Comparing products using simple LCAs

A life cycle assessment (LCA) compares products by considering their environmental impacts from obtaining raw materials through to disposal. A simple comparative LCA weighs the evidence from every stage rather than deciding which product is better from a single feature.

Comparing plastic and paper shopping bags

To compare the bags fairly, consider the same stages for each and how many bags are needed to carry the same amount of shopping.

• Raw materials: Consider the resources needed to make each material, such as fossil resources for many plastic bags and wood for paper bags. Obtaining these resources can have environmental impacts.
• Manufacture: Compare the energy, water and other resources used to turn the raw materials into bags, as well as any pollution produced.
• Transport: Consider the impacts of moving materials and finished bags. The weight of the bags and the distances travelled can affect the fuel needed.
• Use: Consider how many times each bag is used. Reusing a bag means fewer new bags may be needed for the same amount of shopping.
• Disposal or recycling: Consider what happens when each bag is thrown away or recycled. The impacts depend on the disposal or recycling facilities available and on what actually happens to the bag.

Weighing the LCA evidence

A bag may have a lower impact at one stage but a higher impact at another. For example, a bag that uses more resources to manufacture may be reused more often, reducing the number of bags needed. The manufacturing stage alone would not show the full comparison.

Some impacts, such as energy use, are easier to measure than others, such as effects on habitats. A balanced conclusion therefore uses the available evidence across all stages and recognises any gaps or uncertainties. It should not assume that plastic or paper is always the better material.

Life cycle assessment

A life cycle assessment (LCA) judges the environmental impact of a product across its whole life, rather than looking at just one stage. It considers the resources and energy used and the environmental effects produced as the product is made, used and disposed of.

Stages of a life cycle assessment

An LCA follows the product through its life:

1. Raw materials: extracting the materials and processing them into forms that can be used.
2. Manufacture and packaging: making the product and its packaging.
3. Use: using the product throughout its working life.
4. Disposal: dealing with the product when it reaches the end of its useful life.

Transport and distribution must also be considered at each stage. Moving raw materials, components, products and waste uses energy and can create emissions.

Why the whole life cycle matters

Looking at only one stage can give a misleading picture. For example, a product may appear environmentally friendly during use but cause large impacts when it is manufactured or disposed of. An LCA brings these stages together so that the judgement reflects the product’s whole life, not just the part that looks most favourable.

Limitations of life cycle assessments

A life cycle assessment (LCA) considers the environmental impacts of a product across stages of its life. It can provide evidence for comparing products, but it cannot always produce a completely objective answer about which product is greener.

Measured quantities and judgement

Some parts of an LCA can be measured relatively easily. These include the amounts of water, raw materials and energy used, and the amounts of some wastes produced. Measurements provide evidence, but they do not by themselves show how serious every environmental impact is.

For example, different pollutants may cause different kinds of environmental harm. These effects are not always directly comparable, so deciding how much weight to give each one involves judgement. Two assessors using the same measurements could reach different conclusions if they make different assumptions or value the impacts differently.

Selective life cycle assessments

An LCA may also leave out important stages of a product’s life or exclude certain impacts. If the omitted information would change the comparison, the assessment can give a misleading impression.

A selective or abbreviated LCA can therefore be used to support a conclusion chosen in advance. For example, an advertisement might claim that one product is greener than another while relying on an assessment that excludes impacts unfavourable to that product.

LCAs can inform decisions, but their conclusions depend on what is included and on how the impacts are judged.