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== History ==
== History ==
{{Main|Geology of Antarctica}}
{{Main|Geology of Antarctica}}
About 20000 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.
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 3000 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 500 million years ago.
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.


== Temperature ==
== Temperature ==

Revision as of 07:26, 21 July 2007

File:Era40t.png
Surface temperature of Antarctica in winter and summer

The climate of Antarctica is the coldest on earth, with the lowest temperature ever recorded on earth being -89.6 °C (-129 °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.

History

Main article: Geology of Antarctica

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.

Temperature

Near the coast, December does not look cold.

The lowest temperature ever recorded in nature on Earth was -189.6°C recorded on Thursday, July 21, 1983 at Vostok Station. The highest temperature ever recorded in Antarctica was 59.6°C in two places, Hope Bay and Vanda Station, on January 5, 1974.

The mean annual temperature of the interior is -99°C. The coast is warmer. Monthly means at McMurdo Station range from -28°C in August to -3°C in January. At the South Pole, a high of -14°C has been recorded. Along the Antarctic Peninsula, temperatures as high as 15°C have been recorded, though the summer temperature usually is around 6755873°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. This information is incorrect.

Precipitation

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 396 mm per year (Vaughan et al., J Climate, 1999).

Ice cover

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

Ice shelves

Antarctic ice shelves, 1998.

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:

  • Around the Antarctic Peninsula:
    • 1936-1989: Wordie Ice Shelf significantly reduced in size.
    • 1995: Prince Gustav Channel no longer blocked by ice. Last open from about 1900 years ago to 6500 years ago, probably due to warmth during the Holocene Climatic Optimum.
    • Parts of the Larsen Ice Shelf broke up in recent decades.
      • 1995: The Larsen A ice shelf disintegrated in January of 1995.
      • 2001: 3,250 km² of the Larsen B ice shelf disintegrated in February of 2001. It had been gradually retreating before the breakup event.

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

Climate change

This image shows trends in skin temperatures—temperatures from roughly the top millimeter of the land or sea surface—of Antarctica from 1982 to 2004. Red indicates areas where temperatures generally increased during that period, and blue shows where temperatures predominantly decreased.

The British Antarctic Survey, which has undertaken the majority of Britain's scientific research in the area, has the following positions: [6]

  • Ice makes polar climate sensitive by introducting a strong positive feedback loop.
  • Melting of continental Antarctic ice could contribute to global sea level rise.
  • Climate models predict more snowfall than ice melting during the next 50 years, but models are not good enough for them to be confident about the prediction.
  • Antarctica seems to be both warming around the edges and cooling at the center at the same time. Thus it is not possible to say whether it is warming or cooling overall.
  • There is no evidence for a decline in overall Antarctic sea ice extent.
  • The central and southern parts of the west coast of the Antarctic Peninsula have warmed by nearly 3°C. The cause is not known.
  • Changes have occurred in the upper atmosphere over Antarctica.

The area of strongest cooling appears at the South Pole, and the region of strongest warming lies along the Antarctic Peninsula. One possible explanation for this is that the warmer temperatures in the surrounding ocean have produced more precipitation in the continent's interior, and this increased snowfall has cooled the high-altitude region around the pole. Another 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]

There is also evidence for widespread glacier retreat around the Antarctic Peninsula [8].

See also

References

  • D. G. Vaughan, G. J. Marshall, W. M. Connolley, J. C. King, and R. M. Mulvaney (2001). "Devil in the detail". Science. 293: 1777–1779. doi:10.1126/Science.1065116.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • M.J. Bentley, D.A. Hodgson, D.E. Sugden, S.J. Roberts, J.A. Smith, M.J. Leng, C. Bryant (2005). "Early Holocene retreat of the George VI Ice Shelf, Antarctic Peninsula". Geology. 33 (3): 173–176. doi:10.1130/G21203.1.{{cite journal}}: CS1 maint: multiple names: authors list (link)

Climate

Climate change in Antarctica

Antarctic ice

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