Permafrost is permanently frozen ground, including soil, sediment, or rock. In order to be considered permafrost, the ground must remain below freezing for at least two consecutive years. Permafrost can persist for tens of thousands of years or more. Depending on the ground temperature, permafrost can be either continuous or sporadic. Permafrost is composed of different layers. Seasonal frost, which thaws during warmer times of the year, is generally present on top of permafrost and is called the "active layer." In the Arctic zone, permafrost may extend more than 100 meters below an active layer. Sometimes, a layer of unfrozen ground, called a "talik," is sandwiched between the active layer and the permafrost.

Permafrost is most commonly found in high latitudes near the North and South Poles. About half of the world's permafrost is found in Russia and Siberia. Permafrost is found in the Arctic, Alaska, and northern Canada, as well as further south in the Rocky Mountains. In the Southern Hemisphere, permafrost is found in Antarctica and the Andes Mountains.

Although permafrost can persist for thousands of years, it's temperature is often near its melting point (Axelrod, 2004). Therefore, slight changes in ground temperature can quickly affect the distribution and thickness of permafrost. Recent warming trends have caused large sections of permafrost to thaw, decreasing the amount and depth of permafrost observed in many areas. Situations in which the ground thaws deeper than the next winter's freeze can result in a talik forming (Botterill, 2003). This allows heat to accumulate within the ground, accelerating permafrost thaw.

Thawing permafrost can have significant impacts on ecosystems and human infrastructure, as well as potentially contributing to the release of greenhouse gases (GHGs). Roughly one-third of the world's total soil carbon is estimated to be stored in permafrost. GHGs, such as carbon dioxide (CO2) and methane, are often trapped within frozen ground. As permafrost thaws, these gases may potentially be released into the atmosphere. Permafrost-related GHG emissions can contribute to a positive feedback loop as well: As more permafrost thaws, more GHGs are released, increasing the greenhouse effect and warming the climate. Consequently, permafrost thaw increases, releasing more GHGs.

Significant impacts on infrastructure and ecosystems can result from permafrost loss, as pockets of soil that contain large amounts of ice melt, buckling highways and destabilizing building foundations. Ground underneath forests can also cave in, causing what is referred to as "drunken forests," with trees leaning inward at an angle. Permafrost degradation can also result in erosion and landslides. Ecosystem diversity, composition, and productivity are also impacted by declining permafrost.

References

1. Axelrod, Regina S., David Leonard Downie, and Norman J. Vig, eds. The Global Environment: Institutions, Law, and Policy. 2d ed. Washington, D.C.: CQ Press, 2004.

2. Botterill, Linda C., and Melanie Fisher, eds. Beyond Drought: People, Policy, and Perspectives. Collingwood, Vic.: CSIRO, 2003.

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