Snow exerts a huge influence on climate, through its
high reflectivity, insulating properties, and cooling of
the atmosphere, and on surface hydrology, through its
effects on water resources in many parts of the world.
Mean monthly snow-cover extent in the Northern Hemisphere
has decreased at a rate of 1.3 per cent per decade
during the last 40 years, with greatest losses in the
spring and summer months. Climate models project
significant decreases in snow cover by the end of this
century, with reductions of 60 to 80 per cent in snow water
equivalent (depth of water resulting from snow melt)
in most mid-latitude regions. Increases are projected for
the Canadian Arctic and Siberia. Higher temperatures
and rises in snow line are projected for many mountain
regions. Changes in snow cover, such as the formation
of ice layers in snow due to increased frequency of snow
thaw, have widespread impacts as snow is an important
ecological factor. Snow-cover changes also have impacts
on human well-being and economic activities, including
water resources, agriculture, animal husbandry, transportation
and winter recreation such as skiing.
United Nations Environment Programme
