Why Is Arctic Permafrost Thawing and What Are the Risks?
A critical component of the climate system, Arctic permafrost is thawing, altering a foundational element of northern landscapes and the global carbon cycle.
Beneath the landscapes of the far north lies a hidden world of frozen ground known as permafrost. Covering approximately 23 million square kilometers of the Northern Hemisphere, it influences the shape of the land and the global climate. The stability of this frozen layer is now a subject of scientific focus as the Arctic region experiences rapid change.
Defining Arctic Permafrost
Permafrost is ground—soil, rock, or sediment—that stays at or below 0°C (32°F) for at least two consecutive years. It is widespread in the Arctic and sub-Arctic, underlying large portions of Alaska, Canada, Siberia, and Greenland, and can also exist on shallow Arctic Ocean shelves. Its depth ranges from less than a meter to over 1,500 meters.
The composition of permafrost is a mix of soil, gravel, sand, and ice, along with preserved organic matter. The amount of ice within the ground varies, sometimes forming massive underground ice lenses or large, vertical ice wedges.
Permafrost is classified by its landscape coverage. Continuous permafrost underlies 90-100% of the harshest northern regions. Discontinuous permafrost covers 50-90% of the land in warmer zones, while sporadic permafrost covers less than half the area. Above this frozen layer is the “active layer,” a surface soil zone that thaws each summer and refreezes in winter.
Significance of Stable Permafrost
Stable Arctic permafrost is a global reservoir of organic carbon. The frozen conditions have halted the decomposition of vast quantities of dead plants and organic material for millennia. Arctic permafrost holds an estimated 1,400 gigatons of carbon, nearly double the amount currently in Earth’s atmosphere.
The frozen ground also provides structural integrity to the landscape. Ice within the soil acts like cement, binding sediments together into a solid foundation. This stability supports the ground surface and provides a reliable base for ecosystems and human infrastructure.
Permafrost also directs water flow across the Arctic. The frozen layer is impermeable, preventing water from seeping deep into the ground. This influences surface drainage, leading to the formation of the countless lakes and wetlands that characterize many Arctic regions.
The Process of Arctic Thaw
The primary driver of permafrost thaw is the rapid warming of the Arctic, heating up two to three times faster than the global average. Known as Arctic amplification, this phenomenon causes air and ground temperatures to rise. As the ground warms, the active layer thaws more deeply each summer, encroaching on the permafrost below.
Several factors accelerate this process. More frequent wildfires can burn away the insulating layer of vegetation, allowing summer heat to penetrate deeper into the ground. Changes in snow cover can also contribute to warmer permafrost temperatures by altering how the ground is insulated during winter.
When ice-rich permafrost thaws, it can trigger a process called thermokarst. As the ice within the ground melts, the soil loses volume and the ground surface collapses. This creates uneven, hummocky terrain and can lead to abrupt ground subsidence.
Impacts of Thawing Permafrost
A primary impact of thawing permafrost is the release of greenhouse gases. As frozen organic matter thaws, microbes decompose it, releasing carbon dioxide (CO2) and methane (CH4). This process creates a feedback loop, as the released gases contribute to further global warming, which in turn accelerates more thawing.
The physical landscape is also altered. Thermokarst terrain leads to ground subsidence, thaw slumps, and the expansion or drainage of lakes. This destabilization increases erosion along coastlines and riverbanks as the ground loses its structural integrity.
This ground instability threatens human infrastructure. Buildings, roads, airports, and pipelines built on frozen ground are at risk of damage as their foundations weaken and sink. These structural failures lead to high costs for repair and relocation.
Thawing also disrupts local ecosystems and hydrology. Water systems are rerouted as lakes drain and new ones form, affecting water quality and river flows. These changes impact vegetation, wildlife habitats, and migration patterns.
The thaw affects the traditional lifestyles of Indigenous communities, whose food security and cultural practices are connected to the land’s stability. There is also a potential for ancient bacteria and viruses, long dormant in the frozen ground, to be released.