Almost all permafrost in Europe, as well as permafrost tains labile bioavailable organic material, this decom-
along the southern coasts (below 70° N) of Greenland, position process occurs particularly rapidly
43,44
. When
will also be thawing by the end of the 21st century. The thawing occurs in the absence of oxygen, for example,
model predicts permafrost cooling in some regions, due when the permafrost thaws under a lake, decomposi-
to a combination of predicted increase in air tempera- tion of organic matter produces methane
45
(see box
tures with predicted decrease in snow depth and dura- on thermokarst lakes). The warming potential (relative
tion in these regions. greenhouse effect) of methane is 23 times stronger than
that of carbon dioxide, though methane does not persist
in the atmosphere for as long as carbon dioxide. Thus,
Impacts on the carbon cycle – feedback permafrost thawing acts as a positive feedback to global
mechanisms warming that is projected to intensify with further per-
mafrost degradation in the future
34,46
.
The largest global impact of changes in permafrost is
due to its role in the global carbon cycle. Permafrost soils
gradually accumulate organic carbon as they form be- Impacts on ecosystems
cause carbon which has been removed from the atmos-
phere through photosynthesis is stored in the form of Northern ecosystems depend on permafrost and ground
organic matter, as soils freeze and decomposition slows ice conditions. Soil temperature, active-layer thickness,
or stops. The upper part of permafrost (1–25 m below moisture content, presence of unfrozen water, and sur-
the surface) in boreal and Arctic ecosystems is estimated
to contain ~750–950 gigatonnes of organic carbon
38–40
, a
Effects of thawing of ice-rich
quantity that exceeds the 750 gigatonnes of organic car-
permafrost on a forest in Alaska.
bon currently in the atmosphere. This figure does not
Photo: V. Romanovsky
include carbon contained in deeper permafrost, in hy-
drates within or under the permafrost, or other non-per-
mafrost soil carbon pools. The amounts of carbon stored
in some of these locations are still poorly defined, but an
assessment of current understanding was recently pro-
vided through a workshop hosted by the Arctic Coun-
cil’s Arctic Monitoring and Assessment Programme
41
.
Yedoma, an extremely carbon-rich type of permafrost
found mostly in northern and central Siberia, contains
roughly half of the organic carbon in the upper part of
permafrost
38,42
.
When permafrost thaws, decomposition of organic mat-
ter leads to production and emission of the greenhouse
gases, carbon dioxide and methane, to the atmosphere.
If thawing occurs in the presence of oxygen, decomposi-
tion produces carbon dioxide. For yedoma, which con-
CHAPTER 7 FROZEN GROUND 189