This website is a clone of the Fifth National Climate Assessment, as it was originally published by the U.S. Global Change Research Program at the URL nca2023.globalchange.gov. Its content has not been altered from the original in any way; however, this is not an official U.S. government website.

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nca2023.globalchange.gov
Fifth National Climate Assessment

Chapters and Pages

https://nca5.climate.us/chapter/front-matter/
Front Matter
https://nca5.climate.us/chapter/1/
Overview
https://nca5.climate.us/chapter/2/
Climate Trends
https://nca5.climate.us/chapter/3/
Earth Systems Processes
https://nca5.climate.us/chapter/4/
Water
https://nca5.climate.us/chapter/5/
Energy Supply, Delivery, and Demand
https://nca5.climate.us/chapter/6/
Land Cover and Land-Use Change
https://nca5.climate.us/chapter/7/
Forests
https://nca5.climate.us/chapter/8/
Ecosystems, Ecosystem Services, and Biodiversity
https://nca5.climate.us/chapter/9/
Coastal Effects
https://nca5.climate.us/chapter/10/
Ocean Ecosystems and Marine Resources
https://nca5.climate.us/chapter/11/
Agriculture, Food Systems, and Rural Communities
https://nca5.climate.us/chapter/12/
Built Environment, Urban Systems, and Cities
https://nca5.climate.us/chapter/13/
Transportation
https://nca5.climate.us/chapter/14/
Air Quality
https://nca5.climate.us/chapter/15/
Human Health
https://nca5.climate.us/chapter/16/
Tribes and Indigenous Peoples
https://nca5.climate.us/chapter/17/
Climate Effects on US International Interests
https://nca5.climate.us/chapter/18/
Sector Interactions, Multiple Stressors, and Complex Systems
https://nca5.climate.us/chapter/19/
Economics
https://nca5.climate.us/chapter/20/
Social Systems and Justice
https://nca5.climate.us/chapter/21/
Northeast
https://nca5.climate.us/chapter/22/
Southeast
https://nca5.climate.us/chapter/23/
US Caribbean
https://nca5.climate.us/chapter/24/
Midwest
https://nca5.climate.us/chapter/25/
Northern Great Plains
https://nca5.climate.us/chapter/26/
Southern Great Plains
https://nca5.climate.us/chapter/27/
Northwest
https://nca5.climate.us/chapter/28/
Southwest
https://nca5.climate.us/chapter/29/
Alaska
https://nca5.climate.us/chapter/30/
Hawai'i and US-Affiliated Pacific Islands
https://nca5.climate.us/chapter/31/
Adaptation
https://nca5.climate.us/chapter/32/
Mitigation
https://nca5.climate.us/chapter/focus-on-1/
Focus on Compound Events
https://nca5.climate.us/chapter/focus-on-2/
Focus on Western Wildfires
https://nca5.climate.us/chapter/focus-on-3/
Focus on COVID-19 and Climate Change
https://nca5.climate.us/chapter/focus-on-4/
Focus on Risks to Supply Chains
https://nca5.climate.us/chapter/focus-on-5/
Focus on Blue Carbon
https://nca5.climate.us/chapter/appendix-1/
Assessment Development Process
https://nca5.climate.us/chapter/appendix-2/
Information Quality
https://nca5.climate.us/chapter/appendix-3/
Scenarios and Datasets
https://nca5.climate.us/chapter/appendix-4/
Indicators
https://nca5.climate.us/chapter/appendix-5/
Glossary
/credits
Credits
/art-climate
Art x Climate
/downloads
Downloads
/all-figures
All Figures

Key Messages

/chapter/2#key-message-1
KM 2.1. Climate Is Changing, and Scientists Understand Why

/chapter/2#key-message-2
KM 2.2. Extreme Events Are Becoming More Frequent and Severe

/chapter/2#key-message-3
KM 2.3. How Much the Climate Changes Depends on the Choices Made Now

