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 * ABOUT
   About this Report Guide to this Report Report Credits
 * CHAPTERS
   
   
   FRONT MATTER
   
    * About this Report
    * Guide to the Report
   
   Summary Findings
   1. Overview
   
   
   NATIONAL TOPICS
   
    2.  Our Changing Climate
    3.  Water
    4.  Energy Supply, Delivery & Demand
    5.  Land Cover & Land-Use Change
    6.  Forests
    7.  Ecosystems, Ecosystem Services, & Biodiversity
    8.  Coastal Effects
    9.  Oceans & Marine Resources
    10. Agriculture & Rural Communities
    11. Built Environment, Urban Systems, & Cities
    12. Transportation
   
   
   NATIONAL TOPICS (CONT.)
   
    13. Air Quality
    14. Human Health
    15. Tribes & Indigenous Peoples
    16. Climate Effects on U.S. International Interests
    17. Sector Interactions, Multiple Stressors, & Complex Systems
   
   
   REGIONS
   
    18. Northeast
    19. Southeast
    20. U.S. Caribbean
    21. Midwest
    22. Northern Great Plains
    23. Southern Great Plains
    24. Northwest
    25. Southwest
    26. Alaska
    27. Hawai‘i & U.S.-Affiliated Pacific Islands
   
   
   RESPONSES
   
    28. Reducing Risks Through Adaptation Actions
    29. Reducing Risks Through Emissions Mitigation
   
   
   APPENDICES
   
    1. Report Development Process
    2. Information in the Fourth National Climate Assessment
    3. Data Tools & Scenario Products
    4. Looking Abroad
    5. Frequently Asked Questions

 * DOWNLOADS
   View All Report Downloads Full Report PDF Report in Brief PDF Summary
   Findings PDF All Report Figures (.zip) Full Report Bibliography (RIS) Order
   Printed Materials


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FOURTH NATIONAL CLIMATE ASSESSMENT VOLUME II: IMPACTS, RISKS, AND ADAPTATION IN
THE UNITED STATES

The National Climate Assessment (NCA) assesses the science of climate change and
variability and its impacts across the United States, now and throughout this
century.


SUMMARY FINDINGS


REPORT CHAPTERS


OVERVIEW


DOWNLOADS

Volume I presents an assessment of the physical science underlying this report:
science2017.globalchange.gov

 * SUMMARY FINDINGS
 * Background
 * 1. Communities
 * 2. Economy
 * 3. Interconnected Impacts
 * 4. Actions to Reduce Risks
 * 5. Water
 * 6. Health
 * 7. Indigenous Peoples
 * 8. Ecosystems & Services
 * 9. Agriculture
 * 10. Infrastructure
 * 11. Oceans & Coasts
 * 12. Tourism & Recreation





FOURTH NATIONAL CLIMATE ASSESSMENT


SUMMARY FINDINGS

These Summary Findings represent a high-level synthesis of the material in the
underlying report. The findings consolidate Key Messages and supporting evidence
from 16 national-level topic chapters, 10 regional chapters, and 2 chapters that
focus on societal response strategies (mitigation and adaptation). Unless
otherwise noted, qualitative statements regarding future conditions in these
Summary Findings are broadly applicable across the range of different levels of
future climate change and associated impacts considered in this report.


1. COMMUNITIES

> Climate change creates new risks and exacerbates existing vulnerabilities in
> communities across the United States, presenting growing challenges to human
> health and safety, quality of life, and the rate of economic growth.

The impacts of climate change are already being felt in communities across the
country. More frequent and intense extreme weather and climate-related events,
as well as changes in average climate conditions, are expected to continue to
damage infrastructure, ecosystems, and social systems that provide essential
benefits to communities. Future climate change is expected to further disrupt
many areas of life, exacerbating existing challenges to prosperity posed by
aging and deteriorating infrastructure, stressed ecosystems, and economic
inequality. Impacts within and across regions will not be distributed equally.
People who are already vulnerable, including lower-income and other marginalized
communities, have lower capacity to prepare for and cope with extreme weather
and climate-related events and are expected to experience greater impacts.
Prioritizing adaptation actions for the most vulnerable populations would
contribute to a more equitable future within and across communities. Global
action to significantly cut greenhouse gas emissions can substantially reduce
climate-related risks and increase opportunities for these populations in the
longer term.


