High gas prices, the threat of shrinking oil reserves, and global warming guilt are driving interest in ethanol, biodeisel, and other biofuels—energy sources produced from agricultural plant matter rather than fossil fuels such as oil and coal. But can biofuels really replace petroleum products? And are they really better for the environment than fossil fuels?

Soybean-based biodiesel is more environmentally friendly than fossil fuels, a new study says. Corn-grain ethanol, however—currently touted in a General Motors ad campaign titled “Live Green, Go Yellow”—is not. “There are surprisingly large environmental impacts for corn-grain ethanol,” said Jason Hill, a biologist with the University of Minnesota in St. Paul. Hill is the lead author of the analysis reported today in the journal Proceedings of the National Academy of Sciences. The study evaluated what Hill and colleagues call the three E’s of biofuels—their environmental impact, the energy recovered from them, and their economic viability in the marketplace. According to the analysis, significantly less fertilizer and pesticide are required to grow soybeans than corn. In addition, soybean biodiesel produces 93 percent more energy than is expended in its creation. Corn-grain ethanol produces only 25 percent more. And when compared with fossil fuels, biodiesel produces 41 percent less greenhouse gas emissions, while ethanol produces 12 percent fewer. According to Hill, the results of the analysis suggest that “ethanol from corn grain is not simply the environmentally friendly biofuel it’s been made out to be.” This is especially true of E85, a mixture of 85 percent ethanol and 15 percent gasoline promoted by corn growers in the U.S. Midwest, he says. The main advantage of ethanol, according to Hill, is that it can be added to fuel in low concentrations to help reduce carbon monoxide pollution, which contributes to smog. “E85 in many ways is the most irresponsible use of ethanol there is … since there is so little of it and the environmental costs of producing it are so high,” he said. “E85 in many ways is the most irresponsible use of ethanol there is … since there is so little of it and the environmental costs of producing it are so high,” he said. Valuing Biofuels Hill and colleagues used what they call life cycle accounting to appraise the fuels. This meant looking into all the inputs and outputs of the system, including environmental costs, rather than focusing purely on energy costs. The new findings contradict earlier energy-accounting studies that found that biofuels require more energy to produce than they generate. For example, ecologist David Pimentel found that corn ethanol requires 29 percent more energy to produce than the fuel generates. Pimentel, of Cornell University in Ithaca, New York, published his findings last year in the journal Natural Resources Research. Pimentel’s study found that soybean biodiesel creation requires 57 percent more energy than it produces. More energy was also required to produce fuels from switchgrass, wood chips, and sunflower plants than their respective fuels generate. Daniel Kammen is the director of the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley. In a paper published this January in the journal Science, he and colleagues refuted the Pimentel study, and others, by showing a net energy benefit to ethanol similar to the benefit shown by Hill and colleagues in the new study. “It’s nice to see a serious, confirming voice,” Kammen said of Hill’s report. Kammen added, however, that the Hill team’s focus on the benefits of soybean biodiesel versus corn-grain ethanol is flawed. Different methods exist to produce corn, and the differences in their environmental impact are significant, Kammen says. Kammen added that rapid technological advances have been made in the production of cellulosic ethanol—ethanol made from nonfood plants like grasses and agricultural waste. As such, this type of ethanol holds tremendous potential as an easy-to-use fuel in conventional vehicles, he says. “No one really argues in a serious way, saying the way we are going to mass-displace gasoline is by growing food crops the way we do now and getting ethanol from them,” he said. Part of the Pie Hill and colleagues agree that neither soybean biodiesel nor corn-grain ethanol are ready to replace petroleum as the United States’ primary fuel. According to their analysis, even if all U.S. corn and soybean production is dedicated to biofuels, it would only meet 12 percent of the country’s current gasoline demand and 6 percent of the diesel demand. Nevertheless, Hill says, biodiesel and ethanol are steps in the right direction, each accounting for a piece of the overall pie needed to meet the country’s energy needs. “I would say that we really need a multipronged approach to tackle our energy problems, our energy needs,” he said. “One product, one fuel alone is not going to do it.” According to Berkeley’s Kammen, research and development of biofuels is in the early stages—there are no clear winners and losers between ethanol and biodiesel. “We’ve done so little to innovate in either area yet,” he said. “It’s like picking which cell phone company to invest in in the late 1970s.”