Edexcel iGCSE Biology-5.13-5.15 Greenhouse Gases- Study Notes- New Syllabus
Edexcel iGCSE Biology-5.13-5.15 Greenhouse Gases- Study Notes- New syllabus
Edexcel iGCSE Biology-5.13-5.15 Greenhouse Gases- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
5.13 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases
5.14 understand how human activities contribute to greenhouse gases
5.15 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences
Greenhouse Gases
🔹 Introduction
The Earth’s atmosphere acts like a blanket, keeping the planet warm enough for life.
Certain gases trap heat → called greenhouse gases (GHGs).
Without them, Earth would be too cold; but excess GHGs cause global warming.
📌 Main Greenhouse Gases
- Water Vapour (H₂O)
• Most abundant natural greenhouse gas.
• Produced by evaporation of oceans, lakes, rivers.
• Traps heat effectively, but its level depends on temperature (positive feedback). - Carbon Dioxide (CO₂)
• Produced by respiration, combustion of fossil fuels, deforestation.
• Main human-caused greenhouse gas.
• Rising CO₂ = major driver of climate change. - Nitrous Oxide (N₂O)
• Released from fertilisers, burning fossil fuels, industrial processes.
• Very powerful greenhouse gas → about 300× stronger than CO₂ at trapping heat. - Methane (CH₄)
• Produced by decomposition in swamps & rice fields, cattle digestion (cow burps), landfills, and natural gas leaks.
• Stronger than CO₂ in trapping heat but present in smaller amounts. - Chlorofluorocarbons (CFCs)
• Man-made chemicals once used in refrigerators, air conditioners, aerosol sprays.
• Powerful greenhouse gases + also damage the ozone layer.
• Controlled under the Montreal Protocol.
📊 Summary Table
| Greenhouse Gas | Source(s) | Special Note |
|---|---|---|
| Water vapour | Evaporation, transpiration | Natural, most abundant |
| Carbon dioxide | Respiration, burning fossil fuels, deforestation | Main human-caused GHG |
| Nitrous oxide | Fertilisers, burning fuels, industries | 300× stronger than CO₂ |
| Methane | Cattle digestion, rice fields, landfills, gas leaks | Strong but less abundant |
| CFCs | Refrigerants, aerosols (man-made) | GHG + ozone destroyer |
📝 Quick Recap
Main greenhouse gases: H₂O, CO₂, N₂O, CH₄, CFCs.
Trap heat in atmosphere → keep Earth warm.
Excess GHGs → global warming & climate change.
Understand How Human Activities Contribute to Greenhouse Gases
🌱 Introduction
Greenhouse gases (GHGs) are gases in the atmosphere that trap heat and keep the Earth warm – a natural process called the greenhouse effect.
However, human activities have greatly increased their concentration, leading to global warming and climate change.
☁️ Major Greenhouse Gases Affected by Humans
| Greenhouse Gas | Formula | Natural Source | Human-Related Source | Effect |
|---|---|---|---|---|
| Carbon dioxide | CO₂ | Respiration, volcanic activity | Burning fossil fuels, deforestation | Major contributor to global warming |
| Methane | CH₄ | Decay in wetlands | Cattle farming, rice cultivation, landfills | Very strong heat-trapping gas |
| Nitrous oxide | N₂O | Soil bacteria | Fertiliser use, vehicle exhausts | Potent greenhouse gas |
| CFCs | – | None (man-made) | Aerosols, refrigerators, air conditioners | Trap heat + destroy ozone layer |
| Water vapour | H₂O | Evaporation, transpiration | Indirect (increased by global warming) | Amplifies warming (positive feedback) |
🔥 Human Activities Increasing Greenhouse Gases
1. Burning of Fossil Fuels (Coal, Oil, Gas)
- Used in electricity generation, transport, and industry.
- Releases large amounts of CO₂.
- Example: Power stations, vehicles, factories.
- Trick: “Fuel Burn → CO₂ Return”
2. Deforestation
- Trees absorb CO₂ by photosynthesis.
- Cutting and burning trees → reduces CO₂ absorption + adds more CO₂.
- Example: Major issue in tropical rainforests.
- More trees gone = More CO₂ on!
3. Agriculture
- Cattle farming: Methane released during digestion (cow burps & manure).
- Rice fields: Anaerobic bacteria in flooded soils release methane.
- Fertiliser use: Adds nitrous oxide to the air.
- Remember: Cows + Crops → CH₄ + N₂O
4. Waste Management & Landfills
- Organic waste decomposes anaerobically, releasing methane (CH₄).
- Poorly managed landfills are major sources.
- Waste rots → Methane spots!
5. Industrial & Chemical Processes
- Some industries release CO₂ and N₂O (e.g., cement, nylon production).
- Factories and refineries add more GHGs to the atmosphere.
- Industry = Invisible gas factory.
6. Use of CFCs (Chlorofluorocarbons)
- Found in old aerosols, refrigerators, and air conditioners.
- CFCs act as greenhouse gases and also damage the ozone layer.
- Coolers that heat the planet!
7. Urbanisation & Energy Use
- Expanding cities → more vehicles, more electricity → higher CO₂ emissions.
- Increased energy demand worsens the greenhouse effect.
- More cities → More smoke.
