Case Scenario: Citing evidence of global warming and asserting contributions to this warming from automobile pollution, various private organizations petitioned the Environmental Protection Agency to regulate motor vehicle emissions under its Clean Air Act authority. When the EPA refused, stating that it had no authority to address the causes of global warming, Massachusetts joined the organizations in suing to force the EPA to exercise its authority, asserting that global warming would affect its coastline through rising sea levels and injure its citizens. The case reached the Supreme Court on the issues of whether the EPA had authority under the Clean Air Act to regulate greenhouse gases, especially carbon dioxide, as they allegedly cause global warming, and of whether the EPA could refuse to exercise its authority. STEVENS, J.: A well-documented rise in global temperatures has coincided with a significant increase in the concentration of carbon dioxide in the atmosphere. Respected scientists believe the two trends are related. For when carbon dioxide is released into the atmosphere, it acts like the ceiling of a greenhouse, trapping solar energy and retarding the escape of reflected heat. It is therefore a species-the most important species of a "greenhouse gas." In concluding that it lacked statutory authority over greenhouse gases, EPA observed that Congress "was aware of the global climate change issue when it last comprehensively amended the [Clean Air Act] in 1990 " yet it declined to adopt a proposed amendment establishing binding emissions limitations. Congress instead chose to authorize further investigation into climate change.
Having reached that conclusion, EPA believed it followed that greenhouse gases cannot be "air pollutants" within the meaning of the Act. EPA also maintained that its decision not to regulate greenhouse gas emissions from new motor b b vehicles contributes so insignificantly to petitioners' injuries that the agency cannot be hailed into federal court to answer for them. But EPA overstates its case. Reducing domestic automobile emissions is hardly a tentative step. Even leaving aside the other greenhouse gases, the United States transportation sector emits an enormous quantity of carbon dioxide into the atmosphere, more than 1. 7 billion metric tons in 1999 alone. That accounts for more than 6% of worldwide carbon dioxide emissions. Judged by any standard, U.S. motor-vehicle emissions make a meaningful contribution to greenhouse gas concentrations and, hence, to global warming. The Clean Air Act's sweeping definition of "air pollutant" includes any air pollution agent or combination of such agents, including any physical, chemical substance or matter which is emitted into or otherwise enters the ambient air. On its face, the definition embraces all airborne compounds of whatever stripe, and underscores that intent through the repeated use of the word "any." Carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons are without a doubt "physical [and] chemical substances which are emitted into the ambient air."
The statute is unambiguous. The alternative basis for EPA's decision-that even if it does have statutory authority to regulate greenhouse gases, it would be unwise to do so at this time-rests on reasoning divorced from the statutory text. Once EPA has responded to a petition for rulemaking, its reasons for action or in action must conform to the authorizing statute. Under the clear terms of the Clean Air Act, EPA can avoid taking further action only if it determines that greenhouse gases do not contribute to climate change or if it provides some reasonable explanation as to why it cannot or will not exercise its discretion to determine whether they do. Nor can EPA avoid its statutory obligation by noting the uncertainty surrounding various features of climate change and concluding that it would therefore be better not to regulate at this time. If the scientific uncertainty is so profound that it precludes EPA from making a reasoned judgment as to whether greenhouse gases contribute to global warming, EPA must say so. In short, EPA has offered no reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change. Its action was therefore "arbitrary, capricious, ... or otherwise not in accordance with law." We need not and do not reach the question whether EPA must make an endangerment finding, or whether policy concerns can inform EPA's actions in the event that it makes such a finding. We hold only that EPA must ground its reasons for action or in action in the statute.
1. Why did Massachusetts and the organizations want the EPA to regulate new vehicle emissions under the Clean Air Act?
2. What two arguments did the EPA offer in refusing to regulate these emissions?
3. How does the Supreme Court respond to the EPA' s two arguments?
4. Does the Supreme Court require the EPA to limit new vehicle emissions of carbon dioxide? Explain.