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WARMING TREND LINKED TO FIERCER HURRICANES
BUT SOME METEOROLOGISTS QUESTION RESEARCHERSą ANALYSIS
By Joseph B. Verrengia
Associated Press
July 31, 2005

http://www.msnbc.msn.com/id/8776578/

Is global warming making hurricanes more ferocious? New research suggests
the answer is yes.

Scientists call the findings both surprising and "alarming" because they
suggest global warming is influencing storms now -- rather than in the
distant future.

However, the research doesn't suggest global warming is generating more
hurricanes and typhoons.

The analysis by climatologist Kerry Emanuel of the Massachusetts Institute
of Technology shows for the first time that major storms spinning in both
the Atlantic and the Pacific since the 1970s have increased in duration and
intensity by about 50 percent.

These trends are closely linked to increases in the average temperatures of
the ocean surface and also correspond to increases in global average
atmospheric temperatures during the same period.

"When I look at these results at face value, they are rather alarming," said
research meteorologist Tom Knutson. "These are very big changes."

Knutson, who wasn't involved in the study, works in the National Oceanic and
Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in
Princeton, N.J.

Analyzing actual storms

Emanuel reached his conclusions by analyzing data collected from actual
storms rather than using computer models to predict future storm behavior.

Before this study, most researchers believed global warming's contribution
to powerful hurricanes was too slight to accurately measure. Most forecasts
don't have climate change making a real difference in tropical storms until
2050 or later.

But some scientists questioned Emanuel's methods. For example, the MIT
researcher did not consider wind speed information from some powerful storms
in the 1950s and 1960s because the details of those storms are inconsistent.

Researchers are using new methods to analyze those storms and others going
back as far as 1851. If early storms turn out to be more powerful than
originally thought, Emmanuel's findings on global warming's influence on
recent tropical storms might not hold up, they said.

"I'm not convinced that it's happening," said Christopher W. Landsea,
another research meteorologist with NOAA, who works at a different lab, the
Atlantic Oceanographic & Meteorological Laboratory in Miami. Landsea is a
director of the historical hurricane reanalysis.

"His conclusions are contingent on a very large bias removal that is large
or larger than the global warming signal itself," Landsea said.

Details of Emanuel's study appear Sunday in the online version of the
journal Nature.

What theories predict

Theories and computer simulations indicate that global warming should
generate an increase in storm intensity, in part because warmer temperatures
would heat up the surface of the oceans. Especially in the Atlantic and
Caribbean basins, pools of warming seawater provide energy for storms as
they swirl and grow over the open oceans.

Emanuel analyzed records of storm measurements made by aircraft and
satellites since the 1950s. He found the amount of energy released in these
storms in both the North Atlantic and the North Pacific oceans has
increased, especially since the mid-1970s.

In the Atlantic, the sea surface temperatures show a pronounced upward
trend. The same is true in the North Pacific, though the data there is more
variable, he said.

"This is the first time I have been convinced we are seeing a signal in the
actual hurricane data," Emanuel said in an e-mail exchange.

"The total energy dissipated by hurricanes turns out to be well correlated
with tropical sea surface temperatures," he said. "The large upswing in the
past decade is unprecedented and probably reflects the effects of global
warming."

Recent trends

This year marked the first time on record that the Atlantic spawned four
named storms by early July, as well as the earliest category 4 storm on
record. Hurricanes are ranked on an intensity scale of 1 to 5.

In the past decade, the southeastern United States and the Caribbean basin
have been pummeled by the most active hurricane cycle on record. Forecasters
expect the stormy trend to continue for another 20 years or more.

Even without global warming, hurricane cycles tend to be a consequence of
natural salinity and temperature changes in the Atlantic's deep current
circulation that shift back and forth every 40 to 60 years.

Since the 1970s, hurricanes have caused more property damage and casualties.
Researchers disagree over whether this destructiveness is a consequence of
the storms' growing intensity or the population boom along vulnerable
coastlines.

"The damage and casualties produced by more intense storms could increase
considerably in the future," Emanuel said.

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Published by David Sunfellow
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