Hear the word “biofuel,” and you probably think one of two things: restaurant grease (and cars that smell like french fries), or ethanol made from corn. But according to new research, the time may be right for a second-generation of biofuels, these ones made from grass. Not only could they reduce greenhouse gas emissions—they could make economic and ecological sense.
Though biofuels come in different forms, they serve two basic purposes. First, they tend to burn more cleanly than gasoline or diesel. Second, they’re renewable—in the case of ethanol, you just grow more corn. Yet they come with their own problems. Despite there being a black market for restaurant grease, biodiesel made from the stuff isn’t easy to come by. Ethanol has perhaps deeper issues to confront. Using corn to produce ethanol has driven up food prices in recent years, and converting forests and other areas into farmland to grow more corn for biofuels may well negate ethanol’s improved greenhouse gas emissions (GHG).
“Changing the mix of biofuel feedstocks from corn ethanol to high yielding perennial crops could meet the 32-billion-gallon mandate without significantly reducing food production.”
Fortunately, corn isn’t the only source of ethanol—in particular, there are perennial grasses like switchgrass and miscanthus. Those options reduce GHG emissions indirectly through their impacts on land use. Relative to corn, grasses require less fertilizer, less tilling (which helps release carbon stored in the soil into the air), and store more of their carbon underground. In fact, a number of studies have examined the ecological benefits or the economic impacts of growing grasses for biofuels, though the key word is “or.”
The aim of the new study, then, was to combine ecological and economic models into one, to get a better sense of the potential costs and benefits of grasses as biofuels. More specifically, researchers led by the University of Idaho’s Tara Hudiburg merged the DayCent ecological model with another, BEPAM, originally designed to study environmental and economic impacts of proposed biofuel policies, forming a combined model that simultaneously accounts for market forces, land use, transportation costs, and a variety of other factors. Ultimately, their aim was to assess the potential of grasses to reduce GHGs, they write in the journal Nature Energy.
The results are promising. Current policy, known as the Renewable Fuel Standard, calls for the production of 32 billion gallons of biofuels in 2022, half of which is meant to come from sources other than corn. The model predicts GHGs would decline by about seven percent, and tax credits for grass-based ethanol could push that number to about 12 percent. Importantly, land designated for growing grasses would come primarily from land used for grazing or land that’s not being used at all—in other words, food prices would be largely unaffected under both scenarios.
“In contrast to the recent assertion that biofuels rely on reduced food production to provide a GHG benefit, our integrated economic-ecosystem modeling approach predicts that changing the mix of biofuel feedstocks from corn ethanol to high yielding perennial crops could meet the 32-billion-gallon mandate without significantly reducing food production and with modest GHG savings,” the team writes.
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