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The cryosphere is the scientific name for all the frozen water on the Earth’s surface: ice caps, glaciers, sea ice, land ice, frozen lakes, snow, permafrost, etc. The cryosphere makes up an important part of the planet as a whole, providing a cooling effect by reflecting sunlight back into space and causing positive feedback cycles of cooling. The cryosphere is much larger today than it was throughout most of the history of life, when forests extended from pole to pole and glaciation was limited to mountains at extreme latitudes.
As you might guess, the cryosphere is huge. Since Antarctica separated from the continent of Australia 20 million years ago, a freezing circumpolar ocean current has cooled the continent and caused it to become covered in ice year-round. The greatest volume of ice in the cryosphere is concentrated in the East Antarctic Ice Sheet, which can be up to about two miles in depth. 90% of the volume of global ice sheets is found in Antarctica, with another 9.5% in Greenland, and only 0.5% found in other areas such as northern Canada, Russia, Scandinavia, and Alaska. The residence time of a given ice particle in an ice sheet can be very long, ranging from 100,000 to 1 million years. Altogether, the world’s ice sheets contain 77% of the global total of fresh water.
In terms of area, snow-covered ground makes up the second-largest component of the cryosphere, after the ice sheets. The extent of snow-covered ground is very seasonal – the summer snow cover is only about 10% of the winter snow cover. The vast majority of snow-covered ground is located in the Northern Hemisphere, as the Southern Hemisphere lacks ground for snow to cover. Both human tribes and a variety of animal species are able to colonize snow-covered ground, but usually not outright ice sheets, which lack soil for plants to grow. A couple exceptions are polar bears and penguins, which live near the shores and consume fish.
As climate change continues to increase the average global temperature, the extent of the cryosphere is slowly decreasing. It is estimated that the melting cryosphere will add at least a couple of inches to the world’s sea levels by 2100.