While a U.N. report last week left little doubt that scientists think humans are heating the planet, it did nothing to settle the question of whether they are partly responsible for more intense hurricanes.
Nonetheless, weather experts said the report by the Intergovernmental Panel on Climate Change could help convince politicians, regulators and insurers that climate change is here to stay.
The report warned that human activities are contributing to global warming and the result could be more heat waves, droughts and rising seas. But its conclusion on hurricanes was more vague.
The panel said it was “more likely than not” that humans contribute to a trend of increasingly intense hurricanes.
Debate on that issue among scientists has raged since the record-setting 2005 Atlantic season, which saw some of the most powerful hurricanes on record. Katrina killed 1,500 people on the U.S. Gulf Coast and caused $80 billion in damages.
Some researchers say global warming appears to have contributed to more intense hurricanes, while others argue there is no evidence of that.
Leading researchers and scientists say the report would do nothing to sway either side.
Chris Landsea, a prominent U.S. government hurricane researcher who has differed with IPCC methods in the past, wrote in an e-mail that the report was “okay, but a bit incomplete.”
Specifically he said the human contribution to the intensity trend was not quantified and could be “grossly misinterpreted.”
The conclusions of the U.N. climate panel, made up of 2,500 researchers from more than 130 nations, are being hotly debated and already have come under counter-attack by partisan groups.
William Gray, a prominent Colorado State University researcher who pioneered hurricane frequency forecasts, said the panel had bought the argument that humans are having an impact on hurricanes.
“I don’t think that’s right,” he said, adding that “there’s no solid evidence that global or Atlantic hurricane frequency or intensity has been altered due to this global warming in the last century.”
While the panel’s report broke no actual new ground on the hurricane-warming link, some experts said it could have wide influence on politicians, policymakers and regulators.
Kerry Emanuel, an MIT professor whose research has linked warming to hurricane intensity, said rising property damage from hurricanes is partly due to government policies that influence coastal construction, including regulation of insurance markets, federal flood insurance programs that undercharge property owners and disaster relief after storms.
“In the United States it may provide additional incentive for governments ... to take more seriously the threat of hurricanes, even if the climate isn’t changing,” he said. “We have a serious hurricane problem made worse by government policies.”
Hugh Willoughby, a tropical meteorologist at Florida International University, said he was concerned the IPCC report could be used as a weapon by the insurance industry, which paid out about $40 billion in Katrina, to seek higher premiums from customers or to abandoned needy markets like Florida.
“I’m worried that this is going to tend to make windstorm insurers less eager to enter the market and come to think they may experience this kind of loss on a regular basis,” he said.
Willoughby said a hurricane’s greatest impact on humans is due less to global warming than to runaway coastal development and to bad luck -- whether a storm hits a heavily populated area or not.
“The message is that it’s a game of chance. What global warming does is make it a higher-stakes game of chance,” he said. “It’s making all hurricanes a little bit stronger, and that means when we have bad luck it’s going to be worse and when we have good luck it’s not going to be as good.”
Jeff Masters, the founder of weather Web site Weather Underground, said the report did not break any new ground.
“But we do expect there to be an increase in the future in intense hurricanes,” he said, “so that was the right thing to say.”