Global Warming: The Culprit?

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It's not just warmer water on the surface that's powering the hurricanes; deeper warm water is too--at least in the Gulf of Mexico. Extending from the surface to a depth of 2,000 ft. or more is something scientists call the Loop Current, a U-shaped stream of warm water that flows from the Yucatán Straits to the Florida Straits and sometimes reaches as far north as the Mississippi River delta. Hurricanes that pass over the Loop typically get an energy boost, but the extra kick is brief, since they usually cross it and move on. But Rita and Katrina surfed it across the Gulf, picking up an even more powerful head of steam before slamming into the coastal states. Even if those unlucky beelines had been entirely random, the general trend toward warmer Gulf water may well have made the Loop even deadlier than usual.

"We don't know the temperature within the Loop Current," says Nan Walker, director of Louisiana State University's Earth Scan Laboratory. "It's possible that below the surface, it's warmer than normal. This needs to be investigated."

Other greenhouse-related variables may also be fueling the storms. Temperature-boosting carbon dioxide, for example, does not linger in the atmosphere forever. Some of it precipitates out in rain, settling partly on the oceans and sinking at least temporarily out of sight. But the violent frothing of the water caused by a hurricane can release some of that entrained CO2, sending it back into the sky, where it resumes its role in the warming cycle. During Hurricane Felix in 1995, measurements taken in one area the storm struck showed local CO2 levels spiking 100-fold.

So, are hurricanes actually speeding the effects of global warming and thus spawning even more violent storms? That's a matter of some dispute. While many scientists agree that this outgassing process goes on, not everyone agrees that it makes much of a difference. "The amount of CO2 given off is fairly insignificant in terms of the total CO2 in the atmosphere," says atmospheric scientist Chris Bretherton of the University of Washington in Seattle. "I am fairly confident in saying that there is no direct feedback from hurricanes."

Thus scientific uncertainty enters the debate--a debate already intensified by the political passions that surround any discussion of global warming. The fact is, there is plenty of room for doubt on both sides of the argument. Chris Landsea, a science and operations officer at the National Hurricane Center in Miami, is one of many experts who believe that global warming may be boosting the power of hurricanes--but only a bit, perhaps 1% to 5%. "A 100-mile-per-hour wind today would be a 105-mile-per-hour wind in a century," he says. "That is pretty tiny in comparison with the swings between hurricane cycles."

Skeptics are also troubled by what they see as a not inconsiderable bias in how hurricane researchers collect their data. Since most hurricanes spend the majority of their lives at sea--some never making land at all--it's impossible to measure rainfall precisely and therefore difficult to measure the true intensity of a storm.