We dissent in part on the Commission’s consideration of the greenhouse gas (GHG) emissions from the Line CP Modifications and the Gulf Run Pipeline (Projects). The Commission should have prepared a supplemental environmental impact statement (EIS) to examine the effect that the GHG emissions caused by the Projects will have on climate change.
The National Environmental Policy Act (NEPA) requires the Commission to prepare an EIS when issuing a certificate of public convenience and necessity unless the Commission can determine either that the project will not cause any significant adverse impacts or that such impacts will be mitigated. In other words, when there are any “arguably significant” environmental impacts, the Commission must address them in an EIS.
Unlike the Commission’s recent order in Northern Natural, we do not believe that we confidently answer that question one way or another on the present record. As a result, NEPA requires us to perform a supplemental EIS to determine whether the Projects’ adverse effects on climate change are significant—just as we would any other environmental impact. Nevertheless, instead of performing a supplemental EIS, the Commission relies on an environmental assessment that does not assess the significance of the Projects’ GHG emissions or their effect on climate change. Because we believe that is insufficient to satisfy our responsibilities under NEPA, we have no choice but to dissent.
Finally, we observe that finding a project’s GHG emissions to be significant is not a death knell for that project. The Commission may very well conclude that the project’s benefits outweigh even significant adverse impacts. In addition, the Commission could require a pipeline to adopt measures that would mitigate the GHG emissions of the project, or the project developer could propose voluntary measures that would be incorporated as certificate conditions to mitigate those adverse impacts, further increasing the likelihood that a project’s benefits outweigh its adverse impacts. But before the Commission can engage in that balancing process, it must first adequately assess the significance of a project’s adverse impacts, including its impact on climate change.
For these reasons, we dissent in part.
 National Environmental Policy Act of 1969, 42 U.S.C. §§ 4321 et seq.
 E.g., Standing Rock Sioux Tribe v. U.S. Army Corps of Eng’rs, 985 F.3d 1032, 1039 (D.C. Cir. 2021) (‘“If any ‘significant’ environmental impacts might result from the proposed agency action[,] then an EIS must be prepared before agency action is taken.”’ (citing Grand Canyon Trust v. FAA, 290 F.3d 339, 340 (D.C. Cir. 2002) and quoting Sierra Club v. Peterson, 717 F.2d 1409, 1415 (D.C. Cir. 1983))); Myersville Citizens for a Rural Cmty., Inc. v. FERC, 783 F.3d 1301, 1322 (D.C. Cir. 2015) (EIS required where there might be significant impacts unless the impacts are mitigated) (quoting TOMAC v. Norton, 433 F.3d 852, 860 (D.C. Cir. 2006)); see 40 C.F.R. § 1501.3 (2020).
 See Myersville, 783 F.3d at 1322 (quoting TOMAC, 433 F.3d at 860).
 N. Nat. Gas Co., 174 FERC ¶ 61,189 (2021).
 See Sierra Club v. FERC, 867 F.3d 1357, 1373 (D.C. Cir. 2017) (explaining that section 7 of the NGA requires the Commission to balance “‘the public benefits [of a proposed pipeline] against the adverse effects of the project,’ including adverse environmental effects” (quoting Myersville, 783 F.3d at 1309)).