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Ethanol Produced from Sugarcane
Lisboa, C.C., Butterbach-Bahl, K., Mauder, M. and Kiese, R. 2011. Bioethanol production from sugarcane and emissions of greenhouse gases -- known and unknowns. Global Change Biology Bioenergy 3: 277-292.

In introducing their recent review paper in GCB Bioenergy, Lisboa et al. (2011) write that "even though bioethanol production from sugarcane is considered to be a beneficial and cost-effective greenhouse gas (GHG) mitigation strategy, it is still a matter of controversy due to insufficient information on total GHG balance of this system." Hence, they proceed to provide an overview of what has been learned to date from scientific research devoted to probing this still unsettled subject.

What was done
Noting that "aside from the necessity to account for the impact of land use change," they state that "soil N2O emissions during sugarcane production and emissions of GHG due to pre-harvest burning may significantly impact the GHG balance." Thus, they searched the scientific literature to see what has been learned in these insufficiently-studied areas.

What was learned
Based on "a thorough literature review," as they describe it, the four German researchers show that "direct N2O emissions from sugarcane fields due to nitrogen (N) fertilization result in an emission factor of 3.87 ± 1.16%," which is "much higher than suggested by the IPCC (1%)." They also say that "N2O emissions from N fertilization accounted for 40% of the total GHG emissions from ethanol-sugarcane production, with an additional 17% from trash burning." Thus, "if land use change-related GHG emissions are considered," they say that "the total GHG balance turns negative mainly due to vegetation carbon losses." In addition, they note that their study shows that "major gaps in knowledge still exist about GHG sources related to agricultural management during sugarcane production," such as "effects of irrigation, vinasse [the liquid residue that remains after the distillation of ethanol from sugar] and filter cake [the substance that remains on a filter after filtration designed to purify a desired substance] applications."

What it means
All things considered, it is by no means certain that there is any benefit to be accrued from the substitution of bioethanol from sugarcane for fossil fuels. In fact, it could even prove to be counter-productive, as production of ethanol from any crop "may directly compete with food and feed production and requires higher rates of nitrogen fertilizers, contributing to local and regional eutrophication and resulting in increased soil N2O emissions," as Lisboa et al. indicate has been found to be the case with ethanol derived from corn, citing Crutzen et al. (2008) and Fargione et al. (2008). Clearly, therefore (and as they conclude), "more studies are needed to assess if bioethanol from sugarcane is a viable option to reduce energy-related GHG emissions." In fact, such studies are way overdue, as Lisboa et al. report that "54.6% of the sugarcane production in Brazil and 39% in India is used for bioethanol production," in a truly sad example of getting the cart way before horse.

Crutzen, P.J., Mosier, A.R., Smith, K.A. and Winiwarter, W. 2007. N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels. Atmospheric Chemistry and Physics 8: 389-395.

Fargione, J., Hill, J., Tilman, D., Polasky, S. and Hawthorne, P. 2008. Biofuels: effects on land and fire -- response. Science 321: 199-200.

Reviewed 31 August 2011