ABSTRACT
The totality of Earth’s frozen waters constitutes the cryosphere. The cryosphere consists of ice and snow, which is present in the atmosphere, in lakes and rivers, in oceans, on the land, and under the Earth’s surface (Figure 10.1). It constitutes less than 2 per cent of the total water in the hydrosphere, but glaciers and permanent snow account for just over two-thirds of all fresh water (Table 10.1). At present, glaciers cover about 10 per cent of the Earth’s land surface, and pack or
sea ice coats about 7 per cent of the ocean surface (during winter conditions, when such ice is at its maximum extent). Most of the glacier ice is confined to polar latitudes, with 99 per cent being found in Antarctica, Greenland, and the islands of the Arctic archipelago. At the height of the last glaciation, around 18,000 years ago, ice covered some 32 per cent of the Earth’s land surface. Continuous and discontinuous zones of permanently frozen ground underlie another 22 per cent of the Earth’s land surface, but volumetrically they account for less than 1 per cent of all fresh water (Table 10.1).
