Much of this confusion could be eliminated with a biofuels rating system that would reflect the positive or negative environmental impacts of a particular fuel, according to a group of University of California, Berkeley, researchers.

A ratings system, like the Michelin stars for hotels and restaurants, would take into account all environmental aspects of biofuels processing and production, from the way biofuel crops are tilled and fertilized to the kinds of energy -- coal, natural gas or biomass, for example -- used to process them.

Such a system would not only help consumers make decisions about where to fuel up but, perhaps more importantly, stimulate competition among fuel producers to market the greenest fuels possible, driving the less-green biofuels out of the marketplace in favor of ones that really serve the planet.

"We think it's feasible to design a workable and effective ratings system for green biofuels today with the types of information that many farmers and many biofuel production facilities already collect," said study co-author Alex Farrell, assistant professor of energy and resources and director of the campus's Transportation Sustainability Research Center. "The American biofuels industry can produce much greener biofuels than they do today, and I think they can do so at reasonable prices and at a profit."

Such a labeling system would reveal, for example, that a fuel such as ethanol varies widely in its environmental merit depending on its production history, according to co-author Michael O'Hare, UC Berkeley professor of public policy. Some ethanol in current use is not much better, or is even worse, for the environment than gasoline, while other ethanol is beneficial.

Farrell, O'Hare and colleagues in UC Berkeley's Energy and Resources Group and in the Goldman School of Public Policy recently disseminated a research report on the issue in hopes of stimulating discussion around the nation on how best to formulate such a labeling system.

Called "Creating Markets for Green Biofuels: Measuring and Improving Environmental Performance," the study was partially supported by the Natural Resources Defense Council and the National Science Foundation's Climate Decision Making Center at Carnegie Mellon University.

"Biofuels link markets in fuel, food and land in quite complicated ways, and there are no rules about how to judge the environmental and global warming impacts of producing and processing these fuels," said Farrell, who was appointed this week to an international roundtable to draft global standards for sustainable biofuels production and processing. "As these technologies get better and cheaper, there will be competition for use of land, whether for food or wilderness. This is inherently a problem of biofuels. A discussion of biofuel labeling could help the domestic debate about how to develop biofuels."

The report lays out a range of possible options for a Green Biofuels Index, from voluntary labeling akin to the "organic" food label, to mandatory labeling like today's nutrition information, to more stringent government regulations like those required by renewable portfolio standards, which mandate that a state generate a percentage of its electricity from renewable sources.

While Farrell thinks a star system, like the Michelin stars, would be more flexible than a gold-silver-bronze medal system, he stressed that any system could take into account the issues consumers seem most concerned about.

"I think people understand that energy is a product that has lots of environmental implications, and if they had the choice to know what was good or bad, I bet they would like to know that," said Farrell. "It's quite likely that, even if it were required as part of regulation, fuel makers and distributors could develop their own brand and their own marketing strategies around how green their fuel is, using the type of information this will provide."

Today, consumers in the United States have only a few biofuel choices: E85 ethanol, 95 percent of which comes from corn; biodiesel, which comes primarily from soybeans but also from canola and sunflower oils and waste cooking oil or grease; and what's called renewable diesel, which is made from biomass injected into the petroleum diesel process. But Farrell predicts that other fuels will soon reach the market, including biobutanol and synthetic diesel, which is made entirely from biomass.

New research, such as that planned by the Energy Biosciences Institute soon to be established at UC Berkeley and Lawrence Berkeley National Laboratory with $500 million in funding from BP, could produce much greener biofuels, Farrell noted.

If biofuels with the same chemical identity can be distinguished by a rating system such as the authors propose, "markets for green biofuels would stimulate a new wave of innovation, creating high-value and truly green biofuels, and enhancing energy security by diversifying our energy sources," they wrote.

The UC Berkeley group urges environmental, agricultural and regulatory agencies to join forces with local, state and national governments to develop this Green Biofuels Index, and that funding agencies should research ways to measure the environmental performance of biofuels, such as their impacts on global warming or farmland.

Robert Sanders is manager of science communications for the UC Berkeley News Center, and covers science, environment, health and technology issues.