Benefits 

of Global Action

CLIMATE CHANGE IN THE UNITED STATES
FIND US ONLINE

EPA’s climate change website 

features a user-friendly 

interface for this report with 

downloadable graphics. To view 

information about EPA’s Climate 

Change Impacts and Risk 

Analysis (CIRA) project, share 

your thoughts on this effort, 

and access the corresponding 

Technical Appendix for this 

report, please visit EPA’s website 

at: www.epa.gov/cira.
Contents

1

3 INTRODUCTION

6 SUMMARY OF KEY FINDINGS 

10 CIRA FRAMEWORK

12 Temperature Projections

14 Precipitation Projections

15 Sea Level Rise Projections

16 Levels of Certainty

18 Boundaries of Analysis

20 SECTORS

22 Health

24 Air Quality

26 Extreme Temperature

28 Labor

30 Water Quality

32 Infrastructure

34 Bridges

36 Roads

38 Urban Drainage

40 Coastal Property

42 Coastal Property: Environmental Justice

44 Electricity 

46 Electricity Demand

48 Electricity Supply

50 Water Resources

52 Inland Flooding 

54 Drought

56 Water Supply and Demand

58 Agriculture and Forestry

60 Crop and Forest Yields

62 Market Impacts

64 Ecosystems

66 Coral Reefs

68 Shellfish

70 Freshwater Fish

72 Wildfire

74 Carbon Storage

76 OVERVIEW OF RESULTS

78 National Highlights 

80 Regional Highlights 

82 CONCLUSION

84 ENDNOTES
Acknowledgments

2

CONTRIBUTORS

The Climate Change Impacts and Risk Analysis (CIRA) project is coordinated by EPA’s Office of Atmospheric 

Programs - Climate Change Division, with significant contributions from a number of collaborators, 

including the Massachusetts Institute of Technology’s Joint Program on the Science and Policy of Global 

Change, the Pacific Northwest National Laboratory’s Joint Global Change Research Institute, the National 

Renewable Energy Laboratory, academic researchers, and the following consulting firms: Industrial 

Economics, Inc. (IEc), Stratus Consulting, RTI International, and ICF International. Support for the report’s 

production and design was provided by Industrial Economics, Inc. 

PEER REVIEW

The methods and results of the climate change impacts analyses described herein have been peer reviewed 

in the scientific literature. In addition, this summary report was peer reviewed by seven external, independent 

experts, a process coordinated by Eastern Research Group, Inc. EPA gratefully acknowledges the following 

reviewers for their useful comments and suggestions: Donald Boesch, Larry Dale, Kristie Ebi, Anthony 

Janetos, Denise L. Mauzerall, Michael Meyer, and Timothy Randhir. The information and views expressed in 

this report do not necessarily represent those of the peer reviewers, who also bear no responsibility for any 

remaining errors or omissions. Details describing this review, and a comprehensive reference list for the 

CIRA peer reviewed literature, can be viewed in the online Technical Appendix of this report (www.epa.gov/

cira/downloads-cira-report). 

RECOMMENDED CITATION

EPA. 2015. Climate Change in the United States: Benefits of Global Action. United States Environmental 

Protection Agency, Office of Atmospheric Programs, EPA 430-R-15-001.

g
Introduction

3

he Earth’s changing climate is affecting human health and the environment in many 

ways. Across the United States (U.S.), temperatures are rising, snow and rainfall patterns 

are shifting, and extreme climate events are becoming more common. Scientists are 

confident that many of the observed changes in the climate are caused by the increase in 

greenhouse gases (GHGs) in the atmosphere. As GHG emissions from human activities increase, 

many climate change impacts are expected to increase in both magnitude and frequency over 

the coming decades, with risks to human health, the economy, and the environment. 

Actions can be taken now to reduce GHG emissions and avoid many of the adverse impacts of 

climate change. Quantifying the benefits of reducing GHG emissions (i.e., how GHG mitigation 

reduces or avoids impacts) requires comparing projections of climate change impacts and damages in a future with policy actions and a future without policy actions. Looking across a large 

number of sectors, this report communicates estimates of these benefits to the U.S. associated 

with global action on climate change.

T
4

Introduction

About this Report

This report summarizes and communicates the results of EPA’s ongoing Climate Change Impacts and Risk Analysis (CIRA) project. 

The goal of this work is to estimate to what degree climate change impacts and damages to multiple U.S. sectors (e.g., human 

health, infrastructure, and water resources) may be avoided or reduced in a future with significant global action to reduce GHG 

emissions, compared to a future in which current emissions continue to grow. Importantly, only a small portion of the impacts of 

climate change are estimated, and therefore this report captures just some of the total benefits of reducing GHGs.

To achieve this, a multi-model framework was developed to estimate the impacts and damages to the human health and 

welfare of people in the U.S. The CIRA framework uses consistent inputs (e.g., socioeconomic and climate scenarios) to enable 

consistent comparison of sectoral impacts across time and space. In addition, the role of adaptation is modeled for some of the 

sectors to explore the potential for risk reduction and, where applicable, to quantify the costs associated with adaptive actions.

The methods and results of the CIRA project have been peer reviewed in the scientific literature, including a special issue of 

Climatic Change entitled, “A Multi-Model Framework to Achieve Consistent Evaluation of Climate Change Impacts in the United 

States.”1 The research papers underlying the modeling and results presented herein are cited throughout this report and are listed 

in Section B of the Technical Appendix.

Interpreting the Results

This report presents results from a large set of sectoral impact 

models that quantify and monetize climate change impacts in 

the U.S., with a primary focus on the contiguous U.S., in futures 

with and without global GHG mitigation. The CIRA analyses are 

intended to provide insights about the potential direction and 

magnitude of climate change impacts and the benefits (avoided 

impacts) to the U.S. of global emissions reductions. However, 

none of the estimates presented in this report should be 

interpreted as definitive predictions of future impacts at a 

particular place or time. 

The CIRA analyses do not evaluate or assume specific GHG 

mitigation or adaptation policies in the U.S. or in other world 

regions. Instead, they consider plausible scenarios to illustrate 

potential benefits of significant GHG emission reductions 

compared to a business-as-usual future. The results should not 

be interpreted as supporting any particular domestic or global 

mitigation policy or target. A wide range of global mitigation 

scenarios could be modeled in the CIRA framework,2

 and results 

would vary accordingly. For ease of communicating results, 

however, this report focuses on a future where the increase in 

average global temperature is limited to approximately 2°C 

(3.6°F) above preindustrial levels—a goal relevant to international discussions on GHG emission reductions.3

This report includes as many climate change impacts as 

feasible at present, but is not all-inclusive. It is not intended 

to be as comprehensive as major assessments, such as those 

conducted by the U.S. Global Change Research Program 

(USGCRP), which capture a wider range of impacts from the 

published literature.4

 By using a consistent set of socioeconomic and climate scenarios, CIRA produces apples-to-apples 

comparisons of impacts across sectors and regions—something that is not always achieved, or even sought, in the 

major assessments. Also, the assessments typically do not 

monetize damages, nor do they focus on quantifying mitigation benefits. CIRA’s ability to estimate how global GHG 

mitigation may benefit the U.S. by reducing or avoiding 

climate change impacts helps to fill an important literature 

and knowledge gap. 

The CIRA analyses do not serve the same analytical purpose 

nor use the same methodology as the Social Cost of Carbon 

(SCC), an economic metric quantifying the marginal global 

benefit of reducing one ton of carbon dioxide (CO2).5

 In 

addition, the costs of reducing GHG emissions,6 and the health 

benefits associated with co-reductions in other air pollutants, 

are well-examined elsewhere in the literature7 and are beyond 

the scope of this report.
5

Provides an overview of key findings and highlights of the report. 

Introduces the CIRA project, describes and briefly presents the climate projections used in the 

analyses, and discusses key uncertainties and boundaries of analysis.

Summarizes the major findings of each of the 20 impact analyses within the six broad sectors 

listed to the left, including: 

• Background on the impact being estimated, along with a brief summary of the analytical 

approach to estimating the impact;

• Key findings and graphics depicting the risks of inaction and the benefits of global-scale 

GHG mitigation; and 

• References to the underlying peer-reviewed research upon which these estimates are based.

Presents national and regional highlights from the 20 sectoral impact analyses.

Describes the over-arching conclusions of the report. 

• Provides a list of all peer-reviewed research papers underlying the CIRA project;

• Provides comparisons of key CIRA findings to those of the assessment literature; and

• Describes the treatment of adaptation across the sectoral analyses. 

Roadmap to the Report

SUMMARY OF 

KEY FINDINGS 

CIRA FRAMEWORK

SECTORS

Health

Infrastructure

Electricity 

Water Resources

Agriculture and Forestry

Ecosystems

OVERVIEW OF 

RESULTS

CONCLUSION

TECHNICAL APPENDIX

(available at www.epa.gov/cira)
6

Summary of Key Findings

Global GHG 

Mitigation Avoids 

Costly Damages 

in the U.S.

For nearly all sectors 

analyzed, global GHG 

mitigation is projected to 

prevent or substantially 

reduce adverse impacts 

in the U.S. this century 

compared to a future 

without emission reductions. For many sectors, 

the projected benefits of 

mitigation are substantial; 

for example, in 2100 

mitigation is projected to 

result in cost savings of 

$4.2-$7.4 billion associated 

with avoided road maintenance. Global GHG mitigation is also projected to avoid the loss of 230,000-360,000 acres of 

coldwater fish habitat across the country compared to a future without emissions reductions. 

limate change poses significant risks to humans and the environment. The 

CIRA project quantifies and monetizes the risks of inaction and benefits to the 

U.S. of global GHG mitigation within six broad sectors (water resources, electricity, 

infrastructure, health, agriculture and forestry, and ecosystems). Looking across the 

impact estimates presented in this report, several common themes emerge.1

Global GHG 

Mitigation Reduces 

the Frequency of 

Extreme Weather 

Events and 

Associated Impacts

Global GHG mitigation is 

projected to have a substantial 

effect on reducing the 

incidence of extreme temperature and precipitation 

events by the end of the 

century, as well as the impacts 

to humans and the environment associated with these 

extreme events.2 For example, 

by 2100 mitigation is projected to avoid 12,000 deaths 

annually associated with 

extreme temperatures in 49 

U.S. cities, compared to a 

future with no emission 

reductions. Inclusion of the 

entire U.S. population would 

greatly increase the number 

of avoided deaths, while 

accounting for adaptation 

could reduce this number.

The Benefits of GHG Mitigation Increase over Time

For a large majority of sectors analyzed, the 

benefits of GHG mitigation are projected to 

be greater in 2100 than in 2050. In addition, 

the benefits of GHG mitigation are often not 

apparent until mid-century. This delay in 

benefits is consistent with many studies,3 and 

is attributable to inertia in the climate system. 

Therefore, decisions we make today can have 

long-term effects, and delaying action will 

likely increase the risks of significant and costly 

impacts in the future.

C

y y g
7

Adaptation Can Reduce Overall 

Damages in Certain Sectors

Adaptation can substantially reduce certain impacts of 

climate change regardless of whether future GHG levels are 

low or high. For example, the estimated damages to coastal 

property from sea level rise and storm surge in the contiguous U.S. are $5.0 trillion through 2100 (discounted at 3%4

) in 

a future without emission reductions. When cost-effective 

adaptation along the coast is included, the estimated damages are reduced to $810 billion.

Impacts Vary across Time and Space

Important regional changes may be masked when results are presented at the national level. For example, the wildfire analysis 

reveals that the projected changes in the Southwest and Rocky Mountain regions are the primary drivers of national trends of 

increasing wildfire activity over time. 

The temporal scale of climate change impacts is also important. While some impacts are likely to occur gradually over time, 

others may exhibit threshold (tipping point) responses to climate change, as large changes manifest over a short period of time. 

For example, high-temperature bleaching events projected to occur by 2025 are estimated to severely affect coral reefs in the 

Caribbean. Therefore, simply analyzing an impact in one time period (e.g., 2100) may mask important temporal dynamics that are 

relevant to decision makers.
8

 Estimated Benefits to the U.S. in 2100 

* Monetary estimates for this summary are presented for either 2050 or 2100 only, and are undiscounted (2014$). See the Sectors section for the use of discounting throughout this report. 

† Estimated range of results relies upon climate projections from two climate models showing different patterns of precipitation in the U.S. The IGSM-CAM projects a relatively “wetter” future for most of the U.S. 

compared to the drier MIROC model (see the CIRA Framework section of this report for more information). 

This graphic presents a selection of the estimated benefits of global GHG mitigation in 2100 for major U.S. 

sectors. Unless otherwise noted, the results presented below are estimates of annual benefits (or disbenefits) 

of mitigation in the year 2100.* Importantly, only a small portion of the impacts of climate change are estimated, 

and therefore this report captures just some of the total benefits of reducing GHGs.

SUMMARY OF KEY FINDINGS 

COASTAL PROPERTY

Approximately $3.1 

billion in avoided 

damages and 

adaptation costs from 

sea level rise and 

storm surge in 2100

ELECTRICITY 

DEMAND

An avoided 

increase in 

electricity demand 

of 1.1%-4.0% 

in 2050‡

ELECTRICITY 

SUPPLY

An 

estimated 

$10-$34 

billion in 

savings on 

power 

system costs 

in 2050‡

BRIDGES

An estimated 

720-2,200 fewer 

bridges made 

structurally 

vulnerable 

in 2100†

ROADS

An estimated 

$4.2-$7.4 billion 

in avoided 

adaptation costs 

in 2100†

INFRASTRUCTURE

ELECTRICITY

AIR QUALITY

An estimated 57,000 

fewer deaths from 

poor air quality

in 2100

EXTREME TEMPERATURE

In 49 major U.S. cities, 

an estimated 

12,000 fewer deaths 

from extreme 

temperature in 2100

LABOR 

Approximately 

$110 billion 

in avoided 

damages from 

lost labor due 

to extreme 

temperatures 

in 2100

WATER QUALITY

An estimated 

$2.6-$3.0 billion 

in avoided 

damages from 

poor water 

quality in 2100†

HEALTH

URBAN DRAINAGE

In 50 U.S. cities, an 

estimated $50 

million-$6.4 billion in 

avoided adaptation 

costs in 2100†
9

of Reducing Global GHG Emissions

DROUGHT

An estimated 

40%-59% fewer 

severe and extreme 

droughts in 2100†

FORESTRY

An estimated 

$520 million to 

$1.5 billion 

in avoided 

damages to 

forestry in 2100

SUPPLY & 

DEMAND

An estimated 

$11-$180 billion in 

avoided damages 

from water 

shortages in key 

economic sectors 

in 2100†

WATER RESOURCES

INLAND 

FLOODING

Estimates range 

from approximately 

$2.8 billion in 

avoided damages to 

$38 million in 

increased damages 

in 2100†

CARBON 

STORAGE

An estimated 

1.0-26 million 

fewer tons of 

carbon stored 

in vegetation 

in 2100†§

FRESHWATER 

FISH

An estimated 

230,000-360,000 

acres of coldwater fish habitat 

preserved 

in 2100†

WILDFIRE

An estimated 

6.0-7.9 million 

fewer acres 

burned by 

wildfires in 

2100†

ECOSYSTEMS

SHELLFISH

An avoided loss of 

approximately 

34% of the U.S. 

oyster supply, 37% 

of scallops, and 

29% of clams 

in 2100

CORAL REEFS

An avoided loss 

of approximately 

35% of current 

Hawaiian coral in 

2100, with a 

recreational value 

of $1.1 billion

‡ Results reflect the estimated range of benefits from the reduction in demand and system costs resulting from lower temperatures associated with GHG mitigation. The Electricity section in this report presents an analysis 

that includes the costs to the electric power sector of reducing GHG emissions. 

§ See the Carbon Storage section of this report for cumulative results from 2000-2100, which show benefits of GHG mitigation for parts, and in some cases all, of the century. 

AGRICULTURE

An 

estimated 

$6.6-$11

billion in 

avoided 

damages to 

agriculture 

in 2100

AGRICULTURE AND FORESTRY

For detailed information on the results, please refer to the Sectors section of this report. 

g
10

• Temperature

• Precipitation

• Sea level rise

• CO2 concentration

• Sea surface temperature

• Cloud cover

• Wind speed

• Relative humidity

• Solar radiation

Two scenarios are used throughout this report: 

• Business as usual or the “Reference” scenario 

• Global emissions reductions or the “Mitigation” scenario

STEP 1 | DESIGN GHG EMISSIONS SCENARIOS STEP 2 | PROJECT FUTURE CLIMATE

CIRA Framework

GHG emissions from human activities, and 

the resulting climate change impacts and 

damages, depend on future socioeconomic 

development (e.g., population growth, 

economic development, energy sources, and 

technological change). Emissions scenarios 

provide scientifically credible starting points 

for examining questions about an uncertain 

future and help us visualize alternative 

futures.2

 They are neither forecasts nor 

predictions, and the report does not assume 

that any scenario is more or less likely than 

another. GHG emissions scenarios are 

illustrations of how the release of different 

amounts of climate-altering gases and 

particles into the atmosphere will produce 

different climate conditions in the U.S. and 

around the globe.

To allow for a better understanding of the 

potential benefits of global-scale GHG 

mitigation, the CIRA results presented in this 

report consider two emissions scenarios (see 

Table 1): a business-as-usual future in which 

GHG emissions continue to increase 

unchecked (referred to as the Reference 

scenario), and a mitigation scenario in which 

global GHG emissions are substantially 

reduced (referred to as the Mitigation 

scenario).3, 4 These scenarios were developed 

using the Massachusetts Institute of Technology’s Emissions Predictions and Policy Analysis 

(EPPA) model,5 the human systems component within the Integrated Global System 

Model (IGSM). EPPA provides projections of 

world economic development and emissions, 

including analysis of proposed emissions 

he primary goal of the CIRA project is to estimate the degree to which climate change 

impacts in the U.S. are avoided or reduced in the 21st century under significant global GHG mitigation. 

The CIRA framework is designed to assess the physical impacts and economic damages of climate 

change in the U.S. In this report, the benefits (or disbenefits) of global GHG mitigation are assessed as the 

difference between the impacts in futures with and without mitigation policy, using multiple models driven by 

1| Design GHG Emissions Scenarios 

T

Table 1. Characteristics of the Reference and Mitigation Scenarios in 2100

control measures. These measures include, for 

example, limiting GHGs from major emitting 

sectors, such as electricity production and 

transportation. EPPA-IGSM, along with a 

linked climate model, provide a consistent 

framework to develop GHG emission and 

climate scenarios for impacts assessment. 

Table 1 provides information on the 

characteristics of each emissions scenario in 

2100. Similar to the Representative Concentration Pathways (RCPs) used by the Intergovernmental Panel on Climate Change (IPCC) in 

its Fifth Assessment Report,6

 the CIRA 

scenarios are based on different trajectories 

of GHG emissions and radiative forcing—a 

metric of the additional heat added to the 

Earth’s climate system caused by anthropogenic and natural emissions. 

Figure 1 compares the two primary CIRA 

scenarios used throughout this report to the 

RCPs, showing that these scenarios fall within 

the range of IPCC's latest projections. The 

CIRA emissions scenarios provide illustrations 

for analytical comparison and do not 

represent specific policies. For more information about the design of these scenarios, 

please refer to Paltsev et al. (2013).7

BUSINESS AS USUAL 

“REFERENCE”

GLOBAL EMISSIONS REDUCTIONS 

“MITIGATION”

9.8 W/m2

 (8.6 W/m2)

~2.5 x 2005 levels 

826 ppm

1750 ppm

3.6 W/m2

 (3.2 W/m2)

~0.28 x 2005 levels 

462 ppm

500 ppm

GHG RADIATIVE FORCING (IPCC/RCP METHOD)

GLOBAL GHG EMISSIONS

ATMOSPHERIC CO2 CONCENTRATION

ATMOSPHERIC GHG CONCENTRATION (CO2 EQUIVALENT)
2000 2025

0

20

40

60

80

100

120

140

2050 2075 2100

GHG Emissions (GT CO2 Equivalent)

2000 2025 2050 2075 2100

GHG Radiative Forcing (W/m2

)

2

3

4

5

6

7

8

9

10

2025

Reference

RCP 8.5 RCP 6.0 RCP 4.5 RCP 2.6

Mitigation

2000 2050 2075 2100

CO2 Concentration (ppm)

300

400

500

600

700

800

900

1000

11

HEALTH

• Air quality

• Extreme temperature 

• Labor

• Water quality

INFRASTRUCTURE

• Bridges

• Roads

• Urban drainage

• Coastal property

ELECTRICITY

• Electricity demand

• Electricity supply

WATER 

RESOURCES

• Inland flooding

• Drought

• Water supply and 

demand 

AGRICULTURE 

AND FORESTRY

• Crop and forest yields

• Market impacts

ECOSYSTEMS

• Coral reefs

• Shellfish

• Freshwater fish

• Wildfire

• Carbon storage

STEP 3 | ANALYZE SECTORAL IMPACTS

a consistent set of climatic, socioeconomic, and technological scenarios. A three-step approach for assessing 

benefits includes developing GHG emissions scenarios; simulating future climate under these scenarios; and 

applying these projections in a series of coordinated impacts analyses encompassing six sectors (health, 

infrastructure, electricity, water resources, agriculture and forestry, and ecosystems). For more information 

on the objectives and design of the CIRA framework, please refer to Martinich et al. (2015).1

To simulate future climate in the U.S., CIRA primarily uses the IGSM-CAM framework, which 

links the IGSM to the National Center for Atmospheric Research’s Community Atmosphere 

Model (CAM). The IGSM-CAM simulates changes in a large number of climate variables, such 

as temperature and precipitation, at various temporal scales. Other outputs include: sea level 

rise, atmospheric CO2 concentration, cloud cover, wind speed, relative humidity, and solar 

radiation.10 The CIRA climate projections are briefly described in the following pages of this 

report. As described in the Levels of Certainty section, results using other climate models 

with different patterns of projected precipitation are compared to the IGSM-CAM results for 

sectoral analyses that are sensitive to changes in precipitation (e.g., drought and flooding). 

Specifically, results under the IGSM-CAM projections, which estimate a wetter future for most 

of the contiguous U.S., are complemented with drier projections to investigate the influence 

on impact estimates. Additional information on the development and characteristics of the 

CIRA climate projections can be found in Monier et al. (2014).11

2 | Project Future Climate 

3 | Analyze Sectoral Impacts

This report analyzes 20 specific climate change impacts in the U.S., which are categorized 

into six broad sectors (health, infrastructure, electricity, water resources, agriculture and 

forestry, and ecosystems). The impacts were selected based on the following criteria: 

sufficient understanding of how climate change affects the sector; the existence of data to 

support the methodologies; availability of modeling applications that could be applied in 

the CIRA framework; and the economic, iconic, or cultural significance of impacts and 

damages in the sector to the U.S. It is anticipated that the coverage of sectoral impacts in 

the CIRA project will expand in future work. 

To quantify climate change impacts in each sector, process-based or statistical models 

were applied using the socioeconomic and climate scenarios described above. This 

approach, which ensures that each model is driven by the same inputs, enables consistent 

comparison of impacts across sectors and in-depth analysis across regions and time. Many 

of the analyses explore the potential for adaptation to reduce risks and quantify the costs 

associated with adaptive actions (see the Sectors section of this report and Section D of the 

Technical Appendix for more information).12 Lastly, the CIRA analyses investigate key 

sources of variability in projecting future climate, as further discussed in the Levels of 

Certainty section.

Figure 1. Comparison of CIRA 

Scenarios to the IPCC RCPs8

1c. CO2 Concentration

1b. Radiative Forcing9

1a. GHG Emissions
Temperature Projections

12

Temperature Change in the U.S. 

Global mean temperature under the CIRA Reference scenario is projected to increase by over 9°F by 2100 

(Figure 1). This estimated increase is consistent with the USGCRP Third National Climate Assessment, which 

projects a range of 5-11°F by 2100.13,14 To help illustrate the magnitude of such a change in global mean 

temperature, the last ice age, which covered the northern contiguous U.S. with ice sheets, was approximately 

9°F cooler than today. While some areas will experience greater increases than others, Figure 1 presents the 

average change that is projected to 

occur across the globe under the 

Under the Reference scenario, the largest increases in average temperature across the contiguous U.S. by 2100 are projected to occur in the 

Mountain West—up to a 14°F increase from present-day average temperature (Figure 2). The northern regions are also likely to see larger 

temperature increases than the global average (up to 12°F, compared to a global average of 9.3°F), while the Southeast is projected to experience 

a relatively lower level of overall warming (but comparable to the global average increase). Under the Mitigation scenario, temperature increases 

across the country are far lower compared to the Reference, with no regions experiencing increases of more than 4°F.

Figure 2. Distribution of Temperature Change with and without Global GHG Mitigation

Change in annual mean surface air temperature relative to present-day (1980-2009 average) for IGSM-CAM under the Reference and Mitigation scenarios (CS 3°C). 

Global Temperature Change

CIRA FRAMEWORK

Limiting Future 

Warming to 2°C

Limiting the future increase in 

global average surface temperature to below 2°C (3.6°F) above 

preindustrial levels is a commonly regarded goal for avoiding 

dangerous climate change 

impacts.16 Global temperatures, 

however, have already warmed 

0.85°C (1.5°F) from preindustrial 

times.17,18 The level of global GHG 

mitigation achieved under the 

CIRA Mitigation scenario is 

consistent with the amount 

required to meet the 2°C target 

(Figure 1),19 and therefore the 

estimates presented in this 

report describing the potential 

benefits to the U.S. of global 

GHG mitigation are a reasonable 

approximation of the benefits 

that would result from meeting 

this goal. 

Reference and Mitigation scenarios. 

As shown, temperatures in the 

Mitigation scenario eventually 

stabilize, though due to the inertia of 

the climate system, stabilization is 

not reached until several decades 

after the peak in radiative forcing. 

The Reference scenario continues to 

warm, reaching a temperature 

increase of almost five times that of 

the Mitigation scenario by the end of 

the century. This demonstrates that 

significant GHG mitigation efforts 

can stabilize temperatures and avoid 

an additional 7°F of warming this 

century, but due to climate system 

inertia, benefits may not be apparent 

for several decades. 

Figure 1. Change in Global Mean Temperature 

with and without Global GHG Mitigation

Time series of global annual mean surface air temperature 

relative to present-day (1980-2009 mean) for IGSM-CAM under the 

Reference and Mitigation scenarios with a climate sensitivity (CS)15 of 3°C.

Reference

2025 2050

14 °F

7.8

12

6.7

10

5.6

8

4.4

6

3.3

4

2.2

2

1.1

0

0 °C

2075 2100

Mitigation

0

1

2

3

4

5

6

7

8

9

10

2000 2025 2050 2075 2100

Temperature Anomaly ( ̊F)

Reference Mitigation

Temperature Equal to 2°C Above Pre-Industrial

p j
Reference Mitigation

0

0

1

1.8

2

3.6

3

5.4

4

7.2

5

9

6

10.8

7

12.6

8

14.4

°C

°F

13

Seasonal and Extreme Temperatures

Just as presenting global 

average temperature changes 

masks geographic patterns of 

variability, presenting annual 

average temperature changes 

conceals seasonal patterns of 

change. Some seasons are 

expected to warm faster than 

others, and the impacts of warming will also vary by season. For 

example, in some regions, 

greater levels of warming may 

occur in the winter, but warming 

in summer will matter most for 

changes in the frequency and 

intensity of heat waves. Figure 3 

provides an illustrative example 

of the changes in average 

summertime temperature that 

select states may experience 

over time with and without 

global GHG mitigation. Under 

the Reference scenario, summertime temperatures in some 

northern states are projected to 

feel more like the present-day 

summertime conditions in 

southern states. However, under 

the Mitigation scenario, states 

are projected to experience 

substantially smaller changes.

In addition to increasing 

average summertime temperatures, climate change is projected 

to result in an increase in extreme 

temperatures across most of the 

contiguous U.S. In the Mountain 

West, for example, the hottest 

days of the year are estimated to 

be over 14°F hotter than today 

under the Reference scenario by 

the end of the century (Figure 4). 

Many parts of the Midwest and 

Northeast are projected to 

experience increases in extreme 

temperatures ranging from 7-10°F, 

an amount similar to the increase 

in average summertime temperatures. These changes are projected to be far less severe under the 

Mitigation scenario, however, with 

no regions experiencing increases 

of more than 4°F. 

Figure 4. Change in Magnitude of Extreme Heat Events 

with and without Global GHG Mitigation

Change in the extreme heat index (T99)—the temperature of the hottest four days, or 99th percentile, of the year—simulated by 

the IGSM-CAM for 2100 (average 2085-2115) relative to the baseline (average 1981-2010) (CS 3°C).20 

Figure 3. Change in Summertime Temperatures for Select States 

with and without Global GHG Mitigation

The map compares mean summertime (June, July, and August) temperature in South Dakota, Illinois, and Maryland in 

2050 and 2100 under the Reference and Mitigation scenarios to states with similar present-day temperatures. For example, 

the projected mean summertime temperature in Illinois in 2100 under the Reference scenario (83°F) is projected to be 

analogous to the mean summertime temperature in Louisiana from 1980-2009 (81°F). In other words, without global GHG 

mitigation, Illinois summers by 2100 are projected to “feel like” present-day Louisiana summers. The maps are not perfect 

representations of projected climate, as other factors such as humidity are not included, but they do provide a way of 

visualizing the magnitude of possible changes in the summertime conditions of the future. 

SD

IL

MD 2050, 2100

Reference Mitigation

2050

2050

2050

2050

2050

2100

2100 2100

2100

2100
Reference Mitigation

-.23 0 .23 in/day

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 mm/day

less precipitation more precipitation

Precipitation Projections

14

The IGSM-CAM projects future 

changes in annual mean precipitation over the course of the 21st

century under the Reference 

and Mitigation scenarios (Figure 

1). Under the CIRA Reference 

scenario, the model estimates 

increasing precipitation over 

much of the U.S., especially over 

the Great Plains. However, the 

western U.S. is estimated to 

experience a decrease in precipitation compared to present day. 

Under the Mitigation scenario, 

a similar but less intense pattern 

of increasing precipitation is 

projected over much of the 

country, particularly in the 

central states. 

As projections of future 

precipitation vary across 

individual climate models, the 

CIRA analyses use outputs from 

additional climate models (see 

the Levels of Certainty section of 

this report). Compared to 

multi-model ensemble projections presented in the IPCC and 

USGCRP, the CIRA projections 

exhibit some regional differences in the pattern of projected 

precipitation. A comparison 

between the CIRA climate 

projections and those presented 

in these assessment reports can 

be found in Section E of the 

Technical Appendix. 

CIRA FRAMEWORK

Precipitation in the U.S.

Figure 1. Percentage Change in Annual Mean Precipitation 

with and without Global GHG Mitigation

Percentage change in annual mean precipitation from the historical period (1980-2009) for 

IGSM-CAM under the Reference and Mitigation scenarios (CS 3°C). 

Figure 2 shows the change in the intensity of extreme precipitation events from present day to 2100. Blue areas on this map 

indicate that the future’s heaviest precipitation events will be 

more intense compared to today. Under the Reference, the 

IGSM-CAM shows a general increase in the intensity of extreme 

precipitation events, except over California. The increase is 

particularly strong over the Northeast, Midwest, and Southeast. 

Global GHG mitigation is likely to greatly reduce the increase in 

intensity of extreme precipitation events, as shown in the right 

panel of Figure 2. 

Extreme Precipitation Figure 2. Change in the Intensity of Extreme Precipitation 

with and without Global GHG Mitigation

Change in the extreme precipitation index (P99) simulated by IGSM-CAM for the 

2085-2115 period relative to the 1981-2010 period (CS 3°C). The P99 index reflects 

the precipitation of the four most rainy days of the year, or the 99th percentile.21

Reference

2025

2050

2075

2100

% Change

less precipitation more precipitation

-50 -40 -30 -20 -10 0 10 20 30 40 50 60

Mitigation

p j
Sea Level Rise Projections 

Sea Level Rise in 2100

47-55 in (119-139 cm)

56-65 in (142-165 cm)

66-75 in (167-190 cm)

76-87 in (193-220 cm)

15

Figure 1 shows the change in global mean sea level from present 

day to 2100 under the Reference and Mitigation scenarios. 

Global mean sea levels are projected to rise about 56 inches by 

2100 under the Reference and about 37 inches under the 

Mitigation scenario. These results fall within the range for risk 

planning presented in the Third National Climate Assessment 

of 8-79 inches by 2100, with the Reference scenario's rate being 

slightly larger than the Assessment's likely range of 12-48 

inches.22, 23 As shown in Figure 1, global sea level rise is similar 

across the CIRA scenarios through mid-century, primarily due 

to inertia in the global climate system and lasting effects from 

past GHG emissions. As a result, it is not until the second half of 

the century that global GHG mitigation results in a reduction in 

sea level rise compared to the Reference. 

The projections for global sea level rise account for dynamic 

ice-sheet melting by estimating the rapid response of sea levels 

to atmospheric temperature change.24 These adjustments 

incorporate estimates of ice-sheet melt from the empirical 

model of Vermeer and Rahmstorf (2009),25, 26 using the decadal 

trajectory of global mean surface air temperature results from 

the IGSM as inputs.27

Figure 1. Change in Global Mean Sea Level 

with and without Global GHG Mitigation

Figure 2. Projected Sea Level Rise along the Contiguous U.S. Coastline in 2100 

Map shows projected relative (to land) sea level rise under the Reference scenario for select coastal counties in the contiguous 

U.S. Projections are based on global mean sea level rise in 2100 (56 inches), adjusted for local subsidence and uplift.29

CIRA FRAMEWORK

Global Sea Level Rise

Sea Level Rise in the U.S.

Figure 2 shows projected 

relative sea level rise under 

the Reference scenario for 

select areas along the U.S. 

coast in 2100. For each coastal 

area, global rates of sea level 

change under the two 

scenarios were adjusted to 

account for vertical land 

movement (e.g., subsidence 

or uplift) using tide gauge 

data.28 Areas located along 

the Gulf of Mexico and 

Atlantic Coast are projected 

to experience greater sea 

level rise, due to compounding effects of land subsidence, 

while areas along the West 

Coast are estimated to 

experience relatively lower 

levels of rise. 

0

10

20

30

40

50

60

1990 2000 2025 2050 2075 2100

Change in Sea Level from 1990 (in)

Reference Mitigation

j
Levels of Certainty

16

The CIRA modeling project was designed to investigate the relative importance of four key sources of uncertainty inherent to 

projecting future climate: 

The CIRA framework includes scenarios with different levels of 

GHG emissions: a business-as-usual scenario with unconstrained 

emissions (“Reference”) and a total radiative forcing of 9.8 W/m2

 by 

2100 (8.6 W/m2

 using the IPCC method for calculating radiative 

forcing); a stabilization scenario reflecting global-scale reductions 

in GHG emissions, with a total radiative forcing of 4.2 W/m2

 by 

2100 (3.8 W/m2

 using IPCC method; this scenario is not featured in 

this report); and a more stringent stabilization scenario with greater 

emissions reductions (”Mitigation”) and a total radiative forcing of 

3.6 W/m2

 by 2100 (3.2 W/m2 using IPCC method).34 Results using the 

Reference and Mitigation scenarios are the focus of this report.

Emissions Scenarios

CIRA FRAMEWORK

The four climate sensitivity values considered are 2, 3, 4.5, and 6°C, 

which represent, respectively, the lower bound (CS 2°C), best estimate 

(CS 3°C), and upper bound (CS 4.5°C) of likely climate sensitivity based 

on the IPCC Fourth Assessment Report (AR4),36 and a low-probability/

high-risk climate sensitivity (CS 6°C).37 Results using a climate sensitivity 

of 3°C are the focus of this report.

Figure 2. Influence of Climate Sensitivity on Global

Temperature Change Relative to Present Day 

Temperature change relative to the historic baseline (mean 1980-2009) under the 

Reference and Mitigation scenarios. The bold lines represent the results using a 

climate sensitivity of 3°C, and the shaded areas represent the range of temperature 

anomaly outcomes when using climate sensitivities of 2°C and 6°C. 

Climate Sensitivity

Figure 3. Future Temperature Change under 

Different Climate Sensitivities 

Increases in surface air temperature in 2100 (2091-2110 mean) under the 

Reference scenario relative to present-day (1991-2010 mean).38 

Future GHG emissions: Future emissions will be driven by population 

growth, economic growth, technology advancements, and decisions 

regarding climate and energy policy. Sensitivity analyses explore the 

uncertainty associated with varying levels of future GHG emissions 

under different policy scenarios. 

Climate sensitivity: Future climate change depends on the response 

of the global climate system to rising GHG concentrations (i.e., how 

much temperatures will rise in response to a given increase in 

atmospheric CO2). This response is complicated by a series of feedbacks within Earth’s climate system that act to amplify or diminish an 

initial change.30 Climate sensitivity is typically reported as the change 

in global mean temperature resulting from a doubling in atmospheric 

CO2 concentration.

Natural variability: Natural, small- to medium-scale variations within 

Earth’s climate system, such as El Niño events and other recurring 

patterns of ocean-atmosphere interactions, can drive increases or 

2100

Figure 1. Temperature Change in 2100 Relative to 

Present Day for the CIRA Emissions Scenarios

Changes in surface air temperature in 2100 (2091-2110 mean) relative 

to present-day (1991-2010 mean).35

Radiative Forcing 9.8 W/m2

“Reference Scenario”

Stabilization at 4.2 W/m2

(not featured in this 

report)

Stabilization at 3.6 W/m2

 

“Mitigation Scenario” 

0

0

1

1.8

2

3.6

3

5.4

4

7.2

5

9

6

10.8

7

12.6

°C

°F

Temperature Anomaly ( ̊F)

0

2000 2025 2050

Reference Mitigation

2075 2100

2

4

6

8

10

12

14

16

CS 2°C

CS 4.5°C

CS 3°C

CS 6°C

°F

12

18 21.6

10

14.1

8

10.8

6

7.2

4

3.6

2

0

0 °C

y
17

Future Climate 

Change Across 

Uncertainty 

Sources

Climate Model

The results presented in this report rely primarily upon climate projections from the IGSM-CAM. To analyze the 

implications of a broader set of climate model outputs, the CIRA framework uses a pattern scaling method in 

the IGSM40 for three additional climate models, plus a multi-model ensemble mean from the IPCC AR4 archive. 