2. ECONOMY

> Without substantial and sustained global mitigation and regional adaptation
> efforts, climate change is expected to cause growing losses to American
> infrastructure and property and impede the rate of economic growth over this
> century.

In the absence of significant global mitigation action and regional adaptation
efforts, rising temperatures, sea level rise, and changes in extreme events are
expected to increasingly disrupt and damage critical infrastructure and
property, labor productivity, and the vitality of our communities. Regional
economies and industries that depend on natural resources and favorable climate
conditions, such as agriculture, tourism, and fisheries, are vulnerable to the
growing impacts of climate change. Rising temperatures are projected to reduce
the efficiency of power generation while increasing energy demands, resulting in
higher electricity costs. The impacts of climate change beyond our borders are
expected to increasingly affect our trade and economy, including import and
export prices and U.S. businesses with overseas operations and supply chains.
Some aspects of our economy may see slight near-term improvements in a modestly
warmer world. However, the continued warming that is projected to occur without
substantial and sustained reductions in global greenhouse gas emissions is
expected to cause substantial net damage to the U.S. economy throughout this
century, especially in the absence of increased adaptation efforts. With
continued growth in emissions at historic rates, annual losses in some economic
sectors are projected to reach hundreds of billions of dollars by the end of the
century—more than the current gross domestic product (GDP) of many U.S. states.


3. INTERCONNECTED IMPACTS

> Climate change affects the natural, built, and social systems we rely on
> individually and through their connections to one another. These
> interconnected systems are increasingly vulnerable to cascading impacts that
> are often difficult to predict, threatening essential services within and
> beyond the Nation’s borders.

Climate change presents added risks to interconnected systems that are already
exposed to a range of stressors such as aging and deteriorating infrastructure,
land-use changes, and population growth. Extreme weather and climate-related
impacts on one system can result in increased risks or failures in other
critical systems, including water resources, food production and distribution,
energy and transportation, public health, international trade, and national
security. The full extent of climate change risks to interconnected systems,
many of which span regional and national boundaries, is often greater than the
sum of risks to individual sectors. Failure to anticipate interconnected impacts
can lead to missed opportunities for effectively managing the risks of climate
change and can also lead to management responses that increase risks to other
sectors and regions. Joint planning with stakeholders across sectors, regions,
and jurisdictions can help identify critical risks arising from interaction
among systems ahead of time.


4. ACTIONS TO REDUCE RISKS

> Communities, governments, and businesses are working to reduce risks from and
> costs associated with climate change by taking action to lower greenhouse gas
> emissions and implement adaptation strategies. While mitigation and adaptation
> efforts have expanded substantially in the last four years, they do not yet
> approach the scale considered necessary to avoid substantial damages to the
> economy, environment, and human health over the coming decades.

Future risks from climate change depend primarily on decisions made today. The
integration of climate risk into decision-making and the implementation of
adaptation activities have significantly increased since the Third National
Climate Assessment in 2014, including in areas of financial risk reporting,
capital investment planning, development of engineering standards, military
planning, and disaster risk management. Transformations in the energy
sector—including the displacement of coal by natural gas and increased
deployment of renewable energy—along with policy actions at the national,
regional, state, and local levels are reducing greenhouse gas emissions in the
United States. While these adaptation and mitigation measures can help reduce
damages in a number of sectors, this assessment shows that more immediate and
substantial global greenhouse gas emissions reductions, as well as regional
adaptation efforts, would be needed to avoid the most severe consequences in the
long term. Mitigation and adaptation actions also present opportunities for
additional benefits that are often more immediate and localized, such as
improving local air quality and economies through investments in infrastructure.
Some benefits, such as restoring ecosystems and increasing community vitality,
may be harder to quantify.


5. WATER

> The quality and quantity of water available for use by people and ecosystems
> across the country are being affected by climate change, increasing risks and
> costs to agriculture, energy production, industry, recreation, and the
> environment.

