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Global warming may lead to fewer hurricanes

Wed., April 18, 2007, midnight

FORT LAUDERDALE, Fla. – Maybe global warming isn’t spawning more powerful hurricanes, after all.

A new study conducted by two atmospheric experts, one at the University of Miami, has found that global warming is producing increasingly stronger wind shear over the Atlantic, and that might hinder hurricane formation.

That conclusion would seem to temper earlier studies that insist hurricanes are becoming more intense as the atmosphere heats up. Those studies point to storms such as Katrina, Rita and Wilma, all of which reached Category 5 status during the tumultuous 2005 storm season.

The most recent study doesn’t altogether dispute that. Rather, it asserts that wind shear will compete against warmer ocean temperatures, and the stronger force will determine the strength of tropical storms.

“Which one is going to be the dominant factor, the wind shear or the warm ocean, we still don’t know that,” said Gabriel Vecchi, lead author of the paper and a research meteorologist with the National Oceanic and Atmospheric Administration. “They’re kind of conflicting forces.”

The study is to be published today in Geophysical Research Letters, a scientific journal dedicated to studying the Earth’s atmosphere. It is the first analysis to find a steady increase in greenhouse gases will correlate with stronger wind shear.

Wind shear, a change of wind direction or a strengthening of wind speed with altitude, can prevent hurricanes from forming or tear them apart. Because global warming has been in progress for the past few decades, wind shear already is having some impact on storms, but not much, the study’s authors said.

That is because the amount of wind shear is increasing slowly, by about 1.25 mph for every degree increase in the atmosphere’s temperature. During the next century, that should amount to about a 10 to 15 percent increase over current wind shear levels, said Vecchi, who is based in Princeton, N.J.

Practically speaking, he said, that means hurricanes aren’t going to disappear soon.

“Even if there weren’t any warming of the ocean, and wind shear happened by itself, it wouldn’t be enough to get rid of hurricanes altogether,” he said.

The study was conducted by simulating an increase in greenhouses gases in 18 global models. All but five of the models found that wind shear should increase over a large portion of the tropical Atlantic at the same rate that the atmosphere warms.

“This is something that hadn’t been recognized or considered in previous studies,” said Brian Soden, co-author of the study and an associate professor of meteorology and physical oceanography at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

Soden said while the scientific community widely agrees that global warming is for real, its impact on hurricanes remains a major question.

“Certainly, this isn’t the last study,” he said. “There’s going to be a lot more vigorous debate.”


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