Beneath the frozen landscapes of the Arctic and sub-Arctic, a vast reservoir of organic carbon has been locked away in permafrost — permanently frozen ground — for thousands to hundreds of thousands of years. This frozen soil stores an estimated 1,500 billion tonnes of carbon, nearly twice the amount currently in the atmosphere. As global temperatures rise and permafrost thaws, this carbon is being released as carbon dioxide and methane, creating a dangerous positive feedback loop that could significantly accelerate climate change beyond current projections.
What Is Permafrost?
Permafrost is ground that remains at or below 0 degrees Celsius for at least two consecutive years. It underlies approximately 25 percent of the Northern Hemisphere’s land surface, spanning vast areas of Siberia, Alaska, Canada, and the Tibetan Plateau. Some permafrost has been frozen continuously for over 700,000 years, preserving ancient plant material, animal remains, and microbial communities in a deep freeze.
The organic matter trapped in permafrost accumulated over millennia as dead plants and animals were incorporated into soil and frozen before they could fully decompose. This makes permafrost a massive carbon time capsule — when it thaws, dormant microorganisms reactivate and begin decomposing the ancient organic material, releasing greenhouse gases into the atmosphere.
The Thawing Crisis
The Arctic is warming approximately four times faster than the global average. Permafrost temperatures have increased by 0.3 to 1 degree Celsius per decade across much of the Arctic since the 1970s, and thaw is accelerating. In some regions, permafrost that scientists expected to remain stable for centuries is already degrading.
Two forms of thaw are particularly concerning. Gradual thaw occurs as the active layer — the surface soil that thaws each summer and refreezes each winter — deepens year after year, exposing progressively more frozen carbon to decomposition. Abrupt thaw involves sudden ground collapse as ice-rich permafrost melts, creating thermokarst features: landslides, sinkholes, and lakes that can release large quantities of carbon rapidly.
When permafrost carbon thaws in the presence of oxygen, microbes produce carbon dioxide. When it thaws in waterlogged, oxygen-free conditions (as in thermokarst lakes), microbes produce methane — a greenhouse gas roughly 80 times more potent than CO2 over a 20-year timeframe. This distinction matters enormously for climate projections.
Infrastructure and Community Impacts
Permafrost thaw is already causing severe damage to infrastructure and communities across the Arctic. Buildings, roads, pipelines, and airports built on permafrost foundations are subsiding, cracking, and collapsing as the ground beneath them softens. In Russia, several cities built on permafrost are experiencing widespread structural damage. Indigenous communities across the Arctic face threats to traditional food storage, transportation routes, and culturally significant sites.
In Canada, communities in the Northwest Territories, Yukon, and northern Quebec are experiencing accelerating ground subsidence, damage to buildings and roads, and disruption of winter ice roads that serve as vital transportation links. Adaptation costs for Arctic infrastructure are projected to reach tens of billions of dollars across circumpolar nations.
Climate Feedback and Research
The permafrost carbon feedback is not yet fully incorporated into most climate models used for international policy. Current estimates suggest that permafrost thaw could release 150 to 200 billion tonnes of carbon by 2100 under high-warming scenarios — equivalent to several years of global fossil fuel emissions. Some researchers warn that the permafrost feedback alone could add 0.2 to 0.5 degrees Celsius to global warming by the end of the century.
Scientists monitor permafrost using a combination of ground temperature boreholes, satellite remote sensing, and atmospheric measurements of greenhouse gas emissions from Arctic regions. Research stations across the Arctic, including several operated by Canadian institutions, track thaw rates and carbon emissions to improve projections and inform climate policy.
Limiting permafrost thaw ultimately requires rapid reduction of global greenhouse gas emissions. Every fraction of a degree of warming avoided preserves billions of tonnes of frozen carbon and reduces the risk of triggering irreversible feedback that could push the climate system beyond human control.
