April 18, 2007 — The debate over whether global warming affects hurricanes may be running into some unexpected turbulence. Many researchers believe warming is causing the storms to get stronger, while others aren't so sure. Now, a new study raises the possibility that global warming might even make it harder for hurricanes to form.
The findings, by Gabriel A. Vecchi of the National Oceanic and Atmospheric Administration and Brian J. Soden of the University of Miami, are reported in Wednesday's issue of Geophysical Research Letters.
Vecchi and Soden used 18 complex computer climate models to anticipate the effects of warming in the years 2001-2020 and 2018-2100.
Included in the results were an increase in vertical wind shear over the tropical Atlantic and eastern Pacific oceans.
Vertical wind shear is a difference in wind speed or direction at different altitudes. When a hurricane encounters vertical wind shear the hurricane can weaken when the heat of rising air dissipates over a larger area.
On the other hand, warm water provides the energy that drives hurricanes, so warmer conditions should make the storms stronger.
"We don't know whether the change in shear will cancel out the increased potential from warming oceans, but the shear increase would tend to make the Atlantic and East Pacific less favorable to hurricanes," said Vecchi, of NOAA's Geophysical Fluid Dynamics Laboratory in Princeton, N.J.
"Which one of the two — warming oceans or increasing shear — will be the dominant factor? Will they cancel out? We and others are currently exploring those very questions, and we hope to have a better grasp on that answer in the near future," Vecchi said.
"What we can say is that the magnitude of the shear change is large enough that it cannot be ignored," he added.
Any decrease in strength or frequency of storms caused by shear would apply only if all else was equal, Vecchi said, "but all else is not equal, since the shear increase is being driven by global warming."
Soden, of Miami's Rosenstiel School for Marine and Atmospheric Science, added: "This study does not in any way undermine the widespread consensus in the scientific community about the reality of global warming."
The massive destruction caused by Hurricanes Katrina and Rita in 2005 focused attention on tropical cyclones — as these storms are also known — and some well-known researchers suggested the warming seas were fueling stronger storms.
Last year an El Nino — a warming of the water in the tropical Pacific that can affect weather worldwide — dampened the Atlantic hurricane season.
Now, just weeks before the traditional June 1 start of the hurricane season, forecasters and residents of hurricane-threatened regions nervously wait to see what this summer will bring.
The government's hurricane season forecast has yet to be issued, but a top storm researcher has predicted a very active 2007 Atlantic hurricane season. William Gray of Colorado State University expects at least nine hurricanes, with a good chance one will hit the U.S. coast.
