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.

The study will appear today in the journal Geophysical Research Letters.

Michaels did the report with U.Va. environmental science professor
Robert E. Davis and Paul C. Knappenberger, a former graduate student
in environmental sciences at Virginia.

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