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Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Explore the effects of climate change

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Content	Figures	Tables
Highlights
Overview
Cover Letter Overview Separating Human and Natural Influences on Climate Widespread Impacts Response Options	As Oceans Absorb CO₂ They Become More Acidic Observed Change in Very Heavy Precipitation Projected Global Temperature Change Separating Human and Natural Influences on Climate Shells Dissolve in Acidified Ocean Water Ten Indicators of a Warming World	Region Impacts
Climate Trends
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Climate Trends Introduction Key Message 1: Observed Climate Change Key Message 2: Future Climate Change Key Message 3: Recent U.S. Temperature Trends Key Message 4: Lengthening Frost-free Season Key Message 5: U.S. Precipitation Change Key Message 6: Heavy Downpours Increasing Key Message 7: Extreme Weather Key Message 8: Changes in Hurricanes Key Message 9: Changes in Storms Key Message 10: Sea Level Rise Key Message 11: Melting Ice Key Message 12: Ocean Acidification
Report Findings
Our Changing Climate
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Our Changing Climate Introduction Our Changing Climate Climate in the United States is changing. The global warming of the past 50 years is primarily due to human activities, predominantly the burning of fossil fuels.	2000 Years of Heat Trapping Gas Levels Arctic Sea Ice Decline Carbon Emissions in the Industrial Age Global Temperature and Carbon Dioxide Ice Loss from the Two Polar Ice Sheets Measurements of Surface Temperature and Sun’s Energy Muir Glacier Observed Increases in Frost-Free Season Observed U.S. Precipitation Change Observed U.S. Temperature Change Temperature Change by Decade
Extreme Weather
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Extreme Weather Introduction Heat Waves Drought Heavy Downpours Floods Hurricanes Change in Other Storms	Coast-to-Coast 100-degree Days in 2011 Observed U.S. Trends in Heavy Precipitation Texas Summer 2011: Record Heat and Drought Trends in Flood Magnitude
Future Climate
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Future Climate Introduction Sea level rise Where we are heading	Change in Maximum Number of Consecutive Dry Days Emission Levels Determine Temperature Rises Past and Projected Changes in Global Sea Level Projected Changes in Soil Moisture Projected Precipitation Change by Season Projected Temperature Change
Widespread Impacts
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Widespread Impacts Introduction Widespread Impacts Multiple System Failures During Extreme Events Coral Reef Ecosystem Collapse Cascading Effects Across Sectors	Coral Bleaching Katrina Diaspora
Human Health
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Human Health Introduction Key Message 1: Wide-ranging Health Impacts Key Message 2: Most Vulnerable at Most Risk Key Message 3: Prevention Provides Protection Key Message 4: Responses Have Multiple Benefits Air Quality Allergies and Asthma Food and Waterborne Diarrheal Disease Extreme Heat Diseases Carried by Vectors Multiple Benefits	Heavy Downpours are Increasing Exposure to Disease Projected Changes in Tick Habitat Ragweed Pollen Season Lengthens The Hottest Days Will Get Hotter Wildfire Smoke has Widespread Health Effects
Infrastructure
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Infrastructure Introduction Key Message 1: Urbanization and Infrastructure Systems Key Message 2: Essential Services are Interdependent Key Message 3: Social Vulnerability and Human Well-Being Key Message 4: Trends in Urban Adaptation - Lessons from Current Adopters Infrastructure Key Message 1: Reliability and Capacity at Risk Key Message 2: Coastal Impacts Key Message 3: Weather Disruptions Key Message 4: Costs and Adaptation Options Transportation Key Message 1: Disruptions from Extreme Weather Key Message 2: Climate Change and Seasonal Energy Demands Key Message 3: Implications of Less Water for Energy Production Key Message 4: Sea Level Rise and Infrastructure Damage Key Message 5: Future Energy Systems Energy	Gulf Coast Transportation Hubs at Risk Increase in Cooling Demand and Decrease in Heating Demand
Water Supply
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Water Introduction Key Message 1: Changing Rain, Snow, and Runoff Key Message 2: Droughts Intensify Key Message 3: Increased Risk of Flooding in Many Parts of the U.S. Key Message 4: Groundwater Availability Key Message 5: Risks to Coastal Aquifers and Wetlands Key Message 6: Water Quality Risks to Lakes and Rivers Key Message 7: Changes to Water Demand and Use Key Message 8: Drought is Affecting Water Supplies Key Message 9: Flood Effects on People and Communities Key Message 10: Water Resources Management Key Message 11: Adaptation Opportunities and Challenges Changes to Water Demand and Use Water Withdrawals Water Quality Key Message 1: Cascading Events Key Message 2: Options for Reducing Emissions and Climate Vulnerability Key Message 3: Challenges to Reducing Vulnerabilities Energy, Water, and Land Use	Energy, Water, Land, and Climate Interactions Projected Changes in Water Withdrawals Projected Snow Water Equivalent Water Stress in the U. S. Water Supplies Projected to Decline
Agriculture
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Agriculture Introduction Key Message 1: Increasing Impacts on Agriculture Key Message 2: Weeds, Diseases, and Pests Key Message 3: Extreme Precipitation and Soil Erosion Key Message 4: Heat and Drought Damage Key Message 5: Rate of Adaptation Key Message 6: Food Security Agriculture	Crop Yields Decline under Higher Temperatures Key Climate Variables Affecting Agricultural Productivity
Indigenous Peoples
