Frozen carbon bomb is ticking
Thawing frozen ground will unleash yet more carbon into atmosphere
As ground, previously frozen for millennia, begins to thaw out in warmer temperatures, it will unleash vast quantities of carbon into the atmosphere, further confounding attempts to slow down global warming.
"The amount of carbon we are talking about is equivalent to half the amount of carbon released into the atmosphere since the dawn of the Industrial Age," said CIRES scientist Kevin Schaefer, with the National Snow and Ice Data Center (NSIDC) who is looking at the effect of a thawing Arctic on climate. "That is a lot of carbon."
The carbon from the frozen ground — known as permafrost — will make its impact not only on the climate, but also on international strategies to reduce global warming, Schaefer said. "If we want to hit a target carbon concentration, then we have to reduce fossil fuel emissions even lower than previously calculated to
account for the additional carbon from permafrost," Schaefer said.
"Otherwise we will end up with a warmer Earth than we want."
The carbon comes from decaying plant and animal material entombed in soil thousands of years ago. Once the ground froze, in the Ice Age of the Pleistocene, it trapped and preserved the decaying biomass. Schaefer equates the mechanism to the freezing of broccoli in a home freezer: "As long as it stays frozen, it stays stable," he said. "But you take it out of the freezer and you put it in the refrigerator, and it will thaw out and decay."
Now, a warming climate is thawing out the frozen ground and the biomass will start to decay, releasing carbon into the atmosphere like any other decomposing plant material, Schaefer said.
To predict just how much carbon will enter the atmosphere and when, Schaefer and CIRES Fellow Tingjun Zhang (also part of the NSIDC) modeled the thaw and decay of organic matter currently frozen in permafrost under potential future warming conditions as predicted by the Intergovernmental Panel on Climate Change.
They found that between one-third and two-thirds of permafrost will disappear by 2200. "The reason it takes so long is because basically you are talking about melting a huge block of ice," Schaefer said.
The Science
One-third to two-thirds of permafrost will disappear by 2200, according to a new estimate. That thaw could thwart people's efforts to limit greenhouse gas concentrations in the atmosphere.
The scientists used the model to predict how much carbon the thawing will release. They estimate an extra 190 ± 64 gigatons of carbon will enter the atmosphere by 2200 — about one-fifth the total amount of carbon currently in the atmosphere today. Carbon emissions from thawing permafrost will require greater reductions in fossil fuel emissions to limit the atmospheric carbon dioxide. "It means the problem is getting more and more difficult all the time," said Schaefer.
"It is hard enough to reduce fossil fuel emissions in any case, but now we saying that we have to reduce it even more." 