🌡️ Summary: How Humans Add Greenhouse Gases
| Human Activity | Gas Produced | How It Adds to Greenhouse Effect |
|---|---|---|
| Burning fossil fuels | CO₂ | Increases atmospheric CO₂ |
| Deforestation | CO₂ | Reduces CO₂ absorption by plants |
| Cattle & rice farming | CH₄ | Adds methane (very strong GHG) |
| Fertilisers | N₂O | Releases nitrous oxide |
| Landfills | CH₄ | Anaerobic decay emits methane |
| CFC use | CFCs | Man-made GHG + ozone damage |
⚠️ Environmental Impact
- Rising global temperatures
- Melting of glaciers & rising sea levels
- Extreme weather events (heatwaves, floods, droughts)
- Disruption of ecosystems & species extinction
🧾 Quick Recap
Human activities increasing GHGs:
→ Burning fuels, deforestation, farming, fertilisers, landfills, industries, CFCs
Main gases involved:
→ CO₂, CH₄, N₂O, CFCs, H₂O
Result:
→ More heat trapped → Stronger greenhouse effect → Global warming + Climate change
🧠 Mnemonic: “Cars, Forests, Farms, Factories – All Feed the Fire!”
Understand How an Increase in Greenhouse Gases Results in an Enhanced Greenhouse Effect and Its Consequences
🌱 Introduction
The greenhouse effect is a natural process that keeps Earth warm enough to support life.
But when human activities increase the amount of greenhouse gases (GHGs), this effect becomes stronger – leading to an enhanced greenhouse effect.
→ Result: Global warming and major climate changes.
☁️ Natural Greenhouse Effect (Normal Situation)
- Sunlight (short-wave radiation) reaches the Earth.
- Some energy is reflected back into space by clouds, ice, and surfaces.
- Most of it is absorbed by Earth’s surface, warming it.
- Earth’s surface then re-emits heat as infrared (long-wave) radiation.
- Greenhouse gases in the atmosphere absorb some of this outgoing heat, trapping it and keeping the planet warm.
This is essential – without it, Earth would be too cold for life.
🔥 Enhanced Greenhouse Effect (Due to Human Activities)
When human activities add excess greenhouse gases (CO₂, CH₄, N₂O, CFCs, H₂O vapour):
1. More heat is trapped in the atmosphere.
2. Less energy escapes into space.
3. Earth’s average temperature rises → known as global warming.
This is not natural warming – it is accelerated by human actions.
🌫️ Key Greenhouse Gases & Their Effects
| Gas | Main Source | Relative Heating Power | Notes |
|---|---|---|---|
| Carbon dioxide (CO₂) | Burning fuels, deforestation | Moderate | Most abundant human-added GHG |
| Methane (CH₄) | Cattle, landfills, rice fields | Very high (25x CO₂) | Produced by anaerobic decay |
| Nitrous oxide (N₂O) | Fertilisers, exhausts | 300x CO₂ | Long-lasting |
| CFCs | Aerosols, refrigerants | Extremely high | Also destroy ozone |
| Water vapour (H₂O) | Evaporation | Variable | Amplifies other GHGs |
🌡️ Consequences of the Enhanced Greenhouse Effect
- Global Warming – Overall increase in Earth’s average temperature. Disturbs climate balance.
- Melting of Ice Caps & Glaciers – Polar ice melts → sea levels rise. Coastal flooding and habitat loss (e.g., polar bears, penguins).
- Rising Sea Levels – Due to both melting ice and thermal expansion of seawater. Threatens low-lying areas like Bangladesh and the Maldives.
- Extreme Weather Events – More frequent heatwaves, droughts, hurricanes, and floods. Weather patterns become unpredictable.
- Changes in Rainfall Patterns – Some areas become drier, others wetter. Affects agriculture and water availability.
- Loss of Biodiversity – Species unable to adapt or migrate die out. Coral reefs and sensitive ecosystems are worst affected.
- Effects on Humans – Food shortages due to crop failures. Health risks (heat strokes, spread of tropical diseases). Migration and economic instability in vulnerable countries.
🧠 Mnemonic to Remember Consequences
| Letter | Meaning |
|---|---|
| G | Glaciers melt |
| R | Rising sea level |
| E | Extreme weather |
| E | Ecosystem loss |
| N | New disease spread |
| H | Heatwaves increase |
| O | Oceans expand |
| T | Temperature rise |
🔄 Summary Table
| Step | Description | Impact |
|---|---|---|
| 1 | Increase in greenhouse gases | From human activities (burning, farming, etc.) |
| 2 | Enhanced greenhouse effect | More heat trapped in atmosphere |
| 3 | Global warming | Rise in Earth’s average temperature |
| 4 | Environmental effects | Melting ice, sea level rise, extreme weather |
| 5 | Biological & social effects | Crop failure, disease, habitat loss |
📘 Quick Recap
Normal greenhouse effect → Keeps Earth warm enough for life
Enhanced greenhouse effect → Too much heat trapped = warming problem
Main gases → CO₂, CH₄, N₂O, CFCs, H₂O
Main causes → Burning fuels, deforestation, farming, industries
Consequences → Melting ice, floods, extreme weather, biodiversity loss, human health issues
🧩 Trick: “More Gas → More Heat → More Problems”