to-liquid fuels with CCS could replace about 15 percent of the fuel currently consumed in the transportation sector (1.7–2.5 million barrels per day of gasoline equivalent) with near-zero life-cycle CO2 emissions. Coal-to-liquid fuels with CCS could replace about 15–20 percent of current fuel consumption in the transportation sector (2–3 million barrels per day; the lower estimate holds if coal is also used to produce coal-and-biomass-to-liquid fuels) and would have life-cycle CO2 emissions similar to those of petroleum-based fuels. However , these levels of production would require the annual harvesting of 500 million dry tonnes (550 million dry tons) of biomass and an increase in coal extraction in the United States by 50 percent over current levels, resulting in a range of potential environmental impacts on land, water, air, and human health—including increased CO2 emissions to the atmosphere from coal-to-liquid fuels unless process CO2 from liquid-fuel production plants is captured and stored geologically . Commercial demonstrations of the conversion technologies integrated with CCS will have to be pursued aggressively and proven economically viable by 2015 if these technologies are to be commercially deployable before 2020. The development of advanced biomass-conversion technologies will require fundamental advances in bioengineering and biotechnology .
Electrifying the light-duty vehicle fleet through expanded deployment of plug-in hybrids, battery electric vehicles, and hydrogen fuel-cell vehicles. Such a transition would require the development of advanced battery and fuel-cell technologies as well as modernization of the electrical grid to manage the increased demand for electricity .
Sixth, substantial reductions in greenhouse gas emissions from the electricity sector are achievable over the next two to three decades through a portfolio approach involving the widespread deployment of energy efficiency technologies; renewable energy; coal, natural gas, and biomass with carbon capture and storage; and nuclear technologies. Achieving substantial greenhouse gas reductions in the transportation sector over the next two to three decades will also require a portfolio approach involving the widespread deployment of energy efficiency technologies, alternative liquid fuels with low life-cycle CO2emissions, and light-duty vehicle electrification technologies.