Fossil fuels overview
Big idea: Fossil fuels currently provide ~80% of global energy but have significant environmental impacts.
The three fossil fuels
- Coal: Solid; formed from plant material in swamps. Highest carbon content, most polluting. Used for electricity generation and steel production.
- Oil (petroleum): Liquid; formed from marine organisms. Versatile — fuels transport, plastics, chemicals. Most traded commodity globally.
- Natural gas: Gaseous; often found with oil. Cleanest fossil fuel (50% less CO₂ than coal). Used for heating, electricity, and industry.
Formation and extraction
- Formed over millions of years from buried organic matter under heat and pressure
- Finite resource: Cannot be replaced on human timescales
- Extraction methods: Conventional drilling, fracking (hydraulic fracturing), open-pit mining, mountaintop removal
- Energy return on investment (EROI): Declining as easy reserves are depleted
Fossil fuels are essentially stored solar energy from ancient photosynthesis. We are releasing millions of years of stored carbon in just a few centuries.
Exam tip: Be able to compare the three fossil fuels in terms of carbon content, pollution, uses, and abundance.
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Environmental impacts of fossil fuels
Big idea: Fossil fuel use causes environmental damage at every stage — from extraction through combustion — with climate change being the most significant global impact.
Extraction impacts
- Habitat destruction: Mining, drilling sites, pipelines
- Water pollution: Oil spills, fracking fluid contamination, acid mine drainage
- Land degradation: Subsidence, tailings, landscape scarring
- Methane leakage: Natural gas escapes during extraction (potent GHG)
Combustion impacts
- Greenhouse gas emissions: CO₂ is the primary driver of climate change
- Air pollution: SO₂ (acid rain), NOₓ (smog), particulates (respiratory disease)
- Mercury and heavy metals: Coal combustion releases toxic metals
- Thermal pollution: Power plant cooling water affects aquatic ecosystems
Comparing fossil fuels
Coal (most polluting)
- Highest CO₂ per unit energy
- Most SO₂, particulates, mercury
- Mining causes severe land damage
- Cheapest and most abundant
Natural gas (cleanest fossil fuel)
- ~50% less CO₂ than coal
- Minimal SO₂ and particulates
- Fracking has water contamination risks
- Methane leakage reduces climate benefit
Exam tip: Questions often ask you to compare energy sources. Use a consistent set of criteria: GHG emissions, air pollution, water use, land use, reliability, cost.
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IB-style question — Non-renewable energy sources [1]
Figure 1 shows the energy mix of the island nation of Marava: coal 41%, oil 28%, natural gas 19%, hydro 9%, solar 3%. Identify the non-renewable fuel that supplies the largest share of Marava's energy. [1]
How to answer it, step by step
- Read the command term
• "Identify" = one word/value straight off the figure
• No explanation needed for 1 mark - Pick the biggest fossil fuel
• Non-renewables here: coal, oil, gas
• Coal at 41% is the largest share
Final answer
Examiner tip: state only the fuel name (coal) — adding extra detail wastes time on a 1-mark identify.