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 Earth. Antarctica's lowest air temperature record was set on 21 July 1983, with −89.2 °C (−128.6 °F) at Vostok Station. Satellite measurements have identified even lower temperatures, down to −93.2 °C (−135.8 °F) at the cloud free East Antarctic Plateau. It is also extremely dry (technically a desert), averaging 166mm (6.5 in) of precipitation per year. On most parts of the continent the snow rarely melts and is eventually compressed to become the glacier ice that makes up the ice sheet. Weather fronts rarely penetrate far into the continent, because of the Katabatic winds. Most of Antarctica has an ice cap climate (Köppen EF) with very cold, generally extremely dry weather.

Temperature

The lowest reliably measured temperature of a continuously occupied station on Earth of −89.2 °C (−128.6 °F) was on 21 July 1983 at Vostok Station. For comparison, this is 10.7 °C (19.3 °F) colder than subliming dry ice (at sea level pressure). The altitude of the location is 3,900 meters (12,800 feet).

The lowest recorded temperature of any location on Earth's surface was −93.2 °C (−135.8 °F) at , which is on an unnamed Antarctic plateau between Dome A and Dome F, on August 10, 2010. The temperature was deduced from radiance measured by the Landsat 8 satellite, and discovered during a National Snow and Ice Data Center review of stored data in December, 2013. This temperature is not directly comparable to the -89.2 quoted above, since it is a skin temperature deduced from satellite-measured upwelling radiance, rather than a thermometer-measured temperature of the air 1.5 m (4.9 ft) above the ground surface.

The highest temperature ever recorded in Antarctica was 17.5 °C (63.5 °F) at Hope Bay on 24 March 2015. There are reservations about this value. The mean annual temperature of the interior is −57 °C (−70.6 °F). The coast is warmer. Monthly means at McMurdo Station range from −26 °C (−14.8 °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 25 December 2011. Along the Antarctic Peninsula, temperatures as high as 15 °C (59 °F) have been recorded, though the summer temperature is below 0 °C (32 °F) most of the time. 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 on 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 (15 to 25 feet a year) to very low values (as little as 50 mm (2 in) per year) (source needed) 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 various classifications for describing weather conditions in Antarctica; restrictions given to workers during the different conditions vary by station and nation.

See Antarctica Weather Danger Classification

Ice cover

Nearly all of Antarctica is covered by a sheet of ice that is, on average, a mile thick or more (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

About 75% of the coastline of Antarctica is ice shelves. The utmost parts consist of floating ice until the grounding line of land based glaciers is reached, which is determined through affords such as Operation IceBridge. Ice shelves lose mass through iceberg breakup (calving), or basal melting (at the foot of the glacier, when warm ocean water impacts), and this can affect ice sheet stability when the land based glaciers start to retreat; however, melting or breakup of floating shelf ice does not directly affect global sea levels.

Known changes in coastline ice:

• Around the Antarctic Peninsula:
  • 1936–1989: Wordie Ice Shelf significantly reduced in size.
  • 1995: Ice in the Prince Gustav Channel disintegrated.
  • 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.
    • 2015: A study concluded that the remaining Larsen B ice-shelf will disintegrate by the end of the decade, based on observations of faster flow and rapid thinning of glaciers in the area.

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.

Global warming

Main article: Global warming in Antarctica

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:

"We can't pin it down, but it certainly is consistent with the influence of greenhouse gases from fossil fuels", said NASA scientist Drew Shindell, another study co-author. Some of the effects also could be natural variability, he said.

The British Antarctic Survey, which has undertaken the majority of Britain's scientific research in the area, stated in 2009:[1]

• West Antarctic ice loss could contribute to 1.4 m sea level rise
• Antarctica predicted to warm by around 3 °C over this century
• 10% increase in sea ice around the Antarctic
• Rapid ice loss in parts of the Antarctic
• Warming of the Southern Ocean will cause changes in Antarctic ecosystem
• Hole in ozone layer has shielded most of Antarctica from global warming

September 20, 2007 NASA map showing previously un-melted 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 into 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.

Researchers reported December 21, 2012 in Nature Geoscience that from 1958 to 2010, the average temperature at the mile-high Byrd Station rose by 2.4 degrees Celsius, with warming fastest in its winter and spring. The spot which is in the heart of the West Antarctic Ice Sheet is one of the fastest-warming places on Earth.

See also

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

References

Notes

Sources

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
• Taking Antarctica's temperature; Frozen continent may not be immune to global warming July 27, 2013; Vol.184 #2 Science News

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
• Antarctica's central ice cap grows while glaciers melt
• Antarctica Climate and Weather

Climate change in Antarctica

• Western Antarctica warming confirmed December 23, 2012 USA Today
• NASA experts explain ice melt in Antarctica (2014)