Study: Warming May Cut U.S. Hurricane Hits

[January 23, 2008]  WASHINGTON (AP) -- Global warming could reduce how many hurricanes hit the United States, according to a new federal study that clashes with other research. The new study is the latest in a contentious scientific debate over how man-made global warming may affect the intensity and number of hurricanes.

In it, researchers link warming waters, especially in the Indian and Pacific oceans, to increased vertical wind shear in the Atlantic Ocean near the United States. Wind shear -- a change in wind speed or direction -- makes it hard for hurricanes to form, strengthen and stay alive.

So that means "global warming may decrease the likelihood of hurricanes making landfall in the United States," according to researchers at the National Oceanic and Atmospheric Administration's Miami Lab and the University of Miami.

With every degree Celsius that the oceans warm, the wind shear increases by up to 10 mph, weakening storm formation, said study author Chunzai Wang, a research oceanographer at NOAA. Winds forming over the Pacific and Indian oceans have global effects, much like El Nino does, he said.

Wang said he based his study on observations instead of computer models and records of landfall hurricanes through more than 100 years.

His study is to be published Wednesday in Geophysical Research Letters.

Critics say Wang's study is based on poor data that was rejected by scientists on the Nobel Prize-winning Intergovernmental Panel on Climate Change. They said that at times only one in 10 North Atlantic hurricanes hit the U.S. coast and the data reflect only a small percentage of storms around the globe.

Hurricanes hitting land "are not a reliable record" for how hurricanes have changed, said Kevin Trenberth, climate analysis chief for the National Center for Atmospheric Research in Boulder, Colo.

Trenberth is among those on the other side of a growing debate over global warming and hurricanes. Each side uses different sets of data and focus on different details.

One group of climate scientists has linked increases in the strongest hurricanes -- just those with winds greater than 130 mph -- in the past 35 years to global warming. The Intergovernmental Panel on Climate Change has said "more likely than not," manmade global warming has already increased the frequency of the most intense storms.

But hurricane researchers, especially scientists at NOAA's Miami Lab, have argued that the long-term data for all hurricanes show no such trend. And Wang's new research suggests just the opposite of the view that more intense hurricanes result from global warming. The Miami faction points to a statement by an international workshop on tropical cyclones that says "no firm conclusion can be made on this point."

Former National Hurricane Center Director Max Mayfield said regardless of which side turns out to be right, it only takes one storm to be deadly. So the key for residents of hurricane-prone areas, he said, is to be prepared for a storm "no matter what."

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On the Net:

NOAA on the new study:
http://www.noaanews.noaa.gov/
stories2008/20080122_warmeroceans.html

Intergovernmental Panel on Climate Change chapter that includes mention of hurricanes:
http://www.ipcc.ch/pdf/
assessment-report/ar4/wg1/ar4-wg1-chapter9.pdf

Summary statement from international workshop on tropical cyclones:
http://www.wmo.int/pages/prog/arep/
tmrp/documents/iwtc_summary.pdf

[To download Adobe Acrobat Reader for the PDF files, click here.]

[Associated Press; By SETH BORENSTEIN]

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