Carbon Dioxide Levels & the Greenhouse Effect (DP IB Chemistry): Revision Note

Carbon Dioxide Levels & the Greenhouse Effect

Carbon dioxide levels 

Carbon dioxide in the atmosphere is rising due to human activities, including:

• Combustion (mainly fossil fuels):

  • Electricity generation (~85% of fossil fuel use)

  • Transportation

• Construction

• Deforestation (clearing land for farming)

• Livestock farming

  • Cattle release methane, another greenhouse gas

• Carbon dioxide and methane both trap heat and contribute to global warming

• The main driver of rising CO₂ levels is the combustion of fossil fuels, which releases carbon stored for millions of years

  • The increased use of fossil fuels has raised atmospheric CO₂

• Monitoring efforts:

  • Stations like Mauna Loa Observatory take quantitative measurements of atmospheric gases

  • Records:

    • CO₂ data: since 1958

    • Methane data: since 1984

Graph of carbon dioxide levels over time

• The amount of carbon dioxide is constantly changing due to seasonal fluctuations in rates of photosynthesis 

  • Photosynthesis removes carbon dioxide from the atmosphere

What are greenhouse gases?

• Greenhouse gases in the atmosphere have a similar effect to the glass in a greenhouse, hence the term greenhouse gas and their effect is known as the greenhouse effect

• The greenhouse effect keeps Earth warm enough to support life:

  • Without it, Earth’s temperature would swing wildly, like on Mars (from 20 °C to –153 °C)

• Main Greenhouse Gases:

  • Carbon dioxide (CO₂) – from respiration and burning fuels

  • Methane (CH₄) – from livestock, landfills, and mining

  • Nitrous oxides (NO_x) – from impurities in fossil fuels

  • Water vapour (H₂O) – from combustion and natural evaporation

• The major focus of greenhouse gases and the greenhouse effect is the action of atmospheric carbon dioxide

  • Sources of atmospheric carbon dioxide include:

    • Combustion of wood and fossil fuels

    • Respiration of plants and animals

    • Thermal decomposition of carbonate rocks

    • The effect of acids on carbonates

What is the greenhouse effect?

• The sun emits shortwave radiation, which reaches the Earth’s surface

• This energy is absorbed and then re-emitted as longwave infrared radiation

• Some infrared radiation escapes to space, but some is absorbed by greenhouse gases in the atmosphere

• These gases re-radiate the energy in all directions, trapping heat and keeping the Earth warm

• This natural process is called the greenhouse effect

Enhanced Greenhouse Effect

• Human activities (like burning fossil fuels) increase greenhouse gas levels

• More heat is trapped, leading to a rise in Earth’s average temperature

• This is called the enhanced greenhouse effect and contributes to global warming

Greenhouse effect diagram