Int. J. Environ. Res. Public Health 2012, 9 2006 climate change, although EPA argued the Clean Air Act did not contemplate the regulation of substances that contribute to climate change ([62], p. 528). In many environmental statutes, Congress has given EPA undefined directives to do what is necessary to protect the public health, presumably to allow the statute to remain flexible over time so that the Agency could decide whether to restrict pollutants based on the latest scientific advancements affecting the EPA’s understanding of health effects ([62], p. 532). Indeed, in Massachusetts vs. EPA, the Supreme Court explained that although “the Congresses that drafted the [1970 Clean Air Act] might not have appreciated the possibility that burning fossil fuels could lead to global warming, they did understand that without regulatory flexibility, changing circumstances and scientific developments would soon render the Clean Air Act obsolete” ([62], p. 532). Therefore, although one could argue that a court should view the Federal environmental regulatory structure as forbidding EPA to consider cumulative effects of multiple pollutants under a statute that addressed only one medium or type of pollutant, one reading of Massachusetts vs. EPA is that Congress purposefully writes statutes broadly so that EPA can implement them more effectively over time. This reading lends support to the argument that EPA could interpret a broad statutory mandate to protect the public health as permitting it to consider cumulative risks, if the Agency reasonably determined that the consideration of such evidence was necessary to effectively carry out its statutory mandate ([62], pp. 529–532). A challenger also might cite North Carolina vs. EPA, to support an assertion that EPA was without authority to consider the results of a cumulative risk assessment [63]. In that case, the D.C. Circuit rejected EPA’s interpretations of its Clean Air Act authority, finding that the Agency went beyond its statutory authority when it established a regional interstate emissions trading program in an attempt to streamline separate Clean Air Act requirements ([63], pp. 907–922). Some might argue that the court’s analysis in North Carolina vs. EPA signals the D.C. Circuit’s hesitance to permit broad interpretations of the Clean Air Act and other statutes because the court interpreted the provision at issue so narrowly [64]. Others might argue that the North Carolina vs. EPA case implies the court’s willingness to check what might be seen as excessive EPA action, and to require Congressional action to significantly change existing programs. However, the EPA statutory interpretation under review in North Carolina vs. EPA was quite different from the statutory interpretations suggested in this article. In that case, the court vacated an EPA rule for many reasons, but most notably for this discussion, because the statutory provision at issue provided a very specific instruction rather than the broad statutory mandates to protect the public health we are addressing in this article. In pertinent part, the provision at issue said that each State Implementation Plan must ensure the prevention of “any…type of emissions activity” that “contributes significantly to nonattainment in, or interferes with maintenance by, any other State with respect to any [NAAQS]” [65]. This specific instruction contrasts with the broad statutory mandates to protect the public health we are addressing in this article, e.g., to establish standards “requisite to protect the public health” while “allowing an adequate margin of safety” (the NAAQS standard setting authority) [66]. Because these two grants of authority are distinguishable, North Carolina vs. EPA does not preclude the D.C. Circuit from upholding EPA’s interpretation of its authority to consider any information or analyses the Agency reasonably determines is necessary to decide the level at which standards are protective of the public health. In North Carolina vs. EPA, the D.C. Circuit also found that the rule at issue conflicted with the Clean Air Act provision that established a compliance deadline for certain NAAQS. Therefore, in