Stronger Hurricanes Tied to Global Warming
Discovery.Com, March 22, 2006
A 34-year trend of intensifying hurricanes has now been tied to warmer sea surface waters which, in turn, is being caused by global warming, say scientists.
By carefully analyzing climate data from every ocean from 1970 to 2004, researchers at the Georgia Institute of Technology have found that the only factor that has steadily climbed in concert with the power of hurricanes over those 34 years is the surface temperatures of the oceans.
The new study, which appeared in the March 17 issue of Science, is a refinement of a widely reported released late last year, in which many of the same researchers first recognized the hurricane intensification trend.
"What our paper does is firm up the link between hurricane intensification and sea surface temperatures," said Georgia Tech's Judith Curry, one of the authors of the new study.
Curry and her colleagues Paula Agudelo, Carlos Hoyos and Peter Webster used the latest in information and statistical techniques to check which of the many factors matched the hurricane trend.
And while they found that short-term effects like El Niño, air circulation patterns and changes in winds at various elevations (called wind shear) can also affect the strength of hurricanes, the only thing that showed a steady trend in every ocean over the entire 34 years was sea surface temperature.
"Wind shear (for example) can be important for an individual storm or a season," said Curry, "but if you look over the years there is no trend in wind shear."
That said, while the observed intensification of hurricanes matches the theoretical connection between hurricanes and sea surface temperatures, there's still more actual intensification going on than the models predict, said Gavin Schmidt, a climate researcher at NASA's Goddard Institute of Space Studies in New York.
"Based on the theory, you can explain maybe half of the (observed hurricane) changes" with the observed sea surface temperatures, said Schmidt. "We still have a gap either in our theory or our ability to measure changes."
Ultimately, researchers hope that by understanding what's happened in the recent past, they will be in a better position to forecast changes. Already a Japanese team is hard at work on a climate model with the capacity to account for hurricanes, said Curry.
Such work is particularly important because hurricanes are one of planet Earth's mechanisms for redistributing excess heat from the equator towards the poles. The more heat there is at the tropics, so goes the theory, the warmer the water and the more intense the hurricanes.