This website is being hosted by Climate.us. It 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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Fifth National Climate Assessment
Report Key Messages

List of Report Key Messages

  • Key Message 2.1, Climate Is Changing, and Scientists Understand Why
    It is unequivocal that human activities have increased atmospheric levels of carbon dioxide and other greenhouse gases. It is also unequivocal that global average temperature has risen in response. Observed warming over the continental United States and Alaska is higher than the global average . Long-term changes have been observed in many other aspects of the climate system . The Earth system is complex and interconnected, which means changes in faraway regions are to affect the United States .
  • Key Message 2.2, Extreme Events Are Becoming More Frequent and Severe
    Observations show an increase in the severity, extent, and/or frequency of multiple types of extreme events. Heatwaves have become more common and severe in the West since the 1980s . Drought risk has been increasing in the Southwest over the past century , while at the same time rainfall has become more extreme in recent decades, especially east of the Rockies . Hurricanes have been intensifying more rapidly since the 1980s and causing heavier rainfall and higher storm surges . More frequent and larger wildfires have been burning in the West in the past few decades due to a combination of climate factors, societal changes, and policies .
  • Key Message 2.3, How Much the Climate Changes Depends on the Choices Made Now
    The more the planet warms, the greater the impacts—and the greater the risk of unforeseen consequences . The impacts of climate change increase with warming, and warming is to continue if emissions of carbon dioxide do not reach net zero . Rapidly reducing emissions would limit future warming and the associated increases in many risks . While there are still uncertainties about how the planet will react to rapid warming and catastrophic future scenarios that cannot be ruled out, the future is largely in human hands.
  • Key Message 3.1, Human Activities Have Caused the Observed Global Warming
    Human activities—primarily emissions of greenhouse gases from fossil fuel use—have unequivocally caused the global warming observed over the industrial era. Changes in natural climate drivers had globally small and regionally variable long-term effects over that period.
  • Key Message 3.2, The Estimated Range of Climate Sensitivity Has Narrowed by 50%
    Recent improvements in the understanding of how climate feedbacks vary across timescales have narrowed the estimated range of warming expected from a doubling of atmospheric carbon dioxide by 50% to between 4.5°F and 7.2°F .
  • Key Message 3.3, New Data and Analysis Methods Have Advanced Climate Science
    A number of scientific developments have enabled deeper understanding of climate processes and their responses to human influence. Observational records have lengthened, and new observing systems have come online. New scenarios of socioeconomic development, and their associated emissions and land-use changes, drive updated climate projections from Earth system models. Large ensemble simulations from multiple models have enabled scientists to better distinguish anthropogenic climate change from natural climate variability. More targeted model evaluation techniques are using observations to narrow the estimated range of future climatic changes. Finally, advances in methods for extreme event attribution enabled scientists to estimate the contributions of human influence to some types of individual extreme events in near-real-time.
  • Key Message 3.4, Humans Are Changing Earth System Processes
    Human activities cause changes throughout the Earth system, including the land surface, cryosphere, ocean and atmosphere, and carbon and water cycles. The magnitude, and for some processes the direction, of these changes can vary across regions, including within the US. These changes also occur against a background of substantial natural climate variability.
  • Key Message 3.5, Humans Are Changing Weather and Climate Extremes
    Human activities are affecting climate system processes in ways that alter the intensity, frequency, and/or duration of many weather and climate extremes, including extreme heat, extreme precipitation and flooding, agricultural and hydrological drought, and wildfire .
  • Key Message 4.1, Climate Change Will Continue to Cause Profound Changes in the Water Cycle
    Changes to the water cycle pose risks to people and nature. Alaska and northern and eastern regions of the US are seeing and expect to see more precipitation on average, while the Caribbean, Hawai‘i, and southwestern regions of the US are seeing and expect to see less precipitation . Heavier rainfall events are expected to increase across the Nation , and warming will increase evaporation and plant water use where moisture is not a limiting factor . Groundwater supplies are also threatened by warming temperatures that are expected to increase demand . Snow cover will decrease and melt earlier . Increasing aridity, declining groundwater levels, declining snow cover, and drought threaten freshwater supplies .
  • Key Message 4.2, Water Cycle Changes Will Affect All Communities, with Disproportionate Impacts for Some
    Natural and human systems have evolved under the water cycle’s historical patterns, making rapid adaptation challenging. Heavier rainfall, combined with changes in land use and other factors such as soil moisture and snow, is leading to increasing flood damage . Drought impacts are also increasing , as are flood- and drought-related water quality impacts . All communities will be affected, but in particular those on the frontline of climate change—including many Black, Hispanic, Tribal, Indigenous, and socioeconomically disadvantaged communities—face growing risks from changes to water quantity and quality due to the proximity of their homes and workplaces to hazards and limited access to resources and infrastructure .
  • Key Message 4.3, Progress Toward Adaptation Has Been Uneven
    The ability of water managers to adapt to changes has improved with better data, advances in decision-making, and steps toward cooperation. However, infrastructure standards and water allocation institutions have been slow to adapt to a changing climate , and efforts are confounded by wet and dry cycles driven by natural climate variability . Frontline, Tribal, and Indigenous communities are heavily impacted but lack resources to adapt effectively, and they are not fully represented in decision-making .
  • Key Message 5.1, Climate Change Threatens Energy Systems
    Energy supply and delivery are at risk from climate-driven changes, which are also shifting demand . Climate change threats, including increases in extreme precipitation, extreme temperatures, sea level rise, and more intense storms, droughts, and wildfires, are damaging infrastructure and operations and affecting human lives and livelihoods . Impacts will vary over time and location . Without mitigation and adaptation, projected increases in the frequency, intensity, duration, and variability of extreme events will amplify effects on energy systems .
  • Key Message 5.2, Compounding Factors Affect Energy-System and Community Vulnerabilities
    Concurrent changes in technologies, policies, and markets, in addition to their interconnections, can reduce GHG emissions while also increasing vulnerabilities of energy systems and communities to climate change and extreme weather . Compound and cascading hazards related to energy systems and additional stressors, such as cyber and physical threats and pandemics, create risks for all but disproportionately affect overburdened communities .
  • Key Message 5.3, Efforts to Enhance Energy System Resilience Are Underway
    Federal, state, local, Tribal, and private-sector investments are being made to increase the resilience of the energy system to climate-related stressors, and opportunities exist to build upon this progress . Ongoing investments will need to include improvements in energy-efficient buildings; technology to decarbonize the energy system; advanced automation and communication and artificial intelligence technologies to optimize operations; climate modeling and planning methodologies under uncertainties; and efforts to increase equitable access to clean energy . An energy system transition emphasizing decarbonization and electrification would require efforts in new generation, transmission, distribution, and fuel delivery .
  • Key Message 6.1, The Goods and Services Provided by Land Systems Are Threatened by Climate Change
    Climate change has increased regional intensity and frequency of extreme rain, droughts, temperature highs, fires, and urban floods , posing increased risks for roads and other infrastructure, agricultural production, forests, biodiversity, carbon sinks, and human health . Climate-driven increases in wildfire extent and intensity are threatening the ability of some western forests to provide valued goods and services . Climate change has disrupted the ways that people interact with the landscape for spiritual practices, recreation, and subsistence .
  • Key Message 6.2, Changes in Climate and Land Use Affect Land-System Resilience
    Changes in climate and land use affect the resilience of land ecosystems and thus the fate of the services they provide ; for example, increasing drought reduces the ability of forests to store carbon. Climate and land-use change interact, and these interactions present challenges as well as opportunities for maintaining ecosystem resilience .
