Comment on "Life-cycle analysis of alternative automobile fuel/propulsion technologies".

We examine the economic and environmental implications of the fuels and propulsion technologies that will be available over the next two decades for powering a large proportion of the light duty fleet (cars and light trucks). Since R&D change is rapid, we treat the uncertainty about future technologies using bounding calculations. A lifecycle perspective is used to analyze fossil fuels [conventional unleaded and reformulated gasolines, low sulfur reformulated diesel, and compressed natural gas (CNG)], ethanol from biomass, and electricity together with current and advanced internal combustion engines (ICE, indirect (port) and direct injection, spark, and compression ignited) and electric vehicles (battery-powered, hybrid electric, and fuel cell). Technological advances continue to improve the efficiency and environmental performance of ICE automobiles powered by low sulfur fossil fuels. Absent a doubling of petroleum prices or stringent regulation [due, for example, to intense concerns about greenhouse gas (GHG) emissions], ICE using fossil fuels will dominate the market for the next two decades. CNG cars have low emissions, including GHG, but must be redesigned to store enough CNG to achieve the current range. Batterypowered cars have limited range and are expensive, and the life-cycle of battery components leads to discharges of toxic materials. Although both hybrid and fuel cell vehicles promise better fuel economy and lower emissions, in the near term these do not justify their higher costs. If global warming becomes a major concern, CNG offers carbon dioxide emission reductions of up to 30%, and bioethanol could provide a fuel with no net carbon dioxide emissions, although the bioethanol price would be more than twice current petroleum prices.