This removes the core legal predicate the EPA has used to regulate greenhouse gases, weakening the agency’s ability to sustain or expand federal emissions standards through Clean Air Act rulemaking. Because full repeal requires a multi-year administrative process, automakers and regulated fleets face a prolonged period of rule volatility that complicates product planning, compliance investments, and credit/penalty forecasting. The change also signals follow-on rollbacks in other federal air-pollution rules, increasing the likelihood that emissions compliance shifts toward state programs and litigation outcomes rather than stable federal standards.