From Baffin Island to New Orleans

Progressive, The, Dec, 2005 by Bruce E. Johansen

Water temperatures vary for reasons other than global warming. Atlantic hurricanes intensify in twenty to thirty year cycles, following changes in water temperature. We are presently in the active phase of such a cycle, aided by generally rising air and water temperatures. Thus, the number and intensity of hurricanes over Florida and the other Gulf Coast states have been unusually high during the past several years. Hurricanes also intensify under calm high pressure in the upper atmosphere, which reduces wind shear that tears them apart.

Shortly after Katrina pounded the Gulf Coast, P. J. Webster and colleagues, writing in Science, linked rising water temperatures directly to the number, duration, and intensity of tropical cyclones. The researchers found that the number of storms in the two most powerful categories, 4 and 5, had risen to an average of eighteen a year worldwide since 1990, up from eleven in the 1970s. Other studies assert that Webster and colleagues, by going back only to the 1970s, missed a cyclical peak in numbers of hurricanes during the 1960s. The argument about an increase in intensity, however, has stood up to scrutiny.

In addition to cycles in hurricane activity and warming temperatures, the coastline marshes of the Mississippi Delta that once afforded the coast some protection have been subsiding for decades, mainly because water and oil have been pumped out of the ground. The Mississippi Delta also has been laced with oil companies' transport canals, further weakening the coastline.

Each severe hurricane compounds these long-term trends. Most of Katrina's damage resulted from storm surge and flooding, rather than wind. Hurricane Camille's winds were stronger than Katrina's, but thirty-six years ago the storm surge did not reach many areas that were wrecked this year. This may be because as ice melts around the world, sea levels are slowly rising. Warmer water also expands and occupies more space.

Since 1900, sea levels have risen 12.3 inches in New York City, 8.3 inches in Baltimore, 7.3 inches in Key West, 22.6 inches in Galveston, and six inches in San Francisco. The rate of increase has been accelerating over time. (The wide range results from the rising or falling of the land itself. San Francisco is rising; the East and Gulf coasts are subsiding.)

Many scientific studies have forecast that the sea level may rise between eight and twenty inches during the twenty-first century, making life on the East and Gulf coasts of the United States precarious.

All of these factors are cumulative. In coming decades, temperatures will be higher, on average, than today. Hurricanes, when they occur, will be more severe, and the land will have subsided substantially. We can expect intensifying climate calamities, as millions of environmental refugees flee their low-lying homes with the approach of each season's storms.

Among scientists who follow the pace of global warming, I anxiety has been rising that the Earth is reaching (or may even have passed) a "tipping point," with the effects of greenhouse warming surpassing any foreseeable human ability to contain or reverse it.