Did global warming cause Hurricane Katrina or make its impact worse?

Did global warming cause Hurricane Katrina or make its impact worse?

—John O”Dwyer, Hull, MA

No single storm or its intensity can be attributed to climate change alone, but scientists do believe that warmer ocean temperatures as a result of global warming may be intensifying the strength of hurricanes—and therefore could have contributed to Katrina’s fury. The reason is that warmer ocean temperatures, like those that occur in the tropics between June and November, cause instability in the lower atmosphere, which, in turn, “fuels” developing hurricanes. Thus, if ocean temperatures rise a few extra degrees above normal, it follows that the ensuing hurricanes will gain added strength accordingly.

A recent study by climatologist Kerry Emanuel of the Massachusetts Institute of Technology (MIT) concluded that tropical storms and hurricanes in both the Atlantic and Pacific oceans have increased in both duration and intensity by a whopping 50 percent since the 1970s. These increases have taken place over the same time period as average temperatures at the ocean’s surface, suggesting that this warming is responsible for the greater power of the storms.

Indeed, the hottest years in recorded history have been over just the last 15 years, and with worldwide industrial emissions of carbon dioxide at their highest levels ever, most scientists agree that human industrial activity is a significant culprit. Scientists have been predicting that worldwide sea level rises due to melting polar ice caps would bring about frequent flooding of low-lying areas as well as more frequent and intense hurricanes, among other weather irregularities. “My results suggest that future warming may lead to an upward trend in [hurricanes”] destructive potential, and—taking into account an increasing coastal population—a substantial increase in hurricane-related losses in the 21st century,” says MIT’s Emanuel.

Beyond reigniting debate about global warming, Katrina’s impact is also highlighting the consequences of the rapid destruction of wetlands throughout the United States. Louisiana alone has lost more than a million acres of coastal wetlands since the 1940s, and some environmental leaders maintain that the installation of the levees surrounding New Orleans a half century ago led to the decay of nearby wetlands that historically served as buffers in protecting against flooding and other storm damage.

According to the environmental organization, Ducks Unlimited, which has pledged $15 million to help restore coastal wetlands in Louisiana damaged by Hurricane Katrina, as a general rule one mile of marsh can reduce a storm surge by about one foot. “Theoretically,” explains Tom Moorman, director of conservation planning for the group’s Southern Regional Office, “if you had a healthy chunk of marsh when Katrina hit, that could have mitigated some of the damage
the storm surge that hit the Gulf Coast reached some 29 feet, the highest ever recorded. But, in New Orleans, a few miles of marsh may have made a difference.”

CONTACTS: Kerry Emanuel, “Anthropogenic Effects on Tropical Cyclone Activity,” www.wind.mit.edu/~emanuel/anthro2.htm; Ducks Unlimited, www.ducks.org.