Balancing the green carbon cycle - Biogenic carbon within life cycle assessment

PurposeAccurate assessment of environmental impacts is key to the successful implementation of sustainability policies in both the short and long term. A critical component, particularly in assessing areas like the developing bioeconomy, is the handling of carbon of biogenic origin. This paper examines current methodologies and their ability to assess biogenic carbon.MethodsWe quantitatively evaluate different biogenic carbon accounting methodologies using our new conceptual framework - the green carbon cycle (GCC). The GCC is a subcycle of the global carbon cycle and supports understanding the accuracy of methods in capturing all essential biogenic carbon flows. Applying the GCC, we examine the advantages and disadvantages of dynamic LCA, GWPbio, and the - 1/ + 1 method under identical assumptions in four examples.Results and discussionThe methods reveal both differences and similarities, depending on the specific application. When focusing on growth cycles only, dynamic LCA and GWPbio deliver almost identical results for the assessment of biogenic carbon. However, when extending the view to the entire life cycle of a biomass-based facade cladding, dynamic LCA finds significantly lower impacts than GWPbio, mainly due to the different assumptions concerning the timeframe from biomass growth until end of product life. Based on the distinct strengths and weaknesses of applying the GCC, we provide a decision matrix for practitioners to facilitate the right choice for each application.ConclusionThis paper enables researchers and practitioners to accurately assess biogenic carbon and to determine the best available approximation of the conditions in the GCC. It also identifies similarities and differences between the methods and shows how to overcome some of the identified weaknesses.Graphical Abstract(Adapted from Friedlingstein et al. (2023)