Climate of Antarctica

Surface temperature of Antarctica in winter and summer from the European Centre for Medium-Range Weather Forecasts

The climate of Antarctica is the coldest on the whole of Earth. Antarctica has the lowest naturally occurring temperature ever recorded on the ground on Earth: −89.2 °C (−128.6 °F) at Vostok Station. It is also extremely dry (technically a desert), averaging 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 tundra climate (Köppen ET) with a short summer averaging above freezing, and much higher precipitation.

Temperature

The lowest naturally occurring temperature 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 ever recorded was −12.3°C (9.9°F) on December 25, 2011. 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 continent.

Weather condition classification

The weather in Antarctica can be highly variable, and the weather conditions can often change dramatically in short periods of time. There are three classifications for describing weather conditions in Antarctica. At least one of the following criteria must be met for each category.

Condition 1

Windspeed over 55 knots (60 miles per hour)

Visibility less than 100 feet (30 meters)

Wind chill below −100 °F (−73 °C)

Description: Dangerous conditions; outside travel is not permitted.

Condition 2

Windspeed of 48 to 55 knots (55 to 63 miles per hour)

Visibility 1/4 of a mile to 100 feet (402 to 30 meters)

Wind chill of −75 °F (−60 °C) to −100 °F (−73 °C)

Description: Unpleasant conditions; outside travel is permitted but not recommended.

Condition 3

Windspeed below 48 knots (55 miles per hour)

Visibility greater than 1/4 of a mile (402 meters)

Wind chill above −75 °F (−60 °C)

Description: Pleasant conditions; all outside travel is permitted.

Ice cover

Nearly all of Antarctica is covered by an ice sheet that is, on average, at least a mile thick (1.6 km). 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. 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. 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 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, has probably existed for approximately 8000 years, after melting 1500 years earlier. Warm ocean currents may have been the cause of the melting. The idea that it was warmer in Antarctica 10,000 years ago is supported by ice cores, though the timing is not quite right.

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 continent-wide average surface temperature trend of Antarctica is positive and significant at >0.05°C/decade since 1957. The West Antarctic ice sheet has warmed by more than 0.1°C/decade in the last 50 years, and is strongest in winter and spring. Although this is partly offset by fall cooling in East Antarctica, this effect is restricted to the 1980s and 1990s.

Research published in 2009 found that overall the continent had become warmer since the 1950s, a finding consistent with the influence of man-made climate change.

The British Antarctic Survey, which has undertaken the majority of Britain's scientific research in the area, has the following positions: [1]

• 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 previously unmelted snowmelt

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. [2]

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.

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

See also

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

References

Notes

• D. G. Vaughan, G. J. Marshall, W. M. Connolley, J. C. King, and R. M. Mulvaney (2001). "Devil in the detail". Science. 293 (5536): 1777–9. doi:10.1126/science.1065116. PMID 11546858.{{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): 173–6. doi:10.1130/G21203.1.{{cite journal}}: CS1 maint: multiple names: authors list (link)

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. Retrieved May 31, 2005.
• Antarctica Climate and Weather

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. Retrieved Jan 09 2009. {{cite web}}: Check date values in: |accessdate= (help)
• "Coastal-Change and Glaciological Maps of Antarctica". USGS Fact Sheet 2005–3055. Retrieved May 31, 2005.
• "Coastal-Change and Glaciological Maps of Antarctica". USGS Fact Sheet 050–98. 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. 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. 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. Retrieved February 28, 2005.
• "Satellite Image Atlas of Glaciers of the World – Antarctica". U.S. Geological Survey Professional Paper 1386-B. Retrieved February 28, 2005.

Further reading

• Warm Snap Turned Antarctica Green Around the Edges; Thawed-out continent was lined with trees 15 million years ago, study says. June 20, 2012 National Geographic