Hotter Oceans, Fiercer Storms

Hotter Oceans, Fiercer Storms

Posted: January 1, 2006

[Slide Two]

KERRY EMANUEL: I was surprised when I did this analysis in the nature paper. I wasn't even looking for any kind of global trends. Global warming was far from my mind. I was looking for natural variability in the amount of energy expended by hurricanes. You could see the natural variability, but on top of that it's this trend that we couldn't really get rid of, and it became worrying and led to the nature paper.

We find that in the Pacific, as well as in the Atlantic, there's this excellent correlation between this measure of hurricane energy that we developed and the temperature of the tropical ocean. They're just very in concert in all kinds of different timescales, and the amount of energy expended by hurricanes has gone up in the last 50 years by, you know, somewhere between 50 and 80 percent. If all we had to go on was the hurricane data, I don't think we would be terribly alarmed. We'd just say, well it's been changing the last 25, 30 years. So what? It's the correlation with sea surface temperature and the fact that that trend is unprecedented for a long time, that has us worried.

[Slide Six]

PETER WEBSTER: The bottom line of our study is that we find a consistency between the increase of surface temperature in all of the oceans and a change in intensity to more intense storms.

Now if it were natural variability, what one would expect to find is that the variation would be different in each of the basins. I think the first conclusion, perhaps the most important one, is that the characteristic change-up to more intense hurricanes is a global phenomena and not a local phenomena.

Kerry Emanuel went back into the data further than we did, roughly from 1950 onwards, both in the Atlantic Ocean and the North Pacific Ocean, and he found a very, very strong association between intensity of storms and the increase of sea surface temperature, much the same as we did. We also looked at the other ocean basins, the South Pacific and the South Indian Ocean. The Southern Hemisphere accounts for roughly 30 percent of all the storms, so we wanted to make sure that we were doing a global study. So these two different studies, using some common overlap data but different regions tended to support each other quite well.

Audio

Produced by

Susan K. Lewis

Edited by

David Levin

Photos

(palm trees)

Courtesy NOAA

(Hurricane Epsilon)

Courtesy Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center/NASA

(Kerry Emanuel)

Courtesy Donna Coveney/MIT

(Peter Webster)

Courtesy Peter Webster

Images

(PDI vs. September SST, PDI vs. July-November SST, PDI vs. annual average SST)

Courtesy Kerry Emanuel

(summer SST, total number of global number of storms and storm days, number of hurricanes and hurricane days, number and percentage of intense hurricanes)

Reprinted with permission from AAAS from Webster et al, Science 309:1844-46