Climate Change, Global Warming and Ozone Depletion
Exam focus
Greenhouse effect, major GHGs and GWPs, evidence of warming, mitigation versus adaptation, ozone chemistry and the two key treaties.
Core rules
- The greenhouse effect is natural; human enhancement adds CO₂, CH₄, N₂O and fluorinated gases.
- GWP over 100 years: CO₂ = 1, CH₄ ≈ 28–30, N₂O ≈ 265–298. CO₂-equivalent = mass × GWP.
- Mitigation reduces emissions or enhances sinks; adaptation adjusts to actual or expected impacts.
- Ozone depletion is a separate problem: CFCs release chlorine in the stratosphere, catalytically destroying O₃; the Antarctic ozone hole forms in spring. The Montreal Protocol (1987) phases out ozone-depleting substances.
- Global warming is driven by GHGs; ozone depletion is not the main driver of warming.
- UNFCCC 1992; Kyoto Protocol 1997 with Annex I targets; Paris Agreement 2015 with nationally determined contributions and a 1.5–2°C goal.
Worked example
A car emits 120 g CO₂/km. Over 15,000 km/year, CO₂ = 120 × 15,000 = 1,800,000 g = 1.8 t CO₂/year. If methane leakage adds 2 kg CH₄, CO₂-eq = 2 × 28 = 56 kg CO₂-eq. Total ≈ 1.86 t CO₂-eq. Convert units and apply GWP to non-CO₂ gases before adding.
Traps
- Saying the ozone hole causes global warming; they are linked but distinct.
- Using GWP without specifying the time horizon.
- Confusing mitigation with adaptation.
- Forgetting that CO₂ is the reference gas with GWP = 1.