A lot of interest has been sparked by a new study, in Geophysical Research Letters, suggesting that warmer oceans could mean fewer hurricanes hitting the United States. Researchers used past observations to show that increases in sea surface temperature led to increases in vertical wind shear in the region where most Atlantic hurricanes develop. This coincides with less hurricanes making landfall in the United States (research abstract). More wind shear means embryonic storms get torn apart before they can grow bigger.

“Using data extending back to the middle nineteenth century, we found a gentle decrease in the trend of US landfalling hurricanes when the global ocean is warmed up. We looked at US landfalling hurricanes because it is the most reliable Atlantic hurricane measurement over the long term,” says study author Chunzai Wang, of the National Oceanic and Atmospheric Administration (press release).

But the AP highlights critics, who have taken aim at the use of landfalling hurricanes.

Kevin Trenberth, climate analysis chief for the National Center for Atmospheric Research in Boulder, Colorado, told the AP that hurricanes hitting land “are not a reliable record” for changes in overall hurricanes, since only a small percentage of storms ever make landfall.

Some previous studies contradict Wang’s new findings, while others support it. The Seattle Times argues that this new report is “intensifying one of the hottest debates in science”. The South Florida Sun-Sentinel thinks global warming might be a good thing, “at least as it pertains to hurricanes”. In the Miami Herald, NOAA researcher Stanley Goldenberg says, “’This study is one more piece of evidence countering the exaggerated claims by a small group of scientists that warming trends in tropical oceans have been contributing to major increases in hurricane activity.”

That’s not, however, entirely clear. There’s been a growing consensus that rising sea-surface temperatures might lead to more intense hurricanes – though what it means for the frequency of storms is still an open question. As one example of how complicated the field is, Nature had a paper in December that found the response to natural climate variations might be larger than greenhouse-gas induced changes. This is because the latter are uniform while the former tend to involve localized changes, and regions that are warmer than the tropical average seem to have more hurricane potential.

Just to throw one more thing into the mix: an as-yet-unpublished paper on sea temperature and hurricane landfall also suggests that different temperatures don’t increase the landfall rate. However, modelling in this new study suggests temperature changes can change where hurricanes land. “The Yucatan suffers 3 times greater landfall rate in hot years than cold, while the U.S. mid-Atlantic coast exhibits no significant change,” say the researchers.

Maybe Mexico should get ready…

Image: Hurricane Katrina / NOAA