Policy Implications of Warming Permafrost Policy Implications of Warming PermafrostExecutive Summary

• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Canada; Active layer monitoring; Active layer thickness; Ice; permafrost; wedge*; Siberia
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.365.5159; http://www.unep.org/pdf/permafrost.pdf

Permafrost is perennially frozen ground occurring in about 24 % of the exposed land surface in the Northern Hemisphere. The distribution of permafrost is controlled by air temperature and, to a lesser extent, by snow depth, vegetation, orientation to the sun and soil properties. Any location with annual average air temperatures below freezing can potentially form permafrost. Snow is an effective insulator and modulates the effect of air temperature, resulting in permafrost temperatures up to 6°C higher than the local mean annual air temperature. Most of the current permafrost formed during or since the last ice age and can extend down to depths of more than 700 meters in parts of northern Siberia and Canada. Permafrost includes the contents of the ground before it was frozen, such as bedrock, gravel, silt and organic material. Permafrost often contains large lenses, layers and wedges of pure ice that grow over many years as a result of annual freezing and thawing of the surface soil layer. About 24 % of the northern hemisphere land surface contains permafrost, divided into zones of continuous, discontinuous, sporadic and isolated patches of permafrost, depending on how much of the land area contains permafrost. Two global networks monitor permafrost status: the Thermal State of Permafrost (TSP) network measures permafrost temperature at various depths in 860 boreholes, and the Circumpolar Active Layer Monitoring (CALM) network measures the thickness of the active layer at 260 sites. The active layer thickness is the maximum surface thaw depth