Global warming is causing shrinkage in mountain glacier volume, decrease in snow cover, changes in the permafrost and frozen ground, reduction in the Arctic sea ice extent, coastal thinning of the Greenland ice sheet, and reduction in the seasonally frozen ground, river, and lake ice cover. These changes in ice cover contribute to an increase in sea levels.
- The area under frozen ground is observed to have declined by about 7% in the last few decades, with the decrease during the spring season comparatively much higher. Satellite records indicate that the onset dates of thaw in spring and freeze in autumn have advanced by a week or so in Eurasia during 1988 to 2002.
- Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by 27 (2.1 to 3.3) % per decade, with larger decreases in summer of 74 (5.0 to 9.8) % per decade. Mountain glaciers and snow cover, on average, have declined in both hemispheres.
The following graph depicts decadal variations in Northern Hemisphere snow cover for March-April.
Northern Hemisphere snow cover for March-April
You can view an animation depicting projected sea-ice extent at Hadley Centre
Ice sheets are known to respond to changes over very long time scales. Ice shelves lose mass by calving icebergs and melting at the base into the ocean. A warming of about 1 Â°C in the oceans can increase the melting of the base of an ice shelf at a rate of 10 m/year. These are, however, broad estimates, indicative of the reduction in the ice content. Records of previous ice ages indicate that ice sheets have shrunk in response to warming and increased in volume in response to cooling.
How does Cryosphere affect Climate?