IB Environmental systems and societies 6.1C Greenhouse Effect Notes

Greenhouse Gases Trap Heat and Warm the Planet

1. The atmosphere contains gases and particles that control how much heat escapes to space.
2. Greenhouse gases (GHGs) and aerosols absorb and re-emit some of the infrared (long-wave) radiation given off by Earth's warmed surface.
3. This stops part of the outgoing radiation from leaving, warming the atmosphere.
4. Important GHGs include carbon dioxide (CO₂), water vapour (H₂O), methane (CH₄), and nitrous oxide (N₂O).
5. A major warming aerosol is black carbon, which absorbs sunlight and adds to warming.

Key Greenhouse Gases and Their Sources

Water Vapour (H₂O)

1. It is the most abundant greenhouse gas.
2. It comes from evaporation, transpiration, and sublimation.
3. Its concentration rises as temperatures rise, forming a positive feedback loop.
   1. More warming drives more evaporation, which adds more water vapour and causes further warming.
4. It is treated as a feedback rather than a driver humans control directly, because:
   1. its atmospheric lifetime is short,
   2. its concentration changes rapidly with temperature,
   3. and it cannot be mitigated directly.

Carbon Dioxide (CO₂)

1. It comes mainly from the combustion of fossil fuels, deforestation, and industrial processes such as cement production.
2. It is the most influential human-generated greenhouse gas, because it stays in the atmosphere for centuries and exists in high concentrations.
3. Its concentration (about 0.04%) is higher than at any point in at least 800,000 years.

Methane (CH₄)

1. Key sources include livestock digestion, rice paddies, landfills, and natural gas extraction.
2. It is more than 25 times more effective at trapping heat than CO₂ over 100 years.
3. Its concentration is lower than CO₂, but it is highly potent and a significant contributor to warming.

Nitrous Oxide (N₂O)

1. Main sources include agricultural fertilisers, industrial processes, and fossil fuel combustion.
2. Molecule for molecule, it has a warming potential nearly 300 times stronger than CO₂.