October 19, 2006 "It's
the extremes, not the averages, that cause the most damage to society
and to
many ecosystems," says NCAR scientist Claudia Tebaldi, lead author for
the
report. "We now have the first model-based consensus on how the risk of
dangerous heat waves, intense rains, and other kinds of extreme weather
will
change in the next century." Tebaldi
and colleagues based their work on simulations from nine different
climate
models for the periods 1980–1999 and 2080–2099. The
simulations were created on
supercomputers at research centers in From the
model output, the scientists computed 10 different indices of climate
extremes,
with 5 related to temperature and 5 to moisture. For instance, a frost
days
index measures how many days per year temperatures dip below 32 degrees
Fahrenheit, while a dry days index measures the length of each year's
longest
consecutive string of days without rain or snow. Because the impact of
a given
index can be stronger in one climatic zone than another, the authors
expressed
the results in terms of statistical significance at each location. For all
three greenhouse-gas scenarios, the models agree on several changes by
2080-2099. The
number of extremely warm nights and the length of heat waves will
increase
significantly over nearly all land areas across the globe. During heat
waves,
very warm nights are often associated with fatalities because people
and
buildings have less chance to cool down overnight. Dry
spells could lengthen significantly across the western The
average growing season could increase significantly across most of
North
America and Most of
these trends are significantly weaker for the lowest-emission scenario
than for
the moderate and high-emission scenarios. Thus, the authors add,
lowering the
output of greenhouse gases over the next century should reduce the risk
that
the most severe changes will occur. The research was
supported by the
National Science Foundation, which is NCAR's primary sponsor, as well
as by the
U.S. Department of Energy and Environmental Protection Agency. ##
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