Permafrost

Permafrost is any subsurface earth material that remains below 0 °C for at least two consecutive years, including the intervening summer. Currently, permafrost covers approximately 25% of the Northern Hemisphere land surface and approximately 25% of the Antarctic continent. Permafrost may also be found as “subsea permafrost” on the seafloor bottom, particularly on the northern continental shelves of North America and Eurasia. In regions where average annual surface air temperatures are 0 °C or less, permafrost develops and thickens because ground freezing penetrates more deeply than summer thawing can reverse. Thus, each year will bring about deeper and deeper frozen ground until the geothermal regime deep within the Earth counteracts this downward freezing process.

Ultimately, equilibrium will be established, therefore providing a stable permafrost depth. ...