Scientist dispute tie between global warming, hurricanes

Houston Chronicle:

At its essence, hurricane season moves to a simple rhythm.

Sea temperatures rise in June, allowing the first, weak storms to form. Hurricane activity peaks in early fall, when the seas are warmest. The storms don't ebb until November, as the oceans cool.

This correlation led many scientists to conclude that as global warming heated the oceans, so, too, would hurricanes become more powerful and seasons longer. But in the wake of two relatively quiet Atlantic storm years, two climate scientists have completed a study that sharply contradicts this conclusion.

The scientists, Gabriel Vecchi, of the National Oceanic and Atmospheric Administration, and Brian Soden, of the University of Miami, found that natural climate variations such as El Niño likely have a larger effect on hurricanes than global warming.

And since these regional patterns oscillate over time, the scientists concluded, there is likely to be no discernible trend in the number or intensity of hurricanes in coming decades, even though the oceans will likely warm by 4 or 5 degrees Fahrenheit.

"We were very surprised to find that there wasn't a uniform rise in hurricane activity as well," said Soden, co-author of a paper in today's journal Nature that reports the results.

There has been a scientific debate in recent years over whether global warming will produce more and stronger hurricanes. But until now, much of the objection to linking the two has come from scientists who say the record of past hurricanes is too shoddy to say definitively that activity in the modern era has increased.

This new study appears to bolster the naysayers by providing some scientific rigor to arguments against a strong link between global warming and more intense hurricanes. It offers an explanation why the atmosphere may not favor stronger storms in a warmer world.

Although sea surface temperatures are expected to increase during the coming century, the warming also will likely extend into the upper atmosphere. A hurricane derives its power from the differential between surface and upper atmosphere temperatures. A greater differential translates into more energy for the storm and leads to more powerful hurricanes.

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It sounds like global warming may actually mean fewer storms because of the warming of the upper atmosphere. This has to be a political blow to Democrats who have tried to blame President Bush for hurricanes in recent years. Don't expect them to necessarily agree with science though. That would be too inconvenient.