Congress instructed EPA to add power plants to the program if (but only if) the Agency finds regulation “appropriate and necessary.” §7412(n)(1)(A). One does not need to open up a dictionary in order to realize the capaciousness of this phrase. In particular, “appropriate” is “the classic broad and all-encompassing term that naturally and traditionally includes consideration of all the relevant factors.” 748 F. 3d, at 1266 (opinion of Kavanaugh, J.). Although this term leaves agencies with flexibility, an agency may not “entirely fai[l] to consider an important aspect of the problem” when deciding whether regulation is appropriate. State Farm, supra, at 43.Read naturally in the present context, the phrase “appropriate and necessary” requires at least some attention to cost. One would not say that it is even rational, never mind “appropriate,” to impose billions of dollars in economic costs in return for a few dollars in health or environmental benefits. In addition, “cost” includes more than the expense of complying with regulations; any disadvantage could be termed a cost. EPA’s interpretation precludes the Agency from considering any type of cost— including, for instance, harms that regulation might do to human health or the environment. The Government concedes that if the Agency were to find that emissions from power plants do damage to human health, but that the technologies needed to eliminate these emissions do even more damage to human health, it would still deem regulation appropriate. See Tr. of Oral Arg. 70. No regulation is “appropriate” if it does significantly more harm than good.
June 30, 2015 at 4:26 PM EDT