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What is the Cryosphere


Past Variability of Canadian Glaciers

The 'Pleistocene' is the geological term given to last two million years of earth history, during which the earth underwent several periods of deep glaciation (lasting hundreds of thousands of years), followed by shorter interglacial periods (measured in tens of thousands of years). The last cold phase ended just 10,000 years ago, so it is likely that the earth is presently just between two glaciations. A more recent advance of mountain glaciers took place during the 'Little Ice Age', beginning about 900 years ago and peaking around 1850. Since then, however, global glaciers have shrunk dramatically (click here to see trends in length changes of mountain glaciers). There is increasing evidence that global warming may be playing its part in this modern glacial meltdown.

Terminus fluctuations at Saskatchewan and Athabasca Glaciers since 1700

Figure 1: Terminus fluctuations at Saskatchewan and Athabasca Glaciers since 1700.

Historic fluctuations of Canadian glaciers are reconstructed from old maps, photographs, analysis of direct measurements and data on the glacier form and composition. Studies using these methods all indicate that most Canadian mountain glaciers have melted by between 25% and 75% since the peak of the Little Ice Age. Fresh moraines from this time are clearly evident in the Rocky Mountains, hundreds of metres beyond the present glacier margins. For example, the early travelers between Banff and Jasper used the Wilcox pass because the terminus of the Athabasca glacier was in bottom of the valley now traversed by the Icefields Parkway. Past data for high Canadian arctic glaciers and ice caps is sparse, although recent data also suggests that these are melting.

Glacier terminus fluctuations and volume changes provide important clues into climate change since glacier variations are controlled by precipitation, temperature, and cloudiness. Figure 1 above shows the terminus fluctuations of the Saskatchewan and Athabasca Glaciers since 1700. Note the dramatic retreat of both glaciers since early 1900 until about 1950-80 when a slowdown in the retreat rate occurred, and nearly an advance of Athabasca Glacier. More recently, both glaciers have shown enhanced retreat again. Results from 1990s interferometric studies of the Columbia Icefield (compared to previous studies carried out in the 1950s and 1960s) also indicate that the icefield glaciers have dramatically thinned and retreated in recent decades, and that an acceleration in the flow from the accumulation area has occurred. Generally speaking, small mountain glaciers across the world show similar patterns with those of the Canadian Rockies; their mass loss being most extensive during the first half of the 20th century, followed by more modest losses and even occasional sustained mass gains in the 1970s and early 1980s.

peyto glacier in 1966 in the Canadian Rockies

Figure 2: The Peyto Glacier (Canadian Rockies) in 1966 (W.E.S. Henoch photograph). Such photographs are helpful to scientists when re-constructing the historic variability of a glacier.

Peyto Glacier Case Study

The Peyto Glacier (see figure 2) is located in the Canadian Rocky Mountains at an altitude between 2140 m and 3180 m above sea level and covers an area of approximately 12 km2. It contributes flow to the two important river catchments, the Mistaya (12% glacier cover) and the North Saskatchewan rivers. The glacier snout is subject to high rates of melt, and there is marked surface lowering on several parts of the glacier.

mass balance of Peyto glacier 1966-1997

Figure 3a: Specific winter, summer and net mass balance time series for Peyto Glacier; 3b) cumulative percentage departure from the mean for the specific winter and summer balance (updated from Demuth and Keller, 1997).

The variation of the seasonal and net mass balance time series of the Peyto Glacier between 1966 and 1997 is shown in Figure 3. From the graph, we can see that the winter has played a dominant role in the evolution of the net balance for this period. A major shift occurred after 1976, exhibiting a step change of approximately -515 mm w.e. This shift to lower winter balance for Peyto Glacier is synchronous with an increase in the frequency of non-snow producing synoptic weather types and a decrease in the frequency of snow producing weather types (caused by a modulation of the Pacific-North-American (PNA) circulation pattern and the El Niño Southern Oscillation (ENSO) - see Hodge et al (1999) for more information).

Past-century and recent decadal-order variations in mass balance of Peyto glacier

Figure 4: Past-century and recent decadal-order variations in mass balance of the Peyto glacier.

Figure 4 shows the past-century variations in mass balance of the Peyto glacier. In agreement with the general global pattern, the Peyto Glacier underwent spectacular mass loss during the first half of the 20th century followed by a pronounced abatement after the mid-century. More recently, but particularly during the mid-1970s, the rate of mass loss approached that of the early century again, even showing signs of acceleration broadly consistent with estimated man-induced radiative forcing (several W/m2). However, a gradual attenuation of this pattern occurred from 1988 onwards, with winter accumulations slowly returning to their long-term average. Interestingly, the drastic early-century variations took place during relatively weak anthropogenic forcing.