The big idea
Count what goes in and out
A life-cycle analysis counts the materials and energy going INTO a product at every stage, and the emissions and waste coming OUT.
Use evidence
It is an inventory, not an opinion — and because it counts, it regularly contradicts what everybody assumed.
Five stages, each with what goes in and what comes out counted separately.
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| Impact category | What it counts | Where it usually comes from |
|---|---|---|
| Global warming potential | Greenhouse gases, converted into kilograms of CO₂ equivalent so different gases can be added together | Energy in extraction and manufacture, and for a powered product the energy used while it is in service |
| Air pollution | Particulates, sulphur and nitrogen oxides, and volatile organic compounds | Smelting, firing, solvent-based finishing, and every transport stage |
| Water pollution | Chemicals and heat discharged into rivers and groundwater | Plating baths, dyeing, paper and textile processing, and mine drainage |
| Soil pollution | Contamination from spills, landfill leachate and mine tailings | Disposal, and the extraction stage that most consumers never see |
| Ecotoxicity | Harm to living things — not just to people | Heavy metals, persistent chemicals, and microplastics released in use and at disposal |
| Resource depletion | How much of a finite material is used up for good | Rare metals in electronics, and any material that is downcycled rather than recycled |
CO₂ equivalent is why totals can be added
Use a common measure
Methane traps far more heat than carbon dioxide, so a life-cycle analysis converts every gas into the mass of CO₂ that would do the same damage.
Add comparable figures
That is what lets a single number be quoted for a whole product, and it is why the unit is kg CO₂e rather than kg CO₂.
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| The assumption | What counting shows | Why |
|---|---|---|
| A cotton bag is better than a plastic one | The break-even point depends on the study and the number of reuses | Compare farming, processing and washing with plastic production for the same number of shopping trips |
| Recycling solves the problem | It helps, but does not remove impacts from the other life-cycle stages | Recycling can reduce demand for virgin material; its own collection and processing still need energy |
| Transport is the big impact | Its importance depends on mass, distance, transport mode and packing | A container ship moves a tonne a very long way for very little fuel; a lorry moving air in bulky packaging is a different matter |
| A biodegradable material is better | Only if it reaches the conditions it needs | Some materials require industrial composting. Decomposition depends on temperature, moisture, oxygen and the material |
| A longer-lasting product costs more impact | It can reduce the production impact per year of service | With unchanged production impacts, doubling useful life halves those impacts per year; maintenance and use still need to be counted |
An LCA is only as honest as its boundary: Where the analysis starts and stops decides the answer. Leave out the extraction stage and a recycled product looks free; leave out the use stage and an inefficient appliance looks harmless.
So the first question about any LCA is what was counted, and the second is who paid for it.
Why an LCA takes time and money
Collect the inventory
For a repairable lamp, request material, energy and transport data from each supplier. Missing or incompatible records take time to check.
Analyse the impacts
A specialist must select appropriate data and assumptions. A small company may need to buy software or outside expertise.
Check the conclusion
Test different lifetimes and energy supplies. The comparison is only useful if both lamp designs provide the same lighting service.
How this is tested — explaining and discussing life-cycle analysis considerations. It comes up two ways:
Paper 1 — multiple choice
- Identify the impact category a described effect belongs to.
- Choose the stage that dominates for a named product.
Paper 2 — analysing a product
- Explain the considerations an LCA measures for a named product.
- Evaluate an LCA result that contradicts a common assumption.
The trap: Treating an LCA as a general argument that something is bad for the environment. It is an inventory, and the marks are for naming the category, the stage and the number.
A supermarket claims its cotton bag always has a lower environmental impact than disposable plastic bags. For 100 shopping trips, an illustrative LCA gives a reusable cotton bag 8 kg CO₂e before use and a disposable plastic bag 0.08 kg CO₂e per bag. Washing is excluded. Evaluate the claim that the cotton bag always has a lower environmental impact.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.