Greenhouse gases and human activitiesSpec 4.13, 4.14
In short
Greenhouse gases are the gases that cause the greenhouse effect: carbon dioxide, methane, nitrous oxide, CFCs and water vapour. Human activities add to them. Burning fossil fuels and deforestation increase carbon dioxide, cattle, rice paddy fields and landfill release methane, nitrogen fertilisers release nitrous oxide, and old refrigerators and aerosols released CFCs.
The greenhouse effect keeps the Earth warm enough for life. The gases that cause it are called greenhouse gases. You must know five of them and how human activities add to them.
| Greenhouse gas | How human activities add to it |
|---|---|
| Carbon dioxide (CO₂) | Burning fossil fuels in power stations, vehicles and homes; burning forests when land is cleared (deforestation, which also removes trees that take in CO₂) |
| Methane (CH₄) | Cattle and other farm animals, which release it from their digestion; rice paddy fields; rotting waste in landfill sites |
| Nitrous oxide (N₂O) | Use of nitrogen fertilisers on fields; burning fuels in vehicles |
| CFCs (chlorofluorocarbons) | Released from old refrigerators, air conditioners and aerosol sprays (CFCs are now banned in most countries) |
| Water vapour (H₂O) | Mostly from evaporation of water from oceans and land. Burning fuels also releases it, and a warmer atmosphere holds more of it. |
Most of the increase in carbon dioxide over the last 200 years is from burning fossil fuels and deforestation. Methane and nitrous oxide increase as more land is farmed to feed a growing human population.
Give a specific source. 'Pollution' or 'factories' is too vague. Say 'burning fossil fuels' for carbon dioxide and 'cattle' or 'rice fields' for methane.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026