/chapter/3#key-message-1
KM 3.1. Human Activities Have Caused the Observed Global Warming

/chapter/3#key-message-2
KM 3.2. The Estimated Range of Climate Sensitivity Has Narrowed by 50%

/chapter/3#key-message-3
KM 3.3. New Data and Analysis Methods Have Advanced Climate Science

/chapter/3#key-message-4
KM 3.4. Humans Are Changing Earth System Processes

/chapter/3#key-message-5
KM 3.5. Humans Are Changing Weather and Climate Extremes

/chapter/4#key-message-1
KM 4.1. Climate Change Will Continue to Cause Profound Changes in the Water Cycle

/chapter/4#key-message-2
KM 4.2. Water Cycle Changes Will Affect All Communities, with Disproportionate Impacts for Some

/chapter/4#key-message-3
KM 4.3. Progress Toward Adaptation Has Been Uneven

/chapter/5#key-message-1
KM 5.1. Climate Change Threatens Energy Systems

/chapter/5#key-message-2
KM 5.2. Compounding Factors Affect Energy-System and Community Vulnerabilities

/chapter/5#key-message-3
KM 5.3. Efforts to Enhance Energy System Resilience Are Underway

/chapter/6#key-message-1
KM 6.1. The Goods and Services Provided by Land Systems Are Threatened by Climate Change

/chapter/6#key-message-2
KM 6.2. Changes in Climate and Land Use Affect Land-System Resilience

/chapter/6#key-message-3
KM 6.3. Mitigation and Adaptation Priorities Will Increasingly Constrain Future Land-Use Options

/chapter/7#key-message-1
KM 7.1. Forests Are Increasingly Affected by Climate Change and Disturbances

/chapter/7#key-message-2
KM 7.2. Climate Change Affects Ecosystem Services Provided by Forests

/chapter/7#key-message-3
KM 7.3. Adaptation Actions Are Necessary for Maintaining Resilient Forest Ecosystems

/chapter/8#key-message-1
KM 8.1. Climate Change Is Driving Rapid Ecosystem Transformations

/chapter/8#key-message-2
KM 8.2. Species Changes and Biodiversity Loss Are Accelerating

/chapter/8#key-message-3
KM 8.3. Impacts to Ecosystem Services Create Risks and Opportunities

/chapter/9#key-message-1
KM 9.1. Coastal Hazards Are Increasing Due to Accelerating Sea Level Rise and Changing Storm Patterns

/chapter/9#key-message-2
KM 9.2. Coastal Impacts on People and Ecosystems Are Increasing Due to Climate Change

/chapter/9#key-message-3
KM 9.3. Adaptation Reduces Risk and Provides Additional Benefits for Coastal Communities

/chapter/10#key-message-1
KM 10.1. Unprecedented Climate Impacts Threaten Ecosystems and Human Well-Being

/chapter/10#key-message-2
KM 10.2. Climate Change Is Altering Marine-Related Economic Activities

/chapter/10#key-message-3
KM 10.3. Our Future Ocean Depends on Decisions Today

/chapter/11#key-message-1
KM 11.1. Agricultural Adaptation Increases Resilience in an Evolving Landscape

/chapter/11#key-message-2
KM 11.2. Climate Change Disrupts Our Food Systems in Uneven Ways

/chapter/11#key-message-3
KM 11.3. Rural Communities Face Unique Challenges and Opportunities

/chapter/12#key-message-1
KM 12.1. Urban Areas Are Major Drivers of Climate Change

/chapter/12#key-message-2
KM 12.2. Attributes of the Built Environment Exacerbate Climate Impacts, Risks, and Vulnerabilities

/chapter/12#key-message-3
KM 12.3. Urban Environments Create Opportunities for Climate Mitigation and Adaptation

/chapter/12#key-message-4
KM 12.4. Community-Led Actions Signal a Shift Toward Equitable Climate Governance