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Indigenous Introduction Key Message 1: Forests, Fires, and Food Key Message 2: Water Quality and Quantity Key Message 3: Declining Sea Ice Key Message 4: Permafrost Thaw Key Message 5: Relocation Indigenous Peoples Alaska Natives Face Multiple Climate Impacts
Ecosystems and Biodiversity
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Ecosystems Introduction Key Message 1: Water Key Message 2: Extreme Events Key Message 3: Plants and Animals Key Message 4: Seasonal Patterns Key Message 5: Adaptation Ecosystems Key Message 1: Increasing Forest Disturbances Key Message 2: Changing Carbon Uptake Key Message 3: Bioenergy Potential Key Message 4: Influences on Management Choices Forests Key Message 1: Effects on Communities and Ecosystems Key Message 2: Effects on Climate Processes Key Message 3: Adapting to Climate Change Key Message 4: Reducing Greenhouse Gas Levels Land Use and Land Cover Change Key Message 1: Human-Induced Changes Key Message 2: Sinks and Cycles Key Message 3: Impacts and Options Biogeochemical Cycles	Building Loss by Fires at California Wildland-Urban Interfaces Forest Growth Provides an Important Carbon Sink Major North American Carbon Dioxide Sources and Sinks Many Factors Combine to Affect Biogeochemical Cycles Species Responses to Climate Change
Oceans
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Oceans Introduction Key Message 1: Rising Ocean Temperatures Key Message 2: Ocean Acidification Alters Marine Ecosystems Key Message 3: Habitat Loss Affects Marine Life Key Message 4: Rising Temperatures Linked to Diseases Key Message 5: Economic Impacts of Marine-related Climate Change Key Message 6: Initiatives Serve as a Model Oceans Acidification Diseases	Coral Bleaching Fisheries Shifting North Observed Ocean Warming Ocean Acidification Reduces Size of Clams Ocean Impacts of Increased Atmospheric Carbon Dioxide
Responses
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Responses Introduction Key Message 1 Key Message 2 Key Message 3 Key Message 4 Key Message 5 Key Message 6 Adaptation Key Message 1 Key Message 2 Key Message 3 Key Message 4 Key Message 5 Mitigation Federal Actions City, State, and Regional Actions Voluntary Actions Managing Land for Mitigation Key Message 1 Key Message 2 Key Message 3 Key Message 4 Key Message 5 Decision Support	Decision-Making Elements and Outcomes Decision-Making Framework
Regions
Northeast
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Northeast Introduction Key Message 1: Climate Risks to People Key Message 2: Stressed Infrastructure Key Message 3: Agricultural and Ecosystem Impacts Key Message 4: Planning and Adaptation Northeast Hurricane Vulnerability	Sea Level is Rising Urban Heat Island
Southeast
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Southeast Introduction Key Message 1: Sea Level Rise Threats Key Message 2: Increasing Temperatures Key Message 3: Water Availability Southeast	Billion Dollar Weather/Climate Disasters 1980-2012 Southeast Temperature: Observed and Projected Vulnerability to Sea Level Rise
Midwest
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Midwest Introduction Key Message 1: Impacts to Agriculture Key Message 2: Forest Composition Key Message 3: Public Health Risks Key Message 4: Fossil-Fuel Dependent Electricity System Key Message 5: Increased Rainfall and Flooding Key Message 6: Increased Risks to the Great Lakes Midwest	Great Lakes Ice Cover Decline Projected Climate Change
Great Plains
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Great Plains Introduction Key Message 1: Energy, Water and Land Use Key Message 2: Sustaining Agriculture Key Message 3: Conservation and Adaptation Key Message 4: Vulnerable Communities Key Message 5: Opportunities to Build Resilience Great Plains
Southwest
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Southwest Introduction Key Message 1: Reduced Snowpack and Streamflows Key Message 2: Threats to Agriculture Key Message 3: Increased Wildfire Key Message 4: Sea Level Rise and Coastal Damage Key Message 5: Heat Threats to Health Southwest	Longer Frost-free Season Increases Stress on Crops Selected Responses
Northwest
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Northwest Introduction Key Message 1: Water-related Challenges Key Message 2: Coastal Vulnerabilities Key Message 3: Impacts on Forests Key Message 4: Adapting Agriculture Northwest	Future Shift in Timing of Streamflows Insects and Fire in Northwest Forests
Alaska
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Alaska Introduction Key Message 1: Disappearing Sea Ice Key Message 2: Shrinking Glaciers Key Message 3: Thawing Permafrost Key Message 4: Changing Ocean Temperatures and Chemistry Key Message 5: Native Communities Alaska	Rising Temperatures The Big Thaw
Hawai'i
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Hawai‘i Introduction Key Message 1: Changes to Marine Ecosystems Key Message 2: Decreasing Freshwater Availability Key Message 3: Increased Stress on Native Plants and Animals Key Message 4: Sea Level Rising Key Message 5: Threats to Lives, Livelihoods, and Cultures Hawai‘i	Higher Sea Level Rise in Western Pacific
Rural Communities
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Rural Communities Introduction Key Message 1: Rural Economies Key Message 2: Responding to Risks Key Message 3: Adaptation Rural Communities	Many Rural Areas are Losing Population
Coasts
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Coasts Introduction Key Message 1: Coastal Lifelines at Risk Key Message 2: Economic Disruption Key Message 3: Uneven Social Vulnerability Key Message 4: Vulnerable Ecosystems Key Message 5: The State of Coastal Adaptation Coasts Lifelines at Risk Economic Disruption Socioeconomic Disparities Vulnerable Ecosystems	Coast-to-Inland Economic Connections Coastal Climate Change Threats Around the U.S. Paths of Hurricanes Katrina and Rita Relative to Oil and Gas Production Facilities

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Full Report
Our Changing Climate
Introduction
Our Changing Climate Introduction What's New?
