Antarctica is the coldest continent on Earth.
Larger than Europe, with a roughly circular shape, this continent is nearly centred on the South Pole, and is surrounded by the three oceans of the Southern Hemisphere, namely, Atlantic, Pacific and Indian.
The situation is quite the opposite in the Arctic region, where there is a frozen ocean (the Arctic Ocean) surrounded by continents.

Glaciers in Antarctica

The South Pole colder than the North Pole, precisely because of this different geographical configuration, to which must be added the influence of altitude: due to the huge ice sheet covering the continent (about 90% of the ice, which corresponds to about 70% of freshwater on our Planet, is found in Antarctica), the average altitude is around 2,000/2,400 metres (6,600/8,000 feet), with large areas above 3,000 metres (9,800 feet), far higher than in the other continents, where it's around 700/800 metres (2,300/2,600 feet).
These factors cause, at least in the lower layers of the atmosphere, an atmospheric circulation that prevents the penetration of mild ocean winds towards the interior: both air and sea currents flow around the continent with an almost circular motion, from west to east (the so-called Antarctic Circumpolar Current).
Below the ice cap, there are plains and even depressions, caused also by the enormous weight of the ice itself. However, there are mountains as well, culminating in the 4,892 metres (16,050 feet) high Mount Vinson, not far from the Weddell Sea.
Along with the Ross Sea, the Weddell Sea is a large and partially (but permanently) frozen sea, which penetrates the continent.
The total size of the ice sheet (the one that covers the mainland plus the marine one) vary from about 14 million square kilometres (5.4 million square miles) in March, to about 22 million km² (8.5 million mi²) in September: in autumn the ice advances by about 4 km (2.5 mi) a day, and at the end of winter, virtually the entire continent is surrounded by sea ice. The largest iceberg that calved from the ice, was 40 km (25 mi) wide and 400 km (250 mi) long, so it was larger than Belgium.

Temperatures

The average temperatures of the continent are extremely low. At the South Pole, 2,800 metres (9,200 feet) above sea level, the average annual temperature is -49 °C (-56 °F): in the warmest month (January) it's about -28 °C (-18 °F), while in the coldest month (July) it's about -59.5 °C (-74.5 °F). The lowest recorded temperature is -83 °C (-117 °F), while the highest is -12 °C (10 °F).
Here are the average temperatures of the South Pole (Amundsen–Scott Station).
Average temperatures - South Pole
South PoleJanFebMarAprMayJunJulAugSepOctNovDec
South PoleJFMAMJJASOND
Min (°C)-30-43-57-61-62-63-63-63-62-54-40-29
Max (°C)-26-38-50-53-54-54-55-55-54-48-36-26
Min (°F)-22-45-71-78-80-81-81-81-80-65-40-20
Max (°F)-15-36-58-63-65-65-67-67-65-54-33-15

However, the lowest temperature ever recorded in the continent, which is also the world record, belongs to the Soviet station of Vostok, 3,500 metres (11,500 feet) above sea level, where in 1983 the temperature reached as low as -89.2 °C (-128.6 °F). Here the highest temperature ever measured is -14 °C (7 °F). This station is located near the geometric centre of the continent: this shows how even in Antarctica, continentality is a determining factor in the distribution of temperatures, even more than latitude.
Here are the average temperatures of the Vostok station.
Average temperatures - Vostok
VostokJanFebMarAprMayJunJulAugSepOctNovDec
VostokJFMAMJJASOND
Min (°C)-38-50-62-68-69-69-70-72-70-63-50-38
Max (°C)-32-44-58-65-66-65-67-68-66-57-43-32
Min (°F)-36-58-80-90-92-92-94-98-94-81-58-36
Max (°F)-26-47-72-85-87-85-89-90-87-71-45-26

