people depend
on for livelihoods, protection, and well-being
are increasingly at risk from the impacts ofclimate change. Sea level rise will result in the
rapid conversion of coastal, terrestrial, andfreshwater ecosystems to tidal saline habitats.
Reductions in the frequency and intensity ofcold winter temperature extremes are alreadyallowing tropical and subtropical species tomove northward and replace more temperate
species. Warmer winter temperatures arealso expected to facilitate the northward

movement of problematic invasive species,
which could transform natural systems north oftheir current distribution. In the future, risingtemperatures and increases in the duration andintensity of drought are expected to increase
wildfire occurrence and also reduce the effectiveness of prescribed fire practices.
Many in rural communities are maintaining
connections to traditional livelihoods andrelying on natural resources that are inherently vulnerable to climate changes. Climate
trends and possible climate futures show
patterns that are already impacting—and areprojected to further impact—rural sectors,
from agriculture and forestry to human healthand labor productivity. Future temperature
increases are projected to pose challenges tohuman health. Increases in temperatures, water
stress, freeze-free days, drought, and wildfire
risks, together with changing conditions forinvasive species and the movement of diseases,
create a number of potential risks for existing
agricultural systems. Rural communities tend
to be more vulnerable to these changes due
to factors such as demography, occupations,earnings, literacy, and poverty incidence. In
fact, a recent economic study using a higher
scenario (RCP8.5) suggests that the southernand midwestern populations are likely to suffer
the largest losses from future climate changes
in the United States. Climate change tends tocompound existing vulnerabilities and exacerbate existing inequities. Already poor regions,
including those found in the Southeast, areexpected to continue incurring greater losses
than elsewhere in the United States.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/southeast.

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Historical Changes in Hot Days and Warm Nights

Sixty-one percent of major Southeast cities are exhibiting some aspects of worsening heat waves, which is a higher percentage
than any other region of the country. Hot days and warm nights together impact human comfort and health and result in theneed for increased cooling efforts. Agriculture is also impacted by a lack of nighttime cooling. Variability and change in (top)the annual number of hot days and (bottom) warm nights are shown. The bar charts show averages over the region by decadefor 1900–2016, while the maps show the trends for 1950–2016 for individual weather stations. Average summer temperaturesduring the most recent 10 years have been the warmest on record, with very large increases in nighttime temperatures andmore modest increases in daytime temperatures, as indicated by contrasting changes in hot days and warm nights. (top left) The
annual number of hot days (maximum temperature above 95°F) has been lower since 1960 than the average during the first halfof the 20th century; (top right) trends in hot days since 1950 are generally downward except along the south Atlantic coast and in
Florida due to high numbers during the 1950s but have been slightly upward since 1960, following a gradual increase in average
daytime maximum temperatures during that time. (bottom left) Conversely, the number of warm nights (minimum temperature
above 75°F) has doubled on average compared to the first half of the 20th century and (bottom right) locally has increased atmost stations. From Figure 19.1 (Sources: NOAA NCEI and CICS-NC).

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Historical Change in Heavy Precipitation

The figure shows variability and change in (left) the annual number of days with precipitation greater than 3 inches (1900–2016)averaged over the Southeast by decade and (right) individual station trends (1950–2016). The number of days with heavy precipitation
has increased at most stations, particularly since the 1980s. From Figure 19.3 (Sources: NOAA NCEI and CICS-NC).

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20 U.S. Caribbean

Key Message 1

San Juan, Puerto Rico

Freshwater
Freshwater is critical to life throughout the Caribbean. Increasing global carbon
emissions are projected to reduce average rainfall in this region by the end of the
century, constraining freshwater availability, while extreme rainfall events, which canincrease freshwater flooding impacts, are expected to increase in intensity. Saltwater
intrusion associated with sea level rise will reduce the quantity and quality of freshwaterin coastal aquifers. Increasing variability in rainfall events and increasing temperatures
will likely alter the distribution of ecological life zones and exacerbate existing problems
in water management, planning, and infrastructure capacity.

Key Message 2
Marine Resources
Marine ecological systems provide key ecosystem services such as commercial andrecreational fisheries and coastal protection. These systems are threatened by changes
in ocean surface temperature, ocean acidification, sea level rise, and changes in thefrequency and intensity of storm events. Degradation of coral and other marine habitats
can result in changes in the distribution of species that use these habitats and the lossof live coral cover, sponges, and other key species. These changes will likely disrupt
valuable ecosystem services, producing subsequent effects on Caribbean island
economies.

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Key Message 3
Coastal Systems
Coasts are a central feature of Caribbean island communities. Coastal zones dominate
island economies and are home to critical infrastructure, public and private property,
cultural heritage, and natural ecological systems. Sea level rise, combined with stronger
wave action and higher storm surges, will worsen coastal flooding and increase coastal
erosion, likely leading to diminished beach area, loss of storm surge barriers, decreased
tourism, and negative effects on livelihoods and well-being. Adaptive planning andnature-based strategies, combined with active community participation and traditional
knowledge, are beginning to be deployed to reduce the risks of a changing climate.

Key Message 4
Rising Temperatures
Natural and social systems adapt to the temperatures under which they evolve andoperate. Changes to average and extreme temperatures have direct and indirect effects
on organisms and strong interactions with hydrological cycles, resulting in a varietyof impacts. Continued increases in average temperatures will likely lead to decreases
in agricultural productivity, changes in habitats and wildlife distributions, and risks
to human health, especially in vulnerable populations. As maximum and minimum
temperatures increase, there are likely to be fewer cool nights and more frequent hot
days, which will likely affect the quality of life in the U.S. Caribbean.

Key Message 5
Disaster Risk Response to Extreme Events
Extreme events pose significant risks to life, property, and economy in the Caribbean,
and some extreme events, such as flooding and droughts, are projected to increasein frequency and intensity. Increasing hurricane intensity and associated rainfall rates
will likely affect human health and well-being, economic development, conservation,
and agricultural productivity. Increased resilience will depend on collaboration andintegrated planning, preparation, and responses across the region.

Key Message 6
Increasing Adaptive Capacity Through Regional Collaboration
Shared knowledge, collaborative research and monitoring, and sustainable institutional
adaptive capacity can help support and speed up disaster recovery, reduce loss oflife, enhance food security, and improve economic opportunity in the U.S. Caribbean.
Increased regional cooperation and stronger partnerships in the Caribbean can expand
the region’s collective ability to achieve effective actions that build climate change
resilience, reduce vulnerability to extreme events, and assist in recovery efforts.

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Historically, the U.S.
Caribbean region has
experienced relatively stable seasonal rainfall
patterns, moderate annual temperature fluctuations, and a variety of extreme weather events,
such as tropical storms, hurricanes, and drought.
However, the Caribbean climate is changing andis projected to be increasingly variable as levels ofgreenhouse gases in the atmosphere increase.

plants) is vulnerable to the effects of sea level rise,storm surge, and flooding. In the USVI, infrastructure and historical buildings in the inundation
zone for sea level rise include the power plants on
both St. Thomas and St. Croix; schools; housing
communities; the towns of Charlotte Amalie,
Christiansted, and Frederiksted; and pipelines forwater and sewage.

The high percentage of coastal area relative tothe total island land area in the U.S. Caribbean
means that a large proportion of the region’s
people, infrastructure, and economic activity
are vulnerable to sea level rise, more frequent
intense rainfall events and associated coastal
flooding, and saltwater intrusion. High levelsof exposure and sensitivity to risk in the U.S.
Caribbean region are compounded by a low level of adaptive capacity, due in part to the highcosts of mitigation and adaptation measuresrelative to the region’s gross domestic product,
particularly when compared to continental
U.S. coastal areas. The limited geographic andeconomic scale of Caribbean islands meansthat disruptions from extreme climate-related
events, such as droughts and hurricanes, candevastate large portions of local economies
and cause widespread damage to crops, watersupplies, infrastructure, and other criticalresources and services.
The U.S. Caribbean territories of Puerto Ricoand the U.S. Virgin Islands (USVI) have distinct
differences in topography, language, population
size, governance, natural and human resources,and economic capacity. However, both are highly
dependent on natural and built coastal assets;
service-related industries account for more than
60% of the USVI economy. Beaches, affected bysea level rise and erosion, are among the main
tourist attractions. In Puerto Rico, critical infrastructure (for example, drinking water pipelines
and pump stations, sanitary pipelines and pumpstations, wastewater treatment plants, and power

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Climate change will likely result in water
shortages due to an overall decrease in annual
rainfall, a reduction in ecosystem services, andincreased risks for agriculture, human health,wildlife, and socioeconomic development in the
U.S. Caribbean. These shortages would result
from some locations within the Caribbean
experiencing longer dry seasons and shorter,
but wetter, wet seasons in the future. Extended
dry seasons are projected to increase firelikelihood. Excessive rainfall, coupled withpoor construction practices, unpaved roads,
and steep slopes, can exacerbate erosion rates
and have adverse effects on reservoir capacity,water quality, and nearshore marine habitats.
Ocean warming poses a significant threat tothe survival of corals and will likely also cause
shifts in associated habitats that compose
the coral reef ecosystem. Severe, repeated, or
prolonged periods of high temperatures leading
to extended coral bleaching can result in colony
death. Ocean acidification also is likely todiminish the structural integrity of coral habitats. Studies show that major shifts in fisheries
distribution and changes to the structure andcomposition of marine habitats adversely affectfood security, shoreline protection, and economies throughout the Caribbean.
In Puerto Rico, the annual number of days withtemperatures above 90°F has increased overthe last four and a half decades. During that
period, stroke and cardiovascular disease, which
are influenced by such elevated temperatures,
became the primary causes of death. Increases in128

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average temperature and in extreme heat events
will likely have detrimental effects on agriculturaloperations throughout the U.S. Caribbean region.
Many farmers in the tropics, including the U.S.
Caribbean, are considered small-holding, limited
resource farmers and often lack the resources
and/or capital to adapt to changing conditions.
Most Caribbean countries and territories share
the need to assess risks, enable actions acrossscales, and assess changes in ecosystems to

inform decision-making on habitat protection
under a changing climate. U.S. Caribbean
islands have the potential to improve adaptation and mitigation actions by fostering stronger collaborations with Caribbean initiatives on
climate change and disaster risk reduction.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/caribbean.

Observed and Projected Sea Level Rise(top) Observed sea level rise trends in Puerto Rico and the U.S. Virgin Islands reflect an increase in sea level of about 0.08 inches (2.0mm) per year for the period 1962–2017 for Puerto Rico and for 1975–2017 for the U.S. Virgin Islands. The bottom panels show a closer
look at more recent trends from 2000 to 2017 that measure a rise in sea level of about 0.24 inches (6.0 mm) per year. Projections of sea
level rise are shown under three different scenarios of Intermediate-Low (1–2 feet), Intermediate (3–4 feet), and Extreme (9–11 feet)sea level rise. The scenarios depict the range of future sea level rise based on factors such as global greenhouse gas emissions andthe loss of glaciers and ice sheets. From Figure 20.6 (Sources: NOAA NCEI and CICS-NC).

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Climate Risk Management Organizations

Some of the organizations working on climate risk assessment and management in the Caribbean are shown. Joint regional
efforts to address climate challenges include the implementation of adaptation measures to reduce natural, social, andeconomic vulnerabilities, as well as actions to reduce greenhouse gas emissions. See the online version of this figure at
http://nca2018.globalchange.gov/chapter/20#fig-20-18 for more details. From Figure 20.18 (Sources: NOAA and the USDA
Caribbean Climate Hub).

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21 Midwest

Carson, Wisconsin

Key Message 1
Agriculture

The Midwest is a major producer of a wide range of food and animal feed for national
consumption and international trade. Increases in warm-season absolute humidity andprecipitation have eroded soils, created favorable conditions for pests and pathogens,and degraded the quality of stored grain. Projected changes in precipitation, coupledwith rising extreme temperatures before mid-century, will reduce Midwest agricultural
productivity to levels of the 1980s without major technological advances.

Key Message 2
Forestry
Midwest forests provide numerous economic and ecological benefits, yet threats froma changing climate are interacting with existing stressors such as invasive species andpests to increase tree mortality and reduce forest productivity. Without adaptive actions,these interactions will result in the loss of economically and culturally important tree
species such as paper birch and black ash and are expected to lead to the conversion ofsome forests to other forest types or even to non-forested ecosystems by the end of the
century. Land managers are beginning to manage risk in forests by increasing diversity
and selecting for tree species adapted to a range of projected conditions.

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Key Message 3
Biodiversity and Ecosystems
The ecosystems of the Midwest support a diverse array of native species and provide
people with essential services such as water purification, flood control, resource
provision, crop pollination, and recreational opportunities. Species and ecosystems,
including the important freshwater resources of the Great Lakes, are typically most at
risk when climate stressors, like temperature increases, interact with land-use change,
habitat loss, pollution, nutrient inputs, and nonnative invasive species. Restoration ofnatural systems, increases in the use of green infrastructure, and targeted conservation
efforts, especially of wetland systems, can help protect people and nature from climatechange impacts.

Key Message 4
Human Health
Climate change is expected to worsen existing health conditions and introduce newhealth threats by increasing the frequency and intensity of poor air quality days,
extreme high temperature events, and heavy rainfalls; extending pollen seasons; andmodifying the distribution of disease-carrying pests and insects. By mid-century, theregion is projected to experience substantial, yet avoidable, loss of life, worsened healthconditions, and economic impacts estimated in the billions of dollars as a result of
these changes. Improved basic health services and increased public health measures—
including surveillance and monitoring—can prevent or reduce these impacts.

Key Message 5
Transportation and Infrastructure
Storm water management systems, transportation networks, and other criticalinfrastructure are already experiencing impacts from changing precipitation patterns
and elevated flood risks. Green infrastructure is reducing some of the negative impacts
by using plants and open space to absorb storm water. The annual cost of adapting
urban storm water systems to more frequent and severe storms is projected to exceed$500 million for the Midwest by the end of the century.

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Key Message 6
Community Vulnerability and Adaptation
At-risk communities in the Midwest are becoming more vulnerable to climate change
impacts such as flooding, drought, and increases in urban heat islands. Tribal nations
are especially vulnerable because of their reliance on threatened natural resources
for their cultural, subsistence, and economic needs. Integrating climate adaptation
into planning processes offers an opportunity to better manage climate risks now.
Developing knowledge for decision-making in cooperation with vulnerable communities
and tribal nations will help to build adaptive capacity and increase resilience.

