One model puts a number on the estimated CO2 release from permafrost. It's a big one:
One- to two-thirds of Earth’s permafrost will disappear by 2200, unleashing vast quantities of carbon into the atmosphere, says a study by researchers at the Cooperative Institute for Research in Environmental Sciences (CIRES) National Snow and Ice Data Center (NSIDC).
“The amount of carbon released is equivalent to half the amount of carbon that has been released into the atmosphere since the dawn of the industrial age,” said NSIDC scientist Kevin Schaefer. “That is a lot of carbon.”
That's an understatement. We're talking about the same amount of carbon released over the past fifty years. The total increase measured in the modern instrumental record.
Permafrost melting is not modeled in the IPCC's assessments. It was believed for many years to be too slow a feedback to matter on a human timescale. Would it were so. But maybe it's an over-estimate? Those wacky climate scientists, always chasing the headline? What about it, guys?
This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost.