Permafrost, the Earth’s permanently frozen ground, significantly impacts the global climate. As temperatures rise, permafrost can thaw, influencing the climate in a cyclical process that amplifies warming.
Permafrost Basics
Permafrost is ground, including soil, rock, or organic material, that remains frozen at or below 0°C (32°F) for at least two consecutive years. It is found predominantly in the Arctic and high-altitude regions, covering about 24% of the Northern Hemisphere’s land area. The depth of permafrost can vary significantly, ranging from less than a meter to over 1,500 meters. This frozen ground often contains ice lenses and layers, and it usually lies beneath an “active layer” of soil that thaws and refreezes seasonally.
The Concept of a Feedback Loop
A feedback loop describes a process where the output of a system acts as an input that influences the same system. In a positive feedback loop, an initial change leads to further changes in the same direction, amplifying the original effect. An example is the screech produced when a microphone picks up sound from a speaker, and that amplified sound is fed back into the microphone, creating a louder squeal. This self-reinforcing cycle illustrates how a small initial disturbance can grow into a much larger phenomenon.
The Permafrost-Climate Feedback Loop
The permafrost-climate feedback loop begins as global temperatures increase, causing the permafrost to thaw. This thawing exposes organic matter, such as ancient plant and animal remains, preserved for thousands of years. Microbes then decompose this organic material, releasing greenhouse gases, specifically carbon dioxide and methane, into the atmosphere. These released gases trap more heat, contributing to further global warming. The increased warming, in turn, causes more permafrost to thaw, accelerating the entire cycle in a self-reinforcing manner.
Gases Released from Thawing Permafrost
Thawing permafrost releases two primary greenhouse gases: carbon dioxide (CO2) and methane (CH4). Carbon dioxide is produced when organic matter decomposes in aerobic (oxygen-rich) conditions. Methane is generated under anaerobic (oxygen-poor) conditions, often occurring in thawed wetlands and lakes. Methane is a potent greenhouse gas, trapping significantly more heat per molecule than carbon dioxide; for instance, its warming potential is estimated to be around 80 times higher than CO2 over a 20-year period, though this ratio decreases to about 25 times over a 100-year period.
Broader Consequences of Permafrost Thaw
Permafrost thaw has several other consequences affecting natural and human systems. Thawing ground can destabilize infrastructure, leading to damage to buildings, roads, railways, pipelines, and airports. This destabilization results from ground subsidence and erosion as ice within the permafrost melts. Permafrost thaw also alters hydrological patterns, affecting water flow and the formation of new lakes. Changes in permafrost distribution can modify soil moisture, connectivity of inland waters, and streamflow seasonality, impacting both surface and groundwater systems. There is also a concern about the potential release of ancient pathogens, such as long-dormant bacteria and viruses, that have been preserved in the frozen ground for millennia. These changes collectively result in shifts in vegetation and wildlife habitats, further impacting Arctic ecosystems.