Rescission of the Greenhouse Gas Endangerment Finding and Motor Vehicle Greenhouse Gas Emission Standards Under the Clean Air Act

The EPA received comments from a variety of stakeholders supporting and criticizing the legal rationale set out in the proposed rule. Commenters supporting the rescission and repeals pointed to West Virginia as virtually conclusive with respect to the applicability and outcome of the major questions doctrine analysis. These commenters generally agreed that the Endangerment Finding itself runs afoul of the doctrine by launching the EPA into a policy field that Congress has not decided whether and how to enter as a regulatory matter and, separately, that the EPA's increasing trend in GHG emission standard rulemakings toward forcing a shift toward EVs also runs afoul of the doctrine. Some commenters argued that the doctrine applied to the GHG emission standards but not the Endangerment Finding, including because the standards have increasingly trended toward forcing a shift to EVs. Commenters opposing the rescission and repeals generally argued that the Supreme Court's decision in Massachusetts must be read as shielding CAA section 202(a) from the major questions analysis. Some of these commenters also insisted that the regulation of GHG emissions from new motor vehicles and engines is not economically or politically significant, or that CAA section 202(a)(1) expressly authorizes the EPA to assert such authority by using broad language intended to achieve what they assert is the statute's precautionary purpose. The final rationale set out in the preceding section of the preamble reflects this input by including certain contentions raised by commenters and additional analysis developed in response to criticisms raised during the public comment period. In this subsection, we summarize major themes presented in the comments received along with our high-level responses. For detailed comment summaries and our full responses thereto, please see the Response to Comments document in the docket for this rulemaking.

Comment: Commenters supportive of the proposal agreed that prescribing GHG emission standards in response to global climate change concerns is a major question of social, economic, and political importance and that the EPA lacked clear congressional authorization to issue the Endangerment Finding and associated GHG emission standards authorized by that invocation of authority. These commenters argued that by purporting to resolve significant aspects of the climate change debate by deciding the Nation's policy response for itself in the first instance, the EPA asserted an unheralded authority that infringed on Congress's prerogatives. Several of these commenters argued that the Endangerment Finding preempted Congress by purporting to resolve an issue that was being actively debated and negotiated on the House and Senate floors in 2009 and identified additional instances in which Congress considered but declined to adopt legislation that would have granted the very authority that the EPA asserted in the Endangerment Finding. Such commenters also argued that congressional inaction means that we

never had authority to regulate GHGs in this manner, and that authority cannot be manufactured by placing the burden on Congress in the aftermath of the Endangerment Finding to affirmatively intervene to override the Agency's actions.

Response: The EPA agrees with the commenters that the major questions doctrine applies to the authority we asserted under CAA section 202(a)(1) for the first time in the 2009 Endangerment Finding. In that standalone action, the EPA established the legal foundation to regulate GHG emissions under CAA section 202(a)(1) and knowingly triggered a statutory obligation to regulate GHG emissions not only in the transportation sector, but in other respects as well, including the stationary source permitting context. The importance and extraordinary consequences of that decision were both foreseeable and foreseen by the EPA at the time, as evidenced by the 2008 ANPRM and statements made and actions taken by the EPA in 2009 and 2010. See, e.g., 73 FR 44355 (“[I]f EPA were to regulate [GHG] emissions from motor vehicles under the Clean Air Act, then regulation of smaller stationary sources that also emit GHGs--such as apartment buildings, large homes, schools, and hospitals--could also be triggered. . . . The potential regulation of greenhouse gases under any portion of the [CAA] could result in an unprecedented expansion of EPA authority that would have a profound effect on virtually every sector of the economy and touch every household in the land.”); 74 FR 66502 (“Once the final affirmative contribution and endangerment findings are made, EPA has the authority to issue the final emission standards for new light-duty motor vehicles.”). Intervening events, including those addressed in UARG and West Virginia, have further demonstrated what was widely understood in 2009--the Endangerment Finding launched an entirely new field of regulation in which the EPA has applied, or attempted to apply, significant and costly regulations on virtually all major sectors of the American economy.

