Why does anaerobic decomposition in thawed permafrost produce methane?

When permafrost thaws, the ground often becomes saturated and boggy because the underlying frozen layer prevents water from draining, creating an oxygen-poor (anaerobic) environment. In these conditions, specialized microorganisms known as methanogenic archaea thrive.12

These methanogens produce methane through the anaerobic decomposition of organic matter—such as plants and animals—that was previously trapped in the frozen soil. The process typically involves a community of bacteria: other anaerobic microorganisms first break down complex organic materials into simpler substances like acetate, carbon dioxide, and hydrogen gas. The methanogens then utilize these products to generate methane. By consuming hydrogen gas during this metabolic process, methanogens also support the continued activity of the other anaerobic bacteria, facilitating further decomposition.32

This release of methane is a significant environmental concern, as methane is a potent greenhouse gas that contributes to atmospheric warming, which in turn accelerates the thawing of additional permafrost.3