But according to a pair of studies published in the journal Science recently, biofuels may not fulfill that promise — and in fact, may be worse for the climate than the fossil fuels they're meant to supplement. According to researchers at Princeton University and the Nature Conservancy, almost all the biofuels used today cause more greenhouse gas emissions than conventional fuels, if the full environmental cost of producing them is factored in. As virgin land is converted for growing biofuels, carbon dioxide is released into the atmosphere; at the same time, biofuel crops themselves are much less effective at absorbing carbon than the natural forests or grasslands they may be replacing. "When land is converted from natural ecosystems it releases carbon," says Joseph Fargione, a lead author of one of the papers and a scientist at the Nature Conservancy. "Any climate change policy that doesn't take this fact into account doesn't work."
Many environmentalists have been making the case against biofuels for some time, arguing that biofuel production takes valuable agricultural land away from food, driving up the price of staple crops like corn. But the Science papers make a more sweeping argument. In their paper, Fargione's team calculated the "carbon debt" created by raising biofuel crops — the amount of carbon released in the process of converting natural landscapes into cropland. They found that corn ethanol produced in the U.S. had a carbon debt of 93 years, meaning it would take nearly a century for ethanol, which does produce fewer greenhouse gases when burned than fossil fuels, to make up for the carbon released in that initial landscape conversion. Palm tree biodiesel in Indonesia and Malaysia — one of the most controversial biofuels currently in use, because of its connection to tropical deforestation in those countries — has a carbon debt of 86 years. Soybean biodiesel in the Amazonian rainforest has a debt of 320 years. "People don't realize there is three times as much carbon in plants and soil than there is in the air," says Fargione. "Cut down forests, burn them, churn the soil, and you release all the carbon that's been stored."