Geology Reference
In-Depth Information
hydrocarbon. Large reserves occur in western Siberia (Makogon et al., 1972), the
Mackenzie Delta and Arctic islands (Judge, 1982), and the Alaska North Slope (Collett,
1983). Since signifi cant quantities of methane are trapped within gas hydrates, methane
will be released to the atmosphere as permafrost degrades. This may lead to an addi-
tional 0.4 °C increase in global temperatures by 2020 and a 0.6-0.7 °C increase by 2050
(Street and Melnikov, 1990).
15.3.4. Seasonally-Frozen Ground
Climate warming will affect the extent of seasonally-frozen ground and the depth of
frost penetration. Areas experiencing seasonal frost will be reduced in extent. For
example, calculations based on degree days below 0°C for Calgary and Toronto, two
cities in Canada which experience seasonal frost, indicate that frost penetration will be
reduced by 50-60% and 75-85%, respectively, as a result of an increase of 6 °C in the
mean annual air temperature. Similar changes will occur in the northern United States,
Sweden, northern Japan, Russia, and China, and all areas where seasonal frost is wide-
spread. It can be anticipated that frost damage to roads and structures will be reduced
signifi cantly.
15.3.5. Boreal Forest, Tundra, and Polar Desert Ecosystems
Higher temperatures in winter and changed precipitation patterns will signifi cantly affect
vegetation zonation and agricultural practices in the sub-arctic. In particular, the treeline
and the northern limit of the boreal forest will move northwards. Figure 15.6A shows the
possible northward shift in position of the boreal forest in Western Canada. This is based
upon the 600- and 1300-growing-degree-day isolines as approximations of the northern
and southern boundaries. While the shift in the northern boundary ranges from about
100 km to 700 km, the shift in the southern boundary is much greater, about 250-900 km
(Table 15.3). Such predictions are based on climate-change models assuming two-time
CO
2
increases. One may question whether the rate of forest movement will be a direct
response to a change in the thermal conditions and whether the growing-degree-day
method is suitable for examining forest zone shifts. However, such predictions highlight
the major changes in vegetation, land use, and agricultural practice that will follow upon
warming in northern Canada. In general, in sub-arctic regions, the potential for agricul-
ture would increase signifi cantly if the growing season lengthened by 30 - 40%. Growing
conditions in Whitehorse and Yellowknife, for example, would become similar to those
today in Edmonton and Calgary, approximately 1000 km to the south.
Similar scenarios are predicted for Scandinavia (Boer et al., 1990) assuming a 3°C
mean annual temperature increase. One prediction indicates the northward movement of
oak trees to areas currently experiencing only 116 growing days (Figure 15.6B). It is also
predicted that the lower altitudinal limit of coniferous forest would rise by about 600 m
and that boreal forest would disappear from all of Sweden except at elevations in excess
of 1350 m.
In the polar deserts of the high latitudes, the limiting factors for viable plant communi-
ties relate to the availability of nutrients and water rather than to temperature. It follows
that climate warming will infl uence arctic vegetation according to its effect on soil mois-
ture and nutrients, especially nitrates. These changes are diffi cult to quantify at present,
but we might expect a subtle but signifi cant change in the distribution of tundra species,
and their assemblages.