As shown in Figure 5, there is better agreement across climate models with regard to temperature projections, 

and higher variability with regard to precipitation projections.41

• The NCAR Community Climate System Model version 3 (CCSM3.0) was chosen to compare with the IGSM- CAM model. Both have the 

same atmospheric and land components and similar biases over land. 

• Bjerknes Centre for Climate Research Bergen Climate Model version 2.0 (BBCR_BCM2.0) was chosen because this model projects the 

largest increases in precipitation over the contiguous U.S. 

• Model for Interdisciplinary Research on Climate version 3.2 medium resolution (MIROC3.2_medres) was chosen because this model 

projects decreases in precipitation over much of the contiguous U.S. Results using this “drier” pattern are shown in several sections of this 

report to provide comparison to the “wetter” IGSM-CAM simulations, which generally show increases in precipitation for much of the 

country (excluding the West). This comparison helps to bound uncertainty in future changes in precipitation for the contiguous U.S. 

Investigation of the relative 

contribution of the four 

sources of uncertainty 

described in this section 

reveals that temperature 

change is most influenced by 

decisions regarding whether 

to reduce GHG emissions and 

the value of climate sensitivity 

used (GHG emissions scenario 

being the dominant 

contributor). The contributions from different climate 

models and natural variability 

for temperature change are 

small in comparison. It is 

worth noting that the GHG 

emissions scenario is the only 

source of uncertainty that 

society has control over. 

Conversely, these same four 

sources of uncertainty 

contribute in roughly equal 

measure to projected 

changes in precipitation over 

the U.S., with large spatial 

differences.42

For each emissions scenario and climate sensitivity combination, the IGSM-CAM was simulated five times with slightly different initial conditions 

(“initializations”) to account for uncertainty due to natural variability. Some sectors in the report use the average result of the five initializations. 

Natural Variability

decreases in global or regional temperatures, as well as affect 

precipitation and drought patterns around the world. These types of 

natural variability cause uncertainty in temperature and precipitation 

patterns over timescales ranging from months up to a decade or more, 

but have a smaller effect on Earth’s climate system over longer periods 

of time.31

Climate model: Different types of global-scale physical and statistical 

models are used to study aspects of past climate and develop 

projections of future change. The climate is very complex and is 

influenced by many uncertain factors; as a result, each model is 

different and produces different results. These complex models 

provide useful information both individually, by allowing the exploration of potential futures, and collectively, by providing insight on the 

level of agreement across models.

The CIRA uncertainty framework, described in detail in Monier et al. 

(2014),32 explores these four major sources of uncertainty, including 

the influence that each could have on future temperature or precipitation in the U.S. While the effects of each source of uncertainty are not 

described for each sectoral impact discussed in this report, some of 

the impacts described in the Sectors section explore the potential 

influence of these factors. Maps presented in this section are adapted 

from Monier et al. (2014).33

Figure 4. The Effect of Natural Variability on Future Climate Projections

Increases in surface air temperature in 2100 (2091-2110 mean) relative to present-day (1991-2010 mean) for each of the IGSM-CAM initializations.39

Figure 5. Climate Model Uncertainty for Future Projections

Changes in temperature and precipitation in 2100 (2091-2110 mean) relative to present-day (1991-2010 mean) 

for different climate models. Values assume a climate sensitivity of 3°C under the Reference scenario. 

INITIAL CONDITION 1 INITIAL CONDITION 2 INITIAL CONDITION 3 INITIAL CONDITION 4 INITIAL CONDITION 5

0

0

1

1.8

2

3.6

3

5.4

4

7.2

5

9

6

10.8

7

12.6

°C

°F

0

0

1

1.8

2

3.6

3

5.4

4

7.2

5

9

6

10.8

7

-.6 -.4 -.2 0 .2 .4 .6

12.6

°C

mm/day

°F

CCSM

Temperature

Precipitation

(Same atmosphere as IGSM-CAM) BCCR MIROC MULTI-MODEL MEAN
Boundaries of Analysis

18

CIRA FRAMEWORK

The design of the CIRA project allows the results to be interpreted as the potential benefits (avoided 

impacts) to many economically important sectors of the U.S. due to global-scale actions to mitigate GHG 

emissions. The analytical approach offers a number of advantages, including consistency in the use of socioeconomic and climate change scenarios across a wide range of sectoral impact and damage models, and 

exploration of the changes in impacts and damages across key sources of uncertainty.

As with any study, there are some analytical boundaries of the CIRA project and its underlying analyses that 

are important to consider, several of which are described below.43 Future work to address these limitations 

will strengthen the estimates presented in this report, including the broader use of ranges and confidence 

intervals.Limitations specific to the individual sectoral analyses are described in the Sectors section of this 

report, as well as in the scientific literature underlying the analyses.

y

Variability Across Climate Models

The choice of climate model in an impact analysis can influence patterns of future climate change. Within 

a number of the CIRA analyses, this uncertainty was evaluated through the use of “pattern scaling,” a 

method by which the average change produced by running a climate model is combined with the specific 

geographic pattern of change calculated from a different model in order to approximate the result that 

would be produced by the second model. In this report, analyses that are sensitive to changes in precipitation are presented using both the IGSM-CAM (relatively wetter for the contiguous U.S.) and MIROC 

(relatively drier) climate models. However, not all sectoral impact models used pattern scaling in addition 

to the IGSM-CAM simulations, particularly for those impacts primarily driven by temperature, where there 

is generally more agreement across climate models. Finally, we note the limitation that pattern scaling is 

not a perfect representation of alternate models.45

Emission and 

Climate Scenarios

With the goal of presenting a 

consistent and straightforward set of climate change 

impact analyses across 

sectors, this report primarily 

presents results for the 

Reference and Mitigation 

scenarios under a single 

simulation (initialization) of 

the IGSM-CAM climate model 

and assumes a climate 

sensitivity of 3°C. As described in the Levels of 

Certainty section, a large 

number of emissions and 

climate scenarios were 

developed under the CIRA 

project, reflecting various 

combinations of emissions 

scenarios, climate models, 

climate sensitivity, and climate 

model initializations. However, 

only some of these emissions 

and climate scenarios have 

been simulated across all 

sectoral analyses, primarily 

due to the level of effort 

necessary to run each scenario 

through the large number of 

sectoral models of the CIRA 

project. Analyzing results 

under the full set of scenarios 

would further characterize the 

range and potential likelihood 

of future risks. 

Coverage of Sectors and Impacts

The analyses presented in this report cover a broad range of potential 

climate change impacts in the U.S., but there are many important 

impacts that have not yet been modeled in CIRA. Examples of these 

impacts include changes in vector-borne disease, morbidity from 

poor air quality, impacts on specialty crops and livestock, and a large 

number of effects on ecosystems and species. Without information 

on these impacts, this report provides only partial insight into the 

potential risks of climate change, and therefore does not account for 

all potential benefits of mitigation. 

In addition, it is important to note that impacts are only partially 

valued economically in some sectors. For example, the Wildfire section presents estimated response and 

fuel management costs, but not other damages (e.g., health effects from decreased air quality, and property 

damages). A more complete valuation approach would likely increase the damages described in this report. 

Finally, this report does not present results on the possibility of large-scale, abrupt changes that have 

wide-ranging and possibly catastrophic consequences, such as the intensification of tropical storms, or the 

rapid melting of the Greenland or West Antarctic ice sheets.44 In general, there are many uncertainties 

regarding the timing, likelihood, and magnitude of the impacts resulting from these abrupt changes, and 

data limitations have precluded their inclusion in the analyses presented in this report. Their inclusion 

would assist in better understanding the totality of risks posed by climate change and the potential for 

GHG mitigation to reduce or avoid these changes. 

©National Oceanic and Atmospheric Administration
19

Feedbacks

The CIRA project uses a linear 

path from changes in 

socioeconomics and the 

climate system to impacts 

(with consistent inputs across 

multiple models). The 

socioeconomic scenarios that 

drive the CIRA modeling 

analyses do not incorporate 

potential feedbacks from 

climate change impacts to the 

climate system (e.g., GHG 

emissions from forest fires) 

and from sectoral damages to 

the economy (e.g., significant 

expenditures on “climate 

defensive” adaptation would 

likely reduce available financial 

capital to the economy for 

productive uses, or increase 

the cost of financing capital 

expenditures). 

Sectoral Impacts Modeling 

With the exception of the electricity demand and 

supply sections of this report, the impact estimates 

presented were developed using a single sectoral 

impact model. While these models are complex 

analytical tools, the structure of the model, and 

how it may compare to the design of similar 

applications, can create important uncertainties 

that affect the estimation of impacts.46 The use of 

additional models for each sector would help 

improve the understanding of potential impacts in 

the future. The results presented in this report were 

developed with little or no interactions among the impact sectors. As a result, the estimated impacts 

may omit important and potentially unforeseen effects. For example, the wildfire projections presented in this report will likely generate meaningful increases in air pollution, a potentially important 

linkage for the air quality analysis. Similarly, there are numerous connections among the agriculture, 

water, and electricity sectors that affect the impacts estimates in each.47 Although some of these 

interactions are captured within integrated assessment models, it is difficult for these broader 

frameworks to capture all of the detail provided in the CIRA sectoral analyses. Improved connectivity 

between CIRA sectoral models will aid in gaining a more complete understanding of climate change 

impacts across sectors in the U.S. 

Geographic Coverage

The report does not examine 

impacts and damages 

occurring outside of U.S. 

borders. Aside from their own 

relevance for policy-making, 

these impacts could affect the 

U.S. through, for example, 

changes in world food 

production, migration, and 

concerns for national security. 

In addition, the primary 

geographic focus of this report 

is on the contiguous U.S., with most of the sectoral analyses 

excluding Hawaii, Alaska, and the U.S. territories. This omission is 

particularly important given the unique climate change vulnerabilities of these high-latitude and/or island locales. Finally, several 

sectoral analyses assess impacts in a limited set of major U.S. cities, 

and incorporation of additional locales would gain a more 

comprehensive understanding of likely impacts. 

Variability in Societal Characteristics

The impacts of climate change will not affect Americans equally. In addition to regional differences in 

impacts, socioeconomic factors (e.g., income, education) affect adaptive capacity and can make some 

communities more vulnerable to impacts. These issues are explored in the Coastal Property section, but 

the rest of the sectors do not analyze impacts across different levels of social vulnerability.

Use of Point 

Estimates

Results in this report are 

primarily presented as point 

estimates. For some sectors, 

ranges are provided based on 

the design of the underlying 

modeling analysis (i.e., the 

approach yields confidence 

intervals) or because of the 

scenarios used in that sector. 

Regarding the latter, the use 

of wetter and drier climate 

projections for sectors 

sensitive to changes in 

precipitation provides ranges 

of estimates bounding this 

uncertainty source. The 

uncertainties and limitations 

described in this section, 

along with others detailed 

throughout this report and in 

the underlying CIRA literature, 

signify that the estimates 

described in this report should 

not be interpreted as definitive predictions of future 

impacts at a particular place 

and time. The further 

exploration of these uncertainties, including the 

development of ranges for all 

impact projections, will further 

strengthen the CIRA results.
20

Sectors

Health 22 Infrastructure32 Electricity 44

24 | Air Quality

26 | Extreme 

Temperature

28 | Labor

30 | Water Quality

34 | Bridges 

36 | Roads

38 | Urban Drainage

40 | Coastal Property

46 | Electricity 

Demand

48 | Electricity 

Supply

ABOUT THE RESULTS

Unless otherwise noted, results presented in this section were developed using the following: 

Emissions scenarios: The results are presented for the 

CIRA Reference and Mitigation scenarios.

Climate models: The results primarily rely upon climate 

projections from the IGSM-CAM. For sectors sensitive 

to changes in precipitation, results are also presented for 

the drier MIROC climate model.

Climate sensitivity: The results assume a climate sensitivity 

of 3.0°C.

Accounting for inflation: The results are presented in 

constant 2014 dollars.1 

Discounting: To estimate present value, annual time 

series of costs are discounted at a 3% annual rate, with a 

base year of 2015.2 Annual estimates (i.e., costs in a given 

year) are not discounted.

Reporting of estimates: For consistency, results are 

reported with two significant figures. 
21

Water 

Resources

Agriculture 50 and Forestry 58 Ecosystems 64

52 | Inland Flooding

54 | Drought

56 | Water Supply 

and Demand 

60 | Crop and Forest 

Yields

62 | Market Impacts

66 | Coral Reefs

68 | Shellfish

70 | Freshwater Fish

72 | Wildfire

74 | Carbon Storage
Extreme Temperature 

Air Quality

Health

SUBSECTORS 
Labor Water Quality

eather and climate play a

significant role in our health 

and well-being. As a society, we 

have structured our day-to-day behaviors 

and activities around historical and current 

climate conditions. Increasing GHGs in the 

atmosphere are changing the climate faster 

than any time in recent history.3

 As a result, 

the conditions we are accustomed to and 

the environment in which we live will change 

in ways that affect human health. In addition 

to creating new problems, changes in the 

climate can exacerbate existing human health 

stressors, such as air pollution and disease. 

Many of the adverse effects brought on by 

climate change may be compounded by how 

our society is changing, including population 

growth, an aging population, and migration 

patterns that are concentrating development 

in urban and coastal areas.

HOW ARE PEOPLE VULNERABLE 

TO CLIMATE CHANGE? 

Climate change is projected to harm human 

health in a variety of ways through increases 

in extreme temperature, increases in 

extreme weather events, decreases in air 

quality, and other factors.4

 Extreme heat 

events can cause illnesses and death due to 

heat stroke, cardiovascular disease, respiratory disease, and other conditions. Increased 

ground-level ozone is associated with a 

variety of health problems, including reduced 

lung function, increased frequency of asthma 

attacks, and even premature mortality.5

Higher temperatures and changes in the 

timing, intensity, and duration of precipitation affect water quality, with impacts on the 

surface water we use. There are a variety of 

other impacts driven by climate change that 

are expected to pose significant health hazards, including increases in wildfire activity 

(see the Wildfire section of this report).6

WHAT DOES CIRA COVER? 

CIRA analyzes the potential impacts of 

climate change on human health by focusing 

on air quality, extreme temperature mortality, labor, and water quality. Analyses of many 

other important health effects are not included in CIRA; these include, for example, 

impacts from increased extreme weather 

events (e.g., injury or death from changes in 

tropical storms), air pollution from wildfires, 

and vector-borne disease (e.g., Lyme disease 

and West Nile virus).

W
Changes in climate are projected to affect air 

quality across the U.S. In already polluted 

areas, warmer temperatures are anticipated 

to increase ground-level ozone (O3), a 

component of smog, and increase the 

number of days with poor air quality.7

Changes in weather patterns may also affect 

concentrations of fine particulate matter 

(PM2.5), a mixture of particles smaller than 2.5 

micrograms per cubic meter (μg m-3), emitted 

from power plants, vehicles, and wildfires. 

Inhaling ozone and fine particulate matter can lead to a broad range of adverse health effects, 

including premature mortality and aggravation of cardiovascular and respiratory disease.8, 9 

24

KEY FINDINGS Climate Change and 

1 Air Quality Health Effects 

2

Unmitigated climate 

change is projected to 

worsen air quality across 

large regions of the U.S., 

especially in eastern, midwestern, and southern 

states. Impacts on ozone 

and fine particulate matter 

pollution are projected to 

be especially significant for 

densely-populated areas. 

The analysis holds emissions 

of traditional air pollutants 

constant at current levels to 

isolate the climate change 

related impact on air quality. 

Global GHG mitigation is 

projected to reduce the 

impact of climate change 

on air quality and the 

corresponding adverse 

health effects related to air 

pollution. Mitigation is 

estimated to result in 

significant public health 

benefits in the U.S., such as 

avoiding 13,000 premature 

deaths in 2050 and 57,000 

premature deaths in 2100. 

Economic benefits to the 

U.S. of avoided premature 

deaths are estimated at 

$160 billion in 2050, and 

$930 billion in 2100.

Without global GHG mitigation, climate change is projected to have a substantial effect on air 

quality across the contiguous U.S., with important regional differences (Figure 1). Ozone 

concentrations are projected to increase in the Reference scenario in more densely-populated 

regions, such as the East, Midwest, and South, while some less densely-populated areas 

experience decreases in ozone concentrations.10 Although the national annual average ozone 

concentration is projected to decrease slightly (1.3 ppb +/- 0.2) by 2100, human exposure to 

ozone is projected to increase, driven by increasing concentrations in densely-populated areas. 

Climate-driven ozone increases are especially substantial during summer months. By 2100, the 

U.S.-average 8-hour-maximum ozone concentration in June-August is projected to increase 

4.7 ppb (95% confidence interval ± 0.5).11

Unmitigated climate change is projected to exacerbate fine particulate matter pollution, 

especially in the Midwest and East. The annual U.S.-average PM2.5 concentrations are projected to 

increase by 0.3 μg m-3 (± 0.1) in 2050 and 0.7 μg m-3 (± 0.1) in 2100 in the Reference scenario.12

Projections that climate change will lead to increased ozone in polluted regions are consistent with the assessment literature. There is less agreement regarding the magnitude of climate 

change effects on particulate matter, with the exception of increasing wildfire activity on 

particulates.13 The results presented in this report add to this emerging area of research.

Risks of Inaction

Air Quality

-11 - -10

-9.9 - -7.5

-7.4 - -6.5

-6.4 - -5.5

-5.4 - -4.5

-4.4 - -3.5

-3.4 - -2.5

-2.4 - -1.5

-1.4 - -0.5

-0.4 - 0.5

0.6 - 1.51.6 - 2.5

2.6 - 3.53.6 - 4.5

4.6 - 5.5

5.6 - 6.5

6.6 - 7.5

7.6 - 8

-7.5 -6.5 -5.5 -4.5 -3.5 -2.5 -1.5 -0.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 .8

Ozone Fine Particulate

Matter

Figure 1. Projected Impacts of Unmitigated Climate Change 

on Air Pollution in the U.S.

Estimated change in annual-average ground-level hourly ozone (O3, ppb) and fine particulate matter 

(PM2.5, μg m-3) from 2000 to 2100 under the Reference scenario. 
25

Treatment of Co-Benefits

Reducing Impacts through APPROACH

GHG Mitigation

Global GHG mitigation is projected to avoid significant adverse impacts to air quality that 

would occur under the Reference scenario in densely-populated areas. Figure 2 shows air 

quality changes in the Mitigation scenario, which are much smaller than those under the 

Reference (Figure 1). Despite smaller reductions in ozone in some less densely-populated 

areas, global GHG mitigation is projected to reduce the increase in the annual-average, 

8-hour-maximum, population-weighted ozone concentration by approximately 2.6 ppb (95% 

confidence interval ± 0.3) that would occur in the Reference in the U.S. 

Global GHG mitigation is also projected to lessen the adverse effects of climate change 

on fine particulate matter pollution in the U.S. In 2100, the increase in the annual-average 

population-weighted PM2.5 concentration under the Reference is reduced by approximately 

1.2 μg m-3 (± 0.1) under the Mitigation scenario. 

Reducing the impacts of climate change on air quality through global GHG mitigation is 

projected to result in significant health benefits across the U.S. For example, the Mitigation 

scenario is estimated to prevent an estimated 13,000 premature deaths in 2050 (95% confidence 

interval of 4,800-22,000) and 57,000 premature deaths in 2100 (95% confidence interval of 

21,000-95,000) compared to the Reference.14 Economic benefits to the U.S. of these avoided 

deaths are estimated at $160 billion and $930 billion in 2050 and 2100, respectively. In addition 

to reducing premature mortality, global GHG mitigation would result in other health benefits not 

presented here, including reduced respiratory- and cardiovascular-related hospital admissions.15, 16

Figure 2. Projected Impacts on Air Pollution in the U.S. 

with Global GHG Mitigation

Estimated change in annual-average ground-level hourly ozone (O3, ppb) and fine particulate matter 

(PM2.5, μg m-3) from 2000 to 2100 under the Mitigation scenario.

The CIRA analysis assesses the impact 

of climate change on air quality across 

the contiguous U.S. through changes 

in ground-level ozone and fine 

particulate matter (PM2.5) concentrations.19 Future concentrations of these 

pollutants are simulated in an atmospheric chemistry model, driven by 

weather patterns from the CIRA 

climate projections. The analysis 

projects future concentrations for five 

initializations of the IGSM-CAM 

climate model under the Reference 

and Mitigation scenarios in 30-year 

periods centered on 2050 and 2100 

(with 95% confidence intervals based 

on the difference in mean across the 

initializations). Despite assumptions 

about growth in GHG emissions in the 

Reference and Mitigation scenarios, 

emissions of the traditional air pollutants are kept fixed at present-day levels 

to isolate the climate change-related 

impact on air quality. Changes in 

pollution due to projected increases in 

wildfires and changes in sea salt and 

dust are not considered. Pollutant 

concentrations are used to estimate 

changes in air pollution exposure in 

people. The Environmental Benefits 

Mapping and Analysis Program 

(BenMAP) is applied to estimate health 

effects (with 95% confidence interval 

based on concentration response 

functions in BenMAP).20 To monetize 

the effects of changing mortality, a 

value of statistical life (VSL) of $9.45 

million for 2010 (2014$) is used, 

adjusted to future years by assuming 

an elasticity of VSL to gross domestic 

product (GDP) per capita of 0.4.21

For more information on the 

approach, models used, and results 

for the air quality sector, please 

refer to Garcia-Menendez et al. 

(2015).22

This analysis does not quantify the additional 

benefits to air quality and health that would 

stem from simultaneous reductions in 

traditional air pollutants along with GHG 

emissions (both are emitted from many of 

the same sources). Incorporating these 

“co-benefits,” which recent analyses17 and 

assessments18 indicate could provide large, 

near-term benefits to human health, would 

result in a more comprehensive understanding of air quality and climate interactions.

-11 - -10

-9.9 - -7.5

-7.4 - -6.5

-6.4 - -5.5

-5.4 - -4.5

-4.4 - -3.5

-3.4 - -2.5

-2.4 - -1.5

-1.4 - -0.5

-0.4 - 0.5

0.6 - 1.5

1.6 - 2.5

2.6 - 3.5

3.6 - 4.5

4.6 - 5.5

5.6 - 6.5

6.6 - 7.57.6 - 8

-7.5 -6.5 -5.5 -4.5 -3.5 -2.5 -1.5 -0.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 .8

Ozone Fine Particulate

Matter
26

KEY FINDINGS Climate Change and Extreme 

1 Temperature Mortality

2

Without global GHG 

mitigation, the average 

number of extremely hot 

days in the U.S. is projected 

to more than triple from 

2050 to 2100. The projected 

reduction in deaths from 

extremely cold days is more 

than offset by the projected 

increase in deaths from 

extremely hot days. This 

result holds for all reported 

future years, indicating that 

unmitigated climate 

change clearly poses an 

increasing health risk from 

extreme temperatures.

Global GHG mitigation is 

projected to result in 

approximately 12,000 

fewer deaths from extreme 

temperature in the 49 

modeled cities in 2100. 

Inclusion of the entire U.S. 

population would greatly 

increase the number of 

avoided deaths, but accounting for adaptation 

could decrease the number.

Climate change will alter the weather conditions that we 

are accustomed to. Extreme temperatures are projected to 

rise in many areas across the U.S., bringing more frequent 

and intense heat waves and increasing the number of 

heat-related illnesses and deaths.23 Exposure to extreme 

heat can overwhelm the body’s ability to regulate its 

internal temperatures, resulting in heat exhaustion and/or 

heat stroke, and can also exacerbate existing medical 

problems, such as heart and lung diseases.24 During a 1995 

heat wave in Chicago, an estimated 700 individuals died as 

a result of the extreme heat.25 Warmer temperatures are also expected to result in fewer 

extremely cold days, which may also reduce deaths associated with extreme cold.26

Risks of Inaction

Climate change poses a significant risk to human health as more days with extreme heat are 

projected to cause more deaths over time. Without global GHG mitigation, the average number 

of extremely hot days is projected to more than triple from 2050 to 2100, while the number of 

extremely cold days is projected to decrease. The projected increase in deaths due to more 

frequent extremely hot days is much larger than the projected decrease in deaths due to fewer 

extremely cold days, a finding that is consistent with the conclusions of the assessment literature.27 Under the Reference, the net increase in projected deaths from more extremely hot days 

and fewer extremely cold days in 49 cities is approximately 2,600 deaths in 2050, and 13,000 

deaths in 2100, but accounting for adaptation could decrease these numbers. Figure 1 shows the 

net mortality rate from extreme hot and cold temperatures by city in the Reference scenario. 

Figure 1. Projected Extreme Temperature Mortality in Select Cities 

Due to Unmitigated Climate Change 

Estimated net mortality rate from extremely hot and cold days (number of deaths per 100,000 residents) 

under the Reference scenario for 49 cities in 2050 and 2100. Red circles indicate cities included in the analysis; 

cities without circles should not be interpreted as having no extreme temperature impact. 

Extreme Temperature

Combined Mortality Rate 

(deaths/100k)

9 - 10

11 - 14

15 - 18

0 - 2

3 - 4

5 - 8

Baseline 2000

Reference 2050

Reference 2100
As shown in Figure 2, the projected mortality 

rates under the Mitigation scenario show small 

changes through 2100, unlike in the Reference 

where rates increase substantially. As a result, 

the net benefits associated with GHG mitigation increase over time. As shown in Figure 3, 

global GHG mitigation is estimated to result in 

significant public health benefits across the 

U.S. by substantially reducing the risk of 

extreme temperature-related deaths that 

would occur under the Reference. Under the 

Mitigation scenario, extreme temperature 

mortality is reduced by 64% in 2050 and by 

93% in 210028 compared to the Reference. For 

the 49 cities analyzed, global GHG mitigation is 

projected to save approximately 1,700 U.S. 

lives in 2050, and approximately 12,000 U.S. 

lives in 2100 (Figure 3). 

In 2050, the economic benefits of GHG 

mitigation are estimated at $21 billion, 

increasing to $200 billion in 2100 (see the 

Approach section for more information). It is 

important to note that these projections 

reflect only the results for the 49 cities 

included in this study; corresponding national 

benefits would be much larger. 

The analysis also examines the implications 

of adjusting temperature thresholds to 

account for potential adaptation of the human 

body to warmer temperatures. Specifically, 

the analysis assumes that the human health 

response to extreme temperatures in all 49 

cities was equal to that of Dallas. Using this 

approach, results show that mitigation would 

still save a projected 5,500 lives in 2100 

compared to the Reference. 

27

Reducing Impacts through APPROACH

GHG Mitigation

Figure 2. Projected Extreme Temperature Mortality in Select Cities

with Global GHG Mitigation

Estimated net mortality rate from extremely hot and cold days (number of deaths per 100,000 residents) 

under the Mitigation scenario for 49 cities in 2050 and 2100. Red circles indicate cities included in the analysis; 

cities without circles should not be interpreted as having no extreme temperature impact.

Figure 3. Avoided Extreme 

Temperature Mortality 

in 49 U.S. Cities Due to Global 

GHG Mitigation

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

2050 2100

Combined Mortality Rate 

(deaths/100k)

9 - 10

11 - 14

15 - 18

0 - 2

3 - 4

5 - 8

Baseline 2000

Mitigation 2050

Mitigation 2100

The CIRA analysis estimates the 

number of deaths over the course of 

the 21st century attributable to 

extreme temperatures in 49 cities in 

the contiguous U.S., which account 

for approximately one third of the 

national population. City-specific 

relationships between daily deaths (of 

all causes) and extreme temperatures 

are combined with the IGSM-CAM 

projections of extremely hot and cold 

days using city-specific extreme 

temperature thresholds to estimate 

future deaths from heat and cold in 

the Reference and Mitigation scenarios. Extremely hot days are defined as 

those with a daily minimum temperature warmer than 99 percent of the 

days in the period 1989-2000. Extremely cold days are defined as those 

with a daily maximum temperature 

colder than 99 percent of the days in 

the period 1989-2000. As a result, the 

study explicitly addresses the question of the net mortality impact of 

climate change on future extreme 

temperature days. The potential 

impact of future population change is 

accounted for using an EPA demographic model (ICLUS).29 To monetize 

the effects of changing mortality, a 

baseline value of statistical life (VSL) of 

$9.45 million for 2010 (2014$) is used, 

adjusted to future years by assuming 

an elasticity of VSL to GDP per capita 

of 0.4.30 The results presented in this 

section have been updated since Mills 

et al. (2014) to include additional cities 

and more recent mortality rate data.31 

Finally, this analysis did not estimate 

impacts across ages or socioeconomic 

status. As these demographics 

change, they could impact the results 

presented here.

For more information on the CIRA 

approach and results for the 

extreme temperature mortality 

sector, please refer to Mills et al. 

(2014).32
28

KEY FINDINGS Climate Change and Labor

1

2

Without global GHG 

mitigation, labor hours in 

the U.S. are projected to 

decrease due to increases 

in extreme temperatures. 

Over 1.8 billion labor hours 

are projected to be lost in 

2100, costing an estimated 

$170 billion in lost wages.

Global GHG mitigation 

is estimated to save 

1.2 billion labor hours and 

$110 billion in wages in 

2100 in the contiguous 

U.S. that would otherwise 

be lost due to unmitigated 

climate change. 

Climate change may affect labor in a number 

of ways, but projections of hotter summer 

temperatures raise a particular concern. 

Extreme summer heat is increasing in the U.S. 

and will be more frequent and intense in the 

future.33 Heat exposure can affect workers’ 

health, safety and productivity.34 When 

exposed to high temperatures, workers are at 

risk for heat-related illnesses and therefore 

may take more frequent breaks, or have to 

stop work entirely, resulting in lower overall 

labor capacity. This is especially true for 

high-risk industries where workers are doing physical labor and have a direct exposure to 

outdoor temperatures (e.g., agriculture, construction, utilities, and manufacturing).35

Risks of Inaction

Without global GHG mitigation, an increase in extreme heat is projected to have a large 

negative impact on U.S. labor hours, especially for outdoor labor industries. In 2100, over 1.8 

billion labor hours across the workforce are projected to be lost due to unsuitable working 

conditions (95% confidence interval of 1.2-2.4 billion). These lost hours would be very costly, 

totaling over $170 billion in lost wages in 2100 (95% confidence interval of $110-$220 billion).

As shown in Figure 1, the majority of the country is projected to experience decreases in 

labor hours due to extreme temperature effects. In 2100, parts of the Southwest and Florida 

are estimated to experience a decrease in hours worked for high-risk industries ranging from 

-5% to -7%. Although the impacts vary by region, only a limited number of counties are 

projected to experience increases in labor hours. 

Figure 1. Impacts of Unmitigated Climate Change on Labor in the U.S. 

Estimated percent change in hours worked from 2005 to 2050 and 2100 under the Reference scenario. 

Estimates represent change in hours worked at the county level for high-risk industries only, and are normalized 

by the high-risk working population in each county. 

2050

Percent Change 

in Hours Worked

0.1% to 1.3%

-0.9% to 0%

-2.9% to -2%

-3.9% to -3%

-4.9% to -4%

-6.9% to -5%

-1.9% to -1%

2100

Labor
2050 2100

Reference Mitigation

250

200

150

100

50

0

Wages Lost (Billions of Dollars)

29

Reducing Impacts through APPROACH

GHG Mitigation

At the national level, impacts to labor under the Mitigation scenario (Figure 2) are substantially 

smaller compared to the Reference (Figure 1). Counties in the Southwest, Texas, and Florida 

that are estimated to lose up to 7% of high-risk labor hours under the Reference in 2100 do not 

experience such losses under the Mitigation scenario. 

When comparing the two scenarios (Figure 3), global GHG mitigation is projected to prevent 

the loss of approximately 360 million labor hours across the workforce in 2050, saving nearly 

$18 billion in wages. In 2100, the avoided loss of labor hours more than triples, and losses are 

substantially reduced over a majority of the contiguous U.S. Specifically, mitigation is estimated 

to prevent the loss of nearly 1.2 billion labor hours and $110 billion in wages in 2100 compared 

to the Reference. 

Figure 3. Economic Impacts to Labor with and without Global GHG Mitigation

Estimated wages lost under the Reference and Mitigation scenarios for all labor categories in the 

contiguous U.S. (billions 2014$). Error bars represent lower- and upper-95% confidence intervals of the 

dose-response function (see the Approach section for more information).

Figure 2. Labor Impacts in the U.S. with Global GHG Mitigation

Estimated percent change in hours worked from 2005 to 2050 and 2100 under the Mitigation scenario. 

Estimates represent change in hours worked at the county level for high-risk industries only, and are normalized 

by the high-risk working population in each county.

The CIRA analysis focuses on the 

impact of changes in extreme temperatures on labor supply36 across the 

contiguous U.S. Specifically, the 

analysis estimates the number of labor 

hours lost due to changes in extreme 

temperatures using dose-response 

functions for the relationship between 

temperature and labor from Graff Zivin 

and Neidell (2014).37 Mean maximum 

temperatures from the IGSM-CAM are 

projected for two future periods (2050 

and 2100, 5-year averages centered on 

those years) at the county level in the 

CIRA Reference and Mitigation scenarios. The analysis estimates the total 

labor hours lost in all categories of the 

labor force and also for workers in 

high-risk industries (most likely to be 

strongly exposed to extreme temperature), taking into account the CIRA 

county-level population projections 

from the ICLUS model.38 The fraction of 

workers in high-risk industries is 

calculated using Bureau of Labor 

Statistics data from 2003-2007 and is 

assumed to remain fixed over time for 

each county.39 A range of estimates 

for the dose-response function are 

assessed and used to calculate confidence intervals to show the sensitivity 

of the results. The dose-response 

functions are estimates of short-run 

responses to changes in weather, and 

as such do not account for longer-term 

possibilities, such as acclimation of 

workers, relocation of industries, or 

technological advancements to 

reduce exposure.

 The analysis estimates the cost of 

the projected losses in labor hours 

based on the Bureau of Labor Statistics’ estimated average wage in 2005 

($23.02 per hour in a 35 hour work 

week),40 adjusted to 2100 based on the 

projected change in GDP per capita. 

For more information on the 

CIRA approach for the labor 

sector, please refer to Graff Zivin 

and Neidell (2014)41 and Section 

G of the Technical Appendix for 

this report. 

2050 2100

0.1% to 0.6%

-0.9% to 0%

-2.9% to -2%

-3.9% to -3%

-1.9% to -1%

Percent Change 

in Hours Worked
IGSM-CAM

Percent Change 

in the Water 

Quality Index

-26% to -20%

-19% to -15%

-14% to -10%

-9% to -5%

-4% to 0%

MIROC

30

KEY FINDINGS Climate Change and 

Water Quality 1

2

3

Unmitigated climate 

change is projected to 

have negative impacts on 

water quality in the U.S., 

particularly in the Southwest and parts of Texas.

Global GHG mitigation 

is projected to prevent 

many of the water quality 

damages estimated under 

the Reference scenario, 

primarily by reducing the 

warming of water bodies 

across the country. 

Under the Mitigation 

scenario, costs associated 

with decreased water 

quality are reduced approximately 82% in 2100 

compared to the Reference, 

corresponding to cost 

savings of approximately 

$2.6-$3.0 billion.

Climate change is likely to have far-reaching 

effects on water quality in the U.S. due to 

increases in river and lake temperatures and 

changes in the magnitude and seasonality 

of river flows, both of which will affect the 

concentration of water pollutants. These 

physical impacts on water quality will also 

have potentially substantial economic 

impacts, since water quality is valued for 

drinking water and recreational and 

commercial activities such as boating, 

swimming, and fishing.42,43 The analysis 

presented in this section estimates changes 

in water quality, but does not quantify the 

resulting health effects.

Risks of Inaction

Unmitigated climate change is projected to decrease water quality in the U.S. compared to a 

future with no climate change. The Water Quality Index (WQI) calculated in the CIRA analysis 

includes several key water quality constituents, including temperature, dissolved oxygen, total 

nitrogen, and total phosphorus.44 The WQI serves as a measure of water quality; the higher the 

WQI, the higher the water quality. 

As shown in Figure 1, the WQI across the U.S. is projected to decline in the Reference 

scenario in 2100 using both the IGSM-CAM and MIROC climate models. Parts of Texas and the 

Southwest, in particular, are estimated to experience substantial WQI declines of 15-26% in 

2100. Projections that climate change will decrease river and lake water quality are consistent 

with the findings of the assessment literature.45

Figure 1. Effects of Unmitigated Climate Change on U.S. Water Quality in 2100

Percent change in the Water Quality Index in 2100 under the Reference scenario compared to the Control 

(to isolate the effects of climate change). The WQI is calculated for the 2,119 8-digit hydrologic unit codes (HUCs) 

of the contiguous U.S., and aggregated to the 18 Water Resource Regions (2-digit HUCs). 

Water Quality
Reference Mitigation

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

2050 2100 2050 2100

IGSM-CAM MIROC

Billions of 2014$ (undiscounted)

Global GHG mitigation is projected to reduce the increase in water temperature that is 

estimated to occur under the Reference, with corresponding water quality benefits (i.e., 

avoided degradation) primarily due to better oxygenation. The effects of mitigation on total 

nitrogen and total phosphorus concentrations vary by region, but the increase in total nitrogen 

is reduced by up to 80% in some areas of the western U.S. compared to the Reference scenario.

Figure 2 presents the projected change in water quality damages in 2050 and 2100 under 

the Reference and Mitigation scenarios for the IGSM-CAM and MIROC climate models. As 

shown in the figure, increases in damages are projected in both scenarios, but most notably in 

the Reference, where damages are estimated to increase by approximately $3.2-$3.7 billion in 

2100. Under the Mitigation scenario, damages are reduced by approximately 82% compared to 

the Reference in 2100, corresponding to approximately $2.6-$3.0 billion in avoided costs. 

