A new integrated framework to estimate the climate change impacts of biomass utilization for biofuel in life cycle assessment

The urgent need for climate change mitigation and the potential threat of energy crisis have allowed the popularity of biomass for biofuels to increase. However, the approaches to assess the climate change impacts of biomass utilization are still questionable. To allow a more accurate assessment, we developed a new framework by integrating six impact components including (1) fossil fuel-derived greenhouse gas (GHG) emissions, (2) biogenic CO2 emissions-loss, (3) biogenic CO2 emissions-combustion, (4) emissions from land-use practice change, (5) regrowth for compensation, and (6) difference in carbon sequestration. To illustrate the performance of the framework, seven case studies, which covered the first-, second-, and third-generation biofuels, were conducted. The majority of the positive impacts were contributed to by the fossil fuel-derived emissions, biogenic CO2 emissions, and regrowth for compensation. For the first-generation biofuels, the life cycle GHG emissions were much higher than those of energy-equivalent fossil fuels (144 and 218 kg CO2/GJ for Soybean-to-Biodiesel and Corn-to-Ethanol). The second- and third-generation biofuels had less accountable positive GHG emissions (-62 to 53 kg CO2/GJ) due to the offset of negative impacts from land-use practice change and difference in carbon sequestration. However, the negative effects are not determinist. High uncertainty from model-simulated carbon sequestration and decomposition is perceivable. High life cycle GHG emissions for the second- and third-generation biofuels are possible.