Describe the natural greenhouse effect and explain why an increase in the concentration of greenhouse gases in the atmosphere leads to climate change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Greenhouse gases such as water vapour, carbon dioxide and methane are naturally present in the Earth's atmosphere. Human activities, including the burning of fossil fuels, have increased the concentration of these gases over the past two centuries.
Model answer (4 marks)
Greenhouse gases absorb infrared radiation emitted by the Earth’s surface, preventing it from escaping to space. This trapping of heat keeps the atmosphere warm enough to support life.
When the concentration of greenhouse gases rises, more infrared radiation is absorbed and trapped. The extra heat raises global temperatures, which in turn causes climate change.
When the concentration of greenhouse gases rises, more infrared radiation is absorbed and trapped. The extra heat raises global temperatures, which in turn causes climate change.
Examiner tips
- Use the terms ‘absorb’ and ‘trap’ for infrared radiation; mention the Earth’s surface as the source.
- Explain the chain: higher GHG → more IR trapped → higher temperatures → climate change.
- Keep the answer concise – 4 marks can be earned with two short sentences.
- Use UK spelling (e.g. ‘colour’).
Common mistakes
- Confusing absorption with reflection of visible light; the greenhouse effect involves infrared. Failing to mention the source of infrared radiation (the Earth’s surface). Using vague terms like ‘heat’ without linking to infrared radiation and temperature rise.
Mark scheme (4 marks)
- Greenhouse gases trap/absorb infra-red radiation (from the Earth's surface)
- This keeps/raises the temperature of the Earth's atmosphere, making it warm enough to support life
- An increased concentration of greenhouse gases means more infra-red radiation is trapped/absorbed
- This causes a rise in global temperatures / leads to climate change
Key terms in this question
greenhouse effect · greenhouse gases · climate change
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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