The greenhouse effect and global climate change
The greenhouse effect keeps Earth warm enough to support life. Greenhouse gases in the atmosphere absorb infrared radiation that would otherwise escape into space. Without it, Earth's average temperature would be about −18 °C instead of +15 °C.
How it works
- The Sun emits short-wavelength radiation (visible/UV) that passes through the atmosphere and warms the surface.
- The surface emits long-wavelength infrared radiation back toward space.
- Greenhouse gases absorb this IR and re-radiate it in all directions.
- Some IR is sent back to the surface, warming it more.
The main greenhouse gases
| Gas | Source |
|---|---|
| Water vapour H₂O | Evaporation from oceans (largest contributor; depends on temperature) |
| Carbon dioxide CO₂ | Combustion of fossil fuels, deforestation, respiration |
| Methane CH₄ | Cattle farming, rice paddies, landfill, leaking gas pipes |
CO₂ has risen from ~280 ppm in 1750 to ~420 ppm now — a 50% increase due to human activity.
Human activities increasing CO₂
- Burning fossil fuels (cars, factories, electricity generation).
- Deforestation (cutting trees reduces photosynthesis; burning trees releases stored carbon).
- Cement production (heating limestone releases CO₂).
Human activities increasing CH₄
- Cattle farming (digestion produces methane).
- Rice paddies (anaerobic decomposition).
- Landfill sites (organic waste decomposing).
- Leaks from natural gas pipelines.
Consequences of more greenhouse gas
More IR trapped → higher average global temperature → climate change. Effects include:
- Sea level rise (melting ice, thermal expansion of oceans).
- More extreme weather (storms, droughts, heatwaves).
- Changes in rainfall patterns affecting agriculture.
- Loss of habitats and species (coral bleaching, ice habitat loss).
- Ocean acidification (CO₂ + H₂O → H₂CO₃).
Evidence is robust but uncertain in detail
Climate science relies on models and historical data. The scientific consensus (>97% of climate scientists) is that human activity is the main cause of recent warming. Detailed regional predictions remain uncertain.
⚠Common mistakes
- Confusing greenhouse effect with ozone hole — different problems. Greenhouse: heat trapping. Ozone hole: UV protection.
- Saying CO₂ is the only greenhouse gas — water vapour is the largest, methane is more potent per molecule.
- Saying greenhouse effect is bad — it's essential for life. The PROBLEM is the enhanced greenhouse effect from human emissions.
- Confusing weather with climate — weather is short-term; climate is long-term average.
Links
Builds on C9.1, C9.2. Sets up C9.4 (carbon footprint), C10.1 (sustainable resources).
AI-generated · claude-opus-4-7 · v3-deep-chemistry