“… it is not the numbers that matter, it is
also the intensity, duration and size,” he says.
18 May 2008
Climate change ‘to make Atlantic hurricanes rarer’
Increasing frequency of storms in past 25 years
may not continue, although average severity may
Hurricanes may become rarer in the Atlantic
throughout the 21st century if the world
continues to warm, suggests a new study.
The research is the latest to address the
question of how – and whether – global warming
will affect the intensity and frequency of
Globally, the number of major hurricanes has shot
up by 75% since 1970. And although rising ocean
temperatures are generally accepted as the key
culprit – hurricanes can only form where sea
surface temperatures exceed 26ºC – the link to
global warming has remained a contentious issue.
In the new study, published today in Nature
Geoscience 1, Thomas Knutson of the US National
Oceanic and Atmospheric Administration (NOAA) and
colleagues used a regional climate model of the
Atlantic basin to simulate the observed increase
in hurricane activity between 1980 and 2006, on
the basis of observed sea-surface temperatures
and atmospheric conditions.
“The study does not support the notion that
rising greenhouse gases are causing an increase
in tropical storm frequency,” says Knutson.
They then used two versions of the model, one
assuming climate warming of 2.8ºC by 2100, and
one without warming, to estimate whether
hurricane activity will continue to increase in
the region as a result of human-induced climate
Overall, the number of hurricanes will decrease,
with weaker storms feeling the greatest impacts.
Knutson and his team predict a 27% drop in
tropical storms, 18% fewer hurricanes and 8%
fewer ‘major hurricanes’.
So, despite the fact that hurricane activity has
increased dramatically in the Atlantic over the
past 25 years, this trend will not continue until
the end of the century under warmer conditions.
“We can’t simply extrapolate the trend from the
past 25 years into the future,” says co-author
Issac Held, also at NOAA.
The study focused primarily on changes in the
number of hurricanes, but also projected a shift
towards more intense storms and heavier rainfall
events. This largely concurs with recent work by
Kerry Emanuel, a hurricane expert at the
Massachusetts Institute of Technology in
Cambridge. Using a different type of model,
Emanuel projected that global warming will result
in fewer hurricanes globally, but that they will
become more intense in some locations.
Kevin Trenberth, a climatologist at the National
Center for Atmospheric Research in Boulder,
Colorado, who was not involved in the study,
agrees to an extent with the findings. “The
results suggest fewer tropical storms in the
Atlantic, and this seems reasonable given
everything else we know”.
But he cautions that the authors may have
underestimated increases in hurricanes and really
severe storms, owing to the fact that their model
was fairly low-resolution and could not account
for changes in some of the largest of these <http://www.nytimes.com/2008/05/18/magazine/18wwln-phenomenon-t.html?ref=science>
“In this business it is not the numbers that
matter, it is also the intensity, duration and
size,” he says.
1. Knutson, T. R. et al. Nature Geosci. doi:10.1038/ngeo202 (2008).