Study: Climate change likely made storms even stronger
By ERIC BERGER
Copyright 2008 Houston Chronicle
Sept. 4, 2008, 9:47AM
The strongest hurricanes have gotten stronger in nearly all oceans around the world, likely in response to global warming, a new study concludes.
Scientists say the research is noteworthy, because it uses only satellite observations.This may eliminate some of the bias in the historical hurricane record that has made it all but impossible to determine whether monster storms such as Hurricane Katrina are stronger or more frequent than they were a few decades ago.
After reanalyzing 25 years of satellite data from the North Atlantic and the other five ocean basins where tropical cyclones form, the study's authors found that the top 30 percent of each year's storms became measurably stronger between 1981 and 2006. The intensity change was equivalent to about 5 mph for the strongest storms.
"I think this makes the argument much more compelling that climate change is really affecting the most rare, powerful storms by making them even stronger," said James Elsner, a hurricane scientist at Florida State University and lead author of the study published in Nature.
In recent years, especially since the record 2005 tropical season, some hurricane scientists have believed that warmer oceans were producing stronger hurricanes.
But other scientists have said the record of past hurricanes couldn't be compared to that of the modern era, when storms are analyzed in minute detail from space, air and sea. Prior to the use of satellites and aircraft reconnaissance, the ability to measure sustained winds at sea was severely constrained.
One of those researchers, Chris Landsea, of the National Hurricane Center, said the new paper overreaches in its conclusion that global warming has caused the apparent rise in hurricane intensity.
The new paper finds the sharpest rise in intensity for the North Atlantic, Southern Indian and Northern Indian oceans. The trends are more modest in the Western North Pacific and Eastern North Pacific basins, and nonexistent in the South Pacific.
Landsea said the sharp rise in Atlantic intensity is due to the widely held theory that Atlantic activity has been on the upswing since 1995 as part of a decades-long, natural cycle. Under this theory, Atlantic activity is expected to decrease in another decade or two.
As for the Indian Ocean intensity increases, Landsea said there has been a controversy among hurricane scientists about the reliability of Indian Ocean observations due to the launch of the Meteosat-7 satellite in 1997, which changed the angle at which hurricanes were seen.
Such an angle change probably affected the intensity estimates of storms, Landsea said.
"These big trends in the Indian Ocean tropical cyclone intensities may not be real," said Landsea, the science and operations officer at the hurricane center. He said his views are his own and not those of the Hurricane Center.
However, Rob Korty, a Texas A&M climate scientist involved in the hurricane debate, said the new paper lends credence to the view that even moderately warmer water temperatures could raise a hurricane's maximum wind speeds in ideal conditions.
"It's consistent with the earlier papers on this topic," Korty said. "And, I think, it's a nice advance in that it circumvents the big problem with the historical record of hurricane observations."
Despite efforts like Elsner's latest work, however, scientists have been unable to produce markedly stronger hurricanes in climate models that simulate a warmer world.
For example, the most prominent computer model studies have found that the percentage of stronger hurricanes would increase around the world by about 1 percent per degree Fahrenheit. Elsner's work concludes this percentage increase might be as high as 7 percent.
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