Global warming fuelling hurricanes

James Randerson

London: Global warming is increasing the frequency of the most intense hurricanes, insist scientists who have analysed data from six oceans.

The study comes in answer to critics, mostly scientists involved in hurricane prediction, of previous research, who argued that local factors such as the difference in wind direction at various altitudes (known as wind shear) would swamp any effect of warmer oceans.

Hurricanes such as Katrina, which devastated New Orleans last summer, start as clusters of thunderstorms over the tropical oceans. Generally, the rising air pillar can only form if the sea surface is at least 26C. Heat from the ocean ultimately gives the storm its power.

The scientists say a warmer sea equals more intense hurricanes. But critics argue that other factors are important.

They say it is the difference between sea and air temperature that is important in hurricane formation, and global warming might raise both equally. Professor Curry and her colleagues compared the rise, since 1970, in the number of category four and five hurricanes (the most intense) with other factors such as sea temperature. They concluded, as reported in Nature, that sea surface temperature was the only factor that could explain the rise.

Some experts remain to be convinced. Hugh Willoughby, a former head of the U.S. National Hurricane Centre, said that most of the data from before 1980 could not be relied upon because it was not collected via satellites.

``Some of the reported increase in cyclones may not be real''.