This topic summary covers Knowledge Organiser: The Greenhouse Effect within Greenhouse Effect for GCSE Chemistry. Revise Greenhouse Effect in Atmosphere for GCSE Chemistry with 25 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: The Greenhouse Effect
Greenhouse Gases
- Carbon dioxide (CO₂)
- Methane (CH₄)
- Water vapour (H₂O)
- N₂O (nitrous oxide)
- NOT N₂ or O₂
The Mechanism
- Short-wave solar radiation passes through atmosphere
- Earth's surface absorbs and warms
- Long-wave infrared emitted by surface
- Greenhouse gases absorb and re-emit IR
- Some IR returns to surface → warming
Natural vs Enhanced
- Natural: keeps Earth at +15°C (essential)
- Without it: -18°C (frozen)
- Enhanced: extra warming from human activities
- CO₂: 280 ppm → 420+ ppm (human era)
Sources of Greenhouse Gases
- CO₂: fossil fuels, deforestation, cement
- CH₄: cattle, rice paddies, landfill, gas leaks
- N₂O: fertilisers, agriculture
- H₂O: natural (feedback mechanism)
Key Equations
- No calculation equations — descriptive/mechanism topic
- CH₄ + 2O₂ → CO₂ + 2H₂O (combustion of methane — adds CO₂)
- Greenhouse gases absorb infrared radiation and re-emit it back to Earth's surface
Common Mistakes
- Saying the greenhouse effect is all bad: The NATURAL greenhouse effect is essential — without it Earth would be ~−18°C; it is the ENHANCED greenhouse effect (extra warming) that causes problems
- Saying O₂ and N₂ are greenhouse gases: Only polyatomic molecules (CO₂, CH₄, H₂O, N₂O) absorb infrared — diatomic N₂ and O₂ do NOT act as greenhouse gases
- Confusing the mechanism — saying greenhouse gases block sunlight: Greenhouse gases absorb and re-emit INFRARED radiation from Earth's surface — they do not block incoming solar radiation
- Forgetting methane is a significant greenhouse gas: Methane is ~25× more potent a greenhouse gas than CO₂ per molecule — cattle and rice paddies are major sources
Practice questions for Greenhouse Effect
Which of these gases is NOT a greenhouse gas?
Explain why the natural greenhouse effect is important for life on Earth.
Quick recall flashcards
What are the three main greenhouse gases?
Carbon dioxide (CO₂), methane (CH₄), and water vapour (H₂O)
What type of radiation does Earth emit?
Long-wave infrared radiation (heat)