The fuel extracted from plants such as corn doesn't come without environmental problems.© Punchstock

Ethanol's reputation as an environmentally friendly fuel is overblown, say researchers who claim that large-scale farming of sugar cane or corn for alcohol is damaging the planet.

Ethanol is fermented from plant sugars and added to gasoline to boost the oxygen content of car fuels and reduce pollution. Its use is on the rise, particularly in Brazil and the United States.

Its proponents argue that using it helps to reduce the amount of carbon dioxide in the atmosphere, which may lessen global warming. Although ethanol burns just like gasoline, the carbon it releases is absorbed by the plants that will make the next lot of fuel. This means that only a small amount of carbon dioxide (from transport and processing) stays in the atmosphere.

But Burton Vaughan, a biologist at Washington State University, Richland, says that supporters may be ignoring ethanol's other environmental impacts. Vaughan and his colleagues, Marcelo Dias de Oliveira and Edward Rykiel, say that producing ethanol-rich fuels tends to reduce biodiversity and increase soil erosion because of the way that sugar cane is grown.

Growing addiction

In Brazil, ethanol from sugar cane now accounts for about 40% of the fuel in the country's vehicles. In the United States, a relatively cheap blend of fuel, called E85 after its 85% ethanol content, is enjoying a growing popularity. And on 28 June, the US Senate passed an energy bill that requires gasoline suppliers to add 8 billion gallons of ethanol a year to their fuel by 2012, rising from the current consumption of 3 billion gallons.

But Vaughan's team argues this increase is bad news for the environment, given the way that crops are currently grown. When the sugar-cane fields are burned, which is done to make harvesting easier, the fires can spread to nearby native vegetation, explains Dias de Oliveira. The energy needed to generate and transport plant fertilizer leads to significant carbon dioxide emissions, and cleaning the sugar cane also consumes vast quantities of water, he adds.

"In a visit to one of the distilleries I observed about 3,900 litres of water being used per ton of sugarcane," he says. This drain coincides with the dry season, contributing to water shortages and damaging river life, the authors argue in the journal BioScience¹.

Heated issue

The research promises to reignite the debate over whether ethanol is a green energy source. David Pimentel, an agricultural scientist at Cornell University in Ithaca, New York, has famously claimed that ethanol production consumes more energy than it can release in a car². Vaughan supports this view. But it has been contradicted by studies from Argonne National Laboratory³ in Illinois and the US Department of Agriculture⁴.

Vaughan and his colleagues claim that their analysis is more thorough because it accounts for the energy consumed in making fertilizer and farming practice.

Others say that although it is important to consider the environmental implications of ethanol, it may still be a better bet than gasoline. "Ethanol isn't perfect, but I find it hard to believe we'd be better off with 100% petroleum," says Monte Shaw, spokesman for the Renewable Fuels Association, the Washington-based trade group for the US ethanol industry.

Shaw points out that a significant amount of ethanol production makes use of the waste material left over after sugar cane or corn is harvested for food. Better fermentation using different bacteria has also streamlined the extraction process. "Ethanol production efficiency has really improved over the last few years," he says. 

• References

  1. Dias de Oliveira M. E., Vaughan B. E. & Rykiel E. J. Bioscience, 55. 593 - 602 (2005).
  2. Pimentel D. Natural Resources Research, 12. 127 - 134 (2003). | Article |
  3. Wang M. Argonne National Laboratory Ethanol Study (summary), Article (2005).
  4. Shapouri H. & McAloon A. The 2001 Net Energy Balance of Corn-Ethanol, Article (2004).