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Warming's Effect on Hurricanes

Damage caused by Hurricane Dolly in South Padre Island, Texas
UPDATE 8/5/08: COLORADO STATE'S TEAM HAS UPPED ITS FORECAST TO 9 HURRICANES. http://hurricane.atmos.colostate.edu/Forecasts/

Two months into the Atlantic hurricane season, we’ve seen two storms, Bertha and Dolly, reach hurricane status. Only the Category 2 Dolly has made landfall in the U.S.

According to Colorado State University’s hurricane forecast, we’re due for six more hurricanes before the season comes to a close Nov. 30. The CSU report also says there is a 69% chance a major (Category 3-4-5) hurricane will hit somewhere along the U.S. coastline this season, well above the 52% average for the last century.

With hurricane frequency and intensity seemingly on the rise, many are looking into a link between global warming and hurricanes. However, CSU’s Dr. Philip J. Klotzbach says despite the recent uptick (mostly the 2004-2005 seasons) in Atlantic hurricane activity, the storms have not increased worldwide. He and hurricane-report partner Dr. William M. Gray say there is “no valid physical theory as to why hurricane frequency or intensity would necessarily be altered significantly by small amounts (< ±1oC) of global mean temperature change,” and that the recent rise in Atlantic hurricanes is “well within natural bounds of hurricane variation.” You’d think a rise in ocean temperature would lead to more hurricanes. But there are other factors to consider, such as wind shear. Vertical wind shear – shifts in upper-level-atmosphere and lower-level-atmosphere winds – increases along with ocean temps in global warming. This wind shear hinders the growth of storms, possibly enough to counterbalance any growth caused by the ocean temperature rise, a University of Miami study found. But other studies come to different conclusions.

Kerry A. Emanuel, Professor of atmospheric science at MIT, offers a comprehensive Q&A that sums up the difficulty in pinpointing global warming’s effect on hurricanes.

Since Dr. Emanuel is recognized as an authority on the subject, I wanted to speak with him, so first gave the Q&A a look. In my request for an interview, I threw in my reading on his Q&A and Dr. Emanuel kindly informed me that I may have misread it – pretty embarrassing, but also a clue of the complexity of the issue. Here’s what he said:

“I certainly did not mean to imply in the write-up you cite that there is no evidence that global warming is affecting hurricanes. The essay is nuanced, as is reality, and I urge you to read it carefully. There is indeed no evidence that GLOBAL hurricane frequency is changing, but frequency of Atlantic hurricanes (12% of the global total, by the way) is strongly tied to sea surface temperature and there is a great deal of evidence that it has been affected by global warming. Moreover, the intensity of storms almost everywhere appears to be increasing in response to global warming, as theory and models predict.”

So there you have it. Anthropogenic warming does appear to be affecting hurricanes, but there are many questions still to answer.

On the flip side, if you’d like to gain insight into the opposite of how the environment is affecting hurricanes, check out the USGS Center for Coastal & Watershed Studies’ site on how hurricanes affect the environment.

It has info before a storm even arrives in the U.S. on how it will affect the projected landfall area, photos of damage from past storms, and information on topographic changes to coastal areas.

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“Warming's Effect on Hurricanes”