As permafrost thaws in a warming climate, once-frozen organic carbon is broken down by soil microbes, releasing carbon dioxide and methane to the atmosphere. Release of these additional greenhouse gases to the atmosphere accelerates climate change and incurs additional societal costs for mitigation and adaptation.
Why it matters
Sustained and substantial carbon release from the Arctic is a wildcard that could affect how fast climate change happens. While a large proportion of the modern increase in atmospheric carbon is due to human activities, the future trajectory of the atmosphere also depends on the response of land and ocean to climate change. A key societal question is whether there are tipping points: global carbon cycle surprises that will make climate change effects (sea-level rise, extreme weather, droughts, and impacts on agriculture) occur faster than currently projected by models. Permafrost carbon, the remnants of plants, microbes, and animals accumulated in perennially frozen Arctic soil over thousands of years, is a potential climate tipping point.