A coalition of industry and conservative plaintiffs have sued in the D.C. Circuit US Court of Appeals to overturn EPA's "endangerment finding" that carbon dioxide and other greenhouse gases endanger public health and the environment for purposes of regulating motor vehicle emissions of those pollutants under the Clean Air Act. The oral arguments began yesterday and were scheduled to conclude today. From various news reports (e.g., here and here), the outcome sounds like a foregone conclusion, as it should be under conventional standards of judicial deference to decisions dedicated to agency discretion. The plaintiffs, it seems, wanted to put on trial climate science, arguing that too much uncertainty remains to permit EPA to determine that emissions of greenhouse gases pose any real danger to public health and the environment. But the only way the DC Circuit would overturn EPA's determination of endangerment is on a finding that EPA acted arbitrarily or capriciously. The evidentiary record supporting EPA's endangernment finding is much too strong for any court to conclude that EPA's decision was arbitrary or capricious.
Other, related EPA greenhouse gas rules are also being reviewed in this consolidated case. It is possible that the DC Circuit will uphold all of them. I think it pretty likely, however, that the court will overturn one (and only one) of the rules: EPA's "tailoring rule," which represents the agency's best (and truly well-meaning) effort to fit the square peg of carbon dioxide into the round hole of the Clean Air Act's regulatory scheme for major new stationary sources. Applying the literal terms of the statute to greenhouse gases would simply bring too many sources, including very minor ones, within the regulatory ambit, leading to enormous compliance and administrative costs. The "tailoring rule" is designed to avoid that outcome by limiting the number of sources subject to regulation. However, EPA's laudable effort requires deviation from the precise terms of the statute, which the reviewing court might not appreciate (and for good reason).