Climate of Antarctica
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The climate of Antarctica is the coldest on earth, with the lowest temperature ever recorded on earth being -89.4 °C (-129 °F) at Vostok Station. It is also extremely dry, with only an average of 166 mm of precipitation per year, although ice there can last for a long time. Weather fronts rarely penetrate far into the continent.
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History
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 and the Drake Passage opened roughly 30 million years ago. 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.
Southern Ocean
From approximately 65°S, the Southern Ocean surrounds the continent. The Antarctic Circumpolar Current, the world's largest ocean current, moves eastward and connects the Pacific, Indian, and Atlantic oceans.
Temperature
The lowest temperature ever recorded on Earth was -89.4°C (-129°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.
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.
Precipitation
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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).
Ice cover
Nearly all of Antarctica is covered by an ice sheet that is, on average, 2.5 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. 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 [1] (http://www.grida.no/climate/ipcc_tar/wg1/428.htm). 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) Template:Doi.
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
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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.
Changes before the Little Ice Age ended:
- The George VI Ice Shelf has existed for approximately 7945 years, after melting 650 years earlier. Warm ocean currents following the Holocene climatic optimum are believed to have been the cause of the melting.
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
The British Antarctic Survey, which has undertaken the majority of Britain's scientific research in the area, has the following positions: [2] (http://www.antarctica.ac.uk/Key_Topics/Climate_Change/Climate_Change_Position.html)
- Ice makes polar climate sensitive by introducting a strong "feedback" mechanism.
- 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.
- It is not possible to say whether Antarctica is warming or cooling.
- 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.
References
External links
Climate
- Climate data from Antarctic surface stations with trends (http://www.antarctica.ac.uk/met/gjma/)
- Temperature data from the READER project (http://www.antarctica.ac.uk/met/READER/)
- A pamphlet about the weather and climate of Antarctica (http://www.antarctica.ac.uk/met/jds/weather/weather.htm)
- Information concerning recent ice shelf calving (http://www.antarctica.ac.uk/met/bas_publ.html)
- (unreliable) maps of snowfall and temperature (http://www.antarctica.ac.uk/met/climate/wmc/)
- Temperature statistics at the Amundsen-Scott station on the South Pole (http://www.nerc-bas.ac.uk/icd/gjma/pole.temps.html)
- Warmer temperatures, more snow... (http://www.science.org.au/nova/082/082key.htm)
- Antarctica's central ice cap grows while glaciers melt (http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/05/20/MNGS9CS5141.DTL&type=science)
- Template:Web reference
Climate change in Antarctica
- http://www.antarctica.ac.uk/Key_Topics/Climate_Change/Climate_Change_Position.html
- http://www.antarctica.ac.uk/Key_Topics/IceSheet_SeaLevel/ice_shelf_loss.html