The Midwest is home
to over 60 million
people, and its active
economy represents
18% of the U.S. grossdomestic product. The
region is probably best
known for agricultural
production. Increases in growing-season temperature in the Midwest are projected to be
the largest contributing factor to declines in
the productivity of U.S. agriculture. Increases
in humidity in spring through mid-century
are expected to increase rainfall, which will
increase the potential for soil erosion andfurther reduce planting-season workdays due
to waterlogged soil.
Forests are a defining characteristic of manylandscapes within the Midwest, covering morethan 91 million acres. However, a changing
climate, including an increased frequency oflate-growing-season drought conditions, isworsening the effects of invasive species, insect
pests, and plant disease as trees experience
periodic moisture stress. Impacts from humanactivities, such as logging, fire suppression,and agricultural expansion, have lowered thediversity of the Midwest’s forests from thepre-Euro-American settlement period. Natural
resource managers are taking steps to addressthese issues by increasing the diversity oftrees and introducing species suitable for achanging climate.
The Great Lakes play a central role in the
Midwest and provide an abundant freshwater
resource for water supplies, industry, shipping,fishing, and recreation, as well as a rich anddiverse ecosystem. These important ecosystems are under stress from pollution, nutrientand sediment inputs from agricultural systems,
and invasive species. Lake surface temperatures are increasing, lake ice cover is declining,
the seasonal stratification of temperaturesin the lakes is occurring earlier in the year,
and summer evaporation rates are increasing.
Increasing storm impacts and declines incoastal water quality can put coastal communities at risk. While several coastal communities
have expressed willingness to integrate climate
action into planning efforts, access to usefulclimate information and limited human andfinancial resources constrain municipal action.
Land conversion, and a wide range of otherstressors, has already greatly reduced biodiversity in many of the region’s prairies, wetlands,
forests, and freshwater systems. Species are
already responding to changes that haveoccurred over the last several decades, andrapid climate change over the next century is
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Midwest. The loss of species and the degradation of ecosystems have the potential to reduceor eliminate essential ecological services suchas flood control, water purification, and croppollination, thus reducing the potential forsociety to successfully adapt to ongoing changes. However, understanding these relationships
also highlights important climate adaptation
strategies. For example, restoring systems
like wetlands and forested floodplains andimplementing agricultural best management
strategies that increase vegetative cover (covercrops and riparian buffers) can help reduce
flooding risks and protect water quality.
Midwestern populations are already experiencing adverse health impacts from climatechange, and these impacts are expected toworsen in the future. In the absence of mitigation, ground-level ozone concentrations
are projected to increase across most of theMidwest, resulting in an additional 200–550

premature deaths in the region per year by
2050. Exposure to high temperatures impacts
workers’ health, safety, and productivity.
Currently, days over 100°F in Chicago are rare.
However, they could become increasingly morecommon by late century in both the lower andhigher scenarios (RCP4.5 and RCP8.5).
The Midwest also has vibrant manufacturing,retail, recreation/tourism, and service sectors.
The region’s highways, railroads, airports, andnavigable rivers are major modes for commerce
activity. Increasing precipitation, especiallyheavy rain events, has increased the overall
flood risk, causing disruption to transportationand damage to property and infrastructure.
Increasing use of green infrastructure (including nature-based approaches, such as wetland
restoration, and innovations like permeable
pavements) and better engineering practices
are beginning to address these issues.

Conservation Practices Reduce Impact of Heavy Rains

Integrating strips of native prairie vegetation into row crops has been shown to reduce sediment and nutrient loss from fields,
as well as improve biodiversity and the delivery of ecosystem services. Iowa State University’s STRIPS program is actively
conducting research into this agricultural conservation practice. The inset shows a close-up example of a prairie vegetation strip.
From Figure 21.2 (Photo credits: [main photo] Lynn Betts, [inset] Farnaz Kordbacheh).

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Citizens and stakeholders value their healthand the well-being of their communities—allof which are at risk from increased flooding,increased heat, and lower air and water quality
under a changing climate. To better preventand respond to these impacts, scholars andpractitioners highlight the need to engage inrisk-driven approaches that not only focus

on assessing vulnerabilities but also include
effective planning and implementation ofadaptation options.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/midwest.

Forest Diversity Can Increase Resilience to Climate Change

The photo shows Menominee Tribal Enterprises staff creating opportunity from adversity by replanting a forest opening caused
by oak wilt disease with a diverse array of tree and understory plant species that are expected to fare better under future climate
conditions. From Figure 21.4 (Photo credit: Kristen Schmitt).

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Cattle grazing in the plains of western Montana

Key Message 1
Water

Water is the lifeblood of the Northern Great Plains, and effective water management
is critical to the region’s people, crops and livestock, ecosystems, and energy industry.
Even small changes in annual precipitation can have large effects downstream; whencoupled with the variability from extreme events, these changes make managing theseresources a challenge. Future changes in precipitation patterns, warmer temperatures,and the potential for more extreme rainfall events are very likely to exacerbate thesechallenges.

Key Message 2
Agriculture
Agriculture is an integral component of the economy, the history, and the culture of theNorthern Great Plains. Recently, agriculture has benefited from longer growing seasonsand other recent climatic changes. Some additional production and conservation
benefits are expected in the next two to three decades as land managers employ
innovative adaptation strategies, but rising temperatures and changes in extreme
weather events are very likely to have negative impacts on parts of the region.
Adaptation to extremes and to longer-term, persistent climate changes will likely
require transformative changes in agricultural management, including regional shifts ofagricultural practices and enterprises.

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Key Message 3
Recreation and Tourism
Ecosystems across the Northern Great Plains provide recreational opportunities
and other valuable goods and services that are at risk in a changing climate.
Rising temperatures have already resulted in shorter snow seasons, lower summer
streamflows, and higher stream temperatures and have negatively affected highelevation ecosystems and riparian areas, with important consequences for local
economies that depend on winter or river-based recreational activities. Climate-induced
land-use changes in agriculture can have cascading effects on closely entwined natural
ecosystems, such as wetlands, and the diverse species and recreational amenities they
support. Federal, tribal, state, and private organizations are undertaking preparedness
and adaptation activities, such as scenario planning, transboundary collaboration, anddevelopment of market-based tools.

Key Message 4
EnergyFossil fuel and renewable energy production and distribution infrastructure is expanding
within the Northern Great Plains. Climate change and extreme weather events put
this infrastructure at risk, as well as the supply of energy it contributes to support
individuals, communities, and the U.S. economy as a whole. The energy sector is also asignificant source of greenhouse gases and volatile organic compounds that contributeto climate change and ground-level ozone pollution.

Key Message 5
Indigenous Peoples
Indigenous peoples of the Northern Great Plains are at high risk from a variety ofclimate change impacts, especially those resulting from hydrological changes, includingchanges in snowpack, seasonality and timing of precipitation events, and extreme
flooding and droughts as well as melting glaciers and reduction in streamflows. Thesechanges are already resulting in harmful impacts to tribal economies, livelihoods, andsacred waters and plants used for ceremonies, medicine, and subsistence. At thesame time, many tribes have been very proactive in adaptation and strategic climatechange planning.

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In the Northern Great
Plains, the timing andquantity of both precipitation and runoff haveimportant consequences for water supplies,
agricultural activities, and energy production.
Overall, climate projections suggest that the
number of heavy precipitation events (events withgreater than 1 inch per day of rainfall) is projected
to increase. Moving forward, the magnitude of
year-to-year variability overshadows the small
projected average decrease in streamflow. Changes
in extreme events are likely to overwhelm averagechanges in both the eastern and western regionsof the Northern Great Plains. Major flooding acrossthe basin in 2011 was followed by severe drought
in 2012, representing new and unprecedented
variability that is likely to become more common ina warmer world.
The Northern Great Plains region plays a criticalrole in national food security. Among other anticipated changes, projected warmer and generally
wetter conditions with elevated atmosphericcarbon dioxide concentrations are expected toincrease the abundance and competitive ability ofweeds and invasive species, increase livestock production and efficiency of production, and result in
longer growing seasons at mid- and high latitudes.
Net primary productivity, including crop yields
and forage production, is also likely to increase,although an increasing number of extreme
temperature events during critical pollination andgrain fill periods is likely to reduce crop yields.
Ecosystems across the Northern Great Plainsprovide recreational opportunities and othervaluable goods and services that are ingrainedin the region’s cultures. Higher temperatures,
reduced snow cover, and more variable precipitation will make it increasingly challenging tomanage the region’s valuable wetlands, rivers, andsnow-dependent ecosystems. In the mountainsof western Wyoming and western Montana, theU.S. Global Change Research Program

fraction of total water in precipitation that falls assnow is expected to decline by 25% to 40% by 2100
under a higher scenario (RCP8.5), which would
negatively affect the region’s winter recreationindustry. At lower-elevation areas of the Northern
Great Plains, climate-induced land-use changes inagriculture can have cascading effects on closely
entwined natural ecosystems, such as wetlands,
and the diverse species and recreational opportunities they support.
Energy resources in the Northern Great Plains
include abundant crude oil, natural gas, coal,wind, and stored water, and to a lesser extent,
corn-based ethanol, solar energy, and uranium.
The infrastructure associated with the extraction,
distribution, and energy produced from theseresources is vulnerable to the impacts of climatechange. Railroads and pipelines are vulnerable
to damage or disruption from increasing heavy
precipitation events and associated flooding anderosion. Declining water availability in the summer
would likely increase costs for oil production operations, which require freshwater resources. These
cost increases will either lead to lower production
or be passed on to consumers. Finally, higher
maximum temperatures, longer and more severe
heat waves, and higher overnight lows are expected to increase electricity demand for cooling in thesummer, further stressing the power grid.
Indigenous peoples in the region are observing
changes to climate, many of which are impacting
livelihoods as well as traditional subsistence
and wild foods, wildlife, plants and water for
ceremonies, medicines, and health and well-being.
Because some tribes and Indigenous peoples areamong those in the region with the highest rates ofpoverty and unemployment, and because many arestill directly reliant on natural resources, they areamong the most at risk to climate change.
For full chapter, including references and Traceable Accounts, see https://nca2018.globalchange.gov/chapter/northern-great-plains.

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Projected Changes in Very Hot Days, Cool Days, and Heavy Precipitation

Projected changes are shown for (top) the annual number of very hot days (days with maximum temperatures above 90°F, an
indicator of crop stress and impacts on human health), (middle) the annual number of cool days (days with minimum temperatures
below 28°F, an indicator of damaging frost), and (bottom) heavy precipitation events (the annual number of days with greaterthan 1 inch of rainfall; areas in white do not normally experience more than 1 inch of rainfall in a single day). Projections areshown for the middle of the 21st century (2036–2065) as compared to the 1976–2005 average under the lower and higher
scenarios (RCP4.5 and RCP8.5). From Figure 22.2 (Sources: NOAA NCEI and CICS-NC).

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Northern Great Plains Tribal Lands

The map outlines reservation and off-reservation tribal lands in the Northern Great Plains, which shows where the 27 federally
recognized tribes have a significant portion of lands throughout the region. Information on Indigenous peoples’ climate projects
within the Northern Great Plains is described in Chapter 15: Tribes and Indigenous Peoples. From Figure 22.7 (Sources: createdby North Central Climate Science Center [2017] with data from the Bureau of Indian Affairs, Colorado State University, and
USGS National Map).

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23 Southern Great Plains

Whooping cranes in the Aransas National Wildlife Refuge in Texas

Key Message 1
Food, Energy, and Water Resources

Quality of life in the region will be compromised as increasing population, the migrationof individuals from rural to urban locations, and a changing climate redistribute demandat the intersection of food consumption, energy production, and water resources. A
growing number of adaptation strategies, improved climate services, and early warning
decision support systems will more effectively manage the complex regional, national,
and transnational issues associated with food, energy, and water.

Key Message 2
Infrastructure
The built environment is vulnerable to increasing temperature, extreme precipitation,and continued sea level rise, particularly as infrastructure ages and populations shift
to urban centers. Along the Texas Gulf Coast, relative sea level rise of twice the global
average will put coastal infrastructure at risk. Regional adaptation efforts that harden or
relocate critical infrastructure will reduce the risk of climate change impacts.

Key Message 3
Ecosystems and Ecosystem Services
Terrestrial and aquatic ecosystems are being directly and indirectly altered by climatechange. Some species can adapt to extreme droughts, unprecedented floods, andwildfires from a changing climate, while others cannot, resulting in significant impacts
to both services and people living in these ecosystems. Landscape-scale ecologicalservices will increase the resilience of the most vulnerable species.

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Key Message 4
Human Health
Health threats, including heat illness and diseases transmitted through food, water, andinsects, will increase as temperature rises. Weather conditions supporting these healththreats are projected to be of longer duration or occur at times of the year when thesethreats are not normally experienced. Extreme weather events with resultant physicalinjury and population displacement are also a threat. These threats are likely to increasein frequency and distribution and are likely to create significant economic burdens.
Vulnerability and adaptation assessments, comprehensive response plans, seasonal
health forecasts, and early warning systems can be useful adaptation strategies.

Key Message 5
Indigenous Peoples
Tribal and Indigenous communities are particularly vulnerable to climate change due
to water resource constraints, extreme weather events, higher temperature, and otherlikely public health issues. Efforts to build community resilience can be hinderedby economic, political, and infrastructure limitations, but traditional knowledge andintertribal organizations provide opportunities to adapt to the potential challenges ofclimate change.
The Southern Great Plains
experiences weather thatis dramatic and consequential; from hurricanes
and flooding to heat waves
and drought, its 34 million
people, their infrastructure, and economies areoften stressed, greatly
impacting socioeconomic systems. The quality oflife for the region’s residents is dependent upon
resources and natural systems for the sustainable
provision of our basic needs—food, energy, andwater. Extreme weather and climate events
have redistributed demands for consumption,
production, and supply across the region. Adaptation strategies that integrate climate services
and early warning systems are improving ourabilities to develop sustainable infrastructure
and increase agricultural production, yet include
the flexibility needed to embrace any changing
demand patterns.

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Regional adaptation efforts that harden or
relocate critical infrastructure will reduce therisk of climate change impacts. Redesigns ofcoastal infrastructure and the use of green/gray methodologies are improving future coastal
resilience. Energy industry reinvention is ensuring
operations and reliability during extreme climatic
events. Increasingly robust considerations of
economic resilience allow us to anticipate risk,
evaluate how that risk can affect our needs, andbuild a responsive adaptive capacity.
With climate change, terrestrial and aquatic ecosystems, and species within them, have winners
and losers. Those that can adapt are “increasers,”
while others cannot, resulting in impacts to traditional services and the livelihoods of the people
who depend on those resources. The warmingof coastal bay waters has been documented
since at least the 1980s, and those increases inwater temperature directly affect water quality,
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kills—thus lowering the productivity and diversityof estuaries. Natural wetlands like the playa lakes
in the High Plains, which have served for centuries
as important habitat for migrating waterfowl, arevirtually nonexistent during drought.
Direct human health threats follow a similar
pattern of species within our natural ecosystems.
Extreme weather results in both direct andindirect impacts to people; physical injury andpopulation displacement are anticipated to resultwith climate change. Heat illness and diseases
transmitted through food, water, and insects
increase human risk as temperature rises. Acuteawareness of these future impacts allows us toplan for the most vulnerable and adapt throughresponse plans, health forecasting, and early
warning strategies, including those that spantransboundary contexts and systems.
The impacts of climate change in generalbecome more acute when considering tribal andIndigenous communities. Resilience to climatechange will be hindered by economic, political,
and infrastructure limitations for these groups;

at the same time, connectivity of the tribes andIndigenous communities offers opportunities forteaching adaptably through their cultural meansof applying traditional knowledge and intertribalorganization. These well-honed connections ofadapting through the centuries may help all of
us learn how to offset the impacts and potential
challenges of climate change.
The role of climate change in altering the frequency of the types of severe weather most typicallyassociated with the Southern Great Plains, suchas severe local storms, hailstorms, and tornadoes,
remains difficult to quantify. Indirect approaches
suggest a possible increase in the circumstances
conducive to such severe weather, including
an increase in the instances of larger hail sizes
in the region by 2040, but changes are unlikely
to be uniform across the region, and additional
research is needed.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/southern-greatplains.