Rising air and water temperatures and changes in precipitation are intensifying
droughts, increasing heavy downpours, reducing snowpack, and causing declines in
surface water quality, with varying impacts across regions. Future warming will
add to the stress on water supplies and adversely impact the availability of
water in parts of the United States. Changes in the relative amounts and timing
of snow and rainfall are leading to mismatches between water availability and
needs in some regions, posing threats to, for example, the future reliability of
hydropower production in the Southwest and the Northwest. Groundwater depletion
is exacerbating drought risk in many parts of the United States, particularly in
the Southwest and Southern Great Plains. Dependable and safe water supplies for
U.S. Caribbean, Hawai‘i, and U.S.-Affiliated Pacific Island communities are
threatened by drought, flooding, and saltwater contamination due to sea level
rise. Most U.S. power plants rely on a steady supply of water for cooling, and
operations are expected to be affected by changes in water availability and
temperature increases. Aging and deteriorating water infrastructure, typically
designed for past environmental conditions, compounds the climate risk faced by
society. Water management strategies that account for changing climate
conditions can help reduce present and future risks to water security, but
implementation of such practices remains limited.


6. HEALTH

> Impacts from climate change on extreme weather and climate-related events, air
> quality, and the transmission of disease through insects and pests, food, and
> water increasingly threaten the health and well-being of the American people,
> particularly populations that are already vulnerable.

Changes in temperature and precipitation are increasing air quality and health
risks from wildfire and ground-level ozone pollution. Rising air and water
temperatures and more intense extreme events are expected to increase exposure
to waterborne and foodborne diseases, affecting food and water safety. With
continued warming, cold-related deaths are projected to decrease and
heat-related deaths are projected to increase; in most regions, increases in
heat-related deaths are expected to outpace reductions in cold-related deaths.
The frequency and severity of allergic illnesses, including asthma and hay
fever, are expected to increase as a result of a changing climate. Climate
change is also projected to alter the geographic range and distribution of
disease-carrying insects and pests, exposing more people to ticks that carry
Lyme disease and mosquitoes that transmit viruses such as Zika, West Nile, and
dengue, with varying impacts across regions. Communities in the Southeast, for
example, are particularly vulnerable to the combined health impacts from
vector-borne disease, heat, and flooding. Extreme weather and climate-related
events can have lasting mental health consequences in affected communities,
particularly if they result in degradation of livelihoods or community
relocation. Populations including older adults, children, low-income
communities, and some communities of color are often disproportionately affected
by, and less resilient to, the health impacts of climate change. Adaptation and
mitigation policies and programs that help individuals, communities, and states
prepare for the risks of a changing climate reduce the number of injuries,
illnesses, and deaths from climate-related health outcomes.


7. INDIGENOUS PEOPLES

> Climate change increasingly threatens Indigenous communities’ livelihoods,
> economies, health, and cultural identities by disrupting interconnected
> social, physical, and ecological systems.

Many Indigenous peoples are reliant on natural resources for their economic,
cultural, and physical well-being and are often uniquely affected by climate
change. The impacts of climate change on water, land, coastal areas, and other
natural resources, as well as infrastructure and related services, are expected
to increasingly disrupt Indigenous peoples’ livelihoods and economies, including
agriculture and agroforestry, fishing, recreation, and tourism. Adverse impacts
on subsistence activities have already been observed. As climate changes
continue, adverse impacts on culturally significant species and resources are
expected to result in negative physical and mental health effects. Throughout
the United States, climate-related impacts are causing some Indigenous peoples
to consider or actively pursue community relocation as an adaptation strategy,
presenting challenges associated with maintaining cultural and community
continuity. While economic, political, and infrastructure limitations may affect
these communities’ ability to adapt, tightly knit social and cultural networks
present opportunities to build community capacity and increase resilience. Many
Indigenous peoples are taking steps to adapt to climate change impacts
structured around self-determination and traditional knowledge, and some tribes
are pursuing mitigation actions through development of renewable energy on
tribal lands.


