Permafrost soil is ground that remains completely frozen for at least two consecutive years, existing at or below 0 degrees Celsius (32 degrees Fahrenheit). This vast component covers extensive areas globally. Its long-term stability has shaped unique environments and geological processes over millennia.
Understanding Permafrost Soil
Permafrost soil forms over thousands of years through the continuous freezing and compaction of materials. This process occurs in regions where the mean annual air temperature remains below freezing, allowing ice to persist deep within the ground. Permafrost composition varies, incorporating a mixture of soil, rocks, sand, and much ice, which binds these components together.
Near the surface, permafrost contains large quantities of organic carbon from ancient, undecomposed plants and animals. The depth of permafrost can range from less than a meter to over 1,500 meters in colder regions, with some layers more than 30 percent ice by volume. This frozen ground underlies approximately 25 percent of the Northern Hemisphere’s exposed land surface, spanning about 23 million square kilometers (9 million square miles). It is most extensive poleward of 60 degrees North in Russia, Canada, and northern Alaska, and also occurs in high-altitude mountain ranges, such as the Himalayas and the Tibetan Plateau.
Permafrost’s Role in Earth Systems
Permafrost functions as an enormous carbon sink, storing vast amounts of organic material frozen for thousands of years. This ancient biomass, including remnants of plants and animals, has been prevented from decomposing due to the low temperatures. Estimates suggest that permafrost regions in the Northern Hemisphere hold approximately 1,460 to 1,600 billion metric tons of organic carbon, which is nearly twice the amount currently present in Earth’s atmosphere.
Beyond its role in the carbon cycle, permafrost significantly influences regional hydrology. Acting as an impermeable layer, it restricts the downward movement of water, impacting subsurface flow and groundwater systems. This barrier can lead to the formation of perched water tables and surface ponding, contributing to the development of extensive wetlands and lakes characteristic of permafrost landscapes. The stability provided by permafrost also supports unique Arctic ecosystems, forming the foundation for specialized vegetation and wildlife habitats adapted to these cold, often waterlogged conditions.
The Warming Arctic and Permafrost Thaw
Permafrost thawing is driven by global warming, which is amplified in the Arctic region. This “Arctic amplification” refers to the fact that the Arctic is warming at a rate two to four times faster than the global average, largely due to feedback loops such as the diminishing sea ice cover. As air and ground temperatures rise, the frozen ground begins to melt, transforming stable, ice-rich terrain into unstable, waterlogged soil.
Observable changes in permafrost regions include the formation of thermokarst lakes, which are depressions that fill with water as underlying ice-rich permafrost thaws and the ground subsides. This process also leads to more widespread ground subsidence, causing the land surface to compact and sink unevenly. Additionally, the active layer, the uppermost layer of ground that thaws in summer and refreezes in winter, is increasing in thickness, indicating deeper seasonal thawing.
Consequences of Thawing Permafrost
The thawing of permafrost has wide-ranging impacts, particularly on environmental systems and human infrastructure. As the ancient organic matter within the thawing permafrost decomposes, it releases greenhouse gases such as carbon dioxide and methane into the atmosphere. This release creates a positive feedback loop, where increased greenhouse gas concentrations further accelerate global warming, leading to more permafrost thaw. Methane is concerning due to its higher warming potential, approximately 25 times greater than carbon dioxide over a 100-year period, despite its shorter atmospheric lifespan.
The instability caused by thawing permafrost poses challenges to infrastructure in cold regions. Buildings can crack and tilt as their foundations shift, roads may buckle, and pipelines can rupture due to ground subsidence and uneven settling. For example, the Trans-Alaska Pipeline has faced issues where ground thaw has destabilized its supports, and many buildings in Russian Arctic cities have experienced substantial damage. It is projected that between 30 to 70 percent of existing circumpolar infrastructure could be at risk by mid-century.
Local communities, especially Indigenous populations, are directly affected by these changes. Damage to transportation routes, such as roads and runways, limits access to food, essential supplies, and medical services, impacting community well-being and food security. Thawing ground also alters traditional hunting grounds and livelihoods, and there is concern about the potential release of long-dormant pathogens, such as the anthrax outbreak linked to thawing permafrost in northern Russia in 2016.