Carbon footprint of recycled biogenic products: the challenge of modelling CO2 removal credits

Abstract

Current carbon footprinting (CF) and life cycle assessment (LCA) methods do not treat recycled biogenic carbon adequately, because the calculation rules for recycled products and biogenic carbon stored in products are defined independently from each other. Therefore, an improved and consistent calculation rule for the CF of product systems containing both recycling processes and carbon stored in products is proposed. The methodological approach consists of the application of the same allocation principles for both greenhouse gas (GHG) releases and GHG removals: (1) explicit accounting of inputs (GHG removals) and outputs (GHG releases) of biogenic carbon flows instead of assuming carbon neutrality per se; (2) consistent application of allocation rules for environmental benefits and environmental burdens. It is shown that the different modelling approaches (e.g. polluter pays, conservative or partitioning) lead to different results in LCA and CF calculations, e.g. the GHG emissions of first life cycle of the product system calculated here range between − 1.6 units in the polluter pays approach and 4 units in the conservative approach. It is shown that the currently common modelling is an average approach for primary biogenic material, a worst-case approach for recycled biogenic material and a best-case approach for disposed biogenic material. This paper proposes to improve the currently developed standards for CF by adding a requirement to the goal and scope definition phase that ensures the consistent and transparent documentation, how biogenic carbon removal credits are allocated between life cycles.