Observed Change
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Our Changing Climate Introduction Key Message 1: Observed Climate Change Observed Change	2.1 Ten Indicators of a Warming World 2.2 Global Temperature and Carbon Dioxide 2.3 Separating Human and Natural Influences on Climate
Future Climate Change
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Our Changing Climate Introduction Key Message 2: Future Climate Change Future Climate Change	2.4 Emissions Levels Determine Temperature Rises 2.5 Projected Change in Average Annual Temperature 2.6 Projected Change in Average Annual Precipitation
Recent U.S. Temperature Trends
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Our Changing Climate Introduction Key Message 3: Recent U.S. Temperature Trends Recent U.S. Temperature Trends	2.7 Observed U.S. Temperature Change 2.8 Projected Temperature Change 2.9 Newer Simulations for Projected Temperature (CMIP5 models)
Frost-free Season
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Our Changing Climate Introduction Key Message 4: Lengthening Frost-free Season Lengthening Frost-free Season	2.10 Observed Increase in Frost-Free Season Length 2.11 Projected Changes in Frost-Free Season Length
Precipitation Change
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Our Changing Climate Introduction Key Message 5: U.S. Precipitation Change U.S. Precipitation Change	2.12 Observed U.S. Precipitation Change 2.13 Annual Maximum Precipitation 2.14 Projected Precipitation Change by Season 2.15 Newer Simulations for Projected Precipitation Change (CMIP5 models)
Heavy Downpours Increasing
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Our Changing Climate Introduction Key Message 6: Heavy Downpours Increasing Heavy Downpours Increasing	2.16 Observed U.S. Trend in Heavy Precipitation 2.17 Observed Change in Very Heavy Precipitation 2.18 Observed Change in Very Heavy Precipitation 2.19 Projected Change in Heavy Precipitation Events
Extreme Weather
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Our Changing Climate Introduction Key Message 7: Extreme Weather Extreme Weather	2.20 Projected Temperature Change of Hottest and Coldest Days 2.21 Trends in Flood Magnitude 2.22 Projected Changes in Soil Moisture for the Western U.S.
Changes in Hurricanes
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Our Changing Climate Introduction Key Message 8: Changes in Hurricanes Changes in Hurricanes	2.23 Observed Trends in Hurricane Power Dissipation
Changes in Storms
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Our Changing Climate Introduction Key Message 9: Changes in Storms Changes in Storms	2.24 Variation of Storm Frequency and Intensity during the Cold Season (November – March)
Sea Level Rise
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Our Changing Climate Introduction Key Message 10: Sea Level Rise Sea Level Rise	2.25 North Atlantic Sea Level Change 2.26 Past and Projected Changes in Global Sea Level Rise
Melting Ice
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Our Changing Climate Introduction Key Message 11: Melting Ice Melting Ice	2.27 Ice Cover in the Great Lakes 2.28 Decline in Arctic Sea Ice Extent 2.29 Projected Arctic Sea Ice Decline
Ocean Acidification
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Our Changing Climate Introduction Key Message 12: Ocean Acidification Ocean Acidification	2.30 As Oceans Absorb CO₂, They Become More Acidic 2.31 Shells Dissolve in Acidified Ocean Water
Sectors
Water
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Water Introduction Key Message 1: Changing Rain, Snow, and Runoff Changing Rain, Snow, and Runoff Key Message 2: Droughts Intensify Droughts Intensify Key Message 3: Increased Risk of Flooding in Many Parts of the U.S. Increased Risk of Flooding in Many Parts of the U.S. Key Message 4: Groundwater Availability Groundwater Availability Key Message 5: Risks to Coastal Aquifers and Wetlands Risks to Coastal Aquifers and Wetlands Key Message 6: Water Quality Risks to Lakes and Rivers Water Quality Risks to Lakes and Rivers Climate Change Impacts on Water Resource Uses and Management Key Message 7: Changes to Water Demand and Use Changes to Water Demand and Use Key Message 8: Drought is Affecting Water Supplies Drought is Affecting Water Supplies Key Message 9: Flood Effects on People and Communities Flood Effects on People and Communities Key Message 10: Water Resources Management Water Resources Management Key Message 11: Adaptation Opportunities and Challenges Adaptation Opportunities and Challenges	3.1 Projected Changes in Snow, Runoff, and Soil Moisture 3.10 U.S. Water Withdrawal Distribution 3.11 Projected Changes in Water Withdrawals 3.12 Water Challenges in a Southeast River Basin 3.2 Annual Surface Soil Moisture Trends 3.3 Seasonal Surface Soil Moisture Trends 3.4 Streamflow Projections for River Basins in the Western U.S. 3.5 Trends in Flood Magnitude 3.6 Principal U.S. Groundwater Aquifers and Use 3.7 Observed Changes in Lake Stratification and Ice Covered Area 3.8 U.S. Freshwater Withdrawal, Consumptive Use, and Population Trends 3.9 Freshwater Withdrawals by Sector
Energy
