December 4, 2007

Global warming could bring the USA a dramatic increase in the frequency of weather conditions that feed severe thunderstorms and tornadoes by the end of the 21st century, says a study out Monday.

Photo: A severe thunderstorm pops up over Murdo, S.D., in 2005. (By Karen A. Kosiba, Courtesy Purdue University)

Some locations could see as much as a 100% increase in the number of days that favor severe thunderstorms, says the study in Proceedings of the National Academy of Sciences.

"The densely populated regions of the South and East, including New York City and Atlanta, could be especially hard-hit," reports study lead author Jeff Trapp of Purdue University.

A thunderstorm is described as "severe" by the National Weather Service if wind gusts reach 58 mph or faster, if hail is 0.75 of an inch in diameter or larger, or if the thunderstorm produces a tornado or tornadoes.

The fuel for the more intense storms would be the predicted warming of the Earth caused by the burning of fossil fuels that release greenhouse gases.

Trapp and his colleagues used climate models to determine whether increased greenhouse gases, such as carbon dioxide, would affect severe thunderstorms' development. The scientists found that as the temperature of Earth's atmosphere rises, the warm, humid air that helps fuel powerful thunderstorms is also expected to increase throughout the USA.

Based on current carbon emission rates, the Intergovernmental Panel on Climate Change earlier this year forecast that average temperatures will rise by 3 to 7 degrees Fahrenheit worldwide by 2100, which is expected to intensify precipitation.

Although the typically stormy spring could see more storms, "summer should have the highest increases in severe weather," says Trapp. His team reports that by the end of the century, the number of spring days with severe thunderstorm conditions would increase mostly over the southern plains and Florida. But in the summer, almost the entire eastern half of the country might see an increase in days conducive to more severe storms, with the largest increases likely near the Gulf of Mexico and the Atlantic coast.

Kevin Trenbreth, a senior scientist with the National Center for Atmospheric Science in Boulder, Colo., who was not part of this study, says, "What they suggest here seems quite plausible." But he adds that although a study such as this is overdue and welcome, it is not as definitive as he would like because of limitations in the climate models used in the study. However, "conditions may be even worse than depicted," he says.

The new study is the second released this year that uncovered a link between severe thunderstorms and climate change. The first one, released by NASA researchers in August, forecast an increase in the intensity of severe storms throughout the yearyou .

Do you think computer models, such as those detailed in this study, can accurately predict what will happen to the climate for the next 100 years?

http://www.usatoday.com/weather/climate/globalwarming/2007-12-03-severe-thunderstorms_N.htm

www.standeyo.com/NEWS/07_Earth_Changes/071205.USA.storm.increase.html