NASA Study: Global Warming Could Bring More Severe Storms to U.S.
As the world warms, the United States will face more severe
thunderstorms with deadly lightning, damaging hail and the potential
for tornadoes, a NASA study suggests. NASA scientists have developed a
new climate model that indicates that the most violent severe storms
and tornadoes may become more common as Earth's climate warms
Warnings from other of broad weather changes on a large scale,
including more extreme hurricanes and droughts have been known for
months. This new study though predicts that even smaller events like
thunderstorms will be more dangerous because of global warming.
The basic ingredients for more extreme U.S. inland storms are likely
to be more plentiful in a warmer, moister world, said lead author Tony
Del Genio, a NASA research scientist.
"The strongest thunderstorms, the strongest severe storms and
tornadoes are likely to happen more often and be stronger," Del Genio
said in an interview from his office at the Goddard Institute for
Space Studies in New York. The paper he co-authored was published
online this month in the journal Geophysical Research Letters.
With a computer model, Del Genio explores an area that most climate
scientists have avoided. Simple thunderstorms are too small for their
massive models of the world's climate. So Del Genio looked at the
forces that combine to make thunderstorms.
Previous climate model studies have shown that heavy rainstorms will
be more common in a warmer climate, but few global models have
attempted to simulate the strength of updrafts in these storms. The
model developed at NASA's Goddard Institute for Space Studies by
researchers Tony Del Genio, Mao-Sung Yao, and Jeff Jonas is the first
to successfully simulate the observed difference in strength between
land and ocean storms and is the first to estimate how the strength
will change in a warming climate, including "severe thunderstorms"
that also occur with significant wind shear and produce damaging winds
at the ground. This information can be derived from the temperatures
and humidities predicted by a climate computer model, according to the
new study published on August 17 in the American Geophysical Union's
Geophysical Research Letters. It predicts that in a warmer climate,
stronger and more severe storms can be expected, but with fewer storms
overall.
A unique combination of geography and weather patterns already makes
the United States the world's hottest spot for tornadoes and severe
storms in spring and summer. The large land mass that warms on hot
days, the contours of the atmosphere's jet stream, the wind coming off
the Rocky Mountains and warm moist air coming up from the Gulf of
Mexico all combine.
Del Genio's computer model shows global warming will mean more strong
updrafts, when the wind moves up and down instead of sideways. The
Southeast and Midwest lie in the path of most of the most dangerous of
these storms.
However, the new study also forecasts danger for the Western United
States. It predicts lightning will increase about 6 percent as the
amount of carbon dioxide, the chief global warming gas, doubles.
Previous studies have shown that the West will get drier, making it a
tinderbox for more
wildfires. This study shows that there will be more matches in the
form of lightning strikes to start those fires, Del Genio said.
Lightning produced by strong storms often ignites wildfires in dry
areas. Researchers have predicted that some regions would have less
humid air in a warmer climate and be more prone to wildfires as a
result. However, drier conditions produce fewer storms. "These
findings may seem to imply that fewer storms in the future will be
good news for disastrous western U.S. wildfires," said Tony Del Genio,
lead author of the study and a scientist at NASA's Goddard Institute
for Space Studies, New York. "But drier conditions near the ground
combined with higher lightning flash rates per storm may end up
intensifying wildfire damage instead."
One general benefit of global warming is decreased wind shear, which
is the speed of side-to-side wind as the altitude rises, Del Genio
said. That would moderate the effects of updrafts.
However, during certain times of the year and under the right
conditions in the Midwest and Southeast, wind shear will increase.
Combine wind shear and updrafts, and damaging winds result, the
scientist said.
The prediction of stronger continental storms and more lightning in a
warmer climate is a natural consequence of the tendency of land
surfaces to warm more than oceans and for the freezing level to rise
with warming to an altitude where lightning-producing updrafts are
stronger. These features of global warming are common to all models,
but the NASA model is the first climate model to explore the
ramifications of the warming for thunderstorms.
Other pending and recent research, especially from the National
Oceanic Atmospheric Administration, point in the same general
direction, said several scientists who weren't involved in Del Genio's
study. But they said research in this area is so new that the NASA
study is not the final word.
"It's certainly a plausible result," said Leo Donner, a climate
modeling scientist at NOAA's Geophysical Fluid Dynamics Lab in
Princeton, New Jersey. Donner earlier this year came out with a study
predicting more heavy rain as temperatures rise.
Harold Brooks, a top scientist at NOAA's severe storms laboratory in
Norman, Oklahoma, has soon-to-be-published studies finding results
similar to the new NASA study, especially when it comes to hail. Some
of the severe hail that should be increasing could be baseball-sized
and come down at 100 mph, "falling like a major league fastball," he
said.
He said it's not possible to predict more tornadoes will result from
climate change, however.
Sources:
Cable News Network,"Study: Global warming could bring more severe U.S.
storms", accessed August 31, 2007
Sci-Tech Today, "NASA: Global Warming Will Cause Killer Storms",
accessed August 31, 2007
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