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Energy Supply and Use Introduction Key Message 1: Disruptions from Extreme Weather Disruptions from Extreme Weather Key Message 2: Climate Change and Seasonal Energy Demands Climate Change and Seasonal Energy Demands Key Message 3: Implications of Less Water for Energy Production Implications of Less Water for Energy Production Key Message 4: Sea Level Rise and Infrastructure Damage Sea Level Rise and Infrastructure Damage Key Message 5: Future Energy Systems Future Energy Systems	4.1 Paths of Hurricanes Katrina and Rita Relative to Oil and Gas Production Facilities 4.2 Increase in Cooling Demand and Decrease in Heating Demand 4.3 Increasing Numbers of Cooling Degree Days 4.4 Projected Changes in Seasonal Precipitation 4.5 California Power Plants Potentially at Risk from Sea Level Rise	4.1 Changing Energy Use for Heating and Cooling Will Vary by Region 4.2 Possible Climate Resilience and Adaptation Actions in Energy Sector 4.3 Energy Supply: Summary of National and Regional Impacts, Challenges and Opportunities
Transportation
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Transportation Introduction Key Message 1: Reliability and Capacity at Risk Reliability and Capacity at Risk Key Message 2: Coastal Impacts Coastal Impacts Key Message 3: Weather Disruptions Weather Disruptions Risks and Consequences Key Message 4: Costs and Adaptation Options Costs and Adaptation Options	5.1 Possible Future Flood Depths in Mobile, AL with Rising Sea Level 5.2 Airports Vulnerable to Storm Surge 5.3 Gulf Coast Transportation Hubs at Risk 5.4 Hurricane Sandy Causes Flooding in New York City Subway Stations 5.5 Role of Adaptive Strategies and Tactics in Reducing Impacts and Consequences 5.6 Tropical Storm Impact on Vermont Road	5.1 Illustrative Risks of Climate-related Impacts
Agriculture
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Agriculture Introduction Key Message 1: Increasing Impacts on Agriculture Increasing Impacts on Agriculture Impacts on Animal Production from Temperature Extremes Key Message 2: Weeds, Diseases, and Pests Weeds, Diseases, and Pests Key Message 3: Extreme Precipitation and Soil Erosion Extreme Precipitation and Soil Erosion Key Message 4: Heat and Drought Damage Heat and Drought Damage Key Message 5: Rate of Adaptation Rate of Adaptation Key Message 6: Food Security Food Security	6.1 U.S. Agriculture 6.2 Agricultural Distribution 6.3 U.S. Agricultural Trade 6.4 Crop Yield Response to Warming in California's Central Valley 6.5 Projected Changes in Key Climate Variables Affecting Agricultural Productivity 6.6 Reduced Winter Chilling Projected for California 6.7 Runoff Leads to Soil Erosion 6.8 Subsurface Drainage System 6.9 Increasing Heavy Downpours in Iowa
Forests
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Forests Introduction Key Message 1: Increasing Forest Disturbances Increasing Forest Disturbances Key Message 2: Changing Carbon Uptake Changing Carbon Uptake Forest Carbon Sequestration and Carbon Management Key Message 3: Bioenergy Potential Bioenergy Potential Key Message 4: Influences on Management Choices Influences on Management Choices	7.1 Forest Ecosystem Disturbances 7.2 Effectiveness of Forest Management in Reducing Wildfire Risk 7.3 Forest Vulnerability to Changing Climate 7.4 Forests can be a Source - or a Sink - for Carbon 7.5 Forest Growth Provides an Important Carbon Sink 7.6 Forests and Carbon 7.7 Location of Potential Forestry Biomass Resources 7.8 Public and Private Forestlands
Ecosystems
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Ecosystems, Biodiversity, and Ecosystem Services Introduction Key Message 1: Water Water Key Message 2: Extreme Events Extreme Events Key Message 3: Plants and Animals Plants and Animals Key Message 4: Seasonal Patterns Seasonal Patterns Key Message 5: Adaptation Adaptation	8.1 Water Supplies Projected to Decline 8.2 The Aftermath of Hurricanes 8.3 Adaptation Planning and Implementation Framework 8.4 Biological Responses to Climate Change
Human Health
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Human Health Introduction Key Message 1: Wide-ranging Health Impacts Wide-ranging Health Impacts Key Message 2: Most Vulnerable at Most Risk Most Vulnerable at Most Risk Key Message 3: Prevention Provides Protection Prevention Provides Protection Key Message 4: Responses Have Multiple Benefits Responses Have Multiple Benefits	9.1 Climate Change Projected to Worsen Asthma 9.10 Katrina Diaspora 9.2 Ragweed Pollen Season Lengthens 9.3 Wildfire Smoke has Widespread Health Effects 9.4 Projected Temperature Change of Hottest Days 9.5 Projected Changes in Tick Habitat 9.6 Projected Change in Heavy Precipitation Events 9.7 Heavy Downpours Are Increasing Exposure to Disease 9.8 Harmful Bloom of Algae 9.9 Elements of Vulnerability to Climate Change
Energy, Water, and Land
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Energy, Water, and Land Use Introduction Key Message 1: Cascading Events Cascading Events Interactions of Energy, Water, and Land Uses Key Message 2: Options for Reducing Emissions and Climate Vulnerability Options for Reducing Emissions and Climate Vulnerability Key Message 3: Challenges to Reducing Vulnerabilities Challenges to Reducing Vulnerabilities	10.1 Energy, Water, Land, and Climate Interactions 10.10 The Columbia River Basin Land Use and Land Cover 10.2 Coast-to-Coast 100-degree Days in 2011 10.3 Texas Summer 2011: Record Heat and Drought 10.4 Regional Water, Energy, and Land Use, with Projected Climate Change Impacts 10.5 Water Use for Electricity Generation by Fuel and Cooling Technology 10.6 Projected Land-use Intensity in 2030 10.7 Hydraulic Fracturing and Water Use 10.8 Renewable Energy and Land Use 10.9 Water Stress in the U.S.	10.1 Energy, water, and land sectoral impacts
