To address energy security and climate-change concerns, substitutes are needed for petroleum-based transportation fuels. In addition to electricity and natural gas, biofuels are emerging as an important class of substitutes, today dominated by ethanol that is produced from corn and sugar cane. For the future, many alternative pathways are being explored. Features of these alternatives include diversity in feedstocks, fuel composition, and byproducts. Decision-making tools are needed to support choices among these alternatives.

Addressing the world’s need for near-term, cost-effective and reliable production systems for biofuels requires research to overcome technological barriers but must also address social, economic, and environmental challenges in parallel. These challenges include constraints imposed by economics and markets, resource limitations, health risks, climate forcing, nutrient cycle disruption, water demand, and land use. Responding to these challenges effectively requires a life-cycle perspective. Here we summarize seven grand challenges that must be confronted to enable life-cycle assessment (LCA) to effectively evaluate the environmental “footprint” of biofuel alternatives. These challenges may be relevant to many LCA efforts; our focus here is what we have learned in applying LCA to crop/plant-based biofuels.