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MICHIGAN v. EPA KAGAN, J., dissenting

reasoned determination that the benefits of the intended regulation justify its costs”). The reasonableness of the Agency’s decision to consider only the harms of emissions at the threshold stage must be evaluated in that broader context. And in thinking about that issue, it is well to remember the outcome here: a rule whose benefits exceed its costs by three to nine times. In making its “appropriate and necessary” finding, EPA had committed to assessing and mitigating costs throughout the rest of its rulemaking; if nothing else, the findings of the Agency’s cost-benefit analysis—making clear that the final emissions standards were cost-effective—show that EPA did just that. B Suppose you were in charge of designing a regulatory process. The subject matter—an industry’s emissions of hazardous material—was highly complex, involving multivarious factors demanding years of study. Would you necessarily try to do everything at once? Or might you try to break down this lengthy and complicated process into discrete stages? And might you consider different factors, in different ways, at each of those junctures? I think you might. You know that everything must get done in the end—every relevant factor considered. But you tend to think that “in the end” does not mean “in the beginning.” And you structure your rulemaking process accordingly, starting with a threshold determination that does not mirror your end-stage analysis. Would that be at least (which is all it must be) a “reasonable policy choice”? Chevron, 467 U. S., at 845. That is the question presented here, and it nearly answers itself. Setting emissions levels for hazardous air pollutants is necessarily a lengthy and complicated process, demanding analysis of many considerations over many years. Costs are a key factor in that process: As I