Permafrost is frozen land and occurs across the higher latitudes of North America, Europe and Asia. 25% of the Northern Hemisphere is frozen in this way. Whilst in its frozen state, permafrost locks the organic material in soils in its current form, maintaining the carbon stored in this organic matter as a land carbon store.
When permafrost melts, this organic matter undergoes the typical processes that would occur in more temperate climates. Dead vegetation decomposes and is broken down by bacteria. This process releasing carbon from the land store to the atmospheric carbon store in the form of methane, a carbon containing potent greenhouse gas. Permafrost contains an estimated 1,400 gigatonnes of organic matter that is 'locked' in its current state.
As explained elsewhere on this website, as melting permafrost releases greenhouse gases, a positive feedback loop is created whereby the warming resulting from the greehouse gases causes more permafrost to melt, and so on. The New York Times has an infographic providing an overview of permafrost in Alaska available here.
