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There is some evidence, in the form of ice cores drilled to about 400 m (1,300 ft) above the water line, that Lake Vostok's waters may contain microbial life. The frozen surface of the lake shares similarities with Jupiter's moon, Europa. If life is discovered in Lake Vostok, it would strengthen the argument for the possibility of life on Europa.[48][49] On 7 February 2008, a NASA team embarked on a mission to Lake Untersee, searching for extremophiles in its highly alkaline waters. If found, these resilient creatures could further bolster the argument for extraterrestrial life in extremely cold, methane-rich environments. | There is some evidence, in the form of ice cores drilled to about 400 m (1,300 ft) above the water line, that Lake Vostok's waters may contain microbial life. The frozen surface of the lake shares similarities with Jupiter's moon, Europa. If life is discovered in Lake Vostok, it would strengthen the argument for the possibility of life on Europa.[48][49] On 7 February 2008, a NASA team embarked on a mission to Lake Untersee, searching for extremophiles in its highly alkaline waters. If found, these resilient creatures could further bolster the argument for extraterrestrial life in extremely cold, methane-rich environments. | ||
==Geology== | |||
More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time, Gondwana gradually broke apart and Antarctica as we know it today was formed around 25 million years ago. Antarctica was not always cold, dry, and covered in ice sheets. At a number of points in its long history, it was farther north, experienced a tropical or temperate climate, was covered in forests, and inhabited by various ancient life forms. | |||
===Palaeozoic era (540–250 Ma)=== | |||
During the Cambrian period, Gondwana had a mild climate. West Antarctica was partially in the Northern Hemisphere, and during this period large amounts of sandstones, limestones and shales were deposited. East Antarctica was at the equator, where sea floor invertebrates and trilobites flourished in the tropical seas. By the start of the Devonian period (416 Ma), Gondwana was in more southern latitudes and the climate was cooler, though fossils of land plants are known from this time. Sand and silts were laid down in what is now the Ellsworth, [[Horlick Mountains|Horlick]] and Pensacola Mountains. Glaciation began at the end of the Devonian period (360 Ma), as Gondwana became centred on the South Pole and the climate cooled, though flora remained. During the Permian period, the land became dominated by seed plants such as Glossopteris, a pteridosperm which grew in swamps. Over time these swamps became deposits of coal in the [[Transantarctic Mountains]]. Towards the end of the Permian period, continued warming led to a dry, hot climate over much of Gondwana. | |||
===Mesozoic era (250–66 Ma)=== | |||
As a result of continued warming, the polar ice caps melted and much of Gondwana became a desert. In [[Eastern Antarctica]], seed ferns or pteridosperms became abundant and large amounts of sandstone and shale were laid down at this time. ''Synapsids'', commonly known as "mammal-like reptiles", were common in Antarctica during the Early Triassic and included forms such as Lystrosaurus. The Antarctic Peninsula began to form during the Jurassic period (206–146 Ma), and islands gradually rose out of the ocean. Ginkgo trees, conifers, bennettites, horsetails, ferns and cycads were plentiful during this period. In West Antarctica, coniferous forests dominated through the entire Cretaceous period (146–66 Ma), though southern beech became more prominent towards the end of this period. Ammonites were common in the seas around Antarctica, and dinosaurs were also present, though only three Antarctic dinosaur genera (''Cryolophosaurus'' and ''Glacialisaurus'', from the Hanson Formation, and ''Antarctopelta'') have been described to date. It was during this era that Gondwana began to break up. | |||
However, there is some evidence of antarctic marine glaciation during the Cretaceous period. | |||
===Gondwana breakup (160–23 Ma)=== | |||
The cooling of Antarctica occurred stepwise, as the continental spread changed the oceanic currents from longitudinal equator-to-pole temperature-equalising currents to latitudinal currents that preserved and accentuated latitude temperature differences. | |||
