The number of category 4 and 5 hurricanes worldwide has nearly doubled in 35 years, as global sea surface temperatures increased during the same period.

But scientists also found the total number of hurricanes has dropped since the 1990s.



Researchers — including Peter Webster of Georgia Tech’s School of Earth and Atmospheric Sciences and Georgia Tech’s Judith Curry — studied the number, duration, and intensity of hurricanes (also known as typhoons or tropical cyclones) occurring worldwide 1970-to-2004.



What we found was rather astonishing, said Webster. In the 1970s, there was an average of about 10 category 4 and 5 hurricanes per year globally. Since 1990, the number of category 4 and 5 hurricanes has almost doubled, averaging 18 per year globally.



Curry, chairwoman of the School of Earth and Atmospheric Sciences at Georgia Tech, said, category 4 and 5 hurricanes made up about 20 percent of all hurricanes in the 1970s, but over the last decade they accounted for about 35 percent of these storms.



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