Projected Increase in Number of Days Above 100°F

Under both lower- and higher-scenario climate change projections, the number of days exceeding 100°F is projected to increase
markedly across the Southern Great Plains by the end of the century (2070–2099 as compared to 1976–2005). From Figure 23.4
(Sources: NOAA NCEI and CICS-NC).

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24 Northwest

Key Message 1

Four Lakes basin in White Cloud Peaks, Sawtooth National Forest, Idaho

Natural Resource Economy
Climate change is already affecting the Northwest’s diverse natural resources, which
support sustainable livelihoods; provide a robust foundation for rural, tribal, andIndigenous communities; and strengthen local economies. Climate change is expected
to continue affecting the natural resource sector, but the economic consequences
will depend on future market dynamics, management actions, and adaptation efforts.
Proactive management can increase the resilience of many natural resources and theirassociated economies.

Key Message 2
Natural World and Cultural Heritage
Climate change and extreme events are already endangering the well-being of a wide
range of wildlife, fish, and plants, which are intimately tied to tribal subsistence culture
and popular outdoor recreation activities. Climate change is projected to continue tohave adverse impacts on the regional environment, with implications for the values,
identity, heritage, cultures, and quality of life of the region’s diverse population.
Adaptation and informed management, especially culturally appropriate strategies, will
likely increase the resilience of the region’s natural capital.

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Key Message 3
Infrastructure
Existing water, transportation, and energy infrastructure already face challenges fromflooding, landslides, drought, wildfire, and heat waves. Climate change is projected toincrease the risks from many of these extreme events, potentially compromising thereliability of water supplies, hydropower, and transportation across the region. Isolated
communities and those with systems that lack redundancy are the most vulnerable.
Adaptation strategies that address more than one sector, or are coupled with social andenvironmental co-benefits, can increase resilience.

Key Message 4
HealthOrganizations and volunteers that make up the Northwest’s social safety net are alreadystretched thin with current demands. Healthcare and social systems will likely be further
challenged with the increasing frequency of acute events, or when cascading eventsoccur. In addition to an increased likelihood of hazards and epidemics, disruptions inlocal economies and food systems are projected to result in more chronic health risks.
The potential health co-benefits of future climate mitigation investments could help tocounterbalance these risks.

Key Message 5
Frontline Communities
Communities on the front lines of climate change experience the first, and often theworst, effects. Frontline communities in the Northwest include tribes and Indigenous
peoples, those most dependent on natural resources for their livelihoods, and theeconomically disadvantaged. These communities generally prioritize basic needs, suchas shelter, food, and transportation; frequently lack economic and political capital; andhave fewer resources to prepare for and cope with climate disruptions. The social andcultural cohesion inherent in many of these communities provides a foundation forbuilding community capacity and increasing resilience.

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Residents of theNorthwest list theinherent qualities of
the natural environment among the top
reasons to live in theregion. The region is
known for clean air,abundant water, low-cost hydroelectric power,
vast forests, extensive farmlands, and outdoor
recreation that includes hiking, boating, fishing,hunting, and skiing. Climate change, including
gradual changes to the climate and in extreme
climatic events, is already affecting these valued
aspects of the region, including the natural
resource sector, cultural identity and quality oflife, built infrastructure systems, and the healthof Northwest residents. The communities on
the front lines of climate change—tribes andIndigenous peoples, those most dependent on
natural resources for their livelihoods, and theeconomically disadvantaged—are experiencing
the first, and often the worst, effects.
In the Third National Climate Assessment,
the Key Messages for the Northwest focusedon projected climate impacts to the region.
These impacts, many of which are now better
understood in the scientific literature, remain
the primary climate concerns over the coming
decades. In this updated assessment, the Key
Messages explore how climate change could
affect the interrelationships between theenvironment and the people of the Northwest.
The extreme weather events of 2015 provide
an excellent opportunity to explore projectedchanges in baseline climate conditions for the
Northwest. The vast array of climate impacts
that occurred over this record-breaking warmand dry year, coupled with the impacts of amultiyear drought, provide an enlightening
glimpse into what may be more commonplace
under a warmer future climate. Record-low

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snowpack led to water scarcity and large
wildfires that negatively affected farmers,
hydropower, drinking water, air quality,
salmon, and recreation. Warmer than normal
ocean temperatures led to shifts in the marine
ecosystem, challenges for salmon, and a large
harmful algal bloom that adversely affected theregion’s fisheries and shellfish harvests.
Strong climate variability is likely to persist
for the Northwest, owing in part to theyear-to-year and decade-to-decade climate
variability associated with the Pacific Ocean.
Periods of prolonged drought are projected
to be interspersed with years featuring heavy
rainfall driven by powerful atmospheric rivers
and strong El Niño winters associated withstorm surge, large waves, and coastal erosion.
Continued changes in the ocean environment,such as warmer waters, altered chemistry, sealevel rise, and shifts in the marine ecosystems
are also expected. These changes would affect
the Northwest’s natural resource economy,
cultural heritage, built infrastructure, andrecreation as well as the health and welfare of
Northwest residents.
The Northwest has an abundance of examples
and case studies that highlight climate adaptation in progress and in practice—including
creating resilient agro-ecosystems that reduceclimate-related risks while meeting economic,
conservation, and adaptation goals; using“green” or hybrid “green and gray” infrastructure solutions that combine nature-based
solutions with more traditional engineering
approaches; and building social cohesion andstrengthening social networks in frontline
communities to assist in meeting basic needs
while also increasing resilience to futureclimate stressors. Many of the case studies
in this chapter demonstrate the importanceof co-producing adaptation efforts with

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scientists, resource managers, communities,
and decision-makers as the region preparesfor climate change impacts across multiple
sectors and resources.

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/northwest.

Climate Change Will Impact Key Aspects of Life in the Northwest

The climate-related events of 2015 provide a glimpse into the Northwest’s future, because the kinds of extreme events that
affected the Northwest in 2015 are projected to become more common. The climate impacts that occurred during this recordbreaking warm and dry year highlight the close interrelationships between the climate, the natural and built environment, and thehealth and well-being of the Northwest’s residents. From Figure 24.2 (Source: USGCRP).

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Low water levels in Lake Mead

Key Message 1
Water Resources

Water for people and nature in the Southwest has declined during droughts, due inpart to human-caused climate change. Intensifying droughts and occasional large
floods, combined with critical water demands from a growing population, deteriorating
infrastructure, and groundwater depletion, suggest the need for flexible water
management techniques that address changing risks over time, balancing declining
supplies with greater demands.

Key Message 2
Ecosystems and Ecosystem Services
The integrity of Southwest forests and other ecosystems and their ability to provide
natural habitat, clean water, and economic livelihoods have declined as a result ofrecent droughts and wildfire due in part to human-caused climate change. Greenhousegas emissions reductions, fire management, and other actions can help reduce future
vulnerabilities of ecosystems and human well-being.

Key Message 3
The Coast
Many coastal resources in the Southwest have been affected by sea level rise, ocean
warming, and reduced ocean oxygen—all impacts of human-caused climate change—and ocean acidification resulting from human emissions of carbon dioxide. Homes andother coastal infrastructure, marine flora and fauna, and people who depend on coastal
resources face increased risks under continued climate change.

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Key Message 4
Indigenous Peoples
Traditional foods, natural resource-based livelihoods, cultural resources, and spiritualwell-being of Indigenous peoples in the Southwest are increasingly affected by drought,
wildfire, and changing ocean conditions. Because future changes would further
disrupt the ecosystems on which Indigenous peoples depend, tribes are implementing
adaptation measures and emissions reduction actions.

Key Message 5
EnergyThe ability of hydropower and fossil fuel electricity generation to meet growing energy
use in the Southwest is decreasing as a result of drought and rising temperatures.
Many renewable energy sources offer increased electricity reliability, lower water
intensity of energy generation, reduced greenhouse gas emissions, and new economic
opportunities.

Key Message 6
Food
Food production in the Southwest is vulnerable to water shortages. Increased
drought, heat waves, and reduction of winter chill hours can harm crops and livestock;
exacerbate competition for water among agriculture, energy generation, and municipal
uses; and increase future food insecurity.

Key Message 7
Human HealthHeat-associated deaths and illnesses, vulnerabilities to chronic disease, and other
health risks to people in the Southwest result from increases in extreme heat, poor air
quality, and conditions that foster pathogen growth and spread. Improving public healthsystems, community infrastructure, and personal health can reduce serious health risks
under future climate change.

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The Southwest
region encompasses diverse
ecosystems,
cultures, and economies, reflecting
a broad range ofclimate conditions,
including the hottest and driest climate in the
United States. Water for people and naturein the Southwest region has declined during
droughts, due in part to human-caused climatechange. Higher temperatures intensified therecent severe drought in California and areamplifying drought in the Colorado River Basin.
Since 2000, Lake Mead on the Colorado Riverhas fallen 130 feet (40 m) and lost 60% of its
volume, a result of the ongoing Colorado River
Basin drought and continued water withdrawals
by cities and agriculture.
The reduction of water volume in both Lake
Powell and Lake Mead increases the risk ofwater shortages across much of the Southwest.
Local water utilities, the governments of seven
U.S. states, and the federal governments of
the United States and Mexico have voluntarily
developed and implemented solutions tominimize the possibility of water shortages
for cities, farms, and ecosystems. In responseto the recent California drought, the state
implemented a water conservation plan in2014 that set allocations for water utilities andmajor users and banned wasteful practices. As
a result, the people of the state reduced wateruse 25% from 2014 to 2017.
Exposure to hotter temperatures and heatwaves already leads to heat-associated deathsin Arizona and California. Mortality risk during
a heat wave is amplified on days with highlevels of ground-level ozone or particulate
air pollution. Given the proportion of the U.S.
population in the Southwest region, a disproportionate number of West Nile virus, plague,

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hantavirus pulmonary syndrome, and Valley
fever cases occur in the region.
Analyses estimated that the area burned by
wildfire across the western United States from1984 to 2015 was twice what would have burned
had climate change not occurred. Wildfires
around Los Angeles from 1990 to 2009 caused$3.1 billion in damages (unadjusted for inflation).
Tree death in mid-elevation conifer forests
doubled from 1955 to 2007 due, in part, toclimate change. Allowing naturally ignited fires
to burn in wilderness areas and preemptively
setting low-severity prescribed burns in areasof unnatural fuel accumulations can reduce therisk of high-severity fires under climate change.
Reducing greenhouse gas emissions globally
can also reduce ecological vulnerabilities.
At the Golden Gate Bridge in San Francisco, sealevel rose 9 inches (22 cm) between 1854 and2016. Climate change caused most of this riseby melting of land ice and thermal expansion ofocean water. Local governments on the California coast are using projections of sea level
rise to develop plans to reduce future risks.
Ocean water acidity off the coast of California
increased 25% to 40% (decreases of 0.10 to
0.15 pH units) from the preindustrial era (circa1750) to 2014 due to increasing concentrationsof atmospheric carbon dioxide from humanactivities. The marine heat wave along the
Pacific Coast from 2014 to 2016 occurred due
to a combination of natural factors and climatechange. The event led to the mass strandingof sick and starving birds and sea lions, andshifts of red crabs and tuna into the region. The
ecosystem disruptions contributed to closuresof commercially important fisheries.
Agricultural irrigation accounts for approximately three-quarters of water use in theSouthwest region, which grows half of the
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United States. Increasing heat stress during
specific phases of the plant life cycle canincrease crop failures.
Drought and increasing heat intensify the arid
conditions of reservations where the UnitedStates restricted some tribal nations in theSouthwest region to the driest portions of
their traditional homelands. In response to
climate change, Indigenous peoples in theregion are developing new adaptation andmitigation actions.
The severe drought in California, intensified
by climate change, reduced hydroelectric
generation two-thirds from 2011 to 2015.

The efficiency of all water-cooled electric
power plants that burn fuel depends on thetemperature of the external cooling water, so
climate change could reduce energy efficiency
up to 15% across the Southwest by 2050. Solar,
wind, and other renewable energy sources,
except biofuels, emit less carbon and requireless water than fossil fuel energy. Economic
conditions and technological innovations havelowered renewable energy costs and increased
renewable energy generation in the Southwest.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/southwest.

Climate Change Has Increased Wildfire

The cumulative forest area burned by wildfires has greatly increased between 1984 and 2015, with analyses estimating that thearea burned by wildfire across the western United States over that period was twice what would have burned had climate change
not occurred. From Figure 25.4 (Source: adapted from Abatzoglou and Williams 2016).

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Severe Drought Reduces Water Supplies in the Southwest

Since 2000, drought that was intensified by long-term trends of higher temperatures due to climate change has reduced the flow in
the Colorado River (top left), which in turn has reduced the combined contents of Lakes Powell and Mead to the lowest level sinceboth lakes were first filled (top right). In the Upper Colorado River Basin that feeds the reservoirs, temperatures have increased(bottom left), which increases plant water use and evaporation, reducing lake inflows and contents. Although annual precipitation(bottom right) has been variable without a long-term trend, there has been a recent decline in precipitation that exacerbates
the drought. Combined with increased Lower Basin water consumption that began in the 1990s, these trends explain the
recently reduced reservoir contents. Straight lines indicate trends for temperature, precipitation, and river flow. The trends
for temperature and river flow are statistically significant. From Figure 25.3 (Sources: Colorado State University and CICSNC. Temperature and precipitation data from: PRISM Climate Group, Oregon State University, http://prism.oregonstate.edu,
accessed 20 Jun 2018).

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26 Alaska

Anchorage, Alaska

Key Message 1
Marine Ecosystems

Alaska’s marine fish and wildlife habitats, species distributions, and food webs, allof which are important to Alaska’s residents, are increasingly affected by retreating
and thinning arctic summer sea ice, increasing temperatures, and ocean acidification.
Continued warming will accelerate related ecosystem alterations in ways that are
difficult to predict, making adaptation more challenging.

