"These petroleum seeps appear to be activated by periods of climate change," Hill said. "If the Earth is already in a mode of warming, they 'turn on' and become more active, which promotes further warming."
Methane hydrate—a solid form of methane embedded in glacier deposits—is the catalyst that touches off this warming cycle, Hill believes.
As glaciers begin to melt, methane hydrate is expelled from lattices of frozen water molecules.
"When methane hydrate is released, you have a lot of sediment movement. Landslides can occur, and you get big pockmarks in ocean sediments where bubbles of methane come out," Hill said.
"When you cause that much disturbance, you create an avenue for more petroleum-derived methane and oil to come to the surface."
(Related story: "Plants Exhale Methane, Add to Greenhouse Effect, Study Says" [March 2006].)
Catastrophic Results
In the past, geologists have proposed that much of the methane in the atmosphere is a result of emissions from swampy wetland areas such as the Florida Everglades, located on the southern tip of the peninsula (map of Florida).
But if large amounts of unaccounted-for methane begin emanating from ocean sources during the current warming period, the effects could be catastrophic, says Arlene Fiore, a physical scientist with the National Oceanic and Atmospheric Administration in Princeton, New Jersey.
"Methane is a very potent greenhouse gas, so the climatic implications of adding more of it to the atmosphere are grave," Fiore said. "A massive methane release could also affect the atmosphere's ability to cleanse itself."
Typically, pollutants such as nitrogen dioxide and carbon monoxide are neutralized when they bind to hydroxyl (OH) molecules that occur naturally in the lower atmosphere, Fiore says.
But if too much methane were released within a short period of time, it could bond with many of those molecules, leaving fewer to mitigate the effects of other emissions.
(See National Geographic magazine's "Global Warning: Signs From Earth.")
Despite methane's potential to accelerate global warming, the University of California's Hill says that no reliable cleanup strategy has yet been developed.
"We can't control this particular source of methane," she said. "The wiser thing to do would be to think about controlling our overall greenhouse gas emissions. There's a lot more carbon dioxide than methane in the atmosphere."
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