/chapter/13#key-message-1
KM 13.1. Limiting Transportation Sector Emissions and Integrating Climate Projections Can Reduce Risks

/chapter/13#key-message-2
KM 13.2. Climate Change Combined with Other Disruptors Requires New Frameworks and Competencies

/chapter/13#key-message-3
KM 13.3. Sustainable Transportation Would Produce Societal Benefits

/chapter/13#key-message-4
KM 13.4. Equitable Distribution of Transportation Trade-Offs and Benefits Requires Community Involvement

/chapter/14#key-message-1
KM 14.1. Climate Change Will Hamper Efforts to Improve US Air Quality

/chapter/14#key-message-2
KM 14.2. Increasing Wildfire Smoke Is Harming Human Health and Catalyzing New Protection Strategies

/chapter/14#key-message-3
KM 14.3. Air Pollution Is Often Worse in Communities of Color and Low-Income Communities

/chapter/14#key-message-4
KM 14.4. Climate Change Is Worsening Pollen Exposures and Adversely Impacting Health

/chapter/14#key-message-5
KM 14.5. Policies Can Reduce Greenhouse Gas Emissions and Improve Air Quality Simultaneously

/chapter/15#key-message-1
KM 15.1. Climate Change Is Harming Human Health

/chapter/15#key-message-2
KM 15.2. Systemic Racism and Discrimination Exacerbate Climate Impacts on Human Health

/chapter/15#key-message-3
KM 15.3. Timely, Effective, and Culturally Appropriate Adaptation and Mitigation Actions Protect Human Health

/chapter/16#key-message-1
KM 16.1. Indigenous Peoples Face Risks to Well-Being and Livelihoods from Climate Change and Barriers to Energy Sovereignty

/chapter/16#key-message-2
KM 16.2. Self-Determination Is Key to Indigenous Peoples’ Resilience to Climate Change

/chapter/16#key-message-3
KM 16.3. Indigenous Leadership Guides Climate Change Response

/chapter/17#key-message-1
KM 17.1. Interdependent, Systemic Climate-Related Risks Increasingly Affect US Interests

/chapter/17#key-message-2
KM 17.2. Climate Change Exacerbates Risks to National Security

/chapter/17#key-message-3
KM 17.3. Climate Change Presents Risks and Opportunities for US Economics, Trade, and Investments

/chapter/17#key-message-4
KM 17.4. Climate Change Undermines Sustainable Development

/chapter/18#key-message-1
KM 18.1. Human–Nature Interconnections Create Unexpected Climate Risks and Opportunities

/chapter/18#key-message-2
KM 18.2. Complex Climate Impacts and Responses Further Burden Frontline Communities

/chapter/18#key-message-3
KM 18.3. Collaborations Among Diverse Knowledge Holders Improve Responses to Complex Climate Challenges

/chapter/18#key-message-4
KM 18.4. New Governance Approaches Are Emerging, but Gaps in Practice and Evidence Persist

/chapter/19#key-message-1
KM 19.1. Climate Change Affects the Economy Directly

/chapter/19#key-message-2
KM 19.2. Markets and Budgets Respond to Climate Change

/chapter/19#key-message-3
KM 19.3. Economic Opportunities for Households, Businesses, and Institutions Will Change

/chapter/20#key-message-1
KM 20.1. Social Systems Are Changing the Climate and Distributing Its Impacts Inequitably

/chapter/20#key-message-2
KM 20.2. Social Systems Structure How People Know and Communicate About Climate Change

/chapter/20#key-message-3
KM 20.3. Climate Justice Is Possible If Processes like Migration and Energy Transitions Are Equitable

/chapter/21#key-message-1
KM 21.1. Chronic Impacts of Extreme Weather Are Shaping Adaptation and Mitigation Efforts

/chapter/21#key-message-2
KM 21.2. Ocean and Coastal Impacts Are Driving Adaptation to Climate Change