Africa separated from Antarctica in the Jurassic, around 160 Ma, followed by the Indian subcontinent in the early Cretaceous (about 125 Ma). By the end of the Cretaceous, about 66 Ma, Antarctica (then connected to Australia) still had a subtropical climate and flora, complete with a marsupial fauna. In the Eocene epoch, about 40 Ma Australia-New Guinea separated from Antarctica, so that latitudinal currents could isolate Antarctica from Australia, and the first ice began to appear. During the Eocene–Oligocene extinction event about 34 million years ago, CO2 levels have been found to be about 760 ppm and had been decreasing from earlier levels in the thousands of ppm. | |||
Around 23 Ma, the Drake Passage opened between Antarctica and South America, resulting in the Antarctic Circumpolar Current that completely isolated the continent. Models of the changes suggest that declining CO2 levels became more important. The ice began to spread, replacing the forests that then covered the continent. | |||
===Neogene Period (23–0.05 Ma)=== | |||
Since about 15 Ma, the continent has been mostly covered with ice. | |||
Meyer Desert Formation biota | |||
Main article: Meyer Desert Formation biota | |||
Fossil Nothofagus leaves in the Meyer Desert Formation of the Sirius Group show that intermittent warm periods allowed Nothofagus shrubs to cling to the Dominion Range as late as 3–4 Ma (mid-late Pliocene). After that, the Pleistocene ice age covered the whole continent and destroyed all major plant life on it. | |||
===Present-day=== | |||
The geological study of Antarctica has been greatly hindered by nearly all of the continent being permanently covered with a thick layer of [[ice]]. However, new techniques such as remote sensing, ground-penetrating radar and satellite imagery have begun to reveal the structures beneath the ice. | |||
Geologically, Western Antarctica closely resembles the Andes mountain range of South America. The [[Antarctic Peninsula]] was formed by uplift and metamorphism of sea bed sediments during the late Paleozoic and the early Mesozoic eras. This sediment uplift was accompanied by igneous intrusions and volcanism. The most common rocks in West Antarctica are andesite and rhyolite volcanics formed during the Jurassic period. There is also evidence of volcanic activity, even after the ice sheet had formed, in [[Marie Byrd Land]] and [[Alexander Island]]. The only anomalous area of West Antarctica is the Ellsworth Mountains region, where the stratigraphy is more similar to East Antarctica. | |||
East Antarctica is geologically varied, dating from the Precambrian era, with some rocks formed more than 3 billion years ago. It is composed of a metamorphic and igneous platform which is the basis of the continental shield. On top of this base are coal and various modern rocks, such as sandstones, limestones and shales laid down during the Devonian and Jurassic periods to form the [[Transantarctic Mountains]]. In coastal areas such as Shackleton Range and Victoria Land some faulting has occurred. | |||
The main mineral resource known on the continent is coal. It was first recorded near the [[Beardmore Glacier]] by Frank Wild on the Nimrod Expedition, and now low-grade coal is known across many parts of the Transantarctic Mountains. The Prince Charles Mountains contain significant deposits of iron ore. The most valuable resources of Antarctica lie offshore, namely the oil and natural gas fields found in the [[Ross Sea]] in 1973. Exploitation of all mineral resources is banned until 2048 by the Protocol on Environmental Protection to the [[Antarctic Treaty]]. | |||
==Climate== | |||
Antarctica is the coldest of Earth's continents. It used to be ice-free until about 34 million years ago, when it became covered with ice. The coldest natural air temperature ever recorded on Earth was −89.2 °C (−128.6 °F) at the Soviet (now Russian) Vostok Station in Antarctica on 21 July 1983.[63] For comparison, this is 10.7 °C (20 °F) colder than subliming dry ice at one atmosphere of partial pressure, but since CO2 only makes up 0.039% of air, temperatures of less than −140 °C (−220 °F) would be needed to produce dry ice snow in Antarctica. A lower air temperature of −94.7 °C (−138.5 °F) was recorded in 2010 by satellite—however, it may be influenced by ground temperatures and was not recorded at a height of 7 feet above the surface as required for the official air temperature records. Antarctica is a frozen desert with little precipitation; the [[South Pole]] itself receives less than 10 cm (4 in) per year, on average. Temperatures reach a minimum of between −80 °C (−112 °F) and −89.2 °C (−128.6 °F) in the interior in winter and reach a maximum of between 5 °C (41 °F) and 15 °C (59 °F) near the coast in summer. Sunburn is often a health issue as the snow surface reflects almost all of the ultraviolet light falling on it. Given the latitude, long periods of constant darkness or constant sunlight create climates unfamiliar to human beings in much of the rest of the world. | |||
