August 15, 2006

Global warming affects hurricane intensity: study

By Jim Loney

MIAMI (Reuters) - Global warming is affecting the intensity
of Atlantic hurricanes, according to a new study by a
university professor in Florida who says his research provides
the first direct link between climate change and storm

James Elsner of Florida State University said he set out to
perform a statistical analysis of the two theories in a raging
debate within the scientific community: Whether recent intense
hurricanes are the result of climate change or natural ocean
warming and cooling cycles.

"Is the atmosphere forcing the ocean or the ocean forcing
the atmosphere?" Elsner asked.

The issue has a wide-ranging impact on insurance companies,
municipal planners, some 50 million residents of
hurricane-prone U.S. coastal communities and millions of others
in Mexico, Central America and the Caribbean islands.

The 2005 hurricane season produced 28 tropical storms and
hurricanes, shattering the old record of 21 set in 1933.

Four of the hurricanes were Category 5, the strongest on
the five-step Saffir-Simpson scale. One of those, Wilma, was
the most intense Atlantic hurricane ever recorded.

The season also produced Katrina, which killed more than
1,300 people and caused about $80 billion in damage when it
swamped New Orleans and other parts of the U.S. Gulf coast.

Elsner looked at 135 years of records to examine the
statistical connection between Atlantic sea surface
temperatures and air temperatures near the sea surface, and
then compared them to records of hurricane intensities.

Atlantic hurricanes draw their energy from the warm waters
of the Atlantic Ocean, Gulf of Mexico and Caribbean Sea.

He found that average air temperatures during hurricane
season between June and November were useful in predicting sea
surface temperatures, but not the other way around.

"It appears that atmospheric warming comes before sea
warming," he said, indicating that hurricane damage will be
likely to continue increasing because of greenhouse warming.

The study was scheduled to be published August 23 in
Geophysical Research Letters, a journal of the American
Geophysical Union.

Many hurricane researchers say the Atlantic basin moved
into a period of increased hurricane activity about a decade
ago and predicted it could last 25 to 40 years.

Some say it is due to a natural fluctuation in sea surface
temperatures called the Atlantic Multidecadal Oscillation.

But a growing body of research indicates human-induced
global warming -- driven by heat-trapping gases in air
pollution from cars and factories -- could be heating sea
water, which in turn fuels stronger hurricanes.

Elsner described himself as "sympathetic" to the idea of
human-induced global warming but said his research merely tried
to determine whether there was a link between climate change
and intense hurricanes.

"I think there are ocean currents that warm and cool the
oceans," he said. "But it's not clear that kind of change is a
multidecadal change and I'm not clear that there is a strong
natural variability in the Atlantic."