Some 55 million years ago, during the Paleocene epoch, the earth entered into a period of global warming that would last 100,000 years and eventually raise the temperature by 13 degrees Fahrenheit. The event that sparked this episode, scientists have proposed, was a tremendous release of frozen methane¿a greenhouse gas¿from beneath the seafloor. Problematically, however, observations have failed to find evidence of the carbon dioxide predicted to result from methane entering the atmosphere under such circumstances. To that end, findings being presented today in San Francisco at the fall meeting of the American Geophysical Union offer new insight.

Previously, researchers thought that all of the methane released during such an event would have been converted into CO2. But using a computer simulation to model ancient climate, Gavin Schmidt of the NASA Goddard Institute for Space Studies and his colleagues showed that in fact the atmospheric molecules thought to convert methane into CO2 get depleted quickly. The excess methane then hangs around for hundreds of years and heats up the environs. "Ten years of methane is a blip, but hundreds of years of atmospheric methane is enough to warm up the atmosphere, melt ice in the oceans and change the whole climate system," Schmidt remarks. "So we may have solved a conundrum."

According to Schmidt, the study results also have implications for understanding current greenhouse warming. "If you want to think about reducing future climate change, you also have to be aware of greenhouse gases other than carbon dioxide, like methane and chlorofluorocarbons," he asserts. "It gives a more rounded view, and in the short term, it may end up being more cost-efficient to reduce methane in the atmosphere than it is to reduce carbon dioxide."

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