Urban
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Urban Systems, Infrastructure, and Vulnerability Introduction Key Message 1: Urbanization and Infrastructure Systems Urbanization and Infrastructure Systems Key Message 2: Essential Services are Interdependent Essential Services are Interdependent Key Message 3: Social Vulnerability and Human Well-Being Social Vulnerability and Human Well-Being Key Message 4: Trends in Urban Adaptation - Lessons from Current Adopters Trends in Urban Adaptation – Lessons from Current Adopters	11.1 Blackout in New York and New Jersey after Hurricane Sandy 11.2 Urban Support Systems are Interconnected 11.3 New York City and Sea Level Rise
Indigenous Peoples
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Indigenous People Introduction Climate Change and Traditional Knowledge Key Message 1: Forests, Fires, and Food Forests, Fires, and Food Key Message 2: Water Quality and Quantity Water Quality and Quantity Key Message 3: Declining Sea Ice Declining Sea Ice Key Message 4: Permafrost Thaw Permafrost Thaw Key Message 5: Relocation Relocation	12.1 Indigenous Populations Extend beyond Reservation Lands 12.2 Many Tribes, Many Climate Change Initiatives 12.3 Sand Dune Expansion 12.4 Sea Ice Cover Reaches Record Low 12.5 Arctic Marine Food Web 12.6 Thawing Permafrost in Alaska
Land Use and Land Cover Change
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Land Use Introduction Recent Trends Projections Key Message 1: Effects on Communities and Ecosystems Effects on Communities and Ecosystems Key Message 2: Effects on Climate Processes Effects on Climate Processes Key Message 3: Adapting to Climate Change Adapting to Climate Change Key Message 4: Reducing Greenhouse Gas Levels Reducing Greenhouse Gas Levels	13.1 U.S. Land-Cover Composition in 2000 13.2 Projections of Settlement Densities (2010-2050) 13.3 Projected Land Covers (2010-2050) 13.4 Building Loss by Fires at California Wildland-Urban Interfaces	13.1 Land Cover Statistics 13.2 Percent Change in Land Cover
Rural Communities
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Rural Communities Introduction Key Message 1: Rural Economies Rural Economies Key Message 2: Responding to Risks Responding to Risks Key Message 3: Adaptation Adaptation	14.1 Rural Counties 14.2 Economic Dependence Varies by Region 14.3 Growing Season Lengthens 14.4 Climate Change Impacts on Summertime Tourism 14.5 Many Rural Areas are Losing Population
Biogeochemical Cycles
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Biogeochem Introduction Key Message 1: Human-Induced Changes Human-Induced Changes State of the Carbon Cycle Sources and Fates of Reactive Nitrogen Phosphorus and Other Elements Key Message 2: Sinks and Cycles Sinks and Cycles Carbon Nitrogen and Phosphorus Other Effects: Sulfate Aerosols Key Message 3: Impacts and Options Impacts and Options Climate-Biogeochemistry Feedbacks Biogeochemistry, Climate, and Interactions with Other Factors	15.1 Major North American Carbon Dioxide Sources and Sinks 15.2 Human Activities that Form Reactive Nitrogen and Resulting Consequences in Environmental 15.3 Nitrogen Emissions 15.4 Many Factors Combine to Affect Biogeochemical Cycles 15.5 U.S. Carbon Sinks Absorb a Fraction of CO₂ Emissions 15.6 U.S. Carbon Sources and Sinks from 1991 to 2000 and 2001 to 2010	15.1 Ecosystem Carbon Sinks
Regions
Northeast
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Northeast Introduction Observed Climate Change Key Message 1: Climate Risks to People Climate Risks to People Key Message 2: Stressed Infrastructure Stressed Infrastructure Key Message 3: Agricultural and Ecosystem Impacts Agricultural and Ecosystem Impacts Key Message 4: Planning and Adaptation Planning and Adaptation	16.1 Sea level is Rising 16.2 Projected Increases in the Number of Days over 90°F. 16.3 Flooding and Hurricane Irene 16.4 Coastal Flooding along New Jersey's Shore 16.5 Urban Heat Island 16.6 Coney Island after Hurricane Irene 16.7 Connecticut Coastline and Expanding Salt Marshes 16.8 Storm Surge Barrier	16.1 Impacts of sea level rise
Southeast
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Southeast Introduction Observed and Projected Climate Change Key Message 1: Sea Level Rise Threats Sea Level Rise Threats Key Message 2: Increasing Temperatures Increasing Temperatures Key Message 3: Water Availability Water Availability	17.1 Billion Dollar Weather/Climate Disasters 17.10 Ground-level Ozone 17.11 Trends in Water Availability 17.12 A Southeast River Basin Under Stress 17.2 Shrinking Lands for Tribal Communities 17.3 Southeast Temperature: Observed and Projected 17.4 Projected Change in Number of Days Over 95°F 17.5 Projected Change in Number of Nights Below 32°F 17.6 Vulnerability to Sea Level Rise 17.7 Highway 1 to Port Fourchon: Vulnerability of a Critical Link for U.S. Oil 17.8 South Florida: Uniquely Vulnerable to Sea Level Rise 17.9 Local Planning
Midwest
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Midwest Introduction Key Message 1: Impacts to Agriculture Impacts to Agriculture Key Message 2: Forest Composition Forest Composition Key Message 3: Public Health Risks Public Health Risks Key Message 4: Fossil-Fuel Dependent Electricity System Fossil-Fuel Dependent Electricity System Key Message 5: Increased Rainfall and Flooding Increased Rainfall and Flooding Key Message 6: Increased Risks to the Great Lakes Increased Risks to the Great Lakes	18.1 Temperatures are Rising in the Midwest 18.2 Projected Mid-Century Temperature Changes in the Midwest 18.3 Crop Yields Decline under Higher Temperatures 18.4 Forest Composition Shifts 18.5 Reducing Emissions, Improving Health 18.6 When it Rains, it Pours 18.7 Ice Cover in the Great Lakes
