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MICHIGAN v. EPA KAGAN, J., dissenting

must divide sources into categories and subcategories and then set “floor standards” that reflect the average emissions level already achieved by the best-performing 12% of sources within each group. See §7412(d)(3); ante, at 3. Every 12% floor has cost concerns built right into it because the top sources, as successful actors in a market economy, have had to consider costs in choosing their own emissions levels. Moreover, in establishing categories and subcategories at this first stage, EPA can (significantly) raise or lower the costs of regulation for each source, because different classification schemes will alter the group—and so the emissions level—that the source has to match.1 Once the floor is set, EPA has to decide whether to impose any stricter (“beyond-the-floor”) standards, “taking into consideration,” among other things, “the cost of achieving such emissions reduction.” §7412(d)(2); see ante, at 3. Finally, by virtue of a longstanding Executive Order applying to significant rules issued under the Clean Air Act (as well as other statutes), the Agency must systematically assess the regulation’s costs and benefits. See Exec. Order No. 12866, 58 Fed. Reg. 51735, 51738, 51741 (1993) (applying to all rules with an annual economic effect of at least $100 million). Congress modified that regulatory scheme for power plants. It did so because the 1990 amendments established a separate program to control power plant emissions contributing to acid rain, and many thought that just by complying with those requirements, plants might —————— 1 Consider

it this way: Floor standards equal the top 12% of something, but until you know the something, you can’t know what it will take to attain that level. To take a prosaic example, the strongest 12% of NFL players can lift a lot more weight than the strongest 12% of human beings generally. To match the former, you will have to spend many more hours in the gym than to match the latter—and you will probably still come up short. So everything depends on the comparison group.