AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    (HT only) The temperature of the Earth depends on many factors including:…

    Full specification wording

    Perfect black bodies and radiation: (HT only) The temperature of the Earth depends on many factors including: the rates of absorption and emission of radiation, reflection of radiation into space.

    This is Higher tier only.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 4 of 6
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    This is Higher tier only. The Earth absorbs mostly short wavelength radiation from the Sun and emits longer wavelength infrared out to space, because the Earth is far cooler than the Sun. Its mean temperature is steady only while those two rates are equal. Three factors therefore matter. First, the rate at which radiation is absorbed by the surface and the atmosphere. Second, the rate at which infrared is emitted back into space. Third, the fraction reflected straight back into space without ever being absorbed, mainly by clouds, ice and snow. Greenhouse gases such as carbon dioxide (CO₂) and methane absorb outgoing infrared and re-emit some of it downwards, cutting the rate of loss to space.

    What earns the marks

    • Naming the rate of absorption of radiation from the Sun as a factor.
    • Naming the rate of emission of infrared radiation from the Earth into space as a factor.
    • Naming the fraction of radiation reflected back into space, by clouds or by ice, as a factor.
    • Stating that carbon dioxide is a greenhouse gas that absorbs infrared, so the Earth's temperature rises.

    Common mistakes and how to put them right

    • Saying greenhouse gases reflect the outgoing infrared rather than absorbing and re-emitting it.

    • Confusing the greenhouse effect with damage to the ozone layer and ultraviolet.

    • Treating the Earth's temperature as set only by the output of the Sun.

    • Claiming that more reflection into space would warm the Earth.

    Exam tips

    • A list of factors must contain genuinely different factors, not the same idea twice.
    • Name the greenhouse gas rather than writing 'gases in the atmosphere'.
    • This statement is Higher tier only; expect it alongside the radiation balance argument.

    Try the lesson

    The start of the Perfect black bodies and radiation: (HT only) The temperature of the Earth depends on many factors including: the rates of absorption and emission of radiation, reflection of radiation into space. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which change would tend to lower the average temperature of the Earth's surface?

    Listen

    This is Higher tier only. The Earth absorbs mostly short wavelength radiation from the Sun and emits longer wavelength infrared out to space, because the Earth is far cooler than the Sun. Its mean temperature is steady only while those two rates are equal. Three factors therefore matter. First, the rate at which radiation is absorbed by the surface and the atmosphere. Second, the rate at which infrared is emitted back into space. Third, the fraction reflected straight back into space without ever being absorbed, mainly by clouds, ice and snow. Greenhouse gases such as carbon dioxide (CO₂) and methane absorb outgoing infrared and re-emit some of it downwards, cutting the rate of loss to space. A strong answer earns marks for these points. naming the rate of absorption of radiation from the Sun as a factor. naming the rate of emission of infrared radiation from the Earth into space as a factor. naming the fraction of radiation reflected back into space, by clouds or by ice, as a factor. stating that carbon dioxide is a greenhouse gas that absorbs infrared, so the Earth's temperature rises. Exam tip: A list of factors must contain genuinely different factors, not the same idea twice.

    See it

    A top-down flowchart. At the top, a node labelled 'Radiation from the Sun' branches into two nodes: 'Rate of absorption of radiation' and 'Fraction reflected back into space by clouds and ice'. The absorption node leads down to a node labelled 'Earth's mean surface temperature'. A separate node, 'Rate of emission of infrared radiation into space', also leads into that temperature node. To the side, a node labelled 'Greenhouse gases such as carbon dioxide and methane' leads to 'Absorb outgoing infrared and re-emit some downwards', which in turn leads into the emission-rate node. Finally, the temperature node leads to 'Steady while absorption and emission rates are equal'.
    Shows the factors the teaching note gives for the Earth's mean surface temperature, including how greenhouse gases affect the rate of infrared loss to space.

    Key words

    Say what each word means before you turn the card.

    absorption by the Earth

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    emission into space

    Try answering aloud or in your head before turning the card.

    reflection by clouds and ice

    Try answering aloud or in your head before turning the card.

    greenhouse gases

    Try answering aloud or in your head before turning the card.

    See every definition
    absorption by the Earth
    The rate at which radiation is absorbed by the surface and the atmosphere is one factor the Earth's temperature depends on.
    emission into space
    The rate at which infrared is emitted back into space is one factor the Earth's temperature depends on.
    reflection by clouds and ice
    The fraction reflected straight back into space without ever being absorbed, mainly by clouds, ice and snow.
    greenhouse gases
    Gases such as carbon dioxide and methane that absorb outgoing infrared and re-emit some of it downwards, cutting the rate of loss to space.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. At the top, a node labelled 'Radiation from the Sun' branches into two nodes: 'Rate of absorption of radiation' and 'Fraction reflected back into space by clouds and ice'. The absorption node leads down to a node labelled 'Earth's mean surface temperature'. A separate node, 'Rate of emission of infrared radiation into space', also leads into that temperature node. To the side, a node labelled 'Greenhouse gases such as carbon dioxide and methane' leads to 'Absorb outgoing infrared and re-emit some downwards', which in turn leads into the emission-rate node. Finally, the temperature node leads to 'Steady while absorption and emission rates are equal'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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