Great Plains
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Great Plains Introduction Projected Climate Change Key Message 1: Energy, Water and Land Use Energy, Water and Land Use Key Message 2: Sustaining Agriculture Sustaining Agriculture Key Message 3: Conservation and Adaptation Conservation and Adaptation Key Message 4: Vulnerable Communities Vulnerable Communities Key Message 5: Opportunities to Build Resilience Opportunities to Build Resilience	19.1 Temperature and Precipitation Distribution in the Great Plains 19.10 Days Above 100ºF in Summer 2011 19.2 Projected Change in Number of Hot Days 19.3 Projected Change in Number of Warm Nights 19.4 Projected Change in Number of Heavy Precipitation Days 19.5 Projected Change in Number of Consecutive Dry Days 19.6 Increases in Irrigated Farmland in the Great Plains 19.7 Historical and Current Range of Sage Grouse Habitat 19.8 Population Change in the Great Plains 19.9 Tribal Populations in the Great Plains
Southwest
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Southwest Introduction Observed and Projected Climate Change Key Message 1: Reduced Snowpack and Streamflows Reduced Snowpack and Streamflows Key Message 2: Threats to Agriculture Threats to Agriculture Key Message 3: Increased Wildfire Increased Wildfire Key Message 4: Sea Level Rise and Coastal Damage Sea Level Rise and Coastal Damage Key Message 5: Heat Threats to Health Heat Threats to Health	20.1 Projected Temperature Increases 20.2 Projected Snow Water Equivalent 20.3 Scenario for Greenhouse Gas Emissions Reductions in the Electricity Sector 20.4 Longer Frost-Free Season Increases Stress on Crops 20.5 Coastal Risks Posed by Sea Level Rise and High Tides 20.6 Urban Heat and Public Health
Northwest
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Northwest Introduction Observed Climate Change Projected Climate Change Key Message 1: Water-related Challenges Water-related Challenges Key Message 2: Coastal Vulnerabilities Coastal Vulnerabilities Key Message 3: Impacts on Forests Impacts on Forests Key Message 4: Adapting Agriculture Adapting Agriculture	21.1 Observed Shifts in Streamflow Timing 21.2 Future Shift in Timing of Stream Flows Reduced Summer Flows 21.3 Projected Relative Sea Level Rise for the Latitude of Newport, Oregon 21.4 Rising Sea Levels and Changing Flood Risks in Seattle 21.5 Adapting the Nisqually River Delta to Sea Level Rise 21.6 Forest mortality 21.7 Insects and Fire in Northwest Forests
Alaska
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Alaska Introduction Observed Climate Change Projected Climate Change Key Message 1: Disappearing Sea Ice Disappearing Sea Ice Key Message 2: Shrinking Glaciers Shrinking Glaciers Key Message 3: Thawing Permafrost Thawing Permafrost Key Message 4: Changing Ocean Temperatures and Chemistry Changing Ocean Temperatures and Chemistry Key Message 5: Native Communities Native Communities	Muir Glacier 22.1 Alaska Will Continue to Warm Rapidly 22.2 Declining Sea Ice Extent 22.3 Sea Ice Loss Brings Big Changes to Arctic Life 22.4 Newtok, Alaska 22.5 The Big Thaw 22.6 Mounting Expenses from Permafrost Thawing 22.7 Drying Lakes and Changing Habitat 22.8 Alaska Coastal Communities Damaged
Hawai'i and Pacific Islands
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Hawaii Introduction Key Message 1: Changes to Marine Ecosystems Changes to Marine Ecosystems Key Message 2: Decreasing Freshwater Availability Decreasing Freshwater Availability Key Message 3: Increased Stress on Native Plants and Animals Increased Stress on Native Plants and Animals Key Message 4: Sea Level Rising Sea Level Rising Key Message 5: Threats to Lives, Livelihoods, and Cultures Threats to Lives, Livelihoods, and Cultures	23.1 U.S. Pacific Islands Region 23.2 “High” and “Low” Pacific Islands Face Different Threats 23.3 Increased Acidification Decreases Suitable Coral Habitat 23.4 Observed Changes in Annual Rainfall in the Western North Pacific 23.5 Native Plants at Risk 23.6 Saltwater Intrusion Destroys Crops 23.7 Residents of Low-lying Islands at Risk 23.8 Higher Sea Level Rise in Western Pacific
Oceans
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Oceans Introduction Key Message 1: Rising Ocean Temperatures Rising Ocean Temperatures Key Message 2: Ocean Acidification Alters Marine Ecosystems Ocean Acidification Alters Marine Ecosystems Key Message 3: Habitat Loss Affects Marine Life Habitat Loss Affects Marine Life Key Message 4: Rising Temperatures Linked to Diseases Rising Temperatures Linked to Diseases Key Message 5: Economic Impacts of Marine-related Climate Change Economic Impacts of Marine-related Climate Change Key Message 6: Initiatives Serve as a Model Initiatives Serve as a Model	Shells Dissolve in Acidified Ocean Water 24.1 Observed Ocean Warming 24.2 Ocean Impacts of Increased Atmospheric Carbon Dioxide 24.3 Ocean Acidification Reduces Size of Clams 24.4 Warming Seas Are a Double-blow to Corals 24.5 Fisheries Shifting North
Coasts
