The Fragile Gulf

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The Gulf's busy oil-and-gas industry doesn't help matters. Extracting those resources below the Gulf floor is like sticking a straw into the ground and sucking out all the liquid: ultimately you pull up the very material that's holding up the surrounding terrain. One study found that the greatest loss of Gulf wetlands coincided with the greatest extraction of oil and gas in the 1970s and '80s. Houston is thought to be sinking for much the same reason.

In Louisiana, the shrinkage is most dramatic. The state has lost 1 million acres of coast--11/2 times the area of Rhode Island--since 1930, nearly half of that vanished land lying between New Orleans and the Gulf. The city proper is estimated to be sinking 3 ft. per century. And while the whole world is struggling with rising sea levels, New Orleans and its environs hurt more than most. The State of Louisiana is estimated to be losing land at the alarming rate of about two acres every hour.

The forces that have caused the coast to subside are pretty well understood. What's far less clear is the possible role of global warming. That rising temperatures heat the ocean and melt ice caps is undisputed. Most climate models also predict that turning up the worldwide thermometer will lead to more extreme weather patterns--hotter hots, colder colds, harder rains. Hurricanes would seem to be especially sensitive to climate changes, since warm ocean waters are the fuel that drives the storms.

But while that is an easy argument to make, it's a hard one to prove. There were a record 33 hurricanes in the Atlantic between 1995 and 1999, and that doesn't take into account blockbusters like Katrina or 1992's Andrew. But the period from 1991 to 1994 was one of the quietest in history. And while the Pacific has seen an increase in hurricanes and typhoons in recent years, the southwestern Indian Ocean has remained stable and the northern Indian Ocean has actually seen a drop. Around the world, all that amounts to a statistical wash. "It's an unresolved issue," says atmospheric scientist Kerry Emanuel of the Massachusetts Institute of Technology, "but we do not see any increase at all in the frequency of hurricanes globally."

Emanuel and others believe that even if greenhouse heating does not spawn more hurricanes, it may make the ones that do occur more powerful. In an extensive study published this summer in the journal Nature, Emanuel surveyed roughly 4,500 storms brewed in the North Atlantic and western north Pacific since the middle of the 20th century. He found that the average power of the storms increased 50% in those 50 years. It's a change that, he has little doubt, is linked to global warming. A slightly weaker Katrina may have made all the difference to New Orleans, where the levees were made for withstanding a Category 3 storm but not the more powerful Category 4 (like Katrina when it made landfall) or Category 5 (like Katrina the day before).

As the city staggers back to its feet, fixing those broken levees will be a first priority. But such gap plugging is just triage in a woefully outdated system of ramparts that need extensive rebuilding and modernizing. The failed 17th Street levee had been strengthened not long before Katrina hit--an upgrade that obviously did not do the job. Now merely pumping the city free of the water the levees let in may take as long as nine weeks.