Global warming making tropical cyclones fiercer: Study

This bolsters the theory already put forward that global warming is a contributing factor in increasing intensity of hurricanes in the Atlantic over last 30 years.

Using global satellite data, researchers found that ocean temperatures play a role in driving this trend which, they say, is consistent with “heat-engine” theory of cyclones.

The study was conducted by Florida State University’s (FSU) professor James B Elsner University of Wisconsin Professor James P Kossin and FSU postdoctoral researcher H Jagger.

“As seas warm, the ocean has more energy that can be converted to tropical cyclone wind,” Elsner said.

“Our results do not prove the heat-engine theory. We just show that the data are quite consistent with it.”

Kerry Emanuel of the Massachusetts Institute of Technology first suggested the possible connection between global warming and increases in tropical cyclone intensity in a 2005 paper. He linked the increased intensity of storms to the heating of the oceans, which has been attributed to global warming.

Elsner’s team addressed both issues by using globally consistent, satellite-derived tropical cyclone wind speeds as opposed to the observational record and by focusing on the highest wind speeds of the strongest tropical cyclones each year.

Emanuel’s theory is that the intake of warm air near the ocean surface and the exhaust of colder air above the cyclone is what drives a hurricane. Other factors being equal, the warmer the ocean, the warmer the intake of air. This heat-engine theory of how hurricanes increase their intensity is well accepted, but there are many environmental factors, such as wind shear, that might prevent a hurricane from strengthening, Elsner said.

To address that problem, Elsner’s team looked at a subset of hurricanes that are closest to their maximum possible intensity (MPI).

Under the heat-engine theory, every storm will lose some energy through inefficiency, and that loss will limit the storm’s potential.

The MPI represents the storm’s maximum potential under ideal environmental conditions.

“We speculated that you might not see a trend in the intensity of typical hurricanes due to environmental factors, but if the heat-engine theory is correct, you should see a trend in the intensity of hurricanes at or near their MPI,” Elsner said.

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