Alpine glaciers and permanent ice and snow patches in western Canada approach their smallest sizes since the mid-Holocene, consistent with global trends.

Most alpine glaciers in the Northern Hemisphere reached their maximum extents of the Holocene between ad 1600 and 1850. Since the late 1800s, however, glaciers have thinned and retreated, mainly because of atmospheric warming. Glacier retreat in western Canada and other regions is exposing subfossil tree stumps, soils and plant detritus that, until recently, were beneath tens to hundreds of metres of ice. In addition, human artefacts and caribou dung are emerging from permanent snow patches many thousands of years after they were entombed. Dating of these materials indicates that many of these glaciers and snow patches are smaller today than at any time in the past several thousand years. This evidence, in turn, suggests that glacier recession in the 20th century is unprecedented during the past several millennia and that glaciers in western Canada have reached minimum extents only 150–300 years after they achieved their maximum Holocene extents. [ABSTRACT FROM AUTHOR]