Permafrost is permanently frozen ground that remains at or below 0°C for at least two consecutive years. It is found in polar regions and high-altitude areas and plays a critical role in the Earth’s climate system, particularly in the carbon cycle, as it stores large amounts of organic carbon that can be released as greenhouse gases when thawed.
Source Brown, J., et al. (1998). “Circumpolar Active Layer Monitoring (CALM) Program: Description and Data.” CD-ROM. National Snow and Ice Data Center.