Hurricanes, Politics, and the Battle Over Global Warming
Harcourt. 288 pp. $26
Friday, July 27, 2007
Chimneys and Whirlpools
Communities and nations, and especially their ships and navies, have been ravaged by hurricanes from time immemorial. The ancient Mayans, who dubbed their storm god hunraken, wisely built their cities inland from the coasts. The thirteenth-century Japanese blessed the kamikaze ("divine wind") for not once but twice wiping out the invading fleets of Mongol ruler Kublai Khan. In 1502, during his fourth and final voyage to the New World, the fleet of Christopher Columbus weathered a hurricane while docked at the island of Hispaniola in the Caribbean Sea.
Yet beyond scattered accounts from mariners who had lived through storms they described as whirlwinds-and ancient images from Caribbean civilizations, whose iconic depictions of the storm god featured counterclockwise spirals-hurricanes remained almost entirely mysterious up through the eighteenth century. It wasn't until 1745 that Benjamin Franklin first conceived of storms in general as collectives of wind and clouds traveling together over large areas, an insight that may well mark the beginning of modern meteorology.
In the early nineteenth century, scientific understanding finally began to penetrate the storm vortices that form over tropical oceans. Yet even then, researchers did not always see their work as an attempt to explain the nature of one particular type of storm rather than that of all storms (or at least the majority of them). An accurate meteorological taxonomy of large-scale cyclonic storm systems-one that distinguished the warm-core cyclones of the tropics from the more massive cold-core or "extra-tropical" cyclones of the middle and higher latitudes, which frequently dump snow rather than torrential rain and whose energy derives from the clash of warm tropical and cold polar air along a front-only arrived later.
In part because of this vagueness about the central object of study; in part because meteorology itself, and the massive data-gathering needed to support it, had not yet become fully established and institutionalized; and in part because modern standards governing scientific debate and disputation did not yet exist; the so-called American Storm Controversy of the nineteenth century raged on for decades. The squabble had its origins in a simple set of observations taken following a devastating hurricane. By the end, it had grown into an international conflict implicating the very nature of science, as the debate's two chief disputants split over whether storm studies should be rooted in the careful collection of data and observations or in theory-based deduction from the laws of physics.
The divide between these two approaches to conducting research-as the British physicist Ernest Rutherford famously put it, "All science is either physics or stamp collecting"-has long dogged meteorology. It reemerges at the heart of the current conflict over the relationship between hurricanes and global warming, a debate in which longtime hurricane specialist William Gray, who trained as a traditional map-reading weather forecaster, holds out for data-driven approaches even as his more mathematically inclined critics, like Emanuel, apply data as well as theory, equations, and computer models to the problem. In Rutherford's admittedly biased (and overly crude) classification scheme, Gray would be the stamp collector, Emanuel the physicist.
In the nineteenth century just as today, then, meteorologists who adopted different styles of research often arrived at different conclusions. The American Storm Controversy thus prefigured today's battle over hurricanes and climate, as well as shaping the development of knowledge about hurricanes more generally. As we'll see, the controversy's resolution shows that scientific debates, whether over the influence of global warming on hurricanes or simply over the nature of storms, can be settled by the discovery of new data, the development of new theories, or some combination of both.
The American storm saga began in 1831 when William Redfield, an amateur and self-taught weather researcher who ran a steamboat business and dabbled in a variety of scientific pursuits on the side, published a very important study in the American Journal of Science and Arts. The work presented a range of evidence suggesting that storms, and especially hurricanes, are giant rotating bodies whose winds move much more rapidly around the storm center than the storm itself moves over land or water.
The central data that Redfield used to substantiate this view came from his own experience, ten years earlier, of the devastation left behind by the great Norfolk and Long Island Hurricane of 1821, which delivered a direct hit to New York City. Even at low tide, the storm flooded the Battery and overflowed wharves, and then proceeded to rampage across New England. Shortly after it passed by, Redfield took a journey by foot through the countryside and examined a large number of trees that had been felled by it. Amid the destruction, he detected a pattern. Trees in the northwestern part of Connecticut and nearby Massachusetts had been "prostrated towards the south-east" by winds blowing hard from the northwest, Redfield observed; yet in central Connecticut, the winds at the same time seemed to have blown in the opposite direction, toward the northwest, and "fruit trees, corn, &c." had fallen in this direction. How could two locations within the same state have experienced such different winds? Redfield saw only one solution: "This storm," he wrote, "was exhibited in the form of a great whirlwind."
