The Consequential Climate Impact of Bioenergy and Wood Products: A New Framework for the Assessment of Biogenic Carbon

ABSTRACT

The utilization of woody biomass plays a key role in the path towards a sustainable future for many stakeholders. To assess the climate impact of wood energy and products, it is essential to assess the impact of biogenic carbon, which has become a topic of increasing interest. The goal of this study is to build on existing approaches for the assessment of biogenic CO ₂ and provide a new framework termed the Green Carbon Cycle (GCC) Approach. This new framework brings together key methods for biogenic carbon assessment into one consistent framework for practitioners of LCA to follow. The GCC Approach includes the whole life cycle of biogenic carbon from the removal from the atmosphere by forest growth, harvesting and use of wood products and fuelwood until the end of life by natural decay or combustion. It covers five steps: (1) Analysis of the biomass source and affected GCC flows, (2) formulation of use‐ and counterfactual scenario, (3) simulation or calculation of emission profiles, (4) application of dynamic LCA to calculate emission factors, and (5) implementation of emission factors in LCA. Beyond presenting this framework, its implementation compared to existing methods and generic emission factors for wood is shown. To calculate forestry based biogenic emission factors the carbon dynamics of five representative forest stands typical for Germany were simulated with different harvest intensities compared to a non‐harvest scenario. Forest residues were analyzed in contrast to a non‐use natural decay scenario. From the differences to the baseline scenarios global warming potential (GWP) _bio 20 and GWP _bio 100 factors were calculated. The generic emission factors show a strong impact of harvest intensity and species mix in a forest stand. With high harvest intensities leading to consistently higher emission factors and in most cases resulting in climate‐positive factors for coniferous wood and climate negative ones for deciduous species.