September 27, 2005
No one can say if warming caused Katrina, Rita
By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - Scientists say it's not easy to tell
if global warming caused hurricanes Katrina and Rita but on
Monday they forecast more unpredictable weather as Earth gets
Even skeptics agree that global warming is under way and
that human activity is at least in part responsible. Climate
experts also agree that this warming is likely to make the
weather more extreme -- colder in some places, hotter in
others, with droughts and severe rainstorms both more common.
"Global warming, I think, is playing a role in the
hurricanes," said Kevin Trenberth, a senior scientist at the
National Center for Atmospheric Research in Boulder, Colorado.
"But a lot of what is going on is natural. What global
warming may be doing is making them somewhat more intense,"
said Trenberth, a member of the U.N. Intergovernmental Panel on
James Elsner, professor of geography at Florida State
"Certainly this is an unusual season," he said in a
telephone interview. "However, the question of attribution I
don't think is very simple."
Katrina slammed into southern Louisiana and Mississippi on
August 29, wiping out entire towns, triggering the devastating
flooding of New Orleans and causing more than 1,000 deaths.
Then on Saturday along came Rita, which briefly hit Category 5
strength with winds higher than 155 mph (249 kph) before
dropping Category 3 by the time it hit the Texas-Louisiana
"We have seen unusual seasons in the past and so we
understand that we tend to see more strong storms when the
Atlantic Ocean temperatures are warmer, which has been the case
in the last 10 years or so," Elsner said.
"It was warm in the 1940s and '50s and we saw lots of
strong storms during that period."
So far, 2005 has not been the busiest year for storms, even
though there have been 17 named tropical storms in the
Atlantic, Caribbean and Gulf of Mexico.
"That distinction belongs to the year 1933, in which there
were 21 storms that reached tropical storm strength," said Eric
Gross, an associate professor of history at Harding University
in Searcy, Arkansas, who studies hurricanes and other natural
There were 19 tropical storms in 1995, Gross said in a
In theory, warmer temperatures could bring more and fiercer
hurricanes, experts agree. Hurricanes are fed by warm ocean
surface temperatures and by higher amounts of water vapor.
Kerry Emanuel, a professor of meteorology at the
Massachusetts Institute of Technology, published a study in the
journal Nature last July that found big storms are 50 percent
more intense and last 50 percent longer than those in the
"My results suggest that future warming may lead to an
upward trend in tropical cyclone destructive potential and --
taking into account an increasing coastal population -- a
substantial increase in hurricane-related losses in the
twenty-first century," he wrote.
Emanuel also has found that the IPCC-predicted rise in sea
surface temperatures -- 3.6 degrees Fahrenheit (2 degrees
Celsius) -- would raise a storm's intensity by 10 percent.
This temperature increase, Trenberth said, will add water
vapor to fuel a hurricane's fury.
Even if storms are not yet affected by global warming,
experts like Emanuel and Trenberth predict they will be.
"Global warming is remorselessly going on," Trenberth said.
"This is something that when you take action, the benefits take
place in 50 years and beyond. It is not something you can