Life Cycle Assessment, Explained

Life cycle assessment has a reputation for being either authoritative or arbitrary depending on who is describing it. Both readings come from the same source: the standard fixes how a study is conducted, not what it must conclude.

ISO 14040 sets the principles and framework; ISO 14044 sets the requirements. Understanding the four phases makes clear which parts are method and which are judgement, and therefore where to look when reading somebody else’s numbers.

Phase one decides the answer

Goal and scope definition sounds procedural and is the phase with the greatest influence on the result. It fixes the functional unit, the system boundary, the allocation approach and what is excluded.

The functional unit deserves particular attention because it is the basis of every comparison. Assessing per item, per kilogram, or per year of delivered service produces different rankings between the same two products, and all three can be defensible.

Phase two is where the work is

Inventory analysis compiles the inputs and outputs across the system boundary — energy, materials, emissions, waste. It is the longest phase and the one that determines data quality.

Every inventory mixes primary data measured from actual operations with secondary data from background databases. The ratio is a quality indicator that studies rarely publish and readers rarely ask for, despite it being the single best predictor of how much the result would move under scrutiny.

Replacing a background average with a supplier-specific figure commonly moves a product result by tens of per cent, because averages describe a global production mix rather than the specific supplier you buy from.

Phase three converts flows into impacts

Impact assessment translates inventory flows into environmental categories: climate change, acidification, eutrophication, resource depletion and others. This is where characterisation factors enter, and where method choice shows.

• Category selection. A study reporting only climate change may be hiding a trade-off where the lower-carbon option is worse on water or toxicity.
• Characterisation method. Different methods assign different factors to the same flow, so results are not portable between methods.
• Normalisation and weighting. Optional under ISO 14044 and inherently value-laden, which is why comparative assertions disclosed to the public face additional requirements.

The single-category study is the most common trap in practice. Carbon has become shorthand for environmental performance, and a product optimised for carbon alone can perform worse across categories that were simply not reported.

Phase four is where honesty shows

Interpretation identifies significant issues, evaluates completeness and consistency, and states limitations. It is the phase most often reduced to a summary slide.

A sensitivity analysis belongs here and is the most useful part of any study for a reader. It shows how much the conclusion moves when a contested assumption changes, which is precisely the question a sceptical reader has.

How to read someone else’s study

Four questions expose most of what a summary omits, and all four are answerable from a properly reported study.

What is the functional unit, and would a different one reverse the conclusion. What share of the inventory is primary data. Which impact categories were assessed, and which were assessed and not reported. Was the study critically reviewed, which ISO 14044 requires for comparative assertions disclosed publicly.

A study that cannot answer these is not necessarily wrong. It is unverifiable, which for a claim intended to influence a purchasing decision amounts to the same thing.

Where LCA meets the passport

A passport does not perform an assessment. It records the resulting figure together with the method behind it, so a reader can tell whether two figures are comparable.

That is a more useful role than it sounds. The recurring failure in supply chain carbon data is not that figures are wrong but that incompatible figures are aggregated, and a passport that carries the boundary and functional unit alongside the number is what allows a receiving system to detect the incompatibility rather than silently summing it.