May 31, 2006 -- To anyone who spent time watching hurricane forecasts last summer, Max Mayfield may seem like a hero. The director of the National Hurricane Center predicted many of the season's worst storms.
But a day before the start of the 2006 hurricane season, environmental groups called for Mayfield and other officials at the National Oceanic and Atmospheric Administration, or NOAA, to resign.
"NOAA is actively covering up the strong and growing scientific link between more powerful hurricanes and global warming," said Mike Tidwell, who represents a group called the U.S. Climate Emergency Council.
The groups demanded that Mayfield and NOAA administrator Conrad Lautenbacher step down.
"They must resign immediately," said Tidwell, in front of about 30 protesters who'd gathered for a morning rally outside NOAA headquarters in Silver Spring, Md.
NOAA officials declined to be interviewed today but released a statement saying the agency had not taken a specific position on the relationship between global warming and hurricane behavior.
"We recognize there is an ongoing scientific debate and will continue to support research that might identify detectable influences of global warming in hurricane frequency and/or intensity," the statement said.
One NOAA official, speaking on background, said today that not all of the agency's scientists agree a global warming-hurricane link exists. Mayfield put the blame on natural climate cycles when he testified before Congress in September 2005.
"The increased activity since 1995 is due to natural fluctuations and cycles of hurricane activity," he said at the time.
But a growing body of peer reviewed scientific evidence -- including a study released today by researchers at Pennsylvania State University and MIT -- downplays the role of natural cycles and blames global warming -- brought on by human activities -- as a factor heating the Atlantic Ocean, which in turn fuels more intense hurricanes that may affect the United States.
"There have been some views put forward that what we are seeing in the Atlantic is due to a natural variability," said Greg Holland, a climatologist at the National Center for Hurricane Research. "The problem is that what we're seeing in the Atlantic is mirrored all the way around the world. We're actually looking at an entire world that is heating up, not just the Atlantic Ocean, which is why we are absolutely convinced that there is a very large greenhouse warming signal in what we're seeing."
Recent studies have shown that while the overall number of hurricanes has not increased significantly, their intensity has increased. Holland said the frequency of the strongest Category 4 and 5 hurricanes has almost doubled around the world since 1970.
Climate scientists say the increase is a result of warmer water temperatures that put more water vapor into the atmosphere, which acts as fuel.
"A hurricane reaches out and grabs the available water vapor, sucks it into the storm, and then dumps it down and concentrates it," says Kevin Trenberth, a climatologist at the National Center for Hurricane Research. "So when it rains, it pours now much more than it did 30 years ago."
Scientists like Trenberth try to quantify just how much impact global warming has on storms.
"We think that probably the best number we can put on it about now is something like 8 percent," he said. "So in New Orleans [during Katrina], where they had 12 inches of rain, about 1 inch of that was probably due to global warming and the other 11 would have happened maybe anyway."
But following the 2005 season, NOAA released a statement discounting any link between global warming and worsening hurricanes. It set off a furor among some NOAA scientists, who charged the agency prevented them from speaking freely about climate change issues.
NOAA backed away from that statement in February, and NOAA administrator Lautenbacher sent an e-mail to agency staff.
"I am a strong believer in open, peer reviewed science as well as in the right and duty of scientists to seek the truth and to provide the best scientific advice possible," the e-mail read. Lautenbacher encouraged scientists "to speak freely and openly" with journalists.
As for Mayfield, he suggested in a recent interview that he'd be willing to see more evidence that hurricanes are getting worse because of global warming.
"I'm willing to be convinced either way here," Mayfield told ABC's Ned Potter. "I'm always looking forward to looking at new data. If I get convinced, so be it. But I'm not convinced yet."