May 31, 2006, 21:06 GMT
Washington - Global warming is affecting not only the strength but also the increased number of hurricanes witnessed in the North Atlantic, two studies said Wednesday.
National Oceanic and Atmospheric Administration (NOAA) satellite image of Hurricane Wilma as it moved up the East Coast of the US October 2005. EPA/NOAA / HANDOUT
'Human induced climate change, rather than naturally occurring ocean cycles, may be responsible for the recent increases in frequency and strength of North Atlantic hurricanes,' wrote researchers Kerry Emanuel of the Massachusetts Institute of Technology and Michael Mann of Pennsylvania State University.
'If you add up every puff of wind associated with tropical cyclones annually, that number has increased substantially,' says Matthew Huber of Purdue University in Indiana, in a separate study also released Wednesday.
Huber points to two possible explanations. 'Either storms are getting stronger or there are more of them,' he says.
Tropical storm activity has doubled over the last 40 years, during which time Huber says the average global ocean temperature has increased by 0.25 degrees celsius. He expects a further two-degree- celsius increase over the next century.
Peter Webster, a professor at the Georgia Institute of Technology, said the findings were 'helpful in understanding the future state of hurricanes in a warming world.'
Professor Webster conducted research last year showing that the number of Category 4 and Category 5 hurricanes (the strongest levels) had almost doubled in the last 35 years.
While it is relatively undisputed that global warming has contributed to the strength of recent hurricanes, there has been much debate over climate change's impact on their frequency.
The increased frequency has in the past been considered part of a natural cycle that has played itself out over hundreds of years, which suggests the number of hurricanes climbs and diminishes every 20 to 25 years.
Emmanuel and Mann say the cycles have had little or no effect.
The studies were released a day before hurricane season officially begins in the US.
The US National Hurricane Centre earlier this month predicted a 'very active' season ahead, in a closely watched prognosis, after last year's devastating hurricane Katrina killed more than 1,500 people in the US and caused more than 100 billion dollars in damage.
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