What Is Permafrost? Permanently Frozen Ground Explained

Permafrost is ground — including soil, rock, and sediment — that remains at or below 0°C (32°F) continuously for at least two consecutive years. It underlies approximately 25 percent of the Northern Hemisphere's land surface, spanning vast areas of Siberia, Canada, Alaska, Greenland, and parts of Scandinavia and the Tibetan Plateau.

Introduction

Permafrost can extend from just below the surface to depths exceeding 1,500 meters. Some of the deepest permafrost in Siberia has been continuously frozen for hundreds of thousands of years, preserving ancient plant material, animal remains, and enormous quantities of organic carbon that are now at risk of being released as the Arctic warms.

Definition & Structure

• Definition: Ground that stays at or below 0°C for at least two consecutive years
• Active Layer: The top layer that thaws each summer and refreezes in winter
• Continuous Permafrost: Underlies the surface everywhere in the coldest regions
• Discontinuous Permafrost: Found in patches where conditions are marginal for freezing

Permafrost is defined purely by temperature and time — it must remain at or below freezing for at least two consecutive years. Above the permafrost lies the active layer, a thin zone (30 cm to several meters deep) that thaws each summer and refreezes each winter. Most biological activity, plant root growth, and soil processes in permafrost regions occur in this active layer.

In the coldest areas (northern Siberia, central Arctic islands), continuous permafrost underlies the entire surface and may be hundreds of meters thick. Moving southward, the permafrost becomes patchy (discontinuous), existing only in shaded areas, north-facing slopes, or beneath insulating peat layers. Further south still, isolated patches of permafrost persist only in the most favorable locations.

Where Permafrost Is Found

• Siberia: Contains the deepest and most extensive permafrost on Earth, over 1,500 m deep in places
• Canada: About half of Canada's land area is underlain by permafrost
• Alaska: Permafrost underlies about 80% of Alaska's land area
• Tibetan Plateau: High-altitude permafrost covering roughly 1.5 million km²
• Other Regions: Scandinavia, Greenland, parts of Mongolia and northeastern China

Russia contains more permafrost than any other country — roughly 65 percent of its land area is underlain by frozen ground. The deepest known permafrost is in Yakutia (Sakha Republic) in northeastern Siberia, where it extends to over 1,500 meters below the surface. These deep layers have been continuously frozen since the Pleistocene epoch, over 100,000 years.

Permafrost is not limited to polar regions. The Tibetan Plateau hosts roughly 1.5 million square kilometers of high-altitude permafrost, which plays a critical role in the hydrology of Asia's major rivers. Alpine permafrost also exists in the European Alps, the Rocky Mountains, and other high mountain ranges, where its thawing is destabilizing slopes and threatening infrastructure.

What Permafrost Stores

• Carbon: An estimated 1,500 billion tons of organic carbon — twice the current atmospheric CO₂
• Methane: Decomposition under anaerobic conditions produces the potent greenhouse gas methane
• Ancient Organisms: Preserved viruses, bacteria, plants, and animals from thousands of years ago
• Ice: Massive ice wedges, lenses, and layers that can be meters thick

Permafrost is a massive carbon reservoir. Over thousands of years, dead plant material accumulated in cold, waterlogged soils where decomposition was extremely slow. The frozen ground preserved this organic matter like a natural freezer. Scientists estimate that Arctic permafrost contains roughly 1,500 billion tons of organic carbon — about twice the amount currently in the atmosphere as CO₂.

When permafrost thaws, microbial decomposition resumes, converting the stored organic carbon into CO₂ (in aerobic conditions) or methane (in anaerobic, waterlogged conditions). Methane is roughly 80 times more potent as a greenhouse gas than CO₂ over a 20-year period. The release of even a fraction of the permafrost carbon store could significantly accelerate global warming, creating a dangerous positive feedback loop.

Permafrost & Infrastructure

• Building Foundations: Buildings on thawing permafrost sink, crack, and may collapse
• Roads & Railways: Thawing creates uneven ground, buckling roads and railway tracks
• Pipelines: The Trans-Alaska Pipeline is elevated to prevent heat transfer to permafrost
• Cost: Permafrost thaw could cost billions in infrastructure damage in Arctic regions

Building on permafrost requires special engineering techniques because frozen ground is stable but thawed ground often becomes a waterlogged, unstable slurry. The standard approach is to prevent heat from buildings reaching the ground, using elevated structures on piles, ventilated foundations, or refrigeration systems. The Trans-Alaska Pipeline is elevated on supports to prevent its warm oil from thawing the underlying permafrost.

As the Arctic warms, thawing permafrost is already damaging infrastructure across Russia, Canada, and Alaska. Buildings in Siberian cities are cracking and tilting. Roads buckle and sink. Runways deform. A 2021 study estimated that permafrost thaw could damage 70 percent of current infrastructure in the Arctic by 2050, with repair and replacement costs in the tens of billions of dollars.

Climate Change & Permafrost Thaw

• Accelerating Thaw: Arctic warming is causing permafrost to thaw at unprecedented rates
• Carbon Feedback: Thawing releases CO₂ and methane, further warming the climate
• Thermokarst: Thawing creates sunken, waterlogged terrain as ice-rich ground collapses
• Irreversibility: Once released, permafrost carbon cannot be refrozen on human timescales

Permafrost is thawing across the Arctic. Ground temperatures in permafrost regions have risen by up to 2°C since the 1970s, and the southern boundary of continuous permafrost is shifting northward. In some areas, permafrost that has been continuously frozen for thousands of years is now thawing for the first time.

The thawing of permafrost creates a climate feedback loop: warming causes permafrost to thaw, which releases greenhouse gases, which causes more warming, which thaws more permafrost. Scientists call this the "permafrost carbon feedback" and consider it one of the most significant tipping points in the climate system. Current climate models may underestimate future warming because many do not fully account for permafrost carbon emissions.

Key Facts

• Permafrost is ground that stays frozen for at least two consecutive years.
• It underlies about 25% of the Northern Hemisphere's land surface.
• Arctic permafrost stores an estimated 1,500 billion tons of carbon.
• The active layer above permafrost thaws each summer and refreezes in winter.
• Permafrost thaw is a significant climate feedback that could accelerate global warming.

Fun Facts

• The deepest known permafrost in Siberia extends over 1,500 meters below the surface.
• Woolly mammoth carcasses have been preserved in Siberian permafrost for over 40,000 years.
• Ancient viruses have been revived from Siberian permafrost after being frozen for tens of thousands of years.
• The Trans-Alaska Pipeline is elevated to prevent its warm oil from melting the permafrost below.

Final Thoughts

Permafrost is far more than just frozen ground — it is a critical component of Earth's climate system, storing twice as much carbon as the entire atmosphere. As Arctic temperatures rise at two to three times the global average, this frozen carbon vault is beginning to open, potentially releasing enough greenhouse gases to significantly accelerate warming. The fate of the world's permafrost is one of the most consequential unknowns in climate science.