Stronger Hurricanes Linked to Climate Change

A new study of climate data suggests that global warming is causing the Atlantic Ocean to generate deadlier hurricanes. Hurricanes have become stronger in recent decades, in apparent correlation with the raise in atmospheric temperatures. Indeed James Elsner of Florida State University in Tallahassee reports in Geophysical Research Letters that there is in fact a clear cause-and-effect link.

Less than three weeks after Hurricane Katrina, a study published in Science showed that, while the number of tropical cyclones had not increased between 1970 and 2004, their strength had surged: Category-4 or -5 hurricanes where more than 50 percent more frequent in the second half of that period than in the first (Webster et al., Science, 16 September 2005).

The same period saw a rise in global atmospheric temperatures -- widely attributed to the accumulation of greenhouse gases such as CO₂ -- and in sea-surface temperatures in the Atlantic, where hurricanes are born. Some climatologists believe that global (atmospheric) warming is causing the oceans' temperatures to rise, and that warmer sea surfaces can in turn add to a hurricane's strength. But others attributed nature's increased wrath to a long-term cyclic fluctuation in sea temperatures called the Atlantic Multidecadal Oscillation. Opinions also varied on whether a warmer atmosphere can significantly make the oceans warmer, and on the extent to which sea temperatures contribute to hurricane strength.

Elsner (jelsner@garnet.acns.fsu.edu, 850-644-8374) used an elaborate statistical method (first devised by economics Nobel Prize winner Clive Granger) to answer the first of those two questions. He examined spikes in global atmospheric temperature (using satellite and ground-based data collected by the Intergovernmental Panel on Climate Change) and compared them to seasonal changes in average sea-surface temperatures for the entire northern-hemisphere part of the Atlantic (based on National Atmospheric and Oceanic Administration data). His analysis showed that the spikes in atmospheric temperature mostly tended to come right before hurricane-season spikes in oceanic temperature, suggesting that the first were causing the second. Global warming could indeed be causing stronger hurricanes.

Elsner, Geophysical Research Letters, 23 August 2006
Contact James Elsner
Florida State University in Tallahassee
Tel: 850-644-8374
jelsner@garnet.acns.fsu.edu