When scientists talk about the cryosphere, they mean the places on Earth where water is in its solid form, frozen into ice or snow. Read more ...
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This map shows three definitions of the Arctic: the tree line; the 10 degrees Celsius isotherm, and the Arctic Circle at 66° 32" North. Click on image for a higher resolution version.
—Credit: Map courtesy The Perry-Castañeda Library Map Collection. Treeline added at NSIDC based on information from National Geographic 1983, Armstrong et al. 1978, and Young 1989.
The region surrounding the North Pole consists of a large ocean surrounded by land. This ocean, called the Arctic Ocean, is like no other ocean on Earth; and because of its special location and climate, the lands that surround it are unique.
Most commonly, scientists define the Arctic as the region above the Arctic Circle, an imaginary line that circles the globe at 66° 32" N (dashed blue circle in the map at right). The Arctic Circle marks the latitude above which the sun does not set on the summer solstice, and does not rise on the winter solstice. At the North Pole, the sun rises once each year and sets once each year: there are six months of continuous daylight and six months of continuous night. At lower latitudes, but north of the Arctic Circle, the duration of continuous day and night are shorter.
But other people use different definitions when talking about the Arctic. Some scientists define the Arctic as the area north of the arctic tree line (green line in map at right), where the landscape is frozen and dotted with shrubs and lichens. Other researchers define Arctic based on temperature. Using this definition, the Arctic includes any locations in high latitudes where the average daily summer temperature does not rise above 10 degrees Celsius (50 degrees Fahrenheit).