East Antarctica is colder than its western counterpart because of its higher elevation. Weather fronts rarely penetrate far into the continent, leaving the center cold and dry. Despite the lack of precipitation over the central portion of the continent, ice there lasts for extended periods. Heavy snowfalls are common on the coastal portion of the continent, where snowfalls of up to 1.22 meters (48 in) in 48 hours have been recorded. | |||
At the edge of the continent, strong [[katabatic wind]]s off the polar plateau often blow at storm force. In the interior, wind speeds are typically moderate. During clear days in summer, more solar radiation reaches the surface at the South Pole than at the equator because of the 24 hours of sunlight each day at the Pole. | |||
Antarctica is colder than the Arctic for three reasons: First, much of the continent is more than 3,000 m (9,800 ft) above sea level, and temperature decreases with elevation in the troposphere. Second, the Arctic Ocean covers the north polar zone: the ocean's relative warmth is transferred through the icepack and prevents temperatures in the Arctic regions from reaching the extremes typical of the land surface of Antarctica. Third, the Earth is at aphelion in July (i.e., the Earth is farthest from the Sun in the Antarctic winter), and the Earth is at perihelion in January (i.e., the Earth is closest to the Sun in the Antarctic summer). The orbital distance contributes to a colder Antarctic winter (and a warmer Antarctic summer) but the first two effects have more impact. | |||
The ''[[aurora australis]]'', commonly known as the southern lights, is a glow observed in the night sky near the South Pole created by the plasma-full solar winds that pass by the Earth. Another unique spectacle is diamond dust, a ground-level cloud composed of tiny ice crystals. It generally forms under otherwise clear or nearly clear skies, so people sometimes also refer to it as clear-sky precipitation. A sun dog, a frequent atmospheric optical phenomenon, is a bright "spot" beside the true sun. | |||
==Human population== | |||
Several governments maintain permanent manned research stations on the continent. The number of people conducting and supporting scientific research and other work on the continent and its nearby islands varies from about 1,000 in winter to about 5,000 in the summer, giving it a population density between 70 and 350 inhabitants per million square kilometers (180 and 900 per million square miles) at these times. Many of the stations are staffed year-round, the winter-over personnel typically arriving from their home countries for a one-year assignment. An Orthodox church—Trinity Church, opened in 2004 at the Russian Bellingshausen Station—is manned year-round by one or two priests, who are similarly rotated every year. | |||
The first semi-permanent inhabitants of regions near Antarctica (areas situated south of the Antarctic Convergence) were British and American sealers who used to spend a year or more on South Georgia, from 1786 onward. During the [[whaling]] era, which lasted until 1966, the population of that island varied from over 1,000 in the summer (over 2,000 in some years) to some 200 in the winter. Most of the whalers were Norwegian, with an increasing proportion of Britons. The settlements included Grytviken, Leith Harbour, King Edward Point, Stromness, Husvik, Prince Olav Harbour, Ocean Harbour and Godthul. Managers and other senior officers of the whaling stations often lived together with their families. Among them was the founder of Grytviken, Captain Carl Anton Larsen, a prominent Norwegian whaler and explorer who, along with his family, adopted British citizenship in 1910. | |||
The first child born in the southern polar region was Norwegian girl Solveig Gunbjørg Jacobsen, born in Grytviken on 8 October 1913, and her birth was registered by the resident British Magistrate of South Georgia. She was a daughter of Fridthjof Jacobsen, the assistant manager of the whaling station, and Klara Olette Jacobsen. Jacobsen arrived on the island in 1904 and became the manager of Grytviken, serving from 1914 to 1921; two of his children were born on the island. | |||
Emilio Marcos Palma was the first person born south of the 60th parallel south (the continental limit according to the [[Antarctic Treaty]]), as well as the first one born on the Antarctic mainland, in 1978 at Base Esperanza, on the tip of the [[Antarctic Peninsula]]; his parents were sent there along with seven other families by the Argentine government to determine if the continent was suitable for family life. In 1984, Juan Pablo Camacho was born at the Frei Montalva Station, becoming the first Chilean born in Antarctica. Several bases are now home to families with children attending schools at the station. As of 2009, eleven children were born in Antarctica (south of the 60th parallel south): eight at the Argentine Esperanza Base and three at the Chilean Frei Montalva Station. | |||
