BROOKLIN, Canada, (IPS) - The number of super-powerful storms like Hurricane

Katrina has nearly doubled and there will be even more in the future as the

world's oceans continue to warm, scientists say.

The number of Category 4

and 5 hurricanes worldwide has nearly doubled over the past 35 years, according

to a new study published Friday in the journal Science.

"Warmer sea

surface temperatures have increased the amount of water vapour, which is the

fuel for hurricanes," said study co-author Peter Webster of Georgia Institute of

Technology's School of Earth and Atmospheric Sciences.

"I think it's

clear that global warming is causing oceans to warm," he said.

Hurricane

Katrina offers a good illustration of the role of warm water, Webster

said.

Before it struck the US Gulf Coast, Hurricane Katrina made landfall

in Florida as a Category 1. When it crossed over into the Gulf of Mexico,

however, there was a huge, deep pool of very warm water that served as the

storm's high-octane fuel, he said.

Practically overnight, Katrina turned

into a Category 5 super storm.

At landfall, Katrina weakened to a

Category 4. But with its exceptionally large size, the damage it caused will

cost the U.S. at least 200 billion dollars.

"I wasn't surprised by

[Webster's] results," said Kevin Trenberth, head of the climate analysis section

of the National Centre for Atmospheric Research in Boulder, Colorado.

"We

may differ on the details but there is no doubt there has been an increase in

intensity of storms," Trenberth said.

The North Atlantic ocean is

exceptionally hot this year - about 1.5 degrees C warmer than average - and

that's why double the normal number of hurricanes and tropical storms have been

forecast. That extra heat translates into an average intensity or power of these

storms that is also likely to be 15 to 20 percent higher, he said.

And it

should not be forgotten that as the oceans warm, sea levels rise due to thermal

expansion, making storms even more damaging.

"The next 30 years will not

be like the last 30 years. We're in a new regime of stronger hurricanes and

cyclones, we have to plan for that," said Webster.