Do Biofuels Reduce Greenhouse Gases?
A new study fuels the debate over the impact of growing crops for fuel.
Greenhouse-gas emissions from biofuels, such as ethanol and biodiesel, may be lower than many researchers have estimated, according to a new study. The findings could further fuel a debate over whether biofuels actually reduce greenhouse-gas emissions compared to gasoline, and if so, by how much.
Some recent studies have suggested that the indirect effects of biofuels production, such as higher food prices, could encourage farmers to clear forested land to grow more crops—thereby worsening climate change. At least one study suggested that the emissions resulting from such decisions would make biofuels—even advanced biofuels made from cellulosic materials such as switchgrass—worse for the environment than gasoline. These studies use economic analysis to predict the effect of future biofuels production on land use, while attempting to control for other factors that influence farmers, such as the amount of grain stocks on hand and changes in food demand.
The new study, to be published in an upcoming issue of the journal Biomass and Bioenergy, uses analysis of historical data instead of economic models. It found no statistical correlation between changes in biofuel production in the U.S. from 2002 to 2007 and recorded changes in cropland use outside of the country. “There is no evidence for indirect land use change,” says Bruce Dale, a professor of chemical engineering at Michigan State University, who led the study.
Jason Hill, a professor of bioproducts and biosystems engineering at the University of Minnesota, says that it’s not surprising that the study found no correlation, given that there are many competing forces that influence crop use. “It’s difficult to distinguish the signal from the noise,” he says.
Indeed, another study, due out in July, draws different conclusions from an analysis of historical data, says Wallace Tyner, a professor of agricultural economics at Purdue University, who is one of this study’s authors. He says that the data shows a large increase (27 million hectares) in the amount of land under cultivation for key crops from 2006 to 2011, a time when biofuels production rapidly increased. Most of the land was cultivated for corn, soybeans, and rapeseed, all biofuels crops. Tyner attributes the increase to biofuels production and factors such as growth in demand from China. But he says the only way to estimate how much of that increase in cropland was due to biofuels production would be to run an economic simulation. Using one such model, he recently estimated that the share of the increase from U.S. biofuels production was about 2 million hectares.
Given the lack of scientific consensus around the impacts of land use changes on greenhouse-gas emissions—and the likelihood that there will always be some uncertainty in the estimates—some researchers have recommended policies that account for a range of possible impacts.
They think, for example, that policymakers should weigh the risk that a biofuel will increase greenhouse-gas emissions against the risk of not using the biofuel, and using gasoline instead. This would resemble the way that regulators weigh the risks and benefits of new drugs, says Michael O’Hare, a professor of public policy at the University of California at Berkeley.
Others, including representatives of the biofuels industry, argue that policymakers should ignore the effect of land use change until there is better research. They also say that if indirect effects of biofuels are to be estimates, studies of indirect effects of gasoline production should also be considered when comparing gasoline and biofuels.
For example, a recent study suggested that factoring in the impact of land use changes from mining oil sands in Canada could increase estimates of carbon-dioxide emissions. Including such emissions could make gasoline look worse than it does now, and make biofuels look better.
Couldn't get to Cambridge? We brought EmTech MIT to you!Watch session videos here