Key Message 2
Terrestrial Processes
Alaska residents, communities, and their infrastructure continue to be affected bypermafrost thaw, coastal and river erosion, increasing wildfire, and glacier melt. Thesechanges are expected to continue into the future with increasing temperatures, which
would directly impact how and where many Alaskans will live.

Key Message 3
Human Health
A warming climate brings a wide range of human health threats to Alaskans, including
increased injuries, smoke inhalation, damage to vital water and sanitation systems,
decreased food and water security, and new infectious diseases. The threats are
greatest for rural residents, especially those who face increased risk of storm damage
and flooding, loss of vital food sources, disrupted traditional practices, or relocation.
Implementing adaptation strategies would reduce the physical, social, and psychologicalharm likely to occur under a warming climate.

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Key Message 4
Indigenous Peoples
The subsistence activities, culture, health, and infrastructure of Alaska’s Indigenous
peoples and communities are subject to a variety of impacts, many of which are
expected to increase in the future. Flexible, community-driven adaptation strategies
would lessen these impacts by ensuring that climate risks are considered in the fullcontext of the existing sociocultural systems.

Key Message 5
Economic Costs
Climate warming is causing damage to infrastructure that will be costly to repair or
replace, especially in remote Alaska. It is also reducing heating costs throughout thestate. These effects are very likely to grow with continued warming. Timely repair
and maintenance of infrastructure can reduce the damages and avoid some of theseadded costs.

Key Message 6
Adaptation
Proactive adaptation in Alaska would reduce both short- and long-term costs associatedwith climate change, generate social and economic opportunity, and improve livelihood
security. Direct engagement and partnership with communities is a vital element ofadaptation in Alaska.

Alaska is thelargest statein the Nation,
almost onefifth the sizeof the combined lower 48
United States,
and is rich in natural capital resources. Alaska
is often identified as being on the front linesof climate change since it is warming fasterthan any other state and faces a myriad ofissues associated with a changing climate. The
cost of infrastructure damage from a warming
climate is projected to be very large, potentially
ranging from $110 to $270 million per year,
assuming timely repair and maintenance.

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Although climate change does and will continue
to dramatically transform the climate andenvironment of the Arctic, proactive adaptationin Alaska has the potential to reduce costs
associated with these impacts. This includes thedissemination of several tools, such as guidebooks to support adaptation planning, someof which focus on Indigenous communities.
While many opportunities exist with a changing
climate, economic prospects are not well captured in the literature at this time.
As the climate continues to warm, there is likely
to be a nearly sea ice-free Arctic during thesummer by mid-century. Ocean acidification isan emerging global problem that will intensify
with continued carbon dioxide (CO2) emissions

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and negatively affects organisms. Climatechange will likely affect management actions
and economic drivers, including fisheries, incomplex ways. The use of multiple alternativemodels to appropriately characterize uncertainty in future fisheries biomass trajectories
and harvests could help manage these challenges. As temperature and precipitation increase
across the Alaska landscape, physical andbiological changes are also occurring throughout Alaska’s terrestrial ecosystems. Degradationof permafrost is expected to continue, withassociated impacts to infrastructure, river andstream discharge, water quality, and fish andwildlife habitat.
Longer sea ice-free seasons, higher groundtemperatures, and relative sea level rise are
expected to exacerbate flooding and accelerate
erosion in many regions, leading to the loss ofterrestrial habitat in the future and in somecases requiring entire communities or portionsof communities to relocate to safer terrain.
The influence of climate change on humanhealth in Alaska can be traced to three sources:
direct exposures, indirect effects, and social
or psychological disruption. Each of these will
have different manifestations for Alaskans whencompared to residents elsewhere in the UnitedStates. Climate change exerts indirect effects
on human health in Alaska through changes
to water, air, and soil and through ecosystemchanges affecting disease ecology and foodsecurity, especially in rural communities.
Alaska’s rural communities are predominantly
inhabited by Indigenous peoples who may bedisproportionately vulnerable to socioeconomicand environmental change; however, they also
have rich cultural traditions of resilience andadaptation. The impacts of climate change will
likely affect all aspects of Alaska Native societies,
from nutrition, infrastructure, economics, andhealth consequences to language, education, andthe communities themselves.
The profound and diverse climate-drivenchanges in Alaska’s physical environment
and ecosystems generate economic impacts
through their effects on environmental services. These services include positive benefits
directly from ecosystems (for example, food,water, and other resources), as well as services
provided directly from the physical environment (for example, temperature moderation,
stable ground for supporting infrastructure,and smooth surface for overland transportation). Some of these effects are relatively
assured and in some cases are already occurring. Other impacts are highly uncertain, due
to their dependence on the structure of global
and regional economies and future humanalterations to the environment decades into the
future, but they could be large.
In Alaska, a range of adaptations to changing
climate and related environmental conditions
are underway and others have been proposed
as potential actions, including measures toreduce vulnerability and risk, as well as more
systemic institutional transformation.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/alaska.

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Adaptation Planning in Alaska

The map shows tribal climate adaptation planning efforts in Alaska. Research is considered to be adaptation under someclassification schemes. Alaska is scientifically data poor, compared to other Arctic regions. In addition to research conducted
at universities and by federal scientists, local community observer programs exist through several organizations, including the
National Weather Service for weather and river ice observations; the University of Alaska for invasive species; and the Alaska
Native Tribal Health Consortium for local observations of environmental change. Additional examples of community-based
monitoring can be found through the website of the Alaska Ocean Observing System. From Figure 26.9 (Source: adapted from
Meeker and Kettle 2017).

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27 Hawai‘i and U.S.-Affiliated Pacific Islands

Honolulu, Hawai‘i

Key Message 1
Threats to Water Supplies

Dependable and safe water supplies for Pacific island communities and ecosystems are
threatened by rising temperatures, changing rainfall patterns, sea level rise, and increased riskof extreme drought and flooding. Islands are already experiencing saltwater contamination due
to sea level rise, which is expected to catastrophically impact food and water security, especiallyon low-lying atolls. Resilience to future threats relies on active monitoring and management ofwatersheds and freshwater systems.

Key Message 2
Terrestrial Ecosystems, Ecosystem Services, and Biodiversity
Pacific island ecosystems are notable for the high percentage of species found only in the region,and their biodiversity is both an important cultural resource for island people and a source ofeconomic revenue through tourism. Terrestrial habitats and the goods and services they provide
are threatened by rising temperatures, changes in rainfall, increased storminess, and land-use
change. These changes promote the spread of invasive species and reduce the ability of habitats
to support protected species and sustain human communities. Some species are expected to
become extinct and others to decline to the point of requiring protection and costly management.

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Key Message 3
Coastal Communities and Systems
The majority of Pacific island communities are confined to a narrow band of land within a few
feet of sea level. Sea level rise is now beginning to threaten critical assets such as ecosystems,
cultural sites and practices, economies, housing and energy, transportation, and other forms ofinfrastructure. By 2100, increases of 1–4 feet in global sea level are very likely, with even higher
levels than the global average in the U.S.-Affiliated Pacific Islands. This would threaten the foodand freshwater supply of Pacific island populations and jeopardize their continued sustainability
and resilience. As sea level rise is projected to accelerate strongly after mid-century, adaptation
strategies that are implemented sooner can better prepare communities and infrastructure for themost severe impacts.

Key Message 4
Oceans and Marine Resources
Fisheries, coral reefs, and the livelihoods they support are threatened by higher ocean
temperatures and ocean acidification. Widespread coral reef bleaching and mortality have been
occurring more frequently, and by mid-century these events are projected to occur annually,
especially if current trends in emissions continue. Bleaching and acidification will result in loss ofreef structure, leading to lower fisheries yields and loss of coastal protection and habitat. Declines
in oceanic fishery productivity of up to 15% and 50% of current levels are projected by mid-century
and 2100, respectively, under the higher scenario (RCP8.5).

Key Message 5
Indigenous Communities and Knowledge
Indigenous peoples of the Pacific are threatened by rising sea levels, diminishing freshwater
availability, and shifting ecosystem services. These changes imperil communities’ health, wellbeing, and modern livelihoods, as well as their familial relationships with lands, territories, andresources. Built on observations of climatic changes over time, the transmission and protection of
traditional knowledge and practices, especially via the central role played by Indigenous women,
are intergenerational, place-based, localized, and vital for ongoing adaptation and survival.

Key Message 6
Cumulative Impacts and Adaptation
Climate change impacts in the Pacific Islands are expected to amplify existing risks and lead tocompounding economic, environmental, social, and cultural costs. In some locations, climatechange impacts on ecological and social systems are projected to result in severe disruptions
to livelihoods that increase the risk of human conflict or compel the need for migration. Earlyinterventions, already occurring in some places across the region, can prevent costly and lengthy
rebuilding of communities and livelihoods and minimize displacement and relocation.

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The U.S. PacificIslands areculturally andenvironmentally diverse,
treasured by
the 1.9 million
people who call them home. Pacific islands
are particularly vulnerable to climate change
impacts due to their exposure and isolation,
small size, low elevation (in the case of atolls),
and concentration of infrastructure and economy along the coasts.
A prevalent cause of year-to-year changes inclimate patterns around the globe and in the
Pacific Islands region is the El Niño–Southern
Oscillation (ENSO). The El Niño and La Niña
phases of ENSO can dramatically affect precipitation, air and ocean temperature, sea surface
height, storminess, wave size, and trade winds.
It is unknown exactly how the timing andintensity of ENSO will continue to change inthe coming decades, but recent climate model
results suggest a doubling in frequency of both
El Niño and La Niña extremes in this century ascompared to the 20th century under scenarioswith more warming, including the higher
scenario (RCP8.5).
On islands, all natural sources of freshwater
come from rainfall received within their limited
land areas. Severe droughts are common,
making water shortage one of the most important climate-related risks in the region. As
temperature continues to rise and cloud coverdecreases in some areas, evaporation is expected to increase, causing both reduced watersupply and higher water demand. Streamflow
in Hawai‘i has declined over approximately
the past 100 years, consistent with observed
decreases in rainfall.
The impacts of sea level rise in the Pacificinclude coastal erosion, episodic flooding,permanent inundation, heightened exposure
to marine hazards, and saltwater intrusion
to surface water and groundwater systems.
Sea level rise will disproportionately affectthe tropical Pacific and potentially exceed theglobal average.
Invasive species, landscape change, habitat
alteration, and reduced resilience have resulted
in extinctions and diminished ecosystem function. Inundation of atolls in the coming decades
is projected to impact existing on-island ecosystems. Wildlife that relies on coastal habitats
will likely also be severely impacted. In Hawai‘i,coral reefs contribute an estimated $477 million
to the local economy every year. Under projected warming of approximately 0.5°F per decade,all nearshore coral reefs in the Hawai‘i andPacific Islands region will experience annual
bleaching before 2050. An ecosystem-based
approach to international management of open
ocean fisheries in the Pacific that incorporates
climate-informed catch limits is expected to
produce more realistic future harvest levels andenhance ecosystem resilience.
Indigenous communities of the Pacific derive
their sense of identity from the islands.
Emerging issues for Indigenous communities of the Pacific include the resilience ofmarine-managed areas and climate-induced
human migration from their traditional lands.
The rich body of traditional knowledge is placebased and localized and is useful in adaptation
planning because it builds on intergenerational
sharing of observations. Documenting the kindsof governance structures or decision-making
hierarchies created for management ofthese lands and waters is also important as
a learning tool that can be shared with otherisland communities.
Across the region, groups are coming together
to minimize damage and disruption fromcoastal flooding and inundation as well as other

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Climate Indicators and Impacts

Monitoring regional indicator variables in the atmosphere, land, and ocean allows for tracking climate variability and change.
(top) Observed changes in key climate indicators such as carbon dioxide concentration, sea surface temperatures, and species
distributions in Hawai’i and the U.S.-Affiliated Pacific Islands result in (bottom) impacts to multiple sectors and communities,
including built infrastructure, natural ecosystems, and human health. Connecting changes in climate indicators to how impacts
are experienced is crucial in understanding and adapting to risks across different sectors. From Figure 27.2 (Source: adaptedfrom Keener et al. 2012).

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climate-related impacts. Social cohesion isalready strong in many communities, making it
possible to work together to take action. Earlyintervention can lower economic, environmental, social, and cultural costs and reduceor prevent conflict and displacement fromancestral land and resources.

For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/hawaii-pacific.

Projected Onset of Annual Severe Coral Reef Bleaching

The figure shows the years when severe coral bleaching is projected to occur annually in the Hawaiʻi and U.S.-Affiliated PacificIslands region under a higher scenario (RCP8.5). Darker colors indicate earlier projected onset of coral bleaching. Under
projected warming of approximately 0.5°F per decade, all nearshore coral reefs in the region will experience annual bleaching
before 2050. From Figure 27.10 (Source: NOAA).

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Banner Photo Credits
18. Northeast: Bartram Bridge in Pennsylvania. © Thomas
James Caldwell/Flickr. CC BY-SA 2.0,
https://creativecommons.org/licenses/by-sa/2.0/legalcode.
19. Southeast: Red mangrove in Titusville, Florida. © Katja
Schulz/Flickr. CC BY 2.0, https://creativecommons.org/
licenses/by/2.0/legalcode.
20. U.S. Caribbean: San Juan, Puerto Rico. © stevereidlphoto/
iStock/Getty Images
21. Midwest: Carson, Wisconsin. © William Garrett/Flickr. CC BY
2.0, https://creativecommons.org/licenses/by/2.0/legalcode.
22. N. Great Plains: Cameron, Montana. Paul Cross/U.S.
Geological Survey.
23. S. Great Plains: Whooping cranes in the Aransas National
Wildlife Refuge in Texas. Jon Noll/U.S. Departmentof Agriculture.
24. Northwest: Four Lakes basin in White Cloud Peaks,
Sawtooth National Forest, Idaho. Mark Lisk/USDA
Forest Service.
25. Southwest: Low water levels in Lake Mead. © Wayne Hsieh/
Flickr. CC BY-NC 2.0, https://creativecommons.org/licenses/
by-nc/2.0/legalcode.
26. Alaska: Anchorage, Alaska. © Rocky Grimes/
istock/Getty Images.
27. Hawai‘i & Pacific Islands: Honolulu, Hawai‘i. NOAA Teacher
at Sea Program, NOAA Ship Hi’ialakai.
Note: Photos have been cropped from their original size in order
to fit the report template.

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Responses
Executive Summaries

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28 Reducing Risks Through Adaptation Actions

Seawall surrounding Kivalina, Alaska

Key Message 1
Adaptation Implementation Is Increasing

Adaptation planning and implementation activities are occurring across the UnitedStates in the public, private, and nonprofit sectors. Since the Third National Climate
Assessment, implementation has increased but is not yet commonplace.

