Landscape and climate change in the central Canadian Rockies during the 20th century

This paper reviews selected evidence of environmental changes in the centra l Canadian Rockies during the 20th century. The instrumental climate record shows that mean annual temperatures have risen ca. 1.4 degrees C over the last 100 years but seasonal patterns of change are complex. The greatest in creases have been in winter temperatures (3.2 degrees C/century). Precipita tion data, though limited, show variable patterns of change on decadal scal es with generally higher levels of precipitation in the mid-20th century. T he longest streamflow record also shows considerable variability, with high est flows in the 1950s. A tree-ring-based temperature reconstruction indica tes summer and spring temperatures in the last half of the 20th century are higher than any equivalent period over the last 900 years. Although no acc urate regional estimates exist, glaciers have probably lost ca. 25% of thei r area in the last 100 years and may be smaller now than they have been at any time in the last 3000 years. These two lines of evidence suggest that t he climate of the late 20th century is exceptional in the context of the la st 1000 to 3000 years. Small but significant vegetation changes are taking place at the upper tree line ecotone in response to climate changes over the 20th century (e.g., se edling establishment). However, the most significant landscape change in th e last 100 years is the transformation of the character of the montane fore st due to a reduction in forest fire frequency, largely due to an active po licy of fire suppression.