Another study weighing in against biofuels, this time by Nobel Prize winning Paul Crutzen. Yes, I said that just to wind up Maribo – read his take. I’ve long been skeptical (septical?) of the biofuels stuff, especially corn-based ethanol, which looks more like pork for farmers than a sensible policy. On the conventional view, CBE is at best marginally useful in reducing CO2 emissions (but in which case the same money would be far better off spent elsewhere) or actually harmful. In a sense, this doesn’t matter, because its driven by pork barrel politics not science, but I suppose we can hope to keep the science somewhere in the picture.
So the new argument is N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels and the argument is that “The relationship, on a global basis, between the amount of N fixed by chemical, biological or atmospheric processes entering the terrestrial biosphere, and the total emission of nitrous oxide (N2O), has been re-examined, using known global atmospheric removal rates and concentration growth of N2O as a proxy for overall emissions. The relationship, in both the pre-industrial period and in recent times, after taking into account the large-scale changes in synthetic N fertiliser production and deforestation, is consistent, showing an overall conversion factor of 3-5%. This factor is covered only in part by the ~1% of “direct” emissions from agricultural crop lands estimated by IPCC (2006), or the “indirect” emissions cited therein. This means that the extra N2O entering the atmosphere as a result of using N to produce crops for biofuels will also be correspondingly greater than that estimated just on the basis of IPCC (2006). When the extra N2O emission from biofuel production is calculated in “CO2-equivalent” global warming terms, and compared with the quasi-cooling effect of “saving” emissions of fossil fuel derived CO2, the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), can contribute as much or more to global warming by N2O emissions than cooling by fossil fuel savings“. So this means (if correct) that only by considering N2O you get a net warming, let alone all the CO2 emissions in producing them. The difference, as Maribo points out, is their using 3-5% rather than 1%. C et al. know they are doing this, and think they are justified (e.g. response here).
Quite who is right is not clear to me; but this is only the “under review” copy of the paper so it will be interesting to see what changes occur during the review process. At the moment it looks to me as though C et al. aren’t giving any ground.