Researchers at the University of Minnesota have found that electric cars may not be as a good of a weapon for fighting global warming as we thought, and that they are actually making it worse.

The study focused on the source of the electricity produced for such vehicles, such as coal, which produces 3.6 times more soot and smog deaths than gas due to pollution coming from the act of generating electricity, according to the Associated Press.

Electric vehicles were found to be worse at heat-trapping carbon dioxide, which makes global warming worse, and ethanol was not as green of a source as people thought.

"It's kind of hard to beat gasoline," for public and environmental health, said Julian Marshall, engineering professor at the University of Minnesota and co-author of the study. "A lot of the technologies that we think of as being clean ... are not better than gasoline."

All electric vehicles were found to have caused 86 percent more deaths from air pollution than cars that were running on regular gasoline, and the Department of Energy said coal produces 39 percent of electricity in the U.S.

However, all-electric cars that run on natural gas produce half as many air pollution health problems as cars powered by gas, and those that run on wind, water or wave energy produce about one-quarter of the deaths from air pollution.

The Department of Energy said the states with the highest percentage of electricity coming from coal are West Virginia, Ohio, Illinois, North Dakota and Wyoming, the Associated Press reported.

The study says that while ethanol has a huge air pollution mortality, hybrid and diesel engines cause fewer air pollution deaths and release less heat-trapping gases, making them a cleaner alternative to gas.

"If we're using ethanol for environmental benefits, for air quality and climate change, we're going down the wrong path," said study co-author and fellow engineering professor, Jason Hill.

The results of the study were published Monday by the Proceedings of the National Academy of Sciences.