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.
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 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.
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.
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 fore
st
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.
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