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The Antarctic Ecosystem » Antarctica: Location and Climate

What you'll learn this session

Study time: 30 minutes

Cambridge spec: 3.1.1, 3.1.2

Where Antarctica is and how big it is
The main features of the Antarctic climate
Why it is so cold and so dry
How to read a polar climate graph

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Where is Antarctica?

Antarctica is a continent around the South Pole, at 90 degrees south. It is surrounded by the Southern Ocean, which separates it from South America, Africa and Australia. Almost all of it lies inside the Antarctic Circle, the line of latitude at about 66.5 degrees south.

It covers about 14 million km². That makes it the fifth largest continent, bigger than both Europe (about 10 million km²) and Australia (about 7.7 million km²). About 98% of it is covered by an ice sheet, a huge layer of ice that is about 2 km thick on average and over 4 km thick in places. It holds about 90% of all the ice on Earth.

Key terms:

Antarctica: the continent around the South Pole, covered by an ice sheet.
Southern Ocean: the ocean that surrounds Antarctica.
Antarctic Circle: the line of latitude at about 66.5 degrees south.
Ice sheet: a very large, thick mass of ice that covers land.

What is the Antarctic climate like?

🌡️ Very cold

It is the coldest place on Earth. The lowest air temperature ever measured at a weather station is about -89°C, at Vostok in 1983. The South Pole averages about -49°C over a year. On the coast, summer temperatures reach around 0°C.

❄️ Very dry

The interior gets about 50 mm of precipitation a year or less, which is as dry as many hot deserts. Coasts get more. Nearly all of it falls as snow.

💨 Very windy

Strong winds blow off the ice sheet. On parts of the coast, gusts can reach about 200 km/h.

Because it is so dry, Antarctica is a polar desert. Snow that falls does not melt, so it builds up over thousands of years and turns to ice.

Why is Antarctica so cold and dry?

1. Latitude. Antarctica is at the highest latitudes on Earth. The sun is never high in the sky there, so it gives little heat.

2. The low angle of the sun. Sunlight arrives at a low angle. The same energy is spread over a larger area of ground, so each square metre gets less heat. The rays also travel through more atmosphere, which weakens them. The tilt of the Earth also gives months of darkness and months of daylight. At the South Pole the sun is up for about six months and down for about six months. At the Antarctic Circle there is just one day of continuous daylight and one of darkness. In the dark months there is no heat from the sun at all.

3. The albedo effect. Albedo is how much sunlight a surface reflects. Fresh snow and ice reflect a very large share of the sunlight that reaches them, up to about 80% or more. Only a little is absorbed as heat. The sea is dark and absorbs much more. So the ice stays cold, and the cold ice keeps reflecting.

4. High pressure. Cold air is dense and sinks. Over Antarctica air sinks from high in the atmosphere, which creates an area of high pressure at the surface. Sinking air does not form clouds, so skies are mostly clear and very little snow falls. That is why it is a polar desert.

5. Katabatic winds. Cold dense air over the high ice sheet flows downhill under gravity towards the coast. These are katabatic winds. They get stronger as the slope steepens, and they carry cold air to the coast.

Key terms:

Polar desert: a cold area with very low precipitation.
Albedo: the share of sunlight a surface reflects.
High pressure: an area where air is sinking, usually with dry, clear weather.
Katabatic wind: a strong, cold wind that flows downhill off the ice sheet.

How to write the explanation

Link each point in a chain. For example: "Antarctica is at a high latitude (1), so the sun is low in the sky (1), so its energy is spread over a large area (1), so temperatures are very low (1)."

Reading a polar climate graph

A climate graph shows monthly temperature as a line and monthly precipitation as bars. Here we read the same information from a table. Fig. 1.1 shows made-up data for a coastal weather station, Station Z.

Month	J	F	M	A	M	J	J	A	S	O	N	D
Temperature (°C)	-3	-6	-11	-15	-18	-21	-23	-24	-21	-15	-8	-4
Precipitation (mm)	10	10	12	14	14	14	13	13	12	12	10	10

Follow three steps. First, read the temperature: it is below 0°C all year, from -3°C in January to -24°C in August. Second, work out the range: -3 minus -24 gives 21°C. Third, read the precipitation: the total is 144 mm, with no month above 14 mm. Remember the seasons are the other way round to the UK, so the Southern Hemisphere summer is December to February.

Notice that even the warmest month is below freezing, so the precipitation falls as snow. How to draw a climate graph is taught later, in Climate Graphs, Hydrographs, Kite Graphs and Rose Charts.

Common mistakes

Writing that Antarctica is cold "because it is far from the sun". The Earth is not noticeably further from the sun there; the sun's rays arrive at a low angle. Another mistake is saying it is very snowy. It gets very little snow, so it is a desert. Also, do not mix up the Antarctic (south) and the Arctic (north).

Exam-style question

Fig. 1.1 is the table of made-up climate data for Station Z, a coastal weather station in Antarctica, shown above.

(a) Identify the highest temperature shown in Fig. 1.1. [1]

(b) State the latitude of the Antarctic Circle. [1]

(d) Explain why Antarctica has a very cold and very dry climate. [6]

Model answer

(a) -3°C (1)

(b) About 66.5 degrees south (1)

(c) Temperatures are below 0°C in every month (1). They fall steadily from -3°C in January to a low of -24°C in August (1), then rise again to -4°C in December. The annual range is 21°C (1).

(d) Full-marks answer: Antarctica is at a very high latitude, so the sun is always low in the sky (1). The sun's energy is spread over a large area, so each square metre gets little heat (1), and in winter there are months of darkness with no sun at all (1). The ice and snow have a high albedo, so they reflect most of the sunlight and the ground stays cold (1). Cold air sinks over the continent, creating high pressure (1). Sinking air gives clear skies and very little snow, so Antarctica is a polar desert (1).

Exam tip

In a 6-mark "Explain" question, give at least three separate reasons and join each one to the result with "so" or "because".

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