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Scientists say global warming's toasty water has a connection to Gustav |
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Written by Seth Borenstein, THE ASSOCIATED PRESS
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Sunday, 31 August 2008 |
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Global warming has probably made Hurricane Gustav a bit stronger and wetter, say some top scientists, but the specific connection between climate change and stronger hurricanes remains an issue of debate.
The Atlantic is seeing an increase in storms rated among the strongest.
In the past four years, Hurricanes Gustav and Katrina reached Category 4 with sustained winds of at least 210 km-h.
Research says six other storms have reached that level or been even stronger.
Six scientists contacted by The Associated Press say this shows some effect of global warming, but they differ on the size of the effect.
Judith Curry, chairman of Earth and atmospheric sciences at Georgia Tech, says officials are seeing a lot more Categories 4 and 5 globally than ever before.
Measurements of the energy pumped into the air from the warm waters - essentially fuel for hurricanes - has increased dramatically since the mid 1990s, mostly in the strongest of hurricanes, according to a soon-to-be published paper.
It will appear in the journal Geochemistry, Geophysics, Geosystems and was prepared by by Kevin Trenberth, climate analysis chief at National Centre for Atmospheric Research in Boulder, Colo.
The same scientists also caution it is impossible to blame global warming for any single weather event and that some form of Gustav (and other hurricanes) would have likely still formed and turned deadly without man-made climate change.
Yet the fingerprint of global warming on the strongest storms is becoming clearer with new research, scientists said, and that includes Gustav, which reached Category 4 status Saturday before weakening.
"The strongest storms are expected to be stronger," said Gabriel Vecchi, a research oceanographer for a National Oceanic and Atmospheric Administration lab in Princeton, N.J.
"And since Gustav is a very strong storm, you'd expect Gustav to have had an effect from human-induced global warming."
But how much of an effect is where it gets tricky.
Vecchi said he can't tell how much, which makes him uncomfortable as a scientist.
Trenberth calculated, in an earlier journal article, that major storms like Katrina and Gustav probably have increased their rainfall by about six to eight per cent because of global warming.
Warmer water makes the surface air warmer, which means it could contain more moisture.
That means more hot moist air rises up the hurricane, serving as both fuel for the storm and extra rainfall coming back down, said Peter Webster, professor of atmospheric sciences at Georgia Tech.
For the past several years, scientists have traded papers and jibes about the effect global warming has already had - if any - on hurricanes.
Some scientists, such as Christopher Landsea at the National Hurricane Centre, have faulted the quality of storm numbers and the length of time used for historical study used by Curry, Webster and others to connect to hurricanes to global warming.
"Yes, climate change is impacting hurricanes," Landsea said. But the effect on storm intensity now is "very small," something that can't be noticed in a storm so big, he said.
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