Climate of Antarctica

Surface temperature of Antarctica in winter and summer

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.^[1] It is also extremely dry (technically a desert), with an average of only 166 mm (6.5 in) of precipitation per year. Even so, on most parts of the continent the snow rarely melts and is eventually compressed to become the glacial ice that makes up the ice sheet. Weather fronts rarely penetrate far into the continent. Most of Antarctica has an ice cap climate (Köppen EF) with very cold, generally extremely dry weather throughout the year and no month averaging above 0 °C (32 °F). Some fringe coastal areas have a polar climate (Köppen ET) with a short summer averaging above freezing, and much higher precipitation.

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. 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

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. For comparison, this is 11 °C colder than subliming dry ice. 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, the highest temperature recorded was −14°C (7°F). Along the Antarctic Peninsula, temperatures as high as 15°C (59°F) have been recorded, though the summer temperature is usually around 2°C (36°F).

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

Map of average annual precipitation on Antarctica (mm liquid equivalent)

The total precipitation in Antarctica, averaged over the entire continent, is about 166 mm (6.5 in) per year (Vaughan et al., J Climate, 1999). The actual rates vary widely, from high values over the Peninsula (meters/yards per year) to very low values (as little as 50 mm (2 in) per year) in the high interior. Areas that receive less than 250 mm (10 in) of precipitation per year are classified as deserts. Almost all Antarctic precipitation falls as snow. Note that the quoted precipitation is a measure of its equivalence to water, rather than being the actual depth of snow. The air in Antarctica is also very dry. The low temperatures result in a very low absolute humidity, which means that dry skin and cracked lips are a continual problem for scientists and expeditioners working in the field.

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.

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 1995.
    • 2001: 3,250 km² of the Larsen B ice shelf disintegrated in February 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

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 temperature record for Antarctica goes back to the 1950s. The record consists of data from a sparse network, with relatively few stations reporting data for more than a few decades. Antarctica as a continent is somewhat specific in its recent temperature history, for unlike all other continents, it has warmed very little over the past half-century. Indeed, from 1965 onwards it has even cooled slightly. At least four comprehensive studies were conducted in recent years,^{[2] [3] [4]} collecting temperature data over Antarctica for the period since the 1950s until the 2000s. All of these studies have found slight warming in the earliest portion of the record (circa 1957-1965). Since the mid-1960s, all major studies have reported cooling over most of Antarctica. The only place that exhibits strong warming for the entire record is the Antarctic Peninsula, which amounts to 0.5% of the land mass of Antarctica.

In a paper published in the journal Nature in 2002, Doran et al reported overall cooling over Antarctica. This study concludes there has been “a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn.”^[5]

Chapman and Walsh, (2007) in the paper published by Journal of Climate collected temperature in and around Antarctica from 460 locations including 19 manned surface observation stations located on the continent, 73 automated weather stations, and the 2° latitude by 2° longitude gridded sea surface temperature time series. They found little change in temperature over Antarctica in last 50 years (apart from the Peninsula). From the beginning of record until about 1965 they find slight warming, since 1965 slight cooling: “Trends computed using these analyses show considerable sensitivity to start and end dates with starting dates before 1965 producing overall warming and starting dates from 1966 to 1982 producing net cooling rates over the region.”^[6]

Monaghan et al (2008) in the paper published by Journal of Geophysical Research, similarly finds that “prior to 1965 the continent-wide annual trends (through 2002) are slightly positive, but after 1965 they are mainly negative (despite warming over the Antarctic Peninsula).”^[7]

Steig et al 2009 in the paper published by Nature, unlike all other major works, find significant warming trend over Antarctica 1957-2006, of 0.1 C per decade, although Steig’s reconstruction agree to greater extent with other studies in showing little temperature change since late 1960s.^[8]

Overall sea ice on Antarctica has increased since satellite measurements began in 1979. Sea ice was reported to be at a record level in 2008, and 2009 is also significantly above average.^[9]

Although the melting of the Antarctic ice sheet is widely believed to be associated with global warming, ice sheets on Antarctica have actually grown, rather than shrunk. Wingham et al 20 showed “the Antarctic ice sheet growing at 5 ± 1 mm year-1 in period 1992-2003”.^[10] Using satellite altimetry technique, authors show that “72% of the Antarctic ice sheet is gaining 27 ± 29 gigatons per year.”

