P6 Global Challenges
Global energy use and demand
World energy demand is increasing due to:
- Population growth
- Increasing industrialisation in developing countries
- Greater use of electrical devices
The vast majority (~85%) of world energy comes from non-renewable fossil fuels (coal, oil, gas).
The greenhouse effect and climate change
The greenhouse effect is a natural and essential process:
- The Sun emits short-wavelength radiation (UV and visible) that passes through the atmosphere.
- Earth absorbs this and re-emits longer-wavelength infrared (IR) radiation.
- Greenhouse gases (CO₂, methane, water vapour, N₂O) absorb this IR and re-radiate it in all directions, including back to Earth — warming the surface.
Enhanced greenhouse effect: burning fossil fuels increases atmospheric CO₂ (and other greenhouse gases), trapping more IR → global temperature rise.
Evidence for climate change
- Rising global average temperatures
- Melting ice caps and glaciers → rising sea levels
- More extreme weather events
- Ocean acidification (CO₂ dissolves in seawater → carbonic acid)
Correlation vs causation: the correlation between rising CO₂ and temperature rise is strong, but scientists note natural variability (volcanic eruptions, solar cycles) also affect climate. The scientific consensus is that human activity is the dominant driver.
Energy from fuels — chemical store to thermal to electrical
Fossil fuel power station chain: Chemical energy (fuel) → thermal energy (combustion) → steam → kinetic energy (turbine) → kinetic energy (generator) → electrical energy.
Overall efficiency of a typical UK coal station ~35–40%; gas ~50–60% (combined cycle).
Biofuels (wood, biodiesel, biogas): considered carbon-neutral in principle — CO₂ released on burning equals CO₂ absorbed during plant growth. However, land use and transport have their own carbon costs.
Nuclear energy — fission vs fossil fuels
| Fossil fuels | Nuclear fission | |
|---|---|---|
| CO₂ emissions | High | Near zero (in operation) |
| Energy density | Low | Extremely high |
| Waste | CO₂ + SO₂ + particulates | Long-lived radioactive waste |
| Risk | Pollution | Radiation risk (meltdown scenarios) |
| Fuel availability | Finite | U-235 also finite, but longer reserves |
| Startup cost | Low-moderate | High |
Nuclear fusion (future technology): deuterium + tritium → helium + neutron + enormous energy. Fuel source (hydrogen isotopes from seawater) effectively unlimited. No long-lived waste. Major engineering challenge: maintaining plasma at >10⁷ K (e.g. JET, ITER projects).
Space physics — OCR Gateway context
Life cycle of a star:
- Nebula → gravitational contraction → protostar → main sequence star (equilibrium: gravity inward = radiation pressure outward)
- Low mass star: red giant → planetary nebula → white dwarf
- High mass star: red supergiant → supernova → neutron star or black hole
Doppler effect and red shift: light from distant galaxies is red-shifted (wavelength increased, frequency decreased), indicating galaxies are moving away. The further the galaxy, the greater the red-shift → universe is expanding. Evidence for the Big Bang.
Cosmic microwave background radiation CMB: thermal radiation left over from the Big Bang (~380,000 years after) — detected from all directions. Strong evidence for the Big Bang model.
Sustainable energy
Sustainable use means meeting present needs without compromising future generations' ability to meet their needs.
Strategies for sustainability:
- Switch from fossil fuels to renewables (wind, solar, tidal, hydro)
- Improve efficiency of energy use (insulation, efficient appliances, LEDs)
- Carbon capture and storage (CCS) — sequestering CO₂ from power stations
- Smart grids — matching supply and demand in real time; energy storage (batteries, pumped hydro)
- International agreements (Paris Accord — limit warming to 1.5–2°C above pre-industrial)
OCR J259 examiner expectations for P6
- 6-mark QWC questions often ask to "evaluate" a claim about energy sources or climate change — must include evidence for AND against.
- Questions link P5 energy calculations to P6 context (e.g. efficiency of a power station).
- Red shift and CMB are assessed on J259/02 Depth paper — expect a graph question on red shift vs distance.
- Distinguish between: the greenhouse effect (natural, necessary) and the enhanced greenhouse effect (human-caused, problematic).
⚠Common mistakes
- Claiming fusion is already used commercially: fusion is not yet commercially viable (as of 2026). ITER aims to demonstrate scientific feasibility.
- Biofuels are always carbon-neutral: only if sustainably grown with minimal transport/processing emissions.
- Greenhouse effect = bad: the natural greenhouse effect is essential for life on Earth — it's the enhancement that is the problem.
- Red shift = Doppler shift: both are correct descriptions — red shift (light) is a consequence of the Doppler effect applied to EM waves.
- CMB evidence: students describe CMB as "proving" the Big Bang — it is strong evidence, not absolute proof.
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