Oceans Warmer, Hurricanes Stronger

One of the long-standing predictions of global warming research is that extreme climate events will become more frequent. But in a system as complex as the Earth’s climate it is difficult to tie individual events together into trends and then link those trends to global warming. One of the most intense debates in the science community has been about the theory that global warming is contributing to stronger extreme weather events like hurricanes and cyclones.

New research from Florida State University bolsters the contention that the strongest tropical cyclones are getting stronger and links them to an ocean that is warming because of global warming. The research, by a team lead by FSU geographer James Elsner, is based on a “heat-engine” theory put forward by MIT scientist Kerry Emanuel in 2005. That theory, in its simplest form, says that as seas warm, the ocean has more energy that can be converted to tropical cyclone wind, which makes hurricanes stronger. (Emanuel, in a recent paper, modified much of his work predicting that heat engines will trigger more hurricanes, but noted that global warming might still play a role in raising the intensity of hurricanes, which is the focus of Elsner's research).

Elsner and his team looked at 30 years of data and focused on storms
that were closest to the maximum possible intensity, or as strong as
they could be given the environmental conditions. They found that
the strongest tropical cyclones are getting stronger, particularly
over the North Atlantic and Indian oceans. Wind speeds in the
strongest storms increased from an average of 140 miles-per-hour in
1981 to 156 miles-per-hour in 2006. During this period the ocean
temperature, averaged globally over all the regions where tropical
cyclones form, increased from 82.7 to 83.3 degrees Fahrenheit. “By
looking only at the strongest tropical cyclones, where the
relationship between storms and climate is most pronounced, we are
able to observe the increasing trends in storm intensity that both
the theory and models say should be there,” Elsner said. The
research appeared in a recent issue of the journal Nature.