In this way, the EPA's invocation of authority in the Endangerment Finding followed by the mandatory issuance of regulations operates similarly to the assertion of authority to which the Supreme Court applied the major questions doctrine in West Virginia. The Agency's emission guidelines for existing power plants under CAA section 111(d) also imposed costs and forced generation shifting in an indirect manner. First, we issued regulations determining the amount of pollution reduction to be achieved; second, States were required to submit plans containing the emissions restrictions they intended to implement and enforce to achieve those reductions; and third, we would review those State plans for consistency with CAA requirements and allow them to enter into force through an approval or substitute State plans for a Federal plan in the event of disapproval. Similarly here, the EPA asserted authority in the Endangerment Finding that, by operation of law, triggered an obligation to prescribe GHG emission standards under CAA section 202(a)(1), triggered stationary source permitting requirements, and served as the basis for extending the reach of GHG emission regulations to additional sources, all as predicted in the 2008 ANPRM.

Further, the new motor vehicle standards issued by the EPA separately and independently trigger the major questions doctrine by forcing a transition toward the use of EVs rather than the ICE in a manner similar to the generation shifting at issue in West Virginia. As early as the EPA's first light-duty vehicle rule in 2010, the Agency relied on and knew its regulations would lead to increased EV production. See 75 FR 25324, 25332 (May 7, 2010) (noting that the “commercialization of [EVs] and plug-in hybrids,” as well as “increased use of start-stop technology,” were available avenues for compliance).

Comment: Adverse commenters asserted that the major questions doctrine does not apply to CAA section 202(a)(1) because of what they describe as a holding in Massachusetts that the regulation of GHGs under that provision is permissible and/or not a major question. These commenters cited to the Supreme Court's discussion of Brown & Williamson in that decision, along with statements made by the Agency in prior GHG emission standards rulemakings, to support the contention that the major questions analysis is inapplicable or that precedent establishes the requisite clear authorization.

Response: The EPA disagrees with these comments. As explained in section V.B.1 of this preamble and discussed further in the Response to Comments document, the Supreme Court drew no such distinctions in West Virginia when it held that the major questions doctrine applies to “all corners of the administrative state,” even if the “regulatory assertions had a colorable textual basis.” 597 U.S. at 721-23 (citation omitted). The Court did not appear to understand itself to be applying the major questions doctrine in Massachusetts, and has not, in subsequent cases, treated Massachusetts as an example of applying or declining to apply the doctrine. Rather, the Court in Massachusetts distinguished Brown & Williamson on its facts. That discussion does not stand for the proposition that CAA section 202(a)(1) is immune from major questions scrutiny, and many of the distinctions drawn in Massachusetts as to Brown & Williamson are now themselves distinguishable given the EPA's subsequent reasoning in the Endangerment Finding and actions taken to implement the Endangerment Finding since 2009.

Comment: Adverse commenters asserted that if major questions doctrine is relevant here, its principles cut against what they described as the EPA's novel interpretation of CAA section 202(a)(1). These commenters argued that for nearly 20 years, Congress has declined to overturn what commenters described as the judicial decisions upholding the EPA's authority to regulate GHG emissions or to amend CAA section 202 to restrict the Agency's authority in this respect. Commenters asserted that rescinding the Endangerment Finding would itself create an abrupt reordering in an area of economic and political significance and is an assertion of authority that would be both novel and dubious and potentially threaten the separation of powers.

Commenters asserted that under the major questions doctrine, the EPA is not able to reverse what they described as the Agency's longstanding interpretation dating back to the Endangerment Finding without being given authority by Congress to do so. Commenters stated that Congress has enacted numerous laws that have recognized GHGs are air pollutants subject to regulation under the CAA. Commenters argued that Massachusetts and the Endangerment Finding have been established law since 2009 and that Congress has known about and enacted legislation on numerous occasions that recognize and affirm the legal interpretations made by the Supreme Court in Massachusetts and by the Agency in the Endangerment Finding.

