Full Title: N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels
Author(s): P. J. Crutzen, et al.
Publisher(s): Atmospheric Chemistry and Physics Discussions
Publication Date: July 1, 2007
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Description (excerpt):
The relationship, on a global basis, between the amount of N fixed by chemical, biolog-
ical or atmospheric processes entering the terrestrial biosphere, and the total emission
of nitrous oxide (N2 O), has been re-examined, using known global atmospheric removal rates and concentration growth of N2 O 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 fer tiliser 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 N2 O 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,15 such as biodiesel from rapeseed and bioethanol from corn (maize), can contribute as much or more to global warming by N2 O emissions than cooling by fossil fuel savings. Crops with less N demand, such as grasses and woody coppice species have more favourable climate impacts. This analysis only considers the conversion of biomass to biofuel. It does not take into account the use of fossil fuel on the farms and for fertilizer and pesticide production, but it also neglects the production of useful co-products. Both factors par tially compensate each other. This needs to be analyzed in a full life cycle assessment.