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Coasts Introduction Climate-related Drivers of Coastal Change Key Message 1: Coastal Lifelines at Risk Coastal Lifelines at Risk Key Message 2: Economic Disruption Economic Disruption Key Message 3: Uneven Social Vulnerability Uneven Social Vulnerability Key Message 4: Vulnerable Ecosystems Vulnerable Ecosystems Key Message 5: The State of Coastal Adaptation The State of Coastal Adaptation	25.1 Population Change in U.S. Coastal Watershed Counties (1970-2010) 25.2 Flooding During High Tides 25.3 Projected Sea Level Rise and Flooding by 2050 25.4 25.5 Adapting Coastal Infrastructure to Sea Level Rise and Land Loss 25.6 Ecosystem Restoration 25.7 Coast-to-Inland Economic Connections 25.8 Coastal Ecosystem Services 25.9 Projected Land Loss from Sea Level Rise in Coastal Louisiana
Response Strategies
Decision Support
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Decision Support Introduction Key Message 1 Key Message 2 Key Message 3 Key Message 4 Key Message 5 Introduction Boundary Processes: Collaboration among Decision-Makers, Scientists, and Stakeholders Using a Decision-Making Framework Defining the Issue and Establishing Decision Criteria Accessing Information Assessing, Perceiving, and Managing Risk Implementation, Continued Monitoring, and Evaluation of Decisions Examples of Decision Support Tools and Methods Incorporating Recent Scientific Advances and Translating Science for Decision-Making Research to Improve Decision Support	26.1 Decision-making Elements and Outcomes 26.2 Boundary Processes Linking Decision-Makers and Scientific/Technical Experts 26.3 Decision-Making Framework 26.4 Linking Risk Assessment and Risk Perception with Risk Management of Climate Change 26.5 Land-use Planning Tool for the Upper Santa Cruz Watershed. 26.6 Scenario Planning	26.1 Examples of decisions at different scales 26.2 Examples of decisions and tools used
Mitigation
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Mitigation Introduction Emissions, Concentrations, and Climate Forcing Key Message 1 Key Message 2 Key Message 3 Key Message 4 Key Message 5 Section 1: U.S. Emissions and Land-Use Change Section 2: Activities Affecting Emissions Section 3: Preparation for Potential Future Mitigation Action Section 4: Research Needs	27.1 Human Activities and the Global Carbon Dioxide Budget 27.2 Drivers of U.S. Fossil Emissions 27.3 Sources and Sinks in U.S. Agriculture and Forests	27.1 Sample Federal Mitigation Measures 27.2 State Climate and Energy Initiatives
Adaptation
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Adaptation Introduction Key Message 1 Key Message 2 Key Message 3 Key Message 4 Key Message 5 Key Message 6 Adaptation Activities in the United States States Tribal Governments Local and Regional Governments Non-governmental and Private Sector Section 1: Adaptation Process Section 2: Barriers to Adaptation and Examples of Overcoming Barriers Section 3: Next Steps Section 4: Case Studies	28.1 Status of State Climate Adaptation Plans 28.2 Effects of Climate Change on... 28.3 Adaptation Process 28.4 Adaptation Activity 28.5 U.S. Drought Monitor August 14, 2012 28.6 Northwoods Climate Change Response Framework Region	28.1 Examples of Individual Federal Agency Actions to Promote, Implement, and Support Adaptation at Multiple Scales* 28.2 Examples of State-Level Adaptation Activities* 28.3 Examples of Local and Regional Adaptation Activities* 28.4 Examples of Non-governmental Adaptation Efforts and Services* 28.5 Examples of Private Sector Actions to Adapt to Climate Risks as Reported to the Carbon Disclosure Project* 28.6 Summary of Adaptation Barriers
Research Needs
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Research Needs Introduction Research Goal 1: Improve understanding of the climate system and its drivers Improve understanding of the climate system and its drivers Research Goal 2: Improve understanding of climate impacts and vulnerability Improve understanding of climate impacts and vulnerability Research Goal 3: Increase understanding of adaptation pathways Increase understanding of adaptation pathways Research Goal 4: Identify the mitigation options that reduce the risk of longer-term climate change Identify the mitigation options that reduce the risk of longer-term climate change Research Goal 5: Improve decision support and integrated assessment Improve decision support and integrated assessment Foundational Cross-Cutting Research Capabilities to Support Future Climate Assessments 1. Integrate natural and social sciences, engineering, and other disciplinary approaches 2. Ensure availability of observations, monitoring, and infrastructure for critical data collection and analysis 3. Build capacity for climate assessment through training, education, and workforce development 4. Enhance the development and use of scenarios 5. Promote international research and collaboration Conclusions
Sustained Assessment
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Sustained Assessment Introduction Contributions of a Sustained Assessment Process Assessment Capacity Data Collection, Access, and Analysis Indicators Special and Foundational Reports A Network to Foster Partnerships, Encourage Engagement, and Develop Solutions Evaluation of the Process Recommendations on Research Priorities Traceable Account
Appendices
Climate Science Supplement
