Geology Reference
In-Depth Information
and nival offsets and the
n
factor (see Chapter 3). The Circumpolar-Active-Layer-
Monitoring (CALM) program is designed to observe the response of the active layer and
near-surface permafrost to climate change. Over 100 standardized sites have been estab-
lished in the northern polar region and a similar observing system is being initiated in the
southern hemisphere. The program is spearheaded by the International Permafrost
Association.
As a generalization, increased thaw penetration and thaw subsidence characterize the
various data sets. At some sites, thermokarst indicates degradation of warmer permafrost.
The relationship with current climate is reasonably clear; for example, during the 1990s
sites in both Alaska and northern Canada experienced maximum and minimum thaw
depths in the years of warmest (1998) and coolest (2000) summers (Brown et al., 2000).
Typical reports of active-layer monitoring programs are those for Alaska (Hinkel and
Nelson, 2003), northern Canada (Smith et al., 2001; Tarnocai et al., 2004), West Green-
land (Humlum, 1998c), Svalbard (Repelewska-Pekalowa and Pekala, 2004), northeast
Russia (Zamolodchikov et al., 2004), Western Siberia (Melnikov et al., 2004), and Eastern
Siberia (Fyodorov-Davydov et al., 2004).
15.2.3. Extent of Permafrost
If warming trends continue, dramatic changes will occur with respect to permafrost dis-
tribution. Figure 8.1 (see p. 187) illustrates the long-term effect of a rise in air tempera-
ture upon the ground thermal regime at two sites representative of continuous and
discontinuous permafrost. In continuous permafrost, the active layer thickens and per-
mafrost decreases in thickness from both top and bottom. In discontinuous permafrost,
the permafrost may actually disappear. The time for this to occur is problematic. The
increased thickness of the active layer would occur at approximately the same time as
the climate warming; the change in permafrost thickness, however, may take several
hundred years. For example, Kane et al. (1991) show that a surface warming of 4 °C over
a 50-year period in northern Alaska would result in an increase in the active layer from
0.50 m to 0.93 m but that the permafrost temperature at a depth of 30 m would increase
by only 1 °C. Likewise, Lachenbruch et al. (1988) demonstrated that the 2 °C increase in
the temperature at the permafrost table over the last 100 years that has been experienced
in Alaska has only penetrated approximately 100 m. This is one of the reasons why relict
permafrost exists (see Chapter 11).
Current degradation (warming) of permafrost is convincingly demonstrated by tem-
perature data obtained from a borehole in the Arctic Wildlife Refuge, Northern Alaska
(Figure 15.2) (Osterkamp and Jorgenson, 2006). The curve in the initial (1985) borehole
temperature plot indicates earlier warming, probably in the 1925-1950 period, while
measurements made in 1998 and 2004 indicate ongoing warming.
Spatial changes in the extent of permafrost will also be very signifi cant. Figures 15.3
and 15.4 indicate the extent to which permafrost may ultimately degrade in Canada and
Siberia, based upon warming scenarios of
2 °C, respectively. In Siberia, it is
estimated that there will be a 10% reduction in permafrost over a 50-year period.
A similar scale of change is predicted for northern Canada. For example, the infl uence
of lakes upon permafrost has been studied in detail by Burn (2002, 2005) in connection
with possible climate change. Today, lakes occupy approximately 25-30% of the surface
area of the Pleistocene Mackenzie Delta region. Many probably originated through the
melt-out of buried ice bodies. Today, only the larger water bodies possess taliks that per-
forate (i.e. penetrate) the permafrost. Geothermal modeling indicates that the critical
dimensions for the development of open taliks are circular lakes of radius 180 m, and oval
+
4 °C and
+
