Some say the death and destruction in Asia are symptoms of climate change and that we can expect worse to come—unless we cut back on emissions of greenhouse gases. Coincidentally, negotiators from around the world are meeting in Warsaw, Poland this week and next to attempt to hammer out a deal that would do just that. But cuts in emissions of greenhouse gases may not be the best way to address the threat of hurricanes and typhoons, even if climate change is making them worse.The terrible toll of Typhoon Haiyan—estimated to have killed more than 4,000 people—reminds us of the often awesome power of the weather.
When it hit the Gulf of Leyte in the Philippines, Haiyan had sustained winds of 145 mph, with gusts of up to 170 mph, making it comparable in intensity to the Great Galveston Hurricane of 1900, which had winds of approximately 145 mph at landfall on the Texas Coast. The loss of life in Leyte, currently estimated at between 3,600 and 4,500, may ultimately be as great or greater than Galveston, where between 8,000 and 12,000—a quarter of the town’s population—are estimated to have died, making it the most deadly natural disaster in U.S. history.
Some activists claim that Haiyan is a symptom of climate change and that it should be a wake-up call to take action to cut emissions of greenhouse gases. Even theologians are getting in on the act, saying that the typhoon is the result of the sin of climate denial! But those may not be the most appropriate lessons. First, because it is far from clear that global warming is leading to an increase in the number or intensity of typhoons and hurricanes. Second, and more importantly, even if global warming does result in more extreme weather events, cutting emissions will likely do little to reduce the damage they inflict, while potentially costing a great deal, thereby reducing people’s ability to take preventative or ameliorative action.
In 1948, Erik Palmén showed that tropical cyclones (the scientific name for hurricanes and typhoons) only occur where sea surface temperatures reach at least 80F (26.5C). This empirical observation was later used by MIT Professor Kerry Emmanuel as a basis for claiming that a rise in global temperatures would result in more violent cyclones. But in a 2006 paper, published in the Journal Geophysical Research Letters, Philip Klotzbach showed that “accumulated cyclone energy”—a measure of the total amount of energy in all tropical cyclones from around the world—showed no trend over the twenty year period from 1986 to 2005, in spite of the rise in recorded temperatures during that period.
Of course, twenty years is a relatively short period. Unfortunately, good data on global cyclone numbers and intensity is not available for much longer periods. However, there exist reasonably reliable estimates of the number and intensity of hurricanes in the North Atlantic going back to 1851. As the figure below shows, over that period, there is no significant trend in either the total number of hurricanes making landfall in the US or the number of major (categories 3, 4 and 5) hurricanes making landfall.
Moreover, as the figure below shows, there is essentially no correlation between the temperature of the sea surface in the Northern tropics (where the majority of hurricanes are initiated), as indicated by the green line, and either the number of hurricanes (blue) or the number of major hurricanes (red) making landfall in the U.S.
For longer-run estimates of tropical cylone numbers in other regions, data is generally less reliable. One of the best efforts comes in the form of a 2004 paper published in the Annals of the American Association of Geographers, which reports on an analysis undertaken by two researchers at the University of Louisiana, Kam-biu Liu and Caiming Shen and a colleague at the University of Hong Kong, Kin-sheun Louie, who used semi-official local gazettes, called Fang Zhi, from China’s Guangdong province, to reconstruct the Typhoon record going back 1,000 years (calibrating their data using reliable observations from 1884-1909). As the authors note: “Remarkably, the two periods of most frequent typhoon strikes in Guangdong (AD 1660–1680, 1850–1880) coincide with two of the coldest and driest periods in northern and central China during the Little Ice Age.” Of course, this analysis is specific to one location and the authors note that “Conceivably, the predominant storm tracks shifted to the south during these cold periods, resulting in fewer landfalls in Japan and the east-central Chinese coast but more typhoons hitting Guangdong.” But even if that is the case, it seems unlikely that the typhoons are any more closely correlated to sea surface temperature than are hurricanes.
In a 2010 paper published in Environmental Research Letters, Professors Ryan P. Crompton of MacQuarie University in Australia, and Roger A. Pielke, Jr. and K. John McAneney of the University of Colorado at Boulder, estimated the time that it would take for signals of human induced climate change “to emerge in a time series of normalized US tropical cyclone losses” and concluded that “[U]nder the projections examined here, the detection or attribution of an anthropogenic signal in tropical cyclone loss data is extremely unlikely to occur over periods of several decades (and even longer). This caution extends more generally to global weather-related natural disaster losses.”
In a subsequent blog post commenting on a recent paper by Kerry Emmanuel, Prof. Pielke reaffirms that “the time to detection of a signal of human-caused climate change, assuming that recent projections are correct, is a long, long time. Like, not in our lifetimes and certainly not now.” So, if anyone claims that there is a link between human-induced climate change and losses due to tropical cyclones—or any other weather-related natural disaster losses—they are either clairvoyant or they are lying.
Given the devastation wrought by tropical cyclones, it certainly makes sense to worry about them. But does that mean—as many activists argue—that global emissions of greenhouse gases should be cut? If it were possible to cut emissions significantly at no cost, then the answer would seem to be, obviously, yes. To that end, it certainly makes sense to remove unnecessary obstacles to lower-emission technologies, such as the production of natural gas through hydraulic fracturing—which has done more than anything to reduce U.S. greenhouse gas emissions over the past decade. But even eliminating greenhouse gas emissions altogether would not stop the scourge of the tropical cyclone.
Fortunately, there are things that can be done to reduce the harm inflicted by cyclones. The response by the survivors of the Galveston Hurricane offers a salutary lesson. They built a massive sea wall, seventeen feet high and ten miles long (two feet higher than the storm surge that accompanied the 1900 hurricane). And they raised the foundations of over 2,000 of the town’s buildings, also by seventeen feet. As a result, when the town was battered again by a massive hurricane fifteen years’ later, the twelve foot storm surge caused considerable economic damage but only 53 people lost their lives.
Such responses help explain why, contrary to claims by some scientists activists, tropical cyclones have become less deadly over time. In the 25 years from 1960 and 1984, approximately 500,000 people died during tropical cyclones. In the next 25 years, from 1985 to 2009, that number fell by 20 per cent, to around 400,000. But over the same period, the world’s population rose by more than 30%, which means that the death rate fell from 0.51 to 0.27 per 100,000, a decline of nearly 50%. (These disaster numbers are from the World Health Organization’s Emergency Events database. The calculations, using population data from the Angus Maddison project, are in an excel spreadsheet available here.
Beyond building sea defenses and raising foundations, death rates have fallen because of the establishment of early warning systems and better infrastructure, which enable earlier and more rapid evacuation, as well as improvements in building technologies, which have meant that more people have had access the kinds of safety previously only available to the rich. After the 1900 Galveston hurricane, most of the buildings still standing were mansions in the town’s wealthy Strand District.