==Animals== | |||
Few terrestrial vertebrates live in Antarctica, and those that do are limited to the sub-Antarctic islands. Invertebrate life includes microscopic mites like the ''Alaskozetes antarcticus'', lice, nematodes, tardigrades, rotifers, [[krill]] and springtails. The flightless midge ''Belgica antarctica'', up to 6 mm (1⁄4 in) in size, is the largest purely terrestrial animal in Antarctica. The [[snow petrel]] is one of only three birds that breed exclusively in Antarctica. | |||
Some species of marine animals exist and rely, directly or indirectly, on the phytoplankton. Antarctic sea life includes penguins, [[blue whale]]s, [[orca]]s, [[colossal squid]]s and fur seals. The [[emperor penguin]] is the only penguin that breeds during the winter in Antarctica, while the [[Adélie penguin]] breeds farther south than any other penguin. The southern rockhopper penguin has distinctive feathers around the eyes, giving the appearance of elaborate eyelashes. [[King penguin]]s, [[chinstrap penguin]]s, and [[gentoo penguin]]s also breed in the Antarctic. | |||
The Antarctic fur seal was very heavily hunted in the 18th and 19th centuries for its pelt by sealers from the United States and the United Kingdom. The [[Weddell seal]], a "true seal", is named after Sir James Weddell, commander of British sealing expeditions in the Weddell Sea. [[Antarctic krill]], which congregate in large schools, is the keystone species of the ecosystem of the [[Southern Ocean]], and is an important food organism for whales, seals, [[leopard seal]]s, fur seals, squid, icefish, penguins, albatrosses and many other birds. | |||
A census of sea life carried out during the International Polar Year and which involved some 500 researchers was released in 2010. The research is part of the global Census of Marine Life (CoML) and has disclosed some remarkable findings. More than 235 marine organisms live in both polar regions, having bridged the gap of 12,000 km (7,456 mi). Large animals such as some cetaceans and birds make the round trip annually. More surprising are small forms of life such as sea cucumbers, and free-swimming snails found in both polar oceans. Various factors may aid in their distribution – fairly uniform temperatures of the deep ocean at the poles and the equator which differ by no more than 5 °C, and the major current systems or marine conveyor belt which transport eggs and larval stages. | |||
==Fungi== | |||
About 1,150 species of fungi have been recorded from Antarctica, of which about 750 are non-lichen-forming and 400 are lichen-forming. Some of these species are cryptoendoliths as a result of evolution under extreme conditions, and have significantly contributed to shaping the impressive rock formations of the McMurdo Dry Valleys and surrounding mountain ridges. The apparently simple morphology, scarcely differentiated structures, metabolic systems and enzymes still active at very low temperatures, and reduced life cycles shown by such fungi make them particularly suited to harsh environments such as the McMurdo Dry Valleys. In particular, their thick-walled and strongly melanised cells make them resistant to UV light. Those features can also be observed in algae and cyanobacteria, suggesting that these are adaptations to the conditions prevailing in Antarctica. This has led to speculation that, if life ever occurred on Mars, it might have looked similar to Antarctic fungi such as Cryomyces antarcticus, and Cryomyces minteri. Some of these fungi are also apparently endemic to Antarctica. | |||
Endemic Antarctic fungi also include certain dung-inhabiting species which have had to evolve in response to the double challenge of extreme cold while growing on dung, and the need to survive passage through the gut of warm-blooded animals. | |||
==Plants== | |||
About 298 million years ago Permian forests started to cover the continent, and tundra vegetation survived as late as 15 million years ago, but the climate of present-day Antarctica does not allow extensive vegetation to form. A combination of freezing temperatures, poor soil quality, lack of moisture, and lack of sunlight inhibit plant growth. As a result, the diversity of plant life is very low and limited in distribution. The flora of the continent largely consists of bryophytes. There are about 100 species of mosses and 25 species of liverworts, but only three species of flowering plants, all of which are found in the Antarctic Peninsula: ''Deschampsia antarctica'' (Antarctic hair grass), ''Colobanthus quitensis'' (Antarctic pearlwort) and the non-native ''Poa annua'' (annual bluegrass). Growth is restricted to a few weeks in the summer. | |||
