Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 241

Results from some GCMs provide insight as to potential future changes in climate.
Barry (1992) stated that most GCMs based on a doubling of CO 2 by 2030 to 2050 sug-
gest a 3° ± 1.5°C increase in mean global surface temperatures. Warming is ampli-
fied two to three times at the North Pole because of greater land area in the northern
hemisphere and positive feedbacks such as reduction of snow and sea ice extent. CO 2
levels have already risen from about 280 ppm (preindustrial) to 379 ppm in 2005. Oth-
er estimates are also available based on a doubling of CO 2 : For the Rocky Mountains,
Beniston (1994) showed a 2-4°C increase in temperature with no increase in precipita-
tion and, for the Alps, a 2-4°C increase in temperature with drier conditions. However,
another regional climate model of the Alps showed a 1.5°C increase in temperature
in winter with more snow, and a 4°C increase in summer with less precipitation. Ac-
cording to data from SNOTEL sites across Colorado, annual median air temperatures
have increased 0.7°C per decade from 1986 to 2007 (Clow 2010). In the Loch Vale wa-
tershed, temperatures have increased 1.3°C per decade from 1983 to 2007. Over the
same period, the D-l station on Niwot Ridge has warmed by 1.0°C per decade (Clow
2010). The time period analyzed is an important consideration: Short-term cooling an-
omalies superimposed on a longer warming trend may cause misinterpretation (Pepin
and Losleben 2002).
According to the Intergovernmental Panel on Climate Change's 4th Assessment Re-
port (Solomon et al. 2007), the next two decades will experience a warming of about
0.2°C per decade. Even if the concentrations of all greenhouse gases and aerosols had
been kept constant at year 2000 levels, a further warming of about 0.1°C per decade
would be expected. Beyond this time frame, temperature projections will depend on
specific emissions scenarios. There is great uncertainty and variability as to feedbacks
that may occur and their impacts on ecosystems. In particular, mountain climatic pro-
cesses must be better understood in order to predict their effects on changing mountain
environments (Beniston 2000).
Several sources of evidence describe the recent effects of climate change on perma-
frost. At a depth of 20 m on the Tibetan Plateau, temperatures have risen by 0.2-0.3°C
over the last two decades. Lachenbruch and Marshall (1986) have shown a 2°C increase
in the upper 2 m of permafrost during the last several decades to a century in Alaska.
Permafrost in the Alps warmed at 0.1°C yr −1 because of warming in the 1980s. The
response is slow because heat takes time to travel to great depths, but it is departing
from the trend of natural variability (Haeberli 1994). Rock glaciers and glaciers in the
Alps have shown accelerated rates of degradation (Haeberli 1994). Permafrost has re-
sponded by a thickening of the active layer, thaw settlement, and the alteration of the
temperature profiles within the permafrost. At Gruben rock glacier, rates of surface sub-
sidence accelerated by a factor of 2 to 3 in the warm 1980s to 1990s compared to the
1970s. Borehole temperatures on Murtèl I rock glacier have also shown an increase in
temperature, a trend that was more consistent at depth as the influence of a seasonal
signal was less. Recent measurements indicate that the ground has warmed by 0.2°C
over the last 10 years in the Rocky Mountain Front Range, and a substantial rate of in-
crease has occurred since 2000 (Caine 2010). Increased stream discharge in the late
summer and fall is the result of increased melting of ice previously stored within per-
mafrost (Caine 2010). The current rate of degradation seems to be evolving beyond the
limit of natural Holocene variability.