Rising ocean temperatures have stoked the growing fury of hurricanes, according to a study made public Thursday that intensifies a debate over the link between global warming and the ferocity of storms.
Of all the factors that drive a major storm -- such as humidity, wind shear or broad air circulation patterns -- only the steady increase in sea surface temperatures over the last 35 years can account for the rising strength of tempests in six oceans around the world, including the North Atlantic, Pacific and Indian oceans, scientists at the Georgia Institute of Technology reported.
"This firms up the link between sea surface temperatures and hurricane intensity," said climate variability expert Judith A. Curry, a senior author of the study who heads Georgia Tech's School of Earth and Atmospheric Sciences. "It is an important piece of the global warming debate."
Their research revealed that the increase in the most severe storms -- category 4 and 5 hurricanes have doubled since 1990 -- was directly linked to the rising temperatures of tropical oceans, which warmed globally by 1 degree Fahrenheit during the same period. Warm water vapor rising from the sea helps energize massive storms.
Though many hurricane experts remained unconvinced of the connection between global warming and storm intensity, Curry said: "This trend can't be explained by natural cycles because the cycles are different for each basin.... This is not natural variability."
The Georgia Tech study, published Thursday in the online edition of the journal Science, comes after several unusually disruptive storm seasons worldwide.
Hurricanes during the 2005 North Atlantic storm season set records not only for their severity but also for the number that made landfall, such as Hurricane Katrina, which killed more than 1,300 people in Louisiana and Mississippi.
Also last year, five fully developed cyclones raged through the Cook Islands in a five-week period.
In March 2004, communities in southern Brazil suffered severe damage in the region's first recorded severe cyclone, as hurricanes are known in the South Atlantic. Meanwhile in the Pacific, 10 major tropical cyclones made landfall in Japan during 2004.
MIT meteorologist Kerry Emanuel said that the mercurial variables of local weather might be important for storms during a single hurricane season but that only sea surface temperatures showed any long-term significance.
