Greenhouse Effect – IGCSE Chemistry Definition
IGCSE Chemistry definition of greenhouse effect: the trapping of infrared radiation by atmospheric gases. Covers mechanism, consequences, and exam tips for 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
The greenhouse effect is tested as both a mechanism (how does it work?) and an impact question (what are the consequences?). The mechanism carries 2–3 marks and requires precise language about infrared radiation, not vague statements about “heat being trapped.”
The 0620 definition
The greenhouse effect is the process by which greenhouse gases in the atmosphere absorb infrared radiation emitted by the Earth’s surface and re-emit it, warming the lower atmosphere and the surface.
The mechanism (step by step)
- The Sun emits short-wavelength radiation (visible light and UV), which passes through the atmosphere
- The Earth’s surface absorbs this radiation and warms up
- The warm surface re-emits longer-wavelength infrared radiation
- Greenhouse gases (CO₂, CH₄, H₂O) absorb this infrared radiation
- The gases re-emit the infrared radiation in all directions — some goes back toward the Earth
- This keeps the Earth warmer than it would be without an atmosphere
Natural vs enhanced
| Feature | Natural greenhouse effect | Enhanced greenhouse effect |
|---|---|---|
| Cause | Naturally occurring CO₂, H₂O, CH₄ | Human activities increasing these gases |
| Effect | Keeps Earth at ~15 °C | Causes additional warming (global warming) |
| Desirable? | Yes — essential for life | No — causes climate change |
Human activities causing enhancement
- Burning fossil fuels (coal, oil, natural gas) → increased CO₂
- Deforestation → less CO₂ absorbed by photosynthesis
- Agriculture (cattle, rice) → increased CH₄
- Landfill sites → increased CH₄
Consequences of enhanced greenhouse effect
- Rising global temperatures (climate change)
- Melting ice caps and glaciers → rising sea levels → coastal flooding
- More extreme weather — droughts, floods, hurricanes
- Changes to ecosystems — species migration, coral bleaching
- Impact on agriculture — changed rainfall patterns, crop failure
Worked exam question
Explain how the greenhouse effect causes the temperature of the Earth to be higher than it would be without an atmosphere. [3]
Mark scheme
Short-wavelength radiation from the Sun reaches and warms the Earth’s surface [1]; the surface emits infrared / long-wavelength radiation [1]; greenhouse gases absorb and re-emit this infrared radiation back toward the Earth / in all directions, warming the atmosphere [1]
Common exam mistakes
- Saying the greenhouse effect is entirely bad — the natural greenhouse effect is essential for life. Only the enhanced effect causes problems.
- Using “heat” instead of “infrared radiation” — the examiner wants the specific term.
- Confusing the greenhouse effect with ozone depletion — these are completely separate environmental issues.
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