Explain why scientists are concerned about the increasing concentration of carbon dioxide in the atmosphere.

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

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

Carbon dioxide is released into the atmosphere from a number of human activities. Its concentration in the atmosphere has risen significantly since the beginning of industrialisation.

Model answer (4 marks)

Carbon dioxide is a greenhouse gas that absorbs infrared radiation emitted by the Earth’s surface.
Higher concentrations of CO₂ increase the amount of heat trapped in the atmosphere – the enhanced greenhouse effect.
This causes the average temperature of the Earth to rise, i.e. global warming.
The warming leads to climate‑change consequences such as rising sea levels, melting polar ice, more extreme weather and altered rainfall patterns.

Examiner tips

  • Use the exact terms ‘greenhouse gas’, ‘infrared radiation’, ‘enhanced greenhouse effect’, ‘global warming’, and give one named consequence.
  • Show the causal chain – each point builds on the previous one – to earn all four marks.

Common mistakes

  • Confusing CO₂ with other gases or saying it ‘releases heat’ instead of ‘absorbs infrared’. Giving a vague consequence such as ‘more weather’ without naming a specific effect.

Mark scheme (4 marks)

  1. Carbon dioxide is a greenhouse gas (that absorbs/traps heat/infrared radiation)
  2. Higher concentration of CO2 means more heat/infrared radiation is trapped/absorbed (enhanced greenhouse effect)
  3. This causes the average temperature of the Earth to rise / global warming
  4. This leads to a named consequence of climate change (e.g. rising sea levels / melting of polar ice / more frequent extreme weather events / changes in rainfall patterns)

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