Advances and Emerging Issues in Life-Cycle Assessment for Biofuel Policy

Many policies for reducing the emissions intensity of transportation fuels rely on the outputs of life-cycle assessment (LCA) models to incentivize the production of biofuels and other alternative fuels. This approach is essential to account for greenhouse gas emissions, sequestration, and avoidance throughout the supply chain and use of each fuel. Since the creation of the United States' Renewable Fuel Standard and California's Low Carbon Fuel Standard, there has been broader adoption of LCA-based regulations and incentives, accompanied by an evolution in modeling approaches. There is general agreement that regulatory impact assessment and policy design/implementation are distinct, where the latter benefits from transparent models that capture clear cause-and-effect relationships between measures taken to reduce emissions and a fuel's carbon intensity score. However, there is not yet convergence on a range of methodological choices that impact LCA outputs relevant for fuels and a host of other emerging applications, such as private carbon markets. Numerous recent studies have explored existing LCA methods and developed new approaches for applications where consensus has not yet been reached, such as soil organic carbon accounting, forest biomass carbon accounting, crediting of avoided emissions, and defining wastes. Simultaneously, new and revised LCA-based biofuel policies have leveraged these approaches, and in some cases, used fit-for-purpose solutions. This article reviews the state of policy-relevant biofuel LCA methods and tools, compares and contrasts established and emerging approaches within current policies at the state, federal, and international levels, and identifies key challenges that require further research and coordination to establish best practices. These issues have implications beyond biofuel policies, extending to power generation and carbon dioxide removal crediting.