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.
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.
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.