With this discovery, Redfield launched an influential career of storm research that culminated when he became the first president of the American Association for the Advancement of Science in 1848. Throughout that career, Redfield hewed to a strict empiricist methodology-or at least so he claimed. He collected a large array of data on storms from ship's logs and their captains, from eyewitnesses who'd been present when storms made landfall, and from other sources. When it came to theorizing, however, Redfield aligned himself with the seventeenth-century English thinker Francis Bacon, who had described science as an "inductive" process of reasoning in which open-minded investigators painstakingly gather observations about the natural world and only then seek to generalize from them, rather than beginning with a commitment to any particular theory or interpretation.
Scientists' rhetoric about methodology can diverge from their actual practices, however, and Redfield did in fact have a "theory" about the origins of hurricanes and other rotary storms, such as tornadoes. He considered these phenomena the atmospheric equivalent of water in a pot being stirred, meaning that whirlwinds and whirlpools were very similar phenomena in his mind. "The analogy between the tides and currents of the ocean, and of the atmosphere, is perhaps sufficient for our argument," Redfield wrote. In turn, Redfield ascribed the behavior of atmospheric tides to "mechanical gravitation." His theoretical account wasn't particularly convincing, however, and later, one of his own supporters faulted him for violating his principles by advancing it.
The strength of Redfield's argument lay in his data. He soon attracted a group of allies who supported and tried to extend his interpretation of storms, both by gathering together more observations and by applying them practically to ensure safe navigation for ships at sea. Redfield's work had a considerable influence on British researcher William Reid, who experienced a deadly hurricane in Barbados in 1831 and later confirmed the rotational nature of storms with much additional data, and on Henry Piddington, a former ship commander and president of Marine Courts of Enquiry in Calcutta, India. Piddington coined the term cyclone (meaning "coil of a snake") and published a book for sailors detailing what he called the "Law of Storms," which provided tips on how to steer your vessel clear of a hurricane's most powerful winds.
In the Northern Hemisphere, hurricane winds whirl in a counter-clockwise direction; in the Southern Hemisphere it's the opposite. Redfield, Piddington, and their supporters didn't understand the true reason for this (that would come later), but they recognized the value of such knowledge for safe navigation. In the Northern Hemisphere, whichever direction a hurricane is heading its right front quadrant will be the most dangerous for a ship, since the winds in this quadrant will have the storm's own forward momentum behind them. In the Southern Hemisphere, the reverse is the case. Piddington therefore counseled ship's captains to determine the direction in which a storm was moving and steer for its weakest quadrant.
For much like the work of today's Miami-based hurricane forecasters, the Redfield-Reid-Piddington school of storm studies had a strongly practical orientation. The research focused on protecting mariners from having their masts torn off by shrieking hurricane winds, and their ships engulfed by massive hurricane waves. This was not so much about scientific theory as it was about saving lives. In his 1848 book, Piddington even announced his intention to write in what he called "the familiar terms of common sailor-language," eschewing "more scientific forms of expression."
Yet even as some navigators began putting Redfield's findings about rotating storms into practice, James Pollard Espy, the so-called "Storm King," denounced them as sheer bunkum. A theorist and popularizer who in 1842 became the de facto national meteorologist with the U.S. War Department and later worked at the Smithsonian Institution, Espy had been influenced by the English chemist John Dalton, who experimented with the properties of gases and derived the first modern atomic theory. This background led him to a very different view of storms from Redfield's. Espy highlighted the key role of what we now call "latent heat" in storm development, and then used this insight to forge a theory with a strong thermodynamic emphasis, one that placed phase changes of molecules of water (most centrally, evaporation and condensation) at its very center.
Today, the concept of "latent" or hidden heat seems almost intuitive. In the process of evaporation, heat drawn from the environment allows energized molecules of water to escape from their liquid phase. A commonly used analogy is that of getting out of a swimming pool or the shower. As water evaporates from your skin you feel a chill, because heat is being pulled into the air and away from your body. The heat has now taken the form of "latent heat" and become locked within the molecules of water vapor. It will be released again into the air as "sensible heat"-heat you can actually feel-when the vapor condenses back into liquid water.
Espy combined this notion of latent heat release (or as he called it, "latent caloric") with the atmospheric process of convection-the transfer of heat upward by rising currents of air-and used it to explain the formation of clouds and rain. When the sun heats the Earth's surface, warm air rises, carrying heat as well as water vapor aloft. Indeed, the more water vapor the air contains, the more buoyant it becomes, and thus the more likely it is to rise in the first place.
