Beyond GWP: why the other impact categories matter

Reducing the sustainability conversation to carbon is understandable for communication but risky technically. A life cycle assessment produces more than fifteen indicators, and they do not always point the same way. A decision taken on GWP alone can make things worse in another dimension.

Acidification

Sulphur dioxide, nitrogen oxides and ammonia emissions acidify soil and water. This indicator is high in coal-burning processes and metallurgical operations. Switching from fossil fuel to biomass lowers GWP but, depending on combustion conditions, can raise nitrogen oxide emissions and increase acidification.

Eutrophication

Nitrogen and phosphorus loads entering aquatic ecosystems drive excessive algal growth and oxygen depletion. EN 15804+A2 splits this three ways: freshwater, marine and terrestrial. It is decisive in any product chain with agricultural inputs, and in food, textile and bio-based material studies it discriminates better than GWP.

Ozone depletion and photochemical ozone

The two get confused but operate in opposite layers. Stratospheric ozone depletion is halogenated compounds thinning the protective ozone layer in the upper atmosphere; thanks to the Montreal Protocol it is now a low indicator for most products. Photochemical ozone formation is the creation of harmful ground-level ozone from volatile organic compounds and nitrogen oxides — decisive in processes using paints, adhesives and solvents.

Toxicity and resource depletion

In EN 15804+A2, toxicity indicators and resource depletion are reported as additional indicators and carry high uncertainty. They should not be ignored on that account: in metal plating, electronics and chemical products they reveal differences GWP cannot show.

• Abiotic resource depletion is reported as a separate indicator for minerals and metals
• Fossil resource depletion correlates strongly with GWP but is not identical to it
• Human toxicity and ecotoxicity indicators carry high uncertainty — read them relatively, not absolutely
• The land use indicator is decisive for bio-based materials
• The radioactive waste indicator stands out on grids with a high nuclear share

Catching burden shifting

The real function of multi-indicator assessment is seeing whether solving one problem creates another. A practical method is placing design alternatives side by side across all indicators on a normalised chart. An alternative that improves every indicator is rare; most decisions are trade-offs, and the trade-off should be made knowingly.