Global Outlook for Ice & Snow

Glaciers and Ice Caps

Summary Glaciers and ice caps are among the most fascinating elements of nature, an important freshwater resource but also a potential cause of serious natural hazards. Because they are close to the melting point and react strongly to climate change, glaciers are important indi- cators of global climate. Glaciers reached their Holocene (the past 10 000 years) maximum extent towards the end of the Little Ice Age (the Little Ice Age extended from the early 14th to mid-19th century.) Since then, glaciers around the globe have been shrinking dramatically, with increasing rates of ice loss since the mid-1980s. On a time-scale of decades, glaciers in various mountain ranges have shown intermittent re- advances. However, under the present climate scenarios, the ongoing trend of worldwide and fast, if not accelerat- ing, glacier shrinkage on the century time-scale is not a periodic change and may lead to the deglaciation of many mountain regions by the end of the 21st century. Glacial retreat and melting of permafrost will shift cry- ospheric hazard zones. This, in combination with the increasing socio-economic development in mountain regions, will most probably lead to hazard conditions beyond historical precedence. Changes in glaciers may strongly affect the seasonal availability of freshwater, es- pecially when the reduction of glacier runoff occurs in combination with reduced snow cover in winter and ear- lier snowmelt, less summer precipitation, and enhanced

Glacier: a mass of surface-ice on land which flows downhill under gravity and is constrained by internal stress and fric- tion at the base and sides. In general, a glacier is formed and maintained by accumulation of snow at high altitudes, bal- anced by melting at low altitudes or discharge into the sea. Ice cap: dome-shaped glacier with radial flow, usually cover- ing a highland area. Much smaller than an ice sheet.

Glaciers and ice caps (lowest and [highest] estimates): Area Covered (million square km)

0.51 [0.54] 0.05 [0.13] 15 [37]

Ice Volume (million cubic km) Potential Sea Level Rise (cm) Source: IPCC 2007 1

evaporation due to warmer temperatures. The most criti- cal regions will be those where large populations depend mainly on water resources from glaciers during the dry season and glaciated mountain ranges that are densely populated and highly developed. This chapter on glaciers and ice caps is divided into two parts: 1) Global Overview and Outlook, and 2) Glacier Changes around the World.

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GLOBAL OUTLOOK FOR ICE AND SNOW