Models foresee more hurricanes that are more intense

Richard A. Kerr in Science: Fewer but fiercer and more-destructive hurricanes will sweep the Atlantic Basin in the 21st century as climate change continues, a new modeling study by U.S. government researchers suggests. The results, reported on page 454, bear out tentative forecasts from earlier studies, although the researchers caution that this is still far from the last word.

"The models seem to be converging," says tropical meteorologist James Kossin of the National Climate Data Center's office at the University of Wisconsin, Madison, who was not involved in the work. Plenty of uncertainties remain, Kossin notes, but compared with earlier studies, this one "is more credible; ... it's important."

What makes the new study more realistic is its sharper picture of the atmosphere. In low-resolution models such as global climate models, the fuzzy rendition of the atmosphere can't generate any hurricanes, much less the intense ones that account for most of the damage hurricanes cause. The high-resolution models used by the U.S. National Weather Service to forecast hurricane growth and movement do produce a realistic mix of both weak and strong storms, but those models can't simulate global warming.

…The group calculates that although the overall number of hurricanes would decline in a warmer world, they would still cause more damage, according to the modeling. Category 3 to 5 hurricanes have accounted for 86% of all U.S. damage despite constituting only 24% of U.S. landfalls, the group notes. That's because when storms move up from one category to the next, the potential damage roughly doubles. The group finds that in the models, the increase in the rare, most intense storms dominates, leading to a net increase in potential damage of roughly 30%.

The researchers note that the new modeling offers no support for claims that global warming has already noticeably affected hurricane activity. In the real world, the number of Atlantic hurricanes observed during the past 25 years has doubled; in the model, global warming would cause a slight decline in the number over the same period. Given that the mid-resolution model used by the group duplicates the observed rising trend, it may be natural. And the group estimates—very roughly—that so far any effect greenhouse warming has had on hurricane intensity should still be unrecognizable amid natural variations in hurricane activity….

Hurricane Wilma in 2005, bearing down on Cozumel