Response: The EPA disagrees with commenters and concludes the major questions doctrine supports the rescission of the Endangerment Finding and repeal of associated GHG emission standards. The EPA's interpretation of CAA section 202(a)(1) is not novel. As explained in sections III.A and IV.A of this preamble, it reflects the Agency's longstanding practice in applying CAA section 202(a)(1) for the four decades

prior to 2009. Moreover, rescinding the Endangerment Finding and repealing the associated GHG emission standards does not trigger the major questions doctrine because an agency's ability to reconsider, revise, and repeal prior actions is not an unheralded assertion of authority. As explained in section IV.A of this preamble, it is well established that an agency may reconsider, revise, and repeal prior actions unless the relevant statute provides otherwise, which is not the case here.

In addition, the EPA disagrees with commenters' representations of the scope of the Supreme Court's decision in Massachusetts and characterizations of congressional actions since 2009. Tellingly, commenters point to no occasion in which Congress has adopted legislation that expands the scope of the EPA's authority to regulate GHG emissions from mobile or stationary sources. As noted elsewhere in this preamble, Congress considered between 2007 and 2009 draft legislation--emphatically supported by President Obama and the Administrator who issued the Endangerment Finding--that would have substantially revised the CAA to give the EPA express authority to regulate GHG emissions, including under Title II. That legislation failed to pass, and the relatively limited number of non-regulatory provisions Congress has enacted since that time relate either to non- regulatory contexts or support our conclusion with respect to CAA section 202(a)(1) by indicating that Congress has adopted more detailed, particular solutions when it sought to address global problems, as with amendments to the RFS program and the AIM Act. This history falls well short of the standard courts have applied for inferring legislative acquiescence to either commenters' reading of Massachusetts or the EPA's assertion of authority in the 2009 Endangerment Finding. Ultimately, commenters appear to be asserting what is more properly understood as reliance interests on prior actions taken by the Agency. Because the EPA concludes that we lack statutory authority to regulate in response to global climate change concerns under CAA section 202(a)(1), we cannot respond to such asserted reliance interests by retaining the Endangerment Finding and associated GHG emission standards on that basis.

Indeed, commenters inadvertently reinforce why the major questions doctrine applies to the Endangerment Finding and necessitates its rescission. If rescission of the Endangerment Finding is significant enough to trigger the major questions doctrine, there is no persuasive reason to conclude that issuing the Endangerment Finding to initiate the resulting GHG regulatory program does not similarly trigger major questions scrutiny. Were commenters correct that only rescission triggers the doctrine, the result would be an untenable rule by which an Agency can expand its statutory authority through attrition even if application of the doctrine would otherwise require a different result.

Comment: Some commenters said that they support the EPA's application of the major questions doctrine to the vehicle standards that effectively mandated EVs as a purported emissions control measure for motor vehicles powered by ICEs. They stated that as the EPA points out in the proposed rule, effectively mandating a shift away from ICE vehicles under CAA section 202(a)(1) is conceptually indistinguishable from the EPA's failed attempt to mandate generation shifting by reduced utilization of coal-fired power plants under CAA section 111(d). Commenters argued that both actions involve claims of novel and expansive regulatory authority under longstanding law, both have fundamental effects on key national industries and on the national economy, Congress has grappled repeatedly over time with whether and how GHG emissions from these industries should be regulated, and neither action is grounded in a clear statutory mandate.

Commenters also said that the EPA's 2024 HD GHG Emission Standards Rule, without question, meet all the criteria for rescission under the major questions doctrine. These commenters argued that the Supreme Court in West Virginia held open the door for the rescission of what commenters described as sweeping EV truck mandates that impact broad segments of the national economy. Commenters argued that these standards are a direct analogue to the regulations invalidated in West Virginia.

Conversely, other commenters argued that the major questions doctrine does not apply to the 2024 GHG Emission Standards Rules and that the EPA did not explain or show awareness of its change in position from what these commenters described as the Agency's detailed consideration and rejection of major questions doctrine arguments in responding to comments on the 2024 GHG Emission Standards Rules.