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Climate Science Supplement Introduction Supplemental Message 1 Supplemental Message 1 Supplemental Message 2 Supplemental Message 2 Supplemental Message 3 Supplemental Message 3 Supplemental Message 4 Supplemental Message 4 Supplemental Message 5 Supplemental Message 5 Supplemental Message 6 Supplemental Message 6 Supplemental Message 7 Supplemental Message 7 Supplemental Message 8 Supplemental Message 8 Supplemental Message 9 Supplemental Message 9 Supplemental Message 10 Supplemental Message 10 Supplemental Message 11 Supplemental Message 11 Supplemental Message 12 Supplemental Message 12	Muir Glacier 33.1 Human Influence on the Greenhouse Effect 33.10 Indicators of Warming from Multiple Data Sets 33.11 Precipitation Trends: Past Century, Past 30+ Years 33.12 1700 Years of Temperature Change from Proxy Data 33.13 La Niña and El Niño Patterns 33.14 Warming Trend and Effects of El Niño/La Niña 33.15 Long-Term Warming and Short-Term Variation 33.16 Detection and Attribution as Forensics 33.17 Human Influences Apparent in Many Aspects of the Changing Climate 33.18 Only Human Influence Can Explain Recent Warming 33.19 Emissions, Concentrations, and Temperature Projections 33.2 Earth’s Energy Balance 33.20 Projected Annually-Averaged Temperature Change 33.21 Projected Wintertime Precipitation Changes 33.22 Projected Summertime Precipitation Changes 33.23 Carbon Emissions: Historical and Projected 33.24 Modeling the Climate System 33.25 Increasing Model Resolution 33.26 Increasing Climate Model Components 33.27 Trends in Maximum and Minimum Temperatures 33.28 U.S. Seasonal Temperatures 33.29 Ice Cover on Lake Mendota 33.3 Carbon Emissions in the Industrial Age 33.30 Streamflow from Snowmelt Coming Earlier in the Year 33.31 Shifts in Plant Hardiness Zones 33.32 Extreme Precipitation 33.33 Percent of West in Summer Drought 33.34 Changing Forest Fires in the U.S. 33.35 Extreme Drought in the U.S. and Mexico, Past and Future 33.36 Change in Maximum Number of Consecutive Dry Days 33.37 Arctic Sea Ice Decline 33.38 Permafrost Temperatures Rising 33.39 Melting of Arctic Land-based Ice 33.4 Heat-Trapping Gas Levels 33.40 Melting Glaciers Lead to Sea Level Rise 33.41 Sea Level Rise, 1993-2012 33.42 Ice Loss from Greenland and Antarctica 33.5 Atmospheric Carbon Dioxide Levels 33.6 Relative Strengths of Warming and Cooling Influences 33.7 Development of Observing Capabilities 33.8 Observed Change in Global Average Temperature 33.9 Temperature Trends: Past Century, Past 30+ Years
FAQs
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FAQs Introduction A: How can we predict what climate will be like in 100 years if we can’t even predict the weather next week? B: Is the climate changing? How do we know? C: Climate is always changing. How is recent change different than in the past? D: Is the globally averaged surface air temperature still increasing? Isn’t there recent evidence that it is actually cooling? E: Is it getting warmer at the same rate everywhere? Will the warming continue? F: How long have scientists been investigating human influences on climate? G: How can the small proportion of carbon dioxide in the atmosphere have such a large effect on our climate? H: Could the sun or other natural factors explain the observed warming of the past 50 years? I: How do we know that human activities are the primary cause of recent climate change? J: What is and is not debated among climate scientists about climate change? K: Is the global surface temperature record good enough to determine whether climate is changing? L: Is Antarctica gaining or losing ice? What about Greenland? M: Weren’t there predictions of global cooling in the 1970s? N: How is climate projected to change in the future? O: Does climate change affect severe weather? P: How are the oceans affected by climate change? Q: What is ocean acidification? R: How reliable are the computer models of the Earth’s climate? S: What are the key uncertainties about climate change? T: Are there tipping points in the climate system? U: How is climate change affecting society? V: Are there benefits to warming? W: Are some people more vulnerable than others? X: Are there ways to reduce climate change? Y: Are there advantages to acting sooner rather than later? Z: Can we reverse global warming?	34.1 U.S. Annual Average Temperature 34.10 Early Scientists who Established the Scientific Basis for Climate Change 34.11 Human Influence on the Greenhouse Effect 34.12 Measurements of Surface Temperature and Sun’s Energy 34.13 Human Influences Apparent in Many Aspects of the Changing Climate 34.14 Only Human Influence Can Explain Recent Warming 34.15 Separating Human and Natural Influences on Climate 34.16 Observed Change in Global Average Temperature 34.17 Ice Loss from the Two Polar Ice Sheets 34.18 Published Climate Change Research Papers 34.19 Observed and Projected U.S. Temperature Change 34.2 Ten Indicators of a Warming World 34.20 Coral Bleaching 34.21 Ocean Acidification and the Food Web 34.22 Climate Models and Temperature Change 34.23 Emissions Levels Determine Temperature Rises 34.24 Potential Tipping Points 34.25 Potential Effects of Climate Change 34.26 Multiple Pathways for Reducing U.S. Emissions 34.27 Two U.S. Emissions-Reduction Pathways 34.28 Emissions Reductions and Carbon Dioxide Concentrations 34.3 Indicators of Warming from Multiple Data Sets 34.4 Carbon Emissions in the Industrial Age 34.5 1700 Years of Temperature Change from Proxy Data 34.6 Short-term Variations Versus Long-term Trend 34.7 Global Temperature Change: Decade Averages 34.8 Temperature Trends, 1900-2012 34.9 Decade-Scale Changes in Average Temperature for U.S. Regions

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