Wednesday, 20 February 2008

nasa study global warming could bring



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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