Empirical Evidence for the Climate Benefits of Decarbonizing US Automotive Transport with Liquid Vs Electric Bioenergy and Carbon Capture and Storage

Climate mitigation scenarios that limit global temperature increases to 1.5 °C rely on decarbonizing vehicle transport with bioenergy production combined with carbon capture and storage (CCS), but climate impacts for producing different bioenergy feedstocks have not been directly compared experimentally nor for alternative end uses. In a field experiment at two Midwest US sites on contrasting soils, yields of seven different feedstocks including maize stover, switchgrass, miscanthus, poplar, native grasses, early successional vegetation, and restored prairie varied substantially within sites but little between sites or among years. When used without CCS to power internal combustion vehicles, greenhouse gas emission intensities ranged from 17 to -183 g CO₂e MJ^-1 in the order maize stover >> miscanthus  switchgrass  native grassesˆ poplar > early successional  restored prairie; direct climate benefits ranged from 80% reductions in CO₂e compared to petroleum for stover to 130% for restored prairie, and were similar for electric vehicles without CCS. Used with CCS, reductions in emission intensities for ethanol powered vehicles ranged, on average, from 180 to 230% and for electric vehicles, from 330 to 410%. Energy production potentials reflected yields and were in the order miscanthus > poplar > switchgrass > native grasses ˆ maize stover > restored prairie ˆ early successional. Extrapolation based on expected U.S. transportation energy needs suggests that negative emissions from bioenergy with CCS for light vehicle use could capture up to 2.2 Gt CO₂e yr^-1.