  • Key Message 6.3, Mitigation and Adaptation Priorities Will Increasingly Constrain Future Land-Use Options
    The future of land use in the United States will depend on how energy and agricultural technology evolves, how the climate changes, and the degree to which we prioritize climate mitigation and adaptation in land-use decisions . US cropland area had been declining but has rebounded somewhat over the last 1–2 decades . Future cropland needs will depend on uncertain factors such as agricultural technology improvements, dietary shifts, and climate change impacts . Decarbonization will require a continued expansion of solar and wind energy generation and transmission infrastructure and may involve large land-use changes toward land-based mitigation measures, including reforestation, other natural climate solutions, and bioenergy crops .
  • Key Message 7.1, Forests Are Increasingly Affected by Climate Change and Disturbances
    Climate change is increasing the frequency, scale, and severity of some disturbances that drive forest change and affect ecosystem services . Continued warming and regional changes in precipitation are expected to amplify interactions among disturbance agents and further alter forest ecosystem structure and function .
  • Key Message 7.2, Climate Change Affects Ecosystem Services Provided by Forests
    Climate change threatens the ecosystem services forests provide that enrich human lives and sustain life more broadly. Increasing temperatures, changing precipitation patterns, and altered disturbances are affecting the capacity of forest ecosystems to sequester and store carbon , provide clean water and clean air , produce timber and non-timber products , and provide recreation , among other benefits. Future climate effects will interact with societal changes to determine the capacity of forests to provide ecosystem services .
  • Key Message 7.3, Adaptation Actions Are Necessary for Maintaining Resilient Forest Ecosystems
    Climate change creates challenges for natural resource managers charged with preserving the function, health, and productivity of forest ecosystems . Forest landowners, managers, and policymakers working at local, state, Tribal, and federal levels are preparing for climate change through the development and implementation of vulnerability assessments and adaptation plans . Proactive adaptation of management strategies that create, maintain, and restore resilient forest ecosystems are critical to maintaining equitable provisioning of ecosystem services .
  • Key Message 8.1, Climate Change Is Driving Rapid Ecosystem Transformations
    Climate change, together with other stressors, is driving transformational changes in ecosystems, including loss and conversion to other states, and changes in productivity . These changes have serious implications for human well-being . Many types of extreme events are increasing in frequency and/or severity and can trigger abrupt ecosystem changes . Adaptive governance frameworks, including adaptive management, combined with monitoring can help to prepare for, respond to, and alleviate climate change impacts, as well as build resilience for the future .
  • Key Message 8.2, Species Changes and Biodiversity Loss Are Accelerating
    The interaction of climate change with other stressors is causing biodiversity loss, changes in species distributions and life cycles, and increasing impacts from invasive species and diseases, all of which have economic and social consequences . Future responses of species and populations will depend on the magnitude and timing of changes, coupled with the differential sensitivity of organisms; species that cannot easily relocate or are highly temperature sensitive may face heightened extinction risks . Identification of risks (e.g., extreme events) will help prioritize species and locations for protection and improve options for management .
  • Key Message 8.3, Impacts to Ecosystem Services Create Risks and Opportunities
    Climate change is having variable and increasing impacts on ecosystem services and benefits, from food production to clean water to carbon sequestration, with consequences for human well-being . Changes in availability and quality of ecosystem services, combined with existing social inequities, have disproportionate impacts on certain communities . Equity-driven nature-based solutions, designed to protect, manage, and restore ecosystems for human well-being, can provide climate adaptation and mitigation benefits .
  • Key Message 9.1, Coastal Hazards Are Increasing Due to Accelerating Sea Level Rise and Changing Storm Patterns
    The severity and risks of coastal hazards across the Nation are increasing , driven by accelerating sea level rise and changing storm patterns, resulting in increased flooding, erosion, and rising groundwater tables. Over the next 30 years (2020–2050), coastal sea levels along the contiguous US coasts are expected to rise about 11 inches (28 cm), or as much as the observed rise over the last 100 years . In response, coastal flooding will occur 5–10 times more often by 2050 than 2020 in most locations, with damaging flooding occurring as often as disruptive “high tide flooding” does now if action is not taken .
  • Key Message 9.2, Coastal Impacts on People and Ecosystems Are Increasing Due to Climate Change
    Climate change–driven sea level rise, among other factors, is affecting the resilience of coastal ecosystems and communities . The impacts of climate change and human modifications to coastal landscapes, such as seawalls, levees, and urban development, are both limiting the capacity of coastal ecosystems to adapt naturally and are compounding the loss of coastal ecosystem services . Proactive strategies are necessary to avoid degraded quality of life in the coastal zone, as the combination of reduced ecosystem services and damage to the built environment from exacerbated coastal hazards increasingly burdens communities, industries, and cultures .
  • Key Message 9.3, Adaptation Reduces Risk and Provides Additional Benefits for Coastal Communities
    Accelerating sea level rise and climate change will transform the coastal landscape, requiring a new paradigm for how we live with, or adapt to, these changes . Although incremental in nature, nature-based solutions and planned relocation strategies may help communities adapt to increasing coastal hazards if they are community-led and equity-centered . Maintaining cultural and economic connections within coastal communities will require equitable transformative adaptation that addresses systemic interconnections between ecosystems, communities, and governance .
  • Key Message 10.1, Unprecedented Climate Impacts Threaten Ecosystems and Human Well-Being
    Climate change is significantly altering US marine ecosystems at a pace, magnitude, and extent that is unprecedented over millennia . Changes in species locations, productivity, and seasonal timing are cascading through ecosystems, threatening critical connections between people and the ocean , especially for Indigenous Peoples . Risks to marine ecosystems and the people connected to them will be greater under higher scenarios and will depend on the ability of ecological and social systems to adapt to the pace of climate change . Continued climate change, particularly under higher scenarios, is projected to push many systems toward novel conditions and critical tipping points , beyond which the risk of significant impacts to marine ecosystems, including collapse, is high, adaptation may be insufficient, and human well-being is threatened .
  • Key Message 10.2, Climate Change Is Altering Marine-Related Economic Activities
    Climate change poses a substantial risk to ocean-related industries and economic activities such as fisheries, tourism, recreation, transportation, and energy . As climate change continues, economic and cultural impacts are expected to become larger and more widespread, especially under higher scenarios and in communities that are highly dependent on ocean resources . A range of approaches can facilitate adaptation to some degree of climate change , but higher levels of climate change will limit the success of adaptation measures and markedly increase climate risk to marine-related economic activities .
  • Key Message 10.3, Our Future Ocean Depends on Decisions Today
    Future risks to marine ecosystems, ocean resources, and people will be substantially reduced by implementing adaptation and mitigation actions now . Responding swiftly to climate change will improve outcomes, reduce costs, promote resilience and equity, and allow the widest possible suite of adaptation solutions . Impacts will continue to be uneven across communities, with more harmful outcomes in communities that are highly ocean-reliant and historically marginalized, unless equitable adaptation and mitigation efforts are implemented .
  • Key Message 11.1, Agricultural Adaptation Increases Resilience in an Evolving Landscape
    Climate change has increased agricultural production risks by disrupting growing zones and growing days, which depend on precipitation, air temperature, and soil moisture . Growing evidence for positive environmental and economic outcomes of conservation management has led some farmers and ranchers to adopt agroecological practices , which increases the potential for agricultural producers to limit greenhouse gas emissions and improve agricultural resilience to climate change .
  • Key Message 11.2, Climate Change Disrupts Our Food Systems in Uneven Ways
    Climate change is projected to disrupt food systems in ways that reduce the availability and affordability of nutritious food, with uneven economic impacts across society . Impacts of climate change on other measures of human well-being are also distributed unevenly, such as worsening heat stress among farmworkers and disruptions to the ability of subsistence-based peoples to access food through hunting, fishing, and foraging .
  • Key Message 11.3, Rural Communities Face Unique Challenges and Opportunities
    Rural communities steward much of the Nation’s land and natural resources, which provide food, bioproducts, and ecosystem services . These crucial roles are at risk as climate change compounds existing stressors such as poverty, unemployment, and depopulation . Opportunities exist for rural communities to increase their resilience to climate change and protect rural livelihoods .
