Highlights
Ice and snow are important components of the Earth’s level. Snow and sea ice, with their large areas but relatively
climate system and are particularly sensitive to global small volumes, are connected to key interactions and feed-
warming. Over the last few decades the amount of ice backs at global scales, including solar reflectivity and ocean
and snow, especially in the Northern Hemisphere, has circulation. Perennially frozen ground (permafrost) influ-
decreased substantially, mainly due to human-made glo- ences soil water content and vegetation over continental-
bal warming. Changes in the volumes and extents of ice scale northern regions and is one of the cryosphere com-
and snow have both global and local impacts on climate, ponents most sensitive to atmospheric warming trends.
ecosystems and human well-being. As permafrost warms, organic material stored in perma-
frost may release greenhouse gases into the atmosphere
Snow and the various forms of ice play different roles and increase the rate of global warming. Glaciers and ice
within the climate system. The two continental ice sheets caps, as well as river and lake ice, with their smaller ar-
of Antarctica and Greenland actively influence the global eas and volumes, react relatively quickly to climate effects,
climate over time scales of millennia to millions of years, influencing ecosystems and human activities on a local
but may also have more rapid effects on, for example, sea scale. They are good indicators of climate change.
8 GLOBAL OUTLOOK FOR ICE AND SNOW