8. ECOSYSTEMS AND ECOSYSTEM SERVICES

> Ecosystems and the benefits they provide to society are being altered by
> climate change, and these impacts are projected to continue. Without
> substantial and sustained reductions in global greenhouse gas emissions,
> transformative impacts on some ecosystems will occur; some coral reef and sea
> ice ecosystems are already experiencing such transformational changes.

Many benefits provided by ecosystems and the environment, such as clean air and
water, protection from coastal flooding, wood and fiber, crop pollination,
hunting and fishing, tourism, cultural identities, and more will continue to be
degraded by the impacts of climate change. Increasing wildfire frequency,
changes in insect and disease outbreaks, and other stressors are expected to
decrease the ability of U.S. forests to support economic activity, recreation,
and subsistence activities. Climate change has already had observable impacts on
biodiversity, ecosystems, and the benefits they provide to society. These
impacts include the migration of native species to new areas and the spread of
invasive species. Such changes are projected to continue, and without
substantial and sustained reductions in global greenhouse gas emissions,
extinctions and transformative impacts on some ecosystems cannot be avoided in
the long term. Valued aspects of regional heritage and quality of life tied to
ecosystems, wildlife, and outdoor recreation will change with the climate, and
as a result, future generations can expect to experience and interact with the
natural environment in ways that are different from today. Adaptation
strategies, including prescribed burning to reduce fuel for wildfire, creation
of safe havens for important species, and control of invasive species, are being
implemented to address emerging impacts of climate change. While some targeted
response actions are underway, many impacts, including losses of unique coral
reef and sea ice ecosystems, can only be avoided by significantly reducing
global emissions of carbon dioxide and other greenhouse gases.


9. AGRICULTURE

> Rising temperatures, extreme heat, drought, wildfire on rangelands, and heavy
> downpours are expected to increasingly disrupt agricultural productivity in
> the United States. Expected increases in challenges to livestock health,
> declines in crop yields and quality, and changes in extreme events in the
> United States and abroad threaten rural livelihoods, sustainable food
> security, and price stability.

Climate change presents numerous challenges to sustaining and enhancing crop
productivity, livestock health, and the economic vitality of rural communities.
While some regions (such as the Northern Great Plains) may see conditions
conducive to expanded or alternative crop productivity over the next few
decades, overall, yields from major U.S. crops are expected to decline as a
consequence of increases in temperatures and possibly changes in water
availability, soil erosion, and disease and pest outbreaks. Increases in
temperatures during the growing season in the Midwest are projected to be the
largest contributing factor to declines in the productivity of U.S. agriculture.
Projected increases in extreme heat conditions are expected to lead to further
heat stress for livestock, which can result in large economic losses for
producers. Climate change is also expected to lead to large-scale shifts in the
availability and prices of many agricultural products across the world, with
corresponding impacts on U.S. agricultural producers and the U.S. economy. These
changes threaten future gains in commodity crop production and put rural
livelihoods at risk. Numerous adaptation strategies are available to cope with
adverse impacts of climate variability and change on agricultural production.
These include altering what is produced, modifying the inputs used for
production, adopting new technologies, and adjusting management strategies.
However, these strategies have limits under severe climate change impacts and
would require sufficient long- and short-term investment in changing practices.


10. INFRASTRUCTURE

> Our Nation’s aging and deteriorating infrastructure is further stressed by
> increases in heavy precipitation events, coastal flooding, heat, wildfires,
> and other extreme events, as well as changes to average precipitation and
> temperature. Without adaptation, climate change will continue to degrade
> infrastructure performance over the rest of the century, with the potential
> for cascading impacts that threaten our economy, national security, essential
> services, and health and well-being.