===Other organisms=== | |||
Seven hundred species of algae exist, most of which are phytoplankton. Multicolored snow algae and diatoms are especially abundant in the coastal regions during the summer. Bacteria have been found living in the cold and dark as deep as 800 m (0.50 mi; 2,600 ft) under the ice. | |||
==International politics== | |||
Several countries claim [[sovereignty]] in certain regions. While a few of these countries have mutually recognized each other's claims, the validity of these claims is not recognized universally. | |||
New claims on Antarctica have been suspended since 1959, although in 2015 Norway formally defined Queen Maud Land as including the unclaimed area between it and the [[South Pole]]. Antarctica's status is regulated by the 1959 [[Antarctic Treaty]] and other related agreements, collectively called the Antarctic Treaty System. Antarctica is defined as all land and [[ice-shelf|ice shelves]] south of 60° S for the purposes of the Treaty System. The treaty was signed by twelve countries including the Soviet Union (and later Russia), the United Kingdom, Argentina, Chile, Australia, and the United States. It set aside Antarctica as a scientific preserve, established freedom of scientific investigation and environmental protection, and banned military activity on Antarctica. This was the first arms control agreement established during the Cold War. | |||
In 1983 the Antarctic Treaty Parties began negotiations on a convention to regulate mining in Antarctica. A coalition of international organisations launched a public pressure campaign to prevent any minerals development in the region, led largely by Greenpeace International, which operated its own scientific station—World Park Base—in the [[Ross Sea]] region from 1987 until 1991 and conducted annual expeditions to document environmental effects of humans on Antarctica. In 1988, the Convention on the Regulation of Antarctic Mineral Resources (CRAMRA) was adopted. The following year, however, Australia and France announced that they would not ratify the convention, rendering it dead for all intents and purposes. They proposed instead that a comprehensive regime to protect the Antarctic environment be negotiated in its place. The Protocol on Environmental Protection to the Antarctic Treaty (the "Madrid Protocol") was negotiated as other countries followed suit and on 14 January 1998 it entered into force. The Madrid Protocol bans all mining in Antarctica, designating Antarctica a "natural reserve devoted to peace and science". | |||
The Antarctic Treaty prohibits any military activity in Antarctica, including the establishment of military bases and fortifications, military maneuvers, and weapons testing. Military personnel or equipment are permitted only for scientific research or other peaceful purposes. The only documented military land maneuver has been the small Operation NINETY by the Argentine military in 1965. | |||
The Argentine, British and Chilean claims all overlap, and have caused friction. On 18 December 2012, the British Foreign and Commonwealth Office named a previously unnamed area Queen Elizabeth Land in tribute to Queen Elizabeth II's Diamond Jubilee. On 22 December 2012, the UK ambassador to Argentina, John Freeman, was summoned to the Argentine government as protest against the claim. Argentine–UK relations had previously been damaged throughout 2012 due to disputes over the sovereignty of the nearby Falkland Islands, and the 30th anniversary of the Falklands War. | |||
The areas shown as Australia's and New Zealand's claims were British territory until they were handed over following the countries' independence. Australia currently claims the largest area. The claims of Britain, Australia, New Zealand, France and Norway are all recognised by each other. | |||
Other countries participating as members of the Antarctic Treaty have a territorial interest in Antarctica, but the provisions of the Treaty do not allow them to make their claims while it is in force. | |||
* Brazil has a designated "zone of interest" that is not an actual claim. | |||
* Peru has formally reserved its right to make a claim. | |||
* Russia has inherited the Soviet Union's right to claim territory under the original Antarctic Treaty. | |||
* South Africa has formally reserved its right to make a claim. | |||
* United States reserved its right to make a claim in the original Antarctic Treaty. | |||
==Economy== | |||
