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."

Recent evidence out of Brazil buttresses that point. A team of researchers headed by David Lapola of the University of Kassel in Germany found that 90 percent of Brazil's sugarcane expansion in the last five years displaced cattle rangeland, forcing ranchers to push into the forest. Lapola's team concluded Brazil's plan to expand biofuel cropland over the next decade will push displaced rangeland into more than 47,000 square miles of forest and another 17,760 square miles of other native habitat.

That's a patch of land equal to New York and New Jersey combined.

"It seems like for the U.S. corn ethanol, there would be a lot of friction with food crops and (indirect land-use changes) not only inside the U.S. but abroad, too," Lapola said via email from Germany.

The Obama Administration insists it used the most recent, accurate science. Briefing reporters as the change was unveiled last week, Agriculture Secretary Tom Vilsack noted the science of crop productivity "is constantly evolving."

EPA Administrator Lisa Jackson stood by her agency's scientists amid charges that the agency bowed to pressure from the farm lobby. "I don't agree that we changed the science to fit any outcome," she said. "I would not sign a rule if I didn't believe we had met the requirements of the law."

But in some ways the carbon savings from corn ethanol might be a secondary – or even moot – point.

Announcing the change, the administration highlighted biofuels' potential to create jobs and offer energy independence. President Obama, speaking to governors about the policy shift last week, mentioned climate change once: "Even if you don't believe in the severity of climate change, as I do, you still should want to pursue this agenda."

Plus the administration – and many in the ethanol industry – views corn ethanol as a bridge to less carbon-intensive biofuels. "We believe that's where the market is going," Vilsack said.

But the push to develop corn ethanol has a cost, and NRDC's Greene wonders if that's the wisest policy choice. "It's folly to do what we're doing today, which is mandating it, giving it multiple tax credits and still throwing other government subsidies at it," he said.

"We're bribing the market.... That's $5 billion a year that we could be using to help our farmers and help our industry get to the next generation of this stuff."

Lapola, looking at Brazil, notes some biofuels don't have the huge carbon footprint of sugarcane, soybean or corn. But so long as governments keep a sharp eye on land-use changes, he thinks biofuels make a good "workaround" for petroleum fuels.

"A workaround, but not a complete solution," he added. "The point is that from now on we need to evaluate more carefully our energy matrix to not incur in the same mistakes we made with petroleum."

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.