Greenhouse Gases (Cambridge International IGCSE Environmental Management)

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)

Exam Hint Do not confuse the ozone layer with global warming.

Yes, ozone is a greenhouse gas, but the ozone layer protects the Earth from ultraviolet light.

Ozone is different because it absorbs incoming UV light and outgoing infrared light from the Earth.

The hole in the ozone layer increases the rate of skin cancer by allowing more UV rays to enter the atmosphere. It has no effect on incoming solar energy.

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

Exam Hint Make sure you clearly state what the causes of increased greenhouse gases are. It is not enough to say agriculture; instead, you should say rice growing releases methane.