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The pace of permafrost thawing is "accelerating," says Vladimir Romanovsky, who runs the University of Alaska's Permafrost Laboratory in Fairbanks. He expects widespread degradation will start in a decade or two. By mid-century, his models suggest, permafrost could thaw in at least a third of Alaska and by 2100, in two-thirds of the state.

"This rapid thawing is unprecedented" and is largely due to fossil-fuel emissions, says Kevin Schaefer of the National Snow and Ice Data Center in Boulder, Colo. He says it's already emitting its own heat-trapping carbon dioxide and methane, but the amount will skyrocket in the next 20 to 30 years. "Once the emissions start, they can't be turned off."



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"We're on the edge of a major transition point," Schuur says, pointing to a 2013 report he authored that found tundras worldwide may already be emitting more carbon than they absorb. He says global permafrost emissions will be significant — akin to those from current deforestation — but probably much less than those from power plants, cars and other burning of oil and gas.

These emissions weren't included in the global warming estimates developed by the Intergovernmental Panel on Climate Change (IPCC) and released in September as the first part of its Fifth Assessment Report. The report, which said with heightened certainty that humans are responsible for the planet's rising temperatures, serves as a basis for negotiating future climate treaties.