T<scp>HE</scp>P<scp>OTENTIAL OF</scp>B<scp>IOMASS</scp>F<scp>UELS IN</scp>T<scp>HE</scp>C<scp>ONTEXT OF</scp>G<scp>LOBAL</scp>C<scp>LIMATE</scp>C<scp>HANGE</scp>: Focus on Transportation Fuels

▪ Abstract An ultimate limit on the extent that biomass fuels can be used to displace fossil transportation fuels, and their associated emissions of CO 2 , will be the land area available to produce the fuels and the efficiencies by which solar radiation can be converted to useable fuels. Currently, the Brazil cane-ethanol system captures 33% of the primary energy content in harvested cane in the form of ethanol. The US corn-ethanol system captures 54% of the primary energy of harvested corn kernels in the form of ethanol. If ethanol is used to substitute for gasoline, avoided fossil fuel CO 2 emissions would equal those of the substituted amount minus fossil emissions incurred in producing the cane- or corn-ethanol. In this case, avoided emissions are estimated to be 29% of harvested cane and 14% of harvested corn primary energy. Unless these efficiencies are substantially improved, the displacement of CO 2 emissions from transportation fuels in the United States is unlikely to reach 10% using domestic biofuels. Candidate technologies for improving these efficiencies include fermentation of cellulosic biomass and conversion of biomass into electricity, hydrogen, or alcohols for use in electric drive-train vehicles.