Warm seas may cut hurricanes
2008-01-24 12:53
Miami - Rising ocean temperatures linked
to global warming could decrease the number of hurricanes
hitting the United States, according to new research released
on Wednesday.
The study, published in Geophysical Research Letters,
challenges recent research that suggests global warming could
be contributing to an increase in the frequency and the
intensity of Atlantic hurricanes.
At the same time, it reaffirmed earlier views that warmer
sea waters might result in atmospheric instabilities that could
prevent tropical storms from forming.
Atlantic storms play a pivotal role in the global energy,
insurance and commodities markets, particularly since the
devastating 2004 and 2005 hurricane seasons, which hammered
US oil and gas production in the Gulf of Mexico.
The new study suggests that warmer seas, caused by
greenhouse gases blamed for a rise in global temperatures, are
linked to an increase in vertical wind shear, a difference in
wind speeds at different altitudes that can tear apart nascent
cyclones.
Hurricanes feed on warm water, leading to conventional
wisdom supported by some recent research that global warming
could be revving up more powerful storms.
But the new study, by oceanographer Chunzai Wang of the
National Oceanic and Atmospheric Administration, and Sang-Ki
Lee, a scientist at the University of Miami, examined 150 years
of hurricane records and found a small decline in hurricanes
making landfall in the United States as the oceans warmed.
"The attribution of the recent increase in Atlantic
hurricane activity to global warming is premature. ... Global
warming may decrease the likelihood of hurricanes making
landfall in the United States," the researchers wrote.
Much of the recent research focused on the total number of
tropical storms and hurricanes recorded in the Atlantic Ocean
and Caribbean, but Wang said the number of those hurricanes
actually hitting the United States is a much better indicator.
Prior to the mid-1960s when satellites and other technology
made it easier to spot cyclones, some tropical storms and
hurricanes lived and died far out at sea, undetected.
As a result, scientists trying to track long-term trends in
the frequency of Atlantic storms work with uncertain data.
"We believe US landings for hurricanes are most reliable
measurements over the long term," Wang said.
The study found that warming of the tropical Pacific and
Indian oceans increases Atlantic wind shear while rising sea
temperatures in the tropical North Atlantic decrease shear.
The two effects compete, but the net impact is an increase
in wind shear in the main Atlantic hurricane development zone,
from the west coast of Africa to Central America.
"The Pacific and Indian warming wins and the result is a
decrease in landfalling US hurricanes," Wang said.
In 2004, four strong hurricanes hit Florida, causing
billions of dollars in damage across the state. In 2005, a
record-breaking 28 tropical storms formed, including Katrina,
which killed 1 500 people and caused $80bn damage.
The back-to-back years of unusually intense hurricane
activity fuelled debate about the impact of global warming.