Definition of Permafrost

What Is Permafrost?

Permafrost, also called permafrost soil, is a soil or rock that experiences freezing temperatures at or below the freezing point of water (0 °C or 32 °F) for two or more years. Permafrost is formed when the ground cools sufficiently in winter to produce a layer of frozen soil that then remains frozen throughout the following summer and into the preceding winter.

There are two types of permafrost, continuous and discontinuous. Continuous permafrost forms in zones where the annual soil surface temperatures remain below -5 °C or 23 °F so that the permafrost never thaws. There is a line of continuous permafrost in the Northern Hemisphere, north of which all land is covered by permafrost or glacial ice. Discontinuous permafrost, on the other hand, forms in spots because of variations in shelter and atmospheric temperatures.

Over the last 30 years, records show that permafrost temperatures are warming significantly as a result of climate change; but as permafrost thaws, it has a reciprocal impact on climate change. Top down thawing of permafrost (which is the effect a warming climate has on it) results in the following environmental and climate consequences:

  • Permafrost acts as a perennial storage system for carbon (often called a carbon skin) by significantly slowing the decomposition of organic matter. Melting permafrost will result in significant greenhouse gas emissions (including methane) to be released in large quantities.
  • As permafrost melts in areas where there’s poor drainage, the ground can become saturated, killing trees.
  • Thawing of permafrost can change biodiversity and biomass of certain areas, replacing wet boreal forests with wetlands and dry forests with steppe-like habitats.
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