Antarctica, the fifth-largest continent in the world, is slightly larger than 1.5 times the size of the United States. It covers an estimated area of 14 million sq. km., of which 280,000 sq. km. is ice-free and 13.72 million sq. km. is ice-covered. Speculation over the existence of a southern continent was not confirmed until the early 1820s when British and American commercial operators and British and Russian national expeditions began exploring the Antarctic Peninsula region. It was not until 1840 that Antarctica was established as a continent, rather than a group of islands. Following World War II, there was an upsurge in scientific research on the continent. A number of countries have set up year-round research stations on Antarctica. Seven countries (Argentina, Australia, Chile, France, New Zealand, Norway, and the United Kingdom) have made territorial claims, but not all countries recognize these claims. In order to form a legal framework for the activities of nations on the continent, an Antarctic Treaty was negotiated that neither denies nor recognizes existing territorial claims; signed in 1959, it entered into force in 1961.
Antarctica, mostly uninhabitable, is the coldest, windiest, highest (on average), and driest continent. During the summer, more solar radiation reaches the surface at the South Pole than is received at the Equator in an equivalent period. The climate ranges in lower temperatures which vary with latitude, elevation, and distance from the ocean. The highest temperatures occur in January along the coast and average slightly below freezing. East Antarctica is colder than West Antarctica because of its higher elevation. The Antarctic Peninsula has the most moderate climate.
The terrain consists of 98% thick continental ice sheet and 2% barren rock. Ice-free coastal areas include parts of southern Victoria Land, Wilkes Land, the Antarctic Peninsula area, and parts of Ross Island on McMurdo Sound. Glaciers form ice shelves along about half of the coastline, and floating ice shelves constitute 11% of the area of the continent. The lowest known land point in Antarctica is hidden in the Bentley Subglacial Trench, which is 8,383 ft. below sea level. It is the deepest ice yet discovered and the world's lowest elevation not covered by ocean. Natural hazards include katabatic (gravity-driven) winds blowing coastward from the high interior, frequent blizzards that form near the foot of the plateau, and cyclonic storms which form over the ocean and move clockwise along the coast. Volcanoes occur on Deception Island and isolated areas of West Antarctica. Large icebergs may calve, or break off from ice shelves.
In 1998, NASA satellite data showed that the Antarctic ozone hole was the largest on record, covering 27 million sq. km. The ozone hole is primarily caused by human-produced compounds that release chlorine and bromine gases in the stratosphere. In 2002, significant areas of ice shelves disintegrated in response to regional warming. Colder than average temperatures result in larger and deeper ozone holes, while warmer temperatures lead to smaller ones.
CIA World Factbook; NOAA, 01/2007, 10/2006