  • Key Message 12.1, Urban Areas Are Major Drivers of Climate Change
    Consumption of food, energy, water, and materials is a major driver of global climate change, and these consumption activities are disproportionately concentrated in urban and suburban areas .
  • Key Message 12.2, Attributes of the Built Environment Exacerbate Climate Impacts, Risks, and Vulnerabilities
    Urban development patterns can exacerbate climate change impacts such as increases in heat and flooding . Climate change is amplifying existing loads and stressors on the built environment, and this is expected to continue . Urban areas face elevated risk as both people and the built environment are exposed to climate hazards, and these risks are distributed unevenly across the population .
  • Key Message 12.3, Urban Environments Create Opportunities for Climate Mitigation and Adaptation
    Cities across the country are working to reduce greenhouse gas emissions and adapting to adverse climate impacts . Some states and cities are integrating climate considerations into relevant codes, standards, and policies. However, the pace, scale, and scope of action are not yet sufficient to avoid the worst impacts, given the magnitude of observed and projected climate changes .
  • Key Message 12.4, Community-Led Actions Signal a Shift Toward Equitable Climate Governance
    There is varying progress in considering who benefits from, or bears the burden of, local climate actions . The emergence of local and community-led approaches—coupled with increasing collaboration among city, Tribal, state, and federal governments—indicates a movement toward more inclusive planning and implementation of climate actions .
  • Key Message 13.1, Limiting Transportation Sector Emissions and Integrating Climate Projections Can Reduce Risks
    The transportation sector is the largest source of greenhouse gas emissions in the United States, although transportation emissions sources are changing . The sector also faces increasing risk from climate-related extreme weather . Incorporating climate projections and adaptation and resilience best practices into transportation planning, design, operations, and maintenance can reduce such risks to the sector .
  • Key Message 13.2, Climate Change Combined with Other Disruptors Requires New Frameworks and Competencies
    Climate action creates an opportunity to address concurrent disruptors, including cyber-technology integration, challenges with the condition of existing assets, and a changing workforce . Climate change has accelerated a transition to the use of more advanced approaches, including updated technologies, tools, and best practices . Further recruitment and training of the sector’s workforce is needed to effectively address these fundamental challenges .
  • Key Message 13.3, Sustainable Transportation Would Produce Societal Benefits
    A carbon-free, sustainable, and resilient transportation system would have co-benefits for human health, environmental justice, the natural environment, and economic development . When these co-benefits are considered, the benefits of greenhouse gas mitigation actions in the transportation sector far outweigh the costs .
  • Key Message 13.4, Equitable Distribution of Transportation Trade-Offs and Benefits Requires Community Involvement
    Although implementing adaptation and mitigation measures in the transportation sector will produce essential benefits and co-benefits, including addressing existing inequities, additional consideration is needed to avoid or reduce potential adverse consequences associated with these measures . Moving toward climate resilience and environmental justice requires that these considerations, as well as current and historic inequities, be assessed through transparent and inclusive processes in order to provide equitable protection from environmental and health hazards and equitable access to transportation benefits .
  • Key Message 14.1, Climate Change Will Hamper Efforts to Improve US Air Quality
    Climate change is projected to worsen air quality in many US regions , thereby harming human health and increasing premature death . Extreme heat events, which can lead to high concentrations of air pollution, are projected to increase in severity and frequency , and the risk of exposure to airborne dust and wildfire smoke will increase with warmer and drier conditions in some regions . Reducing air pollution concentrations will unequivocally help protect human health in a changing climate.
  • Key Message 14.2, Increasing Wildfire Smoke Is Harming Human Health and Catalyzing New Protection Strategies
    Wildfires emit gases and fine particles that are harmful to human health, contributing to premature mortality, asthma, and other health problems . Climate change is contributing to increases in the frequency and severity of wildfires, thereby worsening air quality in many regions of the contiguous US and Alaska . Although large challenges remain, new communication and mitigation measures are reducing a portion of the dangers of wildfire smoke .
  • Key Message 14.3, Air Pollution Is Often Worse in Communities of Color and Low-Income Communities
    Communities of color, people with low socioeconomic status, and other marginalized populations are disproportionately harmed by poor air quality . In the coming decades, these same communities will, on average, face worsened cumulative air pollution burdens from climate change–driven hazards . Decision-making focused on the fair distribution of air quality improvements, rather than on overall emissions reductions alone, is critical for reducing air pollution inequities .
  • Key Message 14.4, Climate Change Is Worsening Pollen Exposures and Adversely Impacting Health
    Increased allergen exposure damages the health of people who suffer from allergies, asthma, and chronic obstructive pulmonary disease (COPD) . Human-caused climate change has already caused some regions to experience longer pollen seasons and higher pollen concentrations , and these trends are expected to continue as climate changes . Increasing access to allergists, improved diagnosis and disease management, and allergy early warning systems may counteract the health impacts of increasing pollen exposure .
  • Key Message 14.5, Policies Can Reduce Greenhouse Gas Emissions and Improve Air Quality Simultaneously
    Substantial reductions in economy-wide greenhouse gas emissions would result in improved air quality and significant public health benefits . For many actions, these benefits exceed the cost of greenhouse gas emission controls . Through coordinated actions emphasizing reduced fossil fuel use, improved energy efficiency, and reductions in short-lived climate pollutants, the US has an opportunity to greatly improve air quality while substantially reducing its climate impact, approaching net-zero CO2 emissions .
  • Key Message 15.1, Climate Change Is Harming Human Health
    It is an established fact that climate change is harming physical, mental, spiritual, and community health and well-being through the increasing frequency and intensity of extreme events, increasing cases of infectious and vector-borne diseases, and declines in food and water quality and security. Climate-related hazards will continue to grow, increasing morbidity and mortality across all regions of the US .
  • Key Message 15.2, Systemic Racism and Discrimination Exacerbate Climate Impacts on Human Health
    Climate change unequivocally worsens physical, mental, spiritual, and community health and well-being, as well as social inequities. It is an established fact that climate-related impacts disproportionately harm communities and people who have been marginalized. These include BIPOC (Black, Indigenous, and People of Color), individuals and communities with low wealth, women, people with disabilities or chronic diseases, sexual and gender minorities, and children.
  • Key Message 15.3, Timely, Effective, and Culturally Appropriate Adaptation and Mitigation Actions Protect Human Health
    In every sector of society, implementing timely, effective, and culturally appropriate adaptation measures , creating climate-resilient health systems , and preventing the release of greenhouse gases can protect human health and improve health equity .
  • Key Message 16.1, Indigenous Peoples Face Risks to Well-Being and Livelihoods from Climate Change and Barriers to Energy Sovereignty
    Climate change continues to cause negative effects on critical aspects of Indigenous Peoples’ well-being, including their livelihoods, health, nutrition, and cultural practices, as well as the ecological resilience of their territories . Indigenous Peoples are responding in diverse ways, including through energy sovereignty .
  • Key Message 16.2, Self-Determination Is Key to Indigenous Peoples’ Resilience to Climate Change
    By exercising their right to self-determination, Indigenous Peoples can respond to climate change in ways that meet the needs and aspirations of their communities . However, their ability to exercise this right is often undermined by institutions and policies shaped by the impacts of settler colonialism . Expanded support from federal and state governments has the potential to uphold Indigenous rights to self-determination for guiding climate resilience .
  • Key Message 16.3, Indigenous Leadership Guides Climate Change Response
    Indigenous Peoples lead numerous actions that respond to climate change . Indigenous-led organizations, initiatives, and movements have demonstrated diverse strategies for climate adaptation and mitigation that are guided by Indigenous Knowledges and values and by the pursuit of Indigenous rights .