Figure 3 presents the avoided water quality damages in 2100 under the Mitigation scenario 

compared to the Reference using the IGSM-CAM and MIROC climate models. As shown in the 

figure, global GHG mitigation is projected to result in economic benefits relative to the 

Reference across the entire contiguous U.S. California is projected to experience the greatest 

benefits of mitigation in 2100, ranging from approximately $750 million to $1.0 billion. 

IGSM-CAM

Millions of 

Dollars

0 to 50

51 to 100

101 to 300

301 to 500

501 to 1,000

MIROC

31

Reducing Impacts through APPROACH

GHG Mitigation

Figure 3. Benefits of Global GHG Mitigation for U.S. Water Quality in 2100 

Avoided damages under the Mitigation scenario compared to the Reference in 2100 (millions 2014$). 

Damages are calculated for the 2,119 8-digit HUCs of the contiguous U.S., and aggregated to the 

18 Water Resource Regions (2-digit HUCs).

Figure 2. Change in U.S. Water Quality Damages

with and without Global GHG Mitigation 

The CIRA analysis uses a series of linked 

models to evaluate the impacts of climate 

change on water quality in futures with and 

without global GHG mitigation. The analysis 

relies upon climate projections from two 

climate models: IGSM-CAM, which projects 

a relatively wetter future for most of the 

U.S., and the drier MIROC model. The CIRA 

temperature and precipitation projections 

inform a rainfall-runoff model (CLIRUN-II) 

that estimates river flow.46 A water demand 

model projects water requirements of the 

municipal and industrial (M&I), agriculture, 

and other sectors. The runoff and demand 

projections inform a water supply and 

demand model that estimates reservoir 

storage and release, and in turn produces 

a time series of water allocations for the 

various demands. After this allocation step, 

the analysis relies on the QUALIDAD water 

quality model to simulate a number of 

water quality constituents in rivers and 

reservoirs.47 Changes in overall water 

quality are estimated using changes in the 

Water Quality Index (WQI), a commonly 

used metric that combines multiple 

pollutant and water quality measures. 

Finally, a relationship between changes in 

the WQI and changes in the willingness to 

pay for improving water quality is used to 

estimate the economic implications of 

projected water quality changes. 

Results for the CIRA scenarios are 

compared to a Control to isolate the effect 

of climate change. See the Water Resources 

section of this report for information on 

projected changes in the Inland Flooding, 

Drought, and Water Supply and Demand 

sectors. Decreases in water quality due to 

climate change will likely have an adverse 

effect on human health due to, for example, 

the increased risk of harmful aquatic blooms 

and impacts on sources of drinking water. 

Human health effects due to decreased 

water quality are not estimated, but are 

important considerations to fully understand climate change impacts in this sector. 

Inclusion of these effects would likely 

increase the benefits of GHG mitigation.

For more information on the CIRA 

approach and results for the water 

quality sector, please refer to 

Boehlert et al.48
Infrastructure

Tk Stuff Goes 

Here

Bridges Roads

SUBSECTORS 
nfrastructure makes up the basic

physical and organizational structure of 

our society and is by design interdependent and interconnected. Built infrastructure 

includes urban buildings; systems for energy, 

transportation, water, wastewater, drainage, 

and communication; industrial structures; 

and other products of human design and 

construction.1

 U.S. infrastructure has enormous value, both directly as a capital asset 

and indirectly to support human well-being 

and a productive economy.

Total public spending on transportation and 

water infrastructure exceeds $300 billion 

annually; roughly 25 percent of that total is 

spent at the federal level and accounts for 

three percent of total federal spending.2

Recent analyses point to large gaps between 

existing capital and maintenance spending 

and the level of expenditure necessary to 

maintain current levels of services.3

HOW IS INFRASTRUCTURE VULNERABLE 

TO CLIMATE CHANGE?

Experience over the past decade provides 

compelling evidence of how vulnerable 

infrastructure can be to climate change 

effects, including sea level rise, storm surge, 

and extreme weather events.4

 Climate change 

will put added stress on the nation’s aging 

infrastructure to varying degrees over time. 

Sea level rise and storm surge, in combination 

with the pattern of heavy development in 

coastal areas, are already resulting in damage 

to infrastructure such as roads, buildings, 

ports, and energy facilities. Floods along the 

nation’s rivers, inside cities, and on lakes 

following heavy downpours, prolonged rains, 

and rapid melting of snowpack are damaging 

infrastructure in towns and cities, on farmlands, and in a variety of other places across 

the nation. In addition, extreme heat is damaging transportation infrastructure such as 

roads, rails, and airport runways. 

WHAT DOES CIRA COVER?

CIRA analyzes potential climate change 

impacts and damages to four types of infrastructure in the U.S.: roads, bridges, urban 

drainage, and coastal property. Analyses of 

several important types of infrastructure are 

not included in CIRA, particularly telecommunications and energy transmission networks, 

and the Urban Drainage analysis only analyzes impacts in 50 cities of the contiguous 

U.S. Further, some analyses in this sector 

assume that adaptation measures will be 

well-timed. This likely results in conservative 

estimates of future damages, as history has 

shown that infrastructure investment and 

maintenance are often not implemented in 

optimal, well-timed ways.

I

Urban 

Drainage

Coastal 

Property
Number of Vulnerable 

Bridges 2051-2100 48%

39%

56%

20%

37%

56%

26%

49%

33% 37%

46%

76%

33%

29%

41%

9%

36%

< 1,000

1,001 - 5,000

5,001 - 10,000

10,001 - 20,000

> 20,000

35%

34

Road bridges are a central component of the 

U.S. transportation system. With the average 

U.S. bridge now over 40 years old, however, 

more than 250 million vehicles cross structurally deficient bridges on a daily basis.5

 Similar 

to other transportation infrastructure, bridges 

are vulnerable to a range of threats from 

climate change.6 Currently, most bridge 

failures are caused by scour, where swiftly 

moving water removes sediment from around 

bridge structural supports, weakening or 

destroying their foundations. Increased 

flooding and long-term river flow changes caused by climate change are expected to increase 

the frequency of bridge scour, further stressing the aging U.S. transportation system. 

Bridges

KEY FINDINGS Climate Change and Bridges

1

2

3

Without reductions in 

global GHG emissions, an 

estimated 190,000 inland 

bridges across the nation 

will be structurally vulnerable because of climate 

change by the end of the 

century. In some areas, 

more than 50% of bridges 

are projected to be vulnerable as a result of unmitigated climate change. This 

analysis estimates the 

damages of climate change 

in terms of increased costs 

to maintain current levels 

of service (i.e. adaptation 

costs). Without adaptation, 

climate change could render 

many bridges unusable, 

leading to large economic 

damages.

Global GHG mitigation is 

estimated to substantially 

reduce the number of 

bridges across the U.S. that 

become vulnerable in the 

21st century by reducing the 

projected increase in peak 

river flows under the Reference scenario. 

Global GHG mitigation is 

projected to reduce adaptation costs that would be 

incurred under the Reference scenario. The benefits 

of global GHG mitigation 

are estimated at $3.4-$42 

billion from 2010-2050 and 

$10-$15 billion from 2051-

2100 (discounted at 3%).

Risks of Inaction

Increased inland flooding caused by climate change threatens bridges across the U.S. and risks 

a net increase in maintenance costs. Figure 1 shows the number and percent of bridges in each 

hydrologic region of the contiguous U.S. identified as vulnerable to climate change in the late 21st

century under the Reference scenario using the IGSM-CAM climate model. In total, approximately 

190,000 bridges are identified as vulnerable. In addition, the costs of adapting bridges to climate 

change under the Reference scenario are estimated at $170 billion for the period from 2010 to 

2050, and $24 billion for the period from 2051 to 2100 (discounted at 3%). The higher costs 

during the first half of the century are primarily due to the large number of vulnerable bridges 

that require strengthening in the near term in the face of increasing peak river flows due to 

climate change. These findings regarding near-term bridge vulnerability and adaptation costs 

due to unmitigated climate change are consistent with the findings of the assessment literature.7

Figure 1. Bridges Identified as Vulnerable in the Second Half of the 

21st Century Due to Unmitigated Climate Change

Estimated number of vulnerable bridges in each of the 2-digit hydrologic unit codes (HUCs) of the contiguous 

U.S. in the period from 2051-2100 under the Reference scenario using the IGSM-CAM climate model. The map 

also shows the percentage of inland bridges in each HUC that are vulnerable due to climate change. 
31%

18%

19%

38%

2%

67%

45%

18%

35%

25% 4%

2%

7% 9%

9%

10%

17%

25%

Number of Vulnerable 

Bridges 2051-2100

< 1,000

1,001 - 5,000

5,001 - 10,000

> 20,000

10,001 - 20,000

35

Reducing Impacts through APPROACH

GHG Mitigation

As shown in Figure 2, global GHG mitigation is 

projected to substantially reduce the number 

of vulnerable bridges in many areas of the 

contiguous U.S. compared to the Reference 

scenario (Figure 1). For example, the percentage of vulnerable bridges in the Northwest 

region, which includes Washington and parts 

of Oregon and Idaho, is reduced from 56% 

under the Reference to 25% under the 

Mitigation scenario. At the national scale, the 

total number of vulnerable bridges is reduced 

by roughly 40,000 through 2050 compared to 

the Reference scenario, and by over 110,000 in 

the second half of the century. 

In addition, the analysis estimates that 

global GHG mitigation reduces the costs of 

adaptation substantially relative to the 

Reference scenario. In the period from 2010 to 

2050, costs under the Mitigation scenario are 

approximately $42 billion lower than under 

the Reference (discounted at 3%). Although 

adaptation costs are lower in the second half 

of the century, costs under the Mitigation 

scenario are nearly 60% lower than they are 

under the Reference scenario, with savings 

estimated at $15 billion (discounted at 3%). 

These results rely upon climate projections 

using the IGSM-CAM, which projects a 

relatively wetter future for most of the U.S. 

compared to the MIROC climate model (see 

the Levels of Certainty section of this report for 

more information). The projected benefits of 

global GHG mitigation are lower with the drier 

MIROC model (not shown) for the 2010-2050 

period, at approximately $3.4 billion, but are 

higher in the 2051-2100 period, at approximately $10 billion (discounted at 3%). 

Figure 2. Bridges Identified as Vulnerable in the Second Half of the 

21st Century with Global GHG Mitigation

Estimated number of vulnerable bridges in each of the 2-digit HUCs of the contiguous U.S. in the period 

from 2051-2100 under the Mitigation scenario using the IGSM-CAM climate model. The map also shows 

the percentage of inland bridges in each HUC that are vulnerable due to climate change. 

The CIRA analysis identifies inland 

bridges in the contiguous U.S. that 

may be vulnerable to increased peak 

river flows due to climate change and 

estimates the costs to adapt the at-risk 

infrastructure.8 The analysis relies 

upon climate projections from two 

climate models: IGSM-CAM, which 

projects a relatively wetter future for 

most of the U.S., and the drier MIROC 

model. Bridge performance and 

vulnerability are determined using the 

National Bridge Inventory database 

and are based on the following four 

elements:

• substructure condition;

• channel and channel protection 

condition;

• waterway adequacy; and

• vulnerability to scour.

The analysis estimates the timing of 

bridge vulnerability (based on the 

100-year, 24-hour storm event), and 

the adaptation costs of maintaining 

the current condition and level of 

service of the at-risk bridges. Two 

types of bridge fortification and the 

costs of their implementation are 

analyzed: the use of riprap (large rocks 

and rubble) to stabilize bridge foundations and the use of additional concrete to strengthen bridge piers and 

abutments. Although there will likely 

be significant changes to the nation’s 

bridges over the course of the century—some bridges will be strengthened, some will deteriorate, some will 

be removed, and new bridges will be 

built—this analysis estimates the costs 

of adapting the nation’s existing bridge 

infrastructure to different future 

climates based on its current state (i.e., 

the additional costs due to climate 

change are isolated).9,10

For more information on the CIRA 

approach and results for the 

bridges sector, please refer to 

Neumann et al. (2014)11 and Wright 

et al. (2012).12
KEY FINDINGS Climate Change and Roads

1

2

3

Climate change is projected 

to increase the cost of 

maintaining road infrastructure. This analysis estimates 

the damages of climate 

change in terms of increased costs to maintain 

current levels of service (i.e. 

adaptation costs). Without 

adaptation, climate change 

could render many roadways unusable, leading to 

large economic damages. 

In all regions, adaptation 

costs associated with the 

effects of higher temperatures on paved roadways 

are estimated to increase 

over time. In the central 

regions of the country, in 

particular, changes in 

precipitation patterns are 

projected to increase costs 

associated with re-grading 

unpaved roadways. 

Without global GHG 

mitigation, adaptation 

costs in 2100 in the U.S. 

roads sector are estimated 

to range from $5.8-$10 

billion. 

Global GHG mitigation 

is projected to avoid an 

estimated $4.2-$7.4 billion 

of the damages under the 

Reference scenario in 2100. 

The U.S. road network is one of the nation’s 

most important capital assets. Climate stress 

on roads will likely change in the future, with 

various potential impacts and adaptation 

costs.13 For example, roads may experience 

more frequent buckling due to increased 

temperatures, more frequent washouts of 

unpaved surfaces from increases in intense 

precipitation, and changes in freeze-thaw 

cycles that cause cracking.14

Without reductions in global GHG emissions, the costs of maintaining, repairing, and replacing 

pavement are projected to increase, which is consistent with the findings of the assessment 

literature regarding adaptation costs for road infrastructure.15 Figure 1 presents the estimated 

regional damages (in the form of adaptation costs) to the U.S. road network under the Reference scenario using the ISGM-CAM climate model. The greatest impacts are projected to occur 

in the Great Plains region, where costs are mainly due to erosion of unpaved roads associated 

with increased precipitation. Costs associated with the use of different pavement binders to 

avoid cracking of paved roads are also high, particularly in the Midwest and Southeast regions, 

and they increase over time in all regions due to the projected rise in temperature. Costs of 

resealing roads after freeze-thaw events decrease over time as the climate changes, but the 

magnitude of the decrease does not offset the projected increase in other costs. 

Risks of Inaction

Figure 1. Projected Impacts of Unmitigated 

Climate Change on U.S. Road Infrastructure

Adaptation costs (billions 2014$, undiscounted) under the Reference scenario using the IGSM-CAM climate 

model. Results are presented for the six regions used in the Third National Climate Assessment. 

36

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MIDWEST

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SOUTHWEST SOUTHEAST

Roads

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Paved Roads Reseal Costs Paved Roads Binder Costs Unpaved Roads Costs

Reference Mitigation

2025 2050 2075 2100 2025 2050 2075 2100

Adaptation costs for the 

U.S. road network are 

substantially reduced 

with global GHG mitigation compared to the 

Reference scenario 

(Figure 2). These reductions are due in large part 

to the effect of lower 

temperatures under the 

Mitigation scenario on 

maintenance needs for 

paved roads. Specifically, 

costs associated with 

asphalt binders account 

for a large share of the 

adaptation costs nationally under the Reference, and these costs are 

significantly lower with mitigation. Costs 

associated with adaptation for unpaved roads 

are also substantially lower under the 

Mitigation scenario, as heavy precipitation 

events are projected to be less severe 

compared to the Reference. Costs of resealing 

roads after freeze-thaw cycles are projected 

to decrease under both scenarios, but the 

magnitude of the decrease does not offset 

the projected increase in other costs. 

By 2050, the adaptation costs under the 

Reference scenario are substantially higher, 

illustrating the benefits 

that accrue over time 

with GHG mitigation. In 

addition, although the 

costs of adaptation 

increase over the course 

of the century under 

both scenarios, they do 

so at a much faster rate 

under the Reference. 

Under the Reference, 

adaptation costs are 

estimated at approximately $10 billion in 

2100, whereas under the 

Mitigation scenario costs 

are estimated at $2.6 

billion. As a result, global GHG mitigation is 

projected to avoid over $7 billion in damages in 2100. These results rely upon climate 

projections from the IGSM-CAM, which 

projects a relatively wetter future for most of 

the U.S. compared to the MIROC climate 

model (see the Levels of Certainty section of 

this report for more information). The 

projected benefits of global GHG mitigation 

are lower with the drier MIROC model (not 

shown), at $4.2 billion in 2100, reflecting the 

reduced impact of precipitation on unpaved 

roads under both scenarios.16

Reducing Impacts through APPROACH

GHG Mitigation The CIRA approach assesses four risks 

to road infrastructure associated with 

climate change: 

• rutting of paved roads from 

precipitation;

• rutting of paved roads caused by 

freeze-thaw cycles;

• cracking of paved roads due to 

high temperatures; and

• erosion of unpaved roads from 

precipitation. 

The CIRA analysis examines the 

implications of changes in climate 

over time for the U.S. road network 

based on stressor-response functions 

for each of the above effects. The 

analysis considers the effects of 

temperature and precipitation, but 

does not include impacts due to sea 

level rise and storm surge, which 

would likely increase damages to 

roads. The analysis relies upon climate 

projections from two climate models: 

IGSM-CAM, which projects a relatively 

wetter future for most of the U.S., and 

the drier MIROC model. 

The costs of adaptation to effectively counteract the climate change 

impacts and maintain roads at their 

current levels of service are estimated 

for each of the CIRA scenarios. As 

there will be continued maintenance 

needs over time, this analysis focuses 

on the additional costs due to climate 

change. The response measures 

include more frequent resealing to 

avoid rutting; use of different pavement binders during resurfacing to 

avoid cracking of asphalt-paved 

roads; and more frequent re-grading 

of unpaved roads to minimize erosion 

impacts. This analysis assumes 

well-timed adaptation to maintain 

service levels, a potentially overly 

optimistic assumption given that 

infrastructure investments are 

oftentimes delayed. 

For more information on the CIRA 

approach and results for the roads 

sector, please refer to Neumann et 

al. (2014)17 and Chinowsky et al. 

(2013).18

Figure 2. Projected Impacts on U.S. Road Infrastructure 

with and without Global GHG Mitigation

Costs of adaptation for the Reference and Mitigation scenarios using the IGSM-CAM climate 

model (billions 2014$). The reduction in adaptation costs under the Mitigation scenario relative 

to the Reference reflects the benefits of global GHG mitigation.

37
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Tucson

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Fresno

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Detroit Chicago

Wichita

Phoenix

Houston

El Paso

Memphis

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Raleigh

Columbus

New York

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Portland

Baltimore

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Las Vegas

San Diego

Lexington

Milwaukee

Louisville Chesapeake

Fort Worth

Minneapolis

New Orleans

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San Antonio

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Bakersfield

Jacksonville

Oklahoma City

Corpus Christi

Washington D.C. Colorado Springs

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2050 Costs 2100 Costs 10-year 25-year 50-year

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25-year 50-year

Urban drainage systems capture and treat 

stormwater runoff and prevent urban flooding. 

During storm events, the volume of runoff 

flowing into drainage systems and the ability of 

these systems to manage runoff depend on a 

variety of site-specific factors, such as the 

imperviousness of the land area in the drainage 

basin. Changes in storm intensity associated 

with climate change have the potential to 

overburden drainage systems, which may lead 

to flood damage, disruptions to local transportation systems, discharges of untreated sewage to waterways, and increased human health 

risks.19 In areas where precipitation intensity increases significantly, adaptation investments 

may be necessary to prevent runoff volumes from exceeding system capacity. 

38

Urban Drainage

KEY FINDINGS Climate Change and Drainage

1

2

3

Climate change is projected to result in increased 

adaptation costs for urban 

drainage systems in cities 

across the U.S., particularly 

in the Great Plains region. 

Without global GHG 

mitigation, adaptation 

costs in 2100 associated 

with the 50-year, 24-hour 

storm in 50 major U.S. 

cities are projected to 

range from $1.1-$12 billion. 

Global GHG mitigation 

is projected to result in 

cost savings for urban 

drainage systems in these 

cities ranging from $50 

million to $6.4 billion in 

2100 for the 50-year, 

24-hour storm, depending 

on the climate model used. 

Inclusion of all U.S. cities 

would likely increase the 

cost savings by a substantial amount. 

Without global GHG mitigation, climate change is projected to result in increased adaptation 

costs for urban drainage infrastructure, a finding that is consistent with the conclusions of the 

assessment literature.20 Figure 1 presents the projected costs for the 50 modeled cities in 2050 

and 2100 under the Reference scenario using the IGSM-CAM climate model for the three 

categories of storm events modeled (24-hour events with precipitation intensities occurring 

every 10, 25, and 50 years).21 The average per-square-mile costs are projected to be highest in 

the Great Plains region in both 2050 and 2100 due to the projected increase in heavy precipitation in that region. Adaptation costs are estimated to be relatively low in the Southwest due to 

the projected reduction in precipitation in that region. 

Risks of Inaction

Figure 1. Projected Impacts of Unmitigated Climate Change 

on U.S. Urban Drainage Systems 

Weighted average per-square-mile adaptation costs (millions 2014$, undiscounted) in 2050 and 2100 for the 

10-, 25-, and 50-year storms under the Reference scenario using the IGSM-CAM climate model. Costs for each of 

the 50 modeled cities (shown) are aggregated to the six regions used in the Third National Climate Assessment.
2050 2100

Billions of Dollars (undiscounted)

Reference Mitigation

$0

$5

$10

$15

10-year storm 25-year storm 50-year storm 10-year storm 25-year storm 50-year storm

39

Reducing Impacts through APPROACH

GHG Mitigation

Figure 2. Projected Impacts on Urban Drainage Systems in 50 U.S. Cities 

with and without Global GHG Mitigation

Projected adaptation costs in 2050 and 2100 for the Reference and Mitigation scenarios using the IGSM-CAM 

climate model (billions 2014$). The values of the red bars represent the sum of all adaptation costs 

shown in Figure 1 for the years 2050 and 2100.

The CIRA analysis estimates the costs 

of adapting urban drainage systems 

to meet future demands of increased 

runoff associated with more intense 

rainfall under climate change. The 

analysis relies upon climate projections from two climate models: 

IGSM-CAM, which projects a relatively 

wetter future for most of the U.S., and 

the drier MIROC model. Adaptive 

actions focus on the use of best 

management practices to limit the 

quantity of runoff entering stormwater 

systems. While many site-specific 

factors influence the effect of climate 

change on a given drainage system, 

the CIRA analysis uses a streamlined 

approach that allows for the assessment of potential impacts in multiple 

U.S. cities under the CIRA scenarios.22

Specifically, the analysis uses a 

reduced-form approach for projecting 

changes in flood depth and the 

associated costs of flood prevention, 

based on an approach derived from 

EPA’s Storm Water Management 

Model (SWMM).

The simplified approach yields 

impact estimates in units of average 

adaptation costs per square mile for a 

total of 50 cities across the contiguous 

U.S. (see Figure 1) for three categories 

of 24-hour storm events (those with 

precipitation intensities occurring 

every 10, 25, and 50 years—metrics 

commonly used in infrastructure 

planning) and four future time periods 

(2025, 2050, 2075, and 2100). The 

analysis assumes that the systems are 

able to manage runoff associated with 

historical climate conditions, and 

estimates the costs of implementing 

the adaptation measures necessary to 

manage increased runoff under 

climate change. 

For more information on the CIRA 

approach and results for the urban 

drainage sector, please refer to 

Neumann et al. (2014)23 and Price et 

al. (2014).24,25

Global GHG mitigation is projected to result in 

substantial adaptation cost savings for urban 

drainage systems in the 50 modeled cities 

(Figure 2). Overall, cost savings are projected 

to be higher in 2100 than in 2050, and increase 

according to the intensity of the storm 

modeled, with the greatest savings occurring 

for the 50-year, 24-hour storm. For this 

particular storm event, total adaptation costs 

for the modeled cities are projected to be $12 

billion in 2100 under the Reference. Under the 

Mitigation scenario, these costs are reduced to 

approximately $5.5 billion, which represents a 

cost savings of approximately $6.4 billion. Cost 

savings for the 10- and 25-year storms under 

the Mitigation scenario are approximately $3.9 

billion and $5.1 billion, respectively, in 2100. 

Looking across the contiguous U.S., the Great 

Plains region is projected to experience the 

largest reductions in adaptation costs as a 

result of global GHG mitigation. These results rely upon climate projections from the IGSM-CAM, 

which projects a relatively wetter future for most of the U.S. compared to the MIROC climate 

model (see the Levels of Certainty section of this report for more information). Using the drier 

MIROC model, projected benefits of GHG mitigation for the modeled cities associated with the 

50-year, 24-hour storm event are estimated at $50 million.
40

Coastal Property

KEY FINDINGS Climate Change and 

Coastal Property

Risks of Inaction

1

2

3

4

A large area of U.S. coastal 

land and property is at risk 

of inundation from global 

sea level rise, and an even 

larger area is at risk of 

damage from storm surge, 

which will intensify as sea 

levels continue to rise.

Without adaptation, unmitigated climate change is 

projected to result in 

$5.0 trillion in damages for 

coastal property in the 

contiguous U.S. through 

2100 (discounted at 3%). 

Protective coastal adaptation measures significantly 

reduce total costs to an 

estimated $810 billion. 

Global GHG mitigation 

reduces adaptation costs 

for coastal areas, but the 

majority of benefits occur 

late in the century.

Areas of higher social 

vulnerability are more 

likely to be abandoned 

than protected in response 

to unmitigated sea level 

rise and storm surge. 

GHG mitigation decreases 

this risk.

Coastal areas in the U.S. are some of the most 

densely populated, developed areas in the 

nation, and they contain a wealth of natural 

and economic resources. Rising temperatures 

are causing ice sheets and glaciers to melt and 

ocean waters to expand, contributing to global 

sea level rise at increasing rates. Sea level rise 

threatens to inundate many low-lying coastal 

areas and increase flooding, erosion, wetland 

habitat loss, and saltwater intrusion into 

estuaries and freshwater aquifers. The combined effects of sea level rise and other climate 

change factors, such as increased intensity of 

coastal storms, may cause rapid and irreversible change.26

Sea level rise and storm surge pose increasingly large risks to coastal property, including costs 

associated with property abandonment, residual storm damages, and protective adaptation 

measures (e.g., elevating properties and armoring shorelines). As shown in Figure 1, the analysis 

estimates that under the Reference scenario the cumulative damages to coastal property across 

the contiguous U.S. will be $5.0 trillion through 2100 (discounted at 3%) if no adaptation 

measures are implemented. If adaptation measures are taken, these damages are reduced to 

$810 billion. Projections of increasing risks of sea level rise and storm surge for coastal property, 

and of the potential for adaptation to reduce overall costs, are consistent with the findings of the 

assessment literature.27 The graphic above illustrates the importance of these potential impacts 

at a local scale by identifying at-risk land in the Tampa Bay, FL area. In this locale, approximately 

83,000 acres are projected to be at risk of inundation due to sea level rise by 2100, and an 

additional 51,000 acres are projected to be at risk of significant storm surge. The total area at 

risk (130,000 acres) is approximately one and a half times the size of the City of Tampa. 

Figure 1. Costs of Sea Level Rise and Storm Surge to Coastal Property

with and without Adaptation under the Reference Scenario

The step-wise nature of the graph is due to the fact that storm surge risks are evaluated every ten years, 

beginning in 2005. Costs with adaptation include the value of abandoned property, residual storm 

damages, and costs of protective adaptation measures (trillions 2014$).

0 3.75 7.5 15 Miles

HILLSBOROUGH

COUNTY

PINELLAS

COUNTY

Areas at risk

of inundation 

due to sea 

level rise

Areas at risk

of signicant 

storm surge

damages

Areas at risk from sea level rise and 

storm surge in the Tampa Bay area 

in 2100 under the Reference scenario

Tampa Bay

Costs without Adaptation Costs with Adaptation

0

2000 2025 2050 2075 2100

1

2

3

4

5

6

Trillions of Dollars(discounted 3

%)
41

Reducing Impacts through 

GHG Mitigation

Under the Mitigation scenario, total costs (i.e., property damages and protective investments) 

across the contiguous U.S. are estimated at $790 billion through 2100 (discounted at 3%), about 

3% less than the Reference scenario.28 The effect of global GHG mitigation in reducing adaptation costs is modest and is likely underestimated in this analysis for several reasons. First, as 

described in the CIRA Framework section, global sea level rise is similar under the Reference and 

Mitigation scenarios through mid-century. It is not until the second half of the century when the 

benefits of reduced sea level rise under the Mitigation scenario become apparent. Further, the 

proportional effect of global GHG mitigation in reducing the rate of sea level rise is smaller 

under the CIRA scenarios compared to other scenarios in the literature.29

Second, when considering the present value total cost under the Reference and Mitigation 

scenarios, avoided adaptation costs accrued in later years are more heavily affected by discounting.30 Third, the analysis assumes that coastal areas will implement cost-efficient and well-timed 

adaptation measures in response to the risks under both the Reference and Mitigation scenarios. 

Since many parts of the coastline are not sufficiently protected today, and because adaptation 

measures that are taken are oftentimes not well-timed, the CIRA estimates for this sector likely 

underestimate damages. For comparison purposes, the benefits of global GHG mitigation 

increase by a factor of ten if adaptation measures are not implemented.

Figure 2 shows the costs of adaptation for coastal properties (including the value of properties 

that are abandoned due to the severity of sea level rise or storm surge damages) for 17 key sites 

under the Reference and Mitigation scenarios. As shown, costs are only modestly lower under 

the Mitigation scenario. Costs vary across sites primarily due to the value of property at risk 

and the severity of the storm surge threats. For example, adaptation costs are comparatively 

higher in sites, such as Tampa and Miami, where there are many high-value properties in 

low-lying areas and high levels of storm surge are projected in the future.

The CIRA analysis identifies at-risk coastal 

property across the contiguous U.S. and 

estimates the costs that would be incurred 

due to climate change, with and without 

adaptation. Importantly, impacts to other 

coastal assets (e.g., roads and ecological 

resources) are not estimated in this analysis. 

The analysis relies upon sea level rise 

projections through 210031 that account for 

dynamic ice-sheet melting based on a 

semi-empirical model,32 and are adjusted 

for regional land movement using local tide 

gauge data.33 The analysis then uses a 

tropical cyclone simulator34 and a storm 

surge model35 to estimate the joint effects 

of sea level rise and storm surge for East 

and Gulf Coast sites, and an analysis of 

historic tide gauge data to project future 

flood levels for West Coast sites.36

Using EPA’s National Coastal Property 

Model, the CIRA analysis estimates how 

areas along the coast may respond to sea 

level rise and storm surge and calculates 

the economic impacts of adaptation 

decisions (i.e., damages due to climate 

change). The approach uses four primary 

responses to protect coastal land and 

property: beach nourishment; property 

elevation; shoreline armoring; and 

property abandonment. The model 

projects an adaptation response for areas 

at risk based on sea level rise, storm surge 

height, property value, and costs of 

protective measures. Developed using a 

simple metric to estimate potential 

adaptation responses in a consistent 

manner for the entire coastline, the 

estimates presented here should not be 

construed as recommending any specific 

policy or adaptive action. Further, additional adaptation options not included in this 

analysis, such as marsh restoration, may be 

appropriate and potentially more cost-effective for some locales. The analysis also 

explores the potential impact of climate 

change on socially disadvantaged 

populations (see the Environmental Justice 

section of this report).

For more information on the CIRA 

approach and results for the coastal 

property sector, please refer to Neumann et al. (2014a)37 and Neumann et 

al. (2014b).38

Reference

Mitigation

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$20

$30

$40

$50

$60

$70

$80

$90

$100

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Figure 2. Costs to Coastal Property of Sea Level Rise and 

Storm Surge through 2100

Costs are shown for 17 multi-county coastal areas that were modeled for sea level rise and 

storm surge impacts and potential adaptation response (billions 2014$).

APPROACH
42

uilding on the coastal property impacts described in the previous section, this 

analysis examines the environmental justice implications of projected sea level rise 

and storm surge in the contiguous U.S. Specifically, the approach quantifies how sea 

level rise and storm surge risks are distributed across different socioeconomic populations 

along the U.S. coastline; how these populations are likely to respond; and what adaptation 

costs (i.e., property damage and protection investments) will potentially be incurred. 

The CIRA analysis uses the Social Vulnerability 

Index (SoVI) to identify socially vulnerable 

coastal communities in the U.S.39 SoVI was 

developed to quantify social vulnerability 

using county-level (and later Census 

tract-level) socioeconomic and demographic 

data. The index is a well-vetted tool, and does 

not include any environmental risk factors, 

thereby eliminating the risk of double 

counting climate risk when socioeconomic 

and demographic data are combined with sea 

level rise and storm surge vulnerability.40 The 

CIRA analysis uses Census tract-level SoVI 

values based on 2000 Census data for 26 

demographic variables, capturing information on wealth, gender, age, race, and 

employment. Figure 1 shows the SoVI index 

values for the four coastal regions used in the 

analysis: Pacific (California through Washington), North Atlantic (Maine through Virginia), 

South Atlantic (North Carolina through 

Monroe County, Florida), and Gulf (Collier 

County, Florida through Texas). 

The Social Vulnerability Index

Figure 1. Social Vulnerability Index for the Coastal U.S. 

Census tract-level SoVI values are regionally normalized to allow for comparisons of the SoVI scores within each 

area. Areas with low SoVI scores (i.e., people with lower social vulnerability) are shaded in green and areas with 

higher SoVI scores (i.e., people with greater social vulnerability) are shaded in pink. 

Environmental Justice

COASTAL PROPERTY

B

<-1.5 (Low Vulnerability)

>1.5 (High Vulnerability)

No Data

-1.4 to -0.5

-0.4 to 0.5

0.6 to 1.5

SoVI
400

800

1200

1600

No Adaptation (Storm Surge Damage) Property Abandonment

Property Elevation Beach Nourishment

Shoreline Armoring

0

Area (sq mi)

Less than -1.5 

(Low 

Vulnerability)

 -1.4 to -0.5 -0.4 to 0.5 0.6 to 1.5 Greater than 

1.5 (High 

Vulnerability)

0

500

1000

1500

2000

2500

3000

3500

Population (thousands)

Reference Mitigation

-6%

-6%

-7% -9%

-23%

Less than -1.5 

(Low 

Vulnerability)

 -1.4 to -0.5 -0.4 to 0.5 0.6 to 1.5 Greater than 

1.5 (High 

Vulnerability)

43

EPA’s National Coastal Property Model identifies areas 

along the contiguous U.S. coastline that are likely to be 

at risk from sea level rise and storm surge through 

2100.41, 42 By layering these projections on top of the 

SoVI results, following the approach described in 

Martinich et al. (2013),43 the analysis assesses the 

potential impact of sea level rise and storm surge on 

socially disadvantaged populations in coastal areas. 

Figure 2 presents a case study of the Tampa Bay, Florida 

area (Pinellas and Hillsborough Counties). The area from 

the water to the gray lines represents the projected area 

at risk of inundation due to sea level rise, while the area 

from the water to the black lines represents projected 

areas at risk from significant storm surge damage in 

2100.44 As shown, there are areas with higher socially 

vulnerable populations (pink shading) near the city of 

Tampa, in particular, that are projected to be at risk of 

significant storm surge damages.

Figure 2. Social Vulnerability of Areas at Risk from Sea Level Rise and 

Storm Surge in the Tampa Bay Area by 2100 under the Reference Scenario

Figure 3 compares the number of people in the 17 multi-county 

coastal areas (see previous section for locations) identified as at risk 

due to climate change under the Reference and Mitigation scenarios, 

by SoVI category. As shown, the Mitigation scenario reduces the 

number of at-risk people compared to the Reference scenario for all 

SoVI categories. The benefits of global GHG mitigation are particularly 

high for the population identified by the SoVI as most socially 

vulnerable; for this population, the number of at-risk people is reduced 

by 23% under the Mitigation scenario compared to the Reference. 

The CIRA analysis also projects adaptation responses based on sea 

level rise, storm surge height, property value, and costs of adaptation.45

The model estimates whether people living in coastal areas are likely 

to respond to climate threats by: 1) protecting property through 

beach nourishment, property elevation, or shoreline armoring; 2) 

abandoning property, or 3) incurring storm surge damages without 

adapting. Figure 4 presents the adaptation results, by area, for the five 

SoVI categories in the Reference. More area is likely to be abandoned 

than protected across all social vulnerability categories. However, in 

the most vulnerable SoVI categories (0.6-1.5 and greater than 1.5), a 

relatively larger proportion of the area inhabited is likely to be 

abandoned (89% and 86%, respectively) rather than protected 

through adaptation measures (8% and 10%, respectively). 

Case Study: Tampa Bay Area

National Results 

Figure 3. Social Vulnerability of Populations at Risk 

from Sea Level Rise and Storm Surge through 2100 

with and without Global GHG Mitigation 

Vulnerability estimated in 17 multi-county coastal areas in the contiguous U.S., 

along with the estimated percent changes from Reference to Mitigation.

Figure 4. Adaptation Measures by 

SoVI Category under the Reference Scenario

Tampa

St. Petersburg

Inland boundary of area at risk of significant storm surge damage

Manatee County

Hillsborough County

Pinellas County Hillsborough County

Tampa

Bay

<-1.5 (Low Vulnerability)

-1.4 to -0.5

>1.5 (High Vulnerability)

Inland boundary of area 

at risk of signicant storm 

surge damage

Inland boundary of area 

at risk of inundation due

to sea level rise 

0.6 to 1.5

-0.4 to 0.5

SoVI
Electricity

Electricity 

Demand

SUBSECTORS 

y
Electricity 

Supply

Electricity is an essential element 

of modern life. It lights and cools 

our homes, powers our computers, 

supports the production of goods and services, and enables critical infrastructure 

services such as water treatment and telecommunications. The generation of electricity 

in the U.S., most of which comes from fossil 

fuels, also contributes to climate change, 

accounting for approximately 30% of U.S. 

greenhouse gas emissions.1

HOW IS THE ELECTRICITY SECTOR 

VULNERABLE TO CLIMATE CHANGE? 

Climate change has implications for electricity 

production, distribution, and use.2

 For example, coastal electricity infrastructure, such as 

power plants and substations, are vulnerable 

to storm surge and wind damage. Elevated 

temperatures diminish thermal power plant 

efficiency and capacity, and can reduce the 

capacity of transmission lines. In addition, 

effects on water supply alter the quantity and 

temperature of cooling water available for 

thermoelectric generation.3

 On the demand 

side, warmer winters decrease the demand 

for heating. However, this reduction is smaller 

than the increase in electricity demand for 

cooling due to higher summer temperatures. 