Key Message 2
Climate Change Outpaces Adaptation Planning
Successful adaptation has been hindered by the assumption that climate conditions
are and will be similar to those in the past. Incorporating information on current andfuture climate conditions into design guidelines, standards, policies, and practices
would reduce risk and adverse impacts.

Key Message 3
Adaptation Entails Iterative Risk Management
Adaptation entails a continuing risk management process; it does not have an end
point. With this approach, individuals and organizations of all types assess risks
and vulnerabilities from climate and other drivers of change (such as economic,
environmental, and societal), take actions to reduce those risks, and learn over time.

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Key Message 4
Benefits of Proactive Adaptation Exceed Costs
Proactive adaptation initiatives—including changes to policies, business operations,capital investments, and other steps—yield benefits in excess of their costs in thenear term, as well as over the long term. Evaluating adaptation strategies involves
consideration of equity, justice, cultural heritage, the environment, health, andnational security.

Key Message 5
New Approaches Can Further Reduce Risk
Integrating climate considerations into existing organizational and sectoral policies
and practices provides adaptation benefits. Further reduction of the risks fromclimate change can be achieved by new approaches that create conditions for altering
regulatory and policy environments, cultural and community resources, economic andfinancial systems, technology applications, and ecosystems.

Across the United States, many regions andsectors are already experiencing the direct effects
of climate change. For these communities, climate
impacts—from extreme storms made worse by
sea level rise, to longer-lasting and more extreme
heat waves, to increased numbers of wildfires
and floods—are an immediate threat, not a far-off
possibility. Because these impacts are expected
to increase over time, communities throughout
the United States face the challenge not only of
reducing greenhouse gas emissions, but also ofadapting to current and future climate change tohelp mitigate climate risks.

are often not executed sequentially and theterminology may vary. The Third National Climate
Assessment (released in 2014) found the first
three phases underway throughout the UnitedStates but limited in terms of on-the-ground
implementation. Since then, the scale and scopeof adaptation implementation have increased,
but in general, adaptation implementation is not
yet commonplace.

Adaptation takes place at many levels—nationaland regional but mainly local—as governments,
businesses, communities, and individuals
respond to today’s altered climate conditions andprepare for future change based on the specificclimate impacts relevant to their geography andvulnerability. Adaptation has five general stages:
awareness, assessment, planning, implementation,and monitoring and evaluation. These phases
naturally build on one another, though they

One important aspect of adaptation is theability to anticipate future climate impacts andplan accordingly. Public- and private-sector
decision-makers have traditionally made plans
assuming that the current and future climate intheir location will resemble that of the recent
past. This assumption is no longer reliably true.
Increasingly, planners, builders, engineers,architects, contractors, developers, and otherindividuals are recognizing the need to takecurrent and projected climate conditions into
account in their decisions about the locationand design of buildings and infrastructure,engineering standards, insurance rates,

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property values, land-use plans, disaster
response preparations, supply chains, andcropland and forest management.
In anticipating and planning for climate change,decision-makers practice a form of risk assessment known as iterative risk management.
Iterative risk management emphasizes thatthe process of anticipating and responding toclimate change does not constitute a single
set of judgments at any point in time; rather,
it is an ongoing cycle of assessment, action,
reassessment, learning, and response. In theadaptation context, public- and private-sector
actors manage climate risk using three types ofactions: reducing exposure, reducing sensitivity, and increasing adaptive capacity.
Climate risk management includes some
attributes and tactics that are familiar to mostbusinesses and local governments, since theseorganizations already commonly manage ordesign for a variety of weather-related risks,
including coastal and inland storms, heat waves,water availability threats, droughts, and floods.
However, successful adaptation also requires
the often unfamiliar challenge of using information on current and future climate, rather
than past climate, which can prove difficult for
those lacking experience with climate change
datasets and concepts. In addition, many
professional practices and guidelines, as well as
legal requirements, still call for the use of data
based on past climate. Finally, factors such asaccess to resources, culture, governance, andavailable information can affect not only therisk faced by different populations but also thebest ways to reduce their risks.
Achieving the benefits of adaptation canrequire up-front investments to achieve
longer-term savings, engaging with differingstakeholder interests and values, and planningin the face of uncertainty. But adaptation also

U.S. Global Change Research Program

presents challenges, including difficulties in
obtaining the necessary funds, insufficient
information and relevant expertise, and jurisdictional mismatches.
In general, adaptation can generate significant
benefits in excess of its costs. Benefit–costanalysis can help guide organizations toward
actions that most efficiently reduce risks, inparticular those that, if not addressed, could
prove extremely costly in the future. Beyond
those attributes explicitly measured by benefit–cost analysis, effective adaptation can alsoenhance social welfare in many ways that canbe difficult to quantify and that people willvalue differently, including improving economic
opportunity, health, equity, security, education,social connectivity, and sense of place, as well
as safeguarding cultural resources and practices and environmental quality.
A significant portion of climate risk can beaddressed by mainstreaming; that is, integrating climate adaptation into existing organizational and sectoral investments, policies, andpractices, such as planning, budgeting, policy
development, and operations and maintenance.
Mainstreaming of climate adaptation into
existing decision processes has already begun
in many areas, such as financial risk reporting,capital investment planning, engineering
standards, military planning, and disaster risk
management. Further reduction of the risks
from climate change, in particular those thatarise from futures with high levels of greenhouse gas emissions, calls for new approaches
that create conditions for altering regulatory
and policy environments, cultural and community resources, economic and financial systems,
technology applications, and ecosystems.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/adaptation.

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Five Adaptation Stages and Progress

The figure illustrates the adaptation iterative risk management process. The gray arced lines compare the current status of
implementing this process with the status reported by the Third National Climate Assessment in 2014. Darker color indicatesmore activity. From Figure 28.1 (Source: adapted from National Research Council, 2010. Used with permission from the National
Academies Press, © 2010, National Academy of Sciences. Image credits, clockwise from top: National Weather Service; USGS;
Armando Rodriguez, Miami-Dade County; Dr. Neil Berg, MARISA; Bill Ingalls, NASA).

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29 Reducing Risks Through Emissions Mitigation

Jasper, New YorkKey Message 1
Mitigation-Related Activities Within the United States

Mitigation-related activities are taking place across the United States at the federal,state, and local levels as well as in the private sector. Since the Third National Climate
Assessment, a growing number of states, cities, and businesses have pursued or
deepened initiatives aimed at reducing emissions.

Key Message 2
The Risks of Inaction
In the absence of more significant global mitigation efforts, climate change is
projected to impose substantial damages on the U.S. economy, human health, and theenvironment. Under scenarios with high emissions and limited or no adaptation, annual
losses in some sectors are estimated to grow to hundreds of billions of dollars by theend of the century. It is very likely that some physical and ecological impacts will beirreversible for thousands of years, while others will be permanent.

Key Message 3
Avoided or Reduced Impacts Due to Mitigation
Many climate change impacts and associated economic damages in the United States
can be substantially reduced over the course of the 21st century through global-scale
reductions in greenhouse gas emissions, though the magnitude and timing of avoided
risks vary by sector and region. The effect of near-term emissions mitigation on
reducing risks is expected to become apparent by mid-century and grow substantiallythereafter.

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Key Message 4Interactions Between Mitigation and Adaptation
Interactions between mitigation and adaptation are complex and can lead tobenefits, but they also have the potential for adverse consequences. Adaptation cancomplement mitigation to substantially reduce exposure and vulnerability to climatechange in some sectors. This complementarity is especially important given that acertain degree of climate change due to past and present emissions is unavoidable.
Current and future emissions of greenhousegases, and thus emission mitigation actions, arecrucial for determining future risks and impactsof climate change to society. The scale of risks
that can be avoided through mitigation actions
is influenced by the magnitude of emissions
reductions, the timing of those reductions,and the relative mix of mitigation strategies
for emissions of long-lived greenhouse gases(namely, carbon dioxide), short-lived greenhouse gases (such as methane), and land-based
biologic carbon. Many actions at national,
regional, and local scales are underway to
reduce greenhouse gas emissions, including
efforts in the private sector.
Climate change is projected to significantly
damage human health, the economy, and theenvironment in the United States, particularly
under a future with high greenhouse gas
emissions. A collection of frontier research
initiatives is underway to improve understanding and quantification of climate impacts. Thesestudies have been designed across a variety of
sectoral and spatial scales and feature the useof internally consistent climate and socioeconomic scenarios. Recent findings from these
multisector modeling frameworks demonstrate
substantial and far-reaching changes overthe course of the 21st century—and particularly at the end of the century—with negative
consequences for a large majority of sectors,
including infrastructure and human health. For
sectors where positive effects are observedin some regions or for specific time periods,

the effects are typically dwarfed by changes
happening overall within the sector or atbroader scales.
Recent studies also show that many climatechange impacts in the United States can besubstantially reduced over the course of the
21st century through global-scale reductions ingreenhouse gas emissions. While the difference
in climate outcomes between scenarios is moremodest through the first half of the century, theeffect of mitigation in avoiding climate change
impacts typically becomes clear by 2050 andincreases substantially in magnitude thereafter.
Research supports that early and substantial
mitigation offers a greater chance of avoiding
increasingly adverse impacts.
The reduction of climate change risk due tomitigation also depends on assumptions about
how adaptation changes the exposure and vulnerability of the population. Physical damages tocoastal property and transportation infrastructure
are particularly sensitive to adaptation assumptions, with proactive measures estimated to becapable of reducing damages by large fractions.
Because society is already committed to a certain
amount of future climate change due to pastand present emissions and because mitigation
activities cannot avoid all climate-related risks,
mitigation and adaptation activities can beconsidered complementary strategies. However,adaptation can require large up-front costs andlong-term commitments for maintenance, anduncertainty exists in some sectors regarding the169

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applicability and effectiveness of adaptation in
reducing risk. Interactions between adaptationand mitigation strategies can result in benefits oradverse consequences. While uncertainties still
remain, advancements in the modeling of climate
and economic impacts, including current understanding of adaptation pathways, are increasingly

providing new capabilities to understand andquantify future effects.
For full chapter, including references andTraceable Accounts, see https://nca2018.
globalchange.gov/chapter/mitigation.

Projected Damages and Potential for Risk Reduction by Sector
Annual Economic Damages in 2090
SectorAnnualdamagesunder
RCP8.5

Damages
avoided
under
RCP4.5

Labor

$155B

48%

Extreme Temperature Mortality◊

$141B

58%

Coastal Property◊

$118B

22%

Air Quality

$26B

31%

Roads◊$20B

59%

Electricity Supply and Demand

$9B

63%

Inland Flooding

$8B

47%

Urban Drainage

$6B

26%

Rail◊

$6B

36%

Water Quality

$5B

35%

Coral Reefs

$4B

12%

West Nile Virus

$3B

47%

Freshwater Fish

$3B

44%

Winter Recreation

$2B

107%

Bridges$1B

48%

Munic. and Industrial Water
Supply$316M

33%

Harmful Algal Blooms

$199M

45%

Alaska Infrastructure◊

$174M

53%

Shellfish*

$23M

57%

Agriculture*

$12M

11%

Aeroallergens*
Wildfire$1M

57%−$106M−134%

The total area of each circle represents the projected annual economic damages (in 2015 dollars) under a higher scenario(RCP8.5) in 2090 relative to a no-change scenario. The decrease in damages under a lower scenario (RCP4.5) compared to
RCP8.5 is shown in the lighter-shaded area of each circle. Where applicable, sectoral results assume population change overtime, which in the case of winter recreation leads to positive effects under RCP4.5, as increased visitors outweigh climate losses.
Importantly, many sectoral damages from climate change are not included here, and many of the reported results represent only
partial valuations of the total physical damages. See EPA 2017 for ranges surrounding the central estimates presented in the
figure; results assume limited or no adaptation. Adaptation was shown to reduce overall damages in sectors identified with the
diamond symbol but was not directly modeled in, or relevant to, all sectors. Asterisks denote sectors with annual damages that
may not be visible at the given scale. Only one impact (wildfire) shows very small positive effects, owing to projected landscapescale shifts to vegetation with longer fire return intervals (see Ch. 6: Forests for a discussion on the weight of evidence regarding
projections of future wildfire activity). The online version of this figure includes value ranges for numbers in the table. Due tospace constraints, the ranges are not included here. From Figure 29.2 (Source: adapted from EPA 2017).

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Banner Photo Credits
28. Adaptation: Seawall surrounding Kivalina, Alaska. ©
ShoreZone. CC BY 3.0, https://creativecommons.org/
licenses/by/3.0/legalcode.
29. Mitigation: Jasper, New York. © John Getchel/Flickr.
CC BY-NC 2.0, https://creativecommons.org/licenses/
by-nc/2.0/legalcode.
Note: Photos have been cropped from their original size in order
to fit the report template.

