Is Global Warming Fueling Katrina?

The people of New Orleans are surely not thinking about wind vortices, the coriolis effect or the dampness of the troposphere as they hunker down during hurricane Katrina this morning. Theyre mostly thinking about the savage rains and 140 mph winds that have driven them from their homes. But its that meteorological arcana thats made such a mess of the bayou, and to hear a lot of people tell it, we have only ourselves—and our global-warming ways—to blame.

One things for sure: hurricanes were around a long, long time before human beings began chopping down rainforests and fouling the atmosphere. To get such a tempest going, you dont need much more than ocean temperatures above 80 degrees Fahrenheit; a cool, wet atmosphere above and a warm, wet one near the surface; and a preexisting weather disturbance with a bit of spin to it far enough from the equator (at least 300 miles) so that the rotation of the Earth amplifies the rotation of the storm. The more intense the storm becomes, the more the temperature of its core climbs, accelerating the spin, exacerbating the storm, and leading to the meteorological violence we call a hurricane. And violent it can be: The heat released in an average hurricane can equal the electricity produced by the U.S. in a single year.

So is global warming making the problem worse? Superficially, the numbers say yes—or at least they seem to if you live in the U.S. From 1995 to 1999, a record 33 hurricanes struck the Atlantic basin, and that doesnt include 1992s horrific Hurricane Andrew, which clawed its way across south Florida in 1992, causing $27 billion dollars worth of damage. More-frequent hurricanes are part of most global warming models, and as mean temperatures rise worldwide, its hard not to make a connection between the two. But hurricane-scale storms occur all over the world, and in some places—including the North Indian ocean and the region near Australia—the number has actually fallen. Even in the U.S., the period from 1991 to 1994 was a time of record hurricane quietude, with the dramatic exception of Andrew.

Just why some areas of the world get hit harder than others at different times is impossible to say. Everything from random atmospheric fluctuations to the periodic warming of the Pacific Ocean known as El Nino can be responsible. But even if all these variables have combined to keep the number of hurricanes worldwide about the same, the storms do appear to be more intense. One especially sobering study from the Massachusetts Institute of Technology found that hurricane wind speeds have increased about 50% in the past 50 years. And since warm oceans are such a critical ingredient in hurricane formation, anything that gets the water warming more could get the storms growing worse. Global warming, in theory at least, would be more than sufficient to do that. While the people of New Orleans may not see another hurricane for years, the next one they do see could make even Katrina look mild.

NOAA National Hurricane Center

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New Orleans Hurricane Impact Study Area