FIGURE 2.16 Estimated net life-cycle CO2-equivalent (CO2-eq) emissions for production, transportation, and use of alternative liquid transportation fuels. Emissions are shown in units of tonnes of CO2 equivalent per barrel of gasoline equivalent produced from biomass, coal, or a combination of coal and biomass. For comparison, the CO2-eq emissions for gasoline are shown on the left. Negative CO2-eq emissions mean that on a net life-cycle basis, CO2 is removed from the atmosphere; for example, the negative CO2 emissions for BTL and cellulosic ethanol result from an estimate that the sequestration of biomass carbon in power-plant char or the buildup of carbon in soil and roots will exceed the emissions of carbon in biofuel production. Growing perennial crops for cellulosic fuels provides CO2 benefits because these crops store carbon in the root biomass and the associated rhizosphere, thereby increasing soil carbon sequestration. The precise value of CO2-eq emissions from CBTL depends on the ratio of biomass to coal used. Indirect land-use effects on CO2 emissions are not included.
Note: BTL = biomass-to-liquid fuel; CBFT = coal-and-biomass-to-liquid fuel, Fischer Tropsch; CBMTG = coal-and-biomass-to-liquid fuel, methanol-to-gasoline; CBTL = coal-and-biomass-to-liquid fuel; CCS = carbon capture and storage; CFT = coal-to-liquid fuel, Fischer-Tropsch; CMTG = coal-to-liquid fuel, methanol-to-gasoline; CTL = coal-to-liquid fuel.
Sources: Data from Chapter 5 in Part 2 of this report and from NAS-NAE-NRC (2009b).