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PRINCETON (US)—Biofuels can deliver on their promise of clean energy only if they are produced from renewable biomass, according to a new report by a team of scientists and policy experts.

“The world needs to replace fossil fuels with renewable energy, but recent research findings have thrown the emerging biofuels industry into a quandary,” says David Tilman of the University of Minnesota, lead author of the paper. “We found that the next generation of biofuels can be highly beneficial if produced properly.”

The paper published in the July 17 issue of the journal Science coincides with climate change policy debates in the U.S. Congress and tackles land-use issues that have generated much controversy in recent years. Specifically, the report addresses concerns that clearing land to grow biofuel crops or to grow food crops displaced by biofuel crops can release more greenhouse gases than petroleum use.

Robert Socolow, a Princeton University professor of mechanical and aerospace engineering, says that through careful scientific reasoning the authors of the paper discovered accounting rules to determine which strategies for generating biofuels were promising and which were not.

“It is essential that legislation take the best science into account, even when that requires acknowledging and undoing earlier mistakes,” Socolow says. “Future carbon dioxide concentrations in the atmosphere will tell us when we’re kidding ourselves about what actually works. For carbon management, the atmosphere is the ultimate accountant.”

To balance biofuel production, food security, and emissions reduction, the authors conclude that the biofuels industry must focus on five major sources of renewable biomass, the raw materials used to generate biofuels:

• Perennial plants grown on degraded lands abandoned from agricultural use
• Crop residues
• Sustainably harvested wood and forest residues
• Double crops and mixed cropping systems
• Municipal and industrial wastes

These sources can provide considerable amounts of biomass, at least 500 million tons each year, which could produce enough fuel to meet a significant amount of the U.S. demand for transportation fuels without releasing substantial carbon dioxide through changes in land use, the authors conclude.

The researchers called for biofuels production to transition away from using food crops such as corn to generate fuels and toward the more sustainable sources they identified, which can be produced with much less impact on the environment.

Eric Larson, a researcher at Princeton Environmental Institute, says the new paper recognizes that converting farmland to grow a biofuel crop typically releases carbon dioxide into the atmosphere.

For instance, growing corn produces a significant amount of greenhouse gases through the use of fertilizers and tractor fuel, and processing corn into ethanol requires burning fuels for heat. Some of those emissions would be offset by the carbon the corn absorbs from the atmosphere as it grows, so there would still be some emissions benefit compared to using petroleum-based fuels.

However, forests in other countries probably would be cleared to grow food corn to replace corn from U.S. farms used for fuel, a so-called “indirect land use impact” of biofuels. The researchers calculated it could take up to a century or more for such a tradeoff to result in a net reduction of greenhouse gas emissions, because cutting down forests and tilling freshly cleared land releases greenhouse gases into the atmosphere.

“You have to consider the whole life cycle of producing biofuels and the repercussions of converting new land to biomass production,” says Robert Williams, a senior researcher at Princeton Environmental Institute. “In the petroleum industry they talk about the life cycle efficiency in terms of ‘well to wheels.’ Now we’re talking ‘field to wheels.’”

Princeton University news: www.princeton.edu/main/news