Rise in tornadoes no certainty as Earth warms, scientists say - East Valley Tribune: Living Green

Rise in tornadoes no certainty as Earth warms, scientists say

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Posted: Monday, June 21, 2010 6:00 am

You may have heard that thunderstorms, lightning, sleet, hail, damaging winds, and hurricanes will occur more frequently later this century if the Earth's climate continues to warm as rapidly as America's top climate scientists believe it is now.

But tornadoes? Not so fast.

"This science is in its infancy," explained Tony Del Genio, a climatologist at NASA's Goddard Institute for Space Studies in New York City.

While scientists are convinced the status quo will result in more violent weather years from now, tornadoes are "really beyond the edge of our understanding of things," according to Del Genio, the lead author of a 2007 report which NASA claims broke new ground by the way it connected more dots between anticipated climate change and storm intensity.

That report found there will be fewer soakers and gentle rain showers, and more of the most severe and dangerous storms.

Del Genio said he is hesitant about making predictions about tornadoes, because -- bar none -- they are nature's hardest weather event to predict.

That's especially true of the most dangerous and destructive types of twisters, those classified as EF-5 and EF-4 on what meteorologists refer to as the five-point Enhanced Fujita Scale.

Tornadoes are essentially flukes of nature. Unlike hurricanes, they form spontaneously, are short-lived, and traverse a much smaller land mass by comparison.

Many atmospheric conditions need to converge at the right time for tornadoes to form. They need hot, humid air near the ground with a cool air mass above them.

They also need strong wind velocity at higher altitudes, known as wind shear, to get them spinning, Del Genio said.

Many of those ingredients likely will be in greater abundance as the Earth's climate warms over the next 50 to 100 years, he said.

"We're talking about something our children might see by the time they're old," Del Genio said.

But a more frequent convergence of tornado-inducing atmospheric conditions doesn't necessarily correlate to more twisters, though, he and other scientists say. All it does is improve the odds.

"Just because you have a favorable environment (for tornadoes to form) doesn't mean you'll have a storm," said Harold Brooks, a meteorologist who specializes in tornado research at the National Severe Storm Laboratory in Norman, Okla., operated by the federal government's National Oceanic and Atmospheric Administration.

The Great Lakes region is especially hard for long-range predictions because of the fickle relationship between its enormous bodies of water and the air masses hovering over them, Brooks said.

Other variables include how much wind shear will continue to be a factor.

It tends to be stronger in the winter, when the collision of warm and cold air masses forms the most powerful jet stream.

That's why most tornadoes form in late spring and the first part of summer, as opposed to the dog days of August, according to Brooks, who authored a 2003 NOAA report considered one of the pioneer studies for possible linkages between tornadoes and climate change.

Jeff Masters, director of meteorology for Weather Underground Inc., a private weather-forecasting service in Ann Arbor, said the region's wind shear will keep weakening if the North Pole and South Pole continue to warm.

Oddly enough, though, while tornado reports nationwide have been on the rise since the 1950s, those twisters strong enough to be classified as EF-4s or EF-5s -- a fraction of the total -- occurred less frequently during the 2000s than during the 1990s.

If anything, scientists might have expected more because the climate had slightly warmed.

Some researchers theorize the number of twisters didn't necessarily go up. Because they're usually formed in rural areas, many may have simply gone unreported in years past, they said.

The technology in detecting tornadoes has become much more precise. And there are now more people around to track them, partly because there are more people living in areas that were rural decades ago.

"But even in years they're below normal, that doesn't mean you don't have damaging events," Brooks said. "Very few tornadoes that occur now don't hit anything."

The two most severe types of tornadoes are so rare -- often forming only once or twice a year and usually no more than 10 times -- that it's hard to make much of their statistics, said Jeff Trapp, a Purdue University climate scientist who published a 2007 study on the subject.

"Underlying this frequency issue is the fact that the tornado intensity classification itself is problematic," Trapp said. "It's based solely on damage, which means that if a tornado causes little to no damage, we have no idea how intense it actually was, and therefore how to count it in the tornado record."

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