Describe the greenhouse effect and explain how an increase in greenhouse gases in the atmosphere could lead to global climate change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The Sun emits radiation that passes through the atmosphere and is absorbed by the Earth.
The Earth then re‑emits this energy as infrared radiation.
Greenhouse gases – such as water vapour, CO₂ and CH₄ – absorb the infrared radiation and trap heat in the atmosphere.
If the concentration of these gases rises, more infrared radiation is trapped, the surface temperature rises and global climate change occurs (e.g. higher sea levels, species loss, lower crop yields, migration).
The Earth then re‑emits this energy as infrared radiation.
Greenhouse gases – such as water vapour, CO₂ and CH₄ – absorb the infrared radiation and trap heat in the atmosphere.
If the concentration of these gases rises, more infrared radiation is trapped, the surface temperature rises and global climate change occurs (e.g. higher sea levels, species loss, lower crop yields, migration).
Examiner tips
- Use the sequence Sun → Earth → infrared → greenhouse gases → trapping → warming
- Mention specific gases and a consequence of warming
Common mistakes
- Confusing solar radiation with infrared radiation
- Omitting the role of greenhouse gases in trapping heat
- Failing to give a clear example of climate change
Mark scheme (4 marks)
- Radiation/energy from the Sun passes through the Earth's atmosphere
- The Earth absorbs radiation and re-emits it as infrared radiation
- Greenhouse gases (water vapour, carbon dioxide or methane) absorb this infrared radiation, warming the atmosphere
- An increase in greenhouse gases leads to more infrared radiation being absorbed/trapped, raising the Earth's temperature and causing global climate change (e.g. rising sea levels / extinction of species / decreased crop yield / migration)
Key terms in this question
greenhouse effect · greenhouse gases · global climate change
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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