When permafrost thaws, bacteria and microorganisms will begin breaking down the plant and animal organic matter it contains. As a result, carbon dioxide or methane will be released, depending on how dry or wet the soil remains. Though methane only makes up two per cent of the greenhouse gases released, it's a highly potent gas; its global warming potential over a 100-year time frame is nearly 25 times higher than that of carbon dioxide.
It was previously assumed that permafrost regions are carbon sinks. But there currently are only a few long-term measurement series that examine the carbon balance in permafrost regions year-round. One is from the AWI's Bayelva Permafrost Station near Ny-Ålesund (Svalbard); another is from Alaska. The readings in Alaska confirm that the area surveyed is a carbon sink. However, those from the Svalbard site show an annual carbon balance of about zero. In other words, here we see an equilibrium between the absorption of carbon by vegetation during the summer and the long "winter outgassing", during which microorganisms break down the carbon beneath the snows.
With the help of models, researchers now estimate that if global warming continues unabated, the greenhouse gas emissions from permafrost, disregarding all other sources, could produce an additional temperature increase of up to 0.29 degrees Celsius by the end of the century, and of up to 0.40 degrees by 2300.