August 31, 2007 in Nation/World

Forecast calls for much worse storms

Seth Borenstein Associated Press

Western effects

» The NASA study 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, study co-author Tony Del Genio said.

WASHINGTON – As the world warms, the United States will face more severe thunderstorms with deadly lightning, damaging hail and the potential for tornadoes, a trailblazing study by NASA scientists suggests.

While other research has warned of weather changes on a large scale, like more extreme hurricanes and droughts, the new study predicts even smaller events such as thunderstorms will be more dangerous because of global warming.

The ingredients for 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 Thursday 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.

Other scientists caution that this area of climate research is too difficult and new for this study to be definitive. But some upcoming studies also point in the same direction.

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.

Del Genio’s computer model shows global warming will mean more strong updrafts in the United States, when the wind moves up and down instead of sideways.

“The consequences of stronger updrafts are more lightning and bigger hail,” he said.

The Southeast and Midwest lie in the path of most of the most dangerous of the storms spurred by the updrafts.

Harold Brooks, a top scientist at NOAA’s severe storms laboratory in Norman, Okla., 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.

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