15 October 2005

Hurricanes & Climate Change

Color-enhanced Sea Surface Temperature 50 KM Global Analysis,11-14 October 2005. Archived at the National Climatic Data Center.

Last year, four successive hurricanes crisscrossed Florida; this year Katrina, Rita, and Stan have pummeled the Gulf of Mexico region. According to CNN, tropical storm Vince "strengthened briefly to a hurricane, making 2005 officially the second-busiest hurricane season on record." Vince made landfall in Spain, the first time a cyclone has struck that country in recorded history.

Has this hurricane season been stronger than normal? Is global warming to blame? While pinning the blame on global warming for any single extreme weather event is facile, some recent studies do show an alarming rise in the intensity of tropical storms. Intensity is linked to rising sea surface temperatures. It is widely known that such storms gather strength from warm ocean waters; therefore, as ocean temperatures rise it's likely we'll see more storms of greater violence.

In a recent issue of Science, Peter Webster and Judith Curry document a "60 percent jump in major hurricanes with winds of 131 mph or more and a 1-degree increase in the tropical ocean surface temperature." The study claims that category 4 and 5 hurricanes -- the most intense -- have doubled in the tropics in the last 35 years. Nevertheless, they also warn that more study is needed, given how little is known about the patterns of hurricanes throughout history.

Back in August, NOAA experts determined there were optimal conditions for hurricanes this season, including unusually warm ocean surface temperatures and low wind shear. They upgraded their prediction to "11 to 14 tropical storms from now [then] through November, with seven to nine becoming hurricanes." The greatest hurricane season on record was 1933, "when 21 systems reached tropical storm status or greater. The next most violent year was 1995, with 19 storms."

Thus far, CNN reports, 2005 "is one of the fiercest on record, with more than 17 named storms and nine hurricanes." Not all have hit land, but we have seen the results of those that have and it isn’t comforting. This summer also brought us the earliest Category 4 hurricane recorded in the Caribbean, Dennis, which hit Cuba and Haiti before landing in west Florida from 4-11 July.

Not everyone believes there is a link between the violence of this hurricane season and global warming. Last month, Max Mayfield, director of the National Hurricane Center, told a Senate subcommittee that this is part of a natural cycle that began in 1995 and could last another decade. According to Mayfield, this is "driven by the Atlantic Ocean itself along with the atmosphere above it and not enhanced substantially by global warming."

However, Brenda Ekwurzel, a climate scientist with the Union of Concerned Scientists told CNN in September that, "warmer oceans are converting low-grade storms into powerful hurricanes." She said that warm water to a hurricane is "like throwing gasoline on a fire."

While Webster and others feel secure that global warming may not have an impact on hurricane generation "for another 100 years," most agree the debate on the issue is healthy for science, especially if it leads to further study of one of Mother Nature's cruelest aspects.


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