An updated framework for climate change impact assessment of bioenergy and an application in poplar biomass

Mainstream life cycle assessment (LCA) studies on the climate change impact of bioenergy fail to account for some direct impacts, such as biomass-derived CO2 emissions and potential impacts on future carbon dynamics. For a more persuasive assessment of the climate change impacts of bioenergy, a simplified and comprehensive framework was developed for LCA by integrating the atmospheric carbon cycle model, plant growth model, and biomass decomposition model. The system includes four components: fossil fuel-derived greenhouse gas (GHG) emissions, biogenic CO2 emissions, biomass regrowth for compensation, and the difference in carbon sequestration from the reference scenario. For an illustration purpose, the framework was applied in the study of the climate change impacts of hybrid poplar use for bio-ethanol, bio-diesel, heating, and bio-power. The LCA study indicated that the fossil fuel-derived GHG emissions (15.77–42.55 kg CO2 eq/GJ) from biomass utilization were lower than those from the combustion of fossil fuels. Because the fossil fuel-derived GHG emissions, biogenic CO2 emissions, and biomass regrowth for compensation were positive, the sums of the three components (120.21–243.97 kg CO2 eq/GJ) were higher than the emissions from the combustion of fossil fuels. However, biomass utilization may improve biomass regrowth or avoid biomass decomposition. The differences in carbon sequestration are usually negative and can offset the positive climate change impacts. The final total climate change impacts for the different types of bioenergy were from –26.85 kg CO2 eq/GJ to 1.08 kg CO2 eq/GJ. The newly developed framework is more persuasive and comprehensive than the conventional LCA because it includes all the direct impacts of biomass utilization based on the biomass characteristics. The application of this framework can ensure the sustainable utilization of biomass and avoid ecosystem degradation.