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The climate of Antarctica is the coldest on earth, the lowest temperature ever recorded on earth being −89.2 °C (−128.6 °F) at Vostok Station. It is also extremely dry, with an average of only 166 mm of precipitation per year; however, on most parts of the continent the snow never melts and is eventually compressed to become the glacial ice that makes up the ice sheet. Weather fronts rarely penetrate far into the continent.
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About 200 million years ago Antarctica was joined to South America, Africa, India, Australia, and New Zealand in a single large continent called Gondwana. There was no ice sheet, the climate was warm, and trees and large animals flourished. Today only geological formations, coal beds, and fossils remain as clues to Antarctica\'s temperate past.
According to the plate tectonics theory, after splitting from Gondwana, Antarctica drifted slowly to its present position over the South Pole. Its climate was much warmer before it was finally separated from South America. Around 30 million years ago, the Drake Passage opened. Persistent westerly winds began to circle Antarctica, creating the immense Antarctic Circumpolar Current that flows through the southern parts of the Pacific, Atlantic, and Indian Oceans. This encircling system blocked heat transport, causing the Antarctic to cool. It has been covered with ice since approximately the beginning of the Pliocene, about 5 million years ago.
Near the coast, December does not look cold.
The lowest temperature ever recorded in nature on Earth was −89.2°C (−128.6°F) recorded on Thursday, July 21, 1983 at Vostok Station. The highest temperature ever recorded in Antarctica was 14.6°C (58.3°F) in two places, Hope Bay and Vanda Station, on January 5, 1974.
The mean annual temperature of the interior is −57°C (−70°F). The coast is warmer. Monthly means at McMurdo Station range from −28°C (−18.4°F) in August to −3°C (26.6°F) in January. At the South Pole, a high of −14°C (7°F) has been recorded. Along the Antarctic Peninsula, temperatures as high as 15°C (59°F) have been recorded, though the summer temperature usually is around 2°C.
Severe low temperatures vary with latitude, elevation, and distance from the ocean. East Antarctica is colder than West Antarctica because of its higher elevation. The Antarctic Peninsula has the most moderate climate. Higher temperatures occur in January along the coast and average slightly below freezing. Although the temperature does not affect animals like adélie penguins.
Map of average annual precipitation (liquid equivalent, mm) on Antarctica
Precipitation over Antarctica varies widely, from high values over the Peninsula (meters per year) to very low desert-like values (tens of mm per year) in the high interior. Note that the precipitation is given in water-equivalent, rather than depth of snow. Almost all Antarctic precipitation is snowfall. The total, averaged over the continent, is about 166 mm per year (Vaughan et al., J Climate, 1999).
Nearly all of Antarctica is covered by an ice sheet that is, on average, at least 1.6 kilometres thick. Antarctica contains 90% of the world\'s ice and more than 70% of its fresh water. If all the land-ice covering Antarctica were to melt — around 30 million cubic kilometres of ice — the seas would rise by over 60 metres[1]. This is, however, very unlikely within the next few centuries. The Antarctic is so cold that even with increases of a few degrees, temperatures would generally remain below the melting point of ice. Warmer temperatures are expected to lead to more snow, which would increase the amount of ice in Antarctica, offsetting approximately one third of the expected sea level rise from thermal expansion of the oceans [2]. During a recent decade, East Antarctica thickened at an average rate of about 1.8 centimetres per year while West Antarctica showed an overall thinning of 0.9 centimetres per year (Davis et al., Science 2005) doi:10.1126/science.1110662.
For the contribution of Antarctica to present and future sea level change, see sea level rise.
