By Deborah Zabarenko, Environment Correspondent
These so-called food-based biofuels can actually hurt the environment if they are produced on land that was formerly grassland, rainforest or savanna, the scientists said in the journal Science.
However, biofuels can release carbon even before they are burned, depending on how they are made, said study co-author Jason Hill of the University of Minnesota.
Biofuels grown this way come with a "carbon debt," the researchers found. Instead of cutting greenhouse pollution, the net effect is to increase it.
CENTURIES OF CARBON DEBT
The next worst case was the planting of soybeans in the Amazon, which would not pay for itself in renewable soy biodiesel for 319 years.
"Our group has looked at using diverse mixtures of native species ... (on) prairie land, land that's restored back into prairies," Hill said in a telephone interview. "We essentially have no native prairies left in this nation but we can restore land into prairies, thereby restoring an ecosystem that was natural and also getting the biofuel benefit from it."
"If we take every corn kernel we produce in this nation and convert it to ethanol, we would offset only 12 percent of our gasoline use," he said. "And that doesn't include the energy it took to produce that ethanol in the first place.
(Editing by Xavier Briand)