Most intense cyclones are becoming stronger as seas warm: study

A new study says the most powerful tropical cyclones are becoming more intense over the North Atlantic and northern Indian oceans as sea temperatures continue to rise.

In the study releasedWednesday in the journal Nature, U.S. researchers analyzed 25 years of satellite data to show that maximum wind speeds per cyclone are increasing as the oceans warm and that the stronger the cyclone, the greater the change in wind speed.

"Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind," they report in the study.

James Elsner and Thomas Hagger from Florida State University in Tallahassee, Fla., and James Kossin from the University of Wisconsin-Madison in Madison, Wis., calculated that an increase of one degree Celsius in surface sea temperature could lead to an increase of nearly one- third in the number of strong cyclones.

The researchers noted that previous studies have found that cyclones, over the past 30 years, have become more intense because of rising temperatures in the tropical areas of the Atlantic Ocean.

They said detecting trends elsewhere in the tropics is more difficult because the data for these areas is less detailed.

The researchers looked at the maximum wind speeds that cyclones reach during their lifetimes for the period of 1981 to 2006 and examined storms in the Atlantic, Indian and Pacific oceans. They tallied the total number of storms and the maximum wind speeds achieved during each storm and compared the numbers to sea surface temperatures.

Using a statistical technique, they found a detectable upward trend in maximum wind speeds of the strongest tropical cyclones.

They said the oceans over which tropical cyclones form all show this trend, with the exception of the South Pacific Ocean, but not all are statistically significant. The greatest increases are seen in the North Atlantic and northern Indian oceans.

Their findings, they said, are consistent with the "heat-engine" theory of cyclone activity, which attributes intensity of storms to warming ocean temperatures because oceans are releasing more energy.

The researcherspointed out that the study does not include other factors that may be causing the strongest tropical cyclones to become stronger.

Factors related to the "intense tropical storminess" may include the origin of cyclones and their duration, proximity to land, influence of El Nino and any solar activity.

Tropical cyclones are also known as hurricanes or typhoons, depending on where they are located and their strength.