A Hundred Katrinas: Climate Change and the Threat to the U.S. Coast

As the atmosphere heats up and polar ice caps melt, sea levels are projected to rise significantly, sending water lapping against coastal flood defenses around the world. And if that added heat fuels bigger hurricanes, as many scientists now believe, Katrina-like storms won't strike once a century, but possibly once a generation. And if that still seems infrequent enough, consider this: For every catastrophic storm, we experience dozens of minor disasters, and many of those will strike harder, or in unexpected places. If so far you've been among the majority of Americans who haven't had to worry about floods or hurricanes, that may soon change.

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The Intergovernmental Panel on Climate Change, the global organization distilling the scientific consensus on the issue, estimated this year that seas could rise between 7 and 23 inches by the 2090s. Rising water alone will present serious problems for the United States coastline. A 2001 study by scientists at the Environmental Protection Agency estimated that about 22,000 square miles of the U.S. Atlantic and Gulf coasts lie less than five feet above mean sea level—and thus would likely be flooded by a spring high tide at some point early in the 22nd century. (About 43 percent of that area is in Louisiana, but the remaining area is equal in size to Maryland.)

It's relatively easy to prepare for a high tide. The far less predictable threat from rising seas will be storms. Not every hurricane is a Katrina, but rising sea levels increase the likelihood and the intensity of flooding even from smaller tropical storms and nor'easters. If there's an extra foot or two of water near your home, floods will be deeper, and high water that once came along just once every century may instead happen once a decade. If that weren't enough, many atmospheric scientists are now saying that a hotter planet will also add to hurricane strength, meaning more major storms, massive storm surges, and higher winds.

New Orleans is the American city most vulnerable to this threat, but it's far from the only one. Galveston, Houston, Tampa, Charleston, and even New York are also exposed, and residents all along the Atlantic and Gulf coasts, from Maine to Texas, will face increasing risks. Most of those risks have yet to be studied and quantified, in part because of the uncertainties involved, and in part because few scientists and government agencies have taken up the challenge.

In some sense, we had it coming. Ever-expanding shoreline development has steadily increased the size and costs of disasters—there is simply more stuff to be destroyed along the coast than there used to be. Worldwide, the number of major catastrophes each year has increased from two in the 1950s to about seven now, according to a study by Munich Re, the global reinsurance company. A 2006 paper by Yale economist William Nordhaus estimated that global warming would double the average annual cost of U.S. hurricane disasters—about $8 billion a year in 2005 dollars. Nordhaus also concluded that Katrina-sized disasters would occur more often due to global warming—once every 28 years on average, instead of once every 86 years. Another recent study generated an even more pessimistic number, estimating that by 2050, climate change could more than double annual hurricane losses worldwide. The threat of climate change has understandably set off alarm bells in the insurance industry. A United Nations task force composed of representatives of leading reinsurers and financial service companies concluded back in 2002 that "the increasing frequency of severe climatic events, coupled with social trends, has the potential to stress insurers, reinsurers and banks to the point of impaired viability or even insolvency."

What's the best approach to this problem? A 2005 report by the Association of British Insurers suggested that reducing carbon emissions could reduce insured losses from extreme weather events by 80 percent, or $35 to $50 billion per year, the equivalent of two Hurricane Andrews. But Roger Pielke Jr., a professor of environmental studies at the University of Colorado, says that even if the world enacts the principal fix for global climate change—reducing carbon dioxide emissions—it will probably be too slow and indirect to have much effect on disasters. Instead, he suggests nations do it the old-fashioned way—either protect people or move them out of harm's way.

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