The greenhouse effect
Greenhouse gases keep the Earth warm enough to support life. The
three you need: water vapour , carbon dioxide and
methane How it works:
The Sun sends short wavelength radiation (visible and UV) which
passes through the atmosphere and is absorbed by the Earth's surface
The warmed Earth radiates long wavelength (infrared) radiation
Greenhouse gases absorb this long wavelength radiation and
re-radiate it in all directions, including back to the surface
So energy is trapped and the atmosphere warms
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The greenhouse effect the Earth's surface the atmosphere GHG GHG GHG GHG the Sun short wavelength radiation passes straight through the atmosphere and warms the ground the warm ground gives out long wavelength radiation some escapes to space but some is absorbed by greenhouse gas molecules and re-emitted back down — so the Earth stays warm Water vapour, carbon dioxide and methane are the main greenhouse gases. The effect itself is natural and keeps the Earth warm enough to live on — the problem is that human activity is adding more of these gases, which traps more radiation and raises the temperature. The greenhouse effect: the Sun's short wavelength radiation passing through the atmosphere to the ground, long wavelength radiation leaving the ground, some absorbed by greenhouse gas molecules and re-emitted back down
The explanation must use the two wavelengths : short in, long out,
long absorbed. "Traps heat" on its own is not the mechanism
Water vapour is a greenhouse gas; nitrogen and oxygen are not.
Oxides of nitrogen cause acid rain, not the greenhouse effect
The rest of this topic is in the full Exam Guide The complete AQA GCSE Chemistry guide — every topic, exam checklist and common mistake — is coming soon. Until then, the first topic in every unit is free to read.
In the full topic
• The greenhouse effect• Human activities increasing greenhouse gases• Global climate change• The carbon footprintRead the free chemistry topics →