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Fourth National Climate Assessment Author Teams
1. Overview

3. WaterFederal Coordinating Lead Author

Federal Coordinating Lead Authors

David Reidmiller, U.S. Global Change Research Program

Thomas Johnson, U.S. Environmental Protection Agency
Peter Colohan, National Oceanic and Atmospheric
Administration

Chapter Lead

Alexa Jay, U.S. Global Change Research Program

Chapter Lead

Upmanu Lall, Columbia University

Chapter Authors

Christopher W. Avery, U.S. Global Change
Research Program
Daniel Barrie, National Oceanic and Atmospheric
Administration
Apurva Dave, U.S. Global Change Research Program
Benjamin DeAngelo, National Oceanic and Atmospheric
Administration
Matthew Dzaugis, U.S. Global Change Research Program
Michael Kolian, U.S. Environmental Protection Agency
Kristin Lewis, U.S. Global Change Research Program
Katie Reeves, U.S. Global Change Research Program
Darrell Winner, U.S. Environmental Protection Agency

Chapter Authors

Amir AghaKouchak, University of California, Irvine
Sankar Arumugam, North Carolina State University
Casey Brown, University of Massachusetts
Gregory McCabe, U.S. Geological Survey
Roger Pulwarty, National Oceanic and Atmospheric
Administration

Review Editor

Minxue He, California Department of Water Resources

USGCRP Coordinators

Kristin Lewis, Senior Scientist
Allyza Lustig, Program Coordinator

2. Our Changing Climate
Federal Coordinating Lead Authors

David R. Easterling, NOAA National Centers forEnvironmental Information
David W. Fahey, NOAA Earth System Research Laboratory

Chapter Lead

Katharine Hayhoe, Texas Tech University

Federal Coordinating Lead Author

Craig D. Zamuda, U.S. Department of Energy,
Office of Policy

Chapter Lead

Craig D. Zamuda, U.S. Department of Energy,
Office of Policy

Chapter Authors

Sarah Doherty, University of Washington
James P. Kossin, NOAA National Centers forEnvironmental Information
William V. Sweet, NOAA National Ocean Service
Russell S. Vose, NOAA National Centers forEnvironmental Information
Michael F. Wehner, Lawrence Berkeley National
Laboratory
Donald J. Wuebbles, University of Illinois

Chapter Authors

Daniel E. Bilello, National Renewable Energy Laboratory
Guenter Conzelmann, Argonne National Laboratory
Ellen Mecray, National Oceanic and Atmospheric
Administration
Ann Satsangi, U.S. Department of Energy, Office ofFossil Energy
Vincent Tidwell, Sandia National Laboratories
Brian J. Walker, U.S. Department of Energy, Office ofEnergy Efficiency and Renewable Energy

Technical Contributors

Robert E. Kopp, Rutgers University
Kenneth E. Kunkel, North Carolina State University
John Nielsen-Gammon, Texas A&M University

Review Editor

Sara C. Pryor, Cornell University

Review Editor

Linda O. Mearns, National Center for
Atmospheric Research

USGCRP Coordinators

Natalie Bennett, Adaptation and Assessment Analyst
Christopher W. Avery, Senior Manager

USGCRP Coordinators

David J. Dokken, Senior Program Officer
David Reidmiller, Director

U.S. Global Change Research Program

4. Energy Supply, Delivery, and Demand173

Report-in-Brief | Author Teams
5. Land Cover and Land-Use Change

Review Editor

Gregg Marland, Appalachian State University

Federal Coordinating Lead Author

Thomas Loveland, U.S. Geological Survey

USGCRP Coordinators

Natalie Bennett, Adaptation and Assessment Analyst
Susan Aragon-Long, Senior Scientist

Chapter Lead

Benjamin M. Sleeter, U.S. Geological Survey

7. Ecosystems, Ecosystem Services,and Biodiversity

Chapter Authors

James Wickham, U.S. Environmental Protection Agency
Grant Domke, U.S. Forest Service
Nate Herold, National Oceanic and Atmospheric
Administration
Nathan Wood, U.S. Geological Survey

Federal Coordinating Lead Authors

Shawn Carter, U.S. Geological Survey
Jay Peterson, National Oceanic and Atmospheric
Administration

Technical Contributors

Tamara S. Wilson, U.S. GeologicWal Survey
Jason Sherba, U.S. Geological Survey

Chapter Leads

Georgine Yorgey, Washington State University

Douglas Lipton, National Oceanic and Atmospheric
Administration
Madeleine A. Rubenstein. U.S. Geological Survey
Sarah R. Weiskopf, U.S. Geological Survey

USGCRP Coordinators

Chapter Authors

Review Editor

Susan Aragon-Long, Senior Scientist
Christopher W. Avery, Senior Manager

Lisa Crozier, National Oceanic and Atmospheric
Administration
Michael Fogarty, National Oceanic and Atmospheric
Administration
Sarah Gaichas, National Oceanic and Atmospheric
Administration
Kimberly J. W. Hyde, National Oceanic and Atmospheric
Administration
Toni Lyn Morelli, U.S. Geological Survey
Jeffrey Morisette, U.S. Department of the Interior,
National Invasive Species Council Secretariat
Hassan Moustahfid, National Oceanic and Atmospheric
Administration
Roldan Muñoz, National Oceanic and Atmospheric
Administration
Rajendra Poudel, National Oceanic and Atmospheric
Administration
Michelle D. Staudinger, U.S. Geological Survey
Charles Stock, National Oceanic and Atmospheric
Administration
Laura Thompson, U.S. Geological Survey
Robin Waples, National Oceanic and Atmospheric
Administration
Jake F. Weltzin, U.S. Geological Survey

6. Forests
Federal Coordinating Lead Authors

James M. Vose, U.S. Forest Service, Southern
Research Station
David L. Peterson, U.S. Forest Service, Pacific Northwest
Research Station

Chapter Leads

James M. Vose, U.S. Forest Service, Southern
Research Station
David L. Peterson, U.S. Forest Service, Pacific Northwest
Research Station

Chapter Authors

Grant M. Domke, U.S. Forest Service, Northern
Research Station
Christopher J. Fettig, U.S. Forest Service, PacificSouthwest Research Station
Linda A. Joyce, U.S. Forest Service, Rocky MountainResearch Station
Robert E. Keane, U.S. Forest Service, Rocky MountainResearch Station
Charles H. Luce, U.S. Forest Service, Rocky MountainResearch Station
Jeffrey P. Prestemon, U.S. Forest Service, Southern
Research Station

Review Editor

Gregg Marland, Appalachian State University

USGCRP Coordinators

Matthew Dzaugis, Program Coordinator
Allyza Lustig, Program Coordinator

Technical Contributors

Lawrence E. Band, University of Virginia
James S. Clark, Duke University
Nicolette E. Cooley, Northern Arizona University
Anthony D’Amato, University of Vermont
Jessica E. Halofsky, University of Washington
U.S. Global Change Research Program

174

Report-in-Brief | Author Teams
8. Coastal Effects

USGCRP Coordinators

Fredric Lipschultz, Senior Scientist and Regional
Coordinator
Apurva Dave, International Coordinator andSenior Analyst

Federal Coordinating Lead Authors

Jeffrey Payne, National Oceanic and Atmospheric
Administration
William V. Sweet, National Oceanic and Atmospheric
Administration

10. Agriculture and Rural Communities

Chapter Lead

Elizabeth Fleming, U.S. Army Corps of Engineers

Federal Coordinating Lead Author

Carolyn Olson, U.S. Department of Agriculture

Chapter Authors

Michael Craghan, U.S. Environmental Protection Agency
John Haines, U.S. Geological Survey
Juliette Finzi Hart, U.S. Geological Survey
Heidi Stiller, National Oceanic and Atmospheric
Administration
Ariana Sutton-Grier, National Oceanic and Atmospheric
Administration

Chapter Leads

Prasanna Gowda, USDA Agricultural Research Service
Jean L. Steiner, USDA Agricultural Research Service

Chapter Authors

Tracey Farrigan, USDA Economic Research Service
Michael A. Grusak, USDA Agricultural Research Service
Mark Boggess, USDA Agricultural Research Service

Review Editor

Michael Kruk, ERT, Inc.

Review Editor

Georgine Yorgey, Washington State University

USGCRP Coordinators

Matthew Dzaugis, Program Coordinator
Christopher W. Avery, Senior Manager
Allyza Lustig, Program Coordinator
Fredric Lipschultz, Senior Scientist and Regional
Coordinator

USGCRP Coordinators

Susan Aragon-Long, Senior Scientist
Allyza Lustig, Program Coordinator

11. Built Environment, Urban Systems,
and Cities

9. Oceans and Marine Resources

Federal Coordinating Lead Author

Susan Julius, U.S. Environmental Protection Agency

Federal Coordinating Lead Authors

Roger B. Griffis, National Oceanic and Atmospheric
Administration
Elizabeth B. Jewett, National Oceanic and Atmospheric
Administration

Chapter Lead

Keely Maxwell, U.S. Environmental Protection Agency

Chapter Authors

Chapter Lead

Andrew J. Pershing, Gulf of Maine Research Institute

Chapter Authors

C. Taylor Armstrong, National Oceanic and Atmospheric
Administration
John F. Bruno, University of North Carolina at Chapel Hill
D. Shallin Busch, National Oceanic and Atmospheric
Administration
Alan C. Haynie, National Oceanic and Atmospheric
Administration
Samantha A. Siedlecki, University of Washington (now
University of Connecticut)
Desiree Tommasi, University of California, Santa Cruz

Technical Contributor

Technical Contributors

Julie Blue, Eastern Research Group, Inc.
Kevin Bush, U.S. Department of Housing and Urban
Development (through August 2017)

Review Editor

Jesse Keenan, Harvard University

USGCRP Coordinators

Vicky W. Y. Lam, University of British Columbia

Natalie Bennett, Adaptation and Assessment Analyst
Fredric Lipschultz, Senior Scientist and Regional
Coordinator

Review Editor

Sarah R. Cooley, Ocean Conservancy

U.S. Global Change Research Program

Anne Grambsch, U.S. Environmental Protection
Agency (Retired)
Ann Kosmal, U.S. General Services Administration
Libby Larson, National Aeronautics andSpace Administration
Nancy Sonti, U.S. Forest Service

175

Report-in-Brief | Author Teams
12. Transportation

14. Human HealthFederal Coordinating Lead Author

Federal Coordinating Lead Authors

Michael Culp, U.S. Department of Transportation,Federal Highway Administration

John M. Balbus, National Institute of Environmental
Health Sciences
George Luber, Centers for Disease Control andPrevention

Chapter Lead

Jennifer M. Jacobs, University of New Hampshire

Chapter Lead

Kristie L. Ebi, University of Washington

Chapter Authors

Lia Cattaneo, Harvard University (formerly U.S.
Department of Transportation)
Paul Chinowsky, University of Colorado Boulder
Anne Choate, ICF
Susanne DesRoches, New York City Mayor’s Office of
Recovery and Resiliency and Office of Sustainability
Scott Douglass, South Coast Engineers
Rawlings Miller, WSP (formerly U.S. Department ofTransportation Volpe Center)

Chapter Authors

Jesse Keenan, Harvard University

Aparna Bole, University Hospitals Rainbow Babies &Children’s Hospital, Ohio
Allison Crimmins, U.S. Environmental Protection Agency
Gregory Glass, University of Florida
Shubhayu Saha, Centers for Disease Control andPrevention
Mark M. Shimamoto, American Geophysical Union
Juli Trtanj, National Oceanic and Atmospheric
Administration
Jalonne L. White-Newsome, The Kresge Foundation

USGCRP Coordinators

Technical Contributors

Review Editor

Allyza Lustig, Program Coordinator
Kristin Lewis, Senior Scientist

Stasia Widerynski, Centers for Disease Control andPrevention

Review Editor

13. Air Quality

David D’Onofrio, Atlanta Regional Commission

Federal Coordinating Lead Author

USGCRP Coordinators

Christopher G. Nolte, U.S. Environmental
Protection Agency

Ashley Bieniek-Tobasco, Health Program Coordinator
Sarah Zerbonne, Adaptation and Decision Science
Coordinator
Natalie Bennett, Adaptation and Assessment Analyst
Christopher W. Avery, Senior Manager

Chapter Lead

Christopher G. Nolte, U.S. Environmental
Protection Agency

15. Tribes and Indigenous Peoples

Chapter Authors

Patrick D. Dolwick, U.S. Environmental
Protection Agency
Neal Fann, U.S. Environmental Protection Agency
Larry W. Horowitz, National Oceanic and Atmospheric
Administration
Vaishali Naik, National Oceanic and Atmospheric
Administration
Robert W. Pinder, U.S. Environmental Protection Agency
Tanya L. Spero, U.S. Environmental Protection Agency
Darrell A. Winner, U.S. Environmental Protection Agency
Lewis H. Ziska, U.S. Department of Agriculture

Review Editor

David D’Onofrio, Atlanta Regional Commission

USGCRP Coordinators

Ashley Bieniek-Tobasco, Health Program Coordinator
Sarah Zerbonne, Adaptation and Decision Science
Coordinator
Christopher W. Avery, Senior Manager

U.S. Global Change Research Program

Federal Coordinating Lead Author

Rachael Novak, U.S. Department of the Interior, Bureau
of Indian Affairs

Chapter Lead

Lesley Jantarasami, Oregon Department of Energy

Chapter Authors

Roberto Delgado, National Institutes of Health
Elizabeth Marino, Oregon State University–Cascades
Shannon McNeeley, North Central Climate Adaptation
Science Center and Colorado State University
Chris Narducci, U.S. Department of Housing and Urban
Development
Julie Raymond-Yakoubian, Kawerak, Inc.
Loretta Singletary, University of Nevada, Reno
Kyle Powys Whyte, Michigan State University

Review Editor

Karen Cozzetto, Northern Arizona University

176

Report-in-Brief | Author Teams
USGCRP Coordinators

USGCRP Coordinators

Susan Aragon-Long, Senior Scientist
Allyza Lustig, Program Coordinator

Kristin Lewis, Senior Scientist
Natalie Bennett, Adaptation and Assessment Analyst

16. Climate Effects on U.S.
International Interests

18. Northeast
Federal Coordinating Lead Author

Ellen L. Mecray, National Oceanic and Atmospheric
Administration

Federal Coordinating Lead Author

Meredith Muth, National Oceanic and Atmospheric
Administration

Chapter Lead

Lesley-Ann L. Dupigny-Giroux, University of Vermont

Chapter Lead

Joel B. Smith, Abt Associates

Chapter Authors

Chapter Authors

Alice Alpert, U.S. Department of StateJames L. Buizer, University of Arizona
Jonathan Cook, World Resources Institute (formerly U.S.
Agency for International Development)
Apurva Dave, U.S. Global Change Research Program/ICF
John Furlow, International Research Institute for Climate
and Society, Columbia University
Kurt Preston, U.S. Department of DefensePeter Schultz, ICF
Lisa Vaughan, National Oceanic and Atmospheric
Administration

Review Editor

Diana Liverman, University of Arizona

USGCRP Coordinators

Apurva Dave, International Coordinator andSenior Analyst

Technical Contributors

Zoe P. Johnson, U.S. Department of Defense, Naval
Facilities Engineering Command (formerly NOAA
Chesapeake Bay Office)Amanda Babson, U.S. National Park Service
Elizabeth Pendleton, U.S. Geological Survey
Benjamin T. Gutierrez, U.S. Geological Survey
Joseph Salisbury, University of New Hampshire
Andrew Sven McCall Jr., University of Vermont
E. Robert Thieler, U.S. Geological Survey
Sara L. Zeigler, U.S. Geological Survey

17. Sector Interactions, Multiple
Stressors, and Complex Systems
Federal Coordinating Lead Authors

Leah Nichols, National Science Foundation
Robert Vallario, U.S. Department of Energy

Chapter Lead

Leon Clarke, Pacific Northwest National Laboratory

Review Editor

Jayne F. Knott, University of New Hampshire

Chapter Authors

Mohamad Hejazi, Pacific Northwest National Laboratory
Jill Horing, Pacific Northwest National Laboratory
Anthony C. Janetos, Boston University
Katharine Mach, Stanford University
Michael Mastrandrea, Carnegie Institution for Science
Marilee Orr, U.S. Department of Homeland Security
Benjamin L. Preston, Rand Corporation
Patrick Reed, Cornell University
Ronald D. Sands, U.S. Department of Agriculture
Dave D. White, Arizona State University

USGCRP Coordinators

Christopher W. Avery, Senior Manager
Matthew Dzaugis, Program Coordinator
Allyza Lustig, Program Coordinator

19. Southeast
Federal Coordinating Lead Author

Adam Terando, U.S. Geological Survey, Southeast Climate
Adaptation Science Center

Review Editor

Kai Lee, Williams College (Emeritus) and the Packard
Foundation (Retired)
U.S. Global Change Research Program