Response: The EPA concludes that the major questions doctrine applies to the GHG emissions standards for LD, MD, and HD vehicles that the Agency promulgated in 2024, as discussed in the final rule preamble and with the Response to Comments document. We acknowledge that the Agency previously asserted that the 2024 GHG Emission Standards Rules did not violate the major questions doctrine. As explained in this final action, however, we now conclude that the arc of regulation since 2009 evinces a clear march toward requiring widespread adoption of EVs by manufactures and American consumers, such that the major questions doctrine applies in this respect as well. Accelerating the transition to EVs is realistically the only way for many regulated parties to comply with the stringent emission standards adopted in 2024. At least two auto manufacturers noted the compliance challenges with the current standards and cast doubt on their attainability, particularly in light of reduced EV demand. As demonstrated by the manufacturers' comments, the EPA's GHG emissions standards are difficult to achieve without increasing EV production.

Further, certain events have overtaken aspects of the EPA's analysis in its prior rulemakings. For example, the IRA was largely overtaken by the OBBB, and Congress has disapproved of the EPA's approval of the California waiver under the CRA. The market has also changed since the 2024 GHG Emission Standards Rules: EV demand is down, gas prices are generally down, and EV prices are generally higher than the EPA anticipated.

In effect, the main compliance option for the 2024 GHG Emission Standards Rules was for manufacturers to increase EV production. As discussed in greater detail in the Response to Comments document, the EPA first incentivized EV production in 2010 and projected that compliance with many of its standards in the years since then would include surpassing the amount of EVs that manufacturers would have produced based on market forces alone. The totality of the EPA's actions, when viewed holistically, show a clear path towards a changed reality on the ground of more EVs.

The EPA is also finalizing as proposed that the Agency should not and need not make an endangerment finding under CAA section 202(a)(1) when exercising the regulatory authority conferred by that provision would have no meaningful impact on the identified dangers. The comments and data received in response to the proposed rule, as well as the modeling analysis we performed to evaluate these submissions, indicates that GHG

emission standards under CAA section 202(a)(1) have no more than a trivial effect on the key changes that the Endangerment Finding identified as causing adverse health and welfare impacts. The Endangerment Finding avoided confronting this question by severing the findings from consideration of the resulting regulations, and we focused in subsequent rulemakings on the emissions reductions potential of the standards rather than the impacts on health and welfare. Upon further review, we conclude that this approach is not consistent with the best reading of the statute or the requirement that regulations be reasonable and reasonably explained. CAA section 202(a)(1) instructs the EPA to regulate in furtherance of public health and welfare, not to reduce emissions regardless whether such reductions have any material health and welfare impact.

Specifically, we are finalizing that the potential for emission standards to yield more than de minimis gains for health or welfare are relevant and should be considered when applying CAA section 202(a)(1). We recognized in the Endangerment Finding that the relative contribution of GHG emissions to global concentrations from new motor vehicles and engines in the U.S. must be more than de minimis to invoke our authority but failed to carry this logic through to the remainder of the analysis. Background legal principles instruct that de minimis concerns are not encompassed within the scope of general statutory language, and the ability of regulation to address identified dangers is relevant to whether it can be said that that the emissions contribute to air pollution that endangers public health or welfare in the first instance. As discussed in this subsection, comments and our own analysis in response to comments provides that any potential impact is de minimis. Even a complete elimination of all GHG emissions from new motor vehicles and engines would not address the risks attributed to elevated global concentrations of GHGs. We are finalizing that this futility further demonstrates that CAA section 202(a)(1) does not, as a matter of text and structure, authorize or require the EPA to prescribe emission standards for GHG emissions from new motor vehicles and engines. 1. Final Rationale

As discussed in section VI.A of this preamble, the EPA recognizes that there are significant uncertainties related to climate modeling and recognizes that there is still significant dispute regarding climate science and modeling. However, the EPA is utilizing the climate modeling provided within this section to help illustrate that, even applying the assumptions of these climate models and uncertainties contained therein, that removing all GHG emissions from new and existing LD, MD, and HD vehicles and engines would not materially address the health and welfare dangers attributed to global climate change concerns in the Endangerment Finding.

