Policies and Consumption-Based Carbon Emissions from a Top-Down and a Bottom-Up Perspective

Two major approaches for calculating consumption-based carbon emissions can be distinguished: top-down approaches, in the form of multi-regional input-output (MRIO) models, and bottom-up approaches, in the form of life cycle assessment (LCA). Both approaches have pros and cons and are very data-intensive. Several MRIO databases have been developed and published over the past years. These databases, which have been refined and validated, will be used for policy analysis. As LCA is usually only applied to very specific products and product groups, analysis is limited and many products have not yet been looked at. This paper makes use of both a top-down and bottom-up approach to calculate the impacts of different policy measures on the development of consumption-based carbon emissions in the EU28 and on emissions elsewhere in the world. The policy examples used are the EU’s CO₂ in Cars Regulations and the South African renewable energy initiative. The results from the top-down approach are then compared with those from the bottom-up approach. Both bottom-up and top-down approaches use the same underlying assumptions regarding the impacts, but due to the very different nature of the methodologies, differences in the results are observed, though sign and scope of the results are the same for the two cases. Part of the deviations can be explained by differences in methodology and scenario design due to these differences. It can be concluded that bottom-up and top-down approaches can and need to be applied to different policies and are generally complementary.