Brazil has rapidly become the world's biggest producer of ethanol — an alternative to petroleum-based fuel — from sugar cane. The greenhouse-gas emissions created during sugar-cane ethanol production are lower than those associated with the creation of other biofuels, but a study shows that the process generates up to seven times more air pollutants than previously estimated from remote-sensing data.

Credit: OCEAN/CORBIS

Elliott Campbell at the University of California, Merced, and his colleagues used agricultural survey data from Brazil to calculate emissions of various air pollutants, such as sulphur dioxide and black carbon, from the entire production cycle of sugar-cane ethanol in 2000–08. A major source of emissions is the burning of sugar-cane fields before harvest (pictured). The authors' estimates of emissions from just this burning phase were 1.5–7.3 times higher than those from satellite-based methods. Altogether, the production of sugar-cane ethanol generated more pollutants than petrol or diesel production.

The authors say that even in regions where burning has been scaled back, pollutant emissions continue to grow because of the increase in sugar-cane production in Brazil.

Nature Climate Change 10.1038/nclimate1325 (2011)