Cite as: 531 U. S. 457 (2001)
Opinion of Breyer, J.
consider such background circumstances when "decid[ing] what risks are acceptable in the world in which we live." Natural Resources Defense Council, Inc. v. EPA, 824 F. 2d 1146, 1165 (CADC 1987).
The statute also permits the Administrator to take account of comparative health risks. That is to say, she may consider whether a proposed rule promotes safety overall. A rule likely to cause more harm to health than it prevents is not a rule that is "requisite to protect the public health." For example, as the Court of Appeals held and the parties do not contest, the Administrator has the authority to determine to what extent possible health risks stemming from reductions in tropospheric ozone (which, it is claimed, helps prevent cataracts and skin cancer) should be taken into account in setting the ambient air quality standard for ozone. See 175 F. 3d, at 1050-1053 (remanding for the Administrator to make that determination).
The statute ultimately specifies that the standard set must be "requisite to protect the public health" "in the judgment of the Administrator," § 109(b)(1), 84 Stat. 1680 (emphasis added), a phrase that grants the Administrator considerable discretionary standard-setting authority.
The statute's words, then, authorize the Administrator to consider the severity of a pollutant's potential adverse health effects, the number of those likely to be affected, the distribution of the adverse effects, and the uncertainties surrounding each estimate. Cf. Sunstein, Is the Clean Air Act Unconstitutional?, 98 Mich. L. Rev. 303, 364 (1999). They permit the Administrator to take account of comparative health consequences. They allow her to take account of context when determining the acceptability of small risks to health. And they give her considerable discretion when she does so.
This discretion would seem sufficient to avoid the extreme results that some of the industry parties fear. After all, the EPA, in setting standards that "protect the public health"
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