Exploring a safe operating approach to weighting in life cycle impact assessment – a case study of organic, conventional and integrated farming systems

Normalization and weighting steps used in life cycle impact assessment (LCIA) are often ignored as the weighting factors currently available are seen as being uncertain, subjective and unreliable. This article aims to contribute to the development of a new approach towards weighting, exploring the application of the concept of a planetary safe operating space for human welfare. Based on this approach, the boundaries included in this study relate to: climate change, rate of biodiversity loss, nitrogen cycle, phosphorus cycle, stratospheric ozone depletion, global freshwater use and change in land use. The weighting factors are then applied to a case study comparing environmental impacts of organic, conventional and integrated farming systems with alternative land uses. An integrated farming system that uses a part of the land for natural forest was found to have the lowest total impact score. Conventional farming systems with Miscanthus and managed forest had the highest total impact scores. The main source of uncertainty in the results arose from the wide range of assessments for the safe boundary of the biodiversity loss impact category. As the weighting factors proposed in this paper are not based on the common LCA impact categories, more work is needed to adjust the weighting factors to be suitable for use in LCA studies. More research is also needed for further defining the safe planetary boundaries.