On Thursday in a White House event with President Trump, Environmental Protection Agency (EPA) Administrator Lee Zeldin announced that the EPA is repealing the greenhouse gas endangerment finding and the motor vehicle tailpipe emissions standards.  

Section 202(a)(1) of the Clean Air Act stipulates that if the EPA Administrator judges that air pollutants are endangering public health, then EPA must regulate the emissions of those air pollutants. In 1999, petitioners led by the International Center for Technology Assessment petitioned then-EPA Administrator Carol Browner to begin regulating greenhouse gas (GHG) emissions from motor vehicles based on the EPA’s own reports that increased temperatures will result in more prevalent infectious diseases. Petitioners also cited data from the Intergovernmental Panel on Climate Change (IPCC) on how high temperatures lead to heat stress and death, and CDC data on skin cancer risk and other human health effects of climate change.  

The Clinton Administration did not act on the petition until 2001, when just a week before the inauguration of President Bush, EPA requested comments on the petition. In 2003, in a letter signed by Jeff Holmstead, Assistant Administrator for the Office of Air and Radiation, EPA denied the petition, noting that regulating transportation to address climate change “would have enormous economic, practical, and societal impacts” and concluded that the “casual linkage between the buildup of greenhouse gases in the atmosphere and the observed climate changes during the 20th century cannot be unequivocally established”.  

An appeal of that denial, joined by Massachusetts and 11 other states and various cities, was eventually elevated to the U.S. Supreme Court, which decided the case in favor of the petitioners in 2007 in a five-to-four majority. That Massachusetts v. EPA decision found that the definition of air pollutant under the Clean Air Act included all types of airborne compounds, including greenhouse gases, and that Massachusetts had standing in the suit because EPA’s refusal to regulate greenhouse gases presented an actual or imminent risk of harm to the state. The Supreme Court directed the EPA Administrator to determine whether GHG emissions from motor vehicles cause or contribute to air pollution that endangers public health or welfare, or whether the science is too uncertain to make a reasoned decision.  

In response to the Massachusetts v EPA decision, EPA reconsidered the effect of greenhouse gas emissions and the impact on public health, and released their endangerment finding in 2009. Under the Clean Air Act, once the EPA has determined that a pollutant endangers public health and the environment, they are legally required to regulate that pollutant. The 2009 finding laid the regulatory foundation for motor vehicle emissions standards, first released in 2010 as well as the subsequent regulations for trucks and power plants. 

The news release from EPA doesn’t mention this early history, nor does it discuss the Massachusetts v. EPA Supreme Court decision. Instead Administrator Zeldin describes the 2009 endangerment finding as “an unprecedented move [by] the Obama EPA” using “mental leaps” to reach a “creative interpretation of law.” The repeal action announced on Thursday included not only the endangerment finding itself but also all EPA federal GHG emission standards for all vehicles and engines of model years 2012 to 2027 and beyond. 

In their regulatory analysis for the rule, EPA found that the repeal would result in $1.3 trillion of savings for the American public, driven primarily by reduced costs for new vehicles and avoided costs of purchasing equipment related to EVs. EPA also considers costs associated with the repeal but “does not attempt to monetize the value, if any, of changes in GHG emissions that result from the proposed action.” In January, EPA also announced changes to their method of considering risks to human mortality. Previously, the EPA would estimate the value of a statistical life (VSL), and use a range of VSL to calculate benefits and costs of a rule. For instance in 2024, the EPA used a VSL of $12.6 million in their Heavy Duty Vehicle Emissions rule. The EPA has used a VSL to quantify costs to human health and mortality since the mid-1980s.  

As a result of their policy change, EPA now considers only the estimate of how much people themselves are willing to pay for small reductions in their risks of dying from adverse health conditions that may be caused by environmental pollution. The higher than anticipated consumer preference for gasoline fueled engines over EVs is therefore a basis for not valuing any benefits to human health. The costs cited by EPA derive instead from projected increases in vehicle congestion due to increased vehicle sales that result from lower vehicle prices and increased health costs of $2-$4 billion only from the increase in particulate matter emissions. (These estimates are significantly lower than the prior EPA estimate of $10 billion in PM2.5 cost-reduction reported in the 2024 Light and Medium Duty Vehicle Rule.) 

Notably, while repealing the endangerment finding related to motor vehicles, EPA has not repealed the separate endangerment finding made in 2016 specific to aircraft emissions, nor did it repeal its separate endangerment findings for emissions from “stationary sources” like power plants and oil wells. The power sector has invested heavily in equipment to reduce or capture emissions and does not necessarily welcome a change in regulatory structure for power plants. In comments to EPA, the American Petroleum Institute affirmed its belief in EPA’s authority to regulate greenhouse gas emissions. 

Repealing EPA’s motor vehicle emission standards will not affect the Corporate Average Fuel Economy standards set by the National Highway Traffic Safety Administration, which sets maximum feasible fuel economy standards in accordance with the Energy Policy and Conservation Act of 1975 (EPCA), and which were previously aligned with EPA standards but have already been separated. Locomotive engine standards are also not affected, as those regulations focus on criteria pollutants under the Clean Air Act, such as ozone and carbon monoxide, rather than greenhouse gas emissions. 

EPA is certain to face litigation over this repeal, with some challenges already having been promised, and the change in Supreme Court majority since 2007 may mean the court is now poised to reverse their earlier finding. None of the five Justices who signed the majority decision from the Massachusetts v. EPA remain on the Court, while three of the four dissenting Justices still serve. Chief Justice Roberts penned one of the two dissenting opinions on the case—his dissent questioned the harm to states posed by rising sea levels in coastal areas and the causal link between potential EPA regulations and any meaningful impact in mitigating global warming.  

The scientific consensus on the impact of GHGs in contributing to global warming has only grown stronger in the last 20 years. In reversing the endangerment finding, EPA relied heavily on a report prepared by the “Climate Working Group” on behalf of the Department of Energy, which DOE Secretary Chris Wright described as “faithfully report[ing] the state of climate science today” but which dozens of climate scientists, including several whose work was cited in the report describe as “misrepresent[ing] decades of climate science.” (Earlier this month, a US District Court judge found that DOE had violated the Federal Advisory Committee Act in allowing the group to provide substantive policy recommendations, but declined to throw out the report itself.) 

Potential litigants will benefit from the fact that both the endangerment finding and vehicle emissions rule were previously litigated and both were upheld in 2012 by the DC Circuit, which found that the “Endangerment Finding and Tailpipe Rule are neither arbitrary nor capricious” and that “EPA’s interpretation of the governing CAA provisions is unambiguously correct.” Most recently in 2023, the DC Circuit dismissed a petition that the EPA should reconsider the endangerment finding, and the Supreme Court declined to take up challenges on appeal.  

In addition to the litigation uncertainty regarding the rule itself, the repeal could lead to regulatory fragmentation and the dreaded patchwork of state regulations, as removing federal regulatory authority may be interpreted to void any preemption of state regulations. California and the other states that have historically adopted the California Clean Cars standards would presumably be interested in aggressive climate regulations of motor vehicle emissions. EPA regulation states that though the Clean Air Act restricts their own federal authority to regulate greenhouse gases, it still preempts states’ authority to do so, because new vehicles “would remain subject to Title II of the CAA” which prohibits states from regulating emissions from new motor vehicles (except for where California is granted a waiver). This too is likely to be an area where litigation arises.