Report: Don't blame storms on warming

Global warming by itself cannot be blamed for the increase in severe Atlantic hurricanes, University of Virginia climate researchers report.

"It is too simplistic to only implicate sea-surface temperatures in the dramatic increase in the number of major hurricanes," said the study's lead author, Patrick J. Michaels.

Warm water fuels tropical cyclones. Some hurricane researchers have related warming in the Atlantic basin with greater hurricane severity, pointing to greenhouse-induced atmosphere warming as the cause for the ocean heating.

But hurricanes' ultimate strength is not directly linked to the underlying water temperatures, the Virginia scientists said.

"There are more severe hurricanes appearing than are explainable by the rise in sea-surface temperatures since the 1990s," said Michaels, a professor of environmental sciences and director of the Virginia Climatology Office.

Michaels is a leading skeptic of global warming's potential harm.

To fire off monster hurricanes of Category 3 or stronger, the brewing storm has to move over water with a temperature of at least 83 degrees.

Areas where the water is regularly hotter, such as the Gulf of Mexico and the Caribbean Sea, won't see more intense storms than in the past, Michaels said.

"At that point, other factors take over," he said, "such as the vertical wind profile, and atmospheric temperature and moisture gradients."

The U.Va. climatologists found that increasing water temperatures account for only about half of the increase in strong hurricanes over the past 25 years.

"We should have had 28 Category 3 storms from the warming" between 1995 and 2005, Michaels said. "Instead we had 42." By comparison, 16 such storms developed between 1982 and 1994.

Michaels believes the increase in hurricane activity beginning in the 1990s is related mainly to variation in the North Atlantic's temperature patterns, not temperature change itself.

"The pattern can appear whether it's cool or whether it's warm," he said.

While expanding the 83-degree zone ought to produce more severe hurricanes, Michaels said, that expansion would also place the storms farther north in the Atlantic, "where there are very few things to hit."

"In the future we may expect to see more major hurricanes," Michaels said, "but we don't expect the ones that do form to be any stronger than the ones that we have seen in the past."

The Virginia study looked at the water temperatures along the paths of the 205 Atlantic tropical cyclones since 1982, providing a more precise picture of the tropical environment involved in each hurricane's development.

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