This removes the core legal predicate the EPA has relied on to issue or defend greenhouse-gas standards under the Clean Air Act, forcing any new federal CO2 rules to be rebuilt on a different legal theory or not issued at all. Ongoing and future litigation over vehicle, power-plant, and industrial emissions standards is likely to pivot from rule-specific arguments to whether the agency can regulate greenhouse gases absent the finding, raising the probability of stays, vacaturs, or withdrawals. Companies planning compliance investments tied to federal CO2 standards now face a near-term decision point on whether to pause, re-scope, or shift to state, contractual, or voluntary carbon requirements as the primary driver.