Biofuels are known as an environmentally friendly alternative to gasoline. But two recent studies call into question how green they really are.

According to one study published in the journal Nature Climate Change, fuels derived from corn stover -- or the leftover corn leaves and stalks following a harvest -- can actually emit more carbon dioxide than gasoline.

Researchers found that removing the corn scraps for fuel ended up releasing about 7% more carbon dioxide than regular gasoline over the short run.

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Over the long haul, biofuels are still better for the environment than gas, the report said. However, the study concluded that these kinds of biofuels should not qualify as renewable fuels as defined by the 2007 Energy Independence and Security Act.

In another strike against biofuels, a separate report from the Intergovernmental Panel on Climate Change found that some biofuels release indirect emissions -- including those from crops planted and harvested -- that can contribute to total emissions that are worse than those of gasoline or diesel fuels.

Those reports have amped up debate among environmentalists, lawmakers and the energy industry about the relative benefits of biofuels, which have received millions in federal funding.

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