There are also inland areas, with no weather stations, where even lower temperatures have been measured by satellite, such as Dome A, located at 4,000 metres (13,000 feet) above sea level, where a temperature of -93 °C (-135 °F) has been estimated.
The coastal regions have a much milder climate, due to the lower latitude, to the lower altitude, and to the influence of the sea: here even in winter the temperatures rarely drop below -30 °C (-22 °F), while in summer they can exceed the freezing point. The highest temperatures ever measured in the continent have been 14.5 °C (58 °F), recorded on January 5, 1974, in the former Vanda Station, located near a salt lake in the McMurdo Dry Valleys, at a latitude of 77 degrees South, and 14.8 °C (58.6 °F), recorded in the Argentine base Esperanza (see below).
In the Australian Casey Station, located on the coast of the Indian Ocean, at a latitude of 66 degrees South, the average temperature goes from -15 °C (5 °F) in May, which is oddly the coldest month (probably for the change in atmospheric circulation that occurs in winter), to -0.5 °C (31.5 °F) in January.
Average temperatures - Casey
CaseyJanFebMarAprMayJunJulAugSepOctNovDec
CaseyJFMAMJJASOND
Min (°C)-3-5-10-15-19-18-18-18-17-15-9-4
Max (°C)20-4-8-11-10-10-10-10-8-31
Min (°F)2723145-2000151625
Max (°F)363225181214141414182734

At the Esperanza Base, located in the southernmost and warmest part of Antarctica, at the tip of the Antarctic Peninsula, at a latitude of 63 ° south, the temperature is even higher, so that the average goes from -11 °C (12.5 °F) in June, to 0.5 °C (33 °F) in January.
Average temperatures - Esperanza
EsperanzaJanFebMarAprMayJunJulAugSepOctNovDec
EsperanzaJFMAMJJASOND
Min (°C)-2-3-6-11-13-15-15-15-11-7-5-2
Max (°C)330-3-6-7-6-6-3013
Min (°F)28272112955512192328
Max (°F)373732272119212127323437

Average annual temperatures in Antarctica
Above: the annual average temperature in Antarctica (in degrees Celsius).

Winds

Along with the record of low temperatures, Antarctica holds also the record of the strongest winds: winds between 100 and 200 kilometres (60 and 125 miles) per hour are not uncommon, but sometimes they even exceed 300 kph (185 mph), with maximum guts of about 360 kph (220 mph).
The blizzard is so terrible that it's an obstacle to human activities, even larger than the cold itself. It usually blows from inland to the sea, it's more intense in winter than in summer, and it's due to the huge difference in temperature (hence, in air pressure) that is generated between inland and coastal areas.
These strong winds cause a huge wind chill (the phenomenon whereby a human body perceives a more intense cold, compared to real air temperatures), so that the perceived temperature in the worst moments can be far lower than -100 °C (-150 °F).
The winds that blow from the higher elevations of the interior, and descend in altitude towards the coast, are called katabatic. The general atmospheric circulation plays a role in the formation of these winds: at high altitudes the subtropical winds blow towards the interior, to prevent the continue cooling of the continent, and then these air masses, after having cooled down above the ice cap, come back towards the subtropical latitudes, reaching the coasts as cold and violent downlope winds.
In the station of Dumont d'Urville, for example, there are on average 11.6 days per month in which the wind exceeds 100 kph (60 mph), with a minimum in January (7 days), and a maximum in August and September (14 days).
This station has experienced at least one episode with wind gusts stronger than 230 kph (145 mph) in all the months of the year, and the overall record, which occurred in June, is an astonishing 324 kph (201 mph).
These cold winds, once they reach the sea, feed the low pressure systems that give life to the so-called West Wind Drift, which sweeps the oceans north of Antarctica: the result is a stream of water which travels from west to east at a speed of 20 Km (12 mi) per day.

Precipitation

Winds shape the surface of ice and snow, in a manner similar to sand dunes in the desert. Precipitation in much of Antarctica is desert-like as well: in the interior it's lower than 50 millimetres (2 inches) per year, and only near the coast it exceeds 300 mm (12 in), with peaks of 600 mm (23.5 in). Strange as it may seem, fires are dangerous, due to the limited availability of liquid water.
Average annual precipitation in Antarctica
Above: the average annual rainfall in Antarctica (in millimetres). The coldest areas are also the driest.

