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Factors which influence Factors which influence climate on a global scaleclimate on a global scale

Higher GeographyHigher Geography

AtmosphereAtmosphere

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Introduction

• The Earth receives heat energy (radiation) from the Sun. But not all of the radiation that arrives at the edge of the atmosphere gets to the Earths surface.

• Also, not all latitudes on the surface receive the same amount of radiation (sunlight).

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The global heat budget

• The global heat budget is an atmospheric system which involves inputs, storage and outputs.

• Generally speaking, incoming solar radiation is balanced by outgoing terrestrial (Earth based) radiation.

• The balance between incoming and outgoing radiation is known as the global heat budget.

Hig

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• The earth receives all of its incoming radiation from the sun (solar energy).

100%

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Atmosphere

17% reflected by clouds

23% absorbed by atmosphere

8% reflected by atmospheric gases and dust

6% reflected by surface

46% absorbed by the surface

100%

Solar Energy (short wave)

The global heat budget

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Earths Albedo

• The earths albedo is the reflectiveness of the surface.

• In our diagram this was responsible for 31% of the radiation loss.

Radiation reflected by clouds (17%) + radiation reflected by atmospheric gases and dust (8%) + radiation reflected by the

surface (6%) = 31% (total albedo).

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Outputs• Balancing the input is an equal output

of heat (terrestrial radiation) from the Earth.

• 6% of this energy is radiated back into space. The remaining 94% is absorbed by water vapour and carbon dioxide in the atmosphere and re-radiated.

Carbon dioxide and water vapour are both examples

of greenhouse gases

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The greenhouse effect

• Eventually all radiation returns to space but the atmosphere’s greenhouse effect slows things down.

• The greenhouse effect acts like a huge blanket, limiting the heat energy lost.

Without the greenhouse effect the global temperature would be 33°C lower.

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Energy Receipt with Energy Receipt with LatitudeLatitude

Factors which influence climate on Factors which influence climate on a global scalea global scale

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Insolation

• Insolation is the suns (solar) radiation which is received by the Earth’s surface.

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Tropical latitudes receive more solar radiation than the

polar latitudes for 3 main reasons.

In Polar regions the radiation has to penetrate a greater depth of atmosphere (absorbs more heat).

The same amount of solar energy is received over a much greater area in Polar regions (less heating).

High energy loss at poles because of ice cap albedo.

Equator (0º)

NorthPole

SouthPole

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Albedo Effect

• The amount of energy actually absorbed by the surface depends on the Albedo effect. This is the proportion of radiation which is reflected by different surfaces.

Water – High reflectionForest – Low reflection

Ice and snow – High reflection

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Albedo of various surfaces

Surface % Reflected

Fresh Snow 80 - 85

Old Snow 50 - 60Sand (Beach or Desert) 20 - 30

Grass 25 - 30

Dry Soil 15 - 25

Forest 5 - 10

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What does this mean?

90ºN

60ºN

30ºN

Equator 0º

30ºS

60ºS

90ºS0 100 200 300

Insolation (Joules)Latitude

35ºN

35ºS

Terrestrial Radiation

Insolation

There is a net gain (surplus) of energy in Tropical areas

because incoming radiation exceeds outgoing radiation.

However in polar areas there is a net loss (deficit) of energy because outgoing radiation is

greater that incoming radiation.

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In theory!

• Theoretically, an imbalance in energy receipt should result in the Tropics becoming hotter and the Poles becoming even colder.

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90ºN

60ºN

30ºN

Equator 0º

30ºS

60ºS

90ºS0 100 200 300

Insolation (Joules)Latitude

35ºN

35ºS

EnergySurplus

EnergyDeficit

EnergyDeficit

However, energy is transferred from areas of

surplus (Tropics) to areas of deficit

(Poles) by atmospheric

circulation and by ocean currents.

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