AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Greenhouse gases: Students should be able to describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter.
The Sun emits mainly short wavelength radiation, including visible light and ultraviolet, which passes through the atmosphere and is absorbed by the Earth's surface.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The Sun emits mainly short wavelength radiation, including visible light and ultraviolet, which passes through the atmosphere and is absorbed by the Earth's surface. The warmed surface re-emits energy as longer wavelength infrared radiation. Greenhouse gases such as carbon dioxide, methane and water vapour absorb some of this outgoing infrared, so the energy is re-radiated in all directions, including back towards the surface. This trapped energy keeps the mean surface temperature higher than it would otherwise be. A useful model is a car parked in sunshine: short wavelength light enters through the glass, the interior warms and emits infrared, and the glass reduces the escape of that infrared. The effect is natural and essential; the enhanced greenhouse effect occurs when extra gases strengthen it.
What earns the marks
- Short wavelength radiation from the Sun (visible and ultraviolet) passes through the atmosphere and is absorbed by the Earth's surface, warming it.
- The warmed Earth's surface emits longer wavelength infrared radiation.
- Greenhouse gases in the atmosphere absorb some of this outgoing long wavelength infrared radiation.
- Absorbed energy is re-radiated in all directions, including back towards the Earth's surface, so the surface and lower atmosphere stay warmer than they would without those gases.
- The natural greenhouse effect is essential for life; adding more greenhouse gases enhances the effect and tends to raise the mean global temperature.
Common mistakes and how to put them right
Saying the greenhouse effect is caused only by human activity.
Put it right by stating that it is a natural process and that human activity enhances it.
Claiming that greenhouse gases form a solid barrier or 'hole' that heat cannot cross.
Put it right by describing absorption and re-radiation of infrared in all directions.
Stating that the atmosphere absorbs incoming short wavelength radiation as the main mechanism.
Put it right by explaining that short wavelength radiation mainly reaches the surface, while outgoing long wavelength infrared is what greenhouse gases absorb.
Exam tips
- Use the phrases 'short wavelength radiation' and 'long wavelength infrared radiation' explicitly, because the command word is 'describe' and the specification names both.
- Sequence the account: incoming short wavelength, surface warming, outgoing long wavelength, absorption by greenhouse gases, re-radiation in all directions.
- Link the final point to the consequence for surface temperature rather than stopping at absorption.
Try the lesson
The start of the Greenhouse gases: Students should be able to describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter. lesson, made from checked teaching notes for this specification point.
Have a go first
Which type of radiation from the Sun passes through the atmosphere and warms the Earth's surface?
Listen
The Sun emits mainly short wavelength radiation, including visible light and ultraviolet, which passes through the atmosphere and is absorbed by the Earth's surface. The warmed surface re-emits energy as longer wavelength infrared radiation. Greenhouse gases such as carbon dioxide, methane and water vapour absorb some of this outgoing infrared, so the energy is re-radiated in all directions, including back towards the surface. This trapped energy keeps the mean surface temperature higher than it would otherwise be. A useful model is a car parked in sunshine: short wavelength light enters through the glass, the interior warms and emits infrared, and the glass reduces the escape of that infrared. The effect is natural and essential; the enhanced greenhouse effect occurs when extra gases strengthen it. A strong answer earns marks for these points. Short wavelength radiation from the Sun (visible and ultraviolet) passes through the atmosphere and is absorbed by the Earth's surface, warming it. The warmed Earth's surface emits longer wavelength infrared radiation. Greenhouse gases in the atmosphere absorb some of this outgoing long wavelength infrared radiation. Absorbed energy is re-radiated in all directions, including back towards the Earth's surface, so the surface and lower atmosphere stay warmer than they would without those gases. A common slip: Saying the greenhouse effect is caused only by human activity. Instead, stating that it is a natural process and that human activity enhances it. Exam tip: Use the phrases 'short wavelength radiation' and 'long wavelength infrared radiation' explicitly, because the command word is 'describe' and the specification names both.
Key words
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Short wavelength radiation
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Long wavelength infrared radiation
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Greenhouse gases
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Enhanced greenhouse effect
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See every definition
- Short wavelength radiation
- Radiation from the Sun, including visible light and ultraviolet, which passes through the atmosphere and is absorbed by the Earth's surface.
- Long wavelength infrared radiation
- Radiation emitted by the warmed Earth's surface, some of which is absorbed by greenhouse gases in the atmosphere.
- Greenhouse gases
- Gases such as carbon dioxide, methane and water vapour that absorb some outgoing infrared and re-radiate the energy in all directions.
- Enhanced greenhouse effect
- Occurs when extra gases strengthen the natural effect, which is essential, and tends to raise the mean global temperature.
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