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The Cryosphere World Map Snow and the various forms of ice—the cryosphere—play different roles within the climate system. The two continen- tal ice sheets of Antarctica and Greenland actively influ- ence the global climate over time scales of millennia to millions of years, but may also have more rapid effects on environmental sea level. Snow and sea ice, with their large areas but relatively small volumes, are connected to key interactions and feedbacks at global scales, includ- ing solar reflectivity and ocean circulation. Perennially frozen ground (permafrost) influences soil water content and vegetation over vast regions and is one of the cry- osphere components most sensitive to atmospheric warm- ing trends. As permafrost warms, organic material stored in permafrost may release greenhouse gases into the atmo- sphere and increase the rate of global warming. Glaciers and ice caps, as well as river and lake ice, with their smaller areas and volumes, react relatively quickly to cli- mate effects, influencing ecosystems and human activities on a local scale, and act as good indicators of climate change. Snow cover extent for Northern Hemisphere is represented by the 1966–2005 February average, for Southern Hemisphere by the 1987–2003 August average. Sea ice extent for Northern Hemisphere is represented by the 1979–2003 March average, for Southern Hemisphere by the 1979–2002 September average. Permafrost data for mountain areas and for the Southern Hemisphere are not represented in this map, neither are river and lake ice. UNEP/GRID-Arendal Arendal, Norway By Hugo Ahlenius Contact Hugo Ahlenius Software ArcGIS Desktop 9.2, Adobe Illustrator, Adobe Photoshop Data Sources National Snow and Ice Data Center, World Data Center for Glaciology, National Geospatial-Intelligence Agency Courtesy of UNEP/GRID-Arendal. Environmental Management 35