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U.S. Supreme Court Finds Carbon Dioxide and Other Greenhouse Gases Are Clean Air Act Pollutants


By Larry Kane, Attorney, Bingham Greenebaum Doll LLP

In a decision with potentially profound ramifications, the U.S. Supreme Court has held that carbon dioxide and other “greenhouse gases” are air pollutants under the federal Clean Air Act (CAA). Though arising in the somewhat narrow context of motor vehicle emissions, the decision in Massachusetts v. Environmental Protection Agency, 549 U.S. ____ (2007), announced on April 2, 2007, that greenhouse gases are indeed air pollutants for purposes of the CAA is not necessarily limited to that context.

At issue in the case was EPA’s denial of a petition filed with the agency in 1999 by 19 environmental advocacy organizations for the conducting of rulemaking to adopt standards for regulation of greenhouse gas emissions from new motor vehicles under § 202(a)(1) of the CAA. Nearly four years later, after taking extensive public comment and requesting scientific input from the National Research Council, EPA denied the petition on the grounds that the CAA does not authorize EPA to adopt regulations concerning global climate change and, even if such authority was conferred upon the agency, it would not be wise to undertake such regulation at this time. A challenge to EPA’s decision by several of the environmental organizations and 17 states and local governments was rejected by the U.S. Court of Appeals for the District of Columbia. In a rare move, the Supreme Court noted that it was undertaking review of the case due to the unusual importance of the underlying substantive issue, even though no conflict existed among lower appellate courts.

Roughly a third of the Court’s opinion is invested in an explanation of why the State of Massachusetts had standing to petition EPA for a rulemaking under CAA § 202(a)(1), notwithstanding EPA’s contentions to the contrary. We will omit consideration of this threshold issue to focus on the Court’s reasoning on the merits of the controversy.

The Court gave short shrift to the merits of EPA’s justifications for denial of the petition for rulemaking. The first question considered was whether EPA is authorized under § 202(a)(1) of the CAA to regulate greenhouse gases from new motor vehicles if it were to form a “judgment” that such emissions contribute to climate change. This statutory provision mandates that EPA “shall by regulation prescribe . . . standards applicable to the emission of any air pollutant from any class . . . of new motor vehicles . . . which in [EPA’s] judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” EPA’s contention that carbon dioxide is not an air pollutant within the meaning of § 202(a)(1) was summarily rejected in view of the CAA’s unambiguous and “sweeping definition” of “air pollutant”, 42 U.S.C. § 7602(g), which includes “any air pollution agent . . ., including any physical, chemical . . . substance or matter which is emitted into or otherwise enters the ambient air . . .” Because greenhouse gases, such as carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons, are indisputably “physical [and] chemical substance[s] which [are] emitted into . . . the ambient air”, the Court found such gases to “fit well within the Clean Air Act’s capacious definition of `air pollutant’” and held that EPA has the statutory authority to regulate the emission of such gases from new motor vehicles. In reaching this holding, the Court dispatched several broad policy arguments raised by EPA that had no relation to the statutory interpretation question at issue.

The second question on the merits addressed by the Court was EPA’s alternative contention that, even if it does have statutory authority to regulate greenhouse gases, “it would be unwise to do so” at the present. This contention was found to be “divorced from the statutory text”, which directs EPA to adopt standards to regulate an air pollutant, such as carbon dioxide, emitted from new motor vehicles if EPA forms a judgment that such emissions contribute to global climate change and thus endanger public welfare. In the face of such a statutory directive, EPA could avoid taking action to regulate the greenhouse gas emissions from new motor vehicles only if EPA were to reach a judgment that such emissions do not contribute to climate change or if the agency were to provide a reasonable explanation for why it cannot undertake a determination as to the effects of such greenhouse gas emissions on climate change.

Though petitioned to do so, EPA had refused to broach the determination of whether greenhouse gas emissions from new motor vehicles would contribute to climate change, having offered instead a variety of policy reasons why regulating greenhouse gas emissions was not the preferable course at this time. Such policy reasons included the propositions that the proposed regulation: (i) was unnecessary in view of various voluntary programs of the Executive Branch to respond to climate change; (ii) would hamper the President’s ability to negotiate effectively with developing nations on emission reductions; and (iii) would constitute an inefficient, piecemeal approach to addressing climate change. Because these policy reasons bore no relation to the statutorily prescribed determination on the effects of greenhouse gas emissions on climate change nor provided a reasoned justification for avoiding the making of that determination, and because EPA had not contended that scientific uncertainty on the effects of greenhouse gas emissions on climate was so great that it precluded the making of an informed judgment on those emission impacts, the Court concluded that EPA’s refusal to undertake the determination was arbitrary, capricious and contrary to law. As a result, the Court remanded the case to the Court of Appeals, holding that EPA must base its reasons for action or inaction on regulation of motor vehicle emissions of greenhouse gases pursuant to the CAA provision at issue.

Summing up, the Supreme Court has firmly concluded that greenhouse gases, such as carbon dioxide, are air pollutants under the CAA. EPA, as a result, will be required to confront the question of whether regulation of emissions of those gases from new motor vehicles is warranted under § 202(a)(1). Still unexplored are what effect the identification of greenhouse gases as air pollutants may have on other substantive provisions of the Clean Air Act. Another question may be what effect, if any, this decision will indirectly have on Congress’s consideration of the plethora of legislative proposals for various measures to address climate change.


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