In short, some organization would consider how the fuel was made (energy used to produce it, the type of biomass, etc.) and apply a rating based on how green it is. That's an awful bold idea, and a good one. I can't think of any easy way to implement it, but here's how one of the researchers says it could happen:
"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. 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," said Alex Farrell, assistant professor of energy and resources and director of the campus's Transportation Sustainability Research Center, according to Renewable Energy Today. He continues:
"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. 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."
You can read an abstract or download the paper here.
[Source: Robert Sanders / Renewable Energy Access]