Greenhouse Gases and Climate Change

This lesson covers greenhouse gases, the greenhouse effect, and climate change, as required by AQA GCSE Chemistry specification (5.9.2). You need to understand which gases are greenhouse gases, how the greenhouse effect works, the evidence for climate change, and why it is a cause for concern. This is one of the most frequently examined topics in the Chemistry of the Atmosphere unit.

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What Are Greenhouse Gases?

Greenhouse gases are gases in the atmosphere that absorb and re-emit infrared (heat) radiation, trapping thermal energy in the atmosphere and keeping the Earth warm. Without greenhouse gases, the average temperature of the Earth would be about -18°C instead of the current average of about 15°C.

The main greenhouse gases are:

Greenhouse Gas	Chemical Formula	Main Sources
Carbon dioxide	CO₂	Burning fossil fuels, deforestation, respiration, volcanic activity
Methane	CH₄	Cattle farming (enteric fermentation), rice paddies, landfill sites, natural gas extraction
Water vapour	H₂O	Evaporation from oceans, lakes, and rivers; transpiration from plants

Relative Contributions