The permafrost capping the top of the world is irreversibly thawing and within two decades will release more carbon than it now absorbs, scientists calculate in a new study that makes this dire prediction: Up to 60 percent of Earth's permafrost will have thawed out by 2200.
Why care if you don't live in Siberia, Alaska or northern Canada, where thawing permafrost has already buckled roads and swallowed structures?
Because permafrost — which is ground that's been frozen continuously for two or more years — holds enormous amounts of carbon in the form of frozen plant matter, and adding more of that to the atmosphere would raise temperatures even higher, scientists say.
"The amount we expect to be released by permafrost is equivalent to half of the amount of carbon released since the dawn of the Industrial Age," Kevin Schaefer, lead author and a scientist at the National Snow and Ice Data Center, said in a statement. "That is a lot of carbon."
Here's another way to look at it: The carbon predicted for release through 2200 is about one-fifth of the total amount in the atmosphere today.
Earlier studies have estimated the carbon released from the "active layer" of soil a few inches above the permafrost — soil that freezes and thaws in winter and summer.
But "ours is the first study to estimate how much carbon could be released from thawing permafrost and when," Schaefer told msnbc.com.
If anything, the estimate is very conservative, Schaefer says, because it doesn't include a known "feedback" mechanism: that permafrost carbon release will certainly add to warming, which in turn will accelerate the thawing and then even more carbon emissions.
His team plans to incorporate the feedback estimate into their next modeling attempt, as well as emissions of methane, another greenhouse gas that decaying plant matter emits.
Using computer models, the team estimates that by 2200 between 29 and 59 percent of the permafrost will have disappeared.
So in less than 200 years, permafrost that took thousands of years to form will be gone, Schaefer said.
Anyone who's been to northern Alaska, where wild rides on buckled roads are part of the territory, will appreciate the visible impacts that thaw will cause.
But it's the carbon component that could have broader consequences.
The team predicted that by the mid-2020s the level of permafrost carbon emissions will mean that the Arctic will switch from being an overall "sink" that traps carbon to a "source."
Moreover, the experts wrote, that "source" impact "is strong enough to cancel 42–88 percent of the total global land sink" absorbing carbon.
Having these estimates, Schaefer said, means that policymakers trying to reach set carbon-reduction targets will "have to reduce fossil fuel emissions that much lower than previously calculated to account for this additional carbon from the permafrost. Otherwise we will end up with a warmer Earth than we want."
Schaefer expects the U.N. Intergovernmental Panel on Climate Change will incorporate his team's estimates in its next climate policy reports. And "we're working with other scientists, they are already putting permafrost carbon in their models," he said.
The study was published online this week in the peer-reviewed journal Tellus. Funding came from NASA, NOAA and the National Science Foundation.