State of California v. EPA, 72 F.4th 308

In 2016 the EPA made an endangerment finding that six greenhouse gases from large aircraft (primarily CO2) contribute to climate change, triggering its duty under Clean Air Act §231 to issue emission standards.
ICAO adopted the first international CO2 standards for airplanes; those standards are "technology-following" (reflect existing fleet performance, not technology-forcing).
The EPA promulgated the Aircraft Rule to align U.S. standards with ICAO—matching scope, stringency, and timing—to promote international harmonization and avoid disadvantaging U.S. manufacturers.
Petitioners (12 states + D.C. and three environmental groups) challenged the rule, arguing EPA unlawfully declined to adopt more stringent or technology-forcing standards and failed to consider climate harms, alternatives, and executive-order obligations.
The D.C. Circuit found Massachusetts had standing (following Massachusetts v. EPA) and consolidated the petitions for review.
The court denied the petitions, holding EPA acted within §231 authority and its harmonization rationale was not arbitrary and capricious; claims relying solely on executive orders were unreviewable.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Scope of EPA authority under §231	EPA must consider technological feasibility and adopt technology‑forcing standards	§231 requires only that EPA issue standards after an endangerment finding; it need not adopt specific factors or force technology	EPA has broad discretion under §231; not required to adopt technology‑forcing standards; aligning with ICAO lawful
Arbitrary & capricious: failure to consider climate harms and alternatives	EPA ignored important aspects of the problem and failed to evaluate obvious, more stringent alternatives (fleet-best efficiency, technology‑forcing, operational/alternative‑fuel measures)	EPA reasonably prioritized international harmonization and explained why alternatives would undermine ICAO coordination and delay effective global standards	Court upheld EPA's rationale: harmonization is a reasonable basis; EPA addressed alternatives and permissibly declined them
Reviewability of compliance with Executive Orders 12898 (environmental justice) & 13132 (federalism)	EPA's cursory statements do not satisfy obligations and make the rule arbitrary and capricious	The executive orders are internal management directives that do not create judicially enforceable rights; claims resting solely on them are unreviewable	Claims based only on executive orders are not judicially reviewable; petitioners cannot bootstrap enforcement into APA review

Steel Co. v. Citizens for a Better Env’t, 523 U.S. 83 (jurisdiction/standing principles)
Lujan v. Defs. of Wildlife, 504 U.S. 555 (standing elements: injury, traceability, redressability)
Massachusetts v. EPA, 549 U.S. 497 (state standing to challenge EPA GHG regulation)
Motor Vehicle Mfrs. Ass’n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29 (arbitrary and capricious standard)
Nat’l Ass’n of Clean Air Agencies v. EPA, 489 F.3d 1221 (§231 affords broad EPA discretion; past harmonization with ICAO upheld)
U.S. Telecom Ass’n v. FCC, 359 F.3d 554 (limits on subdelegation)
Whitman v. Am. Trucking Ass’ns, 531 U.S. 457 (delegation and intelligible‑principle doctrine)
Air Transp. Ass’n of Am. v. FAA, 169 F.3d 1 (executive‑order nonreviewability in context of challenges to agency action)