American Scientist

Most scientists specializing in hurricane studies work primarily to increase their physical understanding of the dynamics and thermodynamics of hurricanes and to improve the ability of meteorologists to forecast a storm's track and intensity. Until recently, only a few of them were involved in research related to climate change, but over the past few years, the topic has received a great deal more attention. Interest in it has been piqued by an increase in North Atlantic hurricane activity.

A comparatively quiet period for hurricanes in the 1970s and 1980s came to an abrupt end with the very tempestuous season of 1995, and since that time, activity has in general been unusually high. Of particular note, in 2004 Florida was struck by no fewer than five named storms, and the 2005 season was the most active on record. The devastation brought about by Hurricane Katrina that summer and the record-breaking intensity of Hurricane Wilma just two months later focused the public's attention on hurricanes.

Questions quickly began to surface. Was global warming contributing to upward shifts in hurricane intensity and frequency? If so, how much of this upsurge could be attributed to human activity? Sea-surface temperatures, known to be important to hurricane strength, had been anomalously high in the tropical Atlantic in recent years. Two articles statistically linking those warm temperatures to hurricane activity appeared around the time of Katrina's landfall: In the August 4 issue of Nature, Kerry Emanuel showed a correlation between Atlantic sea-surface temperatures and what he referred to as the power dissipation index (a measure of storm activity that depends on the frequency, duration and strength of storms). And in the September 16 issue of Science, Peter Webster and colleagues maintained that the number of the most intense hurricanes was increasing—a pattern that also followed rising water temperatures.

The implicit take-away message from the articles was that global warming was contributing to the increases in ocean temperatures in the Atlantic, which in turn were fueling hurricane activity. These two publications stimulated a significant and often heated scientific debate, which became fodder for the media during the aftermath of Katrina and for the remainder of the hyperactive 2005 season. As public interest in the topic grew, so did the number of scientists taking an interest in the question of whether climate change was behind all this hurricane activity. Hurricane research, previously somewhat provincial, became more global in scope and acquired a new sense of urgency.

The influx of new researchers and the heightened awareness of the social and economic consequences of any increase in the frequency and intensity of storms brought with it a level of debate not previously seen in the community of hurricane scientists. The big questions were these: Is hurricane activity increasing in concert with global temperatures, or are we just witnessing the crest of a natural cycle? And if hurricane activity is in fact increasing as the world warms, just how much of the increase can one pin on anthropogenic influences? Animosity and open hostility sometimes arose between scientists whose positions on these questions differed, and some disparaging statements found their way into the press. At its lowest points, the discussion degenerated into name calling and ad hominem attacks.

In Storm World, journalist Chris Mooney carefully guides the reader through this turbulent sea with a refreshing combination of objectivity and humanity. Like most good stories, this one has its share of interesting characters, and Mooney describes them with evenhandedness and, in many cases, humor. In describing a debate characterized by lines drawn in the sand, Mooney seems to step effortlessly between the two sides, providing a fair and unbiased view of the issues.

The book begins with a brief but accessible introduction to the physics of hurricanes and offers a concise history of the field. Because the science is largely rooted in the mathematical formulations of fluid dynamics but also relies heavily on empiricism to advance understanding and improve forecasting, the field has always had the right ingredients for conflict between scientists from opposing camps. Mooney does an admirable job of describing this long-standing "theory versus empiricism" dichotomy, thereby setting the stage for the more contentious debates in the post-Katrina era.

The remainder of the book is devoted to a nuanced account of the major areas of disagreement over the possible effects of global warming on hurricanes. Much of the controversy has arisen from questions about the accuracy of the historical records of tropical cyclones—a generic term that encompasses the hurricanes of the North Atlantic and Eastern North Pacific and the typhoons of the Western North Pacific as well as the cyclones of the Northern Indian Ocean and the Southern Hemisphere. Various international governmental agencies record the positions and strengths of active tropical cyclones every 6 hours, and then at the end of each year, these records are appended to a historical archive. However, the collection of this data was never designed for the consideration of long-term trends. These records are heterogeneous in that the presence and intensity of storms was measured using the best means available at the time. But because the technology for doing so evolved and improved over the years, time-dependent biases may have crept into the data, resulting in spurious trends that reflect only improvements in technology rather than actual changes in storm frequency or strength.

Although research addressing problems of incompleteness and hetero­geneity of the data is progressing rapidly, a high level of uncertainty remains about the accuracy of the long-term records, leaving unsettled the question of whether the apparent upward trend in activity is real. Adding to the challenge, the less eventful 2006 and 2007 North Atlantic hurricane seasons have underscored the random aspect of seasonal hurricane activity. This sort of year-to-year variation makes it more difficult to isolate the long-term trend in the hurricane record, particularly given the brief period for which good data are available.

Also controversial are the theoretical underpinnings of the suggested link between tropical cyclone activity and the reported anthropogenic warming of the tropical oceans. The physical connection between the surface temperature of the sea, which is inching upward globally, and the intensity of the storms that travel over and extract their energy from the warmer waters is only one part of a larger picture. Warming temperatures also affect regional patterns of atmospheric circulation, which in turn affect the number, location, duration and intensity of storms. The fact that climate change affects the circulation patterns as well as sea-surface temperatures makes the connection between hurricanes and climate change much more complicated, and this complexity introduces a great deal of uncertainty into efforts to predict the future. This uncertainty is a main source of disagreement between those who say that heightened hurricane activity will endure indefinitely and those who believe that it will continue to rise and fall in a manner that pretty much resembles the pattern of decades past.

Ideally, as evidence mounts and the physical understanding of the problem increases, meteorologists will eventually reach consensus. In the meantime, expect much scientific and political battling. The interplay among science, politics and media coverage is skillfully fleshed out in Storm World, and perhaps most important, the level of uncertainty in this rapidly evolving field is presented in an accurate and nonpartisan manner.

I strongly recommend the book to anyone who is seeking a better understanding of the issues involved or who enjoys a good story with interesting characters. Mooney has crafted a surprisingly accessible book that presents the relevant facts of a complicated issue while being fun to read.