In the summer of 2020 Siberian temperatures reached 38 °C, the highest ever recorded temperature within the Arctic Circle. During the same year, Arctic wildfires released 35% more CO2 than in 2019. The permafrost region contains a massive frozen store of ancient organic carbon, in total about twice the amount of carbon in the Earth’s atmosphere. Warming and thawing of permafrost leads to decomposition of frozen organic matter releasing carbon dioxide and other greenhouse gases into the atmosphere. This release of carbon could turn the Arctic carbon sink into a net source of atmospheric greenhouse gases.
Recent estimates of carbon emissions from gradual permafrost thaw alone range from 22 Gt to 432 Gt of CO2 by 2100 if global carbon emissions are greatly reduced and up to about 550 Gt of CO2 assuming weak climate policies. (For comparison Canada’s CO2 emissions released 157 Gt of carbon into the atmosphere in 2019.) These emissions projections are likely an underestimate, because they do not account for abrupt thaw and wildfire. It is estimated that under a moderate emission scenario, wildfires could increase carbon emissions from soil and permafrost by 30% and abrupt thawing events may increase carbon emissions by 40% by the end of the century.
Permafrost carbon emissions are not accounted for by most Earth system models or the integrated assessment models used for the last assessment report of the Intergovernmental Panel on Climate Change (IPCC). The release of carbon from potential gradual and abrupt permafrost thawing as a result of global warming will only accelerate warming caused by human emissions. This will increase the emissions reductions required to bring global climate temperatures back down to the Paris targets.
Source: Permafrost carbon feedbacks threaten global climate goals, Susan M. Natalia, John P. Holdren, Brendan M. Rogers, Rachael Treharne, Philip B. Duffy, Rafe Pomerance, and Erin MacDonald, PNAS May 25, 2021 118 (21).