Download Week 7, Part 2 - Atmospheric Sciences at UNBC

Permafrost in
Canada and
climate change
Source:
NRC
1
Source: Hinzman et al. (2005)
2
Time to form deep permafrost
Time (yr) Permafrost depth
1
4.44 m
350
79.9 m
3,500
219.3 m
35,000
461.4 m
100,000
567.8 m
225,000
626.5 m
775,000
687.7 m
Source: Wikipedia
3
Snow & permafrost warming
4
Source: Stieglitz et al. (2003)
Source: Hinzman et al. (2005)
5
Permafrost and climate change
• During the past few thousand years,
Earth's climate has been subject of fairly
small changes and world temperatures
have fluctuated only within a couple of
degrees.
• However, higher levels of carbon dioxide
and other greenhouse gases in the
atmosphere may progressively increase
global temperature by as much as 2 to 4oC
over the next century.
6
• In addition to temperature changes, the patterns
of precipitation would undoubtedly change annual totals would likely increase over the
arctic mainland, although current regional
projections are again quite variable between
models.
• Increase of 10 to 50% in summer and as much
as 60% in winter may be anticipated for parts of
the Canadian Arctic.
• Such large and rapid climatic changes would
have serious and far-reaching environmental
and socio-economic effects in permafrost
regions and for the arctic environment as a
whole.
7
• Some might look on the transition to a
warmer Arctic with happy anticipation; in
the long term, it would undoubtedly result
in greatly reduced costs of living and
operating there.
• New resources could become available,
and mining and agriculture, for example,
might expand; however the terrestrial
environment of the north, in which
permafrost plays a major role, would be
profoundly disrupted during the transition.
8
• Permafrost degradation may lead to
another, potentially disastrous, positive
feedback on climate.
• Degrading permafrost may allow the
release of greenhouse gases such as CO2
and CH4 that are currently trapped in
frozen ground (especially in peat bogs).
9
• Let us imagine some change in climatic
conditions which causes the mean annual
surface temperature to fall below 0oC, so
that the depth of winter freezing will
exceed the depth of summer thaw.
• A layer of permafrost would grow
downward from the base of the seasonal
frost, thickening progressively with each
succeeding winter.
10
• Was it not for the effect of heat escaping
from Earth's interior (the geothermal heat
flux), the permafrost would grow to depths
in response to surface temperatures only
slightly below 0oC.
• However, this outward heat flow results in
a temperature increase of about 30 K
km-1, the figure varying with regional
geological conditions.
11
• Thus the base of permafrost approaches
an equilibrium depth where the
temperature increase caused by this
geothermal gradient just offsets the
amount by which the surface temperature
is below freezing.
• Whereas the base of permafrost is
determined by the mean surface
temperature and geothermal heat flow, the
upper layers of permafrost are influenced
more by seasonal and interannual
fluctuations of temperature and snowpack.
12
• The major variation in surface temperature
has a period of one year, corresponding to
the annual cycle of solar radiation (there is
also a diurnal variation corresponding to
the daily cycle of radiation).
• Temperature variations experienced with
the passage of the seasons at the surface
extend in a progressively dampened
manner to a depth of some 10-20 m.
13
• Within the layer of annual variation,
maximum and minimum figures form an
envelope about the mean, and the top of
permafrost is that depth where the
maximum annual temperature is 0oC.
• Superimposed on normal periodic
variations are other fluctuations with
durations from seconds to years; causes
may included sporadic cloudiness,
variations in weather and changes in
climate.
14
Oke (1987)
15
16
• Let us now imagine some change in climatic
conditions which causes mean annual surface
temperature to rise.
• The result would be deepening of the active
layer, as both the mean annual temperature and
the envelope of maximum (summer)
temperatures shift to higher values.
• If climatic warming was sustained, the
permafrost table would recede further year by
year and the base of the permafrost would begin
to rise as surface warming propagated to greater
depths.
17
• If the progressive warming were great
enough, then permafrost could eventually
disappear altogether.
• Since permafrost is a thermal condition, it
is potentially sensitive to changes in
climate.
• However changes in the thermal regime of
the ground that lead to degradation (or
formation) of permafrost can result from
environmental changes other than
fluctuations in climate.
18
• For example, removal, damage, or compaction
of surface vegetation, peat, and soil alters the
balance of surface energy transfers.
• In winter, increases in snow cover accumulation,
as can result from barriers, structures, and
depressions or changes in wind patterns, can
lead to significant warming of the ground.
• Decreases in snow cover, in contrast, lead to
cooling of the ground, other things being equal.
19
• While the effects of surface environmental
changes are usually restricted in areal extent,
climatic change can affect extensive areas of
permafrost.
• Even modest climatic warming could have
drastic effects for terrain conditions and northern
engineering, since thousands of square
kilometers of warm permafrost would be directly
affected.
• While many centuries would be required for
complete degradation of the affected permafrost,
thawing from the surface would begin
immediately, with many potentially serious
results.
20
• There is some evidence that permafrost has
been retreating during the past decades: Syslov
(1961) reports that the permafrost extent at
Mezen (Russia) has retreated northward at an
average rate of 400 m per year since 1837,
whereas similar findings have been reported for
the Mackenzie Valley of Canada.
• Although permafrost is temperature dependent,
the relation with climate is not straightforward,
since the surface temperature regime does not
depend solely on geographic location.
21
• Local surface conditions such as the type of
vegetation, depth of snow cover, soil type, and
moisture content, profoundly affect the surface
energy regime, being interposed between the
atmosphere and the ground.
• Thus myriad local variations of vegetation,
topography, and soil conditions can cause
differences in mean ground temperatures of
several degrees over quite small areas.
Wherever average temperature is within a few
degrees of 0oC, such variation mean that
permafrost occurs in patches, or
discontinuously.
22
• These circumstances, together with the
scattered nature of direct observations,
make precise mapping of permafrost
difficult.
• While cold is usually seen as the singular
feature of high latitudes, problems
resulting from thaw are generally of
greater practical concern.
23
• Where permafrost contains ground ice,
considerable thaw settlement can occur
and such action has been responsible for
significant damage to buildings, roads,
runways, etc. and increased action would
undoubtedly cause additional and severe
maintenance and repair problems.
• Special concern might be directed to
existing water-retaining structures, such as
reservoirs, and hydrodams, especially in
areas of thaw-sensitive permafrost.
24
• Erosion of lake, river, and reservoir shorelines
may increase because of permafrost thawing
and a longer open-water season.
• Greater sediment transport in rivers could
shorten the operating life of hydro-electric
projects, for example.
• The expected rise in sea level accompanying
global warming could accelerate coastal retreat
in permafrost regions and combined with thaw
settlement as permafrost melts, could produce
inundation of low-lying areas.
25
Potential Changes in the Components of the
Surface Water Budget, Kuparuk River Basin
26
Source: Déry et al. (2005), JHM.
27
Source: Anisimov (2006)
Slaymaker and Kelly (2007)
28
Source: Lawrence and Slater (2005)
29
Source: Lawrence and
Slater (2005)
30
Source: Vavrus (2007)
31
32