JimElsner of Florida State University and his colleagues based their conclusion on25 years of satellite data.
"Ifwe look over the entire globe, we see that the strongest tropical cyclones areactually getting stronger. And this increase is most notable over the NorthAtlantic and also the northern Indian Oceans."
Theresearchers found that the top wind speeds in the strongest tropical cycloneshave been increasing. And, the stronger the cyclone, the bigger the increase.
Scientistssay these storms pick up energy from the warm water they pass over. Elsner saysthat's really a simplified version of what's happening.
"Andthis thermodynamic theory of hurricane intensification says that, with all elsebeing equal, the warmer the ocean, the stronger the storms," he said in aninterview. "So it stands to reason that if the theory is correct we shouldsee increases in the intensity of the strongest storms with the warmingocean."
Andthat's exactly what they saw. For their study, Elsner and his colleaguesexamined the top wind speed in a range of storms, from weak to strong.
Theweaker storms showed little or no increase in their maximum wind speed over 25years of observations. But in the same period, the top wind speed in thestrongest storms rose significantly.
"Generallythe wind speed and how much power, destructive power, a hurricane has are verywell correlated," Elsner said.
Althoughthe storm data comes from satellites, Elsner says satellite instruments don'tmeasure the wind speed directly.
"Butwhat you can do is look at how the pattern of the satellite pictures [is]changing over time. If you see how the clouds change from one picture to thenext, you can get some idea of motion. So if you look at where the clouds wereat one time, then later, you get some idea of speed."
Theeffect the researchers observed was not evenly distributed around the world,probably because of different conditions in the various areas where tropicalcyclones occur.
"Well,we speculate that has to do with the amount of warming we're seeing in thedifferent basins," Elsner explained. "So basins that are marginallywarm enough to support tropical cyclones on average and [where temperatures]are increasing, then we expect to see the effect stronger in those basins, andthose include the North Atlantic and Indian Oceans."
So isthis effect related to climate change? Elsner says his study looked at datafrom the past quarter-century, so he says it can't necessarily predict what'sin the future. But warmer oceans could provide the energy to fuel strongerstorms, and he says the data is consistent with the idea that global warmingcould affect sea temperatures.
"Thatgives us some confidence that if the seas continue to warm, we're likely to seethe stronger storms getting stronger."
JimElsner of Florida State University. His paper appears this week in the journal .