Temporal Aspects in Evaluating the Greenhouse Gas Mitigation Benefits of Using Residues from Forest Products Manufacturing Facilities for Energy Production

Methods for carbon footprinting typically combine all emissions into a single result, representing the emissions of greenhouse gases (GHGs) over the life cycle. The timing of GHG impacts, however, has become a matter of significant interest. In this study, two approaches are used to characterize the timing of GHG emission impacts associated with the production of energy from various biomass residues produced by the forest products industry. The first approach accounts for the timing of emissions and characterizes the impact using Intergovernmental Panel on Climate Change (IPCC) 100‐year global warming potentials (GWPs). The second is a dynamic carbon footprint approach that considers the timing of the GHG emissions, their fate in the atmosphere, and the associated radiative forcing as a function of time. The two approaches generally yield estimates of cumulative impacts over 100 years that differ by less than 5%. The timing of impacts, however, can be significantly affected by the approach used to characterize radiative forcing. For instance, the time required to see net benefits from a system using woody mill residues (e.g., bark and sawdust) is estimated to be 1.2 years when using a fully dynamic approach, compared to 7.5 years when using 100‐year GWPs, with the differences being primarily attributable to methane (CH). The results obtained for a number of different biomass residue types from forest products manufacturing highlight the importance of using a fully dynamic approach when studying the timing of emissions impacts in cases where emissions are distributed over time or where CH is a significant contributor to the emissions.