The Obama administration last week gave the green light to corn ethanol as a low-carbon renewable fuel – in apparent contradiction to California's declaration last summer that the biofuel's carbon footprint was too big to help the state mitigate greenhouse gas emissions.
Regulators and policy experts insist there's no conflict: Both rules match the science; it's simply a matter of what year you start counting emissions.
Indeed, timing is everything: California looked at current emissions associated with corn-based ethanol and concluded they were too steep.
The White House, looking to triple annual production to 36 billion gallons a year in 12 years, based its decision on projections for 2022. It assumed higher crop yields, production efficiencies and other breakthroughs would mitigate emissions.
"There's not a conflict," said Stanley Young, a spokesman for the California Air Resources Board, the agency carrying out California's first-in-the-nation global warming initiative. "We use different methodologies."
"Plus we also indicate that there are several pathways to produce corn ethanol that have carbon intensities that come under our standard," he added. "Not all ethanols are created equal."
But the decision generated a bit of head-scratching – and some skepticism – among experts who question whether the administration took advantage of the wiggle room afforded by casting projections into the future to come to a politically expedient conclusion.
"It seems a little far-fetched at first glance," said Nathanael Greene, Natural Resources Defense Council's director of renewable energy policy. "You can kind of talk yourself into it, but in any case they make a lot of assumptions on what yield will look like, what the markets will look like."
"The result is that things look a lot better in that year (2022) than in California's estimates."
To meet the nation's renewable standard, a fuel's "life-cycle" carbon emissions must be at least 20 percent below that of gasoline. Calculating those costs is tricky. Fuel crops tend to displace food crops, resulting in a pulse of emissions as displaced farmers clear forests and cultivate previously undisturbed land to meet food demand.
Those emissions can be considerable. A paper published this week in the Proceedings of the National Academy of Sciences found that Brazil risks incurring a 250-year carbon debt based on the deforestation expected by 2020 as it expands production of sugarcane ethanol and soybean biodiesel.
Researchers are skeptical of federal claims that ethanol's advances would be sufficient enough to counter emissions associated with food-crop displacement.
"It's not consistent with what I have read in the peer-reviewed literature," said David Tilman, a University of Minnesota professor of ecology who has studied biofuels' conflict with food crops.
"You can make very optimistic projections about what yields may be in the future, but if you look at past yield trends, yield improvements even during the Green Revolution have not been enough to meet the demands we have coming in the future."