This topic accounts for approximately 5% of your exam marks.
stable
Rare
Stable5%
Air composition, greenhouse effect and climate implications appear in most series.
How the natural greenhouse effect works
Short-wavelength radiation from the Sun (visible and ultraviolet) passes through the atmosphere and warms the Earth's surface
The warmed surface re-emits energy as infrared radiation with a longer wavelength
Some of this outgoing infrared is absorbed by greenhouse gases in the atmosphere and re-radiated in all directions, including back down toward the surface
The trapped energy keeps the average surface temperature at about +15 °C — without it, the planet would freeze
The main greenhouse gases
Carbon dioxide, CO2
Methane, CH4
Water vapour, H2O
Sources of atmospheric carbon dioxide
Burning fossil fuels (coal, oil, natural gas) and wood
Heating limestone and other carbonate rocks during cement manufacture, releasing CO2 by thermal decomposition
Natural weathering, where acids react with carbonate rocks
Respiration: plants and animals exhale CO2 as a metabolic by-product
Enhanced greenhouse effect
Human activity has raised CO2 and CH4 concentrations above their long-term natural values
More greenhouse gas means more outgoing infrared is trapped, so the average surface temperature drifts upward — the enhanced greenhouse effect
This is the basis of the link between greenhouse gas emissions and global warming and climate change