Abstract:Continued emissions of CO₂ and other "greenhouse" gases are expected to cause substantial global warming with adverse consequences for agriculture and coastal cities, yet emission of greenhouse gases has not been a criterion in evaluation of alternative transportation fuels. In this paper are evaluated emissions of CO₂, CH₄, N₂O, and other greenhouse gases from the use of gasoline and diesel fuel, electricity, methanol, natural gas, and hydrogen in highway vehicles. Emissions from initial resource extraction to end use are estimated. It Is found that the use of coal to make any highway fuel would substantially accelerate greenhouse warming relative to the base-case use of petroleum. The use of natural gas as a feedstock would result in a small reduction. Significant reductions in emissions of greenhouse gases can be achieved only by greatly increasing vehicle efficiency or by using biofuels, electrolytic hydrogen, or nonfossil-fuel-based electricity as the fuel feedstock. Emissions of gases other than CO₂ are likely to contribute appreciably to the warming, but better data are needed. Full social-cost pricing of fuels and increased research and development on sustainable, environmentally sound fuels are recommended.