The EPA utilized the EPA Optimization Model for reducing Emissions of GHGs from Automobiles (OMEGA model) to estimate the global GHG contributions from U.S. light- and medium duty vehicle engines, and the EPA's MOtor Vehicle Emission Simulator (MOVES model) to estimate the global contribution from U.S. heavy-duty vehicle engines (Table 1).\172\ The baseline global emission scenario used for this analysis was Shared socioeconomic pathway 2 with a radiative forcing of 4.5 watts per square meter by 2100 (SSP2-4.5) (Table 1).

\172\ Note that these scenarios did not include additional GHG emissions from upstream refinery or energy generation processes, nor additional emissions of hydrofluorocarbons (HFCs) from vehicle air conditioners. The EPA separately regulates emissions from stationary sources under statutory authorities outside the scope of this rulemaking and, pursuant to separately enacted legislation requiring a phase out of HFCs, regulates permissible uses of HFCs.

The EPA used the Finite amplitude Impulse Response (v2.2.3) climate emulator model (FaIR model) to quantify changes in global CO2 concentration and global surface temperature associated with the marginal change in emissions from each vehicle scenario relative to the baseline. The FaIR model is an open-source emulator that reasonably reflects the best available information and science but does not include all possible Earth system processes. In FaIR, greenhouse gas lifetimes are based on a four-box decay model that is also a function of atmospheric and ocean temperatures and emissions of other gases. The model accounts for radiative forcing from greenhouse gases, aerosols, albedo changes due to land use, solar cycles, and volcanic eruptions, given an externally defined time path for each. FaIR uses three layers for the ocean component, as heat uptake by the ocean controls how fast atmospheric temperature changes after a change in radiative forcing. FaIRv2 includes uncertainty estimates that are based on a calibration to global climate models, historical observations, and parameter uncertainty ranges from the Intergovernmental Panel on Climate Change. Uncertainties in climate model parameters considered in FaIR, include the sensitivity of climate to increases in atmospheric CO2 concentrations, forcing from aerosol interactions with radiation and clouds, forcing from black carbon on snow, and carbon cycle parameters. All simulations were run with historical volcanic and solar cycle forcing, with values held constant (solar) after 2022.

The EPA also used the Building Blocks for Relevant Ice and Climate Knowledge (BRICK) model to quantify changes in GSLR associated with the marginal temperature changes from each vehicle emissions scenario. BRICK is a semi-empirical, open-source model, with four sub-components that each model the physical changes in the four major contributors to GSLR--glaciers and ice caps, land water storage, and ice sheets, and thermal expansion--in response to changes in temperature. Similar to FaIR, the BRICK model is also designed with uncertain parameters intended to encompass the range of possible GSLR responses to a given input of temperature and ocean heat content. Uncertainties in GSLR parameters considered in BRICK include contributions from glaciers and ice caps and the Antarctic and Greenland ice sheets, as well as ocean thermal expansion, and were calibrated through a coupled physical- statistical framework, using an adaptive Markov chain Monte Carlo approach. Reduced complexity models like BRICK and FaIR allow for the flexibility to analyze custom scenarios, quantitatively discern changes between any scenarios, and characterize uncertainties surrounding global change. The National Academies of Sciences, Engineering and Medicine (NASEM) in a 2017 report endorsed the use of the FaIR model in a 2017 report, and the BRICK model was developed in response to recommendation 4-3 from the 2017 NASEM report.\173\

\173\ National Academies of Sciences, Engineering, and Medicine. 2017. Valuing Climate Damages: Updating Estimation of the Social Cost of Carbon Dioxide. Washington, DC: The National Academies Press. A copy of this report is available in the docket for the rulemaking. Available online: https://doi.org/10.17226/24651.

