Sometime in the next 20 years, Arctic soil that has been frozen since the last ice age will begin thawing in response to rapidly warming polar temperatures and start releasing a vast reservoir of carbon into the atmosphere. A new study puts the first numbers and dates on these “irreversible” permafrost emissions, and it looks like enough to kick the global warming trend into another gear.

The carbon is released by the decay of roots and other organic material exposed to the atmosphere after thousands of years of being locked away in the deep freeze of permanently frozen Arctic dirt.

NEWS: Melting Arctic Could Unleash Vast CO2 Stores

Research scientist Kevin Schaefer at the National Snow and Ice Data Center in Boulder, CO, and colleagues, writing in the journal Tellus, estimate that by 2200, the melting of up to 60 percent of the Northern Hemisphere’s permafrost could add some 190 billion tons of carbon to the atmosphere.

Schaefer says 190 gigatons is “equivalent to roughly half the total fossil fuel emissions since the dawn of the industrial age.” Looked at another way, he says, it represents about 20 percent of the total amount of carbon in the atmosphere today.

The researchers identify a positive permafrost carbon feedback effect on the climate, although they are not yet able to provide estimates of the impact of this feedback on global warming.

“Carbon emissions from thawing permafrost will accelerate or amplify the warming due to the burning of fossil fuels, Shaefer said in an email to Discovery News. “However, we cannot state at this time the exact increase in temperature. We plan to make such estimates in our next round of simulations.”

Those estimates could be crucial to achieving whatever emissions targets may be sought in the years ahead.

“The thaw and decay of permafrost carbon is irreversible and accounting for the PCF (permafrost carbon feedback) will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration,” the scientists write.

Image: Location of Permafrost in the Northern Hemisphere. Glaciers and the Greenland Ice Sheet are violet, and Arctic Sea Ice is light blue. From NSIDC/Wikimedia Commons.