These results are very similar to the findings reported in a paper published in Science by Curt Davis et al (2005), who also used satellite altimetry measurements of Antarctica to calculate mass changes, and estimated that over a similar period Antarctic ice sheets have grown 45 billion of metric tones per year at the pace that cause annual decline in sea level rise of 0.12 mm per year.^[11]

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 introducing 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.

NASA map showing snowmelt in areas where it has not previously been observed.

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.^[12]

There is also evidence for widespread glacier retreat around the Antarctic Peninsula.^[13]

Large ice shelves, such as the Wilkins Ice Shelf, have also been shrinking in size, though because these are already floating in the ocean, this will not cause sea level rise.

See also

• Retreat of glaciers since 1850
• Effects of global warming
• Climate of the Arctic

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. PMID 11546858. 
• 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. 

External links

Climate

• Climate data from Antarctic surface stations with trends
• Temperature data from the READER project
• A pamphlet about the weather and climate of Antarctica
• Information concerning recent ice shelf calving
• (unreliable) maps of snowfall and temperature
• Temperature statistics at the Amundsen-Scott station on the South Pole
• Warmer temperatures, more snow...
• Antarctica's central ice cap grows while glaciers melt
• "AWS and AMRC Real-Time Weather Observations and Data". University of Wisconsin-Madison's Antarctic Weather Stations Project and Antarctic Meteorological Research Center. http://amrc.ssec.wisc.edu/realtime.html. Retrieved May 31 2005. 

[8]

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

Antarctic ice

• "Sea Ice Index - Trends in extent - Southern Hemisphere (Antarctic)". National Snow and Ice Data Center. http://www.nsidc.org/data/seaice_index/. Retrieved Jan 09 2009. 
• "Coastal-Change and Glaciological Maps of Antarctica". USGS Fact Sheet 2005-3055. http://pubs.usgs.gov/fs/2005/3055/. Retrieved May 31 2005. 
• "Coastal-Change and Glaciological Maps of Antarctica". USGS Fact Sheet 050-98. http://pubs.usgs.gov/fs/fs50-98/. Retrieved February 28 2005. 
  • "Coastal-change and glaciological map of the Eights Coast area, Antarctica; 1972-2001". U.S. Geological Survey Scientific Investigations Series Map, I-2600-E. http://pubs.usgs.gov/imap/2600/E. Retrieved February 28 2005. 
  • "Coastal-change and glaciological map of the Bakutis Coast area, Antarctica; 1972-2002". U.S. Geological Survey Scientific Investigations Series Map, I-2600-F. http://pubs.usgs.gov/imap/2600/F. Retrieved February 28 2005. 
  • "Coastal-change and glaciological map of the Saunders Coast area, Antarctica; 1972-1997". U.S. Geological Survey Scientific Investigations Series Map, I-2600-G. http://pubs.usgs.gov/imap/2600/G. Retrieved February 28 2005. 
• "Satellite Image Atlas of Glaciers of the World -- Antarctica". U.S. Geological Survey Professional Paper 1386-B. http://pubs.usgs.gov/prof/p1386b/. Retrieved February 28 2005. 

v • d • e The Continent of Antarctica Main articles Antarctic · History · Climate · Expeditions · Research stations · Territorial claims · Antarctic Treaty System · Communications in Antarctica Antarctica portal Geographic regions Antarctic Peninsula · East Antarctica · West Antarctica · Extreme points of the Antarctic · List of Antarctic and sub-Antarctic islands · Antarctica ecozone Waterways: McMurdo Sound · Ross Sea · Weddell Sea Notable stations Amundsen-Scott South Pole Station (US) · Scott Base (NZ) · McMurdo Station (US) · Palmer Station (US) · Frei Montalva (CL) · Vostok Station (RU) · more... Famous explorers Ernest Shackleton · James Clark Ross · Richard Evelyn Byrd · Roald Amundsen · Douglas Mawson · Robert Falcon Scott · more...