The immediate policy question raised in Mass v EPA is whether EPA must regulate vehicular GHG emissions under Section 202 of the Clean Air Act. Plaintiffs argued in the affirmative, but legislative and regulatory history suggests otherwise. A central purpose of Section 202 since it was enacted in 1970 and amended in 1977 has been to ensure that automobile engines become so clean burning that, ultimately, nothing comes out of the tailpipe except two greenhouse gases: water vapor and CO₂ [see 40 C.F.R. § 85.2122(a)(15)(ii)(A)]. Catalytic converters and oxygenate fuel additives—required by Congress and EPA regulation for decades—increase GHG emissions from automobiles. Throughout Section 202’s 37-year history, federal law and regulation has regarded CO₂ and water vapor as harmless byproducts.
In its brief in Mass v EPA, EPA noted that, during the past quarter century, Congress has either voted against or declined to adopt every regulatory climate proposal it has considered. For example, and most pertinently, during debate on the 1990 Clean Air Act Amendments, Congress decided not to adopt a Senate committee-approved provision requiring EPA to regulate CO₂ emissions from motor vehicles.
The majority deemed such legislative history irrelevant, arguing that Congress’s failure to pass subsequent laws or provisions cannot curtail EPA’s authority under Section 202. But this misses the point. EPA was not suggesting that “post-enactment legislative history” implicitly repeals portions of the Clean Air Act. Rather, EPA was trying to clarify what Congress might or might not have intended when it enacted and amended Section 202. Popular alarm about global warming and congressional support for regulatory climate policy is vastly stronger now than it was in 1970 or 1977. Yet even in recent years, proponents of regulatory climate policy have failed to secure passage of their proposals. It is silly to pretend that in 1970 or 1977, Congress granted EPA authority to regulate greenhouse gases but just forgot to tell anybody.