Greenhouse Gases and Climate Change
The Greenhouse Effect
The greenhouse effect is a natural process that keeps the Earth warm enough to support life. Without it, the Earth's average temperature would be about −18°C instead of the current ~15°C.
How It Works
1. Short-wavelength radiation from the Sun (mainly visible light) passes through the atmosphere and reaches the Earth's surface
2. The Earth's surface absorbs this radiation and warms up
3. The warm surface re-emits longer-wavelength infrared radiation (heat)
4. Greenhouse gases in the atmosphere absorb some of this infrared radiation and re-emit it in all directions, including back towards the Earth
5. This traps energy in the atmosphere, keeping the planet warm
Greenhouse Gases
The main greenhouse gases are:
| Gas | Formula | Sources |
|---|---|---|
| Carbon dioxide | CO₂ | Burning fossil fuels, deforestation, respiration |
| Methane | CH₄ | Agriculture (cattle/rice paddies), landfill, natural gas |
| Water vapour | H₂O | Evaporation (part of the natural water cycle) |
Why CO₂ Levels Are Increasing
Since the Industrial Revolution (around 1750), atmospheric CO₂ has risen from about 280 ppm to over 420 ppm (parts per million). This increase is caused by human activities:
- Burning fossil fuels (coal, oil, natural gas) for energy, transport and industry
- Deforestation — fewer trees to absorb CO₂ by photosynthesis
- Cement manufacture — involves heating limestone (CaCO₃ → CaO + CO₂)
Why Methane Levels Are Increasing
- Livestock farming — cattle produce methane during digestion
- Rice paddies — waterlogged fields provide conditions for methane-producing bacteria
- Landfill sites — decomposing waste produces methane
- Extraction of fossil fuels — methane leaks during drilling and transport
Climate Change
Climate change refers to long-term changes in global weather patterns, including rising average temperatures (often called global warming).
Evidence for Climate Change
- Temperature records — global average temperature has risen by about 1.1°C since 1850
- Ice core data — air bubbles trapped in Antarctic ice cores show CO₂ levels and temperature going back 800,000 years; they correlate closely
- Sea level data — rising due to thermal expansion and melting ice
- Glacier retreat — glaciers worldwide are shrinking
- Changes in wildlife — species migrating to different areas, earlier flowering
Potential Effects of Climate Change
- Sea level rise — due to thermal expansion of water and melting of ice caps/glaciers, threatening coastal areas
- More extreme weather — more frequent and severe floods, droughts, storms and heatwaves
- Changes to ecosystems — species unable to adapt may face extinction; coral bleaching
- Food security — changes in rainfall and temperature affect crop yields
- Water shortages — altered rainfall patterns, glacier loss
- Climate migration — people forced to move from affected areas
Reducing Our Carbon Footprint
The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
Ways to Reduce It
- Use renewable energy (solar, wind, tidal) instead of fossil fuels
- Improve energy efficiency (insulation, LED lighting, efficient appliances)
- Reduce, reuse, recycle — less manufacturing, less waste, less incineration
- Plant trees (reforestation/afforestation) — they absorb CO₂
- Use public transport, walk or cycle instead of driving
- Carbon capture and storage (CCS) — capturing CO₂ from power stations and storing it underground
- Eat less meat — reduces methane from livestock
Challenges
- International agreements are difficult to achieve — countries have different priorities
- Some solutions are expensive or require new infrastructure
- Economic growth vs environmental protection is a constant tension
- Individual action alone is insufficient without government and industry change
- Some people question the scientific consensus, though the overwhelming majority of climate scientists agree that human activities are causing climate change
The Peer Review Process
Climate change science is published through peer review — other scientists check the methods, data and conclusions before publication. This process helps ensure that published findings are reliable and reduces the chance of errors or bias. However, peer review is not perfect, and scientific understanding continues to develop.
Exam Tips
- Know the three main greenhouse gases: CO₂, CH₄ and water vapour
- Be able to explain the greenhouse effect step by step (incoming radiation → absorbed → re-emitted as IR → absorbed by greenhouse gases → re-emitted back)
- Distinguish between the natural greenhouse effect (beneficial) and the enhanced greenhouse effect (caused by human activity)
- Six-mark questions often ask you to discuss actions to reduce climate change — give specific examples and explain why each helps
- Always link increased greenhouse gases to human activities, not just "pollution"