Published November 2006
Thanks to public subsidies and promotion, biodiesel is booming. Output has climbed nearly ten-fold since the mid-1990s, and by the end of the decade it may quadruple again. Why are governments so keen? On the negative side, they fear that crude oil is drying up and that their energy security is threatened. On the positive side, they view crop-based fuels as a great way to subsidize farmers and, as substitutes for conventional fossil fuels, a powerful way to combat global warming.
This study further examines that last claim, which is important for two reasons: 1) diesel combustion contributes significantly to global warming; and 2) the biodiesel/fossil diesel question is a reasonable proxy for the overall biofuels/fossil fuels question – which is even more significant.
Surprisingly, for all the attention these issues have received, analysts are equivocal about the answer. One review of over 60 relevant studies concludes on the one hand that biofuels reduce global warming relative to fossil fuels, yet on the other hand it presents a comparison of biodiesel and mineral diesel that is at best confusing if not misleading. Another review of 12 studies shows a vast range of answers.
So we set out to find an answer – by modeling the greenhouse gas emissions of the production-use systems for both biodiesel and mineral diesel. For biodiesel we used the most common type in Europe and the world, rape methyl ester (RME) derived from transesterification of rapeseed oil. We then compared the net global warming emissions of biodiesel to petroleum diesel, weighted according to global warming potentials as defined by the Intergovernmental Panel on Climate Change. The comparison was made on two bases: energy delivered and arable land used.
We arrived at a clear, unequivocal answer to the critical question: Does switching from petroleum diesel to biodiesel cut global warmer emissions? We also identified some critical conclusions for future policy makers, market planners and marketers. Finally, we uncovered two key areas for further research.