"If you say, 'Hey, the number of Category 4 and 5 storms has doubled since 1970,' you have to ask where is that coming from and can we accept that as true," said co-author Chris Landsea of the National Hurricane Center. "It's the data sets that are faulty."
He cited a 1970 storm that killed more than 300,000 people in Bangladesh but was not counted as a hurricane because forecasters could not estimate its intensity. Today, the storm would have been counted as a Category 4 or 5 hurricane.
"If you miss that one, it shouldn't be shocking if you're missing a whole bunch of others that didn't even hit land," he said. "More satellites with improved imagery mean that you get 'stronger' hurricanes without the hurricanes changing at all."
Landsea said his team found that while global warming might indeed be influencing hurricanes, it is probably by only about 1 to 2 percent, a much lower rate than Massachusetts Institute of Technology climatologist Kerry Emanuel found in August 2005.
Emanuel wrote, "The large upswing in the last decade is unprecedented and probably reflects the effect of global warming." Landsea said the frequency of hurricanes has increased in the Atlantic, but the intensity has not perceptibly gone up. Furthermore, the accumulated power has remained constant in other oceans, casting doubt on global warming as a cause (Martin Merzer, Miami Herald, July 28).
The study's authors recommended an ongoing overhaul of the hurricane database in order to quantify trends. "The resulting higher resolution images and more direct overhead views of tropical cyclones result in greater and more accurate intensity estimates in recent years when using the Dvorak Technique," which is a way of getting estimates from satellite pictures by measuring the difference between the temperature of the warm eye and the surrounding cold cloud tops (Chris Kridler, Florida Today, July 28).
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