Describe the role of methane as a greenhouse gas and explain how the increasing amount of methane in the atmosphere may affect global climate.

Cambridge International IGCSE Chemistry (0620) — 10.3 Air quality and climate · Describe and Explain · 4 marks · View as Markdown

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

Methane is produced from several natural and human-related sources. Its concentration in the atmosphere has more than doubled since pre-industrial times.

Model answer (4 marks)

Methane (CH₄) is a potent greenhouse gas that absorbs infrared radiation emitted by the Earth’s surface.

The absorbed energy is re‑radiated, with a portion directed back towards the surface, thereby warming it.

An increase in atmospheric methane concentration means more infrared radiation is trapped, strengthening the greenhouse effect.

This enhanced trapping of heat leads to global warming and contributes to climate change, raising average global temperatures.

Examiner tips

Use the word ‘absorb’ and ‘re‑radiate’ to show understanding of the greenhouse mechanism.
Explain the chain from higher concentration to more trapped heat and then to temperature rise.
Keep the answer concise – 4 marks can be earned with 4 short sentences.
Mention ‘global warming’ or ‘climate change’ to link to the broader impact.

Common mistakes

Confusing methane with CO₂ or other gases; students sometimes describe only CO₂.
Failing to explain that the trapped heat is re‑radiated back to the surface, not just absorbed.
Using vague terms like ‘warming the planet’ without linking to infrared absorption and trapping.

Mark scheme (4 marks)

Methane is a greenhouse gas that absorbs infrared radiation (heat) from the Earth's surface
The absorbed energy is re-emitted back towards the Earth's surface, warming it
Higher concentration of methane means more infrared radiation is absorbed/trapped
This leads to an enhanced greenhouse effect / global warming / climate change, causing a rise in average global temperatures

Key terms in this question

methane · greenhouse gas