Explain how greenhouse gases cause the Earth's atmosphere to warm up.

AQA GCSE Chemistry (8462) — 4.9.2 Carbon dioxide and methane as greenhouse gases · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Electromagnetic radiation from the Sun passes through the atmosphere and is absorbed by the Earth’s surface.
The surface then re‑emits this energy as infrared radiation.
Greenhouse gases in the atmosphere absorb some of this infrared radiation.
The absorbed energy is re‑radiated in all directions, warming the atmosphere – the greenhouse effect.

Examiner tips

  • Use the exact sequence: solar → absorption → IR emission → absorption by GHGs → warming.
  • Show the direction of energy flow (solar to surface to IR to GHGs).

Common mistakes

  • Confusing visible light with infrared; describing only absorption without re‑radiation.
  • Using vague terms like ‘heat’ instead of ‘infrared radiation’ or ‘energy transfer’.

Mark scheme (4 marks)

  1. Electromagnetic/solar radiation from the Sun passes through the Earth's atmosphere
  2. The Earth absorbs some radiation and re-emits it as infrared radiation
  3. Greenhouse gases in the atmosphere absorb this infrared radiation
  4. This causes the atmosphere to warm up / leads to the greenhouse effect

Key terms in this question

greenhouse gases

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