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Time: Hurricane Rita: Global Warming the Culprit?

Evidence mounts that human activity is helping fuel these monster storms

Time magazine's Jeffrey Kruger takes on the emerging scientific evidence indicating that anthropomorphic climate change is impacting the size, strength, and timing of tropical storms.  

Nature doesn't always know when to quit--and nothing says that quite like a hurricane. The atmospheric convulsion that was Hurricane Katrina had barely left the Gulf Coast before its sister Rita was spinning to life out in the Atlantic. In the three weeks between them, five other named storms had lived and died in the warm Atlantic waters without making the same headlines their ferocious sisters did. With more than two months left in the official hurricane season, only Stan, Tammy, Vince and Wilma are still available on the National Hurricane Center's annual list of 21 storm names. If the next few weeks go like the past few, those names will be used up too, and the storms that follow will be identified simply by Greek letters. Never in the 52 years we have been naming storms has there been a Hurricane Alpha.

If 2005 goes down as the worst hurricane season on record in the North Atlantic, it will join 2004 as one of the most violent ever. And these two seasons are part of a trend of increasingly powerful and deadly hurricanes that has been playing out for more than 10 years. Says climatologist Judy Curry, chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology: "The so-called once-in-a-lifetime storm isn't even once in a season anymore."

Head-snapping changes in the weather like this inevitably raise the question, Is global warming to blame? For years, environmentalists have warned that one of the first and most reliable signs of a climatological crash would be an upsurge in the most violent hurricanes, the kind that thrive in a suddenly warmer world. Scientists are quick to point out that changes in the weather and climate change are two different things. But now, after watching two Gulf Coast hurricanes reach Category 5 in the space of four weeks, even skeptical scientists are starting to wonder whether something serious might be going on.

"There is no doubt that climate is changing and humans are partly responsible," says Kevin Trenberth, head of the climate-analysis section at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. "The odds have changed in favor of more intense storms and heavier rainfalls." Says NCAR meteorologist Greg Holland: "These are not small changes. We're talking about a very large change."

[...]

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 Yucat√°n 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." 
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Published: September 26, 2005