Greenhouse effect — climate change explained
Greenhouse gases trap heat. Natural amount is fine; human-added amounts are warming the planet.
The natural greenhouse effect.
- Sun's rays warm Earth's surface.
- Earth radiates HEAT back as INFRARED radiation.
- Greenhouse gases (CO₂, methane, water vapour) ABSORB this infrared.
- Re-emit some back toward Earth → keeps Earth warmer.
- Without it: Earth would be ~-18°C (frozen). Greenhouse effect makes Earth ~+15°C — habitable.
Human enhancement.
- Burning FOSSIL FUELS releases CO₂.
- Cattle (livestock) and rice paddies release METHANE.
- Deforestation REDUCES CO₂ absorption.
- Industrial processes release other greenhouse gases.
Net effect: more greenhouse gas in atmosphere → more heat trapped → temperatures rising.
Evidence of warming:
- Average global temperature up ~1.1°C since 1880.
- Ice caps and glaciers melting.
- Sea levels rising (~20 cm).
- Hotter heatwaves more frequent.
- Acidifying oceans (CO₂ + water → carbonic acid).
Consequences (in detail):
1. Sea level rise.
- Melting glaciers + thermal expansion of warmer water.
- Coastal flooding; threatens low-lying nations (Bangladesh, Pacific islands).
2. Extreme weather.
- More frequent + severe hurricanes, droughts, floods, heatwaves.
3. Habitat changes.
- Species migrating poleward.
- Polar species (polar bears) running out of habitat.
- Coral bleaching from warmer + more acidic oceans.
4. Agriculture.
- Heat stress, droughts → crop failures.
- Some areas may benefit (longer growing seasons); many worse off.
5. Biodiversity loss.
- Many species can't adapt fast enough.
- Combined with habitat destruction → extinction crisis.
Worked qualitative. Why does CUTTING TREES make global warming WORSE in TWO ways?
- (1) Trees absorb CO₂ via photosynthesis. Cutting REMOVES this CO₂ sink.
- (2) Burning the wood RELEASES the carbon stored in it.
- Double impact: less absorption + more release.
Cambridge tip. Memorise the chain: SUN → EARTH → INFRARED → GAS TRAPS → WARMING. Specifically state INFRARED.
- Greenhouse gases trap infrared radiation.
- CO₂, methane, water vapour main culprits.
- Burning fossils + deforestation = main causes.
- Effects: sea level, weather, biodiversity, agriculture.