Trying to work out whether a product is really greener? Life cycle assessment explained in short: you add up its resource use and emissions from raw materials to disposal, then convert them into comparable impacts.
This guide sits within the wider topic of sustainable manufacturing, where LCA is one of the main tools for testing environmental claims.
| Item | Value |
|---|---|
| Phases in an LCA (ISO 14040 structure) | Four |
| ISO 14044:2006 date of entry into force | 30 June 2006 |
| Methane factor, 100-year GWP (CO₂ = 1) | 29.8 |
| Nitrous oxide factor (CO₂ = 1) | 273 |
| Example cut-off criterion for minor processes | Less than 1% of mass or energy |
| Example building functional unit | 100 m² of usable floor space for 50 years |
These figures come from the UNI listing for ISO 14044:2006 and a step-by-step LCA guide. Figures can change, so check the source before you rely on them.
What does a life cycle assessment measure?
LCA is a technique for assessing the environmental aspects and potential impacts of a product, process or service across its entire life cycle. According to the Battery Design overview of ISO 14040, that runs from raw material extraction through production, use and end-of-life.
The method is set out in a pair of standards. ISO 14040 gives the principles and framework, and the same overview lists its edition as ISO 14040:2006, confirmed in 2023. ISO 14044 is its companion, covering requirements and guidelines.
The UNI listing says the companion standard covers both LCA studies and life cycle inventory (LCI) studies. It also lists reporting, critical review and the limitations of LCA among its topics.
The point of looking at the whole chain is to avoid moving a problem rather than solving it. A product that looks clean at the factory gate may carry its heaviest impacts in raw materials or in use.
The four phases of an LCA
ISO 14040 defines four phases that structure every LCA, and each builds on the one before. The same overview adds that the framework also gives guidance on reporting and critical review.
- Goal and scope definition: what you are measuring, why, and for whom.
- Life cycle inventory (LCI): data on the inputs and outputs of every process.
- Life cycle impact assessment (LCIA): conversion of inventory data into environmental impacts.
- Interpretation: analysis of the results, checks on reliability and conclusions.
The phases are not strictly sequential. ISO 14040 recognises iterative loops between them, so a finding in interpretation can send you back to refine the scope, and data gaps can force boundary changes.
Goal, scope and the functional unit
The goal states the intended application, the reasons for the study and the target audience. The scope then fixes the functional unit, the reference to which all inputs and outputs are normalised. It lets you compare the function a product delivers rather than the object itself.
The decerna guide and the Battery Design overview give these examples:
- Packaging: containing 1 litre of beverage for 30 days.
- Transport: moving one person 10 kilometres.
- Buildings: providing 100 m² of usable floor space for 50 years.
- Batteries: 1 kWh of storage capacity delivered over the battery lifetime.
Next come system boundaries. Cradle-to-grave covers extraction through disposal, while cradle-to-gate stops at the factory gate. If you cut off minor processes, the guide says to state the criterion clearly, for example processes contributing less than 1% of mass or energy.
Data requirements matter too. Primary data comes from direct measurement and secondary data comes from databases. Representativeness counts as well: data from ten years ago might not represent current conditions.
From inventory data to impact categories
The inventory phase is usually the heaviest. The guide notes that it typically consumes most project time and resources, because you need quantities of materials, energy, transport and waste for every process. For background processes, practitioners draw on LCA databases such as ecoinvent for global coverage, GaBi for industrial processes, ELCD for European data and USLCI for United States data.
When one process yields several products, you need allocation rules. A refinery, for example, produces petrol, diesel and heating oil. The decerna guide describes this hierarchy, drawn from ISO 14044:
- Avoid allocation through subdivision or system expansion where possible.
- If it is unavoidable, allocate on physical relationships such as mass or energy content.
- Use economic allocation when physical relationships do not apply.
Impact assessment then makes raw emissions meaningful. Classification assigns inventory flows to impact categories, and characterisation quantifies each contribution. Different greenhouse gases are converted to CO₂ equivalents based on warming potential: CO₂ gets a factor of 1, methane 29.8 on a 100-year basis, and nitrous oxide 273.
Typical impact categories include:
- Climate change
- Ozone depletion
- Acidification
- Eutrophication
- Photochemical ozone formation
- Resource depletion
- Water scarcity
- Toxicity (human and ecological)
The choice of characterisation method also shapes the numbers. The guide lists ReCiPe for comprehensive global coverage, CML for established methodology, TRACI for North American focus and Environmental Footprint for EU alignment.
Because inventory data records the solvents, energy and waste behind a product, it pairs naturally with the green chemistry principles when you are redesigning a chemical process.
How are LCA results interpreted?
Interpretation analyses results and checks their reliability. Hotspot analysis shows where impacts concentrate, which tells you where improvement effort will pay off. Raw material extraction might dominate climate change while manufacturing dominates water use.
Once the hotspots are clear, they can feed into industrial decarbonization strategies that target the stages where emissions concentrate.
Robust conclusions survive sensitivity analysis, which tests how methodological choices affect results. Change the allocation rules or the impact method and see what happens. Primary measured data also carries less uncertainty than estimated values.
Two optional steps involve value judgements. Normalisation compares your results to reference values, and weighting combines categories into a single score. ISO standards allow but do not require them, and the guide advises clear justification before using weighted scores in publicly disclosed comparisons.
Frequently asked questions
What is the difference between cradle-to-gate and cradle-to-grave?
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Cradle-to-grave covers the whole chain from extraction through disposal. Cradle-to-gate stops at the factory gate, so it leaves out use and end-of-life. Your goal decides which one fits.
Is an LCA the same as a carbon footprint?
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Not quite. An LCA reports across several impact categories, and climate change is only one of them. A study that covers only greenhouse gases looks at that single category.
Which standards does an LCA follow?
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ISO 14040 provides the principles and framework, and ISO 14044 provides the requirements and guidelines. Together they cover goal and scope, inventory, impact assessment, interpretation, reporting and critical review.
Can you trust LCA results?
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They are only as good as the data and choices behind them. Check whether the study used measured or database data, how it handled allocation, and whether it ran a sensitivity analysis.
