A new study finds that biofuels—which are derived from plants like corn or soybeans and sometimes considered to be carbon-neutral—may actually be worse for the climate than gas.

University of Michigan (UM) Energy Institute research professor John DeCicco analyzed all the greenhouse gas emissions created in the supply chains of various fuel types. For gas, that meant starting with extraction and transportation, among other parts of the process; for biofuels, it was farming and fertilizer use, but not tailpipe pollution, due to the presumed carbon dioxide offset, the Detroit Free Press explains.

The Free Press reports:

Using U.S. Department of Agriculture cropland production data, determining the chemical composition of crops and accounting for all of the carbon from the plants, DeCicco created a "harvest carbon" factor. Over the past decade, as the consumption of corn ethanol and biodiesel more than tripled in the U.S., the increased carbon uptake by the crops only offset 37 percent of carbon dioxide emissions from biofuel combustion, DeCicco said.

Mathematically speaking, "When it comes to the emissions that cause global warming, it turns out that biofuels are worse than gasoline," he said.

By casting doubts on the efficacy of biofuels, the study has brought on some harsh critiques from those who believe they will help transition to a low-carbon world. Some critics pointed out that the study was funded by the American Petroleum Institute (API), which has a "vested interest" in the failure of the biofuel industry, the Free Press notes.

But the plant-based energy source has come under fire before. A study published last year by the World Resources Institute found that dedicating crops and farmland to the creation of bioenergy "will undercut efforts to combat climate change and to achieve a sustainable food future."

Andrew Steer, president of the World Resources Institute, told the New York Times at the study's publication that "many of the claims for biofuels have been dramatically exaggerated. There are other, more effective routes to get to a low-carbon world."

Timothy Searchinger, a Princeton researcher and biofuel critic, told Climate Central on Thursday that the UM study provides "additional calculation" for the argument that the energy is not, in fact, carbon-neutral.

"The U.S. is not coming close to offsetting the carbon released by burning biofuels through additional crop growth," Searchinger said.