Oceans' trend isn't cool -- Newsday.com

Warmer ocean surfaces around the world can be directly linked to a trend toward more intense hurricanes since 1970, according to a new study likely to fuel the heated debate over global warming's ability to provoke increasingly severe storms.

A statistical analysis by researchers at the Georgia Institute of Technology in Atlanta found that the growing might of satellite-observed hurricanes in six ocean basins is strongly correlated with rising sea surface temperatures - but not with other potential influences such as humidity, air circulation patterns or wind shear.

"It is an important study that increases our confidence that there is a link between global warming and intense tropical storms," said climatologist James Hansen of NASA's Goddard Institute for Space Studies in Manhattan, in an e-mail.

Hansen, who wasn't involved with the research, said the result is logical "because an increase of ocean surface temperature provides more 'fuel' to drive strong storms." That fuel is the 'latent heat' in water vapor, he said, "the same fuel that powers thunderstorms."

A higher sea surface temperature means more water can evaporate from the ocean and offer heat to a storm. Hansen said global warming also has driven up ocean temperatures at intermediate depths, reducing the ability of this cooler water stirred up by a storm to check the hurricane's strength.

Another variable known as wind shear, in which high and low-altitude winds move in opposing directions, can sap a hurricane's power by tearing the funnel's top from its bottom. Although the new research found that wind shear can be an important factor on a seasonal basis, "there is no global trend in wind shear that you can associate with an increased intensity in category 4 and 5 hurricanes," said study co-author Judith Curry, chairwoman of the School of Earth and Atmospheric Sciences at Georgia Tech.

The same was true for air circulation patterns and specific humidity, which relates to the amount of heat-laden moisture in the air, while a trend showed up "big time" for the sea surface temperatures, Curry said.

Other researchers, however, doubt the global warming-hurricane link and questioned the conclusions of the study, released yesterday afternoon in an online version of the journal Science.

Chris Landsea, science and operations officer at National Oceanic & Atmospheric Administration's National Hurricane Center in Miami, said the results conflict with those predicted by climate models, though he and others have argued that real-world observations should take precedence. Nevertheless, he characterized the satellite data used to determine storm intensities as flawed.

In the Atlantic Ocean, he said, the data do indicate an increase in intense storms, but only as part of a natural cycle instead of as a growing trend. The jump elsewhere around the world is likely an artificial one because of the unreliable database and the ability to better observe hurricanes, he added.

Curry conceded that some hurricane data from the North Indian Ocean in the 1970s "is rather dodgy." But the study's conclusions were the same, she said, even when the data from that ocean basin were removed from the overall analysis.

Researchers will need to better understand normal activity cycles in the oceans as well as warming trends, she said, "or no one's going to be able to make any sensible forecasts."