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1.3.2. The Cryosphere

The cryosphere consists of those regions of the globe, both land and sea, covered by snow and ice. These include Antarctica, the Arctic Ocean, Greenland, Northern Canada, Northern Siberia and most of the high mountain ranges throughout the world, where sub-zero temperatures persist throughout the year. The cryosphere plays another important role in the regulation of the global climate system.

Snow and ice have a high albedoThe Albedo of a surface is a measure of its reflectivity, i.e. how much solar radiation is reflected. A value of 1 defines a perfectly reflective surface. White surfaces such as snow and ice have high albedos of the order of 0.8 to 0.9. A value of 0 defines a perfectly absorbing surface. Dark surfaces such as forest and surface ocean have low albedos (0.1 to 0.3). (reflectivity), that is they reflect much of the solar radiation they receive. Some parts of the Antarctic reflect as much as 90% of the incoming solar radiation, compared to a global average of 31% (see section 1.2.4). Without the cryosphere, the global albedo would be considerably lower. More energy would be absorbed at the Earth's surface rather than reflected, and consequently the temperature of the atmosphere would be higher. Indeed, during the Cretaceous Period (120 to 65 million years ago) evidence suggests there was little or no snow and ice cover, even at the poles, and global temperatures were at least 8 to 10�C warmer than today (Frakes, 1979; chapter 5).

The cryosphere also acts to decouple the atmosphere and oceans, reducing the transfer of moisture and momentum, so stabilising the energy transfers within the atmosphere (Henderson-Sellers & Robinson, 1986). The formation of sea ice in polar regions (section 1.3.1) can initiate global thermohaline circulation patterns in the oceans, which greatly influence the global climate system. Finally, the presence of the cryosphere itself markedly affects the volume of the oceans and global sea levels, changes to which can affect the energy budget of the climate system.