Tropical ocean temperatures have risen during a 50-year period.
LOS ANGELES TIMES
Hurricanes are likely to become more destructive in the future because of rising ocean temperatures, according to research published online Sunday in the journal Nature.
Kerry Emanuel, an MIT professor and meteorologist, reviewed about five decades of hurricane and typhoon data and found that both the duration of the storms and the wind speeds they produced had increased by 50 percent.
"When hurricanes do strike in the future they will, on average, have much greater intensity, hitting harder and lasting longer," Emanuel noted.
The increased storm intensity will "substantially increase hurricane-related losses along populated coastlines, hitting people hardest not as previously thought in the tropics but in the middle and high latitudes," he said.
Hurricanes form over tropical waters and gain strength from heat released when evaporated water falls back to Earth in pounding tropical rains.
Emanuel found a "high correlation" between the growth in hurricane power and sea surface temperatures, whose rise he attributed to both human-induced global warming and natural ocean-temperature oscillations.
The surface temperature of tropical oceans has increased by about 0.5 degrees Celsius over the last 50 years.
Previous theories have not given much credence to the power of this temperature rise to increase the intensity of hurricanes because it was thought to be too small.
Hurricane prediction models have proposed that the peak wind speed of hurricanes should rise by only 5 percent for every 1 degree Celsius rise in ocean temperature.
Looking at several factors
Emanuel's research suggests that there must be other forces at work to create the 50 percent increase in hurricane duration and wind speed.
"We're trying to ... close that yawning theoretical gap by identifying all the natural forces that might be contributing to the rise, from vertical wind shear to atmospheric temperature," Emanuel said.
Emanuel noted that his study found no evidence that global warming had increased the frequency of hurricanes.
The hurricane season last year caused billions of dollars in damage in the Caribbean and the United States. Nine storms were officially designated as hurricanes, which are defined as tropical storms with wind speeds greater than 74 mph.
This year, the National Oceanic and Atmospheric Administration is predicting 12 to 15 tropical storms, with seven to nine becoming hurricanes. The agency estimates that three to five could become major hurricanes.