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Fifth National Climate Assessment

Chapters and Pages
Front Matter
Climate Trends
Earth Systems Processes
Energy Supply, Delivery, and Demand
Land Cover and Land-Use Change
Ecosystems, Ecosystem Services, and Biodiversity
Coastal Effects
Ocean Ecosystems and Marine Resources
Agriculture, Food Systems, and Rural Communities
Built Environment, Urban Systems, and Cities
Air Quality
Human Health
Tribes and Indigenous Peoples
Climate Effects on US International Interests
Sector Interactions, Multiple Stressors, and Complex Systems
Social Systems and Justice
US Caribbean
Northern Great Plains
Southern Great Plains
Hawai'i and US-Affiliated Pacific Islands
Focus on Compound Events
Focus on Western Wildfires
Focus on COVID-19 and Climate Change
Focus on Risks to Supply Chains
Focus on Blue Carbon
Assessment Development Process
Information Quality
Scenarios and Datasets
Art x Climate
All Figures

Key Messages

KM 2.1. Climate Is Changing, and Scientists Understand Why

KM 2.2. Extreme Events Are Becoming More Frequent and Severe

KM 2.3. How Much the Climate Changes Depends on the Choices Made Now

KM 3.1. Human Activities Have Caused the Observed Global Warming

KM 3.2. The Estimated Range of Climate Sensitivity Has Narrowed by 50%

KM 3.3. New Data and Analysis Methods Have Advanced Climate Science

KM 3.4. Humans Are Changing Earth System Processes

KM 3.5. Humans Are Changing Weather and Climate Extremes

KM 4.1. Climate Change Will Continue to Cause Profound Changes in the Water Cycle

KM 4.2. Water Cycle Changes Will Affect All Communities, with Disproportionate Impacts for Some

KM 4.3. Progress Toward Adaptation Has Been Uneven

KM 5.1. Climate Change Threatens Energy Systems

KM 5.2. Compounding Factors Affect Energy-System and Community Vulnerabilities

KM 5.3. Efforts to Enhance Energy System Resilience Are Underway

KM 6.1. The Goods and Services Provided by Land Systems Are Threatened by Climate Change

KM 6.2. Changes in Climate and Land Use Affect Land-System Resilience

KM 6.3. Mitigation and Adaptation Priorities Will Increasingly Constrain Future Land-Use Options

KM 7.1. Forests Are Increasingly Affected by Climate Change and Disturbances

KM 7.2. Climate Change Affects Ecosystem Services Provided by Forests

KM 7.3. Adaptation Actions Are Necessary for Maintaining Resilient Forest Ecosystems

KM 8.1. Climate Change Is Driving Rapid Ecosystem Transformations

KM 8.2. Species Changes and Biodiversity Loss Are Accelerating

KM 8.3. Impacts to Ecosystem Services Create Risks and Opportunities

KM 9.1. Coastal Hazards Are Increasing Due to Accelerating Sea Level Rise and Changing Storm Patterns

KM 9.2. Coastal Impacts on People and Ecosystems Are Increasing Due to Climate Change

KM 9.3. Adaptation Reduces Risk and Provides Additional Benefits for Coastal Communities

KM 10.1. Unprecedented Climate Impacts Threaten Ecosystems and Human Well-Being

KM 10.2. Climate Change Is Altering Marine-Related Economic Activities

KM 10.3. Our Future Ocean Depends on Decisions Today

KM 11.1. Agricultural Adaptation Increases Resilience in an Evolving Landscape

KM 11.2. Climate Change Disrupts Our Food Systems in Uneven Ways

KM 11.3. Rural Communities Face Unique Challenges and Opportunities

KM 12.1. Urban Areas Are Major Drivers of Climate Change

KM 12.2. Attributes of the Built Environment Exacerbate Climate Impacts, Risks, and Vulnerabilities

KM 12.3. Urban Environments Create Opportunities for Climate Mitigation and Adaptation

KM 12.4. Community-Led Actions Signal a Shift Toward Equitable Climate Governance

KM 13.1. Limiting Transportation Sector Emissions and Integrating Climate Projections Can Reduce Risks

