Methodology of ecoinvent 3

Methodology of ecoinvent 3

Why is the LCIA score of a certain product negative?

In most these cases, the production of materials and services creates a mix of burdens and credits. When a score is positive, like in most cases, the net effect is a damage on the environment.

However, in some cases, a score is negative, indicating that the credits are larger than the burdens. Several elements can explain a negative score.

Negative characterisation factors


Some substances are paired with a negative characterisation factor (CF). These substances are recognised for example to contribute to global cooling. In the case of CO2, some exchanges represent long-term carbon sequestration. In-depth explanation about this topic can be found in the LCIA implementation report, available in the file section of ecoQuery for the users with a licence.

In the case of water impact assessment, for some methods, water consumed is characterised with a positive CF (water consumption has damaging effect), and water emitted has a negative CF (putting the water back to the environment is beneficial).

Avoided production

Depending on the way multi-output datasets are allocated, or if consequential modelling is applied, the production of a certain intermediate exchanges can result in the decrease of production of another. This avoided production, displayed in the scaling vector with a negative sign, will propagate to this dataset's contribution to the inventory.

Negative emissions

Some substances are emitted with a negative amount. This is the case for example of uptake of certain metal by crops.

It is not possible to guess the cause of a negative impact score. When confronted with this situation, just like any seemingly counterintuitive result in LCA, it is necessary to investigate by analysing the contribution of each unit process and elementary exchange to the final score. Software tools are usually designed to facilitate this kind of assessment.

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