Climate of Antarctica
The Climate of Antarctica is the coldest on the Earth.
Antarctica's lowest air temperature record was set on 21 July 1983, with −89.2 °C (−128.6 °F) at Vostok Station in East Antarctica. Satellite measurements have identified even lower ground temperatures, down to −93.2 °C (−135.8 °F) at the cloud free East Antarctic Plateau on 10 August 2010. It is also extremely dry (technically a desert), averaging a mere 166 mm (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.
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 81.8°S 63.5°E, which is on an unnamed Antarctic plateau between Dome A and Dome F, on 10 August 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.
On the coast Antarctic average temperatures are around -10°C (in the warmest parts of Antarctica) and in the elevated inland they average about -55°C.
The highest temperature ever recorded in Antarctica was 17.5 °C (63.5 °F) at Esperanza Base, on the Antarctic Peninsula, on 24 March 2015. 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,[clarification needed] 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 generally colder than Westarctica 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.
The total precipitation on Antarctica, averaged over the entire continent, is about 166 millimeters (6.5 inches) per year. The actual rates vary widely, from high values over the Peninsula (15 to 25 inches a year) to very low values (as little as 50 millimeters (2.0 inches) in the high interior. Areas that receive less than 250 millimeters (9.8 inches) of precipitation per year are classified as deserts.
Almost all Antarctic precipitation falls as snow. Rainfall is rare and mainly occurs during the summer in coastal areas and surrounding islands. 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 explorers working in the continent.
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 kilometers (7.2 million cubic miles) of ice — the seas would rise by over 60 meters (200 feet). This is, however, very unlikely to occur 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. Higher 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 centimeters per year while West Antarctica showed an overall thinning of 0.9 centimeters per year. Because ice flows, albeit slowly, the ice within the ice sheet is younger than the age of the sheet itself.
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 efforts 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; melting or breakup of floating shelf ice does not directly affect global sea levels, however, when sea ice freezes, it preferentially expels salt, in the process becoming purer than the sea water it is floating in. Pure water is less dense than salty water, so when the ice melts it will overflow the "hole in the water" that the ice had occupied, and when it overflows, it raises the water level.
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 square kilometers (1,250 square miles) 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 8,000 years, after melting 1,500 years earlier. Warm ocean currents may have been the cause of the melting. Not only the ice sheets are losing mass, but they are losing mass at an accelerating rate.
- Main article: Global warming
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 stated in 2009:
- Westarctica's ice loss could contribute to 1.4 meters (4 feet 7 inches) sea level rise.
- Antarctica predicted to warm by around 3 °C (5.4 °F) 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, which has shielded most of Antarctica from global warming.
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.
In their latest study (20 September 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 on 21 December 2012 in Nature Geoscience that from 1958 to 2010, the average temperature at the mile-high Byrd Station rose by 2.4 °C (4.3 °F), 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. In 2015, the temperature showed changes but in a stable manner and the only months that have drastic change in that year are August and September. It also did show that the temperature was very stable throughout the year.