PES » Global Warming » Information Center » Alaska, Northern Canada, and Greenland
	This part of the world is characterized by long cold winters and short cool summers. Four kinds of habitat predominate in this region of the world; sea ice, continental ice, tundra, and boreal forest. Sea Ice Much of the ocean in this part of the world remains frozen year-round. In the winter, the sea ice extends across the entire Arctic Ocean and southward into the Bering Sea and the Hudson Bay. In the summer, the area covered by sea ice decreases, but large parts of the ocean remain frozen.		forward: Questions back: Information Center browse: Table of Contents
	Polar bears are dependent on sea ice for hunting; they wait on ice floes for seals to come to the surface. Seals depend on sea ice as a place to give birth and raise their young.		Comparison of the area covered by sea ice in the Arctic during the winter (left) and summer (right). (Image courtesy NASA Goddard Space Flight Center)
	Continental Ice Continental ice covers most of Greenland. The interior of Greenland is covered with snow and ice year-round because the temperature does not rise above freezing. In some places, the depth of the ice on Greenland is several of thousands of meters deep. This layer of ice is referred to as the Greenland ice cap. An enormous amount of fresh water is stored in the Greenland ice cap.		Polar Bears (Ursus maritimus) in the Arctic. (Photograph courtesy U.S. Fish and Wildlife Service)
	Arctic Tundra Tundra covers the land where climate is too severe for trees to survive. Summers in the Arctic tundra are very short and cool. Winters are long and severe. Day length varies dramatically with season. At the peak of summer, the sun is visible for 24 hours low on the horizon. At the peak of winter, there is no sunlight at all for 24 hours. Average yearly temperatures range from -70 degrees F to 20 degrees F. Although the tundra is a cold place, very little precipitation occurs. On average, less than 200mm (8") of precipitation falls per year. The ground of the tundra is called permafrost. Permafrost extends from the surface to a depth of 300 meters (1000ft). In the summer, the top 10-60 cm (4-24") of the permafrost melts. The permafrost prevents animals from hibernating in burrows in the ground during winter. Tundra vegetation consists of grasses, sedges, lichens and willow shrubs. Most tundra plants grow flat on the ground to avoid the drying cold winds. Shrubs may be several meters high in southern reaches of the tundra, but shorten toward the north until they lie flat along the ground. Some plants are so low and densely packed that they are called “cushion plants”. Not many kinds of animals live year-round in the tundra. Most birds and mammals only use the tundra as a summer home. Mammals that do live year-round in the tundra include the musk-ox, Arctic wolf, and brown bear. Animals that do not live in the tundra year-round migrate during winter to warmer locations. Migrating animals of the tundra include many birds such as the waterfowl and shorebirds. These birds nest in the tundra shrubbery in summer, migrating to the milder climates before the winter season sets in.		Noatak Wild River, Gates of the Arctic National Park and Preserve, Alaska (Photograph courtesy National Park Service) Waters edge tundra on the arctic coastal plain of Alaska. (Photograph courtesy U.S. Fish and Wildlife Service)
	Musk-ox, caribou and reindeer are the dominant grazing animals of the tundra. They feed on grasses, sedge, lichen and willow. Arctic hares, or snowshoe rabbits, and lemmings feed on grass and sedge. Predators include the wolf, arctic fox, polar bear, brown bear, and snowy owl. Some mammals and birds turn white in winter for camouflage, brown again in summer. The permafrost prevents most animals from hibernating in burrows in the ground during winter. The tundra ecosystem is extremely sensitive to disturbance with little ability to restore itself. Disruption of vegetative cover causes permafrost to melt deeply, causing collapse of ground and loss of soil. Boreal Forest Boreal Forest (also called the Taiga) occurs generally to the south of tundra, and receives more precipitation than the tundra. Precipitation tends to be spread throughout the year, with heavy snow during winter, and rain during the summer.		Vegetation on the arctic coastal plain of Alaska . (Photograph courtesy U.S. Fish and Wildlife Service)
	Coniferous trees (or “conifers”) dominate the boreal forest all across the northern hemisphere. Coniferous trees are evergreen (they keep their leaves all year) with needle shaped leaves, and include familiar trees like pines, firs, and spruces. The size of trees in the boreal forest decreases from south to north. As one gets further north, the boreal forest consists of smaller and smaller trees until one reaches land where the climate is too cold and dry for trees to grow at all. Needleleaf trees are well adapted to cold climates—their “Christmas tree” shape helps heavy snow slide off during the winter so that their branches don't break. Mosses and lichens cover the ground beneath the trees. Just like in the tundra habitat, animals in the boreal forest have strategies to avoid the winter season. Many birds migrate and many mammals hibernate in burrows under the snow. Also, just like in the tundra, many mammals that stay active during the winter turn white for camouflage in the winter snow. Common animals of the boreal forest are bald eagles, canada geese, ermines, weasels, moose, red foxes, snowshoe rabbits, wolverines, bears, pine martens, caribou, and lynx.		Evergreens dominate the boreal forest. (Photograph courtesy NASA Goddard Space Flight Center BOREAS Project)
			forward: Questions back: Information Center

	Subscribe to the Earth Observatory About the Earth Observatory Contact Us Privacy Policy and Important Notices Responsible NASA Official: Lorraine A. Remer Webmaster: Goran Halusa We're a part of the Science Mission Directorate