Warmer oceans fire up storms
2008-09-03 22:20
Washington - As the world's oceans get warmer, the strongest tropical storms get stronger, climate scientists reported on Wednesday as the remnants of Hurricane Gustav spun out over the central United States.
"If the seas continue to warm, we can expect to see stronger storms in the future," James Elsner of Florida State University said.
"As far as this year goes, as a season, we did see the oceans warm and I think there's some reason to believe that that's the reason we're seeing the amount of activity we are."
Gustav made landfall on Monday just west of New Orleans; three more storms churned toward the US mainland on Wednesday.
The National Oceanic and Atmospheric Administration predicts 12 to 16 tropical storms between June 1 and November 30 this year, with six to nine hurricanes and two to five major hurricanes.
Many climate scientists have linked stronger storms to rising sea surface temperatures in the North Atlantic and elsewhere, under the so-called heat engine theory: because warm tropical cyclones feed on warm water, the warmer the water, the more intense the storm.
US researchers looked at 26 years of satellite data, from 1981 to 2006, and determined that the strongest storms got stronger as a result of increasing ocean warmth.
Survival of the fittest
"It's almost like a survival-of-the-fittest argument," said Elsner, whose study is published in the journal Nature. Overall, tropical waters that breed cyclones have warmed by about 0.33 degree Celsius since 1981.
The heat engine theory suggests all storms should strengthen as the ocean's surface gets hotter, but in reality, few tropical cyclones achieve their full maximum potential intensity.
A cyclone's intensity can be cut by other factors, such as where they form, how close they are to land, El Nino patterns and solar activity, the researchers said.
Strong storms seem able to overcome these factors and gather more fuel from warming waters, Elsner said.
The study's findings are in line with projections made last year by the UN's Intergovernmental Panel on Climate Change, which said there may be more intense storms due to global warming.
The panel said "more likely than not" that a trend of intense tropical cyclones and hurricanes was caused by human activity.
Elsner's study made no reference to any human cause for rising temperatures in the world's oceans.