The majority also uncritically accepted the linchpin of plaintiffs’ argument—the claim that CO2 is an “air pollutant” within the meaning of the Clean Air Act. Grant that premise, and EPA’s authority to regulate CO2 from vehicles seems to follow, because EPA obviously has authority to regulate air pollutants.
The provision defining “air pollutant” in the Clean Air Act—Section 302(g)—is only two sentences long. Here it is, in full:
The term “air pollutant” means any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive (including source material, special nuclear material, and by-product material) substance or matter which is emitted into or otherwise enters the ambient air. Such term includes any precursors to the formation of any air pollutant, to the extent that the Administrator has identified such precursor or precursors for the particular purpose for which the term “air pollutant” is used.
To accept plaintiffs’ claim that CO2 is an “air pollutant,” the majority had to ignore part of the first sentence and the entire second sentence.
Plaintiffs argued that the term “air pollutant” includes any “substance or matter which is emitted into or otherwise enters the ambient air,” and since CO2 is emitted, EPA may regulate it. Notice, however, that the first sentence does not make “air pollutant” co-extensive with anything and everything emitted into or entering the air. Rather, it says that any “air pollution agent” emitted into or entering the air is an air pollutant. The text does not define “air pollution agent,” but that’s because it does not have to. An air pollution agent is obviously something that causes air pollution. It is something that dirties or fouls the air—something that degrades air quality. Carbon dioxide does not fit that description. A clear, odorless gas, CO2 is non-toxic to humans and other animals at 20 times ambient levels, and the ongoing rise in the air’s CO2 content helps most crops, trees, and other plants grow bigger, produce more fruit, and utilize water more efficiently.
The majority erred in reading the term “air pollution agent” as a synonym for “air pollutant” rather than as a criterion for distinguishing air pollutants from non-pollutants. The effect is to make the first sentence of Section 302(g) hopelessly circular (an “air pollutant” is an “air pollutant”), with the bizarre result that oxygen, water vapor, and even—as Justice Scalia noted—frisbies become “air pollutants.”
The second sentence of 302(g) says that precursors of substances previously designated by EPA as air pollutants are also air pollutants. There would have been no reason for Congress to include this sentence if, as the majority opined, anything emitted into or entering the air is ipso facto an “air pollutant.”
Several other considerations also compel the conclusion that the Clean Air Act does not authorize EPA to administer regulatory climate policies. Most obviously, there is no climate protection title, section, or sub-section in the Clean Air Act. In fact, the terms “greenhouse gas” and “greenhouse effect” do not even appear in the Act. The terms “carbon dioxide” and “global warming” do appear, but only once, in the context of non-regulatory provisions—Sections 103(g) and 602(e). Significantly, those provisions conclude by admonishing EPA not to infer authority for “pollution control requirements” or “additional regulation.” Such caveats would be pointless if, as the majority assumed, the Act’s most general provision—the definition of “air pollutant”—already gave EPA regulatory authority over greenhouse gases.