![]() Scientists are aware of the risks of a rapidly warming Arctic, yet the potential magnitude of the problem is not fully recognized by policy makers or the public. Fire-induced permafrost thaw and the subsequent decomposition of previously frozen organic matter may be a dominant source of Arctic carbon emissions during the coming decades ( 9). This global climate feedback is being intensified by the increasing frequency and severity of Arctic and boreal wildfires ( 8, 9) that emit large amounts of carbon both directly from combustion and indirectly by accelerating permafrost thaw. Extreme weather, such as the recent Siberian heat wave, can trigger catastrophic thaw events, which, ultimately, can release a disproportionate amount of permafrost carbon into the atmosphere ( 7). These collapsed areas can expose deep permafrost, which, in turn, accelerates thaw. Permafrost thaw, which can proceed as a gradual, top-down process, can also be greatly exacerbated by abrupt, nonlinear thawing events that cause extensive ground collapse in areas with high ground ice ( Fig. However, warming and thawing of permafrost promotes decomposition of this once frozen organic matter, threatening to turn the Arctic carbon sink into a net source of greenhouse gases to the atmosphere ( 5, 6). This carbon accumulated over tens of thousands of years when cold and frozen conditions protected the carbon-rich organic material (derived from dead plants and animals) from microbial decomposition. The permafrost region contains a massive frozen store of ancient organic carbon ( 4), totaling approximately twice the amount of carbon as is in Earth’s atmosphere. There is an urgent need to incorporate the latest science on carbon emissions from permafrost thaw and northern wildfires into international consideration of how much more aggressively societal emissions must be reduced to address the global climate crisis. In December 2020, more than 70 countries announced more ambitious nationally determined contributions as part of their Paris Agreement commitments however, the carbon budgets that informed these commitments were incomplete, as they do not fully account for Arctic feedbacks. The Paris Agreement provides ongoing opportunities to increase ambition to reduce society’s greenhouse gas emissions, which will also reduce emissions from thawing permafrost. Carbon emissions from permafrost thaw and Arctic wildfires, which are not fully accounted for in global emissions budgets, will greatly reduce the amount of greenhouse gases that humans can emit to remain below 1.5 ☌ or 2 ☌. Rapid Arctic warming has intensified northern wildfires and is thawing carbon-rich permafrost.
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