Across the U.S., higher minimum temperatures 

increase the number of days in a year when 

air conditioning is needed, and higher 

maximum temperatures increase the peak 

electricity demand, further stressing our 

aging power grid.

WHAT DOES CIRA COVER? 

Numerous studies highlight the potential for 

emission reductions in the electricity sector, 

yet fewer studies have explored the physical, 

operational, and economic impacts of a changing climate on this sector. CIRA assesses the 

impacts of rising temperatures on electricity 

demand, system costs, and the generation mix 

needed to meet increasing demand across the 

contiguous U.S. through 2050.4

 Importantly, 

impacts to the demand and supply of other 

energy sources (e.g., fuel for transportation) 

are not estimated. Also, the electricity supply 

analysis does not include the effects of climate 

change on hydropower and water availability 

for thermoelectric power generation. Additional work is necessary to further evaluate 

climate change impacts on electricity supply, 

particularly the effects of extreme heat events 

and storm damage on capacity and reliability. 

Finally, future work to improve connectivity 

between the CIRA electricity, water, and 

agriculture analyses will aid in better understanding potential cross-sector impacts. 
46

KEY FINDINGS Climate Change and 

1 Electricity Demand

2

Without global GHG 

mitigation, rising temperatures will likely result in 

higher electricity demand 

across the country, as the 

increased need for air 

conditioning outweighs 

decreases in electric heating requirements. The 

estimated percent increase 

in electricity demand for air 

conditioning is highest in 

the Northeast and Northwest regions.

Global GHG mitigation, 

which lessens the rise in 

temperature, is projected 

to lead to lower electricity 

demand across all regions 

of the country relative to 

the Reference scenario. 

 Risks of Inaction

Rising temperatures are projected to increase electricity demands for cooling. Figure 1 shows 

the percent change in regional heating and cooling degree days (HDDs/CDDs, see Approach 

for definitions) from 2005 to 2050 in the Reference scenario. Results are presented for the three 

models used in the analysis (GCAM, ReEDS, and IPM), which exhibit similar trends of falling 

HDDs (shown in purple) and rising CDDs (shown in orange). These trends are consistent with 

projections described in the assessment literature.8 Across the U.S., HDDs decrease between 

18%-29% on average, with greater decreases occurring in the South due in part to already-high 

temperatures. The increase in CDDs is highest in the Northeast and Northwest (68% and 71% on 

average, respectively). The projected changes in HDDs and CDDs have implications for regional 

electricity demand. Average U.S. electricity demand is projected to increase under the Reference 

by 1.5%-6.5% by 2050, compared to a Control with no temperature change. Across the regions 

and models shown in Figure 2, electricity demand is projected to increase by 0.5%-9.0%, with 

the exception of the ReEDS model in the Northwest, which projects a decrease of 0.5%.9

Figure 1. Projected Impact of Unmitigated Climate Change on Regional Heating 

and Cooling Degree Days from 2005 to 2050 

Percent change in HDDs and CDDs from 2005 to 2050 under the Reference compared to a Control with no 

temperature change. Results are presented for six regions and for the three models used in the analysis.

Electricity Demand

-40%

0%

40%

80%

-40%

0%

40%

80%

-40%

0%

40%

80%

-40%

0%

40%

80%

-40%

0%

40%

80%

-40%

0%

40%

80%

NORTHWEST SOUTH CENTRAL MIDWEST NORTHEAST

SOUTHWEST SOUTHEAST

Cooling Degree Days 

(High temperatures, 

A/C needed)

Heating Degree Days 

(Low temperatures, 

heat needed)

GCAM ReEDS IPM GCAM ReEDS IPM GCAM ReEDS IPM GCAM ReEDS IPM

GCAM ReEDS IPM GCAM ReEDS IPM

As air temperatures rise due to climate change, electricity demands for cooling are expected to 

increase in every U.S. region.5

 Higher summer temperatures, particularly during heat waves, will 

likely increase peak electricity demand, placing more stress on the electricity grid and increasing 

electricity costs. Although the majority of U.S. residential and commercial cooling demand is met 

with electricity, less than 9% of heating demand is met with electricity.6, 7 Therefore, although 

higher average temperatures are expected to reduce electricity demands for heating, net electricity use is projected to increase under climate change. This section presents estimated impacts on 

electricity demand, but does not consider impacts on demand for other fuel sources used in 

residential cooling or heating.
47

Reducing Impacts through APPROACH

GHG Mitigation

Global GHG emissions reductions under the Mitigation 

scenario result in smaller increases in temperatures 

compared to the Reference, thereby reducing cooling 

demand across the country. Figure 2 illustrates this 

effect, presenting the change in regional energy 

demand in 2050 in the Reference and Mitigation 

scenarios relative to a Control with no temperature 

change. As shown, the change in demand in the 

Mitigation scenario is consistently lower than in the 

Reference across all of the models. This decrease in 

demand is due in large part to lower temperatures under 

the Mitigation scenario compared to the Reference, and 

in the GCAM and ReEDS models the lower demand is 

also due to an increase in electricity costs associated 

with reducing GHG emissions. The impact of GHG 

mitigation on electricity supply is discussed in greater 

detail in the Electricity Supply section of this report. 

Figure 2. Change in Regional Electricity Demand in 2050 

with and without Global GHG Mitigation 

Change in regional electricity demand for the Reference and Mitigation scenarios relative to a Control 

(no temperature change). Results are presented for six regions and for each of the three 

models used in the analysis (GCAM, ReEDS, and IPM). 

The CIRA analysis examines how 

rising temperatures under climate 

change will affect electricity demand. 

It applies a common set of temperature projections from IGSM-CAM to 

three models of the U.S. electric 

power sector: 

• Global Change Assessment 

Model (GCAM-USA): a detailed, 

service-based building energy 

model for the 50 U.S. states;10, 11

• Regional Electricity Deployment 

System Model (ReEDS): a technology-rich model of the deployment 

of electric power generation 

technologies and transmission 

infrastructure for the contiguous 

U.S.;12 and 

• Integrated Planning Model (IPM®): 

a dispatch and capacity planning 

model used by the public and 

private sectors to inform business 

and policy decisions.13

The models project changes in electricity demand as functions of changes in 

heating and cooling degree-days 

(HDDs/CDDs). HDDs and CDDs are 

one way to measure the influence of 

temperature change on energy 

demand. They measure the difference 

between outdoor temperatures and a 

temperature that people generally find 

comfortable indoors. These measurements suggest how much energy 

people might need to use to heat and 

cool their homes and workplaces. The 

analysis compares the results across 

the CIRA scenarios, while also accounting for non-climate changes in 

electricity demand (e.g., population 

and economic growth). To assess the 

effect of rising temperatures in the 

Reference and Mitigation scenarios, 

changes in heating and cooling degree 

days and electricity demand are 

compared to a Control that assumes 

temperatures do not change over time. 

For more information on the CIRA 

approach and results for the 

electricity demand sector, please 

refer to McFarland et al. (2015).14

NORTHWEST SOUTH CENTRAL MIDWEST NORTHEAST

SOUTHWEST SOUTHEAST

Reference Mitigation

-10%

-6%

-2%

2%

6%

10%

-10%

-6%

-2%

2%

6%

10%

-10%

-6%

-2%

2%

6%

10%

-10%

-6%

-2%

2%

6%

10%

-10%

-6%

-2%

2%

6%

10%

-10%

-6%

-2%

2%

6%

10%

GCAM ReEDS IPM

GCAM ReEDS IPM

GCAM ReEDS IPM GCAM ReEDS IPM GCAM ReEDS IPM

GCAM ReEDS IPM
48

KEY FINDINGS Climate Change and 

Electricity Supply 

Effects on Electricity 

Generation

1

2

Projected electricity supply 

is higher in all three electric 

power sector models under 

the Reference scenario, 

reflecting a higher demand 

for cooling, and lower under 

the Mitigation scenario as a 

result of lower temperatures 

and the demand response 

to GHG mitigation.

The relative magnitude of 

costs to the electric power 

system are similar under 

the Reference and Mitigation scenarios, highlighting 

that the costs associated 

with rising temperatures in 

the Reference are comparable to the costs associated 

with reducing GHG emissions in the Mitigation 

scenario. Specifically, the 

higher demands under 

the Reference scenario 

increase system costs by 

1.7%-8.3% above the Control. Under the Mitigation 

scenario, system costs 

increase by 2.3%-10% 

above the Control, or 0.6%-

5.5% above Reference 

scenario costs. 

As described in the Electricity Demand section, warmer air temperatures under climate change 

are expected to result in higher demand for electricity, leading to the need for increased 

capacity in the power system to meet this demand. At the same time, higher temperatures 

reduce the capacity of both thermal power plants and transmission lines. 

The power sector accounts for the largest share of GHG emissions in the U.S.,15 and is also 

considered the most cost-effective source of emission reductions under mitigation policies.16 

A variety of impacts and changes are therefore expected to occur in this sector, including 

changes in sector emissions, system costs, and generation mix (i.e., the assortment of fuels 

used to generate electricity). 

In the CIRA analyses, a large amount of CO2 reductions in the U.S. under the Mitigation scenario 

occur in the electricity sector.17 As a result, the generation capacity and mix of energy sources 

used to produce electricity is projected to change over time. Figure 1 shows the projected 

change in generation mix in 2050 from the three electric power sector models under the CIRA 

scenarios. Projected electricity supply is higher in all three models under the Reference, 

reflecting a higher demand for cooling, and lower under the Mitigation scenario as a result of 

lower temperatures and the costs of reducing GHG emissions. For any given model, the supply 

mix in the Reference does not differ substantially from the Control, which accounts for future 

population and economic growth, but no temperature change. However, all three models 

under the Mitigation scenario project substantial reductions in coal generation and expanded 

generation from nuclear and renewables. 

0

1

2

3

4

5

6

7

Control

Reference

Mitigation

Control

Reference

Mitigation

Control

Reference

Mitigation

GCAM ReEDS IPM

TkWh per Year

Coal

Coal w/CCS

Gas

Gas w/CCS

Oil

Nuclear

Hydro

Non-Hydro Renewables

Other

1.6% -0.5%

1.7% -0.6%

6.5%

0.8%

Figure 1. Electricity Generation by Technology and Scenario in 2050 

with Percent Change in Generation from Control18

Electricity Supply
49

APPROACH

The CIRA analysis assesses impacts on 

the U.S. electricity sector’s supply side 

using the same three models described 

in the Electricity Demand section. The 

models project changes in the generation mix needed to meet increasing 

demand due to future warming and 

socioeconomic changes (e.g., population and economic growth) under the 

CIRA scenarios. The three models also 

estimate the corresponding system 

costs—comprised of capital, operations and maintenance, and fuel 

costs—and the changes in CO2

emissions over time. This analysis is 

unique compared to the other sectoral 

analyses of this report in that the costs 

of GHG mitigation in the electric 

power sector are estimated alongside 

the benefits. The three electric power 

sector models simulate these costs 

over time, and the rationale for 

presenting them here is to provide a 

comparison between the increase in 

power system costs due to mean 

temperature increases under the two 

scenarios and the costs associated 

with reducing GHG emissions from 

electric power generation. It is important to note that the effect of temperature change on generation accounts 

for only a small portion of the total 

effects of climate change on electricity 

supply. Other important effects, such 

as changes in hydropower generation 

or the availability of cooling water for 

thermoelectric combustion, are not 

included. Inclusion of these impacts on 

the electricity supply system would 

likely increase the benefits of mitigation to this sector. 

For more information on the CIRA 

approach and results for the 

electricity supply sector, please 

refer to McFarland et al. (2015).19

Figure 2. Percent Change in Cumulative System Costs (2015-2050) in the 

Reference and Mitigation Scenarios Compared to the Control 

Grey bars represent the difference between the Reference and Mitigation scenarios.

Reference

12%

10%

0.6%

GCAM ReEDS IPM

5.5%

1.2%

8%

6%

4%

2%

0%

Mitigation

Change in System Costs

Rising temperatures under both scenarios, 

especially under the Reference, result in 

higher demands for electricity and increased 

power system costs to expand capacity. At 

the same time, altering the generation mix to 

reduce GHG emissions imposes costs on the 

power system. Figure 2 presents the percent 

change in cumulative system costs under the 

Reference and Mitigation scenarios compared 

to a Control with no temperature change 

(2015-2050, discounted at 3%). The costs 

increase by 1.7%-8.3% under the Reference 

and by 2.3%-10% under the Mitigation 

scenario. The incremental system costs of the 

Mitigation scenario above the Reference are 

0.6%-5.5%, highlighting that the costs to the 

electric power sector associated with rising 

temperatures in the Reference are comparable to the costs associated with reducing GHG 

emissions in the Mitigation scenario. It is 

important to note, however, that this does 

not account for benefits of GHG mitigation 

outside of the electricity sector, nor does it 

examine other effects of climate change on 

electricity supply, such as changes in cooling 

water availability or extreme weather events. 
Inland Drought

Flooding 

Water Resources

SUBSECTORS 
Water Supply 

and Demand

ater, a resource that sustains life

across the globe, is a vital component of a productive economy, 

providing a critical input to production in a 

number of key economic sectors.1

 In the U.S., 

water is used in many ways, including for 

human consumption, agricultural irrigation, 

power plant cooling, and hydropower generation. In addition, rivers, lakes, and oceans 

allow for navigation, fishing, and recreation 

activities. Water also plays an array of vital 

roles in ecosystems, which in turn provide 

crucial services that support human life. 

Analyzing the effects of climate change on 

water resources can be particularly challenging as climate variables affect both the supply 

and demand of water in different ways, and 

the impacts vary over space and time. 

HOW IS WATER VULNERABLE TO 

CLIMATE CHANGE? 

The water cycle is inextricably linked to 

climate, and climate change has a profound 

impact on water availability at global, 

regional, and local levels. As temperatures 

rise, the rate of evaporation increases, which 

makes more water available in the air for 

precipitation but also contributes to drying 

over some areas.2

 Further, climate change 

will result in increased intensity of precipitation events, leading to heavier downpours. 

Therefore, as climate change progresses, 

many areas are likely to see increased 

precipitation and flooding, while others will 

experience less precipitation and increased 

risk of drought. Some areas may experience 

both increased flooding and drought. Many 

of these meteorological changes, along with 

their associated impacts, are already being 

observed across the U.S. These changes, 

combined with demographic, socioeconomic, 

land use, and other changes, affect the availability, quality, and management of water 

resources in the U.S.3

WHAT DOES CIRA COVER? 

The CIRA analyses estimate impacts and 

damages from three water resource-related 

models addressing flooding, drought, and 

water supply and demand (see the Health 

section of this report for water quality 

impacts). The models differ in the component 

of the water sector assessed and geographic 

scale, but together provide a quantitative 

characterization of water sector effects that 

no single model can capture. As the water 

cycle is sensitive to changes in precipitation, 

the analyses use a range of projections for 

future precipitation (see the CIRA Framework 

section for more information). Finally, future 

work to improve connectivity between the 

CIRA electricity, water, and agriculture analyses will aid in better understanding potential 

impacts to these sectors. 

W
2050

Millions of Dollars

< 100 101 - 500 501 - 1,000 1,001 - 2,000 2,001 - 3,700

2100

52

Inland Flooding

KEY FINDINGS Climate Change and 

1 Inland Flooding

2

©iStock.com/AndreyGatash

Warmer temperatures 

under climate change are 

projected to increase 

precipitation intensity in 

some regions of the contiguous U.S., raising the risk of 

damaging floods. 

The effect of global GHG 

mitigation on flooding 

damages is sensitive to 

projected changes in 

precipitation. The flooding 

analysis using the 

IGSM-CAM climate model, 

which projects relatively 

wet conditions for most of 

the U.S., estimates that 

mitigation will result in a 

reduction in flood damages 

of approximately $2.9 

billion in 2100 compared 

to the Reference. Using 

the drier MIROC model, 

the analysis projects that 

mitigation will result in 

disbenefits of approximately 

$38 million in 2100. 

Extreme precipitation events have intensified 

in recent decades across most of the U.S., 

and this trend is projected to continue.4

Heavier downpours can result in more 

extreme flooding and increase the risk of 

costly damages.5

 Flooding affects human 

safety and health, property, infrastructure, 

and natural resources.6

 In the U.S., non-coastal 

floods caused over 4,500 deaths from 1959 to 

2005 and flood-related property and crop 

damages averaged nearly $8 billion per year7

from 1981 to 2011.8 The potential for 

increased damages is large, given that climate 

change is projected to continue to increase 

the frequency of extreme precipitation events and amplify risks from non-climate factors such 

as expanded development in floodplains, urbanization, and land-use changes.9

Risks of Inaction

Without GHG mitigation, climate change under the IGSM-CAM projections is estimated to 

increase monetary damages associated with inland flooding across most of the contiguous U.S. 

Figure 1 presents the projected flood damages in 2050 and 2100 under the Reference scenario. 

As shown, substantial damages are projected to occur in more regions over time. By 2100, damages are projected to be significantly different from the historic period (at a 90% confidence 

interval) in 11 of the 18 large watersheds (2-digit hydrologic unit codes). The greatest damages 

are projected to occur in the eastern U.S. and Texas, with damages in these regions ranging 

from $1.0-$3.7 billion in 2100.10 Projections of increased flood damages across most of the U.S. 

are consistent with the findings of the assessment literature.11

Figure 1. Estimated Flood Damages Due to Unmitigated Climate Change

Estimated flood damages under the Reference scenario in 2050 and 2100 for the IGSM-CAM climate model 

(millions 2014$). Results are presented for the 18 2-digit hydrologic unit codes (HUCs) of the contiguous U.S. 

Stippled areas indicate regions where the projected damages are significantly different from 

the historic period (at a 90% confidence interval). 
2050

IGSM-CAM 

(comparatively wet)

Percent change in ooding damages

-53% to -40%

MIROC

(comparatively dry)

2100

less damages more damages

-39% to -30% -29% to 0% 1% to 30% 31% to 132%

53

Reducing Impacts through APPROACH

GHG Mitigation

Under the relatively 

wetter IGSM-CAM 

climate projections, 

global GHG mitigation is 

projected to result in 

increased flooding 

damages compared to 

today, but decreased 

damages compared to 

the Reference scenario 

in most regions of the 

contiguous U.S. As 

shown in Figure 2, 

damages are reduced in 

10 out of 18 regions in 

2050 and in 14 out of 18 

regions in 2100, with 

particularly pronounced differences between 

the scenarios in 2100. In 2100, the modeled 

reduction in damages is approximately $2.9 

billion. By the end of the century, substantial 

benefits are projected over much of the Great 

Plains and Midwest regions, where damages 

are estimated to be reduced between 30% 

and 40% in many states. The four regions not 

showing benefits of GHG 

mitigation under the 

IGSM-CAM projections 

are located in the western 

part of the U.S., which 

also faces the highest risk 

of drought, as described 

in the Drought section of 

this report.

Figure 2 also presents 

results using the MIROC 

climate model, which 

projects a drier future 

compared to the 

IGSM-CAM model. Under 

the MIROC projections, 

flooding damages are 

generally reduced under both the Reference 

and Mitigation scenarios and, as a result, 

there are modest disbenefits of mitigation 

across most of the contiguous U.S. in 2050 

and 2100. In 2100, damages are projected 

to increase nationally by $38 million under 

the Mitigation scenario compared to the 

Reference.

Figure 2. Change in Flooding Damages Due to Global GHG Mitigation

Percent change in flooding damages for the Mitigation scenario compared to the Reference. 

Results are presented for the 18 2-digit HUCs of the contiguous U.S. Negative values, shown in green, 

reflect reductions in flooding damages from global GHG mitigation. 

The CIRA analysis quantifies how 

climate change could affect inland 

flooding damages in the contiguous 

U.S. Given the complexities inherent 

in projecting national flood damages, 

including the need for small watershed-scale hydrologic modeling, the 

results presented in this section should 

be considered first-order estimates. 

The analysis estimates changes in 

inland (non-coastal) flood damages 

following the approach described in 

Wobus et al. (2013).12 Specifically, the 

analysis applies statistical relationships between historical precipitation 

and observed flood damages in each 

region of the U.S. to estimate the 

probability of damaging events 

occurring in a given year for the 

baseline period (1983-2008). Flood 

probabilities are then updated based 

on precipitation projections for specific 

events (i.e., 1-, 3-, 5-, and 7-day precipitation totals) under the Reference and 

Mitigation scenarios to estimate future 

flood damages. The analysis relies 

upon climate projections from two 

climate models: IGSM-CAM, which 

projects a relatively wetter future for 

most of the U.S., and the drier MIROC 

model. Damages are aggregated to the 

18 U.S. Geological Survey National 

Water Resource Regions (WRRs) for two 

future periods (2050 and 2100), and are 

then statistically compared to modeled 

damages for the historic period. 

Importantly, the estimated damages 

do not include impacts on human 

health or economic disruption. The 

approach assumes that the distribution 

of monetary damages from flooding, 

including the effects of non-climate 

risk factors, will not change in the 

future.13 Finally, the value of damages 

occurring in the future is scaled to 

account for changes in wealth using 

projected increases in per capita 

income in the two CIRA scenarios. 

For more information on the CIRA 

approach and results for flooding 

damages, please refer to Strzepek et 

al. (2014)14 and Wobus et al. (2013).15
Climate change-related impacts on temperature and 

precipitation are expected to alter the location, frequency, 

and intensity of droughts in the U.S., with potentially devastating socioeconomic and ecological consequences.16 Already, 

many U.S. regions face increasing water management 

challenges associated with drought, such as disruptions in 

navigation and water shortages for irrigation. In recent 

decades, recurring droughts across the West and Southeast 

have had significant socioeconomic and ecological impacts.17

54

Drought

KEY FINDINGS Climate Change 

1 and Drought Risk

2

3

In the absence of global 

GHG mitigation, climate 

change is projected to 

result in a pronounced 

increase in the number 

of droughts in the southwestern U.S. 

Global GHG mitigation 

leads to a substantial 

reduction in the number 

of drought months in the 

southwestern U.S. in both 

climate models analyzed. 

The effect of GHG mitigation in other regions is 

highly sensitive to 

projected changes in 

precipitation. 

The reduction in drought 

associated with GHG 

mitigation provides 

economic benefits to 

the crop-based agriculture 

sector ranging from 

$9.3-$34 billion through 

2100 (discounted at 3%). 

Risks of Inaction

Without global GHG mitigation, climate change threatens to increase the number of droughts in 

certain regions of the U.S. The CIRA analysis uses multiple climate projections, each with unique 

patterns of regional change, to estimate the change in the number of SPI and PDSI droughts 

(see Approach for descriptions).18 As discussed in the CIRA Framework section of this report, the 

IGSM-CAM projects a relatively wetter future for most of the contiguous U.S., while the MIROC 

model projects a drier future. Figure 1 shows that, although the climate models estimate different 

outcomes with respect to drought risk for the central and eastern U.S., they both project that the 

Southwest will experience pronounced increases in both SPI and PDSI drought months. Some 

areas of the country that are projected to experience increases in drought by 2100 are also 

projected to experience higher flooding damages (see the Inland Flooding section). This finding 

should not be interpreted as a conflicting result, and is consistent with the conclusions of the 

assessment literature,19 which describe the drivers of these changes as more intense yet less 

frequent precipitation, and increases in evaporation due to higher temperatures.20

Figure 1. Effects of Unmitigated Climate Change on Drought Risk by 2100

Projected change in number of SPI and PSDI drought months under the Reference scenario over a 

30-year period centered on 2100. Results are presented for the 18 2-digit hydrologic unit codes (HUCs) 

of the contiguous U.S. Changes occurring in the grey-shaded areas should be interpreted as 

having no substantial change between the historic and future periods.

SPI-12 Droughts

IGSM-CAM 

(comparatively wet)

Drought Months over a 30-year Period

-50 to -10

MIROC

(comparatively dry)

Severe and Extreme PDSI Droughts

-9 to 10 11 to 50 51 to 100 101 to 200
55

Reducing Impacts through APPROACH

GHG Mitigation

Global GHG mitigation leads to a substantial reduction in drought risk for many parts of the 

country (Figures 2 and 3). Under the IGSM-CAM climate projections, GHG mitigation substantially reduces drought occurrence across the western U.S., while under the MIROC model, drought is 

reduced over a majority of the country. Both climate models project reductions in drought in the 

Southwest, where the risks of increased droughts were highest under the Reference. 

The overall decrease in the number of droughts under the Mitigation scenario, particularly in 

the West, results in substantial benefits to the crop-based agriculture sector. Through 2100, the 

Figure 3. Effect of Global GHG Mitigation on Drought Risk by 2100 

Estimated change in number of SPI and PDSI drought months under the Mitigation scenario compared to 

the Reference over a 30-year period centered on 2100. Results are presented for the 18 2-digit HUCs of the 

contiguous U.S. Shades of green represent reductions in the number of drought months due to 

GHG mitigation. Changes occurring in the grey-shaded areas should be interpreted as having 

no substantial change between the historic and future periods.

The CIRA analysis estimates the effect 

of climate change on the frequency 

and intensity of droughts across the 

contiguous U.S. The approach is based 

on the methodology from Strzepek et 

al. (2010).21 It relies on two drought 

indices for both the historical and two 

21st century time periods. The drought 

indices account for changes in key 

climate variables: the Standardized 

Precipitation Indices (SPI-5 and SPI-12) 

measure meteorological drought 

based on change in precipitation from 

the historical median, and the Palmer 

Drought Severity Index (PDSI) uses 

precipitation and temperature data 

to estimate the relative changes in 

a particular region’s soil moisture. 

Drought risk is calculated for 99 

sub-basins or watersheds in the 

contiguous U.S. and aggregated to 

18 2-digit HUC regions. 

The analysis then estimates the 

effect on crop-based agriculture of the 

change in frequency and intensity of 

droughts under the CIRA climate 

projections. This approach projects 

impacts using a sectoral model that 

relates historical drought occurrence 

with impacts on crop outputs.22 The 

resulting relationships are then 

applied to climate projections under 

the CIRA Reference and Mitigation 

scenarios using the IGSM-CAM and 

MIROC climate models to estimate the 

economic impacts of climate change 

and effects of GHG mitigation.23 This 

analysis only monetizes the impacts of 

drought on crop-based agriculture, 

and does not include other damages 

(e.g., decreased water availability, 

ecosystem disruption). Therefore the 

results estimated here likely underestimate the benefits of GHG mitigation 

for this sector.

For more information on the 

CIRA approach and results for 

the drought sector, please refer 

to Strzepek et al. (2014)24 and 

Boehlert et al. (2015).25

-100%

-50%

0%

50%

100%

150% IGSM-CAM MIROC

Reference Mitigation

Figure 2. Percentage Change in Number of 

Severe and Extreme Drought Months with and 

without GHG Mitigation 

Change in number of PDSI drought months under the Reference and 

Mitigation scenarios over a 30-year period centered on 2100 in the 

contiguous U.S. Under both climate models, GHG mitigation 

results in fewer drought months compared to the Reference. 

present value benefits of GHG 

mitigation in the agricultural 

sector reach $9.3 billion (discounted at 3%) using the IGSM-CAM 

climate projections, compared to 

the Reference. Using the drier 

MIROC climate model, the 

Mitigation scenario provides 

benefits to the agriculture sector 

of approximately $34 billion 

(discounted at 3%). Projections 

from both climate models 

estimate higher economic 

benefits of GHG mitigation in the 

southwestern U.S., where drought 

frequency is projected to increase 

most dramatically in the absence 

of GHG mitigation. 

SPI-12 Droughts

IGSM-CAM 

(comparatively wet)

Drought Months over a 30-year Period

-209 to -200

MIROC

(comparatively dry)

Severe and Extreme PDSI Droughts

-199 to -100 -99 to -10 -9 to 10 11 to 26
56

Water Supply & Demand

KEY FINDINGS

1

2

3

Unmitigated climate 

change is projected to 

have profound impacts 

on both water availability 

and demand in the U.S., 

compounding challenges 

from changes in demographics, land use, energy 

generation, and socioeconomic factors. 

Without global GHG 

mitigation, damages 

associated with the supply 

and demand of water 

across the U.S. are estimated to range from approximately $7.7-$190 billion in 

2100. The spread of this 

range indicates that the 

effect of climate change on 

water supply and demand 

is highly sensitive to projected changes in runoff 

and evaporation, both of 

which vary greatly across 

future climate projections 

and by U.S. region.

Global GHG mitigation is 

estimated to substantially 

decrease damages compared to the Reference. 

Projected benefits under 

the Mitigation scenario 

range from $11-$180 billion 

in 2100, depending on 

projected future climate. 

Importantly, global GHG 

mitigation is projected to 

preserve water supply and 

demand conditions more 

similar to those experienced today.

Climate Change and Water 

Supply and Demand 

Risks of Inaction

Water management in the U.S. is characterized 

by the struggle to balance growing demand 

from multiple sectors of the economy with 

increasingly limited supplies in many areas. 

Unmitigated climate change is projected to 

have profound impacts on both water availability and demand in the U.S., compounding 

challenges from changes in demographics, land 

use, energy generation, and socioeconomic 

factors. As temperatures rise and precipitation 

patterns become more variable, changes in regional water demand and surface and groundwater 

supplies are expected to increase the likelihood of water shortage for many areas and uses.26

The effect of climate change on water supply and demand is highly sensitive to projected 

changes in runoff and evaporation, both of which vary across future climate projections and 

by U.S. region (Figure 1). Despite these variations, increased damages of unmitigated climate 

change are projected in the Southwest and Southeast regions under both climate models, and 

these damages increase over time. These projections are consistent with the findings of the 

assessment literature.27 Using climate projections from the IGSM-CAM model, the analysis 

estimates damages at $7.7 billion in 2100. Despite the majority of U.S. regions showing modest 

increases in welfare (economic well-being) in 2100, the damages in the Southwest and 

Southeast are much larger in magnitude, and therefore drive the national total. Highlighting 

the sensitivity of this sector to the climate model used, the drier MIROC model estimates that 

net damages could be substantially larger, at approximately $190 billion in 2100.

Figure 1. Projected Impacts of Unmitigated Climate Change on 

Water Supply and Demand

Estimated change in economic damages under the Reference scenario in 2050 and 2100 compared to the 

historic baseline for the IGSM-CAM and MIROC climate models (millions 2014$). Results are presented for the 

18 2-digit hydrologic unit codes (HUCs) of the contiguous U.S. Yellow, orange, and red areas indicate increased 

damages, while blue areas indicate decreased damages.

2050

IGSM-CAM 

(comparatively wet)

Millions of Dollars

-2,000 to 0

MIROC

(comparatively dry)

2100

1 to 500 501 to 1,000 1,001 to 10,000 10,001 to 20,000 20,001 to 53,000
2050

IGSM-CAM 

(comparatively wet)

Percent Change in Economic Damages

-200 to -100

MIROC

(comparatively dry)

2100

-99 to -50 -49 to 0 1 to 100 101 to 200

57

Reducing Impacts through APPROACH

GHG Mitigation

Global GHG mitigation is projected to substantially reduce damages compared to the Reference 

(Figures 2 and 3), and importantly, preserve water supply and demand conditions more similar 

to those experienced today. The IGSM-CAM model estimates that damages are $7.7 billion 

under the Reference scenario in 2100, while the Mitigation scenario results in an increase in 

welfare (collective economic well-being of the population) of $3.4 billion. Therefore, mitigation 

is estimated to result in a total increase in welfare of $11 billion in 2100 compared to the 

Reference. Using the drier MIROC model, the Mitigation scenario yields damages of approximately $19 billion in 2100; however, this represents avoided damages of approximately $180 

billion compared to the Reference scenario (numbers do not sum due to rounding). 

Figure 2. Economic Damages Associated with Impacts on Water Supply and 

Demand with and without Global GHG Mitigation 

The CIRA analysis estimates the 

economic impacts associated with 

changes in the supply and demand 

of water, based on a national-scale 

optimization model developed by 

Henderson et al. (2013).28 The model 

simulates changes in supply and 

demand in 99 sub-regions or watersheds of the contiguous U.S. based on 

changes in runoff and evaporation, 

population, irrigation demand, and 

other inputs that vary over time. 

Economic impact functions are applied 

for a range of water uses including 

irrigated agriculture, municipal and 

domestic water use, commercial and 

industrial water use, hydroelectric 

power generation, and in-stream 

flows.29 The benefits from water use 

are maximized according to a wide 

range of constraints, such as storage 

and conveyance capacities, historic 

irrigated acreage, and renewable 

recharge capacity for groundwater. 

Economic damages are incurred in the 

model when any one of the water 

uses specified above does not receive 

sufficient volume to sustain the 

baseline activity level. Impacts are 

summed across all uses in each 

sub-region and reported as changes in 

economic welfare. Finally, the optimization model is driven by climate 

projections from the IGSM-CAM, as 

well as the MIROC climate model, 

which projects a relatively drier future 

for the contiguous U.S. compared to 

other climate models.30

For more information on the CIRA 

approach and results for the water 

supply and demand analysis, please 

refer to Strzepek et al. (2014)31 and 

Henderson et al. (2013).32

Figure 3. Projected Impacts of GHG Mitigation on Water Supply and Demand 

Estimated percent change in economic damages under the Mitigation scenario in 2050 and 2100 relative to the 

Reference. Results are presented for the 18 2-digit HUCs of the contiguous U.S. Negative values (shown in green) 

indicate decreases in damages, or positive economic benefits, due to global GHG mitigation. 

-10

40

90

140

190

240

IGSM-CAM MIROC IGSM-CAM MIROC

2050 2100

Billions 2014$ (undiscounted)

Reference Mitigation
Crop and 

Forest Yields

SUBSECTORS 

LENA -- FIX DESCENDERS

Agriculture and g
Market Impacts

he U.S. has a robust agriculture sector

that produces nearly $330 billion per 

year in agricultural commodities.1

 The 

sector ensures a reliable food supply and 

supports job growth and economic development.2

 In addition, as the U.S. is currently the 

world’s leading exporter of agricultural products, the sector plays a critical role in the 

global economy.3

U.S. forests provide a number of important 

goods and services, including timber and other 

forest products, recreational opportunities, 

cultural resources, and habitat for wildlife. 

Forests also provide opportunities to reduce 

future climate change by capturing and storing 

carbon, and by providing resources for bioenergy production.4

HOW ARE AGRICULTURE AND FORESTRY 

VULNERABLE TO CLIMATE CHANGE? 

U.S. agricultural and forest production are 

sensitive to changes in climate, including 

changes in temperature and precipitation, 

more frequent and severe extreme weather 

events, and increased stress from pests and 

diseases.5 At the same time, climate change 

poses an added risk to many forests due to 

ecosystem disturbance and tree mortality 

through wildfire, insect infestations, drought, 

and disease outbreaks.6 Climate change has the 

potential to both positively and negatively 

affect the location, timing, and productivity of 

agricultural and forest systems, with economic 

consequences for and effects on food security 

and timber production both in the U.S. and 

globally.7,8 Adaptation measures, such as 

changes in crop selection, field and forest 

management operations, and use of technological innovations, have the potential to delay 

and reduce some of the negative impacts of 

climate change, and could create new opportunities that benefit the sector. 

WHAT DOES CIRA COVER?

The CIRA analysis estimates climate change 

impacts on the agriculture and forestry sectors 

using both biophysical and economic models. 

The agriculture analyses demonstrate effects 

on the yield and productivity of major crops, 

such as corn, soybean, and wheat, but do not 

include specialty crops, such as tree fruits, or 

livestock. Further, the analysis does not explicitly model impacts on biofuel production or 

include technological advances in agricultural 

management practices. The analyses include 

yield and productivity impacts, but do not 

simulate the effects of changes in wildfire, 

pests, disease, and ozone. Future work to 

improve the multiple interactions among the 

CIRA energy, water, and agriculture analyses 

will aid in better understanding potential 

impacts to these sectors. 

T

Forestry
60

Crop & Forest Yields

KEY FINDINGS

1

2

Table 1. Projected Percent Change in U.S. Crop Yields in 2100 

without Global GHG Mitigation

Estimates in this table assume no technological improvements in yields over time such that crop productivity 

in future periods relative to a scenario with no climate change is based purely on differences in climatic 

conditions. This assumption allows the analysis to isolate and evaluate climate change impacts on crops 

without confluence with other factors. Results do not include effects from changes in ozone, pests, and disease. 

Rice and potatoes are simulated under irrigated management only.11 

Unmitigated climate 

change is projected to 

result in substantial decreases in yields for most 

major agricultural crops. 

Global GHG mitigation is 

projected to substantially 

benefit U.S. crop yields 

compared to the Reference 

scenario. 

Without considering the 

influence of wildfires, the 

effect of GHG mitigation on 

forest productivity is less 

substantial compared to 

the response for crops. The 

direction of the effect depends strongly upon climate 

model and forest type 

(hardwood vs. softwood).

Risks of Inaction

Without significant global GHG mitigation, climate change is projected to have a large negative 

impact on the U.S. agriculture sector. Table 1 presents the projected percent change in national 

crop yields in 2100 due to unmitigated climate change under the Reference scenario. For all 

major irrigated crops, with the exception of hay, climate projections from both the IGSM-CAM 

and MIROC models result in decreased yields, with very substantial declines projected for 

soybeans, sorghum, and potatoes. For rainfed crops, climate projections using the drier MIROC 

climate model result in substantial declines for all crops, particularly cotton, sorghum, hay, 

wheat, and barley. Rainfed yields using the wetter IGSM-CAM climate model are more varied, 

ranging from a substantial decrease in hay yields to moderate gains in cotton, sorghum, and 

wheat yields.9

 Projected declines in crop productivity resulting from unmitigated climate change 

over the longer term are consistent with the findings of the assessment literature.10

As shown in Figure 1, the effect of unmitigated climate change on forest productivity in the 

U.S. varies over time and depends on the climate model used. Using the IGSM-CAM projections, 

hardwood yields increase by 2100, while the change in softwood yields is very small. Projections using the drier MIROC climate model result in increased hardwood and softwood yields 

by the end of the century, though the gains are smaller than those projected under the 

Mitigation scenario. 