  • Key Message 17.1, Interdependent, Systemic Climate-Related Risks Increasingly Affect US Interests
    In a globally connected world, climate change impacts on US interests are multifaceted, interconnected, and frequently exacerbated by social unrest and environmental degradation . The scale and speed of climate-related impacts to US interests are expected to increase, due in part to underlying interdependencies and to the projected intensification of climate change . Emerging systems- and scenarios-based approaches to integrative planning are being applied to account for interdependencies and competing priorities .
  • Key Message 17.2, Climate Change Exacerbates Risks to National Security
    Climate change can contribute to political and social instability and, in some instances, to conflict . It impacts the operations and missions of defense, diplomacy, and development agencies critical to US national security . The US Government, bilaterally and in collaboration with international partners, is increasingly addressing these implications through a range of diplomatic, development, and defense responses .
  • Key Message 17.3, Climate Change Presents Risks and Opportunities for US Economics, Trade, and Investments
    The physical impacts of climate change are increasingly affecting global and regional economic growth . These impacts have important implications for US economic, trade, and investment interests . Global mitigation and adaptation responses by governments and businesses will likewise impact US economic interests, presenting both risks and potential opportunities for the US economy . Public- and private-sector institutional, regulatory, financial, and market-based frameworks for climate mitigation and adaptation will influence these risks and opportunities .
  • Key Message 17.4, Climate Change Undermines Sustainable Development
    Climate change undermines the world’s ability to develop sustainably, reverses development gains, and exacerbates inequities . Climate finance is increasing, but global flows continue to fall short of needs . Accelerated deployment of adaptation and mitigation action at scale can yield substantial benefits for sustainable development . Climate action is most effective when co-developed and grounded in equity, local ownership, and inclusive governance .
  • Key Message 18.1, Human–Nature Interconnections Create Unexpected Climate Risks and Opportunities
    Human–natural systems are dynamic and complex. Interconnected networks of people, infrastructure, commodities, goods, and services influence changing climate risks and are increasingly vulnerable to their impacts . The vulnerabilities in these networks, and their effects on human–natural systems, strongly depend on human responses and other compounding stressors . Decision-makers seeking to reduce climate change risks have to navigate diverse and sometimes competing objectives and perspectives across many actors, institutions, and geographic scales while reconciling deep uncertainties and limits to predictability .
  • Key Message 18.2, Complex Climate Impacts and Responses Further Burden Frontline Communities
    Compounding and cascading interactions among sectors, hazards, and geographies magnify the impact of climate change and societal responses for already-overburdened groups . However, social vulnerability assessments tend to evaluate risks and impacts by sector, hazard, or jurisdiction, and most complex-systems models do not yet account for social and political dynamics . Data about how complex systems affect frontline communities under climate change are severely lacking, especially for hard-to-reach populations, and this can lead to disproportionate risks and impacts for these groups .
  • Key Message 18.3, Collaborations Among Diverse Knowledge Holders Improve Responses to Complex Climate Challenges
    Responding effectively to complex climate challenges benefits from integrated frameworks and modeling approaches that incorporate diverse types of knowledges suited to specific contexts and needs . Participatory and collaborative approaches and tools bring together diverse knowledge holders and improve the generation and use of actionable knowledge for complex-systems decision-making . These collaborative approaches help navigate complex challenges, such as competing perspectives and knowledge uncertainties, thereby improving climate responses .
  • Key Message 18.4, New Governance Approaches Are Emerging, but Gaps in Practice and Evidence Persist
    Climate change presents challenges for managing risks and responses across different levels of government, the private sector, and civil society. Current governance entities and their existing jurisdictional authorities are often unable to resolve conflicts posed by the wide-ranging and unprecedented interactions and complexities of climate risks and more localized compounding stressors . Local and regional governments have experimented with alternative institutional arrangements, funding mechanisms, and decision coordination . Thus far, however, there is only preliminary evidence of their effectiveness . These pilots and other innovations developed for climate mitigation and adaptation may well present opportunities for replication and broader successes in other locations and different local contexts .
  • Key Message 19.1, Climate Change Affects the Economy Directly
    Climate change directly impacts the economy through increases in temperature, rising sea levels, and more frequent and intense weather-related extreme events (e.g., wildfires, floods, hurricanes, droughts), which are estimated to generate substantial and increasing economic costs in many sectors . These impacts are projected to be distributed unequally, affecting certain regions, industries, and socioeconomic groups more than others . Adaptation can attenuate some impacts by reducing vulnerability to climate change, but adaptation strategies vary in their effectiveness and costs .
  • Key Message 19.2, Markets and Budgets Respond to Climate Change
    Markets are responding to current and anticipated climate changes, and stronger market responses are expected as climate change progresses . Climate risks are projected to change asset values as markets and prices adjust to reflect economic conditions that result from climate change . New costs and challenges will emerge in insurance systems and public budgets that were not originally designed to respond to climate change . Trade and economic growth are projected to be impacted by climate change directly and through policy responses to climate change .
  • Key Message 19.3, Economic Opportunities for Households, Businesses, and Institutions Will Change
    Climate change is projected to impose a variety of new or higher costs on most households and to impact their employment, income, and quality of life . Climate change will alter the economic landscape that businesses face, generating new risks but also creating new opportunities . Institutions and governments are expected to see existing programs used more intensively or in new ways as populations cope with climate change, generating new system-wide risks . Design, evaluation, and deployment of adaptation technologies and policies will strengthen our national preparedness for climate change .
  • Key Message 20.1, Social Systems Are Changing the Climate and Distributing Its Impacts Inequitably
    Social systems are changing the climate . Societal characteristics and processes shape greenhouse gas (GHG) emissions, primarily through the burning of fossil fuels . Social systems also inequitably distribute the benefits of energy consumption and the impacts of GHG emissions and climate change . Governance is a critical process that distributes these impacts and provides access to adaptation .
  • Key Message 20.2, Social Systems Structure How People Know and Communicate About Climate Change
    People’s histories, educations, cultures, and ethics determine how they understand and experience climate change . These knowledges take multiple forms and generate diverse approaches to climate adaptation and mitigation . Engagement across communities that builds clear objectives and benchmarks has been shown to produce more desired outcomes . Effective engagement is challenging due in part to the complexity and uncertainty associated with climate science and politics . Including community perspectives and multiple forms of knowledge in climate discussions and decision-making helps promote justice .
  • Key Message 20.3, Climate Justice Is Possible If Processes like Migration and Energy Transitions Are Equitable
    Climate justice—the recognition of diverse values and past harms, equitable distribution of benefits and risks, and the procedural inclusion of affected communities in decision-making processes—is possible . Complex social processes such as human migration affect climate inequities . Climate justice is also closely related to just transitions , which involve equitably adapting societies, economies, and energy systems to climate change mitigation strategies and climate impacts .
  • Key Message 21.1, Chronic Impacts of Extreme Weather Are Shaping Adaptation and Mitigation Efforts
    The Northeast continues to be confronted with extreme weather, most notably extreme precipitation—which has caused problematic flooding across the region—and heatwaves . In response, climate adaptation and mitigation efforts, including nature-based solutions, have increased across the region , with a focus on emissions reductions, carbon sequestration, and resilience building .
  • Key Message 21.2, Ocean and Coastal Impacts Are Driving Adaptation to Climate Change
    The ocean and coastal habitats in the Northeast are experiencing changes that are unprecedented in recorded history, including ocean warming, marine heatwaves, sea level rise, and ocean acidification . Changing ocean conditions are causing significant shifts in the distribution, productivity, and seasonal timing of life-cycle events of living marine resources in the Northeast . These impacts have spurred adaptation efforts such as coastal wetland restoration and changes in fishing behavior .
