Environmental Science
How Permafrost Degradation Releases Ancient Carbon and Methane
Quick fact
Permafrost contains roughly twice as much carbon as the Earth's atmosphere holds today.
Why this is interesting
Imagine a giant freezer that has been storing organic matter for thousands of years. What happens when the freezer breaks down?
Read the full explanation
Understanding How Permafrost Degradation Releases Ancient Carbon and Methane
Permafrost is permanently frozen ground, common in polar and high-altitude regions. Because it stays below 0°C year-round, organic matter like dead plants and animals that froze thousands of years ago has not fully decomposed. Think of it like a natural deep-freeze: the freezer stops the decay. When warming thaws the permafrost, the 'freezer' fails. Microbes, which were largely dormant in the frozen soil, become active and begin breaking down that stored organic matter. This decomposition consumes oxygen and produces carbon dioxide in aerobic conditions, or methane in oxygen-poor, waterlogged conditions, especially in wetlands and lake bottoms. Both are greenhouse gases that go into the atmosphere. The ancient carbon is 'young' in terms of its age, but it was safely trapped; now it becomes a modern emission source.
A deeper explanation
The release occurs through a chain of events. First, rising air temperatures warm the ground surface, with the effects enhanced by changes in snow cover, vegetation, and water. This increases the 'active layer' (the top layer that thaws each summer) and causes deeper thaw, exposing previously frozen carbon. Second, this thawed material becomes available for microbial decomposition. Microbes like bacteria and archaea use the organic carbon as their food source, converting it into carbon dioxide (CO₂) if oxygen is available, or methane (CH₄) in oxygen-poor conditions like saturated soil. The type of gas matters: methane is a far more potent greenhouse gas—more than 25 times as effective at trapping heat over a 100-year period compared to carbon dioxide. Third, the release itself can speed up thawing. Thermokarst—the land collapse from thawing ice—can expose more deeper layers, and water bodies formed can warm the ground faster, creating a positive feedback loop: warming thaws more permafrost, which releases more greenhouse gases, which leads to more warming. This feedback is a key concern for climate models, as it represents a large, difficult-to-predict contribution to future climate.