Greenhouse Gases (Cambridge (CIE) IGCSE Environmental Management): Revision Note

What are greenhouse gases?

• A greenhouse gas (GHG) is a gas that absorbs radiation and emits the energy as thermal (heat) energy

  • GHGs trap heat in the atmosphere and regulate Earth's climate through the natural process of the greenhouse effect

• The main greenhouse gases are

  • carbon dioxide (CO₂)

  • methane (CH₄)

  • water vapor (H₂O)

• Other greenhouse gases include:

  • nitrous oxide (N₂O)

  • chlorofluorocarbons (CFCs)

• Carbon dioxide (CO₂) is a colourless, odourless gas that's a natural part of the atmosphere

  • It accounts for 20% of the greenhouse effect

    • Levels have risen from 315 parts per million (ppm) in 1950 to over 421 ppm in 2022

    • 2050 levels are expected to be 550 ppm 

• Methane is a colourless, flammable gas that's a main part of natural gas

  • It accounts for 17% of the natural greenhouse effect 

  • Methane is 28 times stronger than CO₂ at warming the Earth

• Water vapor is the most common greenhouse gas 

  • It accounts for about 95% of GHGs by volume

  • Water vapor is responsible for 50% of the natural greenhouse effect

• Nitrous oxide (N₂O) is also known as laughing gas

  • It is a long-lived GHG that is almost 300 times stronger than CO₂ at warming the Earth

  • It remains in the atmosphere for around 121 years

  • Naturally present in the atmosphere as part of Earth's nitrogen cycle

• Chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs) account for 1.5% of GHGs in the atmosphere

  • HFCs are weak ozone-depleting substances but they are strong greenhouse gases

  • These are man-made chemicals that are

    • 10,000 times stronger than CO₂ at trapping heat

    • Increasing at a rate of 6% per year

    • Banned by many countries as they deplete the ozone layer (1 CFC atom can destroy thousands of ozone molecules)

Causes of increased greenhouse gases

• Human activity is increasing the amount of key greenhouse gases (GHGs) in the atmosphere

  • Carbon dioxide (CO₂) levels in the atmosphere have increased by more than 100 parts per million (ppm) to 422 ppm in 2023

  • Methane, nitrous oxide and fluorocarbons (HFCs and CFCs) are also increasing

• Water vapour levels are affected by human activities indirectly, through:

  • Deforestation, land-use changes, and burning fossil fuels

Fossil fuels 

• Fossil fuels account for almost 50% of global greenhouse gas emissions

• Fossil fuels are used in a number of ways, including industry, transportation, farming and energy production

• Population increase and development increases energy usage, releasing CO₂ into the atmosphere 

Farming

• The use of fertilisers and pesticides releases nitrogen and CO₂

• Dairy and beef cattle farming, as well as rice cultivation, increase methane emissions

• Artificial fertilisers release nitrogen oxide into the atmosphere

• Deforestation to clear land for grazing and crops leads to less CO_₂. being absorbed during photosynthesis

• Deforestation releases CO₂ stored in the wood

• Changes in land use such as wetland drainage, release methane

Industry 

• As well as using fossil fuels, construction, heating, manufacturing, etc. all release greenhouse gases, including methane and N₂O

• Cement manufacture: calcium carbonate (limestone) is heated to produce calcium oxide (lime) and releases CO₂

Transport

• The increase in population has led to more cars, buses, trucks, and planes

• Transport uses petrol or diesel, which comes from oil, which is a fossil fuel, and releases CO_₂.

• Electric vehicles have to be charged using electricity produced by power stations, which release CO_₂.

Energy production

• Electricity and heat are generated by burning fossil fuels

• Making them the largest contributors to GHG emissions

Chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs)

• These are emitted from:

  • Refrigerators and air conditioners

  • Aerosol cans for products like hairsprays and deodorants

  • Insulating foam products