Developers petitioned the Federal Energy Regulatory Commission (FERC) (defendant) to construct a natural-gas pipeline through Alabama, Georgia, and Florida. Pursuant to the National Environmental Policy Act (NEPA), the FERC prepared an environmental impact statement (EIS) as part of its review of the proposal. The EIS stated that 83.7 percent of the pipeline would pass through low-income or minority neighborhoods, known under NEPA as “environmental-justice” communities. The FERC’s EIS discussed alternative routes for the pipeline and explained why those routes were not preferable to the proposed route. Specifically, the FERC explained that the alternatives would affect similar amounts of environmental-justice communities. The EIS did not estimate quantitatively the downstream greenhouse-gas emissions that the pipeline would cause. Ultimately, the FERC approved the pipeline. Sierra Club, other environmental groups, and landowners (plaintiffs) challenged the approval in federal court, arguing that the FERC failed to adequately consider the pipeline’s effects on low-income and predominantly minority communities and the pipeline’s contributions to greenhouse-gas emissions.