Storm world hurricanes, warming, and scientific uncertainty: regardless of how the scientific controversy is resolved over global warming's possible effects on hurricanes, our coastlines are increasingly vulnerable. And the hurricane-climate battle has lessons for scientists working in all controversial areas

What follows is an adaptation from Chris Mooney's new book, Storm World: Hurricanes, Politics, and the Battle over Global Warming. Mooney is Seed magazine's Washington correspondent, a SKEPTICAL INQUIRER contributing editor, and a Committee for Skeptical Inquiry consultant. Having watched as his mother lost her New Orleans home in Hurricane Katrina, he set out to examine the high stakes scientific debate over how hurricanes may be changing because of our changing climate. What resulted, Mooney notes, was "a narrative of scientific understanding developing in real time, in all of its inevitable messiness, under immense political pressure and in the full glare of media scrutiny. Scientists, like hurricanes, do extraordinary things at high wind speeds. Such conflicts may bring out their human side, but also inspire their very best work."

Now, in this excerpt from the book's conclusion, Mooney reflects on what he has learned--about the science but also about hurricane policy and high-profile scientific debates, in general.

There's no doubt about it: Global warming--which is already happening--will change hurricanes. If we know anything about these storms, its that they respond sensitively to conditions in the atmosphere and oceans. Human beings are already changing the environments in which hurricanes form and attain their terrifying strength, which means hurricanes will inevitably change, too. Precisely how and to what extent remains very much unsettled, however, and that makes all the difference.

Despite everything they've learned about hurricanes during the decades since World War II, scientists still do not completely understand all the environmental factors that cause them to develop and deepen. And global warming, which ought to intensify the average hurricane, could also change the regions of storm formation or the numbers of storms that form in the first place. Despite troubling signs, the evidence simply isn't in on all of these changes--not yet. And whatever does ultimately happen, it is unlikely to be simple or straightforward. "Welcome to the wonderful world of projections," says Greg Holland, a hurricane specialist at the National Center for Atmospheric Research in Boulder, Colorado, who has grown increasingly convinced of global warming's discernible impact on hurricanes.

To further complicate matters, the extent of global warming itself depends on our own choices about energy use, population size, and much else in the coming century--including the policies we adopt (or fail to adopt) to restrain greenhouse gas emissions. With all of these variables, the precise global average temperatures that we'll see by 2100, or 2200, can't possibly be predicted. That makes their ultimate impact on hurricanes all the more uncertain.

To grasp just how complex it all really is, consider the well-established effect of El Nino upon hurricanes, which is brought about, among other factors, by the modulation of so-called vertical wind shear over the Atlantic (when winds at different altitudes blow in different directions or at different speeds, they can disrupt the organized structure of a hurricane). Thanks to the pivotal discoveries of scientists beginning with the famed Colorado State University hurricane scientist (and global warming skeptic) William Gray, we now know that El Nino tends to suppress hurricanes in the Atlantic but increase their activity in the Pacific. But how will global warming alter the frequency and strength of what scientists refer to as the El Nino--Southern Oscillation, or ENSO? At this point the question isn't remotely settled, though it makes sense that some type of change ought to occur. If it does, that throws another huge curveball into the hurricane-global warming discussion, particularly as it affects the United States.

Clearly, then, we can't give an exact answer about how global warming will modify hurricanes. Yet just because we can't perfectly quantify changing levels of risk doesn't mean we have no right to feel concerned.

It's an increasingly well-established result of climate science that the heating up of the world's oceans, including the warm pools of the tropics where hurricanes spin up after being triggered by various types of disturbances, has a large human component to it. Meanwhile, scientists going back to the pioneering tropical meteorologist Herbert Riehl have taught us that hurricanes are natural "heat engines" reliant upon ocean warmth for their power, even as modern theoretical and modeling accounts--including the work of MIT hurricane theorist Kerry Emanuel, the National Center for Atmospheric Research's Greg Holland, climate modeler Thomas Knutson of Princeton's Geophysical Fluid Dynamics Laboratory, and others--agree that global warming ought to intensify the average hurricane (though these theoreticians and modelers are still trying to work out precisely how much). Finally, although skeptics remain, at least for the Atlantic there are grounds for suspecting that global warming is contributing to a sharp rise in the total number of storms that form each year, as well as--inevitably--the number of very powerful hurricanes. Not only has a trend emerged; some leading scientists think we're its cause.