  • Key Message 21.3, Disproportionate Impacts Highlight the Importance of Equitable Policy Choices
    Extreme heat, storms, flooding, and other climate-related hazards are causing disproportionate impacts among certain communities in the Northeast, notably including racial and ethnic minorities, people of lower socioeconomic status, and older adults . These communities tend to have less access to healthcare, social services, and financial resources and to face higher burdens related to environmental pollution and preexisting health conditions . Social equity objectives are prominent in many local-level adaptation initiatives, but the amount of progress toward equitable outcomes remains uneven .
  • Key Message 21.4, Climate Action Plans Are Now Being Implemented
    In recent years, there have been substantial advances in the magnitude and scope of climate action across all jurisdictional scales . Almost every state in the region has conducted or updated a climate impact assessment, developed a comprehensive climate action plan, and enacted climate-related laws since 2018 . Innovative approaches to transparent, inclusive, and equitable processes around climate action are being embraced by Tribes, municipalities, and states . Although ambitious emissions reduction targets have been put forward, meeting these goals is expected to be challenging .
  • Key Message 21.5, Implementation of Climate Plans Depends on Adequate Financing
    Options for financing mitigation and adaptation efforts have expanded in recent years, providing households, communities, and businesses with more options for responding to climate change . Flood insurance allows individuals and communities to recover following extreme flooding events, but many at-risk homeowners lack adequate coverage . Although the public sector remains the primary source of funding for adaptation, private capital has started to invest in a variety of mitigation and adaptation projects, including services for monitoring climate risks and community-based catastrophe insurance .
  • Key Message 22.1, Regional Growth Increases Climate Risks
    The Southeast’s population has grown and is expected to continue growing, mostly in metropolitan areas and along its coastline , putting more communities and their assets into harm’s way from increasing risks related to climate and land-use changes . Conversely, many rural places are facing declining populations with a growing percentage of older residents , making these areas particularly vulnerable to the impacts of a changing climate . At the same time, decision-makers frequently use outdated and/or limited information on climate-related risks to inform adaptation plans, which as a result fail to account for worsening future conditions . These climate adaptation efforts also tend to be concentrated in wealthier communities, leaving under-resourced and more rural populations, communities of color, and Tribal Nations at growing and disproportionate risk .
  • Key Message 22.2, Climate Change Worsens Human Health and Widens Health Inequities
    Human health and climate stressors are intimately linked in the Southeast . Community characteristics such as racial and ethnic population, chronic disease prevalence, age, and socioeconomic status can influence how climate change exacerbates, ameliorates, or introduces new health issues . Climate change is already impacting health in the region . There are effective strategies to address the health impacts of climate change in the Southeast that have multiple benefits across social and environmental contexts .
  • Key Message 22.3, Climate Change Disproportionately Damages Southeastern Jobs, Households, and Economic Security
    Over the last few decades, economic growth in the Southeast has been concentrated in and around urban centers that depend on climate-sensitive infrastructure and regional connections to thrive . Simultaneously, rural and place-based economies that rely on the region’s ecosystems are particularly at risk from current and future climate changes . Global warming is expected to worsen climate-related impacts on economic systems, labor, and regional supply chains in the Southeast, with disproportionate effects on frontline communities . A coordinated approach that recognizes present-day inequities and the interdependencies between rural and urban communities will be necessary to secure the region’s economic vitality .
  • Key Message 22.4, Agriculture Faces Growing Threats, but Innovations Offer Help
    Changes in temperature, drought, extreme rainfall, and sea levels are already threatening the Southeast’s agriculture and other food-related systems . Moreover, these climate-related hazards are expected to worsen with every increment of global warming, disproportionately harm farmers and small-scale operations, and increase the competition between urban and rural communities for valuable resources such as water and land . However, innovative agricultural techniques such as precision farming show promise for adapting to future climate changes in the region .
  • Key Message 23.1, Climate-Driven Extreme Events Exacerbate Inequities and Impact Human Health and Well-Being
    Traditionally underserved and disadvantaged communities suffer disproportionate impacts from climate change because they have been systematically excluded from social services, secure livelihoods, quality education, and other social benefits that help sustain health and well-being . Hurricanes and other climate-related extreme events have been associated with higher rates of disease, mental illness, and overall mortality, as well as loss of cultural heritage that is central to community identity . As extreme weather events become more intense and more frequent, residents will continue experiencing increasing levels of noncommunicable diseases, excess mortality, behavioral health challenges, and loss of quality of life . The frequency of heat episodes and the severity of hurricanes are both expected to increase in the region due to human-induced climate change, which will affect public health unless adaptation measures are taken .
  • Key Message 23.2, Ecology and Biodiversity Are Unique and Vulnerable
    Coastal and terrestrial ecosystems provide a large number of goods and services that are vital to the islands’ economies and to the health and well-being of their residents . These essential systems are degraded by human actions and climate change, thereby reducing the benefits they provide to people, as well as their functionality as habitats for protecting biological diversity . Climate change is expected to exacerbate the degradation of ecosystems . The success of climate adaptation strategies will depend on reducing all sources of stress on ecological systems .
  • Key Message 23.3, Climate Change Threatens Water and Food Security
    US Caribbean food and water systems are becoming increasingly vulnerable to the escalation of climate change, including stronger hurricanes, more severe drought, warmer air temperatures, and other extreme weather . Because the territories are heavily reliant on imported foods, they are affected by climate changes occurring both within and outside of the region . Reductions in average annual rainfall, increasing air temperatures, and rising sea levels will adversely affect freshwater availability in the future . Improved adaptation efforts would benefit from a better understanding of the ways food and water systems interrelate and of the cascading impacts generated by climate change .
  • Key Message 23.4, Infrastructure and Energy Are Vulnerable, but Decentralization Could Improve Resilience
    Climate change has created profound risks for the US Caribbean’s critical infrastructure, already weakened from years of disinvestment and deferred maintenance . Increasingly powerful storms, along with rising sea levels, are severely impairing infrastructure systems, with increasing damage projected in future years . Dependence on fossil fuel imports increases energy insecurity . Infrastructure improvements, coupled with a new paradigm focused on decentralization, adoption of distributed solar, and shared governance, could help limit residents’ vulnerability to health and other risks associated with loss of essential services .
  • Key Message 23.5, Adaptation Effectiveness Increases When Coupled with Strategic Governance and Planning
    Climate adaptation in the US Caribbean is challenging because of multiple interacting factors, including high risk exposure, limited or misaligned funding, insufficient institutional and organizational capacity, and siloed approaches to risk reduction and resilience . Effective adaptation to support resilience in the US Caribbean could be enhanced through co-development and integration of robust global, regional, and local climate science and risk-based knowledge into planning and implementation, as well as improved governance arrangements . US Caribbean capabilities in planning and adaptation could be enhanced by strengthening partnerships across the wider Caribbean region and the US mainland .
  • Key Message 24.1, Climate-Smart Practices May Offset Complex Climate Interactions in Agriculture
    Crop production is projected to change in complex ways due to increasing extreme precipitation events and transitions between wet and dry conditions , as well as intensification of crop water loss . Changes in precipitation extremes, timing of snowmelt, and early-spring rainfall are expected to pose greater challenges for crop and animal agriculture, including increased pest and disease transmission, muddier pastures, and further degradation of water quality . Climate-smart agriculture and other adaptation techniques provide a potential path toward environmental and economic sustainability .
  • Key Message 24.2, Adaptation May Ease Disruptions to Ecosystems and Their Services
    Ecosystems are already being affected by changes in extreme weather and other climate-related changes, with negative impacts on a wide range of species . Increasing incidence of flooding and drought is expected to further alter aquatic ecosystems , while terrestrial ecosystems are being reshaped by rising temperatures and decreasing snow and ice cover . Loss of ecosystem services is undermining human well-being, causing the loss of economic, cultural, and health benefits . In response, communities are adapting their cultural practices and the ways they manage the landscape, preserving and protecting ecosystems and the services they provide .
