Life cycle assessment (LCA)
A life cycle assessment is a structured way to evaluate the environmental impact of a product across its entire life — "cradle to grave" — to help compare alternatives or improve design.
The four stages of an LCA
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Extracting and processing raw materials
- Energy used to mine, extract, transport raw materials.
- Pollution generated (mining waste, ore tailings, refining emissions).
- Use of finite resources.
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Manufacturing and packaging
- Energy and water used in production.
- Wastes (chemical, solid).
- Materials used for packaging.
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Using the product
- Energy used during operation (e.g. electricity for a fridge over 10 years).
- Maintenance materials needed.
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Product disposal
- Disposal route: landfill, incineration, recycling.
- Final emissions and impacts.
Some LCAs also include transport between each stage.
What is measured?
- Raw materials used (kg of metal, oil, water).
- Energy used (kWh or kJ).
- Greenhouse gas emissions (kg CO₂-equivalent).
- Other waste/pollution (e.g. SO₂, particulates).
- Final disposal options (recyclable? biodegradable?).
Comparing two products: paper vs plastic bag
- Paper: from renewable forests; biodegradable; but high energy use in pulping; heavy → more transport CO₂; only 3–4 reuses.
- Plastic: from finite oil; non-biodegradable; lightweight; reusable many times; recyclable.
The "winner" depends on which factors you prioritise — LCAs are valuable but subjective.
Limitations of LCA
- Some factors are hard to quantify (e.g. effects on biodiversity).
- Numerical values for "use" stage depend on user behaviour (a bulb only matters if you turn it on!).
- LCAs can be biased to make a product look better — "greenwashing".
- Difficult to compare products with very different functions.
✦Worked example— Worked example — light bulb LCA
LED vs incandescent:
- Raw materials: more rare earth metals for LED.
- Manufacture: LED more energy-intensive.
- Use: LED uses ~10% of incandescent's electricity for same brightness.
- Disposal: LED contains some difficult-to-recycle materials.
Net: over the lifetime, LEDs use far less energy → much lower CO₂ footprint.
⚠Common mistakes
- Forgetting one stage — a complete LCA covers raw materials, manufacture, use, disposal.
- Saying LCAs give one "right" answer — they involve judgement.
- Confusing LCA with carbon footprint — carbon footprint is one component of an LCA.
- Ignoring use phase — for many products it dominates.
Links
Builds on C9.4 (carbon footprint). Connects to C10.6 (recycling) and C10.1 (sustainability).
AI-generated · claude-opus-4-7 · v3-deep-chemistry