/chapter/21#key-message-3
KM 21.3. Disproportionate Impacts Highlight the Importance of Equitable Policy Choices

/chapter/21#key-message-4
KM 21.4. Climate Action Plans Are Now Being Implemented

/chapter/21#key-message-5
KM 21.5. Implementation of Climate Plans Depends on Adequate Financing

/chapter/22#key-message-1
KM 22.1. Regional Growth Increases Climate Risks

/chapter/22#key-message-2
KM 22.2. Climate Change Worsens Human Health and Widens Health Inequities

/chapter/22#key-message-3
KM 22.3. Climate Change Disproportionately Damages Southeastern Jobs, Households, and Economic Security

/chapter/22#key-message-4
KM 22.4. Agriculture Faces Growing Threats, but Innovations Offer Help

/chapter/23#key-message-1
KM 23.1. Climate-Driven Extreme Events Exacerbate Inequities and Impact Human Health and Well-Being

/chapter/23#key-message-2
KM 23.2. Ecology and Biodiversity Are Unique and Vulnerable

/chapter/23#key-message-3
KM 23.3. Climate Change Threatens Water and Food Security

/chapter/23#key-message-4
KM 23.4. Infrastructure and Energy Are Vulnerable, but Decentralization Could Improve Resilience

/chapter/23#key-message-5
KM 23.5. Adaptation Effectiveness Increases When Coupled with Strategic Governance and Planning

/chapter/24#key-message-1
KM 24.1. Climate-Smart Practices May Offset Complex Climate Interactions in Agriculture

/chapter/24#key-message-2
KM 24.2. Adaptation May Ease Disruptions to Ecosystems and Their Services

/chapter/24#key-message-3
KM 24.3. Climate Adaptation and Mitigation Strategies Improve Individual and Community Health

/chapter/24#key-message-4
KM 24.4. Green Infrastructure and Investment Solutions Can Address Costly Climate Change Impacts

/chapter/24#key-message-5
KM 24.5. Managing Extremes Is Necessary to Minimize Impacts on Water Quality and Quantity

/chapter/25#key-message-1
KM 25.1. Climate Change Is Compounding the Impacts of Extreme Events

/chapter/25#key-message-2
KM 25.2. Human and Ecological Health Face Rising Threats from Climate-Related Hazards

/chapter/25#key-message-3
KM 25.3. Resource- and Land-Based Livelihoods Are at Risk

/chapter/25#key-message-4
KM 25.4. Climate Response Involves Navigating Complex Trade-Offs and Tensions

/chapter/25#key-message-5
KM 25.5. Communities Are Building the Capacity to Adapt and Transform

/chapter/26#key-message-1
KM 26.1. How We Live: Climate Change Is Degrading Lands, Waters, Culture, and Health

/chapter/26#key-message-2
KM 26.2. How We Work: Climate Changes Are Creating Economic Challenges and Opportunities

/chapter/26#key-message-3
KM 26.3. How We Play: Climate Extremes Are Endangering Sports, Recreation, and Leisure

/chapter/26#key-message-4
KM 26.4. How We Heal: Climate Change Is Exacerbating Existing Social and Environmental Disparities

/chapter/26#key-message-5
KM 26.5. How We Serve: Climate Change Is Straining Public Infrastructure and Services

/chapter/27#key-message-1
KM 27.1. Frontline Communities Are Overburdened, and Prioritizing Social Equity Advances Regional Resilience

/chapter/27#key-message-2
KM 27.2. Ecosystems Are Transitioning in Response to Extreme Events and Human Activity

/chapter/27#key-message-3
KM 27.3. Impacts to Regional Economies Have Cascading Effects on Livelihoods and Well-Being

/chapter/27#key-message-4
KM 27.4. Infrastructure Systems Are Stressed by Climate Change but Can Enable Mitigation and Adaptation

/chapter/27#key-message-5
KM 27.5. Climate Change Amplifies Health Inequities

/chapter/27#key-message-6
KM 27.6. Climate Change Affects Heritage and Sense of Place

