The Little Ice Age in the Canadian Rockies

This paper reviews the evidence and history of glacier fluctuations during the Little Ice Age (LIA) in the Canadian Rockies. Episodes of synchronous glacier advance occurred in the 12th-13th, early 18th and throughout the 19th centuries. Regional ice cover was probably greatest in the mid-19th century, although in places the early 18th century advance was more extensive. Glaciers have lost over 25% of their area in the 20th century. Selective preservation of the glacier record furnishes an incomplete chronology of events through the 14th-17th centuries. In contrast, varve sequences provide continuous, annually resolved records of sediments for at least the last millennium in some highly glacierized catchments. Such records have been used to infer glacier fluctuations. Evaluation of recent proxy climate reconstructions derived from tree-rings provides independent evidence of climate fluctuations over the last millennium. Most regional glacier advances follow periods of reduced summer temperatures, reconstructed from tree rings particularly ca. 1190-1250, 1280-1340, 1690s and the 1800s. Reconstructed periods of higher precipitation at Banff, Alberta since 1500 are 1515-1550, 1585-1610, 1660-1680 and the 1880s. Glacier advances in the early 1700s, the late 1800s and, in places, the 1950-1970s reflect both increased precipitation and reduced summer temperatures. Negative glacier mass balances from 1976 to 1995 were caused by decreased winter balances. The glacier fluctuation record does not contain a simple climate signal: it is a complex response to several interacting factors that operate at different timescales. Evaluation of climate proxies over the last millennium indicates continuous variability at several superimposed timescales, dominated by decade-century patterns. Only the 19th century shows a long interval of sustained cold summers. This suggests that simplistic concepts of climate over this period should be abandoned and replaced with more realistic records based on continuous proxy data series. The use of the term LIA should be restricted to describing a period of extended glacier cover rather than being used to define a period with specific climate conditions. (C) 2000 Elsevier Science B.V. All rights reserved.