Climate change and extreme weather events are expected to increasingly disrupt
our Nation’s energy and transportation systems, threatening more frequent and
longer-lasting power outages, fuel shortages, and service disruptions, with
cascading impacts on other critical sectors. Infrastructure currently designed
for historical climate conditions is more vulnerable to future weather extremes
and climate change. The continued increase in the frequency and extent of
high-tide flooding due to sea level rise threatens America’s trillion-dollar
coastal property market and public infrastructure, with cascading impacts to the
larger economy. In Alaska, rising temperatures and erosion are causing damage to
buildings and coastal infrastructure that will be costly to repair or replace,
particularly in rural areas; these impacts are expected to grow without
adaptation. Expected increases in the severity and frequency of heavy
precipitation events will affect inland infrastructure in every region,
including access to roads, the viability of bridges, and the safety of
pipelines. Flooding from heavy rainfall, storm surge, and rising high tides is
expected to compound existing issues with aging infrastructure in the Northeast.
Increased drought risk will threaten oil and gas drilling and refining, as well
as electricity generation from power plants that rely on surface water for
cooling. Forward-looking infrastructure design, planning, and operational
measures and standards can reduce exposure and vulnerability to the impacts of
climate change and reduce energy use while providing additional near-term
benefits, including reductions in greenhouse gas emissions.


11. OCEANS & COASTS

> Coastal communities and the ecosystems that support them are increasingly
> threatened by the impacts of climate change. Without significant reductions in
> global greenhouse gas emissions and regional adaptation measures, many coastal
> regions will be transformed by the latter part of this century, with impacts
> affecting other regions and sectors. Even in a future with lower greenhouse
> gas emissions, many communities are expected to suffer financial impacts as
> chronic high-tide flooding leads to higher costs and lower property values.

Rising water temperatures, ocean acidification, retreating arctic sea ice, sea
level rise, high-tide flooding, coastal erosion, higher storm surge, and heavier
precipitation events threaten our oceans and coasts. These effects are projected
to continue, putting ocean and marine species at risk, decreasing the
productivity of certain fisheries, and threatening communities that rely on
marine ecosystems for livelihoods and recreation, with particular impacts on
fishing communities in Hawai‘i and the U.S.-Affiliated Pacific Islands, the U.S.
Caribbean, and the Gulf of Mexico. Lasting damage to coastal property and
infrastructure driven by sea level rise and storm surge is expected to lead to
financial losses for individuals, businesses, and communities, with the Atlantic
and Gulf Coasts facing above-average risks. Impacts on coastal energy and
transportation infrastructure driven by sea level rise and storm surge have the
potential for cascading costs and disruptions across the country. Even if
significant emissions reductions occur, many of the effects from sea level rise
over this century—and particularly through mid-century—are already locked in due
to historical emissions, and many communities are already dealing with the
consequences. Actions to plan for and adapt to more frequent, widespread, and
severe coastal flooding, such as shoreline protection and conservation of
coastal ecosystems, would decrease direct losses and cascading impacts on other
sectors and parts of the country. More than half of the damages to coastal
property are estimated to be avoidable through well-timed adaptation measures.
Substantial and sustained reductions in global greenhouse gas emissions would
also significantly reduce projected risks to fisheries and communities that rely
on them.


12. TOURISM AND RECREATION

> Outdoor recreation, tourist economies, and quality of life are reliant on
> benefits provided by our natural environment that will be degraded by the
> impacts of climate change in many ways.

Climate change poses risks to seasonal and outdoor economies in communities
across the United States, including impacts on economies centered around coral
reef-based recreation, winter recreation, and inland water-based recreation. In
turn, this affects the well-being of the people who make their living supporting
these economies, including rural, coastal, and Indigenous communities. Projected
increases in wildfire smoke events are expected to impair outdoor recreational
activities and visibility in wilderness areas. Declines in snow and ice cover
caused by warmer winter temperatures are expected to negatively impact the
winter recreation industry in the Northwest, Northern Great Plains, and the
Northeast. Some fish, birds, and mammals are expected to shift where they live
as a result of climate change, with implications for hunting, fishing, and other
wildlife-related activities. These and other climate-related impacts are
expected to result in decreased tourism revenue in some places and, for some
communities, loss of identity. While some new opportunities may emerge from
these ecosystem changes, cultural identities and economic and recreational
opportunities based around historical use of and interaction with species or
natural resources in many areas are at risk. Proactive management strategies,
such as the use of projected stream temperatures to set priorities for fish
conservation, can help reduce disruptions to tourist economies and recreation.




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