On July 29, 2025, EPA proposed to rescind the 2009 Greenhouse Gas Endangerment Finding. The public comment period ended on September 22, 2025. So, it remains to be seen if EPA finalizes this proposal and, if so, if it survives legal challenges. Nonetheless, it is a serious proposal and it’s worth exploring what the regulatory ramifications are if EPA does rescind the Endangerment Finding.
But first, let’s look at some relevant background information as well as the United States Department of Energy’s latest analysis of the impact of greenhouse gas emissions on the climate in the United States.
Regulation of Greenhouse Gases under the Clean Air Act
Dating back to the origin of the Clean Air Act through the Clean Air Act Amendments of 1990, greenhouse gases were not regulated as air pollutants. As climate change became more of a concern, interested parties began to evaluate the possibility of using the Clean Air Act to do so by using a section that gives EPA the authority to regulate “new” air pollutants that were not specifically identified in the Clean Air Act.
In 2003, EPA denied a rulemaking petition to regulate greenhouse gases (GHGs). The agency gave the following two reasons for its decision:
- EPA lacked authority under the Clean Air Act to regulate carbon dioxide for climate change purposes.
- Even if EPA did have such authority, it would exercise its discretion to decline as a matter of policy.
EPA’s denial was challenged, and the case made its way to the U.S. Supreme Court as Massachusetts v. EPA. In 2007, the court ruled in a 5-4 decision that EPA could regulate greenhouse gas emissions in motor vehicles under Section 202(a)(1) of the Clean Air Act if EPA first determined that the greenhouse gas emissions from motor vehicles endangered public health or welfare. By 2009 another presidential election had occurred, and the new administration was supportive of regulating GHGs under the Clean Air Act and the Endangerment Finding was completed to make that happen.
Because GHGs weren’t explicitly listed in the Clean Air Act as air pollutants, it wasn’t entirely clear how and when GHGs would become regulated pollutants at stationary sources under the Title V and PSD air permitting programs. EPA explored this issue in a December 18, 2008 memo, “EPA’s Interpretation of Regulations that Determine Pollutants Covered by Federal Prevention of Significant Deterioration (PSD) Permit Program” (also known as the “Johnson Memo”). The conclusions in this memo were revisited and refined in a rule titled, “Reconsideration of Interpretation of Regulations That Determine Pollutants Covered by Clean Air Act Permitting Programs” (also known as the “Timing Rule”) – 63 FR 17004, April 2, 2010. EPA concluded that “new” pollutant(s) become “subject to regulation” under PSD (and Title V) once there is:
- Endangerment finding; and
- The first emission limits on a pollutant take effect (in a final & effective rule)
In the nearly twenty years that have passed since the Massachusetts v. EPA decision, many people have forgotten that GHG regulation isn’t hard-wired into the Clean Air Act, how narrow the margin was in the Supreme Court’s decision, and how controversial EPA’s subsequent decision to regulate GHGs was.
Impacts of Greenhouse Gas Emissions on the U.S. Climate
In the proposed rule for rescinding the Endangerment Finding, EPA cited updated scientific data that challenge the assumptions behind the original 2009 Endangerment Finding. Cited data includes updated studies and information in the Department of Energy’s 2025 Climate Work Group report, “A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate,” that was concurrently being released for public comment. The report found:
- Climate change is real, and it deserves attention.
- Elevated concentrations of CO2 directly enhance plant growth, globally contributing to “greening” the planet and increasing agricultural productivity.
- The combination of overly sensitive models and implausible extreme scenarios for future emissions yields exaggerated projections of future warming.
- Most extreme weather events in the U.S. do not show long-term trends. Claims of increased frequency or intensity of hurricanes, tornadoes, floods, and droughts are not supported by U.S. historical data.
- US. policy actions are expected to have undetectably small direct impacts on the global climate, and any effects will emerge only with long delays.
While all of this is still in the proposal stage, and there are certainly going to be opposing views on the scientific conclusions, it appears like EPA is heading towards a decision that GHGs should not be regulated under the Clean Air Act in light of the significant cost of regulation compared to the small climate benefits that result.
What Happens if the Endangerment Finding is Rescinded?
The Endangerment Finding was a prerequisite for regulating emissions from new motor vehicles and new motor vehicle engines. Absent this finding, EPA lacks statutory authority under Section 202 of the Clean Air Act to prescribe standards for GHG emissions.
An argument can be made that with the rescission of the Endangerment Finding, EPA would lack authority to regulate GHG emissions from stationary sources under the PSD and Title V permitting programs since GHGs would no longer be “subject to regulation.” Furthermore, there would be no legal foundation for regulating GHGs under the Section 111 CAA programs for new source performance standards (e.g. 40 CFR 60 Subparts TTTT and TTTTa) or existing source performance standards (e.g. Clean Power Plan 2.0 under 40 CFR 60 Subpart UUUUb). In other words, stationary source GHG regulations would likely collapse unless Congress stepped in with new authority. And existing stationary source permits with GHG requirements could be modified to remove those requirements.
What Should Air Permittees with GHG Permit Conditions Do?
Of course, all of this is in the early stages of the rulemaking process and litigation seems certain to follow. Nevertheless, these developments are worth following to ensure that permittees are well positioned to adapt to this rapidly changing regulatory environment.
Air permittees looking for assistance with upcoming permit applications or guidance in navigating these fast-moving changes, please contact your local Trinity Consultants office.
