BOULDER - The planet may be warming, but what started out as a polite discussion about hurricane trends turned plain hot here Wednesday.
At issue was the role - if any - that global warming plays in fueling monster storms.
But illustrating the volatile nature of the debate, the scientific conference descended into name calling.
Colorado State University's William Gray, one of the nation's preeminent hurricane forecasters, called noted Boulder climate researcher Kevin Trenberth an opportunist and a Svengali who "sold his soul to the devil to get (global warming) research funding."
Trenberth countered that Gray is not a credible scientist.
"Not any more. He was at one time, but he's not any more," Trenberth said of Gray, one of a handful of prominent U.S. scientists who question whether humans play a significant role in warming the planet by burning fossil fuels that release heat-trapping gases.
"He's one of the contrarians, some of whom get money to spread lies about global warming," Trenberth said during a break following his presentation at the 31st annual Climate Diagnostics & Prediction Workshop. About 150 scientists from more than 10 countries are attending the weeklong meeting.
Trenberth and Gray traded barbs during Trenberth's presentation to the group. But the harshest comments were made during interviews with a reporter afterward.
Even before last year's record-smashing Atlantic hurricane season ended, scientists began debating global warming's role.
Trenberth noted Wednesday that the 2005 Atlantic hurricane season spawned the greatest number of named tropical storms and the most hurricanes on record. It was the only year with three Category 5 hurricanes (winds of 156 mph and higher) and produced the most costly storm on record, Katrina, with damage estimates as high as $200 billion.
The tropical oceans, which provide the fuel for hurricanes, have warmed 0.9 degrees Fahrenheit since 1970.
Trenberth and his colleagues say there's little doubt the warming is due in part to the buildup of heat-trapping greenhouse gases, such as carbon dioxide.
At the same time, there's been a surge over the past 35 years in the number and proportion of intense hurricanes, Trenberth said. It's highly likely that greenhouse gases are partly to blame and that the trend will continue, he said.
"The prospects are for more intense storms, heavier rainfall and flooding, and more coastal damage," Trenberth told the group.
He said that global warming boosted the amount of rainfall in several of the most powerful 2005 hurricanes - including Katrina and Rita - by 7 percent.
But Gray said there's no evidence that hurricanes are intensifying and that "everything he (Trenberth) has shown can be refuted."
And Gray wasn't the only audience member to question some of Trenberth's assertions.
"It's impossible to say the exact percentage one can attribute to the impact of global warming," said Muthuvel Chelliah of the U.S. Climate Prediction Center.
In addition, Trenberth failed to adequately explain why - if global warming continues to heat the waters that fuel powerful hurricanes - the 2006 Atlantic hurricane season has been so much wimpier than last year's, Chelliah said.
During a break, Trenberth said the milder 2006 season was due largely to an unexpected Pacific El Niño that suppressed hurricanes in the Atlantic.
Natural climate variability - including the periodic swings between El Niño and La Niña conditions in the Pacific - will sometimes overshadow global warming's influence on hurricanes, Trenberth said.
"Global warming is still there," he said. "But this year, natural variability, especially El Niño, overwhelmed the contribution from global warming."
For the record, it is my opinion that Bill Gray is a dinosaur who is not changing his opinions with progress in science. I also feel that there is a detectable global warming signal in hurricane patterns. For more information on global warming and hurricanes, see the work done by Kerry Emanuel, one of the field's leading hurricane scientists, from MIT.