Sunday, August 20, 2006

Hurricanes and Global Warming

Last year's active hurricane season, which included several very powerful storms, provided a vivid foretaste of what a significantly warmer world could look like: flooded cities, high death tolls, and massive property destruction. Just as last year's active season encouraged much talk of global warming causing hurricanes, this year's relatively quiet season (so far) has brought out the skeptics. This morning's Washington Post looks at the connection between global warming and hurricane formation, and some areas of disagreement.

Scientists who doubt a link with global warming say this year's average Atlantic hurricane season simply shows how variable weather can be. Christopher Landsea, who works in the National Oceanic and Atmospheric Administration's Hurricane Research Division, published an opinion piece in the journal Science late last month in which he argued that data indicating that recent hurricanes have been more intense than those in the 1970s and '80s may be based on flawed information. Measurement technologies were less sophisticated then and may have underestimated the strength of earlier storms, he said.
The Post notes that the Pacific is more active than normal this year, unlike the Atlantic. The focus on Atlantic cycles is understandable since that affects us the most, but limited in the information it provides about global change.
Studies supporting a link between global warming and storm intensity keep coming. The latest will be published this week by Florida State University geography professor James B. Elsner in the journal Geophysical Research Letters. Elsner found that average air temperatures during hurricane season predict the Atlantic Ocean's surface temperatures, not vice versa, which he said means it is "much more likely the atmosphere is warming the ocean" and helping create more severe storms.

And Judith A. Curry, of Georgia Tech's School of Earth and Atmospheric Sciences, who co-authored a paper last year suggesting that rising sea temperatures have been accompanied by more intense hurricanes, has challenged Landsea's critique. She said Landsea and like-minded researchers have not "done the hard work" to reanalyze the entire historic hurricane database to determine whether it really is skewed. She does not go as far as Elsner, however, saying his paper identifies "an interesting statistical relationship" but does not physically explain how warmer air might be heating the Atlantic.

Curry's work, in turn, has been challenged by Phil Klotzbach, a research associate at Colorado State University, who published a paper in May suggesting that, since 1986, there has been no global trend in hurricane intensity. Klotzbach's paper, in Geophysical Research Letters, looked at a 20-year period rather than the 35-year period Curry and others examined, which explains how he reached different conclusions.
There probably will be disagreement about how to interpret these data for quite some time. The hurricane question involves both short term cycles and long term trends. The first is important for forecasting, but the latter is important for the question of what role global warming has to play. The idea of global warming causing individual storms or events, in particular, is at best unprovable, and at worst distorts the real problems we face. Activists would be best served not to go far out on a limb in the meantime; making claims that current research cannot support adequately may end up undermining serious efforts in the long run.