Permafrost is ground that remains frozen for at least two consecutive years, consisting of soil, rock, and ice at or below 0 degrees Celsius. This long-frozen ground, which has persisted for thousands of years, is now thawing. This process represents a global concern with implications for natural systems and human activities across affected regions.
Understanding Permafrost
Permafrost is a mixture of soil, rock, and ice, where ice acts as a cementing agent. It can range in thickness from less than a meter to over a thousand meters, reaching depths of approximately 1,500 meters in parts of Siberia. This frozen ground forms in areas where the annual mean air temperature is below freezing, allowing cold temperatures to persist over geological timescales.
It is found across vast areas of the Arctic and sub-Arctic regions, covering about 15% of the Northern Hemisphere’s land. High-altitude mountain regions globally also contain permafrost. Over millennia, organic matter, such as ancient plant and animal remains, has accumulated and been preserved within these frozen layers, remaining undecomposed due to the cold, anaerobic conditions.
Causes of Permafrost Thawing
The primary driver of permafrost thawing is the warming global climate. Rising air temperatures in Arctic and sub-Arctic regions directly increase ground temperatures, causing the ice within permafrost to melt. This warming trend is observed globally, with polar regions experiencing amplified temperature increases compared to the global average. The insulating layer of snow cover also influences permafrost temperatures; changes in snow depth and duration can either protect or expose the ground to warming.
Wildfires are another factor contributing to permafrost thaw, particularly in boreal forests and tundra. These fires remove vegetation and the organic layer on the surface, which insulate the permafrost from solar radiation. Without this protective layer, the ground absorbs more heat, accelerating thawing. Human disturbances, such as the construction of buildings, roads, and pipelines, also contribute to localized permafrost degradation. The heat transferred from infrastructure and altered surface hydrology can initiate or accelerate thawing.
Consequences of Thawing
Thawing permafrost releases previously frozen organic matter, which then decomposes. This decomposition, carried out by microbes, releases greenhouse gases—primarily carbon dioxide and methane—into the atmosphere. This gas release contributes to further atmospheric warming, creating a positive feedback loop that accelerates additional permafrost thawing. Scientists estimate permafrost holds about 1,700 billion metric tons of organic carbon, more than twice the amount currently in the atmosphere.
Permafrost thawing also directly leads to landscape changes, forming thermokarst features. These include slumping, sinkholes, and ground collapse as the ice melts and the ground loses structural integrity. Coastal erosion is another significant consequence, particularly in Arctic regions, where thawing permafrost cliffs become more susceptible to wave action and storm surges. This erosion can cause land loss and reshape coastlines.
Human infrastructure on permafrost is vulnerable to these landscape changes. Roads buckle, buildings settle unevenly, and pipelines can be damaged as the ground beneath them becomes unstable. For example, damage to infrastructure from thawing permafrost could cost trillions of dollars globally by the end of the century. Ecosystems are also affected, with shifts in hydrology as drainage patterns change, leading to new wetlands or dried-out areas. Vegetation patterns can also change, with some areas becoming more susceptible to shrub encroachment or forest changes.
Monitoring and Adaptation
Scientists use various methods to track permafrost changes globally. Satellite imagery provides broad insights into surface changes, like thermokarst features and vegetation cover. On the ground, temperature sensors in boreholes directly measure permafrost temperatures at different depths, offering precise data on warming trends. Fieldwork, including ground-penetrating radar and direct core sampling, allows for detailed analysis of permafrost composition and ice content.
Communities in affected regions are implementing strategies to adapt to the challenges of thawing permafrost. Engineers are developing new building techniques, such as using thermosyphons to keep the ground frozen beneath structures or employing adjustable foundations that can be re-leveled as the ground shifts. Relocating vulnerable infrastructure, like roads or buildings, away from rapidly thawing areas is another approach being considered or undertaken in some places. Developing community-level resilience plans, which might involve detailed mapping of thaw susceptibility and identifying safe zones for future development, helps manage the risks associated with an unstable landscape.
References
1. Schuur, E. A. G., et al. “Climate change and the permafrost carbon feedback.” Nature 520.7546 (2015): 171-179.
2. Melvin, A. M., et al. “Climate change damages to Alaska public infrastructure and the impacts of accelerated permafrost thaw.” Proceedings of the National Academy of Sciences 116.35 (2019): 17203-17208.