The average wind speed of cyclones increased radically, pushing up the average number of extreme cyclones per year from 13 to 17. New analyses were reported in the September 4 Nature. James P. Kossin, an atmospheric scientist at the University of Wisconsin, Madison, said that that the largest increases in cyclone peak winds were in the North Atlantic and eastern North Pacific oceans, regions where sea surface temperatures had warmed from 1981 to 2006. The effect the researchers noticed was not evenly distributed around the world, probably because of different conditions in the various areas where tropical cyclones occur.

The number of weaker storms, however, has not noticeably altered. But in the same period, the top wind speed in the strongest storms rose significantly. "Generally the wind speed and how much power, destructive power, a hurricane has are very well correlated," said Jim Elsner of Florida State University.

Hurricanes or typhoons, as they are called in the Pacific and Indian oceans, have winds that blow with at least 74 miles per hour. A hurricane's intensity can be diminished by other factors, such as where they form, how close they are to land, El Nino patterns and solar activity.

U.S. researchers looked at the 26 years of satellite data, from 1981 to 2006, and determined that the strongest storms got stronger as a result of increasing ocean warmth.

Strong storms have increased more in the North Atlantic and Indian oceans than in the South Pacific.