West Antarctica, or Lesser Antarctica, one of the two major regions of Antarctica, is the part of that continent that lies within the Western Hemisphere, and includes the Antarctic Peninsula. It is separated from East Antarctica by the Transantarctic Mountains and is covered by the West Antarctic Ice Sheet. It lies between the Ross Sea (partly covered by the Ross Ice Shelf), and the Weddell Sea (largely covered by the Filchner-Ronne Ice Shelf). It may be considered a giant peninsula stretching from the South Pole towards the tip of South America.
West Antarctica is largely covered by the Antarctic ice sheet, but there have been signs that climate change is having some effect and that this ice sheet may have started to shrink slightly. The coasts of the Antarctic Peninsula are the only parts of West Antarctica that become (in summer) ice-free. These constitute the Marielandia Antarctic tundra and have the warmest climate in Antarctica. The rocks are clad in mosses and lichens that can cope with the intense cold of winter and the short growing-season.
Lying on the Pacific Ocean side of the Transantarctic Mountains, West Antarctica comprises the Antarctic Peninsula (with Graham Land and Palmer Land) and Ellsworth Land, Marie Byrd Land and King Edward VII Land, offshore islands such as Adelaide Island, and ice shelves, notably the Filchner-Ronne Ice Shelf on the Weddell Sea, and the Ross Ice Shelf on the Ross Sea. The Ross Sea and the Weddell Sea separate West Antarctica from the main land-mass of the continent: one can think of West Antarctica as a giant peninsula that stretches roughly from the South Pole towards the southern tip of South America.