Describe the greenhouse effect and explain how greenhouse gases lead to an increase in the temperature of the Earth's atmosphere.

Edexcel GCSE Chemistry (1CH0) — 8.2 Earth and atmospheric science · Describe · 4 marks · View as Markdown

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

Scientists have measured a steady rise in the average temperature of the Earth's atmosphere over the last century. This rise is linked to increasing concentrations of greenhouse gases such as carbon dioxide, methane and water vapour.

Model answer (4 marks)

The Sun’s radiation reaches the Earth’s surface and heats it, so the surface emits infra‑red radiation.
Greenhouse gases in the atmosphere absorb some of this infra‑red radiation.
The absorbed energy is re‑emitted in all directions, including back towards the surface, which raises the temperature of the atmosphere.
If the concentration of greenhouse gases increases, more infra‑red radiation is trapped, so the atmospheric temperature rises further, enhancing the greenhouse effect.

Examiner tips

  • Use the exact sequence of steps: Sun → surface heating → IR emission → absorption by GHGs → back‑radiation → temperature rise. Show the link between higher GHG concentration and increased trapping of IR. Keep the answer concise – one sentence per point.
  • common_mistakes
  • :
  • Mixing up the direction of radiation (e.g., saying GHGs emit only upwards). Failing to mention the back‑radiation to the surface. Using vague terms like “heat” instead of “infra‑red radiation”.

Mark scheme (4 marks)

  1. The Sun's radiation reaches the Earth's surface and warms it, causing the surface to emit infra-red radiation.
  2. Greenhouse gases in the atmosphere absorb/trap the infra-red radiation emitted by the Earth's surface.
  3. The absorbed infra-red radiation is re-emitted in all directions, including back towards the Earth's surface, raising the temperature of the atmosphere.
  4. An increase in the concentration of greenhouse gases means more infra-red radiation is trapped, leading to a greater rise in atmospheric temperature / enhancing the greenhouse effect.

Key terms in this question

greenhouse effect · greenhouse gases

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