  • Key Message 24.3, Climate Adaptation and Mitigation Strategies Improve Individual and Community Health
    Climate change has wide-ranging effects on lives and livelihoods , healthcare systems , and community cohesion . These diverse impacts will require integrated, innovative response from collaborations between public health and other sectors, such as emergency management, agriculture, and urban planning. Because of historical and systemic biases, communities of color are especially vulnerable to these negative impacts . Mitigation and adaptation strategies, such as expanded use of green infrastructure, heat-health early warning systems, and improved stormwater management systems, when developed in collaboration with affected communities, have the potential to improve individual and community health .
  • Key Message 24.4, Green Infrastructure and Investment Solutions Can Address Costly Climate Change Impacts
    Increases in temperatures and extreme precipitation events are already challenging aging infrastructure and are expected to impair surface transportation, water navigation, and the electrical grid . Shifts in the timing and intensity of rainfall are expected to disrupt transportation along major rivers and increase chronic flooding . Green infrastructure and public and private investments may mitigate losses, provide relief from heat, and offer other ways to adapt the built environment to a changing climate ).

  • Key Message 24.5, Managing Extremes Is Necessary to Minimize Impacts on Water Quality and Quantity
    Climate-related changes to water quantity and quality are increasing the risks to ecosystem health, adequate food production, surface water and groundwater uses, and recreation . Projected increases in droughts, floods, and runoff events across the Mississippi River basin and the Great Lakes will adversely impact ecosystems through increased erosion, harmful algal blooms, and expansion of invasive species . Federal and state agencies and nongovernmental organizations are cooperating on adaptation efforts related to streamflow, water quality, and other water issues .

  • Key Message 25.1, Climate Change Is Compounding the Impacts of Extreme Events
    The Northern Great Plains region is experiencing unprecedented extremes related to changes in climate, including severe droughts , increases in hail frequency and size , floods , and wildfire . Rising temperatures across the region are expected to lead to increased evapotranspiration , as well as greater variability in precipitation .
  • Key Message 25.2, Human and Ecological Health Face Rising Threats from Climate-Related Hazards
    Climate-related hazards, such as drought, wildfire, and flooding, are already harming the physical, mental, and spiritual health of Northern Great Plains region residents , as well as the ecology of the region . As the climate continues to change, it is expected to have increasing and cascading negative effects on human health and on the lands, waters, and species on which people depend .

  • Key Message 25.3, Resource- and Land-Based Livelihoods Are at Risk
    The Northern Great Plains region is heavily reliant on agriculture and resource-based economies, placing livelihoods at risk from the impacts of climate change and related policy. Agriculture and recreation will see some positive effects but primarily negative effects related to changing temperature and precipitation regimes . Energy-sector livelihoods will be affected as emissions-reductions policies drive shifts away from fossil fuel sources . Climate change is expected to test the adaptive resilience of the region’s residents, in particular rural, Indigenous, and low-income immigrant populations .
  • Key Message 25.4, Climate Response Involves Navigating Complex Trade-Offs and Tensions
    Climate change is creating new, and exacerbating existing, tensions and trade-offs between land use, water availability, ecosystem services, and other considerations in the region, leading to decisions that are expected to benefit some and set back others . Decision-makers are navigating a complicated landscape of shifting demographics, policy and regulatory tensions, and barriers to action . Changes in temperature and precipitation averages, extremes, and seasonality will alter the productivity of working lands, resulting in land-use shifts to alternative crops or conversion to grasslands . Shifts in energy demand, production, and policy will change land-use needs for energy infrastructure .
  • Key Message 25.5, Communities Are Building the Capacity to Adapt and Transform
    Adaptation is underway in the Northern Great Plains to address the effects of climate change. Agricultural communities are shifting toward climate adaptation measures such as innovative soil practices, new drought-management tools, and water-use partnerships . Several Tribal Nations are leading efforts to incorporate Traditional Knowledge and governance into their adaptation plans . Resource managers are increasingly relying on tools such as scenario planning to improve the adaptive capacity of natural ecosystems .
  • Key Message 26.1, How We Live: Climate Change Is Degrading Lands, Waters, Culture, and Health
    Climate change is beginning to alter how we live in the Southern Great Plains, putting us at risk from climate hazards that degrade our lands and waters, quality of life, health and well-being, and cultural interconnectedness . Many climate hazards are expected to become more frequent, intense, or prolonged; to broaden in spatial extent; and to result in more people experiencing costly, deadly, or stressful climate-related conditions . To address the growing risk, effective climate-resilient actions include implementing nature-based solutions; valuing Indigenous, traditional, and local knowledges; and infusing climate change solutions into community planning .
  • Key Message 26.2, How We Work: Climate Changes Are Creating Economic Challenges and Opportunities
    As climate conditions change, businesses and industries across the Southern Great Plains are experiencing disruptions and losses in productivity and profits—but also new economic opportunities . In coming decades, warmer temperatures, more erratic precipitation, and sea level rise are expected to force widespread and costly changes in how we work . Businesses and industries have opportunities to harness their diverse knowledge, resources, and workers to develop products and services in climate mitigation technologies, adaptation strategies, and resilient design that will enhance the region’s economy .
  • Key Message 26.3, How We Play: Climate Extremes Are Endangering Sports, Recreation, and Leisure
    Extreme climate-related events are negatively influencing how we play and participate in outdoor sport, recreation, and physical activities in the Southern Great Plains . Climate change is expected to increase heat-related illness and death, reduce outdoor physical activity, and decrease athletic performance . Individuals, communities, and sports organizations can adapt to these hazards through strategies such as modifying the timing, location, intensity, or monitoring of activities .
  • Key Message 26.4, How We Heal: Climate Change Is Exacerbating Existing Social and Environmental Disparities
    Some neighborhoods and communities in the Southern Great Plains are suffering disproportionately from climate-related hazards because of long-standing marginalization, discrimination, and governmental policies . As a result, climate change will compound existing social and environmental burdens on the people, neighborhoods, and communities with the fewest resources to prepare and adapt . Our institutions and governments can play a role in improving outcomes for these people and places by adopting climate adaptation and hazard-mitigation practices and policies that prioritize social equity and justice, aim to reduce community risks, build resilience, and repair past injustices .
  • Key Message 26.5, How We Serve: Climate Change Is Straining Public Infrastructure and Services
    The institutions that serve our communities have been challenged to respond and adapt to more frequent and intense weather events . Without significant adaptation, climate change is expected to strain water supplies, transportation infrastructure, and emergency services across the Southern Great Plains . Actions that can enhance our community resilience include substantially reducing greenhouse gas emissions, installing or retrofitting climate-resilient infrastructure, educating students and the public on climate change, and cultivating the capacity of faith- and volunteer-based aid organizations to assist hazard planning, response, and recovery .
  • Key Message 27.1, Frontline Communities Are Overburdened, and Prioritizing Social Equity Advances Regional Resilience
    Ongoing systemic oppression disproportionately exposes frontline communities in the Northwest—including low-income urban communities of color; rural and natural resource–dependent communities; and Tribes and Indigenous communities—to the consequences of extreme heat, flooding, and wildfire smoke and other climate hazards . Frontline communities often have fewer resources to cope with and adapt to climate change but have been leaders in developing climate solutions within and outside their communities . Actions to limit and adapt to climate change that prioritize climate justice and redirect investments to frontline communities can advance regional resilience .
  • Key Message 27.2, Ecosystems Are Transitioning in Response to Extreme Events and Human Activity
    Ecosystems are expected to change as the climate continues to change and as the magnitude and frequency of extreme events increases . Some historical and ongoing human activities reduce ecosystem resilience and the adaptive capacity of species . These human activities are expected to exacerbate many effects of climate change . Human efforts to enable ecological adaptation founded in ecological theory are expected to improve ecosystem functions and services and reduce exposure to climate-related hazards .
