28 September 2005
Along with ruined homes and upended trees, the recent hurricanes left behind a revived debate about global warming. While some environmentalists point to the wreckage as a kind of retribution for America's failure to control greenhouse gas emissions, right-wing talk show hosts repeat, over and over, that even if global warming did exist, there is no proof it had anything to do with Rita and Katrina.
In a way, they're all right. It is impossible to link Katrina or Rita, or any particular hurricane, specifically to global warming. This does not mean that President Bush and the rest of us should not be connecting the dots. These are natural disasters - but with human fingerprints.
Hurricanes derive their strength from warm ocean waters. Ocean temperatures have been rising over the last 100 years, along with atmospheric temperatures. Hurricanes have therefore become bigger and more destructive and are likely to grow even more violent in the future.
This cycle cannot be reversed any time soon. But one thing humans can do is to reduce their own contribution to global warming by controlling industrial emissions of carbon dioxide and other greenhouse gases. The alarm bells have been ringing for a long time, but Katrina and Rita should serve as yet another warning to an administration that has belittled the science of global warming.
The emerging hurricane problem is size, not quantity. The scientists who have studied the issue have not detected any increase in the number of hurricanes. Yet these same scientists - in research reports appearing in reputable journals like Science, Nature and The Journal of Climate - have detected increases of up to 70 percent in hurricane intensity, a measure that combines the power of a hurricane and its duration. There has been a commensurate increase in damage, mainly because more and more people have stubbornly put themselves at risk by moving to low-lying coastal areas. But the hurricanes' added strength has clearly contributed to the ever-higher toll in lives and property damage.
Being cautious folk, the scientists point out that cyclical lulls and surges in hurricane activity may also have something to do with stronger storms. But even if they are completely wrong in linking warming to intensity, which seems unlikely, global warming will have other undesirable consequences, including a significant rise in sea level. In the last century, sea level rose 4 to 8 inches around the world, and most scientists expect a further rise of 2 to 3 feet in this century.
According to one government study, a 20-inch rise in sea level by 2100 could put 3,500 square miles of the southern coast of the United States underwater - rendering efforts to restore the Everglades and the Louisiana coastline essentially pointless. A large-scale breakup of the polar ice sheets would, of course, make matters much worse. Dikes could protect some regions, like Manhattan and the Netherlands, but most coastlines would be inundated.
Humanity cannot avoid a warmer Earth and some rise in sea level, largely because of the gases we have already deposited in the atmosphere. But the worst outcomes may be avoided if the world takes concerted action to stabilize industrial emissions of greenhouse gases.
This, of course, presupposes aggressive leadership from the United States, which produces more than a quarter of these emissions. But this is a role that Mr. Bush has shown no appetite for at all.
