Years of number crunching that had seemed to corroborate the climate benefits of American biofuels were starkly challenged in a science journal on Thursday, with a team of scientists using a new approach to conclude that the climate would be better off without them.

Based largely on comparisons of tailpipe pollution and crop growth linked to biofuels, University of Michigan Energy Institute scientists estimated that powering an American vehicle with ethanol made from corn would have caused more carbon pollution than using gasoline during the eight years studied.

Corn is the main crop used in the U.S. to produ