-3%

-2%

-1%

0%

1%

2%

3%

4%

5%

Reference - Softwood Mitigation - Softwood

Reference - Hardwood Mitigation - Hardwood

2010 2025 2050 2075 2100 2010 2025 2050 2075 2100 -3%

-2%

-1%

0%

1%

2%

3%

4%

IGSM-CAM 5% MIROC

Figure 1. Projected Change in Potential Forestry Yields with and without 

Global GHG Mitigation

Percent change in potential hardwood and softwood yields across the U.S. relative to the base period 

(1980-2009) under the Reference and Mitigation scenarios for the IGSM-CAM and MIROC climate models. 

Effects of wildfire, pest, and disease on yields are not included. 

3

RAINFED

MIROC

IRRIGATED RAINFED IRRIGATED

CROP

17%

6%

-5%

18%

n/a

-62%

n/a

18%

-16%

-11%

-3%

-20%

-17%

-3%

29%

-33%

-8%

-22%

Cotton

Corn

Soybean

Sorghum

Rice

Hay

Potato

Wheat

Barley

-17%

-10%

-23%

-22%

-3%

32%

-39%

-13%

-11%

-27%

-8%

-19%

-29%

n/a

-65%

n/a

-19%

-29%
Figure 2. Projected Impacts of Global GHG Mitigation on Crop Yields

Percent change in crop yields from the EPIC model in the contiguous U.S. under the Mitigation 

scenario compared to the Reference for the IGSM-CAM and MIROC climate models.14 Rice and potatoes 

are simulated under irrigated management only. 

61

APPROACH

The analysis uses the Environmental Policy 

Integrated Climate (EPIC) model15,16 to 

simulate the effects of climate change on 

crop yields in the contiguous U.S. The 

analysis examines agricultural crop 

productivity for multiple crops, including 

corn, soybean, wheat, alfalfa hay, sorghum, cotton, rice, barley, and potatoes. 

Yield potential is simulated for each crop 

for both rainfed and irrigated production 

with the exception of rice and potatoes, 

which are assumed to be irrigated.17

Because production regions may change 

over time in response to climate change, 

EPIC simulates potential cultivation and 

production in areas within 100 km (62 

miles) of historical production regions.

EPIC is driven by changes in future 

climate from both the IGSM-CAM18 and 

MIROC climate models under the Reference 

and Mitigation scenarios. The results 

presented in this section include the effect 

of CO2 fertilization on crop yields; Beach et 

al. provide a sensitivity analysis of the effect 

of CO2 fertilization on the crop yield results 

from EPIC. 

Changes in forest growth rates are 

simulated using the MC1 dynamic 

vegetation model, consistent with the 

approach described in Mills et al. (2014)19 

and the Wildfire and Carbon Storage 

sections of this report.20 MC1 is also driven 

by the IGSM-CAM and MIROC models, and 

assumes full CO2 fertilization effects. 

The effects of changes in wildfires, 

pests, disease, and ozone are not captured 

in this analysis.21 Inclusion of these effects 

on crop and forest yields would likely 

result in increased benefits of GHG 

mitigation compared to those presented 

in this section.

For more information on the CIRA 

approach and results for agriculture 

and forestry crop yields analysis, 

please refer to Beach et al.22

Reducing Impacts through 

GHG Mitigation

Global GHG mitigation is estimated to 

substantially benefit U.S. crop yields. Figure 2 

presents the projected change in national 

crop yields for key crops under the Mitigation 

scenario compared to the Reference. The 

figure shows changes in rainfed and irrigated 

yields using projections from the IGSM-CAM 

climate model and the relatively drier MIROC 

model. In general, the benefits to crop yields 

of global GHG mitigation increase over the 

course of the century, with the exception of 

rainfed hay (for both climate models) and 

rainfed sorghum (for IGSM-CAM). Global GHG 

mitigation is projected to have a particularly 

positive effect on the future yields of irrigated 

soybeans, irrigated potatoes, and irrigated 

and rainfed barley.

The projected effect of GHG mitigation on 

forest productivity is less substantial compared 

to the response for crops. Figure 1 shows the 

estimated percent change in average national 

forest productivity (contiguous U.S.) under 

the Reference and Mitigation scenarios 

relative to the base period. Although forest 

productivity generally increases with climate 

change under both scenarios, projections 

using the relatively wetter IGSM-CAM climate 

model result in larger gains under the 

Reference scenario, particularly for hardwoods. Higher forest productivity under the 

IGSM-CAM Reference in the future is likely 

driven by the enhanced positive effects of 

CO2 fertilization under the high-emission 

Reference, along with the response to increases in precipitation in many areas of the 

contiguous U.S. that are forested. The MIROC 

climate projections, on the other hand, result 

in slightly rising yields of both hardwoods 

and softwoods through 2100 under the 

Mitigation case. It is important to note that 

these yield estimates do not include the 

effects of wildfire, pests, or disease, which 

would likely decrease simulated productivity 

based on the findings of the assessment 

literature,12 especially under the Reference 

scenario (See Wildfire section of this report).13

Rainfed

MIROC

IGSM-CAM

Irrigated

Barley Corn Cotton Hay Potatoes

Rice Sorghum Soybeans Wheat

-20%

0%

20%

40%

60%

2010 2025 2050 2075 2100 2010 2025 2050 2075 2100

2010 2025 2050 2075 2100 2010 2025 2050 2075 2100

-20%

0%

20%

40%

60%

-20%

0%

20%

40%

60%

-20%

0%

20%

40%

60%
62

Market Impacts

KEY FINDINGS

1

2

3

Based on the projected 

changes in yields, global 

GHG mitigation is estimated to result in lower crop 

prices over the course of 

the 21st century compared 

to the Reference. 

Changes in crop and forest 

productivity alter related 

market dynamics, land 

allocation, crop mix, and 

production practices, 

which in turn affect GHG 

emissions and carbon 

sequestration from the 

agriculture and forestry 

sectors. Global GHG mitigation has a large effect on 

emissions fluxes in managed forests: however, the 

magnitude and direction of 

the effect are sensitive to 

climate model projection.

Under both climate model 

projections, global GHG 

mitigation increases total 

economic welfare in the 

agriculture and forestry 

sectors by $43-$59 billion 

(discounted at 3%) through 

2100 compared to the 

Reference. The magnitude 

of estimated economic 

welfare impacts in the 

agricultural sector is much 

larger than in the forestry 

sector.

Changes in Crop Price 

Changes in Emissions

As described in the Crop and Forest Yields 

section of this report, global GHG mitigation 

is projected to result in generally higher crop 

yields in the U.S. relative to the Reference. As 

a result, mitigation is projected to result in 

less pressure on land resources and declining 

commodity prices. As shown in Figure 1, 

climate projections from both the IGSM-CAM 

and MIROC climate models show steep 

declines in a broad index of crop prices starting 

around 2040. Projections using the drier 

MIROC climate model result in greater declines 

in crop prices by the end of the century than 

those using the wetter IGSM-CAM model. 

Adverse effects of climate change on crop and 

food prices, which are largely avoided in the 

Mitigation scenario, are consistent with the 

findings of the assessment literature.23

Figure 1. Projected Change in 

National Crop Price Index Due to 

Global GHG Mitigation 

Percent change in crop price index under the 

Mitigation scenario relative to the Reference for 

the IGSM-CAM and MIROC climate models.

Changes in land allocation, crop mix, and production practices in turn affect GHG emissions from 

agriculture and forestry practices. Figure 2 shows the estimated changes in cumulative GHG 

emissions under the Mitigation scenario compared to the Reference using projections from the 

IGSM-CAM and MIROC climate models. Under the IGSM-CAM projections, GHG mitigation is 

estimated to increase net GHG emissions from these sectors in the second half of the century. 

The increase is due in large part to the generally lower forest productivity that is projected to 

occur under the Mitigation scenario compared to the Reference, as the latter has higher 

productivity driven by the generally warmer and wetter future climate, as well as the enhanced 

positive effects of CO2 fertilization (see the Crop and Forest Yields section). Thus, global GHG 

mitigation results in less forest carbon sequestration over time. Higher levels of carbon storage 

in forests under the generally warmer and wetter future of the IGSM-CAM Reference scenario 

are consistent with the findings presented in the Carbon Storage section of this report.

Under the MIROC climate projections, on the other hand, forest productivity is enhanced 

under the Mitigation scenario relative to the Reference, and forests take up and store more 

carbon. In addition, although emissions from livestock agriculture rise, GHG emissions related 

to crop production generally decline as less area is devoted to crops due to higher yields. 

Figure 2. Projected Changes in Accumulated GHG Emissions in the Agriculture 

and Forestry Sectors Due to Global GHG Mitigation

Projected change in cumulative GHG emissions by type under the Mitigation scenario relative to the Reference 

for the IGSM-CAM and MIROC climate models (billion metric tons of CO2 equivalent).

-8%

-6%

-4%

-2%

0%

2010 2025 2050 2075 2100

IGSM-CAM MIROC

2010 2025 2050 2075 2100 2010 2025 2050 2075 2100

IGSM-CAM MIROC

Agricultural CH4 & N2O

Soil Sequestration

Crop Management Fuels

Aorestation

Forest Management

6

4

2

0

-2

-4

-6

-8

-10

-12

6

4

2

0

-2

-4

-6

-8

-10

-12
63

Changes in Consumer and APPROACH

Producer Surplus

The changes in crop prices and the level of 

production and consumption of agriculture 

and forestry products have important 

implications for the economic welfare of 

consumers and commodity producers. The 

analysis measures these effects through 

changes in consumer and producer surplus,24

as summarized in Table 1. Using both climate 

model projections, global GHG mitigation 

increases total economic welfare (well-being) in the agriculture and forestry sectors by 

$43 to $59 billion (discounted at 3%) through 

2100 compared to the Reference. Estimated 

consumer surplus is higher under the drier 

MIROC conditions than it is under the 

IGSM-CAM, primarily due to the larger crop 

yields under the Mitigation scenario 

compared to the Reference (see the Crop 

and Forest Yields section). 

The effect of global GHG mitigation on 

producer surplus varies depending on the 

climate model used. The IGSM-CAM climate 

projections result in an increase in producer 

surplus, though not as substantial as the 

projected increase in consumer surplus. The 

drier MIROC projections result in a slight 

decrease in producer surplus due to the 

substantial increase in crop yields and 

resulting decrease in prices. 

Table 1. Projected Effect of Global GHG Mitigation on Consumer and 

Producer Surplus in the Agriculture and Forestry Sectors

Change in cumulative consumer and producer surplus from 2015-2100 under the Mitigation scenario 

compared to the Reference (million 2014$, discounted at 3%). Results are rounded to two significant digits 

and therefore may not sum. In addition, the agriculture and forestry results do not sum to totals 

due to rounding, and because the table reflects independently calculated average 

values for agriculture, forestry, and combined totals.

The CIRA analysis uses the Forest and 

Agricultural Sector Optimization Model 

with Greenhouse Gases (FASOM-GHG)25,26

to estimate changes in market outcomes 

associated with projected impacts of 

climate change on U.S. crop and forest 

yields. As described in the previous section, 

projected yields across regions and crop/

forest types are generated by the EPIC and 

MC1 models. FASOM-GHG is driven by 

changes in potential yield from EPIC and 

MC1 for each of the five initializations of 

the IGSM-CAM climate model for both the 

Reference and Mitigation scenarios,27 as 

well as the drier MIROC climate model. 

FASOM-GHG simulates landowner 

decisions regarding crop mix and production practices, and projects the allocation 

of land over time to competing activities in 

both the forest and agricultural sectors and 

the associated impacts on commodity 

markets.28 Given the changes in potential 

yields projected by EPIC and MC1, 

FASOM-GHG uses an optimization 

approach to maximize consumer and 

producer surplus over time.29, 30 The model 

is constrained such that total production is 

equal to total consumption, total U.S. land 

use remains constant (with the potential 

movement of land from forest to agriculture and vice versa), and non-climate 

drivers in the agriculture and forestry 

sectors are consistent between the 

scenarios to isolate the effect of climate 

change.In addition, the analysis assumes 

no price incentives for avoiding GHG 

emissions or carbon sequestration in the 

agriculture and forestry sectors (i.e., the 

sectors do not participate in the global 

GHG mitigation policy). Finally, although 

the EPIC simulations assume that crops 

can be irrigated to a level that eliminates 

water stress, the FASOM-GHG simulations 

include shifts in water availability for 

irrigation based on data obtained from 

the water supply/demand framework 

described in the Water Quality section of 

this report.31

For more information on the CIRA 

approach and results for the FASOMGHG agriculture and forestry market 

impacts analysis, please refer to Beach 

et al.32

CONSUMER SURPLUS PRODUCER SURPLUS TOTAL

$13,000

$350

$14,000

-$3,300

$920

-$2,400

$43,000

$420

$43,000

$59,000

$750

$59,000

$29,000

$67

$29,000

$62,000

-$160

$62,000

Agriculture

Forestry

TOTAL

Agriculture

Forestry

TOTAL

MIROC
Coral Shellfish

Reefs

Ecosystems

SUBSECTORS 
Freshwater 

Fish

Wildfire Carbon 

Storage

n ecosystem is a community of

organisms interacting with each 

other and their environment. 

People, animals, plants, microbes, water, 

and soil are typical components of ecosystems. 

We constantly interact with the ecosystems 

around us to derive and maintain services 

that sustain us and contribute to our livelihoods. Clean air and water, habitat for 

species, and beautiful places for recreation 

are all examples of these goods and services. 

With the diversity of ecosystem types in the 

U.S. being so great—from the tidal marshes of 

the East Coast to the desert valleys of the 

Southwest to the temperate rainforests of the 

Pacific Northwest—climate change is likely to 

fundamentally alter our nation’s landscape 

and natural resources.1

HOW ARE ECOSYSTEMS VULNERABLE 

TO CLIMATE CHANGE? 

Ecosystems are held together by the interactions and connections among their components. Climate is a central connection in all 

ecosystems. Consequently, changes in climate 

will have far-reaching effects throughout 

Earth’s ecosystems. Climate change can affect 

ecosystems and species in a variety of ways; 

for example, it can lead to changes in the 

timing of seasonal life-cycle events, such as 

migrations; habitat shifts; food chain disruptions; increases in pathogens, parasites, and 

diseases; and elevated risk of extinction for 

many species.2

Climate change directly affects ecosystems 

and species, but it also interacts with other 

human stressors on the environment. Although some stressors cause only modest 

impacts by themselves, the cumulative impact 

of climate and other changes can lead to 

dramatic ecological impacts. For example, 

coastal wetlands already in decline due to 

increasing development will face increased 

pressure from rising sea levels. 

WHAT DOES CIRA COVER?

CIRA analyzes the potential benefits of global 

GHG mitigation on coral reefs and freshwater 

fisheries in the U.S., focusing on changes in 

recreational use of coral reefs and recreational 

fishing. This section also examines the projected impacts of ocean acidification on the U.S. 

shellfish market. Lastly, CIRA quantifies the 

physical and economic impacts of climate 

change on wildfires and terrestrial ecosystem 

carbon storage. Climate change will affect 

many species and ecosystems beyond what is 

explored in this report; consequently, CIRA 

captures only a glimpse of the potential 

benefits of GHG mitigation on this sector.

A
66

Coral Reefs

KEY FINDINGS Climate Change and 

1 Coral Reefs

2

3

Coral reefs, including those found in Hawaii and the 

Caribbean, are unique ecosystems that are home to 

large numbers of marine plant and animal species. 

They also provide vital fish spawning habitat, protect 

shorelines, and are valuable for recreation and 

tourism. However, shallow-water coral reefs are highly 

vulnerable to climate change.3

 High water temperatures can cause coral to expel the symbiotic algae 

that provide nourishment and vibrant color for their 

hosts. This coral bleaching can cause the coral to die. 

In addition, ocean acidification (ocean chemistry 

changes due to elevated atmospheric CO2) can 

reduce the availability of certain minerals in seawater 

that are needed to build and maintain coral skeletons. 

Risks of Inaction

Coral reefs are already 

disappearing due to 

climate change and other 

non-climate stressors. 

Temperature increases and 

ocean acidification are 

projected to further reduce 

coral cover in the future. 

Without global GHG mitigation, extensive loss of 

shallow corals is projected 

by 2050 for major U.S. reef 

locations. Global GHG 

mitigation delays Hawaiian 

coral reef loss compared to 

the Reference scenario, but 

provides only minor benefits to coral cover in South 

Florida and Puerto Rico, as 

these reefs are already close 

to critical thresholds of 

ecosystem loss. 

GHG mitigation results in 

approximately $22 billion 

(discounted at 3%) in 

recreational benefits 

through 2100 for all three 

regions, compared to a 

future without emission 

reductions.

Without GHG mitigation, continued warming and ocean acidification will have very significant 

effects on coral reefs. For major U.S. reefs, projections under the Reference show extensive 

bleaching and dramatic loss of shallow coral cover occurring by 2050, and near complete loss by 

2100. In Hawaii, coral cover is projected to decline from 38% (current coral cover) to approximately 5% by 2050, with further declines thereafter. In Florida and Puerto Rico, where present-day 

temperatures are already close to bleaching thresholds and where these reefs have historically 

been affected by non-climate stressors, coral is projected to disappear even faster.4

 This drastic 

decline in coral reef cover, indicating the exceedance of an ecosystem threshold, could have 

significant ecological and economic consequences at regional levels.These projections of shallow 

coral loss for major U.S. reefs are consistent with the findings of the assessment literature.5

Figure 1. Projected Impact of Unmitigated Climate Change on 

Coral Reef Cover in the U.S. 

Approximate reduction in coral cover at each location under the Reference scenario relative to 

the initial percent cover. Coral icons do not represent exact reef locations. Results for 2075 

are omitted as there is very little change projected between 2050 and 2100. 

2010 2025 2050 2100

Percent coral cover 5% Percent coral cover <1%

Percent coral cover 12% Percent coral cover 3% Percent coral cover <1% Percent coral cover <1%

Percent coral cover 25% Percent coral cover 6% Percent coral cover 1% Percent coral cover 1%

Hawaii

South 

Florida

Puerto 

Rico

Percent coral cover 38% Percent coral cover 36%
67

Reducing Impacts through APPROACH

GHG Mitigation

Mitigating global GHG emissions can reduce 

only some of the projected biological and 

economic impacts of climate change on coral 

reefs in the U.S. Figure 2 shows projected coral 

reef cover over time in Hawaii, South Florida, 

and Puerto Rico under the Reference and 

Mitigation scenarios. In Hawaii, the decline in 

reef cover slows under the Mitigation scenario 

compared to the Reference, as some of the 

extensive bleaching episodes and effects of 

ocean acidification are avoided. But even 

under the Mitigation scenario, Hawaii is 

projected to eventually experience substantial 

reductions in coral cover. In South Florida and 

Puerto Rico, the projected GHG emission 

reductions associated with the Mitigation 

scenario are likely insufficient to avoid 

multiple bleaching and mortality events by 

2025, and coral cover declines thereafter 

nearly as fast as in the Reference.

The delay in the projected decline of coral 

results in an estimated $22 billion in economic 

benefits for recreation across the three sites 

through 2100 (discounted at 3%). The majority 

of these recreational benefits are projected for 

Hawaii, with an average value through 2100 of 

approximately $20 billion (95% confidence 

interval of $10-$30 billion). In Florida, where 

coral reefs have already been heavily affected, 

recreational benefits are also positive, but 

notably lower at approximately $1.4 billion (95% confidence interval of $0.74-$2.1 billion). In 

Puerto Rico, benefits are estimated at $0.38 million (95% confidence interval of $0.20-$0.57 

million), but only represent recreational benefits for permanent residents, and therefore are 

not directly comparable to the other locations where visits from nonresident tourists are also 

included. Including the economic value of other services provided by coral reefs, such as 

shoreline protection and fish-rearing habitat, would increase the benefits of mitigation. 

REPRESENTATIVE PHOTOS 

OF CORAL REEF DECLINE

HEALTHY REEF

40-75% live coral cover

SEVERELY DEGRADED REEF

10-25% live coral cover

NEARLY DEAD REEF

<10% live coral cover

CORAL COVERAGE 

The CIRA analysis examines the 

physical and economic impacts of 

climate change and ocean acidification on coral reefs in Hawaii, South 

Florida, and Puerto Rico. Using the 

COMBO (Coral Mortality and Bleaching Output) model,6,7 the analysis first 

estimates declines in coral reef cover 

(a measure of coral reef health and 

density) using projections of future 

ocean temperature (from the 

IGSM-CAM) and chemistry under the 

CIRA Reference and Mitigation 

scenarios.8 The effects of future 

bleaching events are also estimated. 

Next, the analysis quantifies the 

economic impacts associated with 

coral reef cover loss based on declines 

in reef-based recreation. The analysis 

estimates these impacts using a 

benefit-transfer approach; that is, it 

draws on reef-related recreation 

benefits measured in previously 

published studies conducted at a 

range of coral reef sites to estimate 

the value of reef-related recreation 

benefits in the areas considered in 

this study.9

 Projected impacts to 

recreation at each site are provided 

with confidence intervals based on 

the 95% interval for per-trip recreational values.

For more information on the CIRA 

approach and results for the coral 

reef sector, please refer to Lane et 

al. (2013)10 and Lane et al. (2014).11

Figure 2. Percent Change in Coral Reef 

Cover with and without Global GHG 

Mitigation at Major U.S. Reefs

Hawaii Reference

South Florida

Puerto Rico

Mitigation

2010 2050 2075 2100

0

10

20

30

40

2025

2010 2050 2075 2100

0

10

20

30

40

2025

2010 2050 2075 2100

0

10

20

30

40

2025
The pace of ocean acidification is accelerating. 

Since the Industrial Revolution, the average 

pH of surface ocean waters has fallen by 0.1, 

representing a nearly 30% increase in 

acidity.16 Under the Reference scenario, ocean 

acidification is projected to cause pH to drop 

an additional 0.3, representing a 100% 

increase in acidity from pre-industrial times. 

Continued ocean acidification is estimated to 

reduce the supply of oysters, scallops, and clams in 2100 by 45% (13 million pounds per year), 

48% (21 million pounds), and 32% (31 million pounds), respectively (Figure 2). These decreases 

in supply are projected to result in price increases by 2100 of approximately $2.20 (a 68% 

increase from 2010), $9.10 (140%), and $1.30 (123%) per pound, respectively, and lead to 

consumer losses of roughly $480 million per year by the end of the century. These projections 

are consistent with the findings of the assessment literature, which describe reduced growth 

and survival of U.S. shellfish stocks due to unmitigated ocean acidification.17

68

KEY FINDINGS Ocean Acidification 

1 and Shellfish

2

3

CO2 and other 

greenhouse gases 

mix in atmosphere

Oceans absorb about 1/4 of 

anthropogenic CO2 emissions

Dissolved CO2 changes 

ocean chemistry and 

reduces availability of 

minerals for shell-building 

plants and animals

Acidication reduces the size 

and abundance of shellsh

Fishermen 

experience decreases 

in harvest

Consumers face 

changes in prices

Fish Market

1

2

3

4

5

6

$

Without global GHG 

mitigation, the harvests 

of some shellfish in the U.S. 

are projected to decline by 

32%-48% by the end of 

the century due to ocean 

acidification, though 

estimated impacts vary 

by species.

Demand for shellfish is 

projected to increase 

through the end of the 

century with a growing 

population and rising 

incomes, exacerbating 

the economic impacts in 

this sector. 

Global GHG mitigation is 

projected to avoid $380 

million in consumer losses 

in 2100 compared to the 

Reference scenario by 

preventing most of the 

decreases in the supply of 

select shellfish and the 

resulting price increases.

The ocean absorbs about one quarter of the CO2 released into the atmosphere by human 

activities, primarily from the combustion of fossil fuels. Although the ocean’s ability to absorb 

CO2 prevents atmospheric levels from climbing even higher, measurements made over the last 

few decades have demonstrated that marine CO2 levels have risen, leading to an increase in 

acidity (Figure 1).12 Ocean acidification is projected to adversely affect a number of valuable 

marine ecosystem services by making it more difficult for many organisms to form shells and 

skeletons.13 Some shellfish are highly vulnerable to ocean acidification14 and any impacts to 

these species are expected to negatively affect the economy. Certain species have high 

commercial value; for example, each year in the U.S., oysters, clams, and scallops supply 170 

million pounds of seafood valued at $400 million.15

Figure 1. Ocean Acidification Impact Pathway for Shellfish

Risks of Inaction

 ©Getty Images/John Burke

Shellfish
Percent Change 

in Supply

Percent Change 

in Price

Savings due to 

Mitigation

$1.30 per pound

$.98 per pound

0%

-20%

-40%

-60%

160%

120%

80%

40%

0%

160%

120%

80%

40%

0%

160%

120%

80%

40%

0%

2000 2025 2050 2075 2100 2000 2025 2050 2075 2100

0%

-20%

-40%

-60%

0%

-20%

-40%

-60%

Reference Mitigation

$6.70 per pound

Oysters

Scallops

Clams

69

Reducing Impacts through APPROACH

GHG Mitigation

Reducing global GHG emissions can mitigate the ecological and economic impacts of 

ocean acidification. Figure 2 shows how the supplies of oysters, scallops, and clams 

are projected to fall with ocean acidification under the Reference and Mitigation 

scenarios. Although supplies are estimated to decrease under both scenarios relative 

to present-day supplies, the Mitigation scenario avoids a majority of the impacts, 

particularly for clams. In 2100, global GHG mitigation is projected to avoid the loss of 

54 million pounds of oysters, scallops, and clams, or 34% of the present-day U.S. 

oyster supply, 37% of the scallop supply, and 29% of the clam supply. 

Figure 2 also indicates how the increase in demand and the decrease in supply 

are estimated to affect prices by 2100 for these shellfish under the two scenarios. 

Consumers are likely to substitute away from these shellfish as their prices increase, 

but not entirely, and not without some decrease in satisfaction. The Mitigation 

scenario keeps prices much closer to current levels, as indicated in Figure 2, resulting 

in smaller consumer losses in the shellfish market. In 2100, the benefits to shellfish 

consumers from global GHG emissions reductions under the Mitigation scenario are 

estimated at $380 million. The cumulative benefits over the century are estimated at 

$1.9 billion (discounted at 3%). 

Figure 2. Estimated Impacts on the U.S. Shellfish Industry

Projected changes in the supplies and prices of oysters, scallops, and clams through 2100 under the 

Reference and Mitigation scenarios relative to the base period.

The CIRA analysis models the entire 

“impact pathway” shown in Figure 1, 

which can be divided into biophysical 

and economic components. The 

biophysical impacts are estimated 

using the CIRA CO2 and sea surface 

temperature projections from the 

IGSM-CAM in the CO2SYS model18

to simulate seawater chemistry 

conditions through the 21st century. 

These conditions are then used to 

estimate how the growth rates of 

oysters, scallops, and clams will 

change over time. 

The economic analysis uses the 

projected growth rates of these 

species to estimate changes to the 

U.S. supply of shellfish. A consumer 

demand model of the shellfish market, 

described in Moore (2014),19 projects 

changes in prices and consumer 

behavior under the Reference and 

Mitigation scenarios. This model does 

not estimate producer or supply-side 

welfare effects, which could also show 

benefits of mitigation. Comparing the 

model results under the two scenarios 

provides an estimate of the benefits 

to the shellfish market of avoiding 

significant amounts of CO2 from being 

added to ocean waters. By considering 

impacts to these three species, this 

approach estimates just a fraction of 

the potential economic damages from 

ocean acidification, but, nonetheless, 

provides some insight into the benefits 

of global GHG mitigation. 

In addition, by preventing the loss 

of shellfish populations, global GHG 

mitigation would preserve ecosystem 

services provided by these species 

(e.g., water filtration). Inclusion of 

these effects would likely increase the 

total benefits of GHG mitigation in 

this sector. 

For more information on the 

CIRA approach to estimating 

the economic impacts of ocean 

acidification in the shellfish 

market, see Moore (2015).20
70

Freshwater Fish

KEY FINDINGS Climate Change 

1 and Freshwater Fish

2

3

Trout Salmon Smallmouth Bass Shad

COLDWATER FISHERY EXAMPLES WARMWATER FISHERY EXAMPLES

Warming waters and 

changes in stream flow due 

to climate change will likely 

alter the distribution of 

freshwater fisheries across 

the country. Without global 

GHG mitigation, coldwater 

species are projected to be 

replaced in many areas by 

less economically valuable 

fisheries over the course of 

the 21st century, especially 

in the Mountain West and 

Appalachia. 

Habitat suitable for 

coldwater fisheries is 

estimated to decline 

nationally by approximately 

62% through 2100 under 

the Reference, but by only 

12% under the Mitigation 

scenario. Global GHG 

mitigation is projected to 

preserve coldwater habitat 

in most of Appalachia and 

the Mountain West.

GHG mitigation avoids 

an estimated $380 million 

to $1.5 billion in total 

recreational fishing 

damages through 2100 

compared to the Reference 

(discounted at 3%).

Freshwater fishing is an important recreational activity that contributes significantly to local 

economies in many parts of the country. Most fish species thrive only in certain ranges of water 

temperature and stream flow conditions. For example, trout and salmon can only tolerate 

coldwater streams, while shad and largemouth bass thrive in warmwater habitats (see below 

infographic). Climate change threatens to disrupt these habitats and affect certain fish 

populations through higher temperatures and changes in river flow.21

Risks of Inaction

Without GHG mitigation, climate change is projected to have a significant impact on freshwater 

fishing in the contiguous U.S. Increasing stream temperatures and changes in stream flow are 

likely to transform many habitats that are currently suitable for coldwater fish into areas that are 

only suitable for warmwater species that are less recreationally valuable. Under the IGSM-CAM 

climate projections, coldwater fisheries are estimated to be limited almost exclusively to the 

mountainous West in 2100, and would almost disappear from Appalachia. In addition, substantial 

portions of Texas, Oklahoma, Kansas, and Florida would shift from warmwater to rough habitat 

(Figure 1). Overall, unmitigated climate change is projected to result in a 62% decline in coldwater fish habitat by 2100, which includes approximately 440,000 acres of lost stream habitat. 

Meanwhile, warmwater and rough stream habitats are projected to increase by 1.3 million and 

450,000 acres, respectively. The projected loss of coldwater fish habitat and expansion of 

warmwater and rough fisheries are consistent with the findings of the assessment literature.22, 23

Figure 1. Projected Impact of Unmitigated Climate Change 

on Potential Freshwater Fish Habitat in 2100

Change in distribution of areas where stream temperature supports different fisheries under the 

Reference scenario using the IGSM-CAM climate model. Results are presented for the 8-digit hydrologic unit 

codes (HUCs) of the contiguous U.S. 

Current Cold, Projected Cold 

Current Cold, Projected Warm

Current Warm, Projected Warm

Current Warm, Projected Rough
71

APPROACH

Largemouth Bass Bluegill Carp

ROUGH FISHERY EXAMPLES

Catfish

Global GHG mitigation is projected to prevent much of the loss of 

coldwater fish habitat that occurs in the Reference (Figure 2). 

Although coldwater stream habitat will likely still be reduced 

under the Mitigation scenario (by approximately 85,000 acres by 

2100), mitigation avoids approximately 81% of the losses incurred 

under the Reference, preserving an area equal to approximately 

360,000 acres of suitable stream habitat nationally. This habitat 

supports valuable recreational fishing, especially in Appalachia 

and large areas of the Mountain West. Also, fewer acres are 

converted to less economically valuable warmwater and rough 

fisheries under the Mitigation scenario than under the Reference. 

Specifically, stream habitat suitable for warmwater and rough 

fisheries increase by 450,000 and 13,000 acres, respectively, under 

the Mitigation scenario, which is 36% and 3% of the expansions estimated under the Reference. 

Compared to the Reference, the Mitigation scenario provides economic benefits of approximately $1.5 billion through 2100 for coldwater fishing only, and $380 million when all three 

freshwater fishery types (cold, warm, and rough) are considered (discounted at 3%). These results 

rely upon climate projections from the IGSM-CAM, which projects a relatively wetter future for 

most of the U.S. compared to the MIROC climate model. The projected benefits of global GHG 

mitigation through 2100 are lower with the drier MIROC model (not shown) for coldwater fishing 

only, at approximately $1.2 billion, but higher when all three fisheries are considered, at approximately $1.5 billion (discounted at 3%).24

The CIRA analysis assesses the impacts 

of climate change on the distribution 

of habitat suitable for freshwater 

fish across the U.S. and estimates the 

economic implications of these 

changes. Water temperature changes 

are simulated for the CIRA emissions 

scenarios using the IGSM-CAM and 

MIROC climate models to estimate 

changes in suitable habitat (in stream 

acres) for three types of freshwater 

fisheries: cold, warm, and rough 

(species tolerant to warmest stream 

temperatures). Each fishery type 

represents a categorization of individual species based on their tolerance 

for different river and stream water 

temperatures. This analysis does not 

evaluate impacts to fisheries in lakes 

and reservoirs, which are vulnerable to 

climate change in different ways 

compared to streams and rivers.25 As 

shown at the bottom of this section, 

the coldwater fish guild contains 

species that are the least tolerant to 

increasing stream temperatures, and 

are therefore the most vulnerable to 

climate change. 

Results from habitat modeling 

considering projected changes in both 

water temperature and streamflow 

serve as input to an economic model 

to analyze the impacts of habitat 

change on the value of recreational 

fishing. The model estimates fishing 

behavior as the likelihood that an adult 

in a particular state is an angler and the 

likelihood that an angler fishes for 

species in each fishery type. The fishing 

value for each fishery type is derived by 

multiplying the number of fishing days 

by the value of a fishing trip.26 As 

implications of changes to the distribution of freshwater fisheries extend 

beyond recreational use by humans, 

this analysis underestimates the 

economic benefits of GHG mitigation. 

For more information on the CIRA 

approach and results for the 

freshwater fish sector, please refer 

to Lane et al. (2014)27 and Jones et 

al. (2012).28

Reducing Impacts through 

GHG Mitigation

Figure 2. Projected Impact on Potential Freshwater Fish Habitat in 2100

with Global GHG Mitigation

Change in distribution of areas where stream temperature supports different fisheries under 

the Mitigation scenario using the IGSM-CAM climate model. Results are presented 

for the 8-digit HUCs of the contiguous U.S. 

Current Cold, Projected Cold 

Current Cold, Projected Warm

Current Warm, Projected Warm

Current Warm, Projected Rough
72

KEY FINDINGS Climate Change and Wildfire

1

2

3

Without global GHG 

mitigation efforts, climate 

change is projected to 

dramatically increase 

the area burned by wildfires across most of the 

contiguous U.S., especially 

in the West.

Global GHG mitigation 

is projected to reduce the 

cumulative area burned 

by wildfires over the course 

of the 21st century by 

approximately 210-300 

million acres compared to 

the Reference. 

Global GHG mitigation 

avoids an estimated 

$8.6-$11 billion in wildfire 

response costs and $3.4 

billion in fuel management 

costs on conservation 

lands (discounted at 3%) 

through 2100 compared to 

the Reference. Other impacts, such as property 

damage or health effects 

from decreased air quality, 

are not estimated, but 

could have large economic 

implications. 

Terrestrial ecosystems in the U.S. provide a 

wealth of goods and services such as timber, 

wildlife habitat, erosion management, water 

filtration, recreation, and aesthetic value. 

Climate change threatens these ecosystems 

as heat, drought, and other disturbances 

bring larger and more frequent wildfires. 

Wildfires can damage property, disrupt 

ecosystem services, destroy timber stocks, 

impair air quality, and result in loss of life.29 In 

the last decade (2004-2013), more than 72 

million acres of forest have burned due to 

wildfires, and the U.S. government has spent 

in excess of $15 billion on wildfire suppression.30 Additionally, wildfires release carbon 

stored in terrestrial ecosystems, potentially 

further accelerating climate change.31, 32

Risks of Inaction

Without GHG mitigation, climate change is projected to dramatically increase the area burned 

by wildfires across most of the contiguous U.S., a finding that is consistent with the assessment 

literature.33 Under the Reference using the IGSM-CAM climate projections, approximately 5.3 

million34 more acres—an area greater than the state of Massachusetts—are projected to burn 

each year at the end of the century compared to today. This represents a doubling of acres 

burned compared to today’s rates.35 However, the estimated impacts vary across regions and 

through time (Figure 1). Consistent with the assessment literature,36 the western U.S.37 is projected 

to experience large increases in burned area by the end of the century (an increase of approximately 43%). In particular, the Southwestern region (comprising Arizona, New Mexico, and West 

Texas) is projected to experience increases of 140% on average.38 Wildfire in other regions is not 

projected to change significantly compared to today, and some regions, such as the Northeast, 

are estimated under the IGSM-CAM projections to experience decreases in wildfire activity. 

Figure 1. Projected Impact of Unmitigated Climate Change on Wildfire Activity 

Change in average annual acres burned under the Reference scenario by mid-century (2035-2064) and 

end of century (2085-2114) compared to the historic baseline (2000-2009) using the IGSM-CAM climate model. 

Acres burned include all vegetation types and are calculated at a cell resolution of 0.5° x 0.5°. 

Change in Acres Burned

Mid-Century End-of-Century

-72,000 to -60,000

-59,999 to -30,000

-29,999 to 0

1 to 10,000

10,001 to 20,000

20,001 to 30,000

Wildfire
73

Reducing Impacts through APPROACH

GHG Mitigation

Figure 2. Estimated Acres Burned with and without Global GHG Mitigation 

Estimated acres burned by wildfire in the contiguous U.S. over the course of the 21st century under the Reference 

and Mitigation scenarios using the IGSM-CAM climate model, with trends shown in bold. The large inter-annual 

variability reflects simulated periods of fuel accumulation followed by seasons of large wildfire activity. 

To estimate the effect of climate 

change on areas burned by wildfires, 

the CIRA analysis uses the MC1 

dynamic global vegetation model. 

The model simulates future terrestrial 

ecosystem cover and burned area 

across the contiguous U.S. in the 21st

century. The vegetation model is 

driven by changes in future climate 

(e.g., temperature, precipitation, 

humidity) based on five initializations 

of the IGSM-CAM climate model for the 

Reference and Mitigation scenarios.41,42

Results presented in this section 

represent the average of the initializations. Simulations using the drier 

MIROC model were also performed. 