There is no economic activity in Antarctica at present, except for fishing off the coast and small-scale tourism, both based outside Antarctica. | |||
Although coal, hydrocarbons, iron ore, platinum, copper, chromium, nickel, gold and other minerals have been found, they have not been in large enough quantities to exploit. The 1991 Protocol on Environmental Protection to the Antarctic Treaty also restricts a struggle for resources. In 1998, a compromise agreement was reached to place an indefinite ban on mining, to be reviewed in 2048, further limiting economic development and exploitation. The primary economic activity is the capture and offshore trading of fish. Antarctic fisheries in 2000–01 reported landing 112,934 tonnes. | |||
Small-scale "expedition tourism" has existed since 1957 and is currently subject to Antarctic Treaty and Environmental Protocol provisions, but in effect self-regulated by the International Association of Antarctica Tour Operators (IAATO). Not all vessels associated with Antarctic tourism are members of IAATO, but IAATO members account for 95% of the tourist activity. Travel is largely by small or medium ship, focusing on specific scenic locations with accessible concentrations of iconic wildlife. A total of 37,506 tourists visited during the 2006–07 Austral summer with nearly all of them coming from commercial ships; 38,478 were recorded in 2015–16. | |||
There has been some concern over the potential adverse environmental and ecosystem effects caused by the influx of visitors. Some environmentalists and scientists have made a call for stricter regulations for ships and a tourism quota. The primary response by Antarctic Treaty Parties has been to develop, through their Committee for Environmental Protection and in partnership with IAATO, "site use guidelines" setting landing limits and closed or restricted zones on the more frequently visited sites. Antarctic sightseeing flights (which did not land) operated out of Australia and New Zealand until the fatal crash of Air New Zealand Flight 901 in 1979 on Mount Erebus, which killed all 257 aboard. Qantas resumed commercial overflights to Antarctica from Australia in the mid-1990s. | |||
Antarctic fisheries in 1998–99 (1 July – 30 June) reported landing 119,898 tonnes legally. | |||
About thirty countries maintain about seventy research stations (40 year-round or permanent, and 30 summer-only) in Antarctica, with an approximate population of 4000 in summer and 1000 in winter. | |||
The ISO 3166-1 alpha-2 "AQ" is assigned to the entire continent regardless of jurisdiction. Different country calling codes and currencies are used for different settlements, depending on the administrating country. The "Antarctican dollar", a souvenir item sold in the United States and Canada, is not legal tender. | |||
==Ecological threats== | |||
===Ice mass and global sea level=== | |||
Due to its location at the [[South Pole]], Antarctica receives relatively little solar radiation. This means that it is a very cold continent where water is mostly in the form of [[ice]]. Precipitation is low (most of Antarctica is a desert) and almost always in the form of snow, which accumulates and forms a giant ice sheet which covers the land. Parts of this ice sheet form moving glaciers known as ice streams, which flow towards the edges of the continent. Next to the continental shore are many ice shelves. These are floating extensions of outflowing glaciers from the continental ice mass. Offshore, temperatures are also low enough that ice is formed from seawater through most of the year. It is important to understand the various types of Antarctic ice to understand possible effects on sea levels and the implications of global cooling. | |||
Sea ice extent expands annually in the Antarctic winter and most of this ice melts in the summer. This ice is formed from the ocean water and floats in the same water and thus does not contribute to rise in sea level. The extent of sea ice around Antarctica has remained roughly constant in recent decades, although the thickness changes are unclear. | |||
Melting of floating ice shelves (ice that originated on the land) does not in itself contribute much to sea-level rise (since the ice displaces only its own mass of water). However it is the outflow of the ice from the land to form the ice shelf which causes a rise in global sea level. This effect is offset by snow falling back onto the continent. Recent decades have witnessed several dramatic collapses of large ice shelves around the coast of Antarctica, especially along the Antarctic Peninsula. Concerns have been raised that disruption of ice shelves may result in increased glacial outflow from the continental ice mass. | |||
