By Dan Vergano, USA TODAY
Hurricanes have grown fiercer in recent decades, spurred by global warming, and even tougher storms are likely on the way, a researcher predicts.
In his new study, ocean climatologist Kerry Emanuel of the Massachusetts Institute of Technology, suggests that the power of big ocean storms has increased and will continue to do so, even if their numbers stay the same.
The analysis, released online Monday by the journal Nature, confounds some past studies that had indicated that increasing average temperatures worldwide over this century — a United Nations climate panel has projected that temperatures will rise from 2 to 10 degrees worldwide by 2100 — would have little effect on hurricanes.
"The best way to put it is that storms are lasting longer at high intensity than they were 30 years ago," says Emanuel.
In an analysis of sea surface temperatures and storms since 1930, he found that a combined measure of duration and wind speeds among North Atlantic hurricanes and North Pacific cyclones has nearly doubled since the 1970s. "I was quite surprised by the magnitude of the increase," he says by e-mail.
Scientists had not correlated the frequency, intensity and duration of the storms until now, he says, but past reports have raised questions:
• Hurricane and cyclone reported durations have increased by roughly 60% since 1949.
• Average peak storm wind speeds have increased about 50% since the 1970s.
• Sea surface temperatures have swung upwards since 1975 at rates that exceed normal swings from regular El Niño or Atlantic cycles.
Cyclones and hurricanes do follow decades-long cycles of strengthening and weakening, Emanuel says. But the study effects are above and beyond the current cycle, which has seen stronger hurricanes in recent years.
The report serves as a warning about future global warming effects, says atmospheric scientist Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo. Dollar losses from storms rise with hurricane wind speeds, the study notes. And inland damage from flooding and heavy rains also results from more intense storms, Trenberth says.
"I think that this is very good science and a very important paper, but I don't think it settles every question," says National Oceanic and Atmospheric Administration hurricane expert Chris Landsea. He wants researchers to delve further back into past hurricane records to verify the trend.
"It's a bit of a surprise," he says, given that earlier studies had suggested a warming climate would lead to only small changes in storm wind speeds.
With more people living on coasts in more expensive housing, Landsea says, the study underlines the importance of five-day hurricane forecasts, better building codes and homeowners buying shutters and storm doors.
http://www.usatoday.com/weather/stormcenter/2005-07-31-global-warming-hurricanes_x.htm
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