Permafrost is a portmanteau word formed from perma- and
, describing ground which is permanently
. The minimum time for which the ground in a region must stay at or below zero degrees
(32 degrees
) in order to qualify as permafrost is
years.
It is currently estimated that around
percent of the earth's surface is permafrost, but that has been shrinking in recent years. Most permafrost regions are found in the
, in polar regions such as
, Alaska and Greenland. In the
, there is less permafrost area primarily because there is less land area. Most of
does not qualify, as regions underneath permanent ice sheets are not included.
As polar air temperatures have been increasing over recent years, the ground has been
, leading to surface
. This is a problem for several reasons. First, if there is a lot of
trapped in the frozen region, its melting causes a change of
and reduced rigidity of the ground. When infrastructure (buildings and
, for example) has been constructed on the assumption that the ground is going to remain
at all times, this can cause extensive damage. Permafrost degradation can lead to land
, resulting in a large depression for which the Russian term is 'alas'.
Secondly, the frozen ground of ancient permafrost areas contains a lot of trapped
, from organic substances that did not fully decompose in the frozen ground. As they thaw, bacteria break them down, releasing
and methane into the atmosphere, increasing the concentration of
gases which are of concern for climatologists.
