Life cycle assessment of lignocellulosic ethanol: a review of key factors and methods affecting calculated GHG emissions and energy use

•System boundaries, N2O emissions, soil carbon and LUC remain contentious issues.•Differences in process efficiency and chemical use can strongly impact LCA metrics.•GHG emissions are impacted by allocation methods and co-product credits.•Wide variation in key parameters reported in the literature impacts GHG emissions.•Indirect/consequential effects can be important and warrant further study. Lignocellulosic ethanol has potential for lower life cycle greenhouse gas emissions compared to gasoline and conventional grain-based ethanol. Ethanol production ‘pathways’ need to meet economic and environmental goals. Numerous life cycle assessments of lignocellulosic ethanol have been published over the last 15 years, but gaps remain in understanding life cycle performance due to insufficient data, and model and methodological issues. We highlight key aspects of these issues, drawing on literature and a case study of corn stover ethanol. Challenges include the complexity of feedstock/ecosystems and market-mediated aspects and the short history of commercial lignocellulosic ethanol facilities, which collectively have led to uncertainty in GHG emissions estimates, and to debates on LCA methods and the role of uncertainty in decision making.