Permafrost carbon emissions in a changing Arctic

Arctic permafrost stores nearly 1,700 billion metric tons of frozen and thawing carbon. Anthropogenic warming threatens to release an unknown quantity of this carbon to the atmosphere, influencing the climate in processes collectively known as the permafrost carbon feedback. In this Review, we discuss advances in tracking permafrost carbon dynamics, including mechanisms of abrupt thaw, instrumental observations of carbon release and model predictions of the permafrost carbon feedback. Abrupt thaw and thermokarst could emit a substantial amount of carbon to the atmosphere rapidly (days to years), mobilizing the deep legacy carbon sequestered in Yedoma. Carbon dioxide emissions are proportionally larger than other greenhouse gas emissions in the Arctic, but expansion of anoxic conditions within thawed permafrost and soils stands to increase the proportion of future methane emissions. Increasingly frequent wildfires in the Arctic will also lead to a notable but unpredictable carbon flux. More detailed monitoring though in situ, airborne and satellite observations will provide a deeper understanding of the Arctic's future role as a carbon source or sink, and the subsequent impact on the Earth system. Large stores of carbon could be released to the atmosphere from Arctic warming, driving permafrost thaw. This Review examines the processes that impact Arctic permafrost carbon emissions, how they might change in the future and ways to monitor and predict these changes.