Projected changes in fire regime over 

time are adjusted to account for fire 

suppression tactics. 

The projected impacts of wildfires 

are summarized by scenario and 

geographic area, and then monetized 

using average wildfire response costs 

for each region. These costs include the 

costs associated with labor (e.g., fire 

crews) and equipment (e.g., helicopters, bulldozers) that are required for 

fire-fighting efforts.43 Using the 

approach described in Lee et al. 

(2015),44 the analysis also estimates the 

environmental damages resulting from 

moderate and severe wildfires on 

conservation lands (e.g., Forest Service 

lands, national parks and preserves, 

and other protected lands) across the 

contiguous U.S. under the Reference 

and Mitigation scenarios. To estimate 

the value of the lost ecosystem services 

resulting from these wildfires, the 

analysis quantifies the costs of fuels 

management needed to offset the 

injury caused by wildfires. Air quality 

impacts, property loss, loss of recreation, and the effects of pest infestations (e.g., pine bark beetles) on 

wildfire activity are additional and 

important impacts, but are not 

included in the reported estimates.

For more information on the CIRA 

approach and results for wildfires, 

please refer to Mills et al. (2014)45 

and Lee et al. (2015).46

0

10

20

30

40

50

60

2010 2025 2050 2075 2100

Millions of Acres Burned

Reference Mitigation

As shown in Figure 2, global GHG mitigation 

significantly reduces the area burned by 

wildfire in the U.S. over the course of the 

21st century. By 2100, the Mitigation scenario 

reduces the cumulative area burned by 

approximately 210-300 million acres, 

depending on the climate model used. This 

corresponds to a 13-14% reduction relative 

to the Reference. As shown, the combined 

area of wildfires avoided in the contiguous 

U.S. due to GHG mitigation is equivalent to 

two to three times the size of California. 

These benefits of GHG mitigation would 

largely occur in the West, where approximately 64%-75% of the avoided burned area is located. 

Nationally, the avoided wildfire due to GHG mitigation corresponds $11 billion in reduced 

wildfire response costs and $3.4 billion39 in avoided fuel management costs for conservation 

lands through 2100 (both discounted at 3%). Other economic damages from wildfire that are 

not estimated in this analysis, such as human health effects from decreased air quality, could 

have large implications at national and regional scales. These results rely upon climate 

projections from the IGSM-CAM, which projects a relatively wetter future for most of the U.S. 

compared to the MIROC climate model (see the Levels of Certainty section of this report for 

more information). The projected benefits of global GHG mitigation are slightly lower for the 

drier MIROC model, with wildfire response cost savings estimated at $8.6 billion through 

2100 (discounted at 3%).40

210-300 million fewer acres burned over 

the course of the 21st century, an area 2-3 times

the size of California

+ +
Percent Change in Carbon Stocks

IGSM-CAM MIROC

-15 to -10%

-9 to -5%

-4 to 0%

1 to 5%

6 to 10%

11 to 20%

74

Carbon Storage

KEY FINDINGS Climate Change and Terrestrial 

Carbon Storage 1

2

Changes in vegetative 

carbon storage in the contiguous U.S. are highly 

dependent on the projected 

future climate, with the 

magnitude, regional distribution, and directionality of 

impacts changing over time. 

The estimated effect of 

global GHG mitigation on 

carbon storage ranges from 

a decrease in carbon stocks 

of 0.5 billion metric tons to 

an increase in carbon 

stocks of 1.4 billion metric 

tons by the end of the 

century, depending on the 

climate model used. The 

economic value of these 

changes in carbon storage 

ranges from $9 billion in 

disbenefits to $120 billion 

in GHG mitigation benefits 

(both discounted at 3%). 

Risks of Inaction

Climate change impacts on terrestrial ecosystem carbon storage under the Reference are on 

the order of billions of tons of carbon from 2000 to 2100, with some regions showing 

substantial changes in terrestrial carbon stocks (total amount of carbon in the vegetation). 

Under the IGSM-CAM climate projections, terrestrial ecosystem storage across the contiguous U.S. is projected to increase 3.4% from 2000 to 2100 (equal to 2.9 billion metric tons),50 

primarily due to generally warmer, wetter, and CO2-rich future conditions that are favorable 

to vegetative growth. Much of the national trend is driven by the Rocky Mountains, South, 

and East regions, which have the largest projected increases in terrestrial ecosystem carbon. 

However, as shown in Figure 2, there is substantial regional variation, and projections for 

carbon storage vary greatly depending on the projected future climate. Results using the 

drier MIROC climate model project net reductions in stored carbon under the Reference in 

most regions. These results are consistent with the findings of the assessment literature.51

Figure 2. Projected Impact of Unmitigated Climate Change 

on Stored Carbon in 2100 

Simulated changes in carbon stocks from the baseline (2000-2009 average) projected by the IGSM-CAM and 

MIROC climate models are aggregated by U.S. Forest Service Geographic Area Coordination Center region.

Terrestrial ecosystems influence the climate system 

through their important role in the global carbon 

cycle. These ecosystems capture and store carbon 

from the atmosphere, thereby reducing its climate 

impact. However, they can also act as a source, 

releasing carbon through decomposition and 

wildfires (Figure 1). Terrestrial ecosystems in the 

U.S., which include forests, grasslands, and 

shrublands, are currently a net carbon sink. Today, 

forests store more than 227 million tons of carbon per 

year, which offsets approximately 16% of all annual U.S. 

carbon dioxide emissions from fossil fuel burning.47 Forest carbon 

storage has increased due to net increases in forest area, improved forest management, as 

well as higher productivity rates and longer growing seasons driven by climate change.48 

However, climate-driven changes in the distribution of vegetation types, wildfire, pests, and 

disease are affecting, and will continue to affect, U.S. terrestrial ecosystem carbon storage.49

Figure 1. Carbon Storage Basics

PHOTOSYNTHESIS, 

LITTERFALL, 

SEDIMENTATION

COMBUSTION, 

RESPIRATION, 

DECOMPOSITION
75

Reducing Impacts through APPROACH

GHG Mitigation

The impacts of GHG mitigation on national 

terrestrial ecosystem carbon storage are 

highly dependent upon the projected future 

climate, with the magnitude and even 

directionality of impacts varying over time 

(Figure 3). Across the contiguous U.S., average 

results across the IGSM-CAM initializations 

show that GHG mitigation reduces stored 

carbon compared to the Reference by 0.5 

billion metric tons over the course of the 

century. The economic value of this lost 

carbon under the Mitigation scenario is an 

estimated $9.0 billion (discounted at 3%). As 

shown in Figure 3, carbon stocks under the 

Mitigation scenario are larger than the 

Reference in the first half of the century under 

the IGSM-CAM, but the trend reverses after 

2050, as climate conditions under the 

Reference (generally warmer and wetter) are 

more favorable for vegetative growth. There is 

an early savings from the near-term gain in 

stored carbon of approximately 1.1 billion 

metric tons, estimated at $170 billion by 2030 

(discounted at 3%). However, these initial 

gains are not large enough to offset projected 

losses in the second half of the century.

The projected impacts of climate change 

on vegetative carbon storage and the effects 

of GHG mitigation are different when using 

the relatively drier climate projections from 

the MIROC model (Figure 3). The MIROC 

results project a consistent increase in carbon 

storage benefits when comparing the 

Mitigation scenario to the Reference, with a 

carbon stock increase of 1.4 billion metric 

tons by 2100. The economic value of this 

carbon gain under the Mitigation scenario is 

an estimated $120 billion (discounted at 3%). 

Results using IGSM-CAM projections show 

much more variability over time than the 

MIROC results, which is primarily a reflection 

of the climate projection method.52

Figure 3. Projected Impact of Global GHG Mitigation on 

Carbon Stocks in the Contiguous U.S.

Estimated change in the size of terrestrial ecosystem carbon stocks under the Mitigation scenario 

compared to the Reference. Positive values indicate larger carbon stocks under the Mitigation 

scenario compared to the Reference, and vice versa. The thin lines represent estimated changes in 

carbon stocks under the different initializations of the IGSM-CAM climate model. 

To estimate climate change impacts 

on terrestrial ecosystem carbon 

storage, the MC1 dynamic global 

vegetation model was used to 

simulate terrestrial vegetative growth 

and cover (e.g., grasses, shrubs, hard 

and softwood forests) for the contiguous U.S. from 2000 to 2100.53

Vegetative cover estimates from MC1 

reflect simulated changes in climate, 

biogeography, biogeochemistry, and 

fire dynamics. MC1 was run using the 

five initializations of the IGSM-CAM 

climate model for both the Reference 

and Mitigation scenarios (see the CIRA 

Framework section of this report for 

more information).54 The results 

described in this section represent the 

average of these initializations. 

Because IGSM-CAM projects a wetter 

future for a majority of the nation, 

MC1 was also run using the MIROC 

climate model. These drier climate 

projections for the U.S. were used to 

capture a broader range of possible 

precipitation futures under the same 

GHG emissions scenarios. 

Projected annual changes in terrestrial carbon storage for non-agricultural, 

non-developed lands across the 

contiguous U.S. were summarized by 

scenario and geographic area, and 

then monetized using the central 

estimate of the U.S. Government’s 

updated social cost of carbon (SCC) 

values for the years 2010-2050, with 

extrapolation to 2100.55

This analysis did not consider the 

effects of future changes in ozone, 

pests, and disease, which could 

influence the ability of U.S. terrestrial 

ecosystems to store carbon.

 

For more information on the CIRA 

approach and results for carbon 

storage, please refer to Mills et al. 

(2014).56

-4

-3

-2

-1

0

1

2

3

4

2010 2025 2050 2075 2100

Billions of Metric Tons of Carbon

IGSM-CAM Average MIROC
76

Overview of Results
77

This section provides an overview of the national and 

regional results for all sectors included in the report. The 

National Highlights section presents the estimated physical 

and monetary benefits (avoided impacts) to the U.S. of the 

global GHG mitigation scenario compared to the Reference 

scenario in 2050 and 2100. 

The Regional Highlights section shows regional impacts 

that are particularly notable, presenting changes in both the 

Reference and Mitigation scenarios to highlight the potential 

benefits of global GHG mitigation. The individual monetized 

estimates presented in these sections are not aggregated, 

as there are differences in the types of costs being quantified 

across sectors; furthermore, not all potential impacts of 

climate change are represented in this report.
78

National Highlights

OVERVIEW OF RESULTS

his section provides an overview of the national-scale results presented 

throughout this report. It presents the estimated physical and monetary benefits 

(avoided impacts) to the U.S. of global GHG mitigation compared to the Reference 

scenario in the years 2050 and 2100. Although not available for all sectors, cumulative 

benefits for the entire 21st century would likely be much larger than the annual estimates 

presented here. In addition, the individual monetized estimates are not aggregated, as 

only a subset of climate change impacts is quantified in this report, and there are differences in the types of costs being quantified across the sectors. For detailed information 

on the results, and a summary of the methodologies used, please refer to the Sectors 

section of this report. 

An estimated 13,000 fewer deaths from poor air quality, 

valued at $160 billion.*

AIR 

QUALITY

INFRASTRUCTURE

ELECTRICITY

In the year 2050, global GHG mitigation 

is projected to result in... 

In the year 2100, global GHG mitigation 

is projected to result in...

HEALTH

An estimated 57,000 fewer deaths from poor air quality, 

valued at $930 billion.*

An estimated 1,700 fewer deaths from extreme heat and 

cold in 49 major U.S. cities, valued at $21 billion.

An estimated 12,000 fewer deaths from extreme heat and 

cold in 49 major U.S. cities, valued at $200 billion.

An estimated avoided loss of 360 million labor hours, 

valued at $18 billion.

An estimated avoided loss of 1.2 billion labor hours, 

valued at $110 billion.

An estimated $507-$700 million in avoided damages from 

poor water quality.†

An estimated $2.6-$3.0 billion in avoided damages from 

poor water quality.†

EXTREME 

TEMPERATURE

LABOR

WATER 

QUALITY

COASTAL

PROPERTY

An estimated $0.14 billion in avoided damages and 

adaptation costs from sea level rise and storm surge.

An estimated $3.1 billion in avoided damages and adaptation costs from sea level rise and storm surge.

DEMAND AND 

SUPPLY

An estimated 1.1%-4.0% reduction in energy demand 

and $10-$34 billion in savings in power system costs.‡

Not estimated.

* These results do not reflect the additional benefits to air quality and human health that would stem from the co-control of traditional air pollutants along with GHG emissions.

† For sectors sensitive to changes in precipitation, the estimated range of results is generated using projections from two climate models showing different patterns of future precipitation in the contiguous U.S. The 

IGSM-CAM model projects a relatively “wetter” future for most of the contiguous U.S. compared to the “drier” MIROC model (see the CIRA Framework section of this report for more information). 

‡ Estimated range of benefits from the reduction in demand and system costs resulting from lower temperatures associated with GHG mitigation. The electricity section in this report presents an analysis that includes 

the costs to the electric sector of reducing GHG emissions. 

T

An estimated 160-960 fewer bridges made structurally 

vulnerable, valued at $0.12-$1.5 billion.†

An estimated 720-2,200 fewer bridges made structurally 

vulnerable, valued at $1.1-$1.6 billion.†

An estimated $0.56-$2.3 billion in avoided adaptation 

costs.†

An estimated $4.2-$7.4 billion in avoided adaptation costs.†

An estimated $56 million to $2.9 billion in avoided adaptation costs from the 50-year, 24-hour storm in 50 U.S. cities.†An estimated $50 million to $6.4 billion in avoided adaptation costs from the 50-year, 24-hour storm in 50 U.S. cities.†

BRIDGES

ROADS

URBAN 

DRAINAGE

g g
79

In the year 2050, global GHG mitigation 

is projected to result in... 

In the year 2100, global GHG mitigation 

is projected to result in...

An estimated change in flooding damages ranging from $260 

million in damages to $230 million in avoided damages.†

INLAND

FLOODING

AGRICULTURE & FORESTRY

ECOSYSTEMS

WATER RESOURCES

An estimated change in flooding damages ranging from 

$32 million in damages to $2.5 billion in avoided damages.†

An estimated 29%-45% fewer severe and extreme droughts, 

with corresponding avoided damages to the agriculture 

sector of approximately $1.2-$1.4 billion.†

An estimated 40%-59% fewer severe and extreme droughts, 

with corresponding avoided damages to the agriculture 

sector of $2.6-$3.1 billion.†

An estimated $3.9-$54 billion in avoided damages due to 

water shortages.†

An estimated $11-$180 billion in avoided damages due to 

water shortages.†

DROUGHT

WATER 

SUPPLY AND

DEMAND

AGRICULTURE An estimated $1.5-$3.8 billion in avoided damages.

Estimated damages of $9.5-$9.6 billion. 

An estimated $6.6-$11 billion in avoided damages.

An estimated $520 million to $1.5 billion in avoided 

damages. 

An estimated avoided loss of 53% of coral in Hawaii, 

3.7% in Florida, and 2.8% in Puerto Rico. These avoided 

losses are valued at $1.4 billion.

CORAL 

REEFS

An estimated avoided loss of 35% of coral in Hawaii, 1.2% 

in Florida, and 1.7% in Puerto Rico. These avoided losses are 

valued at $1.2 billion. 

An estimated avoided loss of 11% of the U.S. oyster 

supply, 12% of the U.S. scallop supply, and 4.6% of the 

U.S. clam supply, with corresponding consumer benefits 

of $85 million.

An estimated avoided loss of 34% of the U.S. oyster 

supply, 37% of the U.S. scallop supply, and 29% of the 

U.S. clam supply, with corresponding consumer benefits 

of $380 million.

An estimated change in recreational fishing ranging from 

$13 million in avoided damages to $3.8 million in damages.†

An estimated $95-$280 million in avoided damages 

associated with recreational fishing.†

An estimated 2.1-2.2 million fewer acres burned and 

corresponding avoided wildfire response costs of $160-$390 

million.†

An estimated 6.0-7.9 million fewer acres burned and 

corresponding avoided wildfire response costs of $940 

million to $1.4 billion.†

SHELLFISH

FRESHWATER

FISH

WILDFIRE

An estimated 26-78 million fewer metric tons of carbon 

stored, and corresponding costs of $7.5-$23 billion.†

An estimated 1-26 million fewer metric tons of carbon stored, 

and corresponding costs of $880 million to $12 billion.†

CARBON 

STORAGE

FORESTRY
Regional Highlights

Estimates are presented in undiscounted 2014 dollars and rely upon climate projections from the IGSM-CAM climate model. Results using projections from other climate models, such as the MIROC model used 

throughout this report, could lead to variations in results for some sectors. 

SHELLFISH

Acidication in the Pacic Northwest is already aecting 

U.S. shellsh harvests. The U.S. supplies of oysters, 

clams, and scallops are projected to decline 45%, 32%, 

and 48%, respectively, in the Reference scenario in 

2100, compared to 11%, 3%, and 11%, respectively, in 

the Mitigation scenario. 

CARBON STORAGE

The Northwest is projected to experience a 6.1% 

decrease in terrestrial carbon storage in 2100 under the 

Reference scenario, compared to a 2.4% decrease in the 

Mitigation scenario. 

WATER SUPPLY AND DEMAND

California is projected to incur $4.5 billion in damages in 

2100 due to changes in water supply and demand in the 

Reference scenario. However, climate change under the 

Mitigation scenario is projected to result in an increase 

in welfare of $40 million. 

DROUGHT

In the Southwest, the number of severe and 

extreme droughts is projected to nearly quadruple 

by the end of the century in the Reference scenario 

compared to today. In the Mitigation scenario, the 

incidence of drought is not projected to change 

substantially from present day. 

WATER QUALITY

The Southwest is projected to experience water quality 

damages of approximately $1.8 billion in 2100 under the 

Reference scenario, compared to $470 million in the 

Mitigation scenario. 

CORAL REEFS

By the end of the century, Hawaii is projected to lose 

98% of its current shallow-water coral in the Reference 

scenario, compared to 64% in the Mitigation scenario. 

LABOR

In 2100, the Southwest is projected to experience a 

3.4% decrease in high-risk labor hours worked in the 

Reference scenario, compared to a decrease of 0.82% 

in the Mitigation scenario. 

INLAND FLOODING

In Texas, projected damages associated with the 

100-year ood event are $3.6 billion in 2100 under the 

Reference scenario, compared to $2.6 billion in the 

Mitigation scenario. 

WILDFIRE

In the Rocky Mountains, an estimated 1.9 million more 

acres are projected to burn in 2100 under the Reference 

scenario compared to today. In the Mitigation scenario, 

an estimated 1.5 million fewer acres are projected to 

burn compared to today. 

*

80

OVERVIEW OF RESULTS

This section highlights regional impacts of climate change in the U.S. For each sector, 

the map presents a region where substantial benefits of global GHG mitigation are projected 

to occur in the years 2050 or 2100.* Note that the geographic scale at which impacts are 

g g g
COASTAL PROPERTY

In 2100, the Tampa Bay area is projected to incur $2.8 

billion in damages from sea level rise and storm surge 

in the Reference scenario without adaptation. When 

adaptation measures are implemented, total costs in 

2100 fall to $500 million in the Reference scenario, 

compared to $450 million in the Mitigation scenario. 

AIR QUALITY

In 2100, areas of the Southeast are projected to 

experience an annual increase in ozone (O3) and ne 

particulate matter (PM2.5) of 0.7 ppb and 1 μg/m-3, 

respectively. In the Mitigation scenario, the levels of 

O3 and PM2.5 are projected to decrease by 120% and 

88%, respectively, compared to the Reference. 

AGRICULTURE

In the Southeast, yields of irrigated soybeans are 

projected to decrease 23% in 2100 under the Reference 

scenario. Under the Mitigation scenario, yields are 

projected to increase 4.7%.

URBAN DRAINAGE

In 2100, major cities analyzed in the Great Plains are 

estimated to incur $2.1 million per square mile in 

damages associated with urban drainage systems in the 

Reference scenario, compared to $750,000 per square 

mile in the Mitigation scenario.

EXTREME TEMPERATURE

Without mitigation, major cities in the Northeast from 

D.C. to Boston are projected to suer a combined 2,600 

extreme temperature mortalities in 2100, compared to 

190 in the Mitigation scenario. 

FRESHWATER FISH

Throughout the Appalachians, global GHG mitigation is 

projected to preserve approximately 70% of habitat for 

coldwater sh species (e.g., trout) that would otherwise 

be lost by the end of the century to rising temperatures 

from unmitigated climate change.

BRIDGES

In the Great Lakes region, approximately 520 bridges are 

projected to be vulnerable in 2100 under the Reference 

scenario, compared to 65 in the Mitigation scenario. 

ROADS

In 2100, the Great Plains region is projected to incur 

road damages of approximately $3.5 billion in the 

Reference scenario, compared to $1.1 billion in the 

Mitigation scenario. 

ELECTRICITY DEMAND

The South Central region is projected to experience 

a 2.0% to 4.2% increase in electricity demand under 

the Reference scenario in 2050. In the Mitigation 

scenario, the projected change in demand ranges 

from -1.4% to 1.6%. 

81

quantified in the sectoral analyses vary. For example, some of the analyses calculate impacts 

for large watersheds, while others use the National Climate Assessment regions. For purposes 

of highlighting regional impacts, this section approximates the regions. 
82

Conclusion

Understanding the potential timing and 

magnitude of climate change impacts in the U.S., and how 

they could be reduced or avoided through GHG mitigation, 

informs near- and long-term policies to address these risks. 

This report describes climate change damages in the U.S. 

across multiple sectors using a consistent set of scenarios 

and underlying assumptions.1

 In doing so, the study 

estimates the physical and economic risks of unmitigated 

climate change and the potential benefits to the U.S. of 

reducing global GHG emissions. Importantly, only a small 

portion of the impacts of climate change are estimated, 

and therefore this report captures just some of the total 

benefits of reducing GHGs. Looking across the large 

number of sectoral impacts described in this report, a 

number of key findings emerge:

• Unmitigated climate change is projected to profoundly 

affect human health, the U.S. economy, and the environment. The CIRA analyses demonstrate substantial and 

far-reaching changes over the course of the 21st century—

and particularly at the end of the century—with negative 

consequences for a large majority of the impact sectors. In 

addition, the analyses suggest that climate change impacts 

will not be uniform across the U.S., with most sectors 

showing a complex pattern of regional-scale impacts.

• Global action to mitigate GHG emissions is projected to 

reduce and avoid impacts in the U.S. that would otherwise occur in a future with continued high growth in 

GHG emissions. Importantly, these benefits are projected 

to increase over the course of the century. The analyses 

indicate that risks and impacts over the long term will not 

be avoided unless there is near-term action to significantly 

reduce GHG emissions. This report presents benefits for one 

illustrative global GHG mitigation scenario. More stringent 

emissions reductions would likely increase the benefits 

compared to the Reference scenario, and, conversely, less 

stringent reductions would likely decrease the benefits.

• Global GHG mitigation substantially reduces the risk of 

some extreme weather events and their subsequent 

impacts on human health and well-being by the end of 

the century. 

• Adaptation, especially in the infrastructure sector, can 

substantially reduce the estimated damages of climate 

change. For some impacts, such as those described in the 

Coastal Property section, well-timed adaptation can have a 

larger effect on reducing the risks of inaction than global 

GHG mitigation, particularly in the near term, highlighting 

the need for concurrent mitigation and adaptation actions.

• For some impacts, the effects of global GHG mitigation 

can vary across different projections of future climate.

This is particularly true for those sectors sensitive to changes 

in precipitation. For a few of these sectors, mitigation results 

in either benefits or disbenefits depending upon the 

simulated level of future precipitation.2

 By analyzing multiple 

types of impacts by sector, such as flooding, drought, water 

quality, and supply/demand in the water realm, and using a 

range of projections for future precipitation, a more comprehensive understanding of potential impacts and mitigation 

benefits is gained. 

©Getty Images/Compassionate Eye Foundation/Justin Pumfrey
83

This report represents a significant and important contribution to estimating the multi-sectoral benefits to the U.S. of global GHG 

mitigation. Although the results presented in this report do not provide comprehensive coverage of all potential impacts, the 

breadth and depth of the analyses will expand in future work within the CIRA project. Comprehensive and quantitative estimates of 

climate change impacts are not only needed to evaluate the benefits of GHG mitigation, but also to evaluate the cost-effectiveness 

of adaptation responses, and to support the improvement of other economic tools used to analyze climate and energy policies. 

Although CIRA only begins to capture many of the dynamics and uncertainties involved in impact analysis (e.g., interactions among 

sectoral models), this report provides timely and quantitative estimates as the science continues to advance in this field. Future work 

to refine projections of how GHG emissions affect the climate, and how these changes affect society and the environment, will 

improve our understanding and confidence in the estimates presented in this report. 

Observed Climate Change

Climate Change Indicators in the United States: EPA publishes a set of indicators describing trends related to the 

causes and effects of climate change. Focusing primarily on the U.S., this resource presents compelling evidence that 

many fundamental measures of observed climate are changing. 

Please visit EPA’s website for more information: http://www.epa.gov/climatechange/science/indicators/index.html

Climate Change Indicators 

in the United States, 2014 Third Edition

EPA’s Climate Change website (www.epa.

gov/climatechange) provides a good 

starting point for further exploration of 

this topic. From this site, you can:

• Read about greenhouse gas emissions, 

look through EPA’s greenhouse gas 

inventories, and explore EPA’s Greenhouse 

Gas Data Publication Tool. 

• Learn about EPA’s regulatory initiatives 

and partnership programs. 

• Find out what you can do at home, on 

the road, at work, and at school to help 

reduce greenhouse gas emissions.

Other government and nongovernment 

websites also provide information about 

climate change. Here are some examples:

• The Intergovernmental Panel on Climate 

Change (IPCC) is the international 

authority on climate change science. The 

IPCC website (www.ipcc.ch/index.htm) 

summarizes the current state of scientific 

knowledge about climate change and 

includes links to their most recent Fifth 

Assessment Report.

• The U.S. Global Change Research Program 

(www.globalchange.gov) is a multi-agency 

effort focused on improving our understanding of the science of climate change 

and its potential impacts on the U.S. 

through reports like the National Climate 

Assessment.

Finally, other groups are working to 

estimate the impacts of climate change in 

the U.S. and/or other world regions. Here 

are some examples:

• The Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP; https://

www.pik-potsdam.de/research/

climate-impacts-and-vulnerabilities/

research/rd2-cross-cutting-activities/

isi-mip) is an international, communitydriven modelling effort bringing together 

impact models across sectors and scales.

• The Risky Business Project (http://

riskybusiness.org/) focuses on quantifying 

and publicizing the economic risks 

from the impacts of a changing climate 

in the U.S.

• The European Commission Joint Research 

Centre’s PESETA II project (Projection of 

Economic impacts of climate change in 

Sectors of the European Union based on 

bottom-up Analysis; http://peseta.jrc.ec.

europa.eu/) is a consistent multi-sectoral 

assessment of the impacts of climate 

change in Europe. 

• AVOID (http://www.metoffice.gov.uk/

avoid/) is a research program that 

provides modeling and scientific information to the U.K. Government on avoiding 

dangerous climate change brought on by 

greenhouse gas emissions.

• The project on the Benefits of Reduced 

Anthropogenic Climate Change (BRACE; 

https://chsp.ucar.edu/brace) focuses on 

differences in impacts resulting from 

climate change driven by high and low 

emissions scenarios.

Additional Climate Change Resources

Next Steps
84

Endnotes

2007. Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations (Part 

A) and Review of Integrated Scenario Development and Application (Part B). A Report 

by the U.S. Climate Change Science Program and the Subcommittee on Global Change 

Research, Clarke, L., J. Edmonds, J. Jacoby, H. Pitcher, J. Reilly, R. Richels, ... and M. 

Webster (Authors). Washington, DC: Department of Energy; Kriegler, E., J.P. Weyant, 

G.J. Blanford, V. Krey, L. Clarke, J. Edmonds, ... and D.P van Vuuren. 2013. The role of 

technology for achieving climate policy objectives: overview of the EMF 27 study 

on global technology and climate policy strategies. Climatic Change. DOI:10.1007/

s10584-013-0953-7; and Kriegler, E., K. Riahi, N. Bauer, V.J. Schwanitz, N. Petermann, 

V. Bosetti, ... and O. Edenhofer. 2015. Making or breaking climate targets: the AMPERE 

study on staged accession scenarios for climate policy. Technological Forecast and 

Social Change. DOI:10.1016/j.techfore.2013.09.021; Energy Economics. Volume 31, Supplement 2, Pages S63-S306 (2009). International, U.S. and E.U. Climate Change Control 

Scenarios: Results from EMF 22. Edited by Leon Clarke, Christoph Böhringer and Tom 

F. Rutherford.

7 Example of co-benefit literature: IPCC. 2014. Climate Change 2014: Mitigation of 

Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the 

Intergovernmental Panel on Climate Change, Edenhofer, O., R. Pichs-Madruga, Y. Sokona, 

E. Farahani, S. Kadner, K. Seyboth, ... and J.C. Minx, Eds. New York, NY: Cambridge 

University Press.

SUMMARY OF KEY FINDINGS

1 This section draws upon conclusions described in the overview paper for the CIRA 

special issue: Waldhoff, S., J. Martinich, M. Sarofim, B. DeAngelo, J. McFarland, L. Jantarasami, K. Shouse, A. Crimmins, S. Ohrel, and J. Li. 2014. Overview of the Special Issue: 

A multi-model framework to achieve consistent evaluation of climate change impacts 

in the United States. Climatic Change. DOI:10.1007/s10584-014-1206-0.

2 Changes in extreme weather events across the CIRA scenarios are discussed in more 

detail in: Monier, E. and X. Gao. 2014. Climate change impacts on extreme events in 

the United States: an uncertainty analysis. Climatic Change. DOI:10.1007/s10584-013-

1048-1.

3 See, for example: 1) Ciscar, J-C, A. Iglesias, L. Feyen, L. Szabó, D. Van Regemorter, B. 

Amelung, ... and A. Soria. 2011. Physical and economic consequences of climate 

change in Europe. Proc Natl Acad Sci USA. DOI:10.1073/pnas.1011612108; 2) Frumhoff, 

P.C., J.J. McCarthy, J.M. Melillo, S.C. Moser, and D.J. Wuebbles. 2007. Confronting 

climate change in the U.S. Northeast: science, impacts, and solutions. Report of the 

Northeast Climate Impacts Assessment. Cambridge, MA: Union of Concerned Scientists; and 3)Hayhoe, K., D. Cayan, C.B. Field, P.C. Frumhoff, E.P. Maurer, N.L. Miller, ... 

and J.H. Verville. 2004. Emissions pathways, climate change, and impacts on California. 

Proc Natl Acad Sci USA. DOI:10.1073/pnas.0404500101.

4 Throughout the report, future benefits—i.e., the annual time series of avoided costs—

are discounted at a 3% rate to reflect their value in the present day, which is defined as 

the year 2015 in this report. In short, discounting provides an equal basis to compare 

the value of benefits (and costs) that occur in different time periods. The discount rate 

itself reflects the trade-off between consumption today and consumption tomorrow, 

meaning that with a positive discount rate, benefits that occur today are worth more 

than they would be tomorrow. A higher discount rate implies a greater preference 

for present-day consumption and a lower present value of future damages. A lower 

discount rate implies a greater value on future damages. That is, the present value 

of future damages calculated at a 5% rate will be lower than those calculated using 

a 3% rate. There are many ways to select a discount rate and little consensus about 

which discount rate is most appropriate, particularly when assessing benefits that span 

multiple generations. Therefore, we selected 3%, a commonly employed rate in the 

climate impacts and benefits literature. This rate was also used to calculate two of the 

U.S. Government’s four Social Cost of Carbon estimates (including the central value), 

which estimate climate damages that occur over long time horizons. In particular, the 

U.S. Government review found that it was consistent with estimates provided in the 

economics literature and noted that 3% roughly corresponds to the after-tax riskless 

interest rate. For a detailed discussion on discount rate selection, please see the Social 

Cost of Carbon Technical Support Document, available at http://www.epa.gov/oms/

climate/regulations/scc-tsd.pdf.

CIRA FRAMEWORK

1 Martinich, J., J. Reilly, S. Waldhoff, M. Sarofim, and J. McFarland, Eds. 2015. Special Issue 

on “A Multi-Model Framework to Achieve Consistent Evaluation of Climate Change 

Impacts in the United States.” Climatic Change.

2 Melillo, J.M., T.C. Richmond, and G.W. Yohe, Eds. 2014. Climate Change Impacts in the 

United States: The Third National Climate Assessment. Appendix 5: Scenarios and 

Models. U.S. Global Change Research Program. DOI:10.7930/J0Z31WJ2.

3 While beyond the scope of this report, analyses of the adequacy of current GHG 

mitigation efforts, at domestic and global scales, relative to the magnitude of climate 

change risks are described in the assessment literature. See, for example: 1) Jacoby, 

H. D., A. C. Janetos, R. Birdsey, J. Buizer, K. Calvin, F. de la Chesnaye, ... and J. West. 

2014. Ch. 27: Mitigation. Climate Change Impacts in the United States: The Third National 

INTRODUCTION

1 Martinich, J., J. Reilly, S. Waldhoff, M. Sarofim, and J. McFarland, Eds. 2015. Special Issue 

on “A Multi-Model Framework to Achieve Consistent Evaluation of Climate Change 

Impacts in the United States.” Climatic Change.

2 While beyond the scope of this report, analyses of the adequacy of current GHG mitigation efforts, at domestic and global scales, relative to the magnitude of climate change 

risks are described in the assessment literature. See: 1) Jacoby, H. D., A. C. Janetos, R. 

Birdsey, J. Buizer, K. Calvin, F. de la Chesnaye, ... and J. West. 2014. Ch. 27: Mitigation. 

In Climate Change Impacts in the United States: The Third National Climate Assessment,

J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds. U.S. Global Change Research 

Program. DOI:10.7930/J0C8276J; and 2) IPCC. 2014. Climate Change 2014: Mitigation 

of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the 

Intergovernmental Panel on Climate Change, Edenhofer, O., R. Pichs-Madruga, Y. Sokona, 

E. Farahani, S. Kadner, K. Seyboth, ... and J.C. Minx, Eds. New York, NY: Cambridge 

University Press.

3 United Nations Framework Convention on Climate Change. 2013. Report of the 

Conference of the Parties on its nineteenth session, held in Warsaw from November 

11-23, 2013. Part one: Proceedings. FCCC/CP/2013/10.

4 CIRA uses sectoral impact models driven by consistent climate and socioeconomic 

scenarios to analyze both physical impacts and economic damages of climate change 

at national and regional scales in the U.S. This unique multi-model design allows for 

‘apples-to-apples’ comparisons of impacts and benefits of global GHG mitigation 

across sectors, but is not comprehensive in scope. The impact estimates presented 

in this report are consistent with the key findings of the U.S. Global Change Research 

Program’s Third National Climate Assessment. See Section H of the Technical Appendix 

for this report for a more detailed comparison of key findings.

5 The Social Cost of Carbon (SCC) is a metric that estimates the economic value of 

impacts associated with the global emission of one ton of carbon dioxide (CO2) or, conversely, the economic benefit of avoiding or reducing one ton of CO2 (in dollars per ton 

of CO2 in a given year). Unlike CIRA, the SCC draws from models of anticipated climate 

change impacts and benefits across the entire globe, not just for the U.S. The SCC has 

already been applied to estimate the global economic benefits of CO2 emission reductions from certain U.S. regulations, but it does not provide explicit information about 

how the actual physical impacts in specific sectors of the U.S. may change over time 

and space. For more information, see: U.S. Interagency Working Group on the Social 

Cost of Carbon. 2013. Technical support document: Technical update of the social cost 

of carbon for regulatory impact analysis under Executive Order 12866.

6 The CIRA project estimates the benefits to the U.S. of global action on climate change. 

Importantly, the costs of GHG mitigation are not assessed in the project. As such, the 

analysis presented in the report does not constitute a cost-benefit assessment of climate policy. The costs of reducing GHG emissions have been well examined in the scientific literature (see references below), where recent assessments have used multiple 

economic models to investigate the sensitivity of costs to policy design, assumptions 

about the availability of low carbon-emitting energy technologies, socioeconomic 

and demographic changes, and other important sources of uncertainty. The one 

instance in the CIRA project where mitigation costs are considered is in the electricity 

sector (see Electricity section for details). For that sector, the impact of climate change 

on costs to the U.S. electric power system is estimated along with the costs associated 

with GHG emission reductions in that sector. See: Fawcett, A., L. Clarke, and J. Weyant. 

2013. Introduction to EMF 24. The Energy Journal. DOI:10.5547/01956574.35.SI1.1; 

White House Council of Economic Advisors. 2014. The Cost of Delaying Action to 

Stem Climate Change. Executive Office of the President of the United States; CCSP. 
85

Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. 

Global Change Research Program. DOI:10.7930/J0C8276J; and 2) IPCC. 2014. Climate 

Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the 

Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Edenhofer, 

O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, ... and J.C. Minx, Eds. 

New York, NY: Cambridge University Press.

4 A third emissions scenario was applied in most CIRA sectoral analyses, as described 

and presented in the research papers supporting the project. In 2100, this scenario, 

called Policy 4.5 in the CIRA project, achieves a radiative forcing of approximately 

4.2 W/m2

 with an atmospheric GHG concentration of 600 ppm (CO2 equivalent). This 

radiative forcing value reflects GHG radiative forcing (i.e., not including aerosols) and 

uses a baseline of 1750 (both of which are necessary adjustments for comparing to the 

IPCC RCPs), therefore making it slightly different than the value reported previously in 

the CIRA literature (4.5 W/m2

).

5 Paltsev, S., J.M. Reilly, H.D. Jacoby, R.S. Eckaus, J. McFarland, M. Sarofim, M. Asadoorian, 

and M. Babiker. 2005. The MIT Emissions Prediction and Policy Analysis (EPPA) model: 

version 4. Report 125, MIT Joint Program on the Science and Policy of Global Change. 

http://globalchange.mit.edu/publications. 

