AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Human activities which contribute to an increase in greenhouse gases in the atmosphere: carbon dioxide
Carbon dioxide is a greenhouse gas released by human activities, chiefly burning fossil fuels such as coal, oil and natural gas, and by deforestation.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Carbon dioxide is a greenhouse gas released by human activities, chiefly burning fossil fuels such as coal, oil and natural gas, and by deforestation. In the atmosphere it absorbs outgoing infrared radiation and re-emits it, warming the Earth's surface: the greenhouse effect. For example, a coal-fired power station burns carbon, forming CO₂; clearing forest removes trees that would otherwise remove CO₂ by photosynthesis, so CO₂ rises further. More CO₂ means more absorption and re-emission of infrared, so average global temperature increases.
What earns the marks
- State that carbon dioxide is a greenhouse gas that absorbs infrared radiation emitted by the Earth's surface.
- Identify burning fossil fuels (coal, oil, natural gas) as a major human source of carbon dioxide.
- Explain that deforestation reduces photosynthesis, so less carbon dioxide is removed from the atmosphere.
- Describe the greenhouse effect: absorbed infrared is re-emitted, warming the Earth's surface and increasing average global temperature.
- Link increased carbon dioxide concentration to consequences such as climate change, including rising sea levels and changing weather patterns.
Common mistakes and how to put them right
Saying carbon dioxide traps heat from the Sun.
Put it right by stating that incoming solar radiation is mainly visible light, while carbon dioxide absorbs outgoing infrared radiation from the Earth.
Confusing the greenhouse effect with the ozone layer or acid rain.
Put it right by keeping the mechanism to absorption and re-emission of infrared radiation by greenhouse gases.
Claiming deforestation directly releases large amounts of carbon dioxide without noting that it also removes a carbon sink.
Put it right by explaining both reduced photosynthesis and any burning of cleared vegetation.
Exam tips
- Name the specific human activity, such as burning coal in power stations, rather than writing only 'pollution'.
- Use the chain 'more carbon dioxide → more infrared absorbed and re-emitted → surface warms' to gain explanation marks.
- If asked to evaluate, compare carbon dioxide with methane by naming a source and relative contribution for each.
Try the lesson
The start of the Human activities which contribute to an increase in greenhouse gases in the atmosphere: carbon dioxide lesson, made from checked teaching notes for this specification point.
Have a go first
Which human activity releases the most carbon dioxide into the atmosphere?
Listen
Carbon dioxide is a greenhouse gas released by human activities, chiefly burning fossil fuels such as coal, oil and natural gas, and by deforestation. In the atmosphere it absorbs outgoing infrared radiation and re-emits it, warming the Earth's surface: the greenhouse effect. For example, a coal-fired power station burns carbon, forming CO₂; clearing forest removes trees that would otherwise remove CO₂ by photosynthesis, so CO₂ rises further. More CO₂ means more absorption and re-emission of infrared, so average global temperature increases. A strong answer earns marks for these points. State that carbon dioxide is a greenhouse gas that absorbs infrared radiation emitted by the Earth's surface. Identify burning fossil fuels (coal, oil, natural gas) as a major human source of carbon dioxide. Explain that deforestation reduces photosynthesis, so less carbon dioxide is removed from the atmosphere. Describe the greenhouse effect: absorbed infrared is re-emitted, warming the Earth's surface and increasing average global temperature. A common slip: Saying carbon dioxide traps heat from the Sun. Instead, stating that incoming solar radiation is mainly visible light, while carbon dioxide absorbs outgoing infrared radiation from the Earth. Exam tip: Name the specific human activity, such as burning coal in power stations, rather than writing only 'pollution'.
Key words
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Greenhouse gases
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Fossil fuel combustion
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Deforestation and carbon sinks
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Climate change
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See every definition
- Greenhouse gases
- Gases in the atmosphere that absorb outgoing infrared radiation and re-emit it, warming the Earth's surface.
- Fossil fuel combustion
- Burning coal, oil and natural gas, a major human source of carbon dioxide.
- Deforestation and carbon sinks
- Clearing forest removes trees that would otherwise remove carbon dioxide by photosynthesis, so carbon dioxide rises further.
- Climate change
- A consequence of increased carbon dioxide concentration, including rising sea levels and changing weather patterns.
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