The EPA modeling described above projects that global atmospheric concentrations of CO2 will be 420.5 parts per million by volume (ppmv) (with an associated 95 percent confidence interval (95 percent CI) of 419.1-422.1 ppmv) in 2027 and are projected to increase in the baseline scenario to a median of 475.4 ppmv by 2050 and 533.6 ppmv by 2100. The 95 percent CI reflects the uncertainty in the FaIR model input parameters and ranges from 461.8-484.3 ppmv in 2050 to

482.5-565.4 ppmv in the year 2100. Relative to 2027, concentrations of CO2 are projected to increase in 2050 and 2100, by 55.0 ppmv and 113.3 ppmv, respectively (Table 3). GHG emissions from on-road vehicle exhaust in the United States are projected to contribute 2.8 ppmv (or 5 percent) and 7.4 ppmv (or 7 percent) to this global increase by 2050 and 2100, respectively (Table 3).

The modeled GMST in 2027 is projected to be 1.35 [deg]C above pre- industrial temperatures, defined as the average between 1850 and 1900 (Table 4). GMST in the baseline scenario is estimated to increase to 1.89 [deg]C (95 percent CI: 1.44-2.37 [deg]C) and 2.66 [deg]C (95 percent CI: 1.86-3.87 [deg]C) above preindustrial temperatures by the years 2050 and 2100, respectively. These changes are +0.53 [deg]C (95 percent CI: 0.32-0.84 [deg]C) and +1.28 [deg]C (95 percent CI: 0.67- 2.42 [deg]C) above 2027 temperatures (Table 5). GHG emissions from on- road vehicle exhaust in the United States are projected to contribute to 0.013 [deg]C (95 percent CI: 0.009-0.017 [deg]C) (or 2 percent) of this increase in GMST by 2050 and 0.037 [deg]C (95 percent CI: 0.024- 0.054 [deg]C) (or 3 percent) of this increase by 2100.

The modeled GSLR is estimated to be 25.8 cm higher in 2027 than during the preindustrial era (1850-1900). GSLR in the baseline scenario is projected to be 38.9 cm (95 percent CI: 28.0-49.1 cm) by 2050 and 94.3 cm (95 percent CI: 59.9-157.9 cm) by 2100 relative to preindustrial (Table 6). These increases are roughly 12.4 cm (95 percent CI: 9.4-20.3 cm) and 69.5 cm (95 percent CI: 35.2-132.7 cm) higher than 2027 levels (Table 7). GHG emissions from on-road vehicle exhaust in the United States contribute to roughly 0.09 cm (0.06-1.06 cm) (or ~1 percent) of this global increase in 2050 and 1.4 cm (0.39- 4.77 cm) (or 2 percent) of this global increase by 2100. BILLING CODE 6560-50-P [GRAPHIC] [TIFF OMITTED] TR18FE26.003

[GRAPHIC] [TIFF OMITTED] TR18FE26.004

[GRAPHIC] [TIFF OMITTED] TR18FE26.005

[GRAPHIC] [TIFF OMITTED] TR18FE26.006

[GRAPHIC] [TIFF OMITTED] TR18FE26.007

[GRAPHIC] [TIFF OMITTED] TR18FE26.008

[GRAPHIC] [TIFF OMITTED] TR18FE26.009

BILLING CODE 6560-50-C

As shown above, the changes in GHG emissions and global GHG concentrations by 2050 and 2100 resulting from the complete elimination of all GHG emissions from new and existing LD, MD, and HD vehicles in the United States would be relatively minor. Importantly, however, changes in global emissions rates and global concentrations are not the focus of the statutory standard for regulation in CAA section 202(a)(1). Rather, the statute instructs that the ultimate regulatory concern is impacts from air pollution on “health or welfare.” The appropriate indicator of impact is not emissions or concentrations, but health and welfare impacts. Given the speculative, multi-faceted, and multi-causal nature of the impacts cited in the Endangerment Finding (e.g., hurricanes, floods, heat waves, ocean acidification, etc.), we used for purposes of this analysis the projected impacts of the elