Corn-based ethanol has suffered a few whacks in recent months. First, new studies suggested that when you took indirect land-use effects into account, corn-based ethanol could produce more greenhouse-gas emissions than gasoline. (That is, when American farmers start planting corn for fuel instead of food, that drives up food prices, which spurs farmers abroad to cut down forests to grow their own corn.) Next, the Obama administration proposed new rules regulating ethanol emissions that were stringent enough to elicit snarls of outrage from Collin Peterson, chairman of the House agricultural committee. Plus, as Tom Lawasky reports, there's growing resistance to a potential EPA rule that would increase the amount of ethanol used in blended gasoline.

Now here comes another whack. Last week, Science published a new study showing that if you want to use corn or other crops to power your car, it's far, far more efficient—and eco-friendly—to burn them as biomass to produce electricity for battery-powered cars, rather than converting the crops into ethanol. How much better depends on various factors, but as an example, an acre of switchgrass could generate enough electricity to power a small, battery-powered SUV 14,000 miles on the highway, but it would produce only enough ethanol to drive a comparable internal combustion engine 9,000 highway miles.

Why is that? "The internal combustion engine just isn't very efficient, especially when compared to electric vehicles," said lead author Elliott Campbell of the University of California, Merced. "Even the best ethanol-producing technologies with hybrid vehicles aren't enough to overcome this." And depending on the fuels compared, the biomass approach saves twice as much carbon-dioxide as ethanol does. As Tom Philpott says, maybe this could persuade policymakers to reconsider the $420 billion (!) in subsidies we're scheduled to pitchfork over to the biofuels industry between now and 2022.

Granted, using biomass wouldn't eliminate all the problems associated with biofuels. If the crops grown for biomass displaced food crops, that could still indirectly increase deforestation, even though the overall process might be cleaner than ethanol. (And wouldn't it be better still to just generate the electricity for plug-in cars with, say, wind power?) But biomass advocates counter that you could plant material like switchgrass on non-cropland—and in theory you could even use the whole biomass process to remove carbon from the air. Matt Wald of The New York Times explains:

If one grows a tree or annual crop, for example, which pulls carbon dioxide out of the air, burns it in a power plant that captures and stores escaping CO2, and then replaces it with another crop, which pulls yet more carbon dioxide out of the air, the process becomes carbon negative.

That's certainly intriguing, especially since we're almost certainly going to need ways to remove carbon from the air if we want to stabilize atmospheric carbon levels below 450 ppm (we're at 386 ppm now and fast rising). The downside is that, as with carbon sequestration for coal-fired plants, this sort of carbon-capture technology isn't commercially ready yet, and could prove pricey. Still, it bears a closer look—especially since the corn lobby isn't going away anytime soon and is dead set on finding some way to grow crops for fuel.

(Flickr photo credit: Melissa Maples)

--Bradford Plumer