Life Cycle Assessment
To judge a product’s true environmental cost, you can’t just look at it in use — you have to follow it from cradle to grave. A life cycle assessment (LCA) works out the environmental impact at every stage of a product’s life.
An LCA follows a product clockwise through four stages — raw materials, manufacture, use and disposal — adding up the environmental impact (and the transport) at each step.
- Raw materials — extracting and processing them uses up finite resources and can damage habitats (mining, deforestation).
- Manufacture & packaging — uses energy, land for factories, and produces waste.
- Use — impact during the product’s lifetime (a car pollutes; a wooden desk barely does).
- Disposal — landfill space, and whether it can be recycled — plus transport at every stage.
- Some things are easy to quantify — the water, energy and resources used, and the waste produced, can be measured.
- Pollutant effects are not. Putting a number on “how bad” a pollutant is requires a value judgement, so two people may score it differently — LCA is not purely objective.
- Beware abbreviated LCAs. Selective LCAs can be misused to reach a pre-decided conclusion — for example in advertising, to make a product look greener than it is.
Run the LCA — plastic vs paper bag
A life cycle assessment follows a product through four stages, adding up the impact at each. Compare the bags stage by stage, then weigh the figures an LCA can actually measure. A company claims the plastic bag has less impact — is it right?
The four stages of the life cycle
Transport adds impact at every stage too.
▼ The figures an LCA can measure (per use)
Show the numbers (Table 1)
| To make one bag | Plastic | Paper |
|---|---|---|
| Raw material | crude oil / gas | wood |
| Energy used (MJ) | 1.5 | 1.7 |
| Solid waste (g) | 14 | 50 |
| CO2 produced (kg) | 0.23 | 0.53 |
| Fresh water (dm3) | 255 | 4520 |
Data values are real AQA-style figures for making one bag. Reusing a bag spreads that one-off impact over more uses, so the bar shows the impact per use = table value ÷ number of uses. Lower is greener. In practice a plastic bag is hard-wearing while a paper bag tears sooner — so durability is part of the comparison too.
🧪 Exam-style questions
Which is not one of the four stages of a life cycle assessment? Tick (✓) one box.
Why is a life cycle assessment not a completely objective process? Tick (✓) one box.
Why should you be cautious about an abbreviated (selective) LCA used in an advert? Tick (✓) one box.
A shopper wants to know whether a paper bag or a plastic bag is the better environmental choice. Use the idea of a life cycle assessment to compare them, and explain why there is no single right answer. A levels-of-response question — compare across the LCA stages and reach a justified judgement. Plan, then compare with the model answer.
Show a model answer
How it is marked (levels of response):
- Level 3 (5–6): compares across the stages and recognises the verdict depends on assumptions/use, with a justified judgement.
- Level 2 (3–4): compares the two bags at one or more stages.
- Level 1 (1–2): one or two simple relevant points.
Indicative content — any of the following are credited.
What the measured data shows (in this kind of LCA the plastic bag is lower on every measured count, supporting the company):
- Energy: the paper bag needs more energy to make (e.g. 1.7 vs 1.5 MJ).
- Solid waste: the paper bag produces far more (e.g. 50 vs 14 g).
- CO2: the paper bag produces more (e.g. 0.53 vs 0.23 kg).
- Fresh water: the paper bag uses dramatically more (e.g. 4520 vs 255 dm3).
What the data leaves out (and why it’s not the whole story):
- The plastic bag is from a finite resource (crude oil/natural gas); the paper bag is from a renewable one (wood).
- The paper bag is biodegradable; the plastic bag is not.
- Some of the paper bag’s CO2 is offset by photosynthesis in the growing wood.
- Judging how bad each pollutant is needs a value judgement, so an LCA is not purely objective.
Allow also: a plastic bag is more durable, so it can be reused, spreading its impact over more uses; transport adds impact at every stage; the figures depend on how many times each bag is used. Do not accept: “plastic is always better” or “paper is always better” with no use of the data or stages.
Conclusion (needed for Level 3) — any justified verdict scores: you could agree (non-renewability matters less than the big savings in water, energy, waste and CO2), disagree (the finite raw material and persistence outweigh them), or say you can’t be certain because the data is incomplete. 6 marks
Reducing the Use of Resources
Metals, glass, building materials, ceramics and most plastics are all made from limited raw materials, using energy from limited resources, and quarrying and mining damage the environment. The way to ease that is the familiar trio: reduce, reuse, recycle.
- Reduce — using less in the first place cuts the use of limited resources, energy and waste.
- Reuse — using a product again as it is. For example, glass bottles can be washed, sterilised and refilled.
- Recycle — processing a used material into something new:
- Metals are melted and recast into new products. Some scrap steel is even added to the iron from a blast furnace, reducing the iron ore needed.
- Glass that can’t be reused is sorted (by colour), crushed and melted to make new glass.
How much separation/sorting is needed depends on the material and the properties required of the final product.
Extracting a metal from its ore (C4) is very energy-intensive (and mining damages the landscape). Recycling a metal — just melting and reshaping it — uses far less energy, saves the finite ore, and cuts waste and landfill. This is why recycling aluminium (expensive to extract by electrolysis) is such a big win.
- Reuse ≠ recycle. Reuse keeps the object as it is (refilling a bottle); recycling breaks it down to make something new (melting glass or metal).
- Recycling isn’t free. Collecting, transporting and sorting materials needs energy and labour, and recycled material may be lower quality — useful points in an evaluate answer.
🧪 Exam-style questions
A glass bottle is washed and refilled. Is this reusing or recycling? Tick (✓) one box.
Give two reasons why metals should be recycled rather than extracted from their ores. Tick (✓) one box.
Give one disadvantage of recycling materials. Tick (✓) one box.
Scrap steel is added to the iron produced in a blast furnace. What does this reduce? Tick (✓) one box.