By JOSEPH B. VERRENGIA, AP Science Writer
Hurricane Katrina's fury has reignited the scientific debate over
whether global warming might be making hurricanes more ferocious.
At least one prominent study suggests that hurricanes have become
significantly stronger in the past few decades during the same period
that global average temperatures have increased. Katrina blew up in
the Gulf of Mexico to a Category 5 hurricane with winds of 175 mph
before slackening a bit Monday when it hit, swamping New Orleans and
the Mississippi coast.
Other leading scientists agree the Atlantic Basin and Gulf Coast
regions are being battered by a severe hurricane phase that could
persist for another 20 years or more. But they believe that a natural
environmental cycle is responsible rather than any human-induced
change, and they point to what they consider to be large gaps in the
global warming analysis conducted by a climatologist at the
Massachusetts Institute of Technology.
Roger Pielke Jr., who studies the social impacts of natural disasters
and climate change at the University of Colorado, said any link
between the intensity of Katrina and other recent hurricanes and
global warming is "premature." Most forecasts suggest climate change
would increase hurricane wind speeds by 5 percent or less later in
Pielke's analysis will be published later this year in the Bulletin of
the American Meteorological Society.
"There are good reasons to expect that any conclusive connection
between global warming and hurricanes or their impacts will not be
made in the near term," he said.
In August, MIT climatologist Kerry Emanuel reported in the journal
Nature that major storms spinning in both the Atlantic and the Pacific
have increased in duration and intensity by about 50 percent since the
1970s. During that period, global average temperatures have risen by
about one degree Fahrenheit along with increases in the level of
carbon dioxide and other heat-trapping pollutants from industry
smokestacks, traffic exhaust and other sources.
Hurricanes rely on huge pools of warm water at the surface of the
ocean to grow for several days. As trade winds spin the storm, it
pulls more heat from the ocean and uses it as fuel. Typically, large
storms require sea surface temperatures of at least 81 F.
Scientists say rising global atmospheric temperatures have been slowly
raising ocean temperatures, although they still vary widely from year
On Web logs, scientists and environmentalists in the United States and
Europe sparred over the possible connection.
The evidence linking global warming and hurricane intensity might be
fuzzy, but it highlights a potential issue worth examining right away,
"Maybe a connection here is yet to be clearly established, but it is
also yet to be ruled out," said Terry Richardson, a physicist at the
College of Charleston in South Carolina on CCNet, a British climate
Pielke and other researchers say Emanuel's evidence is too slim at
The past 10 years have been the most active hurricane seasons on
record, and many researchers say the trend could persist for another
20 years or more. They believe it's a consequence of natural salinity
and temperature change in the Atlantic's deep current circulation --
elements that shift back and forth every 40-60 years.
National Hurricane Center Director Max Mayfield agrees. He said that
while Atlantic hurricane seasons have been active for a decade, that
isn't true around the world.
"In fact, the Asian Pacific is way down the past few years. Is that
due to global warming, a decrease in hurricanes? I haven't bought into
that one yet," he said.
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