Permafrost defined

Permafrost is permanently frozen soil—soil that remains at or below 0°C for at least two consecutive years—and occurs mostly in high latitudes. Permafrost can occur beneath the land surface (terrestrial permafrost) and beneath the seafloor (subsea permafrost).[1]

The ice content and temperature of permafrost are the key parameters that determine its physical state. Scientists use permafrost temperature, measured at a depth where seasonal variations cease to occur, as an indicator of long-term change and to represent the mean annual ground temperature.[2]

Global trends

Permafrost temperatures have increased in most regions since the early 1980s in response to increased surface temperature and changing snow cover.[1] 

By 2100, scientists expect the area of permafrost near the surface to decrease by between 37 to 81 percent, depending on the level of 21st century greenhouse gas emissions.[1]

Alaska trends

Permafrost lays underneath about 80 percent of Alaska’s surface. It is thickest and widespread in northern Alaska, diminishing to a permafrost-free region in the far south.[3] 70 percent of permafrost land in Alaska is vulnerable to land sinkage due to the steady rate of permafrost thaw.[3]

In the arctic region of Alaska, permafrost warmed up to 5.4°F (3°C) from 1980 to 2000.[4] Over the same period in the subarctic region—home to Alaska’s boreal forest—permafrost warmed 0.5-1.8°F (0.3°C-1°C) and is already beginning to thaw.[4]

Some climate models project that near-surface permafrost will be lost entirely from large parts of Alaska by the end of this century.[5] Some areas such as Fairbanks—Alaska’s second-largest city—are particularly vulnerable, because the ground temperature now hovers near the thaw point, making the permafrost on the verge of collapse and prone to thawing unevenly.