Melting permafrost could double amount of greenhouse gas

For the past decade, much of the focus in the Arctic has centered on the rate at which ice melts and its ecological impact. Now, as Arctic ice continues to melt, carbon that has been stored in the frozen tundra for thousands of years is creeping up to the surface and exposed to a new element: sunlight. In a new study, researchers at the University of North Carolina at Chapel Hill reveal that this newly exposed carbon could double the amount of greenhouse gases in the environment – and profoundly change the trajectory of the climate change debate.

“Organic carbon locked into permafrost stores more than twice the amount of carbon that is currently in the atmosphere,” says lead researcher Rose Cory, assistant professor of environmental sciences and engineering at UNC Gillings School of Global Public Health. “But it has always been frozen, so it has not participated in the carbon cycle for thousands of years. With the earth getting warmer, that’s all changing.”

Cory and her team studied 27 melting permafrost sites in Alaska and identified seven thermokarst failures, large patches of the arctic tundra that have melted. The melted ice causes the soil to collapse, creating either a large sinkhole, or if the slope is right, a landslide.

The researchers found that when UV light, a component of sunlight, hits the carbon it bakes it, and this “baked” carbon is more palatable to bacteria than carbon that has not been exposed to sunlight, such that the bacteria convert 40 percent more of it into carbon dioxide gas.

“Sunlight makes carbon better food for bacteria,” Cory says. “What that means is that if that stored carbon is released, exposed to sunlight and consumed by bacteria, it could double the amount of this potent greenhouse gas into the environment.”

The finding has profound implications for the debate on climate change. Cory explains that the likelihood of that doubling is great, given the circularity of the relationship: as the earth warms, the frozen arctic soils also warm, thaw and release more carbon dioxide. The release of the gas accelerates the Earth’s warming, which further accelerates the thawing of arctic soils and the release of even more carbon dioxide. 

The work appears Feb. 11 in the Proceedings of the National Academy of Sciences.

Published February 13, 2013.