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This paper presents examples of environmental changes in the Canadian Rockies in the context of a 1.5 deg. C increase in mean annual temperatures over the last 100 years. During this period increases in winter temperatures have been more than twice as large as those during spring and summer. Glacier cover has decreased by at least 25% during the present century and glacier fronts have receded to positions lastoccupied ca. 3000 years ago. These two lines of evidence suggest that the climate of the late 20th century is exceptional in the context of the last 1000 to 3000 years. Detailed studies in three closely located upper treeline sites document variable responses of vegetation to climate change that reflect species differences as well as local differences in microclimate and site conditions. Treeline has advanced upslope in response to climate warming, but site and species differences control the rate and nature of the advance. Human impacts on the environment compound the changes due to climate warming. Historic photographs indicate significant changes in the type and density of forest cover due to the absence of significant forest fires within these National Parks during the last 70-80 years. The visual impact of these changes, which partially reflects a policy of fire suppression, is far greater than the impact of changes associated with more direct tourist-related impacts. It is therefore important that monitoring programs examine vegetation changes over the entire landscape rather thanfocusing exclusively on supposedly climate-sensitive sites. [ABSTRACT FROM AUTHOR]