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Reality check: "If every one of the 70 million acres on which corn was grown in 2006 was used for ethanol, the amount produced would displace only 12 percent of the U.S. gasoline market. Moreover, the 'new' (non-fossil) energy gained would be very small -- just 2.4 percent of the market. Car tune-ups and proper tire air pressure would save more energy."
That's University of Minnesota researchers David Tilman and Jason Hill in the Washington Post. (Two days later a front-page feature in the Chicago Tribune omitted the big picture, covering only small-towners' questions about whether a new ethanol plant would make the place smell like beer.)
Their point, based on a decade of field research (abstract from Science) on various ways to produce ethanol, is that "renewable" isn't the same as "good." "Ethanol made from prairie grasses, from corn grown in Illinois and from sugar cane grown on newly cleared land in Brazil have radically different impacts on greenhouse gases."
Clearing land releases stored carbon, so that Brazilian sugar cane grown on cleared land releases about 50 percent more greenhouse gases than you'd get from producing and using an equal amount of gasoline.
Tilman and Hill aren't just criticizing. "We planted 172 plots in central Minnesota with various combinations of [native prairie] species, randomly chosen. We found, on this highly degraded land, that the plots planted with mixtures of many native prairie perennial species yielded 238 percent more bioenergy than those planted with a single species. ... little fertilizer or chemical weed or pest killers was required. ... [and the plants] removed carbon dioxide from the air. Much of this carbon ends up stored in the soil." These plants don't require land now used to grow food and fiber.
Unfortunately, there is no industrial-scale prairie-plant lobby to battle with the corn lobby for politicos' wallets and minds.