Key Idea: An LCA counts the materials and energy going IN at every stage and the emissions and waste coming OUT. It is an inventory, not an opinion.\n\nFive stages: raw material, manufacture, distribution, use, disposal — and transport sits between all of them.\n\nGreenhouse gases are converted into kilograms of CO₂ equivalent, which is the only reason totals from different gases can be added at all.\n\nBecause it counts, it regularly contradicts what everybody assumed — the cotton bag, the hand dryer, the electric car.\n\nAn LCA is only as honest as its boundary: change what is counted and you change the answer, which is how the same product is 'proved' both ways.
Paper 1 — multiple choice
- Name the five life-cycle stages in order
- Identify which stage dominates for a given product
- Say what CO₂ equivalent allows
- Recognise a boundary that has been drawn to flatter
Paper 2 — analysing a product
- Identify the dominant stage for a named product and justify it
- Compare two alternatives across the whole life cycle
- Explain why an intuitive answer is wrong once it is counted
- Evaluate an LCA whose boundary excludes something important
Carried into the design project
- Criterion E — an environmental claim needs a stage, not an adjective
- State your boundary before you compare anything
- Say how many uses your reusable product needs to break even
Most LCA questions come down to one judgement: which stage carries most of the impact. Get that right and the rest of the answer follows, because the design response is always aimed at the dominant stage.
| Stage | What is counted | Dominates for |
|---|---|---|
| Raw material | Extraction, refining, processing, and the land and water used | Metals, concrete, and anything with a small amount of a rare element |
| Manufacture | Process energy, scrap, solvents, water and factory emissions | Electronics, especially silicon — a chip's manufacture dwarfs its own lifetime energy |
| Distribution | Packaging, transport mode and distance, and refrigeration in transit | Bottled water, fresh food flown in, and almost nothing else |
| Use | Energy and consumables while the product does its job, and maintenance | Anything powered and long-lived: a fridge, a car, a boiler, a washing machine |
| Disposal | Landfill, incineration, recycling energy, and what escapes into soil and water | Products with hazardous content, and anything that cannot be separated |
Five stages, each with what goes in and what comes out counted separately.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Important: Naming recycling as the answer to a product whose impact is 90% in use — recycling a fridge changes almost nothing about the fridge.\n\nComparing two products without a shared functional unit: one bag against one bag is meaningless if one is used 200 times.\n\nIgnoring the boundary. An LCA that stops at the factory gate can prove anything.\n\nCalling a material 'green' rather than naming a stage and an impact.
| The assumption | What counting shows | Why |
|---|---|---|
| A cotton bag beats a plastic one | Only after roughly a hundred or more uses | Growing and processing cotton is water- and energy-intensive; a thin polyethylene bag costs very little to make |
| A paper cup beats a plastic one | Barely, and sometimes not at all | Paper cups are lined with plastic, are heavier to transport, and are rarely recyclable because of the lining |
| Replacing an old car with an electric one is always better | Not immediately | The new battery's manufacture is a large upfront debt that only pays back over years of driving |
| Local always beats imported | Not if the local version is heated or refrigerated | A heated greenhouse can use more energy than a ship crossing an ocean |
| Recycling solves the problem | It helps least where the impact is largest | For a powered product the use stage dominates, and recycling touches only the material |
Raw material, manufacture, distribution, use, disposal — in that order.\n\nCO₂ equivalent is what makes different gases addable.\n\nPowered and long-lived → the use stage dominates.\n\nElectronics → manufacture dominates, not use.\n\nA functional unit and a boundary come before any comparison.
A school replaces paper hand towels with electric hand dryers. Analyse the change using a life-cycle analysis.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A manufacturer publishes an LCA showing its new laptop is 40% lower impact than the previous model, counting from component delivery to the factory gate. Evaluate this claim.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Explain why designers of a domestic refrigerator concentrate almost entirely on the use stage.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Name the five life-cycle stages in order.
Why is everything converted into CO₂ equivalent?
Which stage dominates, and for what?
What is a functional unit and why must it come first?
How does a boundary change an LCA's answer?
Why does counting so often contradict intuition?
Exam tips
- State the functional unit before you compare anything.
- Name the dominant stage, then aim every design response at it.
- Say cradle to grave and check the boundary in any published claim.
- Use CO₂ equivalent when you add impacts from different gases.
- For a reusable product, give the number of uses needed to break even.
- Never write 'eco-friendly' — name a stage and an impact instead.