|Thaw of the Permafrost
definition of permafrost is: “a soil staying at or below
0 °C for more than two years”.
The annual average temperature is the most important factor for
permafrost existence. In regions covered by permafrost, only the upper
30 to 100 cm of soils (called the active layer) thaws every summer and
then completely refreezes during the winter. The thickness of
permafrost varies from a few meters to more than 150 meters.
Permafrost typically forms in regions with a mean annual air
temperature of less than 0°C. Exceptions are found in moist-wintered
forest climates, such as in Northern Scandinavia and North-Eastern
Russia west of the Urals, where snow acts as an insulating blanket. The
permafrost currently covers 20% of Earth’s land surface
(25 million km²) and 25% of the Northern Hemisphere. The extension of
the permafrost in Asia is very important (see illustration below).
extent in the Northern Hemisphere - Source: UNEP
Permafrost extent in Asia (from deep permafrost in red to shallow
permafrost in light red) - Source: Atlas of the Cryosphere
What is happening to permafrost?
The long-term records of the
near-surface permafrost temperature, obtained from different parts of
the permafrost zone in Northern regions, have shown a significant
warming trend during the last 30 years. Ground
temperature trends generally follow the air temperature trends with a
more pronounced warming in the lower latitudes (between 55° and 65°
North). But the permafrost belt stretching across Siberia to Alaska and
Canada (the continental land mass surrounding the Arctic) could start
melting 3 times faster than expected regarding the speed at which
Arctic Sea ice is disappearing. The smaller the area of sea ice, the
less sunlight is reflected and the more heat is absorbed.
What are the consequences of thawing?
Increasing permafrost temperatures
changes many of its physical properties
which has some negative effects on man-made infrastructures.
The thaw of the
permafrost can also endanger the region's biodiversity. Indeed,
permafrost controls plant communities and biomass production by soil
temperature, active layer thickness, moisture content, presence of
unfrozen water, and surface hydrology. The current changes in the
permafrost thermal regime and active layer thickness affect
plant diversity and biomass in all the regions covered
by this layer of frozen soil.
permafrost degradation will also continuously improve conditions for
the subsurface water drainage (especially in sandy soils) that will
lead to increased dryness of soils,
inducing significant vegetation stress. Improved drainage conditions
will also lead to the reducing of numerous ponds within the degrading
permafrost area dramatically affecting aquatic ecosystems.
And, last but not
least, the melting of the Arctic permafrost could dramatically worsen
global warming by releasing massive amounts of trapped greenhouse
gases, especially methane.
Drew Point, 2004. Coastal erosion of mud-rich permafrost along Beaufort
Sea coastline. Cliff height is 3–4 m. Waves undercut permafrost and
cause block slumping (center of photo). Source: USGS
The release of
methane as consequence of the melting
From the ocean floor
It's always been a disturbing what-if scenario for climate researchers:
gas hydrates stored in the Arctic Ocean floor (hard clumps of ice and
methane, conserved by freezing temperatures and high pressure) could
grow unstable and release massive amounts of methane into the
is a greenhouse gas more than 20
times more powerful than carbon dioxide, the result
would be a drastic acceleration of global warming.
Until now this idea was mostly academic; scientists had warned that
such a thing could happen. Now it seems more likely that it will.
scientists have shown strong evidence that the first stages of melting
are underway. They've studied the largest shelf sea in the world, off
the coast of Siberia. In the permafrost bottom of the 200-meter-deep
sea, enormous stores of gas hydrates lie dormant in mighty frozen
layers of sediment. The carbon content of the ice-and-methane mixture
here is estimated at 540 billion tons. This submarine hydrate was
considered stable until now but the permafrost has grown porous and the
shelf sea has already become "a source of methane passing into the
If this Siberian
permafrost-seal thaws completely and all the stored gas escapes, the methane
content of the planet's atmosphere would increase twelve fold
and the result would be catastrophic global warming.
gathered evidence for the loss of rigour in the frozen sea floor in a
measuring campaign during the Siberian summer. The seawater proved to
be highly oversaturated with solute methane. In the air over the sea,
greenhouse-gas content was measured in some places at 5 times normal
values. In helicopter flights over the delta of the Lena River, higher
methane concentrations have been measured at altitudes as high as 1,800
A recent study of two Siberian thaw lakes has revealed the Northern
wetlands are a much larger source of methane release into the
atmosphere than previously believed. Understanding the contribution of
North Siberia thaw lakes to global atmospheric methane concentration is
critical because the concentration of that potent greenhouse gas, which
is highest at that latitude, has risen sharply in recent decades and
exhibits a significant seasonal jump at those high northern latitudes.
The study has shown
that the thawing permafrost along the margins of the thaw lakes (which
comprise 90 % of the lakes in the Russian permafrost zone) is the
primary source of methane released in the region. An isotopic analysis
to determine the methane's age and origin coupled with measurements of
the methane bubbles' composition has also shown that an expansion of
these lakes between 1974 and 2000, a period of regional warming,
increased methane emissions by 58%. Because the methane now emitted in
this study region dates from the Pleistocene age, it's clear that the
global warming has led to the release of old carbon stocks once stored
in the permafrost.
Arctic thaw threatens Siberian permafrost
A Storehouse of Greenhouse Gases Is Opening in Siberia
How rapidly is permafrost changing and what
are the impacts of these changes?
Geological survey of Canada
Greenhouse Gas Bubbling from Melting
Permafrost Feeds Climate Warming at Much Higher Than Expected Rates
All about Frozen grounds - The National
Snow and Ice Data Center
Frozen Grounds -
Global Outlook for Ice and Snow - UNEP
Spring Thaw on
North Slopeand Frozen Ground: An
Interview with Permafrost Expert