The influence of biogenic carbon assessment assumptions on biogenic global warming results – case study of an innovative mycelium-based composite block

Biobased building materials play a crucial role in reducing the embodied Greenhouse Gas (GHG) emissions of buildings. When quantifying the GHG emissions of biobased materials, the methodological choices made when modelling biogenic carbon in Life Cycle Assessment (LCA) influence the results. To showcase these implications, we applied three different Life Cycle Inventory (LCI) assumptions to the case study of an innovative 10x10x10-cm mycelium composite block: 'dynamic growth before harvest', 'static flux in the year of harvest' and 'dynamic regrowth after harvest'. For the Life Cycle Impact Assessment (LCIA), we applied static and dynamic Characterisation Factors (CFs) to all three assumptions. We present the results over a timeline extending from -120 to +120 years from harvest. When applying static CFs, we observed a biogenic Global Warming Potential (GWP) of 0 kg CO2-eq for all three LCI assumptions. When applying the dynamic CFs, the LCI assumption of 'dynamic growth before harvest' and 'static flux in the year of harvest' resulted in a negative biogenic GWP, while applying the LCI assumption of 'dynamic regrowth after harvest' yielded a positive biogenic GWP. We show that the observed results depend heavily on the given assumptions. While no agreement was found regarding the appropriateness of the different biogenic carbon accounting methods, we transparently show the effects of applying these approaches on the final results obtained for the biogenic GWP over our assessed timeline.