In the project the field of weighting methods is surveyed, developing a framework for typifying options. Next, three basic approaches are chosen, each most consistent in itself, and filled with a number of operational methods. These three approaches are developed operationally for our purpose here. We expanded their applicability to the broadest and most generally specified level, based on the ILCD Handbook on LCIA (EC, 2011) as the reference for characterisation in LCA. To show how they work out, the weighting methods are applied to a time series of emission data for the EU. This data set has been chosen as reflecting the broadest set of environmental interventions for aggregate performance of society now available. Finally, the question is how to deal with these three different weighting options? At an aggregate level of one country, they lead to very similar outcomes. For different countries and sectors the outcomes might be more disparate. And for application at a micro level of specific technologies and policies, they will certainly differ in their outcomes. As they have different strengths and weaknesses a mixed approach is developed, where the methods in the three approaches are combined into one, as a meta-weighting method. The result is available as a spread sheet, applicable to a broad set of environmental interventions. It can also be applied in a disaggregated way, showing the relative importance of specific environmental interventions and of specific impact categories. The easy choice of emphasis between the weighting methods also allows for an active sensitivity analysis.

The list of recommended environmental impact categories is provided by the International Reference Life Cycle Data System (ILCD) Handbook. The ILCD Handbook also gives recommendations on environmental impact assessment models and factors for LCA, which constitute the starting point of this weighting project.

• Huppes, G., L. van Oers, U. Pretato & D.W. Pennington (2012) Weighting environmental effects: Analytic survey with operational evaluation methods and a meta-method.  The International Journal of Life Cycle Assessment, In Press. 
• Huppes, G. & L. van Oers (2011)  Evaluation of Weighting Methods for Measuring the EU-27 Overall Environmental Impact. JRC Scientific and Technical Reports, Luxembourg: Publications Office of the European Union. ISBN 978-92-79-21643-5, ISSN 1831-9424. 
• Huppes, G. & L. van Oers (2011)  Background Review of Existing Weighting Approaches in Life Cycle Impact Assessment (LCIA). JRC Scientific and Technical Reports, Luxembourg: Publications Office of the European Union, ISBN 978-92-79-21751-7, ISSN 1831-9424.