Permafrost holds vast amounts of frozen organic matter accumulated over millennia. Ted Schuur of Northern Arizona University reported in Nature Climate Change that northern permafrost soils store roughly 1,500 gigatons of organic carbon, about twice the carbon currently in the atmosphere. This carbon reservoir is largely inert while soils remain frozen, but thaw exposes organic material to microbial activity, making permafrost one of the critical wildcards in the global carbon cycle.
Mechanisms of carbon release
When permafrost thaws, previously frozen plant and animal matter becomes available to microbes. Under oxygenated conditions microbes respire carbon as carbon dioxide, while waterlogged, anoxic conditions favour methanogenesis, producing methane. Katey Walter Anthony of the University of Alaska Fairbanks has measured large methane emissions from thaw lakes and thermokarst features, demonstrating that methane can be a concentrated and episodic pathway for carbon release. Peter Koven of Lawrence Berkeley National Laboratory has used Earth system models to show how the balance between aerobic and anaerobic decomposition, along with hydrological change, controls the timing and magnitude of greenhouse gas fluxes from thawing soils. These processes also mobilize dissolved organic carbon into rivers and coastal waters, altering aquatic carbon cycling and biogeochemistry.
Climate feedbacks and broader consequences
Carbon released from thawing permafrost acts as a positive climate feedback: added greenhouse gases accelerate warming, which in turn promotes further thaw. Ted Schuur and coauthors estimated that substantial fractions of permafrost carbon could be mobilized this century under high-emission scenarios, potentially adding to global warming beyond current model projections that omit or simplify permafrost dynamics. This feedback is subject to significant uncertainty because decomposition rates, hydrology, and fire interactions vary across landscapes and climates.
Beyond atmospheric impacts, thaw leads to pronounced landscape and societal effects. Thermokarst collapse, coastal erosion, and ground subsidence reshape ecosystems and infrastructure. Vladimir Romanovsky of the University of Alaska Fairbanks has documented warming ground temperatures and their consequences for roads, buildings, and traditional hunting and herding routes used by Indigenous communities. These territorial changes carry cultural and economic consequences that compound the ecological ones.
Permafrost thaw also has regional environmental nuances. Ice-rich Arctic lowlands are particularly vulnerable to abrupt thaw and methane release, while drier tundra and boreal uplands may emit primarily carbon dioxide. Subsea permafrost on continental shelves contains additional organic carbon and methane hydrates, and researchers working in Russian and Scandinavian institutions continue to study these offshore contributions.
Reducing uncertainty requires integrated observation and modeling. Long-term monitoring networks and targeted field studies by teams at universities and government labs are improving estimates of stored carbon, thaw rates, and gas fluxes. Incorporating this evidence into climate policy is essential because the permafrost carbon feedback could erode the effectiveness of mitigation efforts if it is not anticipated, making early cuts in fossil emissions even more important to limit long-term warming.