Explain why scientists are concerned about increasing levels of methane in the Earth's atmosphere.

Eduqas GCSE Chemistry — C9 Chemistry of the atmosphere · Explain · 4 marks · View as Markdown

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

Methane is a greenhouse gas produced by a number of natural and human-related sources. Its concentration in the atmosphere has more than doubled since pre-industrial times.

Model answer (4 marks)

Methane is a greenhouse gas that absorbs infrared radiation.
Higher concentrations of methane mean more infrared radiation is absorbed, trapping more heat in the atmosphere.
This enhances the greenhouse effect, causing the Earth's average temperature to rise.
The resulting global warming can lead to climate change, such as melting polar ice, rising sea levels and more extreme weather events.

Examiner tips

  • Use the exact phrase "greenhouse gas" and "infra‑red radiation". Show the chain: methane → absorption → heat trapped → temperature rise → climate change. Include at least one specific consequence (e.g. melting ice).

Common mistakes

  • Forgetting that methane absorbs infrared radiation. Failing to link the temperature rise to climate change. Using vague terms like "more heat" without explaining the greenhouse effect.

Mark scheme (4 marks)

  1. Methane is a greenhouse gas / methane absorbs (infra-red) radiation
  2. Higher methane concentration means more infra-red radiation is absorbed / more heat is trapped in the atmosphere
  3. This leads to an enhanced greenhouse effect / causes global warming / causes the average temperature of the Earth to rise
  4. This could lead to climate change / melting of polar ice caps / rising sea levels / more extreme weather events

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