For years, Alan Lloyd has regarded diesel as a dirty word, synonymous with brown haze and cancer-causing black soot, according to the Wall Street Journal. It's a view he has shared with environmental activists across the U.S. But in a striking change of heart that could alter the kinds of cars and trucks Americans drive, the chairman of the powerful California Air Resources Board (CARB) is taking a new look at diesel vehicles. According to the Journal, he thinks they're poised to emerge as part of the solution to a different environmental problem that's gaining more attention in the U.S.: global warming. Coming from the head of California's famously feisty clean-air agency, that amounts to environmental apostasy, according to the Journal. But now, Dr. Lloyd is being forced to address the issue of global warming, and here, diesel engines are the greener option because they don't pump out as much so-called greenhouse gas as gasoline engines do.