Extreme weather to increase with climate change
WASHINGTON (AP) - June 19, 2008 Events that have seemed relatively rare will become commonplace,
said the latest report from the U.S. Climate Change Science
Program, a joint effort of more than a dozen government agencies.
There has been an increase in the frequency of heavy downpours,
especially over northern states, and these are likely to continue
in the future, Thomas R. Karl, director of the National Climatic
Data Center, said in a briefing.
For example, Karl said, by the end of this century rainfall
amounts expected to occur every 20 years could be taking place
every five years.
Such an increase "can lead to the type of events that we are
seeing in the Midwest," said Karl, though he did not directly link
the current inundations to climate change.
But the report cautioned that preparing for weather than has
been relatively common can leave people vulnerable as extreme
events occur more and more.
"Moderate flood control measures on a river can stimulate
development in a now 'safe' floodplain, only to see those new
structures damaged when a very large flood occurs," the report
said.
At the same time heavy rains increase, there'll be more
droughts, especially in the Southwest, Karl said.
"When it rains, it rains harder and when it's not raining, it's
warmer - there is more evaporation, and droughts can last longer,"
he explained.
The Southwestern drought that began in 1999 is beginning to
rival some of the greatest droughts on record including those of
the 1930s and 1950s, he added.
Gerald A. Meehl, a senior scientist at the National Center for
Atmospheric Research, said there has been a trend toward increasing
power in hurricanes since the 1970s in the Atlantic and western
Pacific, a change that can be linked to rising sea surface
temperatures.
There is a statistical connection between rising sea surface
temperatures and hurricane activity, Meehl said, but linking
changes in hurricanes to human actions will require more study.
More easily attributed to human impact, through release of
greenhouse gases, is an overall increase in temperatures, he said.
It's not getting as cold at night as it did in earlier decades
and there are fewer nights with frosts, a trend expected to
continue into the future, Meehl said.
"A day so hot that it is experienced only once every 20 years
would occur every three years by the middle of the century," under
the mid-range projections of climate models, the report said.
Researchers can use computer models of climate to separate out
cause and effect of this warming, he explained - looking at the
effect of things like changes in solar radiation or volcanic
eruptions - and the result is to attribute climate warming to the
burning of fossil fuels.
Participating in the Climate Change Science Program are the
Agency for International Development, Department of Agriculture,
National Oceanic and Atmospheric Administration, National Institute
of Standards and Technology, Department of Defense, Department of
Energy, National Institutes of Health, Department of State,
Department of Transportation, U.S. Geological Survey, Environmental
Protection Agency, National Aeronautics and Space Administration,
National Science Foundation and the Smithsonian Institution.
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On the Net:
http://www.usgcrp.gov/usgcrp/default.php
