In Center for Biological Diversity v. National Highway Traffic Safety Administration, governmental and nongovernmental entities challenged a rule issued by the National Highway Traffic Safety Administration (NHTSA), which set fuel economy standards, by asserting that the EA did not adequately assess the cumulative impact of the proposed standards on GHG emissions. 508 F.3d 508 (9th Cir. 2007). The U.S. Court of Appeals for the Ninth Circuit found the EA inadequate and the corresponding Finding of No Significant Impact (FONSI) arbitrary and capricious, and so it remanded and ordered NHTSA to prepare a full EIS. Id. at 554. Specifically regarding the cumulative impact of GHG emissions the court concluded: “the Final Rule clearly may have an ‘individually insignificant but cumulatively significant’ impact with respect to global warming. Evidence that Petitioners submitted in the record also shows that global warming will have an effect on public health and safety. Petitioners do not claim (nor do they have to show) that NHTSA’s Final Rule would be the sole cause of global warming.” Id. at 555 (internal citation omitted).
In 2008, the U.S. Court of Appeals for the Ninth Circuit ultimately decided to defer to the agency as to whether an EA will suffice or whether an EIS is necessary, but the court included some strong language about the potentially significant impact of GHG emissions: “Whether to require an EIS now is a very close question. Petitioners' evidence demonstrates, overwhelmingly, the environmental significance of CO2 emissions and the effect of those emissions on global warming. How NHTSA can, on remand, prepare an EA that takes proper account of this evidence and still conclude that the 2006 Final Rule has no significant environmental impact is questionable. … Although Petitioners' evidence is daunting we cannot, in the abstract, categorically decide that NHTSA's reasons for this conclusion in a revised EA would be unconvincing.” Center for Biological Diversity v. National Highway Traffic Safety Administration, 538 F.3d 1172, 1226 (9th Cir. 2008).