Here is a brief primer on permafrost carbon. Permafrost (frozen soil) stores a HUGE amount of carbon because ancient life took up carbon dioxide, built biomass, then died. These organisms' organic matter (~50% C) slowly accrued in Earth's best freezer for 1000s of yrs. 1/

When frozen organic matter in permafrost warms up, microbial activity speeds up. Microbes use the organic matter in their respiratory processes, which can release a variety of greenhouse gases as byproducts, mostly carbon dioxide but also methane, which make their way to the atmosphere. 2/