Sunday, November 1, 2009

Slow hurricane season for U.S. was the same across the globe

Eric Berger in the Houston Chronicle: Sure, this year's Atlantic hurricane season has been slow with eight named storms, just two hurricanes and about $100,000 in damages to U.S. property. But that's to be expected during El Niño, a warming of the tropical Pacific Ocean that tends to dampen tropical activity on this side of the world. What's more surprising is that, globally, the picture's much the same.

…The National Oceanic and Atmospheric Administration uses a measurement called Accumulated Cyclone Energy, or the ACE Index, to determine a season's activity. Essentially the ACE Index approximates the total energy of a storm from its intensity and duration. A seasonal ACE Index is simply the summation of all the storm values.

For the North Atlantic basin this season, the ACE Index is 45 percent of its normal level, the weakest season since 1997. And globally the ACE Index this past spring and summer were lower than at any point during the last 30 years. .

…This field of scientific inquiry has grown by leaps and bounds since 2005, when Hurricane Katrina lashed the northern Gulf Coast and Massachusetts Institute of Technology hurricane scientist Kerry Emanuel published a paper linking climate change to more powerful hurricanes.

Still, Emanuel said, there's far from a consensus in the field. “We are getting to understand the problem better, thanks in part to the fact that many more scientists are working on it than was the case just a few years ago,” Emanuel said. “But we have a long ways to go.”

….Emanuel continues to believe that oceans in a warming world will produce stronger storms, because the trend over the last 30 years in the Western North Pacific and Atlantic basins is upward. Another scientist who shares this view is Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colo.

Trenberth said the ACE Index is far from a perfect measure for a seasonal hurricane activity because it fails to take a storm's size into account. Hurricane Ike, for example, was such a destructive storm because it was so large and had a massive storm surge, yet its intensity was only that of a Category 2 hurricane. Trenberth said there's little doubt in his mind that a warming climate is making storms more hazardous….

Doctor's Cave Beach in Jamaica on a hurricane-free day, shot by Ezhiki, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License

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