How does permafrost thaw amplify greenhouse gas emissions?

Permafrost soils store vast amounts of organic matter that accumulated over millennia under permanently frozen conditions. Edward Schuur at Northern Arizona University has summarized field and modeling evidence showing that Arctic and sub-Arctic permafrost contain roughly 1,500 billion tonnes of organic carbon, a reservoir comparable to the carbon already in the atmosphere. When those frozen soils thaw, previously inert carbon becomes available for microbial decomposition, converting solid organic matter into carbon dioxide and methane that enter the atmosphere and strengthen the greenhouse effect.

Mechanisms of greenhouse gas release

Thawing alters soil physical and hydrological conditions in ways that change which gases are produced. In aerobic, well-drained thawed soils microbes oxidize carbon into carbon dioxide. Where thaw produces waterlogged conditions, such as in depressions or newly formed thermokarst wetlands, anaerobic microbes generate methane, a molecule that traps heat far more effectively than carbon dioxide over short time spans. Katey Walter Anthony at University of Alaska Fairbanks has documented that thermokarst lakes and abrupt thaw features can become hotspots for methane emissions, releasing pulses of methane as old organic matter is rapidly decomposed. Abrupt permafrost collapse exposes deep, previously frozen carbon directly to microbial action, speeding emissions compared with slow, surface-layer thaw.

Feedbacks and human consequences

The emission of additional greenhouse gases from thawing permafrost is a positive climate feedback: warming causes thaw, thaw releases greenhouse gases, and those gases cause further warming. The Intergovernmental Panel on Climate Change identifies this permafrost carbon feedback as a potential amplifier of long-term warming, although the magnitude and timing remain uncertain because emissions depend on local thaw patterns, hydrology, and vegetation changes. Beyond the global climate signal, thaw has immediate local and regional consequences. Infrastructure such as roads, pipelines, and buildings in Arctic settlements degrade as ground ice melts and land subsides, imposing economic and cultural costs on Indigenous and rural communities in Alaska, northern Canada, Greenland, and Siberia. Changing thaw patterns also alter river chemistry and sediment transport, with downstream effects on fisheries and water quality.

Environmental and cultural nuances

Permafrost thaw interacts with fire regimes, vegetation shifts, and human land use. Warmer, drier summers increase wildfire frequency, which consumes surface organic layers and can accelerate deeper thaw. In some areas, new plant growth may partially offset carbon losses by taking up carbon, but this regrowth is often slower and less extensive than the carbon liberated from deep soils. For Arctic communities, these changes threaten culturally significant landscapes, traditional hunting and travel routes, and the structural integrity of seasonal camps. Environmentally, the spatially heterogeneous nature of thaw—abrupt collapses next to relatively intact ground—creates a mosaic of emissions sources that complicates monitoring and modeling.

Monitoring, modeling, and mitigation efforts focus on improving estimates of how much carbon will be released and over what timescale, and on strategies to reduce global warming to limit further thaw. The interplay of microbial ecology, hydrology, landforms, and human infrastructure makes permafrost thaw both a local hazard and a globally significant amplifier of climate change.