Climate Change Impacts on the United States (Nov 2000)
- Climate Change Impacts on the United States
The Potential Consequences of Climate Variability and Change
Overview: Key Findings By the National Assessment Synthesis Team, US
Global Change Research Program - Published in 2000
The National Assessment Overview and Foundation Reports were produced
by the National Assessment Synthesis Team, an advisory committee
chartered under the Federal Advisory Committee Act, and were not
subjected to OSTP's Information Quality Act Guidelines. The National
Assessment was forwarded to the President and Congress in November
2000 for their consideration.
1. Increased warming
Assuming continued growth in world greenhouse gas emissions, the
primary climate models used in this Assessment project that
temperatures in the US will rise 5-9�F (3-5�C) on average in the next
100 years. A wider range of outcomes is possible.
2. 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.
3. 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
grasslands, 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.
4. Widespread water concerns
Water is an issue in every region, but the nature of the
vulnerabilities varies. Drought is 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.
5. 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.
6. 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
7. 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.
8. 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.
9. 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.
10. 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.
US Climate Change Science Program / US Global Change Research Program,
Suite 250, 1717 Pennsylvania Ave, NW, Washington, DC 20006.