The term “desert” was once confined to hot, arid regions of the tropics and subtropics. However, the central place given to the absence or sparsity of vegetation in many definitions of the term has led to the development of the concept of the “cold desert”—a terrain in which low temperatures and physiological drought drastically inhibit plant growth. Such conditions are, of course, most typically found in the earth's polar regions—the Arctic and Antarctica—leading to the concept of the “polar desert.”
True polar desert is surprisingly rare in the Arctic. Most of the central north polar region comprises the Arctic Sea; the Arctic's land area is made up of the northernmost parts of the North American and Asian continents as well as of a large number of islands, notably Greenland, the Canadian Arctic Archipeiago, and the SvaJbard group, Lack of snowfall and relatively moderate temperatures, created especially where Arctic climates are tempered by maritime currents, also mean that less than two-fifths of this land is permanently covered with ice.
More typical of the Arctic is the low-lying scrubland that lies beyond the tree line—usually known as tundra, but in its American incarnation often known as the Barren Grounds. However, a few areas, such as the heavily glaciated inland of Greenland and its arid northern coast, resemble hot deserts in that plant life is minimal. However, as in the hot desert environment, some plants have evolved strategies to survive not only the bitter cold but also the long winter nights and long summer days. Many Arctic plants reproduce asexually, and many have a swift life cycle—growing, blooming, and seeding in a few weeks during the brief Arctic summer. Exposed rocks are home to numerous species of lichen, while even permanent ice supports algae.
Animals have adapted less well to Arctic conditions, perhaps because the relative swiftness of glaciation in the region meant that there was little time for adaption to take place. In the Arctic and Subarctic just a few species—such as the polar bear and fox, snowy owl, and gyrfalcon—tend to exist In relatively large numbers, In contrast to the Arctic, Antarctica is a continent all of its own and is almost entirely covered with ice; indeed, the Antarctic ice sheet accounts for some 90 percent of the earth's ice. This is the so-called White Desert, where winter temperatures can fall as low as ?89.2°C (?128.6°F), far colder than even the Arctic. The continent is also subject to fierce blizzards, as cold winds sweep down from the interior highlands and sweep up the loose snow—just as hot desert winds whip up sands into blinding dust storms. Moreover, despite the presence of vast quantities of water in the form of ice, there is little precipitation in Antarctica—the equivalent of only about 50 millimeters rainfall.
Extreme cold, high winds and blizzards, and the scarcity of moisture mean that little plant or animal life can survive on Antarctica, although, by contrast, the surrounding seas are home to a rich variety of flora and fauna. Cold-adapted life tends to congregate around the more hospitable microclimates created where high altitudes combine with northerly, coastal latitudes to attract a higher degree of solar radiation. In total, there are only about 800 plant species in Antarctica, of which almost half are lichens, which are able to remain dormant during the long winter months. Animal life is still rarer. Apart from tiny arthropods such as mites and lice, the principal Antarctic animals are birds, most notably Adelie and emperor penguins, whose immense rookeries are crammed along the coastline. Other Antarctic species include petrels, albatrosses, and cormorants. With the exception of the great emperor penguin, all these birds migrate northward with the growth of the winter ice.
Hot deserts are remarkably stable environments. Their polar counterparts, by contrast, have proved much more susceptible to human interference. The development of whaling stations in the past and today's scientific stations and tourism have introduced many alien species of plants and even animals; on some subarctic islands rabbits and sheep have decimated local plant species. Of more concern is the threat of global warming and the melting of both Arctic and Antarctic glaciers, although as yet no clear environmental trends are discernible. Antarctica's probable great mineral wealth is a great temptation for the world's nations. At present, however, international treaties protect the White Desert from mineral exploitation, and there are plans afoot to make the continent a vast “world park.”