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This section contains the nature of the case and procedural background.

After Massachusetts v. EPA, wherein greenhouse gases were determined to be an 'air pollutant' subject to regulation under the Clean Air Act (CAA), D promulgated a series of greenhouse gas-related rules. The CAA requires D to establish motor-vehicle emission standards for 'any air pollutant . . . which may reasonably be anticipated to endanger public health or welfare,' D issued an Endangerment Finding, in which it determined that greenhouse gases may 'reasonably be anticipated to endanger public health or welfare.' D then set emission standards for cars and light trucks. D then determined under the CAA that major stationary sources of greenhouse gases must obtain construction and operating permits. Ps argue that all these rules and regulations are based on improper constructions of the CAA and are otherwise arbitrary and capricious. Ps contend that the CAA does not restrict D to a science-based judgment devoid of considerations of policy concerns and regulatory consequences. They assert that CAA § 202(a)(1) requires D to consider, e.g., the benefits of activities that require greenhouse gas emissions, the effectiveness of emissions regulation triggered by the Endangerment Finding, and the potential for societal adaptation to or mitigation of climate change.

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