Climate change impacts on the
United States
Climate science is developing rapidly and scientists are increasingly
able to project some changes at the regional scale, identifying
regional vulnerabilities, and assessing potential regional impacts.
Science increasingly indicates that the Earth's climate has changed
in the past and continues to change, and that even greater climate
change is very likely in the 21st century.
The National assessment of the potential consequences of climate
variability and change has begun a national process of research,
analysis and dialogue about the coming changes in climate, and their
impacts, and what Americans can do to adapt to an uncertain and
continuously changing climate. This Assessment is built on a solid
foundation of science conducted as part of the United States Global
Change Research Program (USGCRP).
Key findings
- Increased warming.
Assuming continued growth in world greenhouse gas emissions, the
primary climate change models used in this Assessment project
that temperatures in the US will rise 5-9ºF (3-5ºC)
on average in the next 100 years. A wider range of outcomes is
possible.
- Differing regional impacts.
Climate change will vary widely across the US. Temperature increases
will vary somewhat from one region to the next. Heavy and extreme
precipitation events are likely to become more frequent, yet some
regions will get drier. The potential impacts of climate change
will also vary widely across the nation.
- Vulnerable ecosystems.
Many ecosystems are highly vulnerable to the projected rate and
magnitude of climate change. A few, such as alpine meadows in
the Rocky Mountains and some barrier islands, are likely to disappear
entirely in some areas. Others, such as forests of the Southeast,
are likely to experience major species shifts or break up into
a mosaic of grassland, woodlands, and forests. The goods and services
lost through the disappearance or fragmentation of certain ecosystems
are likely to be costly or impossible to replace.
- Widespread water concerns.
Water is an issue in every region, but the nature of the vulnerabilities
varies. Drought s an important concern in every region. Floods
and water quality are concerns in many regions. Snowpack changes
are especially important in the West, Pacific Northwest, and Alaska.
- Secure food supply.
At the national level, the agriculture sector is likely to be
able to adapt to climate change. Overall, US crop productivity
is very likely to increase over the next few decades, but the
gains will not be uniform across the nation. Falling prices and
competitive pressures are very likely to stress some farmers,
while benefiting consumers.
- Near-term increase in forest growth.
Forest productivity is likely to increase over the next several
decades in some areas as trees respond to higher carbon dioxide
levels. Over the longer term, changes in larger-scale processes
such as fire, insects, droughts, and disease will possibly decrease
forest productivity. In addition, climate change is likely to
cause long-term shifts in forest species, such as sugar maples
moving north out of the US.
- Increased damage in coastal and permafrost areas.
Climate change and the resulting rise in sea level are likely
to exacerbate threats to buildings, roads, powerlines, and other
infrastructure in climatically sensitive places. For example,
infrastructure damage is related to permafrost melting in Alaska,
and to sea-level rise and storm surge in low-lying coastal areas.
- Adaptation determines health outcomes.
A range of negative health impacts is possible from climate change,
but adaptation is likely to help protect much of the US population.
Maintaining our nation's public health and community infrastructure,
from water treatment systems to emergency shelters, will be important
for minimizing the impacts of water-borne diseases, heat stress,
air pollution, extreme weather events, and diseases transmitted
by insects, ticks, and rodents.
- Other stresses magnified by climate change.
Climate change will very likely magnify the cumulative impacts
of other stresses, such as air and water pollution and habitat
destruction due to human development patterns. For some systems,
such as coral reefs, the combined effects of climate change and
other stresses are very likely to exceed a critical threshold,
bringing large, possibly irreversible impacts.
- Uncertainties remain and surprises are expected.
Significant uncertainties remain in the science underlying regional
climate changes and their impacts. Further research would improve
understanding and our ability to project societal and ecosystem
impacts, and provide the public with additional useful information
about options for adaptation. However, it is likely that some
aspects and impacts of climate change will be totally unanticipated
as complex systems respond to ongoing climate change in unforeseeable
ways.
Source: National Assessment Synthesis Team, Climate Change Impacts
on the United States: The Potential Consequences of Climate Variability
and Change, US Global Research Program, 400 Virginia Avenue,
SW Suite 750, Washington DC 20024. The report was published in 2000.
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