Warming Making
Hurricanes Stronger, Study Says
August 01, 2005 — By Joseph B. Verrengia, Associated Press
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.
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.
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."
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.
Source: Associated Press |