[Editors] MIT validates hurricane/climate change link

[Elizabeth Thomson]

For Immediate Release
THURSDAY, APR. 17, 2008
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

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New MIT study validates hurricane prediction
--Confirms that climate change intensifies storms
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CAMBRIDGE, Mass.--Hurricanes in some areas, including the North  
Atlantic, are likely to become more intense as a result of global  
warming even though the number of such storms worldwide may decline,  
according to a new study by MIT researchers.

Kerry Emanuel, the lead author of the new study, wrote a paper in  
2005 reporting an apparent link between a warming climate and an  
increase in hurricane intensity. That paper attracted worldwide  
attention because it was published in Nature just three weeks before  
Hurricane Katrina slammed into New Orleans.

Emanuel, a professor of atmospheric science in MIT's Department of  
Earth, Atmospheric and Planetary Sciences, says the new research  
provides an independent validation of the earlier results, using a  
completely different approach. The paper was co-authored by  
postdoctoral fellow Ragoth Sundararajan and graduate student John  
Williams and appeared last week in the Bulletin of the American  
Meteorological Society.

While the earlier study was based entirely on historical records of  
past hurricanes, showing nearly a doubling in the intensity of  
Atlantic storms over the last 30 years, the new work is purely  
theoretical. It made use of a new technique to add finer-scale detail  
to computer simulations called Global Circulation Models, which are  
the basis for most projections of future climate change.

“It strongly confirms, independently, the results in the Nature  
paper,” Emanuel said. “This is a completely independent analysis and  
comes up with very consistent results.”

Worldwide, both methods show an increase in the intensity and  
duration of tropical cyclones, the generic name for what are known as  
hurricanes in the North Atlantic. But the new work shows no clear  
change in the overall numbers of such storms when run on future  
climates predicted using global climate models.

However, Emanuel says, the new work also raises some questions that  
remain to be understood. When projected into the future, the model  
shows a continuing increase in power, “but a lot less than the factor  
of two that we've already seen” he says. “So we have a paradox that  
remains to be explained.”

There are several possibilities, Emanuel says. “The last 25 years'  
increase may have little to do with global warming, or the models may  
have missed something about how nature responds to the increase in  
carbon dioxide.”

Another possibility is that the recent hurricane increase is related  
to the fast pace of increase in temperature. The computer models in  
this study, he explains, show what happens after the atmosphere has  
stabilized at new, much higher CO2 concentrations. “That's very  
different from the process now, when it's rapidly changing,” he says.

In the many different computer runs with different models and  
different conditions, “the fact is, the results are all over the  
place,” Emanuel says. But that doesn't mean that one can't learn from  
them. And there is one conclusion that's clearly not consistent with  
these results, he said: “The idea that there is no connection between  
hurricanes and global warming, that's not supported,” he says.

The work was partly funded by the National Science Foundation.

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Written by David Chandler, MIT News Office