As widely reported in today’s news, Scott Pruitt, the new Administrator of the United States Environmental Protection Agency (EPA), stated that carbon dioxide is not a primary contributor to global warming. Appearing on a March 9 CNBC program, Mr. Pruitt said, “I think that measuring with precision human activity on the climate is something very challenging to do and there’s tremendous disagreement about the degree of impact, so no, I would not agree that it’s a primary contributor to the global warming that we see.”

Mr. Pruitt’s challenge of the conclusion that carbon dioxide emissions are a primary contributor to global warming is one that he is now raising in the media. But notably, while serving as Oklahoma’s attorney general, he unsuccessfully raised the same challenge in federal court, where evidence in support of a claim is required. (Coalition for Responsible Regulation v. Environmental Protection Agency, 684 F.3d 102 (D.C. Cir. 2012)).

In Coalition for Responsible Regulation, Mr. Pruitt and the other petitioners contended that EPA’s scientific basis for its “Endangerment Finding” – a finding that human-caused greenhouse gas emissions may “reasonably be anticipated to endanger public health or welfare” – was inadequate. The petitioners presented their scientific evidence in support of that contention. EPA presented its scientific evidence in response. The Court of Appeals for the District of Columbia Circuit rejected the petitioners’ contention, finding that “[t]he body of scientific evidence marshaled by EPA in support of the Endangerment Finding is substantial,” and that the petitioners had shown only “some residual uncertainty” about the effects of human emissions of greenhouse gases. Relying on the U.S. Supreme Court’s decision in Massachusetts v. Environmental Protection Agency, the court held that the existence of “some residual uncertainty” does not excuse EPA from performing its congressionally mandated duty of regulating greenhouse gases when the air pollution at issue “may reasonably be anticipated to endanger public health or welfare.” Again relying on the Supreme Court’s decision in Massachusetts, the court said that “to avoid regulating emissions of greenhouse gases, EPA would need to show ‘scientific uncertainty . . . so profound that it precludes EPA from making a reasoned judgment as to whether greenhouse gases contribute to global warming.’”

Thus, although Mr. Pruitt said on the CNBC program that “there’s tremendous disagreement about the degree of impact” resulting from human emissions of carbon dioxide, the federal appellate court to which he took that argument did not see it in Mr. Pruitt’s proofs. Litigation over the impending EPA dismantlement of the Endangerment Finding (and other aspects of currently in-place EPA regulations relating to climate change) will necessarily come to a point on this question: Does Mr. Pruitt have evidence of profound scientific uncertainty regarding the impact of human emissions of carbon dioxide on global warming that he did not have when he presented his case in Coalition for Responsible Regulation?