On the continent itself, the large volume of ice present stores around 70% of the world's fresh water. This ice sheet is constantly gaining ice from snowfall and losing ice through outflow to the sea. Overall, the net change is slightly positive at approximately 82 gigatonnes (Gt) per year (with significant regional variation), reducing global sea-level rise by 0.23 mm per year. However, NASA's Climate Change website indicates an overall trend of greater than 100 gigatonnes of ice loss per year since 2002. | |||
East Antarctica is a cold region with a ground base above sea level and occupies most of the continent. This area is dominated by small accumulations of snowfall which becomes ice and thus eventually seaward glacial flows. The mass balance of the [[East Antarctic Ice Sheet]] as a whole is thought to be slightly positive (lowering sea level) or near to balance. However, increased ice outflow has been suggested in some regions. | |||
===Effects of global warming=== | |||
Some of Antarctica has been warming up; particularly strong warming has been noted on the Antarctic Peninsula. A study by Eric Steig published in 2009 noted for the first time that the continent-wide average surface temperature trend of Antarctica is slightly positive at >0.05 °C (0.09 °F) per decade from 1957 to 2006. This study also noted that West Antarctica has warmed by more than 0.1 °C (0.2 °F) per decade in the last 50 years, and this warming is strongest in winter and spring. This is partly offset by autumn cooling in East Antarctica. There is evidence from one study that Antarctica is warming as a result of human carbon dioxide emissions, but this remains ambiguous. The amount of surface warming in West Antarctica, while large, has not led to appreciable melting at the surface, and is not directly affecting the West Antarctic Ice Sheet's contribution to sea level. Instead the recent increases in glacier outflow are believed to be due to an inflow of warm water from the deep ocean, just off the continental shelf. The net contribution to sea level from the Antarctic Peninsula is more likely to be a direct result of the much greater atmospheric warming there. | |||
In 2002 the Antarctic Peninsula's Larsen-B ice shelf collapsed. Between 28 February and 8 March 2008, about 570 km2 (220 sq mi) of ice from the Wilkins Ice Shelf on the southwest part of the peninsula collapsed, putting the remaining 15,000 km2 (5,800 sq mi) of the ice shelf at risk. The ice was being held back by a "thread" of ice about 6 km (4 mi) wide, prior to its collapse on 5 April 2009. According to NASA, the most widespread Antarctic surface melting of the past 30 years occurred in 2005, when an area of ice comparable in size to California briefly melted and refroze; this may have resulted from temperatures rising to as high as 5 °C (41 °F). | |||
A study published in Nature Geoscience in 2013 (online in December 2012) identified central West Antarctica as one of the fastest-warming regions on Earth. The researchers present a complete temperature record from [[Westarctica]]'s [[Byrd Station]] and assert that it "reveals a linear increase in annual temperature between 1958 and 2010 by 2.4±1.2 °C". | |||
===Ozone depletion=== | |||
There is a large area of low ozone concentration or "ozone hole" over Antarctica. This hole covers almost the whole continent and was at its largest in September 2008, when the longest lasting hole on record remained until the end of December. The hole was detected by scientists in 1985 and has tended to increase over the years of observation. The ozone hole is attributed to the emission of chlorofluorocarbons (CFCs) into the atmosphere, which decompose the ozone into other gases. | |||
Some scientific studies suggest that ozone depletion may have a dominant role in governing climatic change in Antarctica (and a wider area of the Southern Hemisphere). Ozone absorbs large amounts of ultraviolet radiation in the stratosphere. Ozone depletion over Antarctica can cause a cooling of around 6 °C in the local stratosphere. This cooling has the effect of intensifying the westerly winds which flow around the continent (the [[polar vortex]]) and thus prevents outflow of the cold air near the South Pole. As a result, the continental mass of the East Antarctic ice sheet is held at lower temperatures, and the peripheral areas of Antarctica, especially the [[Antarctic Peninsula]], are subject to higher temperatures, which promote accelerated melting. Models also suggest that the ozone depletion/enhanced polar vortex effect also accounts for the recent increase in sea ice just offshore of the continent. | |||
[[Category:Geography of Westarctica]] | [[Category:Geography of Westarctica]] | ||