KM 13.2. Climate Change Combined with Other Disruptors Requires New Frameworks and Competencies

KM 13.3. Sustainable Transportation Would Produce Societal Benefits

KM 13.4. Equitable Distribution of Transportation Trade-Offs and Benefits Requires Community Involvement

KM 14.1. Climate Change Will Hamper Efforts to Improve US Air Quality

KM 14.2. Increasing Wildfire Smoke Is Harming Human Health and Catalyzing New Protection Strategies

KM 14.3. Air Pollution Is Often Worse in Communities of Color and Low-Income Communities

KM 14.4. Climate Change Is Worsening Pollen Exposures and Adversely Impacting Health

KM 14.5. Policies Can Reduce Greenhouse Gas Emissions and Improve Air Quality Simultaneously

KM 15.1. Climate Change Is Harming Human Health

KM 15.2. Systemic Racism and Discrimination Exacerbate Climate Impacts on Human Health

KM 15.3. Timely, Effective, and Culturally Appropriate Adaptation and Mitigation Actions Protect Human Health

KM 16.1. Indigenous Peoples Face Risks to Well-Being and Livelihoods from Climate Change and Barriers to Energy Sovereignty

KM 16.2. Self-Determination Is Key to Indigenous Peoples’ Resilience to Climate Change

KM 16.3. Indigenous Leadership Guides Climate Change Response

KM 17.1. Interdependent, Systemic Climate-Related Risks Increasingly Affect US Interests

KM 17.2. Climate Change Exacerbates Risks to National Security

KM 17.3. Climate Change Presents Risks and Opportunities for US Economics, Trade, and Investments

KM 17.4. Climate Change Undermines Sustainable Development

KM 18.1. Human–Nature Interconnections Create Unexpected Climate Risks and Opportunities

KM 18.2. Complex Climate Impacts and Responses Further Burden Frontline Communities

KM 18.3. Collaborations Among Diverse Knowledge Holders Improve Responses to Complex Climate Challenges

KM 18.4. New Governance Approaches Are Emerging, but Gaps in Practice and Evidence Persist

KM 19.1. Climate Change Affects the Economy Directly

KM 19.2. Markets and Budgets Respond to Climate Change

KM 19.3. Economic Opportunities for Households, Businesses, and Institutions Will Change

KM 20.1. Social Systems Are Changing the Climate and Distributing Its Impacts Inequitably

KM 20.2. Social Systems Structure How People Know and Communicate About Climate Change

KM 20.3. Climate Justice Is Possible If Processes like Migration and Energy Transitions Are Equitable

KM 21.1. Chronic Impacts of Extreme Weather Are Shaping Adaptation and Mitigation Efforts

KM 21.2. Ocean and Coastal Impacts Are Driving Adaptation to Climate Change

KM 21.3. Disproportionate Impacts Highlight the Importance of Equitable Policy Choices

KM 21.4. Climate Action Plans Are Now Being Implemented

KM 21.5. Implementation of Climate Plans Depends on Adequate Financing

KM 22.1. Regional Growth Increases Climate Risks

KM 22.2. Climate Change Worsens Human Health and Widens Health Inequities

KM 22.3. Climate Change Disproportionately Damages Southeastern Jobs, Households, and Economic Security

KM 22.4. Agriculture Faces Growing Threats, but Innovations Offer Help

KM 23.1. Climate-Driven Extreme Events Exacerbate Inequities and Impact Human Health and Well-Being

KM 23.2. Ecology and Biodiversity Are Unique and Vulnerable

KM 23.3. Climate Change Threatens Water and Food Security

KM 23.4. Infrastructure and Energy Are Vulnerable, but Decentralization Could Improve Resilience

KM 23.5. Adaptation Effectiveness Increases When Coupled with Strategic Governance and Planning

KM 24.1. Climate-Smart Practices May Offset Complex Climate Interactions in Agriculture

KM 24.2. Adaptation May Ease Disruptions to Ecosystems and Their Services

KM 24.3. Climate Adaptation and Mitigation Strategies Improve Individual and Community Health

KM 24.4. Green Infrastructure and Investment Solutions Can Address Costly Climate Change Impacts

