from model simulations to a data set derived from NOAA Snow as an ecological factor
visible band imagery found the model simulations of an-
nual and interannual variability in snow-covered area to The importance of snow as an ecological factor has been
be reasonable at continental to hemispheric scales
28
. At recognized by science since at least the beginning of the
regional scales, however, significant model biases were 20th century
37,38
. However, even today many observations
identified over Eurasia at the southern boundary of the remain anecdotal. In the 1950s, Gjaerevoll
39
analysed the
seasonal snow cover. A simulation from one such model way in which the alpine plant community structure was
projects decreases of 60–80 per cent in monthly maxi- shaped by snow. Within the past decade, snow manipula-
mum snow water equivalent over most middle latitudes tion experiments have explored the effects of snow depth
by the end of this century (Figure 4.6). The largest de- and snow-cover duration on plant communities and eco-
creases are projected over Europe, while simulated in- system processes
40–42
. Recently, models of snow cover
creases are seen in the Canadian Arctic and Siberia. have been applied to ecological problems
43
.
Snow cover plays a dual role in terms of temperature
regulation. The high albedo of snow cover reduces net
radiation, and snow also acts as a heat sink, removing
energy from the atmosphere in the form of heat. This
means that the presence of snow cover inhibits soil
warming until the snow melts, preventing biological
activity that requires temperatures above 0
o
C. However,
snow is an efficient insulator, keeping soil temperatures
near 0
o
C and reducing the extremes of temperature ex-
perienced by vegetation and soil in the zone under the
snow (subnivean cavity). In autumn, the insulation
effect of snow on unfrozen ground can even result in
fungal decay of the vegetation, which can kill reindeer
calves when they eat the vegetation
44
. The subnivean en-
vironment is also very humid. Under thin snow packs
Projected % change in SWE between 1981-2000 and in spring, light levels permit limited photosynthesis for
2081-2100 by the ECHAM5 model (scenario SRES A2)
lichens and evergreen tundra shrubs
45
. This is an impor-
tant adaptation given the short growing season. Plants in
-98 - -75 -75 - -50 -50 - -10 -10 - +10 +10 - +50%
the “greenhouse of snow” created by the subnivean cav-
Figure 4.6: Percent change in monthly maximum snow water
ity can start to grow weeks before neighbouring plants
equivalent (SWE) between 1981–2000 and 2080–2100, simulated
covered by deep snow.
by the ECHAM5 climate model under conditions defined by the
SRES A2 emission scenario (RUN 2). Results are plotted for grid Snow exerts forces on the objects that it covers. For ex-
points with a mean maximum SWE of 10 mm in 1981–2000.
ample, snow in southern Finland at the end of March,
Source: R. Brown, Environment Canada; data from ESG 2007
29
estimated to weigh 100–120 kg per m
2
, compresses the
46 GLOBAL OUTLOOK FOR ICE AND SNOW