A life cycle assessment (LCA) evaluates the environmental impact of a product from raw material extraction through manufacture and use to disposal. It covers energy use, water use, waste produced, and pollution at every stage. LCAs help scientists and companies compare materials and make more sustainable choices about manufacturing and consumption.
What is a life cycle assessment?
A life cycle assessment (LCA) is a systematic method for evaluating the total environmental impact of a product or material across its entire life — from the extraction of raw materials right through to its final disposal. This is sometimes called a "cradle to grave" analysis.
An LCA considers multiple types of environmental impact, including:
- Energy consumption (and the emissions associated with generating that energy)
- Water use
- Greenhouse gas emissions (CO₂, methane, N₂O)
- Other air, water, and soil pollutants
- Solid waste produced
- Land use
By adding up all these impacts across all stages of a product's life, scientists and policymakers can compare different materials or products on a fair, whole-system basis — rather than just looking at one stage (such as manufacturing) in isolation.
What are the four stages of a life cycle assessment?
Every LCA covers four main stages:
| Stage | What it includes | Examples of impacts |
|---|---|---|
| 1. Raw material extraction and processing | Mining, quarrying, forestry, farming | Energy to extract, habitat destruction, water use, CO₂ from transport |
| 2. Manufacturing and packaging | Making the product, creating packaging | Energy to run factories, emissions, waste materials, water use |
| 3. Use | Energy and materials needed during the product's working life | Electricity to run appliances, water for washing, fuel for cars |
| 4. Disposal | End-of-life treatment | Landfill space, emissions from incineration, energy recovered from recycling |
Some LCAs extend to "cradle to cradle" — considering how materials at Stage 4 might become raw materials for new products (recycling loops).
How is an LCA used to compare materials?
A classic GCSE comparison is plastic carrier bags versus cotton tote bags:
Plastic carrier bag:
- Stage 1: crude oil is extracted and refined (fossil fuel extraction, CO₂ emissions)
- Stage 2: manufacturing uses relatively little energy per bag; packaging is minimal
- Stage 3: used for a short time (often a single trip)
- Stage 4: most go to landfill (non-biodegradable; persist for hundreds of years) or litter
Cotton tote bag:
- Stage 1: growing cotton requires enormous water use (1 kg cotton ≈ 10,000 litres of water) and pesticides/fertilisers
- Stage 2: processing cotton fibres and weaving fabric is energy intensive
- Stage 3: durable and reusable — if used many times, the environmental cost per use falls sharply
- Stage 4: biodegradable in soil; can also be recycled
The result depends critically on how many times the cotton bag is reused. Studies suggest a cotton bag needs to be used at least 50–150 times to have a lower overall carbon footprint than a single-use plastic bag — a fact that surprises many people and illustrates why LCAs must consider all stages.
How is an LCA conducted in practice?
A formal LCA follows four steps:
- Goal and scope: define the purpose of the assessment, the functional unit (e.g. "delivering 1 kg of goods"), and the system boundaries (which stages to include).
- Inventory analysis: collect data on all inputs (energy, materials, water) and outputs (products, by-products, waste, emissions) for each stage.
- Impact assessment: convert the data into measures of environmental impact categories (climate change potential, acidification, eutrophication, etc.).
- Interpretation: draw conclusions, identify the most significant impacts, and make recommendations.
What are the limitations of a life cycle assessment?
LCAs are useful but not perfect:
| Limitation | Detail |
|---|---|
| Subjective choices | Deciding which environmental categories to include and how to weight them against each other is a value judgement |
| Data quality | Real data on energy use, water use, and emissions may be unavailable, estimated, or outdated |
| Manipulation | Companies commissioning LCAs may present data selectively to favour their own products ("greenwashing") |
| Geographic variation | The carbon footprint of electricity varies by country (coal-heavy vs renewable grids), so the same manufacturing process can have very different impacts in different locations |
| Functional assumptions | How many times a cotton bag will actually be used is an assumption, not a measurement |
Because of these limitations, two LCAs of the same product by different organisations can reach different conclusions. It is important to look at who funded the study and what assumptions were made.
Frequently asked questions
What is the difference between a life cycle assessment and the 6Rs?
The 6Rs (Refuse, Reduce, Reuse, Repair, Recycle, Rethink) are practical strategies for reducing environmental impact, while an LCA is an analytical tool for measuring that impact. An LCA might reveal, for example, that recycling a particular material actually costs more energy than making it from scratch — a result that challenges the assumption that recycling is always the best option. The 6Rs provide the action framework; an LCA provides the evidence base for deciding which actions are most effective for a specific product.
Why do LCAs sometimes produce surprising results?
Because an LCA considers all stages rather than just one, the "obvious" environmentally friendly choice is sometimes not what it seems. For example, a glass bottle appears recyclable and natural, but producing it requires very high temperatures (energy intensive), and it is heavy (more fuel to transport). A lightweight PET plastic bottle has a lower production energy and transport footprint, but may end up in landfill. The best choice depends on the local recycling infrastructure and how many times each is reused. LCAs make these trade-offs visible.
How does recycling appear in an LCA?
At Stage 4 (disposal), recycling typically reduces the impacts compared with landfill or incineration because it avoids the need to extract and process virgin raw materials at Stage 1. For example, recycling aluminium uses only about 5% of the energy needed to extract aluminium from bauxite ore. An LCA that accounts for this shows recycling as highly beneficial for aluminium. However, the recycling process itself has energy and water costs that must be included, and not all materials are equally recyclable — the benefit varies widely by material.
What does "functional unit" mean in an LCA?
The functional unit is the standard measure used to compare different products in an LCA on a fair, equivalent basis. For example, when comparing paper cups with reusable ceramic mugs, the functional unit might be "500 hot drinks served". You would then calculate the full LCA for 500 paper cups (made, used once, discarded) versus 1 ceramic mug (made, washed and reused 500 times). Using the functional unit prevents misleading comparisons — for instance, comparing the carbon footprint of making one paper cup with making one ceramic mug would heavily favour paper, ignoring the fact that the ceramic lasts hundreds of uses.
For Socratic GCSE chemistry with Professor Curie — tracing materials from particle-level extraction through to whole-system environmental impact — visit aitutors.me.