Eight Principles of Uncertainty for Life Cycle Assessment of Biofuel Systems

New environmental regulations in the USA and Europe require a reduction of greenhouse gas (GHG) emissions from transportation fuels as a component of climate change mitigation policy. The US Energy Independence and Security Act of 2007 (EISA) requires GHG emission reductions from the life cycles of biofuels compared to gasoline, by 20% for ethanol from maize grain (maizeethanol), 60% for cellulosic ethanol, and 50% for other advanced biofuels. To determine these reductions, the US Environmental Protection Agency (EPA) employs life cycle assessment (LCA) methods which were not used previously in national environmental regulations. These regulations, entitled the “Renewable Fuel Standard 2” (RFS2), build on concurrent state efforts by the California Air Resources Board (CARB) under the Low Carbon Fuel Standard (LCFS). These regulations can affect billions of dollars in financial incentives and market access for the existing biofuel industry and they will determine how new feedstocks for biofuels are developed in the future. Over roughly the last twenty years, LCA has been applied to biofuel production systems for determining GHG emissions and energy efficiency, but these evolving methods have been inconsistent [1–3]. These methods are used to estimate direct emissions from the life cycle from crop production to finished fuels, while also considering upstream emissions such as from fertilizer production. Contrary to these relatively simple analyses, the assessments currently developed under state and federal law are generally far more complex by including global modeling. The use of global models has been encouraged by findings that indirect effects from biofuel production, which are international in scope, lead