6 By 2100 (using a baseline of 1750), the CIRA Reference scenario has a total radiative 

forcing of 9.8 W/m2

, which appears considerably larger than RCP 8.5. However, the 

contrast is primarily due to differences in how forcing is calculated by different GCMs 

used in developing those scenarios. The IGSM radiation code was derived from the 

GISS climate model, and therefore when calculating radiative forcing due to increased 

concentrations in the IGSM, forcing functions fit to the GISS code were used rather 

than the more common approach of using simplified equations, such as those defined 

in IPCC’s Third Assessment Report. Using these simplified equations, total radiative 

forcing for the CIRA Reference is 8.6 W/m2

, and 3.2 W/m2 for the Mitigation scenario. 

Other differences between the IGSM scenarios and the RCPs are due to differences in 

anthropogenic emissions, natural emissions responses to warming, and atmospheric 

chemistry.

7 Paltsev, S., E. Monier, J. Scott, A. Sokolov, and J. Reilly. 2013. Integrated economic and 

climate projections for impact assessment. Climatic Change. DOI:10.1007/s10584-

013-0892-3. We also note that the Reference scenario is calibrated using historic GHG 

emissions through 2010; see Paltsev et al. (2013) for more information. 

8 Paltsev, S., E. Monier, J. Scott, A. Sokolov, and J. Reilly. 2013. Integrated economic and 

climate projections for impact assessment. Climatic Change. DOI:10.1007/s10584-013-

0892-3. 

9 Radiative forcing (including CO2, CH4, N2O, PFCs, SF6, HFCs, CFCs and HCFCs) for the 

Reference and Mitigation scenarios (see Paltsev et al. 2013), compared to the four RCPs 

(data from Meinshausen et al. 2011). The negative forcing effects of aerosols are not 

included. See: Meinshausen, M., S. J. Smith, K. V. Calvin, J. S. Daniel, M. L. T. Kainuma, J.-

F. Lamarque, ... and D. van Vuuren. 2011. The RCP Greenhouse Gas Concentrations and 

their Extension from 1765 to 2300. Climatic Change. DOI:10.1007/s10584-011-0156-z.

10 Please see the literature underlying the CIRA project for information on post-processing 

and bias-correction of climate outputs for use in the sector analyses. 

11 Monier, E., X. Gao, J.R. Scott, A.P. Sokolov, and C.A. Schlosser. 2014. A framework for 

modeling uncertainty in regional climate change. Climatic Change. DOI:10.1007/

s10584-014-1112-5.

12 Adaptive actions modeled in the sectoral analyses of this report should not be interpreted as recommendations of these particular strategies. 

13 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, ... and R. Somerville. 

2014. Chapter 2: Our Changing Climate. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, R.C. Richmond, and G. W. Yohe, Eds. 

U.S. Global Change Research Program. DOI:10.7930/J0KW5CXT. 

14 The U.S. Global Change Research Program’s National Climate Assessment (NCA) results 

are reported for the RCP 8.5 scenario, using a range (5th-95th percentile) of results from 

a suite of climate models, adjusted to match the same baseline period used for the 

IGSM-CAM model. The NCA also presents results from the older SRES models: the A2 

scenario from SRES was projected to warm by 5-8°F by 2100.

15 Future climate change depends on the response of the global climate system to rising 

GHG concentrations (i.e., how much temperatures will rise in response to a given 

increase in atmospheric CO2). Assumptions about this relationship are referred to as 

climate sensitivity.

16 IPCC. 2014. Summary for Policymakers. In: Climate Change 2014, Mitigation of Climate 

Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. 

Farahani, S. Kadner, K. Seyboth, ... and J.C. Minx, Eds. New York, NY.

17 IPCC. 2013. Summary for Policymakers. In: Climate Change 2013: The Physical Science 

Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, 

J. Boschung, ... and P.M. Midgley, Eds. New York, NY. 

18 The estimate of warming from the historical period (0.65°C) used in Figure 1 of the 

Temperature Projections section is slightly less than the IPCC’s estimate of 0.85°C because the former utilizes a 30-yr average (1980-2009) to represent the current period.

19 Warming from the historical period (0.65°C) comparing 1880-1909 to 1980-2009 was 

calculated using the NOAA Global Historical Climatology Network GHCN-3 dataset of 

Global Land and Ocean Temperature Anomalies (available at http://www.ncdc.noaa.

gov/cag/time-series/global/globe/land_ocean/ytd/12/1880-2014.csv). Combined 

with this historical warming, the 2°C target (relative to preindustrial) is equivalent to a 

warming of 2.43°F (relative to the 1980-2009 baseline period), as shown in Figure 1 of 

the Temperature Projections section. This value is consistent with the average of the 

last two decades of the century (2081-2100) for the CIRA Mitigation scenario: 2.23°F. 

20 Monier, E. and X. Gao. 2014. Climate change impacts on extreme events in the United 

States: an uncertainty analysis. Climatic Change, DOI:10.1007/s10584-013-1048-1.

21 Ibid.

22 The CIRA sea level rise scenarios are at the high end of projected sea level rise rates for 

similar scenarios based on recent publications (Horton et al. 2014, Kopp et al. 2014). 

However, we also note that the effect of GHG mitigation on reducing the increase in 

future sea level was found to be larger in these studies. The use of a smaller sea level 

rise would likely lead to a decrease in total damages, but a larger reduction in sea level 

rise due to the Mitigation scenario would likely yield larger economic benefits than 

those presented in this report. See: 1) Horton, B.J., S. Rahmstorf, S.E. Engelhart, and A.C. 

Kemp. 2014. Expert assessment of sea-level rise by AD 2100 and AD 2300. Quaternary 

Science Reviews. DOI:10.1016/j.quascirev.2013.11.002; and 2) Kopp, R.E., R.M. Horton, 

C.M. Little, J.X. Mitrovica, M. Oppenheimer, D.J. Rasmussen, B.H.Strauss, and C. Tebaldi. 

2014. Probabilistic 21st and 22nd century sea-level projections at a global network of 

tide-gauge sites. Earth’s Future. DOI:10.1002/2014EF000239. 

23 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, ... and R. Somerville. 

2014. Chapter 2: Our Changing Climate. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, R.C. Richmond, and G. W. Yohe, Eds. 

U.S. Global Change Research Program. DOI:10.7930/J0KW5CXT. 

24 Meier, M.F., M.B. Dyurgerov, U.K. Rick, S. O’Neel, W.T. Pfeffer, R. S. Anderson, S.P. Anderson, and A.F. Glazovsky. 2007. Glaciers dominate eustatic sea-level rise in the 21st 

century. Science. DOI:10.1126/science.1143906.

25 Vermeer, M., and S. Rahmstorf. 2009. Global sea level linked to global temperature. 

Proceedings of the National Academy of Sciences. DOI:10.1073/pnas.0907765106. 

26 The CIRA sea level rise projections were estimated following the methodology of 

Vermeer and Rahmstorf (2009). The methodology of Vermeer and Rahmstorf builds 

off that from Rahmstorf (2007) and is described in detail in those papers. In short, projections were estimated using an empirical relationship between global air temperature and sea level change, including contributions from glaciers and ice sheets. This 

relationship was then applied to the ambient average air temperature trajectories from 

the IGSM-CAM model (Paltsev et al. 2013) to project future sea levels. 

27 Paltsev, S., E. Monier, J. Scott, A. Sokolov, and J. Reilly. 2013. Integrated economic and 

climate projections for impact assessment. Climatic Change. DOI:10.1007/s10584-013-

0892-3.

28 For each scenario, a site-specific, fixed annual rate of land subsidence or uplift is 

estimated, which combines with the SLR scenario to yield site-specific relative sea 

level rise. Historical vertical land movement is based on annual average measurements 

from National Oceanic and Atmospheric Administration (NOAA) tide gauge data from 

68 sites with at least 25 years of continuous measurements and linear interpolation of 

subsidence rates for all cells that lie between the selected sites. An estimated 1.7 mm/

year is subtracted from the tide gauge annual average to account for the component 

of relative sea level rise that is accounted for by 20th century sea level change, yielding 

the site-specific subsidence/uplift rate.

29 The CIRA approach for calculating relative sea level rise assumes that the difference 

in rate between global and relative sea level change will continue into the future. 

Because some physical processes (e.g., changes in differential ocean heating) will likely 

change in the future at rates different from what is reflected in historical tide gauge 

data, the CIRA approach does not capture all of these dynamics. For more information, see: Neumann, J., D. Hudgens, J. Herter, and J. Martinich. 2010. The Economics of 

Adaptation along Developed Coastlines. Wiley Interdisciplinary Reviews: Climate Change. 

DOI:10.1002/wcc.90.

30 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, ... and R. Somerville. 

2014. Appendix 3: Climate Science Supplement. Climate Change Impacts in the United 

States: The Third National Climate Assessment, J.M. Melillo, T.C. Richmond, and G.W. 

Yohe, Eds., U.S. Global Research Program. DOI:10.7930/J0KS6PHH. 

31 Ibid.

32 Monier, E., X. Gao, J.R. Scott, A.P. Sokolov, and C.A. Schlosser. 2014. A framework for 

modeling uncertainty in regional climate change. Climatic Change. DOI:10.1007/

s10584-014-1112-5.
86

Endnotes

33 Ibid.

34 All three CIRA emissions scenarios contain the same level of global and U.S. population 

change over time. 

35 For each emissions scenario, values represent the ensemble mean of the five 

IGSM-CAM initializations using a climate sensitivity of 3°C.

36 IPCC. 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working 

Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change,

Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, ... and P.M. Midgley, Eds. New York, NY: Cambridge University Press.

37 A climate sensitivity of 6°C is considered “low probability” when considering feedbacks 

expected over the next century. However, there is literature suggesting that slower 

feedbacks involving ice sheet and vegetation changes can lead to higher “Earth 

System Sensitivity” on timescales of several centuries, such that a sensitivity of 6°C will 

have a higher probability on these longer timescales. Additional feedbacks including 

methane and carbon cycles are not included in the climate sensitivity definition.

38 Mapped values represent the ensemble mean of the five IGSM-CAM initializations with 

different climate sensitivities under the Reference scenario. 

39 All five maps assume a climate sensitivity of 3°C under the Reference scenario. 

40 A method by which the average change produced by running a climate model is 

combined with the specific geographic pattern of change calculated from a different 

model in order to approximate the result that would be produced by the second 

model. 

41 Please refer to: 1) Monier, E., X. Gao, J.R. Scott, A.P. Sokolov, and C.A. Schlosser. 2014. A 

framework for modeling uncertainty in regional climate change. Climatic Change. DOI: 

10.1007/s10584-014-1112-5; and 2) Flato, G., J. Marotzke, B. Abiodun, P. Braconnot, 

S.C. Chou, W. Collins, ... and M. Rummukainen. 2013. Evaluation of Climate Models. In: 

Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the 

Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Stocker, T.F., 

D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. 

Midgley, Eds. New York, NY: Cambridge University Press.

42 Monier, E., X. Gao, J.R. Scott, A.P. Sokolov, and C.A. Schlosser. 2014. A framework for 

modeling uncertainty in regional climate change. Climatic Change. DOI:10.1007/

s10584-014-1112-5.

43 This section draws upon conclusions described in the overview paper for the CIRA 

special issue: Waldhoff, S., J. Martinich, M. Sarofim, B. DeAngelo, J. McFarland, L. Jantarasami, K. Shouse, A. Crimmins, S. Ohrel, and J. Li. 2014. Overview of the Special Issue: 

A multi-model framework to achieve consistent evaluation of climate change impacts 

in the United States. Climatic Change. DOI:10.1007/s10584-014-1206-0.

44 For more information on these types of impacts, see: National Research Council. 

2013. Abrupt Impacts of Climate Change: Anticipating Surprises. Washington, DC: The 

National Academies Press. 

45 Monier, E., X. Gao, J.R. Scott, A.P. Sokolov, and C.A. Schlosser. 2014. A framework for 

modeling uncertainty in regional climate change. Climatic Change. DOI:10.1007/

s10584-014-1112-5.

46 Ongoing studies are investigating the influence of structural uncertainties across 

sectoral impact models. See: Huber, V., H.J. Schellnhuber, N.W. Arnell, K. Frieler, A.D. 

Friend, D. Gerten, ... and L. Warszawski. 2014. Climate impact research: beyond patchwork. Earth System Dynamics. DOI:10.5194/esd-5-399-2014.

47 For a discussion of interactions among the energy, water, and land use sectors, see: 

Hibbard, K., T. Wilson, K. Averyt, R. Harriss, R. Newmark, S. Rose, E. Shevliakova, and V. 

Tidwell. 2014. Ch. 10: Energy, Water, and Land Use. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, 

and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/J0JW8BSF.

SECTORS

Health

1 The economic estimates described throughout this report are presented in constant 

2014 dollars. The literature underlying the CIRA project presents results primarily in 

2005 dollars. This should be noted when comparing the results presented in this report 

with those in the CIRA literature. Dollar years were adjusted using the U.S. Bureau of 

Economic Analysis’ Implicit Price Deflators for Gross Domestic Product. Source: U.S. 

Bureau of Economic Analysis, Table 1.1.9 Implicit Price Deflators for Gross Domestic 

Product, March 27, 2015, http://www.bea.gov/national/index.htm. 

2 Throughout the report, future benefits—i.e., the annual time series of avoided costs—

are discounted at a 3% rate to reflect their value in the present day, which is defined as 

the year 2015 in this report. In short, discounting provides an equal basis to compare 

the value of benefits (and costs) that occur in different time periods. The discount rate 

itself reflects the trade-off between consumption today and consumption tomorrow, 

meaning that with a positive discount rate, benefits that occur today are worth more 

than they would be tomorrow. A higher discount rate implies a greater preference 

for present-day consumption and a lower present value of future damages. A lower 

discount rate implies a greater value on future damages. That is, the present value 

of future damages calculated at a 5% rate will be lower than those calculated using 

a 3% rate. There are many ways to select a discount rate and little consensus about 

which discount rate is most appropriate, particularly when assessing benefits that 

span generations. Therefore, we selected 3%, a commonly employed rate in the 

climate impacts and benefits literature. This rate was also used to calculate two of the 

U.S. Government’s four Social Cost of Carbon estimates (including the central value), 

which estimate climate damages that occur over long time horizons. In particular, the 

U.S. Government review found that it was consistent with estimates provided in the 

economics literature and noted that 3% roughly corresponds to the after-tax riskless 

interest rate. For a detailed discussion on discount rate selection, please see the Social 

Cost of Carbon Technical Support Document, available at http://www.epa.gov/oms/

climate/regulations/scc-tsd.pdf. 

3 IPCC. 2014. Summary for Policymakers. In: Climate Change 2014: Impacts, Adaptation, 

and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II 

to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Field, 

C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, ... and L.L. White, 

Eds. New York, NY: Cambridge University Press.

4 Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, ... and L. Ziska. 2014. 

Ch. 9: Human Health. Climate Change Impacts in the United States: The Third National 

Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. 

Global Change Research Program. DOI:10.7930/J0PN93H5.

5 U.S. Environmental Protection Agency. 2012. Ground Level Ozone: Health Effects. 

http://www.epa.gov/groundlevelozone/health.html. 

6 Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, ... and L. Ziska. 2014. 

Ch. 9: Human Health. Climate Change Impacts in the United States: The Third National 

Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. 

Global Change Research Program. DOI:10.7930/J0PN93H5.

7 Ibid.

8 U.S. Environmental Protection Agency. 2013. Integrated Science Assessment of Ozone 

and Related Photochemical Oxidants (Final Report). EPA/600/R-10/076F.

9 U.S. Environmental Protection Agency. 2009. Integrated Science Assessment for 

Particulate Matter (Final Report). EPA/600/R-08/139F. 

10 A climate-induced drop in ozone is caused by increased atmospheric water vapor 

under a warmer climate. Higher humidity shortens the atmospheric lifetime of ozone 

in low-NOx (typically less densely-populated) conditions by enhancing its breakdown. 

Projected reductions in ground-level concentrations over the northern and western 

parts of the country are largely driven by this decline in background ozone.

11 For comparison, the current national 8-hour daily maximum ozone standard is 75 parts 

per billion: primary and secondary standard in the form of annual fourth-highest daily 

maximum 8-hour concentration averaged over 3 years. 

12 Changes in ozone and PM2.5 concentrations in the Risks of Inaction section and in 

Figures 1 and 2 are not population-weighted. 

13 Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, ... and L. Ziska. 2014. Ch. 

9: Human Health. Climate Change Impacts in the United States: The Third National Climate 
87

Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global 

Change Research Program. DOI:10.7930/J0PN93H5.

14 The ranges in mortality estimates are based on ensemble means and reflect the 95% 

confidence interval in concentration response functions. See Garcia-Menendez et al. 

(2015) for more information. 

15 An additional mortality valuation approach using years of life saved is provided in 

Garcia-Menendez et al. (2015). 

16 Reductions in PM2.5 largely drive the change in mortality. However, the contribution 

of ozone pollution to these estimates increases towards the end of the century and 

accounts for 40% of the projected life years saved by 2100. See Garcia-Menendez et al. 

(2015) for more information. 

17 For example: 1) Thompson, T.M., Rausch S., Saari R.K., and Selin N.E. 2014. A systems approach to evaluating the air quality co-benefits of U.S. carbon policies. Nature Climate 

Change. DOI: 10.1038/nclimate2342; 2) West, J., S. Smith, R. Silva, V. Naik, Y. Zhang, 

Z. Adelman, ... and J. Lamarque. 2013. Co-benefits of mitigating global greenhouse 

gas emissions for future air quality and human health. Nature Climate Change. DOI: 

10.1038/nclimate2009; and 3) U.S. Environmental Protection Agency. 2014. Regulatory 

Impact Analysis for the Proposed Carbon Pollution Guidelines for Existing Power Plants 

and Emission Standards for Modified and Reconstructed Power Plants. Office of Air 

Quality Planning and Standards, Health & Environmental Impacts Division, Air Economics Group. Research Triangle Park, North Carolina. 

18 IPCC. 2014. Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate 

Change, Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 

... and J.C. Minx, Eds. New York, NY: Cambridge University Press.

19 Fine particulate matter constituents analyzed include sulfate, elemental carbon, organic aerosol and ammonium nitrate. 

20 Changes in mortality are estimated by applying the differences in daily-maximum 

8-hour ozone (8-hr-max ozone) between May and September and daily average PM2.5

to the concentration response functions. 

21 At the time of this report’s release, the U.S. Environmental Protection Agency’s 

Guidelines for Preparing Economic Analyses report recommends a VSL of $7.9 million 

(2008$), based on 1990 incomes. To create a VSL using 2014$ and based on 2010 

incomes, the standard value was adjusted for inflation using BEA implicit price inflator 

for gross domestic product and for income growth adjustment based on a method 

described in the user manual of EPA’s BenMAP model (pg. 109). The resulting value, 

$9.45 million for 2010 (2014$), was adjusted to future years by assuming an elasticity of 

VSL to GDP per capita of 0.4. Projections of GDP and population for the CIRA Reference 

scenario were employed. Using this approach, the VSL in 2050 is estimated at $12.53 

million and $16.39 million in 2100. Finally, we note that the VSL values used in this 

report differ slightly from those used in Garcia-Menendez et al. (2015), which therefore 

affects the valuation estimates reported in each. Sources: 1) U.S. Environmental Protection Agency. 2014. Guidelines for Preparing Economic Analyses. National Center for Environmental Economics. http://yosemite.epa.gov/ee/epa/eerm.nsf/vwAN/EE-0568-52.

pdf/$file/EE-0568-52.pdf; 2) U.S. Bureau of Economic Analysis, Table 1.1.9 Implicit Price 

Deflators for Gross Domestic Product, March 27, 2015, http://www.bea.gov/national/

index.htm; and 3) U.S. Environmental Protection Agency. 2012. BenMAP Users Manual. 

Office of Air Quality Planning and Standards.

22 Garcia-Menendez, F., R.K. Saari, E. Monier, and N.E. Selin. (2015) U.S. air quality and 

health benefits from avoided climate change under greenhouse gas mitigation. Environmental Science & Technology. DOI:10.1021/acs.est.5b01324.

23 Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, ... and L. Ziska. 2014. Ch. 

9: Human Health. Climate Change Impacts in the United States: The Third National Climate 

Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global 

Change Research Program. DOI:10.7930/J0PN93H5.

24 U.S. Environmental Protection Agency. 2014. Climate Change Indicators in the United 

States. Third edition. EPA 430-R-14-004. www.epa.gov/climatechange/indicators. 

25 Ibid.

26 Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, ... and L. Ziska. 2014. Ch. 

9: Human Health. Climate Change Impacts in the United States: The Third National Climate 

Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global 

Change Research Program. DOI:10.7930/J0PN93H5.

27 Ibid.

28 Average results for the 49 cities included in the study. 

29 See Mills et al. (2014) and Bierwagen et al. (2010) for details on usage of ICLUS population projections. Sources: 1) Mills, D., J. Schwartz, M. Lee, M. Sarofim, R. Jones, M. 

Lawson, M. Duckworth, and L. Deck. 2014. Climate Change Impacts on Extreme Temperature Mortality in Select Metropolitan Areas in the United States. Climatic Change. 

DOI: 10.1007/s10584-014-1154-8; and 2) Bierwagen, B.G., D.M. Theobald, C.R. Pyke, A. 

Choate, P. Groth, J.V. Thomas, and P. Morefield. 2010. National housing and impervious

surface scenarios for integrated climate impact assessments. Proc Natl Acad Sci. DOI: 

10.1073/pnas.1002096107.

30 At the time of this report’s release, the U.S. Environmental Protection Agency’s 

Guidelines for Preparing Economic Analyses report recommends a VSL of $7.9 million 

(2008$), based on 1990 incomes. To create a VSL using 2014$ and based on 2010 

incomes, the standard value was adjusted for inflation using BEA implicit price inflator 

for gross domestic product and for income growth adjustment based on a method 

described in the user manual of EPA’s BenMAP model (pg. 109). The resulting value, 

$9.45 million for 2010 (2014$), was adjusted to future years by assuming an elasticity of 

VSL to GDP per capita of 0.4. Projections of GDP and population for the CIRA Reference 

scenario were employed. Using this approach, the VSL in 2050 is estimated at $12.53 

million and $16.39 million in 2100. Finally, we note that the VSL values used in this 

report differ slightly from those used in Garcia-Menendez et al. (2015), which therefore 

affects the valuation estimates reported in each. Sources: 1) U.S. Environmental Protection Agency. 2014. Guidelines for Preparing Economic Analyses. National Center for Environmental Economics. http://yosemite.epa.gov/ee/epa/eerm.nsf/vwAN/EE-0568-52.

pdf/$file/EE-0568-52.pdf; 2) U.S. Bureau of Economic Analysis, Table 1.1.9 Implicit Price 

Deflators for Gross Domestic Product, March 27, 2015, http://www.bea.gov/national/

index.htm; and 3) U.S. Environmental Protection Agency. 2012. BenMAP Users Manual. 

Office of Air Quality Planning and Standards.

31 The approach described in Mills et al. (2014) was updated in several ways to develop 

the results presented here. First, the analysis was expanded from 33 cities to encompass a total of 49 out of 50 of the cities (excluding Honolulu) analyzed in the Medina-Ramon and Schwartz (2007) paper that was the foundation of the Mills et al. (2014) 

work. Medina-Ramon and Schwartz did not calculate heat mortality response functions 

for cities where the minimum temperature for the 99 percentile hottest day was equal 

to or below 20°C (8 cities), or cold mortality response functions where the maximum 

temperature for the 1 percentile coldest day was greater than or equal to 10°C (7 

cities), and the choice was made in the Mills et al. (2014) work to not include those 

cities in the projections of future mortality. In a warming climate, cities that were too 

warm to meet the criteria for the cold threshold will continue to be too warm, so the 

lack of a cold mortality response function will not make a difference. However, most 

of the cities that were too cool to meet the criteria for the hot threshold are expected 

to warm enough that their 99 percentile hottest days will exceed 20°C in the future. 

Therefore, inclusion of cities without a heat mortality response function will lead to an 

underestimate of the change in future mortality in those cities, and therefore an underestimate of the benefit of GHG mitigation. However, inclusion of a wider range of cities 

gives a more complete picture of impacts in the U.S. There were a couple of additional 

updates. The first involved limiting the analysis to the actual counties corresponding to 

the cities specified in Medina-Ramon and Schwartz, rather than the MSAs used in Mills 

et al. (2014). This reduces the total population considered within the original 33 cities. 

The second involved updating to the most recent BenMAP data for the all-age mortality rates in the cities, which resulted in some small differences in the calculations.

32 Mills, D., J. Schwartz, M. Lee, M. Sarofim, R. Jones, M. Lawson, M. Duckworth, and L. 

Deck. 2014. Climate Change Impacts on Extreme Temperature Mortality in Select Metropolitan Areas in the United States. Climatic Change. DOI: 10.1007/s10584-014-1154-8.

33 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, ... and R. Somerville. 

2014. Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, 

Eds., U.S. Global Change Research Program. DOI:10.7930/J0KW5CXT. 

34 Graff Zivin, J. and M. Neidell. 2014. Temperature and the allocation of time: implications 

for climate change. Journal of Labor Economics, DOI:10.1086/671766.

35 Ibid.

36 This analysis uses the term labor supply to refer to hours worked, but cannot determine 

whether that choice is driven by employees or employers.

37 Graff Zivin, J. and M. Neidell. 2014. Temperature and the allocation of time: implications for climate change. Journal of Labor Economics, DOI:10.1086/671766.

38 For information on the development and usage of the ICLUS population projections, 

see: Mills, D., J. Schwartz, M. Lee, M. Sarofim, R. Jones, M. Lawson, M. Duckworth, and L. 

Deck. 2014. Climate Change Impacts on Extreme Temperature Mortality in Select Metropolitan Areas in the United States. Climatic Change. DOI: 10.1007/s10584-014-1154-8.

39 Bureau of Labor Statistics, Quarterly Census of Employment and Wages, data accessible at http://www.bls.gov/cew/. High-risk workers were defined as those employed in 

agriculture, forestry, and fishing; hunting, mining, and construction; and manufacturing, transportation, and utilities industries.

40 Bureau of Labor Statistics, Quarterly Census of Employment and Wages, data accessible at http://www.bls.gov/cew/. Average wage ($23.02) calculated using high-risk labor 

categories only, as the majority of extreme temperature impacts on labor hours occur 

in these industries.

41 Graff Zivin, J. and M. Neidell. 2014. Temperature and the allocation of time: implications 

for climate change. Journal of Labor Economics, DOI:10.1086/671766.
88

Endnotes

42 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, Terese (T.C.) Richmond, K. 

Reckhow, K. White, and D. Yates. 2014. Ch. 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) 

Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

J0G44N6T.

43 Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, ... and L. Ziska. 2014. Ch. 

9: Human Health. Climate Change Impacts in the United States: The Third National Climate 

Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global 

Change Research Program. DOI:10.7930/J0PN93H5.

44 Boehlert, B., K. Strzepek, S. Chapra, Y. Gebretsadik, M. Lickley, C. Fant, ... and J. Martinich. (In press). Greenhouse Gas Mitigation Effects on Water Quality Impacts from 

Climate Change in the U.S. Journal of Advances in Modeling Earth Systems.

45 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, Terese (T.C.) Richmond, K. 

Reckhow, K. White, and D. Yates. 2014. Ch. 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) 

Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

J0G44N6T.

46 Strzepek K., M. Jacobsen, B. Boehlert, J. Neumann. 2013. Toward evaluating the effect 

of climate change on investments in the water resources sector: insights from the 

forecast and analysis of hydrological indicators in developing countries. Environmental 

Research Letters, DOI:10.1088/1748-9326/8/4/044014.

47 Chapra, S.C. 2014. QUALIDAD: A parsimonious modeling framework for simulating 

river basin water quality, Version 1.1, Documentation and users manual. Civil and 

Environmental Engineering Dept., Tufts University, Medford, MA.

48 Boehlert, B., K. Strzepek, S. Chapra, Y. Gebretsadik, M. Lickley, C. Fant, ... and J. Martinich. (In press). Greenhouse Gas Mitigation Effects on Water Quality Impacts from 

Climate Change in the U.S. Journal of Advances in Modeling Earth Systems. 

Infrastructure

1 Wilbanks, T., and S. Fernandez. 2012. Climate Change and Infrastructure, Urban 

Systems, and Vulnerabilities: Technical Report to the U.S. Department of Energy 

in Support of the National Climate Assessment. http://www.esd.ornl.gov/eess/

Infrastructure.pdf. 

2 Congress of the United States, Congressional Budget Office. 2010. Public Spending 

on Transportation and Water Infrastructure. http://www.cbo.gov/sites/default/files/

cbofiles/attachments/11-17-10-Infrastructure.pdf. 

3 Congress of the United States, Congressional Budget Office. 2008. Issues and Options in 

Infrastructure Investment. http://www.cbo.gov/sites/default/files/cbofiles/ftpdocs/91xx/

doc9135/05-16-infrastructure.pdf. 

4 Schwarz, H.G., M. Meyer, C.J. Burbank, M. Kuby, C. Oster, J. Posey, E.J. Russo, and A. 

Rypinski. 2014. Chapter 5: Transportation. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, T.C. Richmond, and G.W. Yohe, Eds., 

U.S. Global Research Program. DOI:10.7930/JO6Q1V53.

5 U.S. Department of Transportation. 2013. National Bridge Inventory. 

6 Schwarz, H.G., M. Meyer, C.J. Burbank, M. Kuby, C. Oster, J. Posey, E.J. Russo, and A. 

Rypinski. 2014. Chapter 5: Transportation. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, T.C. Richmond, and G.W. Yohe, Eds., 

U.S. Global Research Program. DOI:10.7930/JO6Q1V53.

7 Ibid.

8 Wright, L., P. Chinowsky, K. Strzepek, R. Jones, R. Streeter, J. Smith, J. Mayotte, A. Powell, 

L. Jantarasami, and W. Perkins. 2012. Estimated effects of climate change on flood 

vulnerability of U.S. bridges. Mitigation and Adaptation Strategies for Global Change. 

DOI:10.1007/s11027-011-9354-2.

9 As such, the costs of future maintenance, and the effects of those efforts in reducing 

vulnerability, are not captured in this analysis.

10 Wright et al. (2012) provides estimates of the total costs for repairing deficient bridges 

both in advance of climate change and as adaptation to climate change. Neumann et 

al. (2014) presents the results of repairing bridges in advance of climate change. The 

results presented in this report are the results of repairing bridges as adaptation to 

climate change. 

11 Neumann, J., J. Price, P. Chinowsky, L. Wright, L. Ludwig, R. Streeter, ... and J. Martinich. 

2014. Climate change risks to U.S. infrastructure: impacts on roads, bridges, coastal 

development, and urban drainage. Climatic Change. DOI:10.1007/s10584-013-1037-4.

12 Wright, L., P. Chinowsky, K. Strzepek, R. Jones, R. Streeter, J. Smith, J. Mayotte, A. Powell, 

L. Jantarasami, and W. Perkins. 2012. Estimated effects of climate change on flood 

vulnerability of U.S. bridges. Mitigation and Adaptation Strategies for Global Change. 

DOI:10.1007/s11027-011-9354-2.

13 Schwarz, H.G., M. Meyer, C.J. Burbank, M. Kuby, C. Oster, J. Posey, E.J. Russo, and A. 

Rypinski. 2014. Chapter 5: Transportation. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, T.C. Richmond, and G.W. Yohe, Eds., 

U.S. Global Research Program. DOI:10.7930/JO6Q1V53.

14 Transportation Research Board. 2008. Potential Impacts of Climate Change on U.S. 

Transportation. Special Report 290, Committee on Climate Change and U.S. Transportation, National Research Council of the National Academies.

15 Schwarz, H.G., M. Meyer, C.J. Burbank, M. Kuby, C. Oster, J. Posey, E.J. Russo, and A. 

Rypinski. 2014. Chapter 5: Transportation. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, T.C. Richmond, and G.W. Yohe, Eds., 

U.S. Global Research Program. DOI:10.7930/JO6Q1V53.

16 For additional explanation of MIROC results, see: Neumann, J., J. Price, P. Chinowsky, 

L. Wright, L. Ludwig, R. Streeter, ... and J. Martinich. 2014. Climate change risks to U.S. 

infrastructure: impacts on roads, bridges, coastal development, and urban drainage. 

Climatic Change. DOI:10.1007/s10584-013-1037-4.

17 Neumann, J., J. Price, P. Chinowsky, L. Wright, L. Ludwig, R. Streeter, ... and J. Martinich. 

2014. Climate change risks to U.S. infrastructure: impacts on roads, bridges, coastal 

development, and urban drainage. Climatic Change. DOI:10.1007/s10584-013-1037-4.

18 Chinowsky, P., J. Price, and J. Neumann. 2013. Assessment of climate change adaptation costs for the U.S. road network. Global Environmental Change. DOI:10.1016/j.

gloenvcha.2013.03.004.

19 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates. 2014. Ch. 3: Water Resources. Climate Change Impacts in the 

United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, and G. 

W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/J0G44N6T.

20 Schwarz, H.G., M. Meyer, C.J. Burbank, M. Kuby, C. Oster, J. Posey, E.J. Russo, and A. 

Rypinski. 2014. Chapter 5: Transportation. Climate Change Impacts in the United States: 

The Third National Climate Assessment, J.M. Melillo, T.C. Richmond, and G.W. Yohe, Eds., 

U.S. Global Research Program. DOI:10.7930/JO6Q1V53.

21 The adaptation costs per square mile, calculated by city, storm, scenario, and year, 

were aggregated to the regions used in the Third National Climate Assessment 

and weighted by area. For example, for a region with 2 cities, each with an area of 

100 square miles, each city’s area is divided by the sum of the areas, resulting in a 

proportion value of 0.5 for each city. This proportion value is then multiplied by each 

calculation of per-square-mile adaptation costs (calculated by storm, scenario, and 

year) to produce a weighted average adaptation cost per square mile. 

22 More detailed models are often used by municipalities for local stormwater management planning, but applying these models across the 50 cities examined in this 

analysis was not practicable.

23 Neumann, J., J. Price, P. Chinowsky, L. Wright, L. Ludwig, R. Streeter, ... and J. Martinich. 

2014. Climate change risks to U.S. infrastructure: impacts on roads, bridges, coastal 

development, and urban drainage. Climatic Change. DOI:10.1007/s10584-013-1037-4.

24 Price, J., L. Wright, C. Fant, and K. Strzepek. 2014. Calibrated Methodology for Assessing 

Climate Change Adaptation Costs for Urban Drainage Systems. Urban Water Journal. 

DOI:10.1080/1573062X.2014.991740.

25 The results presented here apply the methods described in Price et al. (2014) and 

Neumann et al. (2014), with an expansion of the number of cities modeled.

26 Moser, S.C., M.A. Davidson, P. Kirshen, P. Mulvaney, J.F. Murley, J.E. Neumann, L. Petes, 

and D. Reed. 2014. Ch. 25: Coastal Zone Development and Ecosystems. Climate Change 

Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, T.C. 

Richmond, and G.W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

JOMS3QNW.

27 Ibid.

28 Underlying vulnerability exists in both the Reference and the Mitigation scenarios 

within the base or historic period (i.e., today). This vulnerability is depicted for the Reference scenario in Figure 1 as costs occurring in 2000. Removing costs associated with 

baseline vulnerability yields cost estimates with adaptation of $530 billion under the 

Reference scenario and $500 billion under the Mitigation scenario. We’ve included the 

baseline vulnerability costs in our estimates because they may affect future decisions 

about coastal development. We also note that some damages to coastal property are 

due to the effects of land subsidence that occurs regardless of climate change.

29 The CIRA sea level rise scenarios are at the high end of projected sea level rise rates for 

similar scenarios based on recent publications (Horton et al. 2014, Kopp et al. 2014). 

However, we also note that the effect of GHG mitigation on reducing the increase 

in future sea level was found to be proportionally larger in these studies. The use of 

smaller sea level rise rates would likely lead to a decrease in total damages, but a larger 

reduction in sea level rise due to the Mitigation scenario compared to the Reference 

would likely yield larger economic benefits than those presented in this report. See: 

1) Horton, B.J., S. Rahmstorf, S.E. Engelhart, and A.C. Kemp. 2014. Expert assessment 
89

of sea-level rise by AD 2100 and AD 2300. Quaternary Science Reviews, DOI:10.1016/j.

quascirev.2013.11.002; and 2) Kopp, R.E., R.M. Horton, C.M. Little, J.X. Mitrovica, M. 

Oppenheimer, D.J. Rasmussen, B.H.Strauss, and C. Tebaldi. 2014. Probabilistic 21st and 

22nd century sea-level projections at a global network of tide-gauge sites. Earth’s Future, 

DOI:10.1002/2014EF000239. 

30 Without discounting, the cumulative effect of mitigation is larger, reducing impacts by 

about 10% (from $1.2 trillion to $1.0 trillion), and the annual benefits rise rapidly from 

approximately $140 million in 2050 to nearly $3.1 billion in 2100. 

31 The CIRA analysis evaluates risks of inaction and benefits of mitigation through the end 

of the 21st century. The high degree of inertia in processes leading to sea-level rise (i.e., 

the oceans and ice sheets respond slowly to warming conditions at the Earth’s surface) 

suggest that the absence of 21st century GHG mitigation is likely to result in sea level 

rise rates equal to or larger than those experienced this century, with subsequent 

large and long-term implications for coastal development (Horton et al. 2014 and 

Levermann et al. 2013 provide projections of sea level rise beyond 2100). Therefore, 

the difference in sea level change rise between the CIRA Reference and Mitigation 

scenarios will only increase after 2100. This would likely result in larger GHG mitigation 

benefits to the coastal property sector, and it is important to note that these benefits 

would only be realized from GHG reductions occurring in this century. See: Horton, 

B.J., S. Rahmstorf, S.E. Engelhart, and A.C. Kemp. 2014. Expert assessment of sea-level 

rise by AD 2100 and AD 2300. Quaternary Science Reviews 84:1-6; and Levermann, A., P. 

Clark, B. Marzeion, G. Milne, D. Pollard, V. Radic, and A. Robinson. 2013. The multimillenial sea-level commitment of global warming. PNAS, DOI: 10.1073/pnas.1219414110.

