CML 2001 Impact Assessment Method

In 2001 a group of scientists under the lead of CML (Center of Environmental Science of Leiden University) proposed a set of impact categories and characterisation methods for the impact assessment step. A “problem oriented approach” and a “damage approach” are differentiated. Since the damage approaches chosen are the Eco-indicator 99 and the EPS method, the impact assessment method implemented in ecoinvent as CML 2001 methodology is the set of impact categories defined for the midpoint approach.
There will be two version of this method available in SimaPro 7: a ‘baseline’ version; and an extended
version with ‘all impact categories’.



The CML Guide provides a list of impact assessment categories grouped into

A: Obligatory impact categories (Category indicators used in most LCAs)
B: Additional impact categories (operational indicators exist, but are not often included in LCA studies)
C: Other impact categories (no operational indicators available, therefore impossible to include quantitatively in LCA)

In case several methods are available for obligatory impact categories, a baseline indicator is selected, based on the principle of best available practice. These baseline indicators are category indicators at “mid-point level” (problem oriented approach)” and are presented below. Baseline indicators are recommended for simplified studies. The guide provides guidelines for inclusion of other methods and impact category indicators in case of detailed studies and extended studies.


Normalisation is regarded as optional for simplified LCA, but mandatory for detailed LCA. For each baseline indicator, normalisation scores are calculated for the reference situations: the world in 1990, Europe in 1995 and the Netherlands in 1997. Normalisation data are described in the report: Huijbregts et al LCA normalisation data for the Netherlands (1997/1998), Western Europe (1995) and the World (1990 and 1995). 

The normalized result for a given impact category and region is obtained by multiplying the characterisation factors by their respective emissions. The sum of these products in every impact category gives the normalization factor.


 Download the Methods Manual (PDF, 0.6 MB) for a concise overview of the methods in SimaPro.