As soon as a report assessing the economic and environmental impacts of the federal Renewable Fuels Standard (RFS) was issued by the National Research Council (NRC), many questions about the validity of the report's assumptions and the currency of its data began circulating. Everyone from Agriculture Secretary Tom Vilsack to biofuel industry leaders to advocacy groups cast doubts on the congressionally-mandated study. Vilsack said the report bases its conclusions "on information that's not as accurate as it once was." Even the NRC study co-chairs acknowledge in the preface that, "our clearest conclusion is that there is very high uncertainty in the impacts we were trying to estimate. "

Another figure who brings significant credentials to this debate is Dr. Virginia Dale, the director of the Center for BioEnergy Sustainability at DOE's Oak Ridge National Laboratory and one of 16 experts on the NRC committee that crafted the report. Dale acknowledges that, like most NRC reports, the RFS study represented a compromise among the largely academic committee members, including her. But she also says there is a paucity of data on the subject, requiring the committee members to largely base their report on model projections.

Dale goes on to point out that with any scientific process, it is difficult to reach a conclusion when (a) the data are inadequate, (b) some models are applied at scales inappropriate to the situation, or (c) key processes are not included in the theories. All of these limitations, she says, are applicable to current analyses of the effects of biofuels.

Biofuels have the potential for environmental and national security benefits compared to petroleum use. But Dale acknowledges that the outcome depends on many factors, including feedstock, management practices, possible land-use changes and water availability - all variables that are site-specific and continually change with technological advancements and innovation within the industry.

And because of that variability, she said parts of the report can be misleading "if the assumptions of the analysis are not considered appropriately. Strictly speaking, this report is not a conclusion and should not be read as such but rather a report on work in progress," she adds.

She cautions policy makers - all readers, in fact - to read the report details with care, noting that the assumptions, scales and caveats of analyses and results are critical to the interpretation and any extrapolation of the results.

Dale says model projections are not to be "believed" so much as treated as potential futures implied from a set of specified scenarios and assumptions. The environmental researcher says that while models can enhance understanding, they must be validated by empirical information. And so far, she asserts, the empirical evidence provides little, if any, support for modeled projections of land-use change.