Today's third opinion reverses a D.C. Circuit decision, and rules that the EPA interpreted its authorizing statute unreasonably when it concluded it need not consider costs in implementing environmental regulations concerning power plant pollutants, especially mercury. The usual suspects dissented, making it a 5-4 split. The case is captioned Michigan v. EPA but normally is referred to as "Utility Air." The EPA will still have discretion in how to consider costs; the Court ruled, for instance, that it need not conduct a formal cost/benefit analysis, whatever that means. We'll find out on remand, I guess.