/chapter/28#key-message-1
KM 28.1. Drought and Increasing Aridity Threaten Water Resources

/chapter/28#key-message-2
KM 28.2. Adaptation Efforts Increase to Address Accelerating Impacts to the Region’s Coast and Ocean

/chapter/28#key-message-3
KM 28.3. Increasing Challenges Confront Food and Fiber Production in the Southwest

/chapter/28#key-message-4
KM 28.4. Climate Change Compromises Human Health and Reshapes Demographics

/chapter/28#key-message-5
KM 28.5. Changes in Wildfire Patterns Pose Challenges for Southwest Residents and Ecosystems

/chapter/29#key-message-1
KM 29.1. Our Health and Healthcare Are at Risk

/chapter/29#key-message-2
KM 29.2. Our Communities Are Navigating Compounding Stressors

/chapter/29#key-message-3
KM 29.3. Our Livelihoods Are Vulnerable Without Diversification

/chapter/29#key-message-4
KM 29.4. Our Built Environment Will Become More Costly

/chapter/29#key-message-5
KM 29.5. Our Natural Environment Is Transforming Rapidly

/chapter/29#key-message-6
KM 29.6. Our Security Faces Greater Threats

/chapter/29#key-message-7
KM 29.7. Our Just and Prosperous Future Starts with Adaptation

/chapter/30#key-message-1
KM 30.1. Climate Change Impairs Access to Healthy Food and Water

/chapter/30#key-message-2
KM 30.2. Climate Change Undermines Human Health, but Community Strength Boosts Resilience

/chapter/30#key-message-3
KM 30.3. Rising Sea Levels Threaten Infrastructure and Local Economies and Exacerbate Existing Inequities

/chapter/30#key-message-4
KM 30.4. Responses to Rising Threats May Help Safeguard Tropical Ecosystems and Biodiversity

/chapter/30#key-message-5
KM 30.5. Indigenous Knowledge Systems Strengthen Island Resilience

/chapter/31#key-message-1
KM 31.1. Adaptation Is Occurring but Is Insufficient in Relation to the Pace of Climate Change

/chapter/31#key-message-2
KM 31.2. Effective Adaptation Requires Centering Equity

/chapter/31#key-message-3
KM 31.3. Transformative Adaptation Will Be Needed to Adequately Address Climate-Related Risks

/chapter/31#key-message-4
KM 31.4. Effective Adaptation Governance Empowers Multiple Voices to Navigate Competing Goals

/chapter/31#key-message-5
KM 31.5. Adaptation Requires More than Scientific Information and Understanding

/chapter/31#key-message-6
KM 31.6. Adaptation Investments and Financing Are Difficult to Track and May Be Inadequate

/chapter/32#key-message-1
KM 32.1. Successful Mitigation Means Reaching Net-Zero Emissions

/chapter/32#key-message-2
KM 32.2. We Know How to Drastically Reduce Emissions

/chapter/32#key-message-3
KM 32.3. To Reach Net-Zero Emissions, Additional Mitigation Options Need to Be Explored

/chapter/32#key-message-4
KM 32.4. Mitigation Can Be Sustainable, Healthy, and Fair

/chapter/32#key-message-5
KM 32.5. Governments, Organizations, and Individuals Can Act to Reduce Emissions

Likelihood

Virtually CertainVery LikelyLikelyAs Likely as NotUnlikelyVery UnikelyExceptionally Unlikely
99%–100%90%–100%66%–100%33%–66%0%–33%0%–10%0%–1%

Confidence Level

Very HighHighMediumLow
  • Strong evidence (established theory, multiple sources, well-documented and accepted methods, etc.)
  • High consensus
  • Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.)
  • Medium consensus
  • Suggestive evidence (a few sources, limited consistency, methods emerging, etc.)
  • Competing schools of thought
  • Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.)
  • Disagreement or lack of opinions among experts
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