As the air rises through the atmosphere, it experiences a drop in pressure as the cumulative weight of air molecules from above diminishes-the same thing that happens as you ascend a mountain. So the air expands and cools. When it cools sufficiently, the water vapor that it contains begins to condense into droplets of water or change into ice crystals, which organize into clouds. In the process, latent heat gets released, once again becoming sensible heat and thus further enhancing the ascent of warm, moist air. Soon a thunderstorm may emerge.
With this account, Espy articulated several key principles underlying the behavior of thunderstorms and, therefore, of hurricanes (which are gigantic rotating groups of thunderclouds). And he made a major step toward transforming meteorology from a purely observational science, dominated by diarists and data collectors like Redfield, into one that sought to establish universal theories based upon the behavior of heat and gases. If Redfield envisioned storms as analogous to whirlpools, you could say Espy viewed them as more akin to chimneys. And he applied his ideas about latent heat and convection to all storms in all situations, further asserting that storm winds rush straight inward, from all directions, to a central point or region where air pressure is lowest. This led him to dismiss entirely Redfield's arguments about rotating winds. For Espy, all storms were the same, and his theory captured them perfectly.
Given this position, it was probably inevitable that Espy would get drawn into a spat with Redfield over the nature of storms. Their conflict began in the mid-1830s and soon degenerated into personal attacks and accusations of underhanded data manipulation. Writing in 1835, Espy described Redfield's views as "so anomalous and inconsistent with received theories, that I hesitate to put entire confidence in them, and shall continue to doubt, until I have the most certain evidence of the facts." In a bile-filled 1839 rebuttal, Redfield countered, "I did not anticipate so complete an evasion of all the distinguishing points at issue, and so barren an effort at confusing and mystifying the most distinct phenomena of this storm, as is manifested in [Espy's] present examination." Espy, Redfield charged (in typically Baconian language), labored under the "bias of a preconceived hypothesis."
Ultimately the highly public conflict between these two scientists, amplified by the participation of a third scientist, the volatile Robert Hare (who thought Espy and Redfield were both wrong, and ascribed storm formation to electricity), resonated overseas. British scientists sided with Redfield, the French with Espy. The battle helped spur the growth of American meteorology, as the Smithsonian Institution set up a national network of weather observers, as well as a smaller network situated along newly established telegraph lines, to help resolve it. For many years, however, the dispute dragged on, its participants refusing to concede any ground.
Perhaps the most memorable commentary on the controversy came from Joseph Henry, the first secretary of the Smithsonian, who observed that "meteorology has ever been an apple of contention, as if the violent commotions of the atmosphere induced a sympathetic effect on the minds of those who have attempted to study them." Henry suspected future researchers would see that both Espy and Redfield had grasped a part of the truth, and that's precisely what happened. We now know Redfield was correct to describe many storms (especially hurricanes and tornadoes) as whirlwinds. The theory of atmospheric tides that he invoked to explain his observations, on the other hand, had little to recommend it. Espy's basic theory, involving convection and the release of latent heat caused by the condensation of water vapor higher in the atmosphere, was much more sound. But he applied it too broadly and let it lead him down the wrong path with respect to the behavior of storm winds. His "centripetal" theory-that all winds blow straight inward in a storm-has died a merciful death.
The squabbling between Redfield and Espy seems to have prevented each from appreciating the other's insight. But the conflict turned as much on methodology as personalities. Redfield was a "data" guy, a perceptive observer who'd seen a pattern in the arrangement of winds and fallen trees and extrapolated from there. Espy also gathered data, pushed for the formation of weather observation systems, and experimented with the properties of gases on a small scale. But ultimately he was a theoretician who sought the grandest of generalizations-to explain storms based on the behavior of the tiny molecules that comprise them.
The struggle over these two disparate views of how to conduct research was further aggravated by the contrast between Redfield's status as a scientific amateur and Espy's popularity and institutional support. As Espy became increasingly sought after as a lecturer on storms, Redfield looked on with jealousy and resentment. Matters came to a head in 1849 when Espy, in his official capacity, submitted a report to the Navy Department that debunked the rotational theory of storms. Redfield objected that it was inappropriate for the navy to lend the "official endorsement by government" to Espy's theory. He also added that the navy's behavior was downright dangerous: Espy's mistaken understanding of storms could pose deadly risks to mariners who might come in contact with them. Redfield's complaint parallels more recent protestations (from those such as Kerry Emanuel) that in 2005, amidst unprecedented storm destruction, the National Oceanic and Atmospheric Administration inappropriately took sides on the question of whether hurricanes had been amplified by global warming.