DENVER — On Thursday, the U.S. Supreme Court handed down a ruling that significantly limits the Environmental Protection Agency’s ability to regulate greenhouse gas emissions from power plants.Justices ruled 6-3 that the Clean Air Act does not give the agency broad regulatory powers for reducing emissions. Instead, the majority opinion said Congress must specifically authorize agencies to make these types of rulings that are considered transformational to the economy.’In some ways, they are turning to Congress to be more active, despite the fact that everybody knows Congress is not really capable of doing that,’ said Jonathan Skinner-Thompson, a law professor at the University of Colorado in Boulder.