Because ice flows, albeit slowly, the ice within the ice sheet is younger than the age of the sheet itself.
| Morphometric data for Antarctica (from Drewry, 1983) | |||||
|---|---|---|---|---|---|
| Surface | Area (km²) | Percent | Mean ice thickness (m) | Volume (km³) | Percent |
| Inland ice sheet | 11,965,700 | 85.97 | 2,450 | 29,324,700 | 97.39 |
| Ice shelves | 1,541,710 | 11.08 | 475 | 731,900 | 2.43 |
| Ice rises | 78,970 | .57 | 670 | 53,100 | .18 |
| Glacier ice (total) | 13,586,380 | 2,160 | 30,109,800¹ | ||
| Rock outcrop | 331,690 | 2.38 | |||
| Antarctica (total) | 13,918,070 | 100.00 | 2,160 | 30,109,800¹ | 100.00 |
| ¹The total ice volume is different from the sum of the component parts because individual
figures have been rounded. | |||||
| Regional ice data (from Drewry and others, 1982; Drewry, 1983) | |||
|---|---|---|---|
| Region | Area (km²) | Mean ice thickness (m) | Volume (km³) |
| East Antarctica | |||
| Inland ice | 9,855,570 | 2,630 | 25,920,100 |
| Ice shelves | 293,510 | 400 | 117,400 |
| Ice rises | 4,090 | 400 | 1,600 |
| West Antarctica (excluding Antarctic Peninsula) | |||
| Inland ice sheet | 1,809,760 | 1,780 | 3,221,400 |
| Ice shelves | 104,860 | 375 | 39,300 |
| Ice rises | 3,550 | 375 | 1,300 |
| Antarctic Peninsula | |||
| Inland ice sheet | 300,380 | 610 | 183,200 |
| Ice shelves | 144,750 | 300 | 43,400 |
| Ice rises | 1,570 | 300 | 500 |
| Ross Ice Shelf | |||
| Ice shelf | 525,840 | 427 | 224,500 |
| Ice rises | 10,320 | 500 | 5,100 |
| Filchner-Ronne Ice Shelf | |||
| Ice shelf | 472,760 | 650 | 307,300 |
| Ice rises | 59,440 | 750 | 44,600 |
Most of the coastline of Antarctica is ice shelves (floating ice sheet) or ice walls (grounded ice). Melting or breakup of floating shelf ice does not affect global sea levels, and happens regularly as shelves grow.
Known changes in coastline ice:
The George VI Ice Shelf, which may be on the brink of instability [3], has probably existed for approximately 8000 years, after melting 1500 years earlier [4]. Warm ocean currents may have been the cause of the melting [5]. The idea that it was warmer in Antarctica 10,000 years ago is supported by ice cores, though the timing is not quite right.
See also: Ross Ice Shelf, Filchner-Ronne Ice Shelf, Larsen Ice Shelf, Abbot Ice Shelf, Dotson Ice Shelf, Getz Ice Shelf, Shackleton Ice Shelf, West Ice Shelf.
Antarctic Skin Temperature Trends between 1981 and 2007, based on thermal infrared observations made by a series of NOAA satellite sensors. Skin temperature trends do not necessarily reflect air temperature trends.
The British Antarctic Survey, which has undertaken the majority of Britain\'s scientific research in the area, has the following positions: [6]
NASA map showing snowmelt in areas where it never melted before
The area of strongest cooling appears at the South Pole, and the region of strongest warming lies along the Antarctic Peninsula. A possible explanation is that loss of UV-absorbing ozone may have cooled the stratosphere and strengthened the polar vortex, a pattern of spinning winds around the South Pole. The vortex acts like an atmospheric barrier, preventing warmer, coastal air from moving in to the continent\'s interior. A stronger polar vortex might explain the cooling trend in the interior of Antarctica.[7]
In their latest study (September 20, 2007) NASA researchers have confirmed that Antarctic snow is melting farther inland from the coast over time, melting at higher altitudes than ever and increasingly melting on Antarctica\'s largest ice shelf."NASA Researchers Find Snowmelt in Antarctica Creeping Inland" Sept 20, 2007
There is also evidence for widespread glacier retreat around the Antarctic Peninsula [8].
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia
