Sunday, September 18, 2005
Using satellite data, the four researchers found that the average number of Category 4 and 5 hurricanes -- those with winds of 131 mph or higher -- rose from 10 a year in the 1970s to 18 a year since 1990. Average tropical sea surface temperatures have increased as much as 1 degree Fahrenheit during the same period, after remaining stable between 1900 and the mid-1960s.
Georgia Tech atmospheric scientist Judith A. Curry -- co-author of the study with colleagues Peter J. Webster and Hai-Ru Chang, and NCAR's Greg J. Holland -- said in an interview that their survey, coupled with computer models and scientists' understanding of how hurricanes work, has given the researchers a better sense of how rising sea temperatures are linked to more-intense storms.
"There is increasing confidence, as the result of our study, that there's some level of greenhouse warming in what we're seeing," Curry said. "Is it the whole story? We don't know."
Higher ocean temperatures result in more water vapor in the air, which, combined with certain wind patterns, helps power stronger hurricanes, Webster said. Small increases in sea temperature, he added, can "exponentially provide more and more fuel for the hurricanes."Only one degree - what happens with a two, five, or more degree increase?
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