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The "Dark Side" of Sugar-Cane Ethanol Production
Tsao, C.-C., Campbell, J.E., Mena-Carrasco. M., Spak, S.N., Carmichael, G.R. and Chen, Y. 2011. Increased estimates of air-pollution emissions from Brazilian sugar-cane ethanol. Nature Climate Change 2: 53-57.

The authors write that "accelerating biofuel production has been promoted as an opportunity to enhance energy security, offset greenhouse-gas emissions and support rural economies." However, they indicate that "air-pollutant emissions from biofuel production and combustion may have significant impacts on climate and air quality," and that "the change in vehicle emissions that would result from a large-scale conversion from gasoline to E85 (a blend of up to 85% ethanol with gasoline or another hydrocarbon) in the United States could have significant health consequences, by increasing tropospheric ozone concentrations," citing Jacobsen (2007). And they add that Hill et al. (2009) have also demonstrated that "the use of corn ethanol has higher health costs than gasoline."

What was done
Noting that that sugar-cane ethanol is one of the most widely used biofuels, and that Brazil is its largest producer, Tsao et al. developed a set of spatially and temporally explicit estimates of air-pollutant emissions - including volatile organic compounds, nitrogen oxides, particulate matter less than 10 and 2.5 Ám in diameter, sulfur oxides and carbon monoxide - over the entire life cycle of sugar-cane ethanol as produced in Brazil.

What was learned
This work revealed, in the words of the six scientists, that "even in regions where pre-harvest field burning has been eliminated on half the croplands, regional emissions of air pollutants continue to increase owing to the expansion of sugar-cane growing areas," plus the fact that "burning continues to be the dominant life-cycle stage for emissions." In addition, they say that a comparison of their estimates of burning-phase emissions with satellite estimates of burning in the state of Sao Paulo suggests that "sugar-cane field burning is not fully accounted for in satellite-based inventories, owing to the small spatial scale of individual fires," and they add that "accounting for this effect leads to revised regional estimates of burned area that are four times greater than some previous estimates [italics added]."

What it means
As a result of their findings, Tsao et al. warn that biofuels may have larger impacts on human health "than previously thought," which leads us to conclude that both individuals and nations need to think again before committing themselves to a course of action that could have a huge negative impact on the welfare of humanity, both directly via human health concerns, and indirectly via the deleterious influence of ozone on earth's plant life in general and agricultural crops in particular (see Ozone - Effects on Plants in our Subject Index).

Hill, J., Polasky, S., Nelson, E., Tilman, D., Huo, H., Ludwig, L., Neumann, J., Zheng, H. and Bonta, D. 2009. Climate change and health costs of air emissions from biofuels and gasoline. Proceedings of the National Academy of Sciences USA 106: 2077-2082.

Jacobson, M.Z. 2007. Effects of ethanol (E85) versus gasoline vehicles on cancer and mortality in the United States. Environmental Science and Technology 41: 4150-4157.

Reviewed 4 July 2012