KM 24.5. Managing Extremes Is Necessary to Minimize Impacts on Water Quality and Quantity

KM 25.1. Climate Change Is Compounding the Impacts of Extreme Events

KM 25.2. Human and Ecological Health Face Rising Threats from Climate-Related Hazards

KM 25.3. Resource- and Land-Based Livelihoods Are at Risk

KM 25.4. Climate Response Involves Navigating Complex Trade-Offs and Tensions

KM 25.5. Communities Are Building the Capacity to Adapt and Transform

KM 26.1. How We Live: Climate Change Is Degrading Lands, Waters, Culture, and Health

KM 26.2. How We Work: Climate Changes Are Creating Economic Challenges and Opportunities

KM 26.3. How We Play: Climate Extremes Are Endangering Sports, Recreation, and Leisure

KM 26.4. How We Heal: Climate Change Is Exacerbating Existing Social and Environmental Disparities

KM 26.5. How We Serve: Climate Change Is Straining Public Infrastructure and Services

KM 27.1. Frontline Communities Are Overburdened, and Prioritizing Social Equity Advances Regional Resilience

KM 27.2. Ecosystems Are Transitioning in Response to Extreme Events and Human Activity

KM 27.3. Impacts to Regional Economies Have Cascading Effects on Livelihoods and Well-Being

KM 27.4. Infrastructure Systems Are Stressed by Climate Change but Can Enable Mitigation and Adaptation

KM 27.5. Climate Change Amplifies Health Inequities

KM 27.6. Climate Change Affects Heritage and Sense of Place

KM 28.1. Drought and Increasing Aridity Threaten Water Resources

KM 28.2. Adaptation Efforts Increase to Address Accelerating Impacts to the Region’s Coast and Ocean

KM 28.3. Increasing Challenges Confront Food and Fiber Production in the Southwest

KM 28.4. Climate Change Compromises Human Health and Reshapes Demographics

KM 28.5. Changes in Wildfire Patterns Pose Challenges for Southwest Residents and Ecosystems

KM 29.1. Our Health and Healthcare Are at Risk

KM 29.2. Our Communities Are Navigating Compounding Stressors

KM 29.3. Our Livelihoods Are Vulnerable Without Diversification

KM 29.4. Our Built Environment Will Become More Costly

KM 29.5. Our Natural Environment Is Transforming Rapidly

KM 29.6. Our Security Faces Greater Threats

KM 29.7. Our Just and Prosperous Future Starts with Adaptation

KM 30.1. Climate Change Impairs Access to Healthy Food and Water

KM 30.2. Climate Change Undermines Human Health, but Community Strength Boosts Resilience

KM 30.3. Rising Sea Levels Threaten Infrastructure and Local Economies and Exacerbate Existing Inequities

KM 30.4. Responses to Rising Threats May Help Safeguard Tropical Ecosystems and Biodiversity

KM 30.5. Indigenous Knowledge Systems Strengthen Island Resilience

KM 31.1. Adaptation Is Occurring but Is Insufficient in Relation to the Pace of Climate Change

KM 31.2. Effective Adaptation Requires Centering Equity

KM 31.3. Transformative Adaptation Will Be Needed to Adequately Address Climate-Related Risks

KM 31.4. Effective Adaptation Governance Empowers Multiple Voices to Navigate Competing Goals

KM 31.5. Adaptation Requires More than Scientific Information and Understanding

KM 31.6. Adaptation Investments and Financing Are Difficult to Track and May Be Inadequate

KM 32.1. Successful Mitigation Means Reaching Net-Zero Emissions

KM 32.2. We Know How to Drastically Reduce Emissions

KM 32.3. To Reach Net-Zero Emissions, Additional Mitigation Options Need to Be Explored

KM 32.4. Mitigation Can Be Sustainable, Healthy, and Fair

KM 32.5. Governments, Organizations, and Individuals Can Act to Reduce Emissions


Virtually Certain Very Likely Likely As Likely as Not Unlikely Very Unikely Exceptionally Unlikely
99%–100% 90%–100% 66%–100% 33%–66% 0%–33% 0%–10% 0%–1%

Confidence Level

Very High High Medium Low
  • 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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