Increased levels of carbon dioxide in the atmosphere are likely to raise sea surface temperatures, which in turn will trigger more powerful hurricanes in the western Pacific, according to a team of U.S. climate modelers. The finding , published today in Science, removes some of the uncertainty behind earlier studies that lacked the resolution to simulate individual hurricanes.
The work, by a group at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, simulated 51 storms in the western Pacific that developed under current atmospheric and sea surface temperature conditions. They compared the results with storms brewing in a world where C02 levels had risen by 1% a year, doubling in 70 years and more than tripling in 120 years. The projected greenhouse warming would raise tropical sea surface temperatures by 2.2°C, resulting in hurricanes that pack maximum winds an average of 10 miles per hour higher, the group's model suggests.
In 1995, the Intergovernmental Panel on Climate Change reported that it could not determine how typhoons--the name for hurricanes that arise in the Pacific--might be affected by increased atmospheric C02 levels. But meteorologist Thomas Knutson, a co-author on the paper, says the lab's new combined global-hurricane model "is the first with a resolution fine enough to simulate the storms' structures realistically." The actual force of the most intensive storms could be even greater than forecast, he adds, "because even the model's improved resolution can't mimic real storm dynamics perfectly" and tends to understate maximum wind speeds.
The new work confirms other recent research on how CO2 levels affect a hurricane's punch, says Kerry Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology. But he says it leaves open such questions as how higher levels and warmer oceans might change the frequency and average intensity of storms: "The only thing we can say with confidence is that the speed limit increases with temperature. [For the rest], we just plain don't know."