What is permafrost?

Permafrost is a layer of soil, rock or sediment that is frozen for more than two consecutive years. It is commonly found in snowy, high-altitude mountains. About a quarter of the entire northern hemisphere has permafrost, but it is especially prevalent in areas above the 50th parallel north

Permafrost seals highly compressed carbon and methane gases created from decomposed organic and vegetal remains. Greenhouse gases are released when this frozen layer thaws. In areas not overlain by ice, the surface freezes and thaws annually and is called the “active layer”