  • Key Message 27.3, Impacts to Regional Economies Have Cascading Effects on Livelihoods and Well-Being
    Climate change impacts to the Northwest’s natural resource- and outdoor-dependent economies will be variable, given the diversity of industries, land cover, and climatic zones . Impacts to these industries will have cascading effects on community livelihoods and well-being . While some industries and resource-dependent communities are resilient to climate-related stresses, economic responses to climate change can benefit affected industries, workers, and livelihoods .
  • Key Message 27.4, Infrastructure Systems Are Stressed by Climate Change but Can Enable Mitigation and Adaptation
    Recent extreme events have stressed water systems and housing, transportation, and energy infrastructure across the Northwest . Extreme precipitation, droughts, and heatwaves will intensify due to climate change and continue to threaten these interrelated systems . Given the complexity of and interdependencies among infrastructure systems, an impact or a response within one sector can cascade to other sectors . Cross-sectoral planning, which can include redesigning aging infrastructure and incorporating climate considerations into land-use decisions, can increase resilience to future climate variability and extremes .
  • Key Message 27.5, Climate Change Amplifies Health Inequities
    The Northwest’s climate has historically been temperate and relatively mild, but shifting weather patterns associated with climate change are adversely affecting physical, mental, and community health . The incidence of illnesses and death during extreme heat events and wildfire smoke days is increasing, and climate change is stressing health systems . Climate-related health risks disproportionately affect certain individuals and groups . Climate resilience efforts can be leveraged to improve health, especially among the most vulnerable populations .
  • Key Message 27.6, Climate Change Affects Heritage and Sense of Place
    Climate change has disrupted sense of place in the Northwest, affecting noneconomic values such as proximity and access to nature and residents’ feelings of security and stability . Place-based communities, including Tribes, face additional challenges from climate change because of cultural and economic relationships with their locale . Leveraging local or Indigenous Knowledge and value systems can spur climate action to ensure that local heritage and sense of place persist for future generations .
  • Key Message 28.1, Drought and Increasing Aridity Threaten Water Resources
    Climate change has reduced surface water and groundwater availability for people and nature in the Southwest , and there are inequities in how these impacts are experienced . Higher temperatures have intensified drought and will lead to a more arid future ; without adaptation, these changes will exacerbate existing water supply–demand imbalances . At the same time, the region is experiencing more intense precipitation events, including atmospheric rivers, which contribute to increased flooding . Flexible and adaptive approaches to water management have the potential to mitigate the impacts of these changes on people, the environment, and the economy .
  • Key Message 28.2, Adaptation Efforts Increase to Address Accelerating Impacts to the Region’s Coast and Ocean
    Large-scale marine heatwaves and harmful algal blooms have caused profound and cascading impacts on marine coastal ecosystems and economies . Without implementation of adaptation or emissions-reductions measures, human-caused warming will drive more frequent and longer marine heatwaves , amplifying negative coastal effects . Sea level rise, along with associated impacts such as flooding and saltwater intrusion, will have severe and disproportionate effects on infrastructure, communities, and natural resources . The California State Government has applied climate science to planning and decision-making for sea level rise, and multiple regions are moving toward climate-informed and adaptive strategies for fisheries . However, climate planning and adaptation solutions for aquaculture are less clear .
  • Key Message 28.3, Increasing Challenges Confront Food and Fiber Production in the Southwest
    Continuing drought and water scarcity will make it more difficult to raise food and fiber in the Southwest without major shifts to new strategies and technologies . Extreme heat events will increase animal stress and reduce crop quality and yield, thereby resulting in widespread economic impacts . Because people in the Southwest have adapted to drought impacts for millennia, incorporating Indigenous Knowledge with technological innovation can offer solutions to protect food security and sovereignty .
  • Key Message 28.4, Climate Change Compromises Human Health and Reshapes Demographics
    Increases in extreme heat, drought, flooding, and wildfire activity are negatively impacting the physical health of Southwest residents . Climate change is also shaping the demographics of the region by spurring the migration of people from Central America to the Southwest . Individuals particularly vulnerable to increasing climate change impacts include older adults, outdoor workers, and people with low income . Local, state, and federal adaptation initiatives are working to respond to these impacts .
  • Key Message 28.5, Changes in Wildfire Patterns Pose Challenges for Southwest Residents and Ecosystems
    In recent years, the Southwest has experienced unprecedented wildfire events, driven in part by climate change . Fires in the region have become larger and more severe . High-severity wildfires are expected to continue in coming years, placing the people, economies, ecosystems, and water resources of the region at considerable risk . Opportunities for adaptation include pre- and postfire actions that reduce wildfire risk and facilitate ecosystem restoration and include traditional land stewardship practices and the application of Indigenous cultural fire .
  • Key Message 29.1, Our Health and Healthcare Are at Risk
    Health disparities in Alaska, including access to healthcare and health outcomes, are exacerbated by climate change . The well-being of Alaska residents will be further challenged by climate-driven threats and by emerging diseases . Improving health surveillance and healthcare access statewide can increase resilience to events that threaten public health .
  • Key Message 29.2, Our Communities Are Navigating Compounding Stressors
    Climate change amplifies the social and economic challenges facing Alaska communities . Resource shifts, coastal and riverbank erosion, and disproportionate access to services will continue to threaten the physical and social integrity of these communities . Increased adaptation capacity and equitable support have the potential to help rural and urban communities address Alaska’s regionally varied climate-driven threats .
  • Key Message 29.3, Our Livelihoods Are Vulnerable Without Diversification
    Livelihoods, especially those dependent on natural resources, are at risk around Alaska. While advancing climate change has contributed to the collapse of major fisheries and is undermining many existing jobs and ways of life , it may also create some opportunities related to adaptation and response . Economic diversification, especially expansion of value-added industries, can help increase overall livelihood options .
  • Key Message 29.4, Our Built Environment Will Become More Costly
    Much of Alaska’s infrastructure was built for a stable climate, and changes in permafrost, ocean conditions, sea ice, air temperature, and precipitation patterns place that infrastructure at risk . Further warming is expected to lead to greater needs and costs for maintenance or replacement of buildings, roads, airports, and other facilities . Planning for further change and greater attention to climate trends and changes in extremes can help improve infrastructure resilience around Alaska .
  • Key Message 29.5, Our Natural Environment Is Transforming Rapidly
    Alaska’s ecosystems are changing rapidly due to climate change . Many of the ecosystem goods and services that Alaskans rely on are expected to be diminished by further change . Careful management of Alaska’s natural resources to avoid additional stresses on fish, wildlife, and habitats can help avoid compounding effects on our ecosystems .
  • Key Message 29.6, Our Security Faces Greater Threats
    Rapid climate-driven change in Alaska undermines many of the assumptions of predictability on which community, state, and national security are based . Further change, especially in the marine environment with loss of sea ice, will create new vulnerabilities and requirements for security from multiple perspectives and at multiple scales . Greater capacity for identifying and responding to threats has the potential to help reduce security risks in the Alaska region .
  • Key Message 29.7, Our Just and Prosperous Future Starts with Adaptation
    Local and regional efforts are underway around Alaska to prepare for and adapt to a changing climate . The breadth of adaptation needed around the state will require substantial investment of financial resources and close coordination among agencies, including Tribal governments . The effectiveness of adaptation planning and activities can be strengthened by addressing intersecting non-climate stressors, prioritizing the needs of the communities and populations experiencing the greatest impacts, building local capacity, and connecting adaptation efforts to economic and workforce development .
  • Key Message 30.1, Climate Change Impairs Access to Healthy Food and Water
    Access to clean, fresh water and healthy food is expected to be increasingly impaired by climate change . On low-lying atolls, sea level rise has caused saltwater contamination of fresh water . Regionally, food and water availability will be further negatively impacted by increasing temperatures, altered rainfall patterns, increased flooding and pollution, and degradation of nearshore fisheries . Adaptation actions such as traditional farming, fishing, and land-management practices can help build more resilient water and food systems .
