Point 2 of 6 — The Greenhouse Effect, the Carbon Footprint and Sustainable SolutionsQuestion bank: 0 questions (0 with pictures)
02 The greenhouse gases and their sources
Water vapour (H₂O): contributes most of the natural greenhouse effect, but its amount is set by temperature, not directly by emission, so it acts as a feedback, not a forcing.
Carbon dioxide (CO₂): from the combustion of coal, oil and gas, from cement manufacture (CaCO₃ → CaO + CO₂) and from deforestation. Responsible for roughly two thirds of the human forcing; it stays in the atmosphere for a century or more.
Methane (CH₄): rice paddies under water, ruminant digestion, landfills, coal mines and gas leaks; GWP ≈28 over 100 years, lifetime about 12 years.
Nitrous oxide (N₂O): nitrogen fertilisers and biomass burning; GWP ≈265, lifetime over a century, and it also destroys ozone.
Ozone (O₃)in the troposphere: formed secondarily from NOx, carbon monoxide and hydrocarbons in sunlight.
CFCs, HCFCs and their substitutes: GWP in the thousands; hydrofluorocarbons (HFCs) do not harm ozone but are strong greenhouse gases, which is why the Kigali Amendmentphases them down.
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