Geology Reference
In-Depth Information
Table 15.3.
Predicted changes in vegetation zonation for western and northwestern Canada, as
implied by climate change models.
(a) Northward shift (km) in northern and southern boundaries of boreal forest (delimited by
600- and 1300-growing-degree-day isolines)
Forest boundary
Climatic-change model
GISS
GFDL
Northern
80-720
100-730
Southern
470-920
250-900
(b) Changes in vegetation zonation according to GFDL-based model for three locations
Location
Present Zonation
GFDL Zonation
64° N, 120° W
Sub-arctic
Aspen parkland
(southern NWT between Great
Bear and Great Slave Lakes)
59°09
′
N, 120° W
Boreal
Aspen parkland
(northeastern BC\northwestern
Alberta)
55°5
′
N, 105°W
Boreal
Boreal temperate
(northern Saskatchewan)
Source: Wheaton and Singh (1988).
cities, such as Norilsk and Vorkuta, with populations in excess of 50 000-100 000 persons,
and there are the administrative cities of Yakutsk and Tyumen in addition to numerous
smaller settlements and mining towns. No precise fi gures are readily available but the vast
majority of the inhabitants of the periglacial environment live in Russia. Nearly all live in
areas of warm or discontinuous permafrost. Yet it is these marginal permafrost bodies
that will be fi rst affected by climate warming. This will impact upon the urban infrastruc-
tures in many ways. Just two examples are given here.
First, during the 1959-1962 construction of Thompson, a mining town of
10 000
persons in Northern Manitoba, Canada, the city authorities denied building permits to
certain residential lots because of the presence of randomly-distributed and shallow bodies
of frozen ground (Johnston et al., 1963). Most were between 3.0 m and 4.0 m thick and, in
all cases, the permafrost was marginal, possessing mean annual ground temperatures
ranging between
∼
1.5 °C. These plots remained vacant until the 1990s when,
because of increased land values in the city, drilling was undertaken to ascertain whether
permafrost still existed or not. It was found that frozen ground no longer existed on many
plots (French, 1998). It was also determined that mean annual air temperatures at Thomp-
son had probably risen by
−
0.5 °C and
−
0.5 °C during the 1910-1993 period (French and Egorov, 1998)
and, elsewhere in northern Manitoba, it was known that many peaty organic permafrost
bodies had experienced decay during the early 1970s (Thie, 1974; Zoltai and Tarnocai,
1975). As a result, housing permits were issued, land values rose accordingly, and new
houses were constructed in the 1990s.
A far different experience is predicted for many of the large cities that were con-
structed in northern Siberia during the Soviet era. Many have populations in excess of
∼
