Abstract:Governments worldwide are promoting the development of biofuels in order to mitigate the climate impact of using fuels. In this article, I discuss the impacts of biofuels on climate change, water use, and land use. I discuss the overall metric by which these impacts have been measured and then present and discuss estimates of the impacts. In spite of the complexities of the environmental and technological systems that affect climate change, land use, and water use, and the difficulties of constructing useful metrics, it is possible to make some qualitative overall assessments. It is likely that biofuels produced from crops using conventional agricultural practices will not mitigate the impacts of climate change and will exacerbate stresses on water supplies, water quality, and land use, compared with petroleum fuels. Policies should promote the development of sustainable biofuel programs that have very low inputs of fossil fuels and chemicals that rely on rainfall or abundant groundwater, and that use land with little or no economic or ecological value in alternative uses.