32 Vermeer, M., and S. Rahmstorf. 2009. Global sea level linked to global temperature. 

Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0907765106.

33 National Atmospheric and Oceanic Administration (NOAA) Center for Operational 

Oceanographic Products and Services (CO-OPS). Linear mean sea level (MSL) trends 

and 95% confidence intervals in mm/yr. http://tidesandcurrents.noaa.gov/sltrends/

sltrends.html.

34 Emanuel, K., R. Sundararajan, and J. Williams. 2008. Hurricanes and Global Warming: 

Results from Downscaling IPCC AR4 Simulations. Bulletin of the American Meteorological 

Society. DOI:10.1175/BAMS-89-3-347.

35 Jelesnianski, C.P., J. Chen, and W.A. Shaffer. 1992. SLOSH: Sea, lake, and overland surges 

from hurricanes. NOAA Technical Report NWS 48, National Oceanic and Atmospheric 

Administration, U. S. Department of Commerce, Washington, DC.

36 Tebaldi, C., B. Strauss, and C. Zervas. 2012. Modeling sea-level rise impacts on 

storm surges along U.S. coasts. Environmental Research Letters. DOI:10.1088/1748-

9326/7/1/014032.

37 Neumann, J., K. Emanuel, S. Ravela, L. Ludwig, P. Kirshen, K. Bosma, and J. Martinich. 

2014a. Joint Effects of Storm Surge and Sea-level Rise on U.S. Coasts. Climatic Change. 

DOI: 10.1007/s10584-014-1304-z. . 

38 Neumann, J., J. Price, P. Chinowsky, L. Wright, L. Ludwig, R. Streeter, ... and J. Martinich. 

2014b. Climate change risks to U.S. infrastructure: impacts on roads, bridges, coastal 

development, and urban drainage. Climatic Change. DOI:10.1007/s10584-013-1037-4.

39 Cutter, S., B.J. Boruff, and W.L. Shirley. 2003. Social Vulnerability to Environmental 

Hazards. Social Science Quarterly 84(2). 

40 Borden, K., M. Schmidtlein, C. Emrich, W. Piegorsch, and S. Cutter. 2007. Vulnerability 

of U.S. cities to environmental hazards. Journal of Homeland Security and Emergency 

Management, DOI: 10.2202/1547-7355.1279; Schmidtlein, M., R. Deutsch, W. Piegorsch, 

and S. Cutter. 2008. A sensitivity analysis of the social vulnerability index. Risk Analysis, 

DOI: 10.1111/j.1539-6924.2008.01072.x; Wood, N., C. Burton, and S. Cutter. 2010. Community variations in social vulnerability to Cascadia-related tsunamis in the U.S. Pacific 

Northwest. Natural Hazards, DOI: 10.1007/s11069-009-9376-1. 

41 Neumann, J., K. Emanuel, S. Ravela, L. Ludwig, P. Kirshen, K. Bosma, and J. Martinich. 

2014. Joint Effects of Storm Surge and Sea-level Rise on U.S. Coasts. Climatic Change. 

DOI: 10.1007/s10584-014-1304-z. .

42 Neumann, J., J. Price, P. Chinowsky, L. Wright, L. Ludwig, ... and J. Martinich. 2014. 

Climate change risks to U.S. infrastructure: impacts on roads, bridges, coastal development, and urban drainage. Climatic Change, DOI:10.1007/s10584-013-1037-4.

43 Martinich, J., J. Neumann, L. Ludwig, and L. Jantarasami. 2013. Risks of sea level rise to 

disadvantaged communities in the United States. Mitigation and Adaptation Strategies 

for Global Change. DOI: 10.1007/s11027-011-9356-0.

44 Areas with significant storm surge damages are those where the damages from storm 

surge are greater than the value of the property. 

45 The adaptation responses projected by the National Coastal Property Model are 

developed using a cost-benefit framework comparing the costs of protection relative 

to the property value. Developed as a simple metric to estimate potential adaptation 

responses in a consistent manner for the entire coastline, the estimates presented 

here should not be construed as recommending any specific policy or adaptive action. 

Further, additional adaptation options not included in this analysis, such as marsh 

restoration, may be appropriate for some locales. 

Electricity

1 The transportation sector accounts for 27 percent of emissions, followed by the 

residential, commercial, and industrial sectors at 21 percent. The remaining 22 percent 

of emissions come from biomass and various other sectors. The share of electricity 

generated by fossil fuels from 2009-2013 was 69% (42% from coal, 26% from natural 

gas, 0.8% from petroleum). U.S. Department of Energy. 2014. Electric Power Monthly: 

Table 1.1. Net Generation by Energy Source: Total (All Sectors), 2004-February 2014.

2 Dell, J., S. Tierney, G. Franco, R. G. Newell, R. Richels, J. Weyant, and T. J. Wilbanks. 2014. 

Ch. 4: Energy Supply and Use. Climate Change Impacts in the United States: The Third 

National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., 

U.S. Global Change Research Program. DOI:10.7930/J0BG2KWD. 

3 Ibid.

4 Consistent with other electricity and power sector analyses, the CIRA analysis only 

projects impacts through 2050. 

5 Dell, J., S. Tierney, G. Franco, R. G. Newell, R. Richels, J. Weyant, and T. J. Wilbanks. 2014. 

Ch. 4: Energy Supply and Use. Climate Change Impacts in the United States: The Third 

National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., 

U.S. Global Change Research Program. DOI:10.7930/J0BG2KWD.

6 U.S. Department of Energy, U.S. Energy Information Administration. 2009 Residential 

Energy Consumption Survey (RECS): Table CE4.1. http://www.eia.gov/consumption/

residential/data/2009/index.cfm. 

7 U.S. Department of Energy, U.S. Energy Information Administration. 2003 Commercial 

Buildings Energy Consumption Survey (CBECS): Tables E1A and E3A. http://www.eia.

gov/consumption/commercial/data/2003/index.cfm. 

8 Dell, J., S. Tierney, G. Franco, R. G. Newell, R. Richels, J. Weyant, and T. J. Wilbanks. 2014. 

Ch. 4: Energy Supply and Use. Climate Change Impacts in the United States: The Third 

National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., 

U.S. Global Change Research Program. DOI:10.7930/J0BG2KWD.

9 In this instance, the reduction in electric heating is greater than the rise in demand for 

cooling by 0.3%. This reflects a higher level of electricity demand for heating in the 

Pacific Northwest relative to the rest of country.

10 Kyle, P., L. Clarke, F. Rong, and S.J. Smith. 2010. Climate Policy and the Long-Term 

Evolution of the U.S. Buildings Sector. The Energy Journal, 31(2):145-172.

11 Zhou, Y., J. Eom, and L. Clarke. 2013. The effect of global climate change, population 

distribution, and climate mitigation on building energy use in the U.S. and China. 

Climatic Change, DOI:10.1007/s10584-013-0772-x.

12 National Renewable Energy Laboratory. 2014. NREL: Energy Analysis – Regional Energy 

Deployment System (ReEDS) Model. http://www.nrel.gov/analysis/reeds/. 

13 Jaglom, W., McFarland, J., M. Colley, C. Mack, B. Venkatesh, R. Miller, ... and S. Kayin. 

2013. Assessment of projected temperature impacts from climate change on the 

U.S. electric power industry using the Integrated Planning Model. Energy Policy. 

DOI:10.1016/j.enpol.2014.04.032.

14 McFarland, J., Y. Zhou, L. Clarke, P. Sullivan, J. Colman, W. Jaglom, ... and J. Creason. 

2015. Impacts of rising air temperatures and emissions mitigation on electricity 
90

Endnotes

demand and supply in the United States: a multi-model comparison. Climatic Change. 

DOI: 10.1007/s10584-015-1380-8.

15 U.S. Environmental Protection Agency. 2014. Inventory of U.S. Greenhouse Gas 

Emissions and Sinks: 1990–2012, Table 2-1. http://www.epa.gov/climatechange/

Downloads/ghgemissions/US-GHG-Inventory-2014-Chapter-2-Trends.pdf.

16 Clarke, L.E., A.A. Fawcett, J.P. Weyant, J. McFarland, V. Chaturvedi, and Y. Zhou. 2014. 

Technology and U.S. Emissions Reductions Goals: Results of the EMF 24 Modeling 

Exercise. The Energy Journal, DOI: 10.5547/01956574.35.SI1.2.

17 As described in the CIRA Framework section, the Mitigation scenario is not associated 

with any specific policy (e.g., EPA’s Clean Power Plan), and is assumed to be achieved 

through global efforts to reduce GHG emissions. Therefore, projected emissions 

reductions in the U.S. electricity sector are part of a larger global mitigation scenario. 

See McFarland et al. (2015) for information regarding U.S. electricity sector emissions. 

18 Total generation across the models varies because electricity demand is independently 

calculated by each model based on changes in population, GDP, technology costs, and 

other factors. 

19 McFarland, J., Y. Zhou, L. Clarke, P. Sullivan, J. Colman, W. Jaglom, ... and J. Creason. 

2015. Impacts of rising air temperatures and emissions mitigation on electricity 

demand and supply in the United States: a multi-model comparison. Climatic Change. 

DOI: 10.1007/s10584-015-1380-8.

Water Resources

1 U.S. Environmental Protection Agency, Office of Water. 2013. The Importance of Water 

to the U.S. Economy: Synthesis Report. http://water.epa.gov/action/importanceofwater/upload/Importance-of-Water-Synthesis-Report.pdf. 

2 U.S. Environmental Protection Agency. 2014. Climate Change Indicators in the United 

States: Drought. http://www.epa.gov/climatechange/pdfs/print_drought-2014.pdf. 

3 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

4 Ibid.

5 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, ... and R. Somerville. 

2014. Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, 

Eds., U.S. Global Change Research Program. DOI:10.7930/J0KW5CXT.

6 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

7 Damages are in 2011 dollars. 

8 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

9 Ibid.

10 Across the contiguous U.S., damages are projected to decrease relative to the baseline 

period in the following Water Resource Regions (WRRs): Upper Colorado, Lower Colorado, Pacific Northwest, and California. 

11 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

12 Wobus, C., Lawson, M., Jones, R., Smith, J., and Martinich, J. 2013. Estimating monetary 

damages from flooding in the United States under a changing climate. Journal of Flood 

Risk Management. DOI: 10.1111/jfr3.12043.

13 In reality, the distribution of monetary damages from flooding is likely to change: 

changes in floodplain development, modifications to flood protection infrastructure, 

or changes in wealth could all influence the damage incurred by a given magnitude 

of flood event in the future. However, these future demographic and infrastructure 

changes could either increase or decrease damages from flooding in the future: flood 

protection could decrease damages, while increases in development in the floodplain 

could increase them. Without an a priori means of evaluating which path to follow, the 

assumption of stationarity in this distribution is reasonable.

14 Strzepek, K., J. Neumann, J. Smith, J. Martinich, B. Boehlert, ... and J.-H. Yoon. 2014. 

Benefits of Greenhouse Gas Mitigation on the Supply, Management, and Use of Water 

Resources in the United States. Climatic Change. DOI: 10.1007/s10584-014-1279-9.

15 Wobus, C., Lawson, M., Jones, R., Smith, J., and Martinich, J. 2013. Estimating monetary 

damages from flooding in the United States under a changing climate. Journal of Flood 

Risk Management. DOI: 10.1111/jfr3.12043.

16 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

17 National Drought Mitigation Center, University of Nebraska-Lincoln. 2014. Drought 

Impact Reporter. http://drought.unl.edu/MonitoringTools/DroughtImpactReporter.

aspx. 

18 Monier, E., X. Gao, J. Scott, A. Sokolov, and C. Schlosser. 2014. A framework for modeling uncertainty in regional climate change. Climatic Change. DOI: 10.1007/s10584-014-

1112-5.

19 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

20 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, ... and R. Somerville. 

2014. Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, 

Eds., U.S. Global Change Research Program. DOI:10.7930/J0KW5CXT.

21 Strzepek, K., G. Yohe, J. Neumann, and B. Boehlert. 2010. Characterizing changes in drought risk for the United States from climate change. Environ. Res. Lett.

DOI:10.1088/1748-9326/5/4/044012.

22 Boehlert, B., E. Fitzgerald, J. Neumann, K. Strzepek, and J. Martinich. 2015. The Effect 

of Greenhouse Gas Mitigation on Drought Impacts in the U.S. Weather, Climate and 

Society. DOI: 10.1175/WCAS-D-14-00020.1.

23 The impact estimates for drought on crop-based agriculture both complement and 

overlap with the FASOM/EPIC estimates of the impact of climate change on agricultural crops. The drought methodology uses an econometric approach grounded in 

historical expenditures to alleviate historical droughts, and projections of drought 

occurrence—it addresses a subset of effects on agriculture associated with drought 

occurrence. The FASOM/EPIC results are more comprehensive in scope and address 

both droughts and many other aspects of climate change (e.g., changes in the timing 

of rainfall and extreme heat), and adopt a simulation approach which models specific 

actions by farmers and in agricultural markets that might be taken to respond to 

climate impacts. 

24 Strzepek, K., J. Martinich, J. Neumann, B. Boehlert, J. Henderson, M. Hejazi, ... and J. 

Yoon. 2014. Benefits of Greenhouse Gas Mitigation on the Supply, Management, and 

Use of Water Resources in the United States. Climatic Change. DOI: 10.1007/s10584-

014-1279-9.

25 Boehlert, B., E. Fitzgerald, J. Neumann, K. Strzepek, and J. Martinich. 2015. The Effect 

of Greenhouse Gas Mitigation on Drought Impacts in the U.S. Weather, Climate and 

Society. DOI: 10.1175/WCAS-D-14-00020.1.

26 Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, T.C. Richmond, K. Reckhow, 

K. White, and D. Yates, D. 2014. Chapter 3: Water Resources. Climate Change Impacts 

in the United States: The Third National Climate Assessment, J. M. Melillo, T.C. Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program, DOI:10.7930/J0G44N6T.

27 Ibid.

28 Henderson, J., C. Rodgers, R. Jones, J. Smith, K. Strzepek, and J. Martinich. 2013. Economic impacts of climate change on water resources in the coterminous United States. 

Mitig Adapt Strateg Glob Change. DOI:10.1007/s11027-013-9483-x.

29 In-stream flows are modeled such that flows below minimum levels required to sustain 

vulnerable aquatic species are assessed a penalty. In addition, it should be noted that 

the agricultural water use simulated in the CIRA Water Supply and Demand model 

does not link with the model used to estimate impacts in that sector of this report. 

30 While the Water Supply and Demand analysis accounts for reactive adaptation in 

response to changes in water supply, the effects from water resources technology improvements and proactive adaptation planning are not included. Adaptation planning 

in the water resource sector has increased at the federal level in the U.S., e.g., EPA National Water Program’s Response to Climate Change and NOAA’s Regional Integrated 

Sciences & Assessments (RISA) program. 

31 Strzepek, K., J. Martinich, J. Neumann, B. Boehlert, J. Henderson, M. Hejazi, ... and J. 

Yoon. 2014. Benefits of Greenhouse Gas Mitigation on the Supply, Management, and 

Use of Water Resources in the United States. Climatic Change. DOI: 10.1007/s10584-

014-1279-9.

32 Henderson, J., C. Rodgers, R. Jones, J. Smith, K. Strzepek, and J. Martinich. 2013. Economic impacts of climate change on water resources in the coterminous United States. 

Mitig Adapt Strateg Glob Change. DOI:10.1007/s11027-013-9483-x.
91

Agriculture and Forestry

1 Hatfield, J., G. Takle, R. Grotjahn, P. Holden, R.C. Izaurralde, T. Mader, E. Marshall, and 

D. Liverman. 2014. Ch. 6: Agriculture. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, 

Eds., U.S. Global Change Research Program. DOI:10.7930/J02Z13FR. 

2 U.S. Congress. 2013. The Economic Contribution of America’s Farmers and the Importance of Agricultural Exports. http://www.jec.senate.gov/public/?a=Files.Serve&File_

id=266a0bf3-5142-4545-b806-ef9fd78b9c2f.

3 Ibid.

4 Joyce, L.A., S.W. Running, D.D. Breshears, V.H. Dale, R.W. Malmsheimer, R.N. Sampson, B. 

Sohngen, and C.W. Woodall. 2014. Ch. 7: Forests. Climate Change Impacts in the United 

States: The Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and 

G.W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/JOZ60KZC.

5 Hatfield, J., G. Takle, R. Grotjahn, P. Holden, R.C. Izaurralde, T. Mader, E. Marshall, and 

D. Liverman. 2014. Ch. 6: Agriculture. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, 

Eds., U.S. Global Change Research Program, 150-174. DOI:10.7930/J02Z13FR. 

6 Joyce, L.A., S.W. Running, D.D. Breshears, V.H. Dale, R.W. Malmsheimer, R.N. Sampson, 

B. Sohngen, and C.W. Woodall. 2014. Ch. 7: Forests. Climate Change Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/JOZ60KZC.

7 Hatfield, J., G. Takle, R. Grotjahn, P. Holden, R.C. Izaurralde, T. Mader, E. Marshall, and 

D. Liverman. 2014. Ch. 6: Agriculture. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, 

Eds., U.S. Global Change Research Program, 150-174. DOI:10.7930/J02Z13FR.

8 Joyce, L.A., S.W. Running, D.D. Breshears, V.H. Dale, R.W. Malmsheimer, R.N. Sampson, 

B. Sohngen, and C.W. Woodall. 2014. Ch. 7: Forests. Climate Change Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/JOZ60KZC.

9 A wetter future climate, as projected under the IGSM-CAM for many crop-growing 

parts of the U.S., will tend to reduce water stress such that some yields may increase 

even with higher temperatures. In the EPIC modeling, irrigated crops are assumed to 

be able to meet their water needs regardless of climate change effects on precipitation, so a wetter/hotter climate scenario just increases their temperature stress without 

reducing their water stress. This tends to make impacts on rainfed crops more negative 

than for irrigated yields. In addition, the ability of climate models to simulate precipitation as severe storms or as heavy rainfall rather than frequent drizzle is an emerging 

area of research in the climate modeling community. As such, the results presented 

here should be interpreted with acknowledgement of this uncertainty. 

10 Hatfield, J., G. Takle, R. Grotjahn, P. Holden, R.C. Izaurralde, T. Mader, E. Marshall, and 

D. Liverman. 2014. Ch. 6: Agriculture. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, 

Eds., U.S. Global Change Research Program, 150-174. DOI:10.7930/J02Z13FR. 

11 The EPIC simulations assume that crops can be irrigated at a level that eliminates water 

stress. A particular concern for climate change is that in areas where the need for irrigation is greatest due to reduction in precipitation, the supply of water for irrigation will 

also be reduced. To fully consider this risk requires integration of crop modeling with 

hydrologic modeling for projections of future water supply, which was not modeled in 

this biophysical crop yield analysis. 

12 Joyce, L.A., S.W. Running, D.D. Breshears, V.H. Dale, R.W. Malmsheimer, R.N. Sampson, 

B. Sohngen, and C.W. Woodall. 2014. Ch. 7: Forests. Climate Change Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, 

and G.W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/JOZ60KZC.

13 Mills, D., R. Jones, K. Carney, A. St Juliana, R. Ready, A. Crimmins ... and E. Monier. 2014. 

Quantifying and Monetizing Potential Climate Change Policy Impacts on Terrestrial Ecosystem Carbon Storage and Wildfires in the United States. Climatic Change, 

DOI:10.1007/s10584-014-1118-z.

14 The results in Figure 2 from the EPIC model show projected crop yields that do not 

reflect production and market adjustments.

15 Williams, J.R. 1995. The EPIC Model. In Computer Models in Watershed Hydrology, V.P. 

Singh (ed.), pp. 909-1000. Highlands Ranch, CO: Water Resources Publication. 

16 Thomson, A.M., R.A. Brown, N.J. Rosenberg, R.C. Izaurralde, and V. Benson. 2005. 

Climate Change Impacts for the Conterminous USA. Part 3: Dryland production of grain 

and forage crops. Climatic Change. DOI:10.1007/1-4020-3876-3.

17 The EPIC simulations assume that crops can be irrigated at a level that eliminates water 

stress. A particular concern for climate change is that in areas where the need for irrigation is greatest due to reduction in precipitation, the supply of water for irrigation will 

also be reduced. To fully consider this risk requires integration of crop modeling with 

hydrologic modeling for projections of future water supply, which was not modeled in 

this biophysical crop yield analysis. 

18 The analysis uses climate projections from all five initializations of the IGSM-CAM. Given the sensitivity of the EPIC and MC1 models to natural variability, the use of the five 

initializations of the IGSM-CAM climate model, each of which has an equally plausible 

future climate, aids in understanding and constraining the potential magnitude of crop 

and vegetation changes in the future. Please refer to the Levels of Certainty section of 

this report for more information. 

19 Mills, D., R. Jones, K. Carney, A. St Juliana, R. Ready, A. Crimmins ... and E. Monier. 2014. 

Quantifying and Monetizing Potential Climate Change Policy Impacts on Terrestrial Ecosystem Carbon Storage and Wildfires in the United States. Climatic Change, 

DOI:10.1007/s10584-014-1118-z.

20 The change in forest yield was assumed to be equal to the percentage difference 

in net primary productivity between future years and the average for the baseline 

(1980-2009).

21 While beyond the scope of this analysis, the effects of CO2 fertilization on forest growth 

and productivity may be limited by the availability of nitrogen, which could influence 

the results estimated here.

22 Beach, R., Y. Cai, A. Thomson, X. Zhang, R. Jones, B. McCarl,... and B. Boehlert. (In press). 

Climate change impacts on US agriculture and forestry: benefits of global climate 

stabilization. Environmental Research Letters.

23 Hatfield, J., G. Takle, R. Grotjahn, P. Holden, R.C. Izaurralde, T. Mader, E. Marshall, and 

D. Liverman. 2014. Ch. 6: Agriculture. Climate Change Impacts in the United States: The 

Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, 

Eds., U.S. Global Change Research Program, 150-174. DOI:10.7930/J02Z13FR. 

24 Consumer and producer surplus are used to estimate impacts on total economic 

welfare. Consumer surplus is the monetary gain obtained by consumers because they 

are able to purchase a product for a price that is less than the highest price that they 

would be willing to pay. Producer surplus or producers’ surplus is the amount that 

producers benefit by selling at a market price that is higher than the least that they 

would be willing to sell for.

25 Beach, R., D. Adams, R. Alig, J. Baker, G. Latta, B. McCarl, ... and E. White. 2010. Model 

documentation for the Forest and Agricultural Sector Optimization Model with Greenhouse Gases (FASOMGHG). Prepared for U.S. Environmental Protection Agency.

26 EPIC, MC1, and FASOM results in the Agriculture and Forestry sections using the 

IGSM-CAM climate projections represent the average of the five initializations.

27 FASOM has perfect foresight of future climate change effects, and thus can optimize 

near term land owner behavior. The model also simulates changes in agricultural and 

forestry commodities beyond those modeled in EPIC (9 crops) and MC1 (hard and 

softwoods).

28 This analysis does not reflect climate change impacts on international forests and 

agriculture, which would also affect relative returns to different uses of land and trade 

patterns and therefore affect land use decisions. Also, numerous uncertainties remain 

regarding issues such as future changes in crop technology, energy policy, and other 

interactions that could affect market outcomes.
92

Endnotes

29 FASOM-GHG is optimized to maximize consumer and producer surplus in the base, 

but re-adjusts production and consumption patterns to re-optimize in response to 

changes in potential yields.

30 FASOM directly models changes to productivity on private timberland, although 

timber from public lands enters the market exogenously based on public lands policy. 

Impacts on productivity due to climate change are only applied to the private timberland.

31 Boehlert, B., K. Strzepek, S. Chapra, Y. Gebretsadik, M. Lickley, C. Fant, ... and J. Martinich. (In press). Greenhouse Gas Mitigation Effects on Water Quality Impacts from 

Climate Change in the U.S. Journal of Advances in Modeling Earth Systems.

32 Beach, R., Y. Cai, A. Thomson, X. Zhang, R. Jones, B. McCarl,... and B. Boehlert. (In press). 

Climate change impacts on US agriculture and forestry: benefits of global climate 

stabilization. Environmental Research Letters.

Ecosystems

1 Groffman, P. M., P. Kareiva, S. Carter, N. B. Grimm, J. Lawler, M. Mack, V. Matzek, and H. 

Tallis, 2014: Ch. 8: Ecosystems, Biodiversity, and Ecosystem Services. Climate Change 

Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, 

Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 

195-219. DOI:10.7930/J0TD9V7H.

2 Ibid.

3 Melillo, J.M., T.C. Richmond, and G.W. Yohe, Eds. 2014. Climate Change Impacts in the 

United States: The Third National Climate Assessment. U.S. Global Change Research 

Program. DOI:10.7930/J0Z31WJ2.

4 The impacts modeled in COMBO do not include non-climate stressors, such as 

overfishing or water pollution, and do not account for the ability of large-scale reefs 

to contain important refugia for resilient corals that could potentially be used in coral 

restoration efforts. Together, these factors have the ability to adjust the estimates 

presented in this report upwards or downwards.

5 Doney, S., A. A. Rosenberg, M. Alexander, F. Chavez, C. D. Harvell, G. Hofmann, M. 

Orbach, and M. Ruckelshaus. 2014. Ch. 24: Oceans and Marine Resources. Climate 

Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, 

Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. 

DOI:10.7930/J0RF5RZW.

6 Buddemeier, R.W., P.L. Jokiel, K.M. Zimmerman, D.R. Lane, J.M. Carey, G.C. Bohling, 

and J.A. Martinich. 2008. A modeling tool to evaluate regional coral reef responses 

to changes in climate and ocean chemistry. Limn Oceanogr Methods. DOI: 10.4319/

lom.2008.6.395.

7 Buddemeier, R.W., D.R. Lane, and J.A. Martinich. 2011. Modeling regional coral reef 

responses to global warming and changes in ocean chemistry: Caribbean case study. 

Climatic Change. DOI:10.1007/s10584-011-0022-z.

8 The values presented in this section differ slightly from those presented in Lane et al. 

(2014) due to differences in aggregating coral cover changes annually or monthly.

9 Lane, D.R., R.C. Ready, R.W. Buddemeier, J.A. Martinich, K.C. Shouse, and C.W. Wobus. 

2013. Quantifying and valuing potential climate change impacts on coral reefs in 

the United States: Comparison of two scenarios. PLoS ONE. DOI:10.1371/journal.

pone.0082579.

10 Ibid.

11 Lane, D., R. Jones, D. Mills, C. Wobus, R.C. Ready, R.W. Buddemeier, E. English, J. Martinich, K. Shouse, and H. Hosterman. 2014. Climate change impacts on freshwater fish, 

coral reefs, and related ecosystem services in the United States. Climatic Change. DOI: 

10.1007/s10584-014-1107-2.

12 U.S. Environmental Protection Agency. 2014. Climate change indicators in the United 

States. Third edition. EPA 430-R-14-004.

13 Doney, S., A. A. Rosenberg, M. Alexander, F. Chavez, C. D. Harvell, G. Hofmann, M. 

Orbach, and M. Ruckelshaus. 2014. Ch. 24: Oceans and Marine Resources. Climate 

Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, 

Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. 

DOI:10.7930/J0RF5RZW.

14 In early life stages, some species will have higher mortality rates and more developmental abnormalities under acidification conditions expected over the next several 

decades. In addition, adult shellfish tend to grow more slowly and have thinner, more 

fragile shells under these conditions. 

15 National Marine Fisheries Service Commercial Landings for the years 1990-2010. http://

www.st.nmfs.noaa.gov/commercial-fisheries/commercial-landings/annual-landings/

index.

16 Doney, S., A. A. Rosenberg, M. Alexander, F. Chavez, C. D. Harvell, G. Hofmann, M. 

Orbach, and M. Ruckelshaus. 2014. Ch. 24: Oceans and Marine Resources. Climate 

Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, 

Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. 

DOI:10.7930/J0RF5RZW.

17 Ibid.

18 Oak Ridge National Laboratory, Carbon Dioxide Information Analysis Center. 

Program Developed for CO2 System Calculations: CO2SYS. http://cdiac.ornl.gov/

oceans/co2rprt.html. 

19 Moore, C. 2015. Welfare estimates of avoided ocean acidification in the U.S. mollusk 

market. Journal of Agricultural and Resource Economics 40(1): 50-62.

20 Ibid.

21 Groffman, P. M., P. Kareiva, S. Carter, N. B. Grimm, J. Lawler, M. Mack, V. Matzek, and H. 

Tallis. 2014. Ch. 8: Ecosystems, Biodiversity, and Ecosystem Services. Climate Change 

Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, 

Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. 

DOI:10.7930/J0TD9V7H. 

22 Ibid.

23 Horton, R., G. Yohe, W. Easterling, R. Kates, M. Ruth, E. Sussman, ... and F. Lipschultz. 

2014. Ch. 16: Northeast. Climate Change Impacts in the United States: The Third National 

Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. 

Global Change Research Program. DOI:10.7930/J0SF2T3P.

24 Global GHG mitigation is projected to preserve 230,000 acres of coldwater fish habitat 

in 2100 under the MIROC climate projections. For all freshwater fishing guilds, the 

total damages in 2100 are estimated at $1.7 billion in the Reference scenario and $200 

million in the Mitigation scenario. 

25 This analysis does not project changes to fish distribution in lakes and reservoirs, as 

these bodies provide thermal stratification/refugia, and are oftentimes heavily managed (i.e., water level and fish stocking).

26 Jones, R., C. Travers, C. Rodgers, B. Lazar, E. English, J. Lipton, ... and J. Martinich. 2012. 

Climate Change Impacts on Freshwater Recreational Fishing in the United States. Mitigation and Adaptation Strategies for Global Change. DOI: 10.1007/s11027-012-9385-3. 

27 Lane, D., R. Jones, D. Mills, C. Wobus, R.C. Ready, R.W. Buddemeier, ... and H. Hosterman. 

2014. Climate change impacts on freshwater fish, coral reefs, and related ecosystem 

services in the United States. Climatic Change. DOI: 10.1007/s10584-014-1107-2.

28 Jones, R., C. Travers, C. Rodgers, B. Lazar, E. English, J. Lipton, ... and J. Martinich. 2012. 

Climate Change Impacts on Freshwater Recreational Fishing in the United States. Mitigation and Adaptation Strategies for Global Change. DOI: 10.1007/s11027-012-9385-3. 

29 Groffman, P. M., P. Kareiva, S. Carter, N. B. Grimm, J. Lawler, M. Mack, V. Matzek, and H. 

Tallis. 2014. Ch. 8: Ecosystems, Biodiversity, and Ecosystem Services. Climate Change 

Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, 

Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. 

DOI:10.7930/J0TD9V7H.

30 National Interagency Fire Center. 2013. Federal Firefighting Costs (Suppression Only). 

https://www.nifc.gov/fireInfo/fireInfo_documents/SuppCosts.pdf.
31 Groffman, P. M., P. Kareiva, S. Carter, N. B. Grimm, J. Lawler, M. Mack, V. Matzek, and H. 

Tallis. 2014. Ch. 8: Ecosystems, Biodiversity, and Ecosystem Services. Climate Change 

Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese 

(T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. 

DOI:10.7930/J0TD9V7H. 

32 Joyce, L. A., S. W. Running, D. D. Breshears, V. H. Dale, R. W. Malmsheimer, R. N. 

Sampson, B. Sohngen, and C. W. Wood. 2014. Ch. 7: Forests. Climate Change Impacts in 

the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) 

Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

J0Z60KZC.

33 Ibid.

34 Change in annual acres burned at end of century (2085-2114) compared to the historic 

baseline (2000-2009).

35 National Interagency Fire Center. 2013. Federal Firefighting Costs (Suppression Only). 

https://www.nifc.gov/fireInfo/fireInfo_documents/SuppCosts.pdf.

36 Joyce, L. A., S. W. Running, D. D. Breshears, V. H. Dale, R. W. Malmsheimer, R. N. 

Sampson, B. Sohngen, and C. W. Wood. 2014. Ch. 7: Forests. Climate Change Impacts in 

the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) 

Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

J0Z60KZC 

37 Comprised of the following Geographic Area Coordination Center regions: Northern 

Rockies, Rocky Mountain, Southwest, Eastern Great Basin, Western Great Basin, 

Northwest, California North, and California South.

38 Percent changes calculated by comparing acres burned under the Reference scenario 

at the end of the century (average of 2085-2114) compared to the historic baseline 

(average of 2000-2009). 

39 Fuel management costs are estimated at $15 billion under the Reference and $12 

billion under the Mitigation scenario through 2100 (average across all IGSM-CAM 

initializations, 2014$, discounted at 3%), corresponding to avoided costs (benefits) of 

$3.4 billion under the Mitigation scenario.

40 Fuel management costs were not estimated using the MIROC climate model.

41 The CIRA results simulated in the MC1 vegetation model suggest a substantial change 

to the wildfire regime we experience today. Given the sensitivity of the MC1 climate 

model to natural variability, the use of the five initializations of the IGSM-CAM climate 

model, each of which has an equally plausible future climate, aids in understanding 

and constraining the potential magnitude of vegetation changes in the future. For 

example, unmitigated climate change is projected to increase area burned by wildfire 

annually by approximately 45% in California by the end of the century, 64% in the 

Mountain West, and 95% in the Northwest.

42 Because the IGSM-CAM projects a wetter future for a majority of the nation, 

pattern-scaled output from two additional climate models were simulated in MC1 to 

encompass a broader range of possible climate futures. While all three sets of climate 

projections show increases in the area burned by wildfire compared to the historic 

period, only the IGSM-CAM and MIROC climate model results are presented in this 

report. For an in-depth discussion of the results, see: Mills, D., R. Jones, K. Carney, A. St 

Juliana, R. Ready, A. Crimmins, ... and E. Monier. 2014. Quantifying and Monetizing 

Potential Climate Change Policy Impacts on Terrestrial Ecosystem Carbon Storage and 

Wildfires in the United States. Climatic Change. DOI:10.1007/s10584-014-1118-z.

43 National Wildfire Coordinating Group. 2011. Historical incident ICS-209 reports. 

http://fam.nwcg.gov/fam-web/hist_209/report_list_209. 

44 Lee, C., C. Schlemme, J. Murray, and R. Unsworth. 2015. The cost of climate change: 

ecosystem services and wildland fires. Ecological Economics. DOI:10.1016/j.ecolecon.2015.04.020.

45 Mills, D., R. Jones, K. Carney, A. St Juliana, R. Ready, A. Crimmins, ... and E. Monier. 2014. 

Quantifying and Monetizing Potential Climate Change Policy Impacts on Terrestrial 

Ecosystem Carbon Storage and Wildfires in the United States. Climatic Change.

DOI:10.1007/s10584-014-1118-z.

46 Lee, C., C. Schlemme, J. Murray, and R. Unsworth. 2015. The cost of climate change: 

ecosystem services and wildland fires. Ecological Economics. DOI:10.1016/j.ecolecon.2015.04.020.

47 Joyce, L. A., S. W. Running, D. D. Breshears, V. H. Dale, R. W. Malmsheimer, R. N. 

Sampson, B. Sohngen, and C. W. Wood. 2014. Ch. 7: Forests. Climate Change Impacts in 

the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) 

Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

J0Z60KZC.

48 Galloway, J. N., W. H. Schlesinger, C. M. Clark, N. B. Grimm, R. B. Jackson, B. E. Law, ... and 

R. Martin. 2014. Ch. 15: Biogeochemical Cycles. Climate Change Impacts in the United 

States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and 

G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/J0X63JT0.

49 Joyce, L. A., S. W. Running, D. D. Breshears, V. H. Dale, R. W. Malmsheimer, R. N. 

Sampson, B. Sohngen, and C. W. Wood. 2014. Ch. 7: Forests. Climate Change Impacts in 

the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) 

Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program. DOI:10.7930/

J0Z60KZC.

50 Change from the 2000-2009 average to the 2095-2104 average.

51 USDA Forest Service. 2012. Future of America’s Forest and Rangelands: Forest Service 

2010 Resources Planning Act Assessment. Gen. Tech. Rep. WO-87. Washington, DC. 

52 See Mills et al. (2014) for a detailed examination of the differences between the MC1 

simulations using the two climate projection methods (IGSM-CAM and MIROC 

pattern-scaled climate models), as well as a discussion of the drivers behind these 

differences. 

53 Oregon State University. 2011. MC1 dynamic vegetation model. http://www.fsl.orst.

edu/dgvm/. 

54 Given the sensitivity of the MC1 climate model to natural variability, the use of the five 

initializations of the IGSM-CAM climate model, each of which has an equally plausible 

future climate, aids in understanding and constraining the potential magnitude of 

vegetation changes in the future.

55 U.S. Interagency Working Group on Social Cost of Carbon. 2013. Technical support 

document: technical update of the social cost of carbon for regulatory impact analysis 

under Executive Order 12866. http://www.whitehouse.gov/sites/default/files/omb/

inforeg/social_cost_of_carbon_for_ria_2013_update.pdf. 

56 Mills, D., R. Jones, K. Carney, A. St Juliana, R. Ready, A. Crimmins, ... and E. Monier. 2014. 

Quantifying and Monetizing Potential Climate Change Policy Impacts on Terrestrial 

Ecosystem Carbon Storage and Wildfires in the United States. Climatic Change, 

DOI:10.1007/s10584-014-1118-z. 

CONCLUSION

1 The few efforts to date that have estimated multi-sector impacts in a consistent 

framework include the European Commission’s PESETA project (http://peseta.jrc.ec.

europa.eu), and the Risky Business Initiative (http://riskybusiness.org), a project 

focusing on economic risks in the U.S. Integrated assessment models, such as FUND 

(http://fund-model.org), are also being used to estimate the multi-sector social costs of 

GHG emissions. 

2 The use of a climate model that generates a relatively higher amount of future 

precipitation may strongly influence results in a particular sector. For example, inland 

flooding damages may be larger under these wetter climate projections compared to 

those under a drier model. This same sensitivity of sectoral results to the choice of 

climate model could affect a different part of the water sector in complementary ways, 

such that drought damages could be smaller compared to those under a drier model. 
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