While it is important that both the development of feedstocks for biofuels and the expansion of biofuel use in the transportation sector be achieved in a socially, economically, and environmentally sustainable manner, the social, economic, and environmental effects of domestic biofuels production have so far been mixed. In 2007, the United States consumed about 6.8 billion gallons of ethanol, made mostly from corn grain, and 491 million gallons of biodiesel, made mostly from soybean (EIA, 2008b), for a combined total of less than 3 percent of the U.S. transportation-fuel consumption. Diverting corn, soybean, or other food crops to biofuel production induces competition among food, feed, and fuel uses. Moreover, both for corn grain ethanol and soybean biodiesel, the use of fossil fuels and other inputs are substantial, and greenhouse gas reductions compared to petroleum-based gasoline emissions are small at best (Farrell et al., 2006; Hill et al., 2006). Thus, the committee judges that corn grain ethanol and soybean biodiesel are merely intermediates in the transition from oil to cellulosic biofuels or other biomass-based liquid hydrocarbon transportation fuels (for example, biobutanol and algal biofuels).
Assuming that technologies for conversion will be commercially viable, liquid fuels made from lignocellulosic biomass2 can offer major greenhouse gas reductions relative to petroleum-based fuels, as long as the biomass feedstock is a residual product of some forestry and farming operations or is grown on marginal lands that are not used for food and feed crop production. Therefore, the committee focused on the lignocellulosic resources available for producing biofuels, and it assessed the costs of different feedstocks of this type—corn stover, wheat and seed-grass straws, hay, dedicated fuel crops, woody biomass, animal manure, and municipal solid waste—delivered to a biorefinery for conversion. Societal needs were considered by examining recent analyses of trade-offs between land use for biofuel production and land use for growing food, feed, and fiber, as well as for ecosystem services.