In geology, permafrost or cryotic soil is soil at or below the freezing point of water 0 °C(32 °F) for two or more years. Most permafrost is located in high latitudes (i.e. land close to the North and South poles), but alpine permafrost may exist at high altitudes in much lower latitudes. Ground ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost accounts for 0.022% of total water and exists in 24% of exposed land in the Northern Hemisphere.
A global temperature rise of 1.5 °C(2.7 °F) above current levels would be enough to start the melting of permafrost in Siberia, according to one group of scientists.