Global Outlook for Ice and Snow: Chapter 7 - Frozen ground

Permafrost temperatures have increased during the last
20–30 years in almost all areas of the Northern Hemisphere.
An increase in the depth of the active layer above
the permafrost, which thaws in the summer, is less certain.
Further increases in air temperatures predicted
for the 21st century are projected to initiate widespread
permafrost thawing in the subarctic and in mountain
regions in both hemispheres. Widespread thawing of
permafrost will speed up the decomposition of organic
material previously held frozen in permafrost, emitting
large amounts of greenhouse gases into the atmosphere.
Thawing of ice-rich permafrost may also have serious
consequences for ecosystems and infrastructure, and in
mountain regions, may reduce the stability of slopes and
increase the danger of rock falls and landslides