  • Key Message 30.2, Climate Change Undermines Human Health, but Community Strength Boosts Resilience
    Climate change undermines the place-based foundations of human health and well-being in the Pacific Islands . Climate shocks and stressors compromise healthcare services and worsen long-standing social and economic inequities in both mental and physical health , and these negative impacts are expected to increase in the future . Adaptation efforts that build upon existing community strengths and center local and Indigenous Knowledge systems have great potential to boost resilience .
  • Key Message 30.3, Rising Sea Levels Threaten Infrastructure and Local Economies and Exacerbate Existing Inequities
    Climate change, particularly sea level rise (SLR), will continue to negatively impact the built environment and will harm numerous sectors of the islands’ economies . SLR intensifies loss of territory and exclusive economic zones, particularly in low islands . Climate-driven changes will exacerbate existing social challenges by disrupting livelihoods . Adaptation to climate change and recovery from disasters is logistically challenging and disproportionately more expensive in the islands . Government and community groups have developed innovative ways to reduce emissions and improve resilience by moving toward renewable energy and green infrastructure, nature-based urban planning, forward-looking building codes, and sustainable and equitable economic growth, guided by Western science and Traditional Knowledge.
  • Key Message 30.4, Responses to Rising Threats May Help Safeguard Tropical Ecosystems and Biodiversity
    The structure and composition of Pacific Island coastal and marine ecological communities are directly threatened by rising ocean temperatures, ocean acidification, and sea level rise . Increasingly severe droughts and warming are increasing fire risk and will have broad negative impacts on native plants and wildlife, including an increased risk of forest bird extinctions . Adaptation strategies improve the resilience of ecosystems, including ecosystem protection, ecological restoration, invasive species prevention and control, and investments in fire prevention .
  • Key Message 30.5, Indigenous Knowledge Systems Strengthen Island Resilience
    Indigenous Peoples and their knowledge systems are central to the resilience of island communities amidst the changing climate . Reciprocal and spiritual relationships among the lands, territories, waters, resources, and peoples are being strengthened and sustained as communities adapt and manage their resources collectively . Indigenous Peoples are identifying and quantifying the potential loss and migration of critical resources and expanding the cultivation of traditional food crops on high islands .
  • Key Message 31.1, Adaptation Is Occurring but Is Insufficient in Relation to the Pace of Climate Change
    Diverse adaptation activities are occurring across the US . Adaptation activities are increasingly moving from awareness and assessment toward planning and implementation , with limited advancement toward monitoring and evaluation . Numerous social, economic, physical, and psychological barriers are preventing more widespread adoption and implementation of adaptation . Current adaptation efforts and investments are insufficient to reduce today’s climate-related risks and are unlikely to keep pace with future changes in the climate .
  • Key Message 31.2, Effective Adaptation Requires Centering Equity
    People and communities are affected by climate change in different ways . How people and institutions adapt depends on social factors, including individual and community preferences, capacity, and access to resources . Adaptation processes, decisions (about whether, where, and how adaptation occurs), and actions that do not explicitly address the uneven distribution of climate harms, and the social processes and injustices underlying these disparities, can exacerbate social inequities and increase exposure to climate harms .
  • Key Message 31.3, Transformative Adaptation Will Be Needed to Adequately Address Climate-Related Risks
    Climate adaptation actions undertaken in the United States to date have generally been small in scale and incremental in approach, involving minor changes to business as usual . Transformative adaptation, which involves more fundamental shifts in systems, values, and practices, will be necessary in many cases to adequately address the risks of current and future climate change . New monitoring and evaluation methods will also be needed to assess the effectiveness and sufficiency of adaptation and to address equity .
  • Key Message 31.4, Effective Adaptation Governance Empowers Multiple Voices to Navigate Competing Goals
    Adaptation involves actors from government, private-sector, nongovernmental (e.g., nonprofit and for-profit institutions), and civil society organizations, which often have different priorities and approaches . Adaptation decision-makers must balance competing goals while also addressing uncertainties regarding future climate change and the ways that political, social, and technological systems will be transformed . To minimize the potential for adaptation actions to benefit some at the expense of others, adaptation processes must emphasize collaboration, center equity and justice, and incorporate a wide range of values and knowledge sources .
  • Key Message 31.5, Adaptation Requires More than Scientific Information and Understanding
    Effective adaptation to a changing climate requires both decision-relevant climate information and evidence-based decision-making approaches . Adaptation requires that researchers intentionally collaborate with communities to identify goals, assess vulnerability, improve capacity, and address contextual factors, such as values, culture, risk perception, and historic injustices . Climate services can be improved by ensuring access for historically disinvested communities and by attention to procedural and recognitional equity when scientists work with communities and decision-makers .
  • Key Message 31.6, Adaptation Investments and Financing Are Difficult to Track and May Be Inadequate
    Investments in adaptation are being made at the federal, state, territorial, Tribal, and local levels, as well as within the private sector, but they are not always evenly distributed, coordinated, tracked, or reported and may be inadequate . Future adaptation investment needs are expected to be significant, although projected amounts vary due to uncertainty in future emissions trajectories, associated impacts, and the timing of implementation . Proactive adaptation can reduce some of the most severe costs of future climate change, particularly under very high emissions scenarios in the late 21st century , although adaptation is still needed in the present for communities and infrastructure that may not be well adapted to face current climate conditions .
  • Key Message 32.1, Successful Mitigation Means Reaching Net-Zero Emissions
    Greenhouse gas emissions in the United States decreased by 12% between 2005 and 2019, mostly due to replacing coal-fired electricity generation with natural gas–fired and renewable generation . However, US net greenhouse gas emissions remain substantial and would have to decline by more than 6% per year on average, reaching net zero around midcentury, to meet current national climate targets and international temperature goals .
  • Key Message 32.2, We Know How to Drastically Reduce Emissions
    A US energy system with net-zero emissions would rely on widespread improvements in energy efficiency, substantial electricity generation from solar and wind energy, and widespread electrification of transportation and heating . Low-carbon fuels would still be needed for some transport and industry applications that are difficult to electrify . Land-related emissions in the US could be reduced by increasing the efficiency of food systems and improving agricultural practices and by protecting and restoring natural lands . Across all sectors, many of these options are economically feasible now .
  • Key Message 32.3, To Reach Net-Zero Emissions, Additional Mitigation Options Need to Be Explored
    Although many mitigation options are currently available and cost-effective, the level and types of energy technologies and carbon management in net-zero-emissions energy systems depend on still-uncertain technological progress, public acceptance, consumer choice, and future developments in institutions, markets, and policies . Attractive targets for further research, development, and demonstration include carbon capture, utilization, and storage; long-duration energy storage; low-carbon fuels and feedstocks; demand management; next-generation electricity transmission; carbon dioxide removal; modern foods; and interventions to reduce industry and agricultural emissions .
  • Key Message 32.4, Mitigation Can Be Sustainable, Healthy, and Fair
    Large reductions in US greenhouse gas emissions could have substantial benefits for human health and well-being . Mitigation is expected to affect pollution, the use of land and water resources, the labor force, and the affordability, reliability, and security of energy and food . An equitable and sustainable transition to net-zero-emissions energy and food systems in the United States could help redress legacies of inequity, racism, and injustice while maximizing overall benefits to our economy and environment .

  • Key Message 32.5, Governments, Organizations, and Individuals Can Act to Reduce Emissions
    Mitigation efforts can be supported by a range of actors and actions, from choices made by individuals to decisions made by businesses and local, Tribal, state, and national governments . Actions with significant near-term potential include sector-based policies accelerating deployment of low-carbon technologies, city-level efforts to promote public transportation and improve building efficiency, and individual behavioral changes to reduce energy demand and meat consumption .

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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