Metrics Spin: Atmospheric Scientists Spar in a Cordial Debate

Kerry A. Emanuel, professor of atmospheric sciences at the Massachusetts Institute of Technology, believes the active hurricane seasons of 2004 and 2005 in the United States are due to warmer seas and hotter atmospheres, in part because of global warming.

Speaking at the annual conference of The Bond Market Association earlier this year, the noted atmospheric expert said increases in the number of hurricanes over the past two years, and the increase in the storms' power, is "very well correlated with sea surface temperatures."

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In addition, he said, there was little evidence to sustain the theory that hurricane activity is related to what are called "multidecadal cycles," which govern the rise and fall of sea-surface temperatures.

"It's much more likely that the longer-term trends in variability resulted from variations in trends from forced climate change," he said.

Not so fast, said Stanley Goldberg, a meteorologist with the hurricane research division in Miami for the National Oceanic & Atmospheric Administration, who also spoke at the association's annual meeting, providing a counterpoint to Emanuel's position.

In Goldberg's opinion, what he called "vertical shear," or the ability of winds in the atmosphere to tear apart a hurricane in its initial stages, also plays a big part in whether the storm season will be an active one or not.

Though Goldberg agrees that warmer sea temperatures are a factor in the more frequent formation of hurricanes, he also said there's enough data to show a cyclical activity of Atlantic storm seasons over the past 130 years.

The fact that storms are more intense today may simply be a function of our ability to gather better data about the storms, he said. In addition, home and business development has exposed billions of dollars worth of property where once there was empty marsh. As a result, a Category-3 hurricane that makes landfall today is likely to cause far more damage than a similar storm making landfall 50 years ago.

The two experts delivered their comments in June, shortly after weather forecasters predicted the 2006 hurricane season would be an active one, actuaries and analysts were back at their drawing boards recomputing hurricane risks, and insurance buyers were recovering from the shock of premium increases levied by carriers and reinsurers to pay for property damage incurred in 2004 and 2005.

In the end, the 2006 hurricane season turned out to be a very tame affair, with not one storm hitting the U.S. mainland.

December 1, 2006

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