The ‘holy grail’ of biofuels now in sight
Long-promised cellulosic ethanol is in modest production, but hurdles remain.
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Larger climate impact must be weighed
By law, “advanced biofuels” like cellulosic ethanol must be certified by the Environmental Protection Agency (EPA) as producing at least 60 percent less greenhouse gas than gasoline does. Mr. Stowers and others are optimistic that that’s a slam-dunk.
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But what about the climatic impact of biofuels as the result of crop shifts and land-use change worldwide? What would be the impact if farmers plow under marginal grasslands and forests to grow switchgrass? How much agricultural waste can be collected from farm fields before the result is more erosion?
The land-use question over corn-based ethanol has fired debate since last summer, when one study found diversion of US corn production for fuel had cut US corn exports. That, in turn, caused developing nations to plant more corn, a shift that may have negated the advantage of corn ethanol over gasoline in terms of its overall impact on global warming.
Now the same debate is likely to erupt for cellulosic ethanol, not only for its potential effect on food prices but also its net impact on climate.
Food crops vs. fuel crops
“One of the points often made in favor of cellulosic ethanols,” says Lester Brown, president of the Earth Policy Institute, an environmental activist group, “is that the feedstocks for it, like switchgrass, would be grown on marginal land. But if it is that profitable on marginal land, imagine how profitable it would be on prime crop land. There’s nothing to stop it from happening.”
The EPA, charged with evaluating the carbon footprint of cellulosic ethanol to determine if it meets the 60 percent threshold, has done a preliminary land-use impact evaluation. But those tentative results haven’t been released because the methodology is being refined, experts say.
“Indirect land-use impacts is a new analysis area that’s very tough, from a modeling and data point of view,” says Wallace Tyner, professor of agricultural economics at Purdue University in West Lafayette, Ind. “But we’re making progress. Within the next year we are going to narrow the bounds considerably.”
Getting ethanol feedstock right is key
All of this leaves NRDC’s Greene wanting government to take a slower, closer look at potential cellulosic feedstocks like switchgrass, miscanthus, poplar, and other crops in order to get federal policy toward cellulosic right from the start.
“The refining technology is obviously a challenge that will succumb to American innovation,” he says. “But getting the feedstock right is key. If we mow down corn to put in switchgrass, well, you’ve got that food versus fuel trade-off again.”
Harvesting agriculture “wastes” for biofuels also raises critical questions and needs closer analysis. POET, for instance, gets high marks from Greene for its careful evaluation of the impact of removing corn cobs from farm fields, which the company and others say appears to deduct only about 2 to 3 percent of the nutrients.
Even so, it turns out most corn stover – which is everything but the corn kernel (stalk, leaves, and cobs) – is badly needed for soil enrichment and to prevent erosion.
Crop waste helps fields, too
“A portion of the [corn] stover can be made available as feedstock for bioenergy purposes,” say Douglas Karlen, research leader for soil and water quality at the National Soil Tilth Laboratory in Ames, Iowa.
Harvesters would have to be outfitted with software to gauge exactly how much corn stover was taken from the field, he says.
“There’s not a blanket or uniform amount,” Dr. Karlen says. “It has to vary not only by farm, but within an individual field. The amount taken has to vary because the land varies.”