Changes in extreme weather and
climate events have significant impacts and are among the most serious
challenges to society in coping with a changing climate.
Many
extremes and their associated impacts are already changing. For
example, in recent decades most of North America has been experiencing
more unusually hot days and nights, fewer unusually cold days and
nights, and fewer frost days. Heavy downpours have become more frequent
and intense. Droughts are becoming more severe in some regions, though
there are no clear trends for North America as a whole. The power and
frequency of Atlantic hurricanes have increased substantially in recent
decades, though North American mainland land-falling hurricanes do not
appear to have increased over the past century. Outside the tropics,
storm tracks are shifting northward and the strongest storms are
becoming even stronger.
In
the future, with continued global warming, heat waves and heavy
downpours are very likely to further increase in frequency and
intensity. Substantial areas of North America are likely to have more
frequent droughts of greater severity. Hurricane wind speeds, rainfall
intensity, and storm surge levels are likely to increase. The strongest
cold season storms are likely to become more frequent, with stronger
winds and more extreme wave heights.
Current
and future impacts resulting from these changes depend not only on the
changes in extremes, but also on responses by human and natural systems.
For
more information about changing weather and climate extremes in this
country see a 2008 report from the U.S. Global Change Research Program
(USGCRP) / Climate Change Science Program: Weather and Climate Extremes in a Changing Climate. Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands. An illustrated 4-page brochure containing report highlights is also available.
The impacts of changing extremes on specific U.S. regions and sectors are documented in a 2009 report from the USGCRP: Global Climate Change Impacts in the United States.
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