Biofuels made from the leftovers of harvested corn plants are worse than gasoline for global warming in the short term, a study shows, challenging the Obama administration's conclusions that they are a much cleaner oil alternative and will help combat climate change.

A $500,000 study paid for by the federal government and published Sunday in the peer-reviewed journal Nature Climate Change concludes that biofuels made with corn residue release 7% more greenhouse gases in the early years compared with conventional gasoline.

Biofuels are better in the long run, but the study says they won't meet a standard set in a 2007 energy law to qualify as renewable fuel.

The conclusions deal a blow to what are known as cellulosic biofuels, which have received more than a billion dollars in federal support but have struggled to meet volume targets mandated by law. About half of the initial market in cellulosics is expected to be derived from corn residue.

The biofuel industry and administration officials called the research flawed. They said that it was too simplistic in its analysis of carbon loss from soil, which can vary over a single field, and that it vastly overestimated how much residue farmers would remove once the market gets underway.