Sept. 23, 2005 -- For some, the recent hurricanes are seen as God's warning to repent.
Some preachers have said Katrina was meant to punish New Orleans for being a sin city. In Jerusalem, a prominent rabbi says the hurricanes are meant to punish President Bush. An Islamic Web site describes Katrina's destruction as God's fair punishment for America.
And others say it is no more than the natural, historical cycle of weather, that there have always been and always will be clusters of damaging hurricanes.
"This is just the way nature behaves and I find it astounding how tremendously lucky this country's been in the past 20 years in the lack of a major landfall," said Bill Gray, a professor of atmospheric science at Colorado State University. "People need to view this as a tragedy, an event of nature that occasionally occurs, and we shouldn't blame anybody for it."
But there is another explanation, one that is highly controversial, but in the last few weeks has gained significant scientific credibility.
Some people are pointing to global warming, saying that our use of fossil fuels has helped to heat up the planet and its seas, producing much stronger hurricanes.
Warmer Water Is Fuel for Storms
Three new reports authored by prominent scientists -- published in the journals "Nature" and "Science" -- bolster that theory's credibility.
"There's good evidence to show that Category 4 and 5 storms indeed are becoming more common and a bigger part of the overall pictures of the hurricanes in the world," said Kevin Trenberth, a scientist at the government-funded National Center for Atmospheric Research.
Trenberth is the author of one of the papers, which links stronger hurricanes to warmer seas and global warming caused by humans. Global warming, he says, has caused increases in sea levels and in the temperature of the oceans, which increases water vapor in the atmosphere and provides fuel for massive storms.
Using buoys deployed across the world, along with satellites and other measurements, Unites States government scientists have tracked a steady increase in ocean temperature since about 1970.
"The global ocean temperature has gone up, and in the in tropics the ocean temperatures have gone up around .9 degrees Fahrenheit," Trenberth said.
And the recent studies show that as the surface sea temperature have risen steadily, so too has the combined yearly intensity of hurricanes.
"It's not the number of storms, it's the intensity," Trenberth said. "Once we've got a hurricane or a tropical storm, then the storms are apt to be more intense than they otherwise would be."
Trenberth calculates Hurricane Katrina was stronger and dumped an extra inch of rainfall because of global warming -- an inch that could have made a big difference.
"You've heard of the straw that breaks the camels back? An extra inch of rain in New Orleans could be the extra inch of water help helps to break a levee," he said.
More Scientists Get on Board
Many of the scientists at the National Hurricane Center have long been skeptical of linking global warming to more powerful hurricanes. But the former director of hurricane research at NOAA Hugh Willoughby says he has changed his mind because of these new findings.
"These three papers convinced me for several reasons," Willoughby said. "One, the people that are doing them are people whose reputations I respect a lot, and people who would tend to be skeptical."
Willoughby also says the data on increasing surface sea temperatures are hard to ignore.
"If you're a hurricane, that's where you want to be," he said. "It gives you a chance to be an overachiever, like Rita or like Katrina. And that was the thing that provided the energy to let these hurricane turn into, you know, the monster hurricanes that they've become."
Willoughby says government leaders need to pay close attention to the findings that global warming will mean more rainfall in hurricanes.
"If you think about it, raining more doesn't seem like a problem, but Hurricane Jeanne rained an awful lot in Haiti last year and killed 3,000 people," said Willoughby. "Global warming makes this nasty weather nastier. It's getting harder and harder to stick with the, 'There ain't no global warming'...That's harder and harder to say."
Of course, not everyone is convinced. Meteorologist Bill Gray doesn't buy it, because he doesn't even buy the concept there is global warming.
"The humans aren't doing it," he said. "It's nature and it is the nature that's causing all these changes, and we can't do anything about that."