Enter the skeptics, led by Chris Landsea (yes, that's his real name), one of the National Oceanic and Atmospheric Association's top hurricane researchers. The group is made up of meteorologists—scientists who make their living forecasting the annual shifts in hurricane activity and the paths of individual storms. It includes Max Mayfield, the outgoing director of the National Hurricane Center, who famously warned President Bush that Katrina was likely to overwhelm the New Orleans levees. Most aren't global-warming skeptics, but they have attacked Emanuel's research, the Georgia Tech study, and others that suggest a hurricane-warming tie. Their favored technique is to comb the data—which, for meteorologists, is a stock in trade—and expose inconsistencies. They point out that the quality of hurricane measurements varies depending on where and when they were compiled. The technology and standards employed by developing nations in the Pacific basin have historically lagged behind the United States and other nations around the Atlantic basin. Infrared satellite photography of hurricanes—which allows easier assessment of size and strength—didn't begin in earnest until the 1980s. All of these problems, argue the skeptics, fatally compromise the global trend lines that show we're in an emerging era of souped-up megastorms. In a paper published in May, Philip Klotzbach of the University of Colorado—who issues well-known annual hurricane forecasts with William Gray—curtly dismissed the Georgia Tech study's conclusions about more big hurricanes: "Most of this increase is likely due to improved observational technology. These findings indicate that other important factors govern intensity and frequency of tropical cyclones besides SSTs (sea surface temperatures)."
Instead, Landsea and his colleagues have placed their chits—at least as far as the western Atlantic and neighboring eastern Pacific, the main focus of their own research—on a phenomenon called the Atlantic Multidecadal Oscillation. The AMO consists of decades-long ups and downs in sea-surface temperatures. Landsea and his colleagues say it is principally responsible for the sharp rise in hurricane activity since 1995. While a significant leap, they say, it doesn't diverge from dramatic shifts measured over the past century. (One reason storms seem more severe, they correctly note, is that there is simply more human settlement along the coastlines than in the previous up-cycle during the 1920s to the 1960s—ergo, more stuff gets destroyed now than used to.)
Landsea argues that if ocean temperatures are going up, and the worldwide trends toward bigger hurricanes are overstated or nonexistent (he and his allies tie the rise in the Atlantic basin to the AMO and dispute studies that say the same thing is happening elsewhere around the globe), then global warming can't be having much effect. Plus, many other things affect hurricane strength—for example, the shifting pattern in the prevailing winds in the upper atmosphere. Close to the tops of hurricanes, the vertical wind shear—varying wind speed at different altitudes—can make or break a storm. If wind shear is high, it can literally lop off the tops of thunderstorms, stifling nascent hurricanes. And if wind shear is low or nonexistent, hurricanes will flourish unimpeded. No one has yet tied changes in wind shear to global warming.
As it happens, vertical wind shear is particularly hard to incorporate into the global computer models used by scientists chasing the global warming link. And therein lies the chief difference between the two camps. It's not a difference of opinion, but of basic perspective, how different cliques of scientists view the world quite differently. The groups represent two distinct nerd archetypes. The meteorologists of the Landsea group are saying, we know better than anyone how the weather works, and you're oversimplifying it. They're more detail- and history-oriented, involved in short-term forecasting—workaday nerds, in other words, and temperamentally more conservative. "Hurricane forecasters are focused on what is the hurricane out there going to be doing in the next 24 hours," Emanuel says, "and that's not going to have much to do with global warming." And, indeed, their main objections are not a direct rebuttal of the theory on global warming and hurricanes, but a chipping away at the foundations, the data. They have kept their opponents busy rebutting their critiques, but have not really presented a clear argument why global warming should not be disrupting whatever natural cycles exist out there.
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