Scientist downplays global-warming role

"The American president has closed his eyes to the economic and human damage that natural catastrophes such as Katrina — in other words, disasters caused by a lack of climate protection measures — can visit on his country," Jurgen Trittin, Germany's minister of the environment, wrote in an essay quoted by Spiegel Online.

The German publication goes on to denounce Trittin's writing as "a slap in the face to all the victims."

But is there truth in Trittin's implication that global warming caused, or at least vastly increased, the destruction in New Orleans?

No, says Ed Zipser, professor of meteorology at the University of Utah.

"I think I can speak for at least a majority of meteorologists who understand hurricanes pretty well that any change in the frequency and intensity due to global warming is probably a very small effect."

Weather experts would "never, ever" attribute any specific hurricane to global warming. The warming is taking place over a long period, he added.

If there is an effect on hurricanes, it might involve the technical calculation of the "maximum potential intensity." That upper limit depends, among other factors, on the temperature of the sea's surface. But it is more a theoretical figure than an actual effect.

"Any given hurricane is not likely to reach its maximum potential, and you might think of that as an upper limit," Zipser said.

"But most hurricanes don't get anywhere near it."

Also, the effect would be relatively small. Global warming of the sea's surface, which has been measured, is in fractions of a degree. That would change the potential "by a very small amount," he said.

A hurricane like Katrina would have created horrendous damage on the path it took, regardless of whether it was a Category 3, 4 or 5. In this case, the storm actually weakened by 30 miles per hour over the last 24 hours before it hit land, he said.

"And there was no particular reason for the decrease," Zipser added. "I would not have been surprised if it had stayed 175 (mph winds), I would not have been surprised if it had dropped to 125."

Katrina was a huge, intense hurricane. A storm of Category 3 would have done comparable damage wherever it struck.

"To try to talk about the possible effect of a half-degree due to global warming is just missing the whole point," he said.