The number of strong, devastating hurricanes like Katrina significantly increased in the last 35 years, fueled by hotter seas that have been linked to global warming, researchers reported Thursday.
Twice as many of the most powerful hurricanes, those ranked Category 4 or Category 5, have been detected since 1990 as were seen in the period from 1970 to 1985, scientists found in a global survey.
But the overall number of hurricanes has decreased during the last decade, the researchers wrote in a study published in the journal Science.
The rise in intense, destructive hurricanes worldwide goes along with a rise in sea surface temperatures, said Judith Curry of the Georgia Institute of Technology.
"This trend in sea surface temperature that's sort of relentlessly rising and the hurricane intensity that's relentlessly rising (means that) it's with some confidence we can say that these two things are connected and that there's probably a substantial contribution from greenhouse warming," Curry said in a telephone news briefing, reports CNET News.
Hurricanes and tropical cyclones form only when the temperature of the ocean's top layer rises above 26 degrees. The fierce winds are driven by heat from water vapour from the ocean, and it is thought that an increase in the sea's temperature is like adding fuel to the fire.
The researchers restricted their study to the 35 years that satellite observations of storms have been available. Their results were published yesterday in the journal Science.
Kevin Walsh, of the University of Melbourne, said Australian scientists recognised about seven years ago that the number of intense cyclones in their region was increasing, and it was interesting to see this was a global trend.
Associate Professor Walsh said there was not enough evidence yet to say climate change was the cause, because fluctuations in the ocean and atmosphere system occurred on long time scales.
"The good point about the research paper is that it has drawn attention to the issue," he said.
In the 2004 hurricane season an unprecedented four severe hurricanes hit Florida and 10 tropical cyclones hit Japan, informs SMH.
Photo: NASA official web site