Mary D. Lemcke-Stampone, University of
New Hampshire
Glenn A. Hodgkins, U.S. Geological Survey
Erika E. Lentz, U.S. Geological Survey
Katherine E. Mills, Gulf of Maine Research Institute
Erin D. Lane, U.S. Department of Agriculture
Rawlings Miller, WSP (formerly U.S. Department ofTransportation Volpe Center)
David Y. Hollinger, U.S. Department of Agriculture
William D. Solecki, City University of New York–
Hunter College
Gregory A. Wellenius, Brown University
Perry E. Sheffield, Icahn School of Medicine atMount Sinai
Anthony B. MacDonald, Monmouth University
Christopher Caldwell, College of Menominee Nation

Chapter Lead

Lynne Carter, Louisiana State University

177

Report-in-Brief | Author Teams
James P. Kossin, National Oceanic and Atmospheric
Administration
Amanda J. Leinberger, Center for Climate Adaptation
Science and Solutions, University of Arizona
Vanessa I. Marrero-Santiago, Department of Naturaland Environmental Resources, Coastal Zone
Management Program
Odalys Martínez-Sánchez, NOAA National
Weather Service
Kathleen McGinley, USDA Forest Service International
Institute of Tropical Forestry
Melissa Meléndez Oyola, University of New Hampshire
Pablo Méndez-Lázaro, University of Puerto Rico
Julio Morell, University of Puerto Rico
Isabel K. Parés-Ramos, USDA Forest Service
International Institute of Tropical Forestry
Roger Pulwarty, National Oceanic and Atmospheric
Administration
William V. Sweet, NOAA National Ocean Service
Adam Terando, U.S. Geological Survey, Southeast Climate
Adaptation Science Center
Sigfredo Torres-González, U.S. Geological
Survey (Retired)

Chapter Authors

Kirstin Dow, University of South Carolina
Kevin Hiers, Tall Timbers Research Station
Kenneth E. Kunkel, North Carolina State University
Aranzazu Lascurain, North Carolina State University
Doug Marcy, National Oceanic and Atmospheric
Administration
Michael Osland, U.S. Geological Survey
Paul Schramm, Centers for Disease Control andPrevention

Technical Contributors

Vincent Brown, Louisiana State University
Barry Keim, Louisiana State University
Julie K. Maldonado, Livelihoods Knowledge
Exchange Network
Colin Polsky, Florida Atlantic University
April Taylor, Chickasaw Nation

Review Editor

Alessandra Jerolleman, Jacksonville State University

USGCRP Coordinators

Allyza Lustig, Program Coordinator
Matthew Dzaugis, Program Coordinator
Natalie Bennett, Adaptation and Assessment Analyst

Technical Contributors

Mariano Argüelles, Puerto Rico Department ofAgriculture
Gabriela Bernal-Vega, University of Puerto Rico
Roberto Moyano, Estudios Técnicos, Inc.
Pedro Nieves, USVI Coastal Zone Management
Aurelio Mercado-Irizarry, University of Puerto Rico
Dominique Davíd-Chavez, Colorado State University

20. U.S. Caribbean
Federal Coordinating Lead Author

William A. Gould, USDA Forest Service International
Institute of Tropical Forestry

Review Editor

Jess K. Zimmerman, University of Puerto Rico

Chapter Lead

Ernesto L. Díaz, Department of Natural andEnvironmental Resources, Coastal Zone
Management Program

USGCRP Coordinators

Allyza Lustig, Program Coordinator
Apurva Dave, International Coordinator andSenior Analyst
Christopher W. Avery, Senior Manager

Chapter Authors

Nora L. Álvarez-Berríos, USDA Forest Service
International Institute of Tropical Forestry
Felix Aponte-González, Aponte, Aponte & Asociados
Wayne Archibald, Archibald Energy Group
Jared Heath Bowden, Department of Applied Ecology,
North Carolina State University
Lisamarie Carrubba, NOAA Fisheries, Office ofProtected Resources
Wanda Crespo, Estudios Técnicos, Inc.
Stephen Joshua Fain, USDA Forest Service International
Institute of Tropical Forestry
Grizelle González, USDA Forest Service International
Institute of Tropical Forestry
Annmarie Goulbourne, Environmental Solutions Limited
Eric Harmsen, Department of Agricultural andBiosystems Engineering, University of Puerto Rico
Azad Henareh Khalyani, Natural Resource Ecology
Laboratory, Colorado State University
Eva Holupchinski, USDA Forest Service International
Institute of Tropical Forestry

U.S. Global Change Research Program

21. Midwest
Federal Coordinating Lead Author

Chris Swanston, USDA Forest Service

Chapter Lead

Jim Angel, Prairie Research Institute, University
of Illinois

Chapter Authors

Barbara Mayes Boustead, National Oceanic andAtmospheric Administration
Kathryn C. Conlon, Centers for Disease Control andPrevention
Kimberly R. Hall, The Nature Conservancy
Jenna L. Jorns, University of Michigan, Great Lakes
Integrated Sciences and Assessments
Kenneth E. Kunkel, North Carolina State University

178

Report-in-Brief | Author Teams
23. Southern Great Plains

Maria Carmen Lemos, University of Michigan, Great
Lakes Integrated Sciences and Assessments
Brent Lofgren, National Oceanic and Atmospheric
Administration
Todd A. Ontl, USDA Forest Service, Northern Forests
Climate HubJohn Posey, East West Gateway Council of Governments
Kim Stone, Great Lakes Indian Fish and Wildlife
Commission (through January 2018)
Eugene Takle, Iowa State University
Dennis Todey, USDA, Midwest Climate HubFederal Coordinating Lead Author

Bill Bartush, U.S. Fish and Wildlife Service

Chapter Lead

Kevin Kloesel, University of Oklahoma

Chapter Authors

Jay Banner, University of Texas at Austin
David Brown, USDA-ARS Grazinglands ResearchLaboratory
Jay Lemery, University of Colorado
Xiaomao Lin, Kansas State University
Cindy Loeffler, Texas Parks and Wildlife Department
Gary McManus, Oklahoma Climatological Survey
Esther Mullens, DOI South Central Climate Adaptation
Science Center
John Nielsen-Gammon, Texas A&M University
Mark Shafer, NOAA-RISA Southern Climate Impacts
Planning Program
Cecilia Sorensen, University of Colorado
Sid Sperry, Oklahoma Association of Electric
Cooperatives
Daniel Wildcat, Haskell Indian Nations University
Jadwiga Ziolkowska, University of Oklahoma

Technical Contributors

Katherine Browne, University of Michigan
Melonee Montano, Great Lakes Indian Fish and Wildlife
Commission
Hannah Panci, Great Lakes Indian Fish and Wildlife
Commission
Jason Vargo, University of Wisconsin
Madeline R. Magee, University of Wisconsin–Madison

Review Editor

Thomas Bonnot, University of Missouri

USGCRP Coordinators

Kristin Lewis, Senior Scientist
Allyza Lustig, Program Coordinator
Katie Reeves, Engagement and Communications Lead

Technical Contributor

Katharine Hayhoe, Texas Tech University

22. Northern Great Plains

Review Editor

Ellu Nasser, Adaptation International

Federal Coordinating Lead Author

Doug Kluck, National Oceanic and Atmospheric
Administration

USGCRP Coordinators

Susan Aragon-Long, Senior Scientist
Christopher W. Avery, Senior Manager

Chapter Lead

Richard T. Conant, Colorado State University

24. Northwest

Chapter Authors

Mark Anderson, U.S. Geological Survey
Andrew Badger, University of Colorado
Barbara Mayes Boustead, National Oceanic andAtmospheric Administration
Justin Derner, U.S. Department of Agriculture
Laura Farris, U.S. Environmental Protection Agency
Michael Hayes, University of Nebraska
Ben Livneh, University of Colorado
Shannon McNeeley, North Central Climate Adaptation
Science Center and Colorado State University
Dannele Peck, U.S. Department of Agriculture
Martha Shulski, University of Nebraska
Valerie Small, University of ArizonaFederal Coordinating Lead Author

Charles Luce, USDA Forest Service

Chapter Lead

Christine May, Silvestrum Climate Associates

Chapter Authors

Joe Casola, Climate Impacts Group, University ofWashington
Michael Chang, Makah Tribe
Jennifer Cuhaciyan, Bureau of Reclamation
Meghan Dalton, Oregon State University
Scott Lowe, Boise State University
Gary Morishima, Quinault Indian Nation
Philip Mote, Oregon State University
Alexander (Sascha) Petersen, Adaptation International
Gabrielle Roesch-McNally, USDA Forest Service
Emily York, Oregon Health Authority

Review Editor

Kirsten de Beurs, University of Oklahoma

USGCRP Coordinators

Allyza Lustig, Program Coordinator
Kristin Lewis, Senior Scientist

U.S. Global Change Research Program179

Report-in-Brief | Author Teams
26. Alaska

Review Editor

Beatrice Van Horne, USDA Forest Service, Northwest
Climate HubFederal Coordinating Lead Author

Stephen T. Gray, U.S. Geological Survey

USGCRP Coordinators

Natalie Bennett, Adaptation and Assessment Analyst
Christopher W. Avery, Senior Manager
Susan Aragon-Long, Senior Scientist

Chapter Lead

Carl J. Markon, U.S. Geological Survey (Retired)

Chapter Authors

Matthew Berman, University of Alaska, Anchorage
Laura Eerkes-Medrano, University of Victoria
Thomas Hennessy, U.S. Centers for Disease Control andPrevention
Henry P. Huntington, Huntington Consulting
Jeremy Littell, U.S. Geological Survey
Molly McCammon, Alaska Ocean Observing System
Richard Thoman, National Oceanic and Atmospheric
Administration
Sarah Trainor, University of Alaska Fairbanks

25. Southwest
Federal Coordinating Lead Author

Patrick Gonzalez, U.S. National Park Service

Chapter Lead

Gregg M. Garfin, University of Arizona

Chapter Authors

David D. Breshears, University of Arizona
Keely M. Brooks, Southern Nevada Water Authority
Heidi E. Brown, University of Arizona
Emile H. Elias, U.S. Department of Agriculture
Amrith Gunasekara, California Department of Food andAgriculture
Nancy Huntly, Utah State University
Julie K. Maldonado, Livelihoods Knowledge
Exchange Network
Nathan J. Mantua, National Oceanic and Atmospheric
Administration
Helene G. Margolis, University of California, Davis
Skyli McAfee, The Nature Conservancy (through 2017)
Beth Rose Middleton, University of California, Davis
Bradley H. Udall, Colorado State University

Technical Contributors

Todd Brinkman, University of Alaska Fairbanks
Patricia Cochran, Alaska Native Science Commission
Jeff Hetrick, Alutiiq Pride Shellfish Hatchery
Nathan Kettle, University of Alaska Fairbanks
Robert Rabin, National Oceanic and Atmospheric
Administration
Jacquelyn (Jaci) Overbeck, Alaska Department of
Natural Resources
Bruce Richmond, U.S. Geological Survey
Ann Gibbs, U.S. Geological Survey
David K. Swanson, National Park Service
Todd Attwood, U.S. Geological Survey
Tony Fischbach, U.S. Geological Survey
Torre Jorgenson, Arctic Long Term Ecological Research
Neal Pastick, U.S. Geological Survey
Ryan Toohey, U.S. Geological Survey
Shad O’Neel, U.S. Geological Survey
Eran Hood, University of Alaska Southeast
Anthony Arendt, University of Washington
David Hill, Oregon State University
Lyman Thorsteinson, U.S. Geological Survey
Franz Mueter, University of Alaska Fairbanks
Jeremy Mathis, National Oceanic and Atmospheric
Administration
Jessica N. Cross, National Oceanic and Atmospheric
Administration
Jennifer Schmidt, University of Alaska Anchorage
David Driscoll, University of Virginia
Don Lemmen, Natural Resources Canada
Philip Loring, University of Saskatoon
Benjamin Preston, RAND Corporation
Stefan Tangen, University of Alaska Fairbanks
John Pearce, U.S. Geological Survey
Darcy Dugan, Alaska Ocean Observing System
Anne Hollowed, National Oceanic and Atmospheric
Administration

Technical Contributors

Mary E. Black, University of Arizona
Shallin Busch, National Oceanic and Atmospheric
Administration
Brandon Goshi, Metropolitan Water District of Southern
California

Review Editor

Cristina Bradatan, Texas Tech University

USGCRP Coordinators

Fredric Lipschultz, Senior Scientist and Regional
Coordinator
Christopher W. Avery, Senior Manager

Review Editor

Victoria Herrmann, The Arctic Institute

U.S. Global Change Research Program180

Report-in-Brief | Author Teams
Neal Fujii, State of Hawai‘i Commission on Water
Resource Management
Ruth Gates, University of Hawai‘i at Mānoa, School of
Ocean and Earth Science and Technology
Christian Giardina, USDA Forest Service, Institute ofPacific Islands Forestry
Scott Glenn, State of Hawai‘i Department of Health,
Office of Environmental Quality Control
Matt Gonser, University of Hawai‘i Sea Grant
Jamie Gove, NOAA Pacific Islands Fisheries
Science Center
Robbie Greene, CNMI Bureau of Environmental andCoastal Quality
Shellie Habel, University of Hawai‘i at Mānoa, School of
Ocean and Earth Science and Technology
Justin Hospital, NOAA Pacific Islands Fisheries
Science Center
Darcy Hu, National Park Service
Jim Jacobi, U.S. Geological Survey
Krista Jaspers, East-West Center, Pacific RISA
Todd Jones, NOAA Pacific Islands Fisheries
Science Center
Charles Ka‘ai‘ai, Western Pacific Regional Fishery
Management Council
Lauren Kapono, NOAA Papahānaumokuākea Marine
National Monument
Hi‘ilei Kawelo, Paepae O He‘eia
Benton Keali‘i Pang, U.S. Fish and Wildlife Service
Karl Kim, University of Hawai‘i, National Disaster
Preparedness Training Center
Jeremy Kimura, State of Hawai‘i Commission on Water
Resource Management
Romina King, University of Guam and Pacific Islands
Climate Adaptation Science Center
Randy Kosaki, National Oceanic and Atmospheric
Administration
Michael Kruk, ERT, Inc.
Mark Lander, University of Guam, Water andEnvironmental Research InstituteLeah Laramee, State of Hawai‘i, Department of Land andNatural Resources
Noelani Lee, Ka Honua Momona
Sam Lemmo, State of Hawai‘i Department of Land
and Natural Resources, Interagency Climate
Adaptation Committee
Rhonda Loh, Hawai‘i Volcanoes National Park
Richard MacKenzie, USDA Forest Service, Institute ofPacific Islands Forestry
John Marra, National Oceanic and Atmospheric
Administration
Xavier Matsutaro, Republic of Palau, Office of
Climate ChangeMarie McKenzie, Pacific Islands Climate Change
Cooperative
Mark Merrifield, University of Hawai‘i at Mānoa
Wendy Miles, Pacific Islands Climate Change Cooperative
Lenore Ohye, State of Hawai‘i Commission on Water
Resource Management
Kirsten Oleson, University of Hawai‘i at Mānoa

