For example, if farmers in Brazil burn and clear more rainforest to grow food because farmers in the U.S. are using their land to grow grain for fuel, that could mean a net increase in emissions of carbon dioxide, the main "greenhouse gas" linked to climate change.
The issue has been heating up for months in scientific, corporate and environmental circles. Now, the Environmental Protection Agency has indicated it plans to measure each biofuel's emissions based partly on the ripple effect that its production in the U.S. can have overseas, and is preparing to seek comments on a proposal. Some scientists, as well as General Motors Corp., DuPont Co., Archer-Daniels-Midland Co. and other companies with an interest in the outcome, are warning of a muddled calculus.
"If population grows in America and therefore ... we need to build a new Wal-Mart, are we going to debit that pregnant woman with the indirect life-cycle greenhouse-gas footprint of her decision to have that child?" says Michael Parr, a senior government affairs manager at DuPont.