An environmental, climate mitigation rationale for research and development on liquid transportation fuels derived from plants emerged among many scientists and engineers during the last decade. However, between 2006 and 2010, this climate ethic for pursuing biofuel became politically entangled and conceptually confused with rationales for encouraging greater use of plant-based ethanol that were both unconnected to climate ethics and potentially in conflict with the value-commitments providing a mitigation-oriented reason to promote and develop new and expanded sources of biofuel. I (...) argue that the conceptual construct of technological trajectories provides a fecund approach to the ethical evaluation of R&D strategies in the case of plant-based liquid transportation fuels. The idea of a trajectory has a current use in the literature of science studies and aptly summarizes a number of themes that are critical to the evaluation of tools and techniques whose future shape, design, applications and potential consequences are necessarily somewhat speculative. In the case of biofuels, it is the imagined future trajectory that provides the basis for resistance to an emerging technology, rather than the present-day technical capabilities and the unexpected consequences of biofuel development. (shrink)