The Frozen Planet

I have been really enjoying the BBC’s latest wildlife spectacle Frozen Planet.  In fact, I’ve enjoyed it so much that I signed up for the related Open University science short course.

First of all, samples of the course can be tried, and poster can be downloaded as a PDF or ordered through the OpenLearn website.

I’ve now worked through chapter 1, which outlines a definition of the Antarctic and the Arctic, and gives a broad overview of why the polar regions have the climate that they have. I’ve come across many of the concepts before but will provide an outline of the chapter below.

Both polar regions are named after Ancient Greek words: Arktos which means “to the north”, and Ant Arktos which means “to the south”.

What affects the climate in both polar regions?

The Earth’s axis is inclined at 23.4° to the plane of the orbit around the Sun, this causes the Earth’s seasons as the planet orbits the Sun.  It is summer in the Northern Hemisphere when that side of the Earth is tilted towards the Sun, and winter in the Southern Hemisphere. However, due to this tilt, and the curvature of the Earth, solar energy must pass through more of the atmosphere, and it falls on a wider area, so it is less able to heat the polar regions.

There are four dates that define the seasons:

• 21 March: this is the northern spring equinox when the Sun is directly over the Equator
• 21 June: this is the northern summer solstice when the Sun is directly over the Tropic of Cancer (23.4° N) and the Northern Hemisphere has its longest day of the year
• 21 September: this is the northern autumn equinox when the Sun is directly over the Equator
• 21 December: this is the northern winter solstice when the Sun is directly over the Tropic of Capricorn (23.4° S) and the Southern Hemisphere has its shortest day of the year

Each polar region experiences a polar day, or “midnight Sun” throughout the summer when the Sun does not set, and a polar night during the winter when the Sun does not rise.  The lowest latitudes in which this can be seen are 66.6° N and 66.6° S.  These are the Arctic and Antarctic Circles respectively.

Other factors that affect local climate include albedo which is a measure of the amount of reflectivity of a particular surface. The ocean has an albedo of 3% which means that 97% of energy from the Sun is absorbed by the ocean, a conifer forest in summer has an albedo of 9%, and fresh snow 80-90%.

Different materials also have specific heat capacities, this describes how much energy it takes to increase 1 kg of that object by 1 °C – a metal doesn’t take a lot of energy to heat up, unlike water.

What is energy? Energy (in this example this refers to kinetic energy) describes the speed of movement of atoms or molecules in a substance.  An increase in energy in an object corresponds to increased temperature.

The temperature range over a year in each polar region is approximately 30 °C. The Arctic shows a smooth progression from cold to warmer and back to cold as the year passes, whereas the Antarctic shows sustained periods of constant temperature, with a sharp change before summer and winter.

How is the Arctic and Antarctic defined?

The Arctic is defined using two factors:

• the treeline – the treeline gives way to the tundra in the north
• 10 °C July isotherm – this is a measure of where the mean surface temperature is 10 °C in July

The Antarctic is defined by the Antarctic Circumpolar Current – this current flows clockwise around the Antarctic and separates warmer water in the north from colder water in the south.  This current also forms a Polar Front, south of this is the Antarctic.

The cryosphere

The cryosphere includes all the physical components of the polar environment, and these comprise of seven main parts: icebergs, ice shelves, glaciers, sea ice, permafrost, ice sheets and snow.

The cryosphere is not limited to the polar regions, for example, snow falls in northern Europe and North America, and permafrost is found in parts of the US.

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