Warming to bring stronger hurricanes
Study
By SETH BORENSTEIN, AP Science Writer Seth Borenstein, Ap
Science Writer – Sun Feb 21, 1:38 pm ET
WASHINGTON – Top researchers now agree that the world is likely to get
stronger but fewer hurricanes in the future because of global warming,
seeming to settle a scientific debate on the subject. But they say
there's not enough evidence yet to tell whether that effect has already
begun.
Since just before Hurricane Katrina hit Louisiana and Mississippi in
2005, dueling scientific papers have clashed about whether global
warming is worsening hurricanes and will do so in the future. The new
study seems to split the difference. A special World Meteorological
Organization panel of 10 experts in both hurricanes and climate change —
including leading scientists from both sides — came up with a consensus,
which is published online Sunday in the journal Nature Geoscience.
"We've really come a long way in the last two years about our knowledge
of the hurricane and climate issue," said study co-author Chris Landsea,
a National Oceanic and Atmospheric Administration top hurricane
researcher. The technical term for these storms are tropical cyclones;
in the Atlantic they get called hurricanes, elsewhere typhoons.
The study offers projections for tropical cyclones worldwide by the end
of this century, and some experts said the bad news outweighs the good.
Overall strength of storms as measured in wind speed would rise by 2 to
11 percent, but there would be between 6 and 34 percent fewer storms in
number. Essentially, there would be fewer weak and moderate storms and
more of the big damaging ones, which also are projected to be stronger
due to warming.
An 11 percent increase in wind speed translates to roughly a 60 percent
increase in damage, said study co-author Kerry Emanuel, a professor of
meteorology at MIT.
The storms also would carry more rain, another indicator of damage, said
lead author Tom Knutson, a research meteorologist at NOAA.
Knutson said the new study, which looks at worldwide projections,
doesn't make clear whether global warming will lead to more or less
hurricane damage on balance. But he pointed to a study he co-authored
last month that looked at just the Atlantic hurricane basin and
predicted that global warming would trigger a 28 percent increase in
damage near the U.S. despite fewer storms.
That study suggests category 4 and 5 Atlantic hurricanes — those with
winds more than 130 mph — would nearly double by the end of the century.
On average, a category 4 or stronger hurricane hits the United States
about once every seven years, mostly in Florida or Texas. Recent
category 4 or 5 storms include 2004's Charley and 1992's Andrew, but not
Katrina which made landfall as a strong category 3.
Outside experts praised the work.
The study does a good job of summarizing the current understanding of
storms and warming, said Chunzai Wang, a researcher with NOAA who had no
role in the study.
James Lee Witt, former director of the Federal Emergency Management
Agency, said the study "should be a stern and stark warning that America
needs to be better prepared and protected from the devastation that
these kinds of hurricanes produce."
The issue of hurricanes and global warming splashed onto front pages in
the summer of 2005 when MIT's Emanuel published a paper in Nature saying
hurricane destruction has increased since the mid-1970s because of
global warming, adding it would only get worse.
Several weeks later Hurricane Katrina struck, killing 1,500 people and
the 2005 hurricane season was the busiest on record with 28 named storms
and seven major hurricanes. But then other scientists led by Landsea
disputed the conclusions that storms were already increasing in number
or intensity.
Now Landsea and Emanuel are co-authors on the same paper with Knutson.
In 2007, the authoritative Intergovernmental Panel on Climate Change
said it was "more likely than not" that man-made greenhouse gases had
already altered storm activity, but the authors of the new paper said
more recent evidence muddies the issue.
"The evidence is not strong enough that we could make some kind of
statement" along those lines, Knutson said. It doesn't mean the IPCC
report was wrong; it was just based on science done by 2006 and recent
research has changed a bit, said Knutson and the other researchers.
Lately, the IPCC series of reports on warming has been criticized for
errors. Emanuel said the international climate panel gave "an accurate
summary of science that existed at that point."
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