As globe warms, hurricanes may speed up.

Climbing ocean temperatures during the next century could raise the speed limit for hurricane winds, leading to more intense tropical storms, according to computer simulations of a warmer world.

Hurricanes draw their power from the heat within tepid tropical waters, and theory suggests that greenhouse warming could pump up the winds in such storms. Meteorologists, however, have debated whether hurricanes would respond in any obvious way.

The new study describes the most detailed simulations of future hurricanes to date, say Thomas R. Knutson and his colleagues at the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Fluid Dynamics Laboratory in Princeton, N.J. The researchers used a global climate model to simulate storms in a world gradually warmed by increasing carbon dioxide in the air. They focused on storms in the northwest Pacific Ocean, where the most intense hurricanes occur, and compared 51 in the warming scenario with an equal number in simulations of the present climate.

Because the global model covers such a large area, its resolution is limited and it produces only fuzzy versions of hurricanes. To sharpen the picture, the researchers reran each of the 102 simulated storms on a smaller-scale, higher-resolution model. Meteorologists use this technique for tracking actual hurricanes.

When tropical sea surface temperatures in the model increased by 2.2 [degrees] C, the wind speeds in the strongest storms were 5 to 12 percent higher than in the strongest storms of the control runs, the researchers report in the Feb. 13 Science. That amounts to a surge of 7 to 16 miles per hour.

With this enhanced power, such storms could batter coastal regions with unprecedented force. "If the strongest ones get stronger by about 10 miles per hour, that might double their damage," comments Christopher W, Landsea, a meteorologist at NOAA's Hurricane Research Division in Miami.

The simulations do not examine what would happen to hurricanes outside the northwest Pacific or whether the frequency of hurricanes would change. Hurricanes in the Atlantic Ocean could occur less frequently if global warming caused El Ninos to appear more often in the Pacific, says Landsea. El Ninos inhibit hurricane formation in the Atlantic.

If a small proportion of hurricanes grows stronger, most people may not notice the shift, says Kerry A. Emanuel of the Massachusetts Institute of Technology. Hurricane behavior varies tremendously from year to year and decade to decade, tending to drown out subtle changes in strength.

Common sense might suggest that the spawning grounds of hurricanes should expand as ocean temperatures climb, but researchers say the physics of the atmosphere argues otherwise. "The broad geographic regions of cyclogenesis, and therefore also the regions affected by tropical cyclones, are not expected to change significantly," reports a group of 11 storm specialists in the January Bulletin of the American Meteorological Society.