Bigger, Badder Tropical Blows
Katrina's fury had not yet subsided last week when Germany's environment minister sparked a minitempest of his own. Writing in the Frankfurter Rundschau newspaper, Jurgen Trittin suggested that the hurricane's severity was at least partly a result of global warming and charged that "the American president is closing his eyes to the economic and human costs" of refusing to sign the Kyoto Protocol, which seeks to limit production of climate-warming greenhouse gases.
Trittin's message of "you asked for it" certainly won't be winning him any awards for tact. But with this year threatening to overtake last as the most expensive American hurricane season ever, it's hard not to wonder if maybe he has a point. Are hurricanes getting worse? And if so, is global warming to blame?
Simple enough questions, but the answers are less so. There certainly have been more Atlantic hurricanes recently. According to the National Oceanic and Atmospheric Administration, the Atlantic has kicked up an average of 7.8 hurricanes and 3.8 major hurricanes per year since 1995, compared with an annual average of just five hurricanes and 1.5 major hurricanes over the preceding 25 years. But most scientists agree that the increased frequency is caused by a natural cycle, not global warming. And over the past 50 years at least, increased numbers of hurricanes in the Atlantic are generally offset by fewer tropical cyclones in the Pacific and Indian oceans; the global average is holding steady at about 90 per year.
Still, there is growing evidence that global warming is making the storms stronger and wetter. For all the unstoppability of a fully formed hurricane, a nascent tropical cyclone is a fairly fussy thing, says climate researcher Tom Murphree of the Naval Postgraduate School in Monterey, Calif., requiring just the right conditions in the sea and the air to develop into a destructive powerhouse like Katrina. In a June article in Science, head climate analyst Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo., warned that global warming may already be nudging some of those conditions--like warm surface waters and increased moisture in the air--in directions that intensify storms.
Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology, thinks he has found evidence of that trend. In a study published last month in Nature, Emanuel calculated the intensity and duration of tropical cyclones for the past 75 years, estimating each storm's destructive power. "When you look at the numbers globally," he says, "you see a 70 to 80 percent increase in the potential destructiveness of tropical cyclones over the last 30 years. That's much more than anyone expected." And that surprising jump, he says "is strongly in concert with increases in the tropical sea surface temperature over the same time period." Many oceanographers are convinced that those warmer seas are the direct result of human-caused global warming.
Building boom. Even though hurricane activity along the Gulf Coast and up the Atlantic is expected to stay high for years, and maybe even intensify, official warnings and expert opinion apparently do nothing to dampen people's desire for living on or near the water. "People think a hurricane might not hit, or it might not flood, for 20 years," says Chip Law, an insurance industry analyst with SNL Financial, a research firm. Coastal development in the hurricane zone has been booming for years, he says, and even after Katrina, "it's not going to slow down."
Understanding hurricanes better may help scientists predict their severity. But thanks to the building boom--aided, in some cases, by taxpayer-backed federal flood insurance--limiting storm damage in the future won't depend on brilliant atmospheric science nearly so much as it will on common-sense planning and regulation.
TRACKING HURRICANE HISTORY
The specific conditions that control hurricane formation in the North Atlantic are still somewhat mysterious, but scientists know that busy hurricane seasons tend to come in cycles of two to four decades. There have been two slow periods over the past century, and the current busy phase started in 1995.
[labels]
22 years (1903-1925)
44 years (1926-1970)
23 years (1971-1994)
9 years (1995-2004)
Hurricane paths
Source: NOAA
Rob Cady-- USN&WR
This story appears in the September 12, 2005 print edition of U.S. News & World Report.
advertisement
