Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic

Rapid Arctic environmental change affects the entire Earth system as thawing permafrost ecosystems release greenhouse gases to the atmosphere. The permafrost soil carbon pool contains three times as much carbon as in the atmosphere, with 1440-1600 Pg C known, and another ~960 Pg C in other deep sediments and subsea. The permafrost region contains 50% of the soil carbon found in all other Earth’s biomes (0-3m) in only 15% of the global soil area, and this is likely a minimum. Understanding how much permafrost carbon will be released, over what time frame, and what the relative emissions of carbon dioxide and methane will be is key for understanding the impact on global climate. In addition, the response of vegetation in a warming climate has the potential to offset at least some of the accelerating feedback to the climate from permafrost carbon. Temperature, organic carbon, and ground ice are key regulators for determining the impact of permafrost ecosystems on the global carbon cycle. Together, these encompass services of permafrost relevant to global society as well as to the people living in the region and help to determine the landscape-level response of this region to a changing climate.

Nine scenarios of cumulative net carbon dioxide and methane emissions over this century were developed to encompass the full range permafrost carbon emissions projections linked to global and Arctic warming. These cumulative permafrost carbon emission scenarios range from 55 to 230 Pg C (C-CO₂-equivalent units) and represent future Arctic carbon emissions that can be compared relative to national-level emissions that are the focus of climate change mitigation conversations. This helps to place these scenarios alongside policy conversations aimed at reducing national greenhouse gas emissions. Many of the modeled climate change trajectories where mitigation of human carbon emissions leads to various global temperature targets do not necessarily contain all of the detailed information for the Arctic carbon cycle as compared to the projections reviewed here. In this way, it can be helpful to view potential Arctic carbon emissions as the equivalent of an additional large industrialized nation of carbon emissions that must be accounted for in order to reach specific temperature targets. Arctic carbon emissions accelerate climate change, adding 10-15% to future fossil fuel emissions, potentially decreasing the land carbon sink by 33-50%. Accounting for these additional greenhouse gas emissions will help to slow climate change and potentially avoid Arctic carbon cycle surprises from abrupt thaw and other threshold events.