USGCRP Coordinators

Fredric Lipschultz, Senior Scientist and Regional
Coordinator
Susan Aragon-Long, Senior Scientist

27. Hawai‘i and U.S.-AffiliatedPacific Islands
Federal Coordinating Lead Author

David Helweg, DOI Pacific Islands Climate Adaptation
Science Center

Chapter Lead

Victoria Keener, East-West Center

Chapter Authors

Susan Asam, ICF
Seema Balwani, National Oceanic and Atmospheric
Administration
Maxine Burkett, University of Hawai‘i at Mānoa
Charles Fletcher, University of Hawai‘i at Mānoa
Thomas Giambelluca, University of Hawai‘i at Mānoa
Zena Grecni, East-West Center
Malia Nobrega-Olivera, University of Hawai‘i at Mānoa
Jeffrey Polovina, NOAA Pacific Islands Fisheries
Science Center
Gordon Tribble, USGS Pacific Island Ecosystems
Research Center

Technical Contributors

Malia Akutagawa, University of Hawai‘i at Mānoa,Hawai‘inuiākea School of Hawaiian Knowledge,
Kamakakūokalani Center for Hawaiian Studies, William
S. Richardson School of Law, Ka Huli Ao Center for
Excellence in Native Hawaiian Law
Rosie Alegado, University of Hawai‘i at Mānoa,Department of Oceanography, UH Sea Grant
Tiffany Anderson, University of Hawai‘i at Mānoa,Geology and Geophysics
Patrick Barnard, U.S. Geological Survey–Santa Cruz
Rusty Brainard, NOAA Pacific Islands Fisheries
Science Center
Laura Brewington, East-West Center, Pacific RISA
Jeff Burgett, Pacific Islands Climate Change Cooperative
Rashed Chowdhury, NOAA Pacific ENSO Applications
Climate Center
Makena Coffman, University of Hawai‘i at Mānoa, Urban
and Regional Planning
Chris Conger, Sea Engineering, Inc.
Kitty Courtney, Tetra Tech, Inc.
Stanton Enomoto, Pacific Islands Climate Change
Cooperative
Patricia Fifita, University of Hawai‘ii, Pacific Islands
Climate Change Cooperative
Lucas Fortini, USGS Pacific Island Ecosystems
Research Center
Abby Frazier, USDA Forest Service
Kathleen Stearns Friday, USDA Forest Service, Instituteof Pacific Islands Forestry

U.S. Global Change Research Program

181

Report-in-Brief | Author Teams
Tom Oliver, University of Hawai‘i at Mānoa, Joint
Institute for Marine and Atmospheric Research
Tara Owens, University of Hawai‘i Sea Grant
Jessica Podoski, U.S. Army Corps of Engineers—
Fort Shafter
Dan Polhemus, U.S. Fish and Wildlife Service
Kalani Quiocho, NOAA Papahānaumokuākea Marine
National Monument
Robert Richmond, University of Hawai‘i, Kewalo
Marine Lab
Joby Rohrer, O‘ahu Army Natural Resources
Fatima Sauafea-Le‘au, National Oceanic and Atmospheric
Administration—American Sāmoa
Afsheen Siddiqi, State of Hawai‘i, Department of Land
and Natural Resources
Irene Sprecher, State of Hawai‘i, Department of Land
and Natural Resources
Joshua Stanbro, City and County of Honolulu Office of
Climate Change, Sustainability and Resiliency
Mark Stege, The Nature Conservancy—Majuro
Curt Storlazzi, U.S. Geological Survey–Santa Cruz
William V. Sweet, National Oceanic and Atmospheric
Administration
Kelley Tagarino, University of Hawai‘i Sea Grant
Jean Tanimoto, National Oceanic and Atmospheric
Administration
Bill Thomas, NOAA Office for Coastal Management
Phil Thompson, University of Hawai‘i at Mānoa,Oceanography
Mililani Trask, Indigenous Consultants, LLC
Barry Usagawa, Honolulu Board of Water Supply
Kees van der Geest, United Nations University, Institutefor Environment and Human Security
Adam Vorsino, U.S. Fish and Wildlife Service
Richard Wallsgrove, Blue Planet Foundation
Matt Widlansky, University of Hawai‘i, Sea Level Center
Phoebe Woodworth-Jefcoats, NOAA Pacific Islands
Fisheries Science Center
Stephanie Yelenik, USGS Pacific Island Ecosystems
Research Center

Review Editor

Jo-Ann Leong, Hawai‘i Institute of Marine Biology

USGCRP Coordinators

Allyza Lustig, Program Coordinator
Fredric Lipschultz, Senior Scientist and Regional
Coordinator

Kate Gordon, Paulson Institute
Katherine Greig, Wharton Risk Management
and Decision Processes Center at University ofPennsylvania (formerly New York City Mayor’s Office of
Recovery and Resiliency)
Cat Hawkins Hoffman, National Park Service
Dale Sands, Village of Deer Park, Illinois
Caitlin Werrell, The Center for Climate and Security

Technical Contributors

Lauren Kendrick, RAND Corporation
Pat Mulroy, Brookings Institution
Costa Samaras, Carnegie Mellon University
Bruce Stein, National Wildlife Federation
Tom Watson, The Center for Climate and Security
Jessica Wentz, Columbia University

Review Editor

Mary Ann Lazarus, Cameron MacAllister GroupUSGCRP Coordinators

Sarah Zerbonne, Adaptation and Decision Science
Coordinator
Fredric Lipschultz, Senior Scientist and Regional
Coordinator

29. Reducing Risks ThroughEmissions Mitigation
Federal Coordinating Lead Author

Jeremy Martinich, U.S. Environmental Protection Agency

Chapter Lead

Jeremy Martinich, U.S. Environmental Protection Agency

Chapter Authors

Benjamin DeAngelo, National Oceanic and Atmospheric
Administration
Delavane Diaz, Electric Power Research InstituteBrenda Ekwurzel, Union of Concerned Scientists
Guido Franco, California Energy Commission
Carla Frisch, U.S. Department of Energy
James McFarland, U.S. Environmental Protection Agency
Brian O’Neill, University of Denver (National Center for
Atmospheric Research through June 2018)

Review Editor

Andrew Light, George Mason University

28. Reducing Risks ThroughAdaptation Actions

USGCRP Coordinators

David Reidmiller, Director
Christopher W. Avery, Senior Manager

Federal Coordinating Lead Authors

Jeffrey Arnold, U.S. Army Corps of Engineers
Roger Pulwarty, National Oceanic and Atmospheric
Administration

Appendix 1. Report Development Process

Chapter Lead

Federal Coordinating Lead Author

Robert Lempert, RAND Corporation

U.S. Global Change Research Program

Chapter Authors

David Reidmiller, U.S. Global Change Research Program

182

Report-in-Brief | Author Teams
Lead Author

Contributing Author

Christopher W. Avery, U.S. Global Change Research
Program/ICF

Apurva Dave, U.S. Global Change Research Program/ICF

Appendix 5. Frequently Asked Questions(FAQs)

Contributing Authors

Therese (Tess) S. Carter, U.S. Global Change Research
Program/ICF
Katie Reeves, U.S. Global Change Research Program/ICF
Kristin Lewis, U.S. Global Change Research Program/
Straughan Environmental

Federal Coordinating Lead Author

David Reidmiller, U.S. Global Change Research Program

Lead Author

Appendix 2. Information in the Fourth National
Climate Assessment

Contributing Authors

Christopher W. Avery, U.S. Global Change Research
Program/ICF
Allison Crimmins, U.S. Environmental Protection Agency
LuAnn Dahlman, National Oceanic and Atmospheric
Administration
David R. Easterling, NOAA National Centers forEnvironmental Information
Rachael Gaal, National Oceanic and Atmospheric
Administration
Emily Greenhalgh, National Oceanic and Atmospheric
Administration
David Herring, National Oceanic and Atmospheric
Administration
Kenneth E. Kunkel, North Carolina State University
Rebecca Lindsey, National Oceanic and Atmospheric
Administration
Thomas K. Maycock, North Carolina State University
Roberto Molar, National Oceanic and Atmospheric
Administration
Brooke C. Stewart, North Carolina State University
Russell S. Vose, NOAA National Centers forEnvironmental Information

Federal Coordinating Lead Author

David Reidmiller, U.S. Global Change Research Program

Lead Author

Kristin Lewis, U.S. Global Change Research Program/
Straughan Environmental

Contributing Author

Christopher W. Avery, U.S. Global Change Research
Program/ICF

Appendix 3. Data Tools andScenario ProductsFederal Coordinating Lead Author

David Reidmiller, U.S. Global Change Research Program

Lead Author

Christopher W. Avery, U.S. Global Change Research
Program/ICF

Contributing Authors

Michael Kolian, U.S. Environmental Protection Agency
Kenneth E. Kunkel, North Carolina State University
David Herring, National Oceanic and Atmospheric
Administration
Reid Sherman, U.S. Global Change Research Program/
Straughan Environmental
William V. Sweet, National Oceanic and Atmospheric
Administration
Christopher Weaver, U.S. Environmental
Protection Agency
Kathryn Tipton, U.S. Global Change Research
Program/ICF

Technical Contributors

C. Taylor Armstrong, National Oceanic and Atmospheric
Administration
Edward Blanchard-Wrigglesworth, University ofWashington
James Bradbury, Georgetown Climate Center
Delavane Diaz, Electric Power Research InstituteJoshua Graff-Zivin, University of California, San Diego
Jessica Halofsky, University of Washington
Lesley Jantarasami, Oregon Department of Energy
Shannon LaDeau, Cary Institute of Ecosystem Studies
Elizabeth Marino, Oregon State University
Shaima Nasiri, U.S. Department of Energy
Matthew Neidell, Columbia University
Rachael Novak, U.S. Department of the Interior
Rick Ostfeld, Cary Institute of Ecosystem Studies
David Pierce, Scripps Institute of Oceanography
Catherine Pollack, National Oceanic and Atmospheric
Administration
William V. Sweet, National Oceanic and Atmospheric
Administration
Carina Wyborn, University of Montana
Laurie Yung, University of Montana–Missoula
Lewis Ziska, U.S. Department of Agriculture

Appendix 4. Looking Abroad:
How Other Nations Approach a
National Climate Assessment
Federal Coordinating Lead Author

David Reidmiller, U.S. Global Change Research Program

Lead Author

Katherine Weingartner, U.S. Global Change Research
Program/ICF (through September 2017)
U.S. Global Change Research Program

Matthew Dzaugis, U.S. Global Change Research
Program/ICF

183

Report-in-Brief | Staff

USGCRP National Climate Assessment Staff
David Reidmiller, Director

Anthony Flowe, Engagement andCommunications Associate

Christopher W. Avery, Senior Manager

Kristin Lewis, Senior Scientist

Bradley Akamine, Chief Digital
Information Officer

Fredric Lipschultz, Senior Scientist and Regional
Coordinator

Reuben Aniekwu, Global Change Information
System Intern

Allyza Lustig, Program Coordinator

Susan Aragon-Long, Senior Scientist

Vincent O’Leary, Assessment Intern

Natalie Bennett, Adaptation andAssessment Analyst

Katie Reeves, Engagement andCommunications Lead

Ashley Bieniek-Tobasco, Health Program
Coordinator

Reid Sherman, Global Change Information
System Lead

Mathia Biggs, Office Coordinator

Mark Shimamoto, Program Coordinator (until
August 2017)

Therese (Tess) S. Carter, Program Coordinator(until June 2017)

Kathryn Tipton, Software Engineer

Apurva Dave, International Coordinator andSenior Analyst

Katherine Weingartner, Program Assistant (until
September 2017)

David J. Dokken, Senior Program Officer

Sarah Zerbonne, Adaptation and Decision
Science Coordinator

Matthew Dzaugis, Program Coordinator
Amrutha Elamparuthy, Data Manager

U.S. Global Change Research Program

184

Report-in-Brief | Staff

NOAA Technical Support UnitDavid R. Easterling, NCA Technical Support
Unit Director, NOAA National Centers forEnvironmental Information

Andrew Thrasher, Software Engineer, North
Carolina State University
Andrea McCarrick, Editorial Assistant, North
Carolina State University

Kenneth E. Kunkel, Lead Scientist, North
Carolina State University

Tiffany Means, Editorial Assistant, North
Carolina State University

Sara W. Veasey, Creative Director, NOAA
National Centers for Environmental Information

Andrew Buddenberg, Software Engineer, North
Carolina State University (until October 2017)

Brooke C. Stewart, Managing Editor and Lead
Science Editor, North Carolina State University
Sarah M. Champion, Data Architect and Lead
Information Quality Analyst, North Carolina State
University

Liz Love-Brotak, Graphic Designer, NOAA NCEI
Deborah Misch, Graphic Designer, TeleSolv
Consulting
Deborah B. Riddle, Lead Graphic Designer(Report-in-Brief), NOAA NCEI

Katharine M. Johnson, Web Developer and GIS
Specialist, ERT, Inc.

Mara Sprain, NCEI Librarian, LAC GroupJames C. Biard, Software Engineer, North
Carolina State University

Barbara Ambrose, Graphic Designer, Mississippi
State University, Northern Gulf InstituteJessicca Griffin, Visual Communications
Specialist and Graphic Designer, North Carolina
State University

Andrew Ballinger, Research Scientist, North
Carolina State University

Angel Li, Web Developer, North Carolina State
University

Jennifer Fulford, Editorial Assistant, TeleSolv
Consulting

Thomas K. Maycock, Science Editor, North
Carolina State University

Kristy Thomas, Metadata Specialist, ERT, Inc.
Terence R. Thompson, Climate Data Analyst, LMI

Laura E. Stevens, Research Scientist, North
Carolina State University

Caroline Wright, GIS Intern, North Carolina State
University

Liqiang Sun, Research Scientist, North Carolina
State University

U.S. Global Change Research Program

Samantha Heitsch, Technical Writer, ICF

185

Report-in-Brief | Staff

UNC Asheville’s National Environmental Modeling and Analysis Center (NEMAC)John Frimmel, Principal Software Developer

Karin Rogers, Director of Operations /Research Scientist

Ian Johnson, Geospatial and Science
Communications Associate

U.S. Global Change Research Program186

This document responds to the requirements of Section 106 of the Global Change Research Act of1990 (http://www.globalchange.gov/about/legal-mandate), and it meets all federal requirements
associated with the highly influential scientific assessment (HISA) standard of the Information
Quality Act (see Appendix 2: Information in the Fourth National Climate Assessment).

nca2018.globalchange.gov
For an assessment of the physical science (NCA4 Vol. I) underlying this report, visit:science2017.globalchange.gov

U.S. Global Change Research Program

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