Looking at the last two maps, we can see that there is a correspondence between temperature and precipitation. An average temperature of -25 °C (-13 °F) roughly corresponds to an average precipitation of 400 mm (16 in), while temperatures below -55 °C (-67 °F) correspond to precipitation below 50 mm (2 in). This is explained by the fact that at -55 °C (-67 °F), the saturated vapor pressure is 30 times lower than at -25 °C (-13 °F): in other words, the air can hold much less moisture, therefore it can produce poor precipitation.
And so the colder areas are extremely arid, among the most arid in the world: precipitation in the South Pole amounts to just 2 mm (0.1 inch) per year, so practically it never snows (or at most a very light snow falls), and at Vostok about 20 mm (0.9 in) per year, although the wind can carry the snow and accumulate it where it encounters obstacles (for example, the buildings of a station).
Here is average precipitation in the Casey Station, which being on the coast receives a higher amount of precipitation, largely in the form of snow. However, given the temperature, it is possible that in summer some rain may fall.
Average precipitation - Casey
CaseyJanFebMarAprMayJunJulAugSepOctNovDecYear
CaseyJFMAMJJASONDY
Prec. (mm)91518212628292117171313227
Prec.(in)0.40.60.70.811.11.10.80.70.70.50.58.9
Days789910111089866101

Temperature inversion and optical phenomena

The sunshine amount is not very abundant in peripheral and coastal areas: the autumn and winter months, in which the days are very short, are followed by the spring and summer months, when the sun is often shielded by clouds. On the contrary, in the central part of the continent, such as the South Pole and Vostok, while it is true that in the long polar night the sun never rises, in the summer months, not only the sun is always above the horizon, but also the sky is almost always clear.
However, snow and ice cap reflect most of the solar radiation that reaches the ground, while in winter the absence of sunlight causes a radiation deficit, so that the soil cools down. This produces a unique temperature inversion, which in winter can exceed 30 degrees Celsius (55 degrees Fahrenheit) between the ground and an altitude of 1,000 metres (3,300 feet) above, also due to the warmer subtropical currents which flow, as mentioned, at high altitudes. In July 1989, at Vostok, a difference of 34 °C (61 °F) were recorded between the ground, where the temperature was -78 °C (-108 °F) and 600 metres (2,000 feet) above, where it was -44 °C (-47 °F): still at 8,000 metres (2,600 feet) the temperature was -73 °C (-99 °F), so it was higher than at ground level.
Along with electromagnetic factors, temperature inversion is responsible for curious optical phenomena, such as sundogs and halos around the sun or moon.
Due to low temperatures and strong winds, in Antarctica the air has exceptional transparency, brightness and acoustics: it is possible to spot mountains even at a distance of 550 km (340 mi).
The absence of objects such as trees and houses, however, makes it very difficult to evaluate the distances. Effects such as light refraction and reflection cause also frequent mirages, favored by the presence of tiny ice crystals that are formed continuously in the air due to low temperatures.

Sundogs in Antarctica

Meteorological observations in Antarctica started very late, partly because of the adverse environmental conditions. Prior to 1957-58, the International Geophysical Year, the only stations had been installed in the Antarctic Peninsula and the Ross Sea. But it did not take long for scientists to understand the importance of knowing the climate of the continent, as well as of the fact that it offers a privileged point of observation for studying the past and present climate of the Earth (ice layers preserve the memory of the chemical composition of the atmosphere of past ages, from which we can deduce the air temperature), but also for the climate prediction of the future. Phenomena such as global warming and the ozone hole, which was discovered here and here has its greatest intensity, have attracted and still attract groups of scientists who continually defy the cold and the wind to carry out their studies.

Changes and trends

In Antarctica the temperature variations from year to year are considerable: the standard deviation of the mean annual temperature is generally around 0.61/1.56 °C (1/2.8 °F), while for example in London it's 0.5 °C (0.9 °F).
The difference in the average temperature from one year to another can be as high as 4 °C (7 °F).
As for the trend, the South Pole does not show a clear tendency of temperature rise, while coastal areas show a remarkable rise of almost 0.3 °C (0.5 °F) every 10 years in the last 4 decades, with peaks of 0.5 °C (0.9 °F), i.e. more than three times the world average.
On the contrary, until not many years ago there seemed not to be any increasing trend in temperature in the Arctic.
Contrary to what happens in the rest of the world, where the glaciers are retreating both in the mountains and in the Arctic region (Greenland and Arctic Ocean), the extent of the ice in Antarctica has actually increased (though less than it has declined in the rest of the world). Contrary to what one might think, even this phenomenon may be due to global warming: on the one hand because in cold regions an increase in temperature allows for an increase in snowfall (as long as the temperature remains below freezing), on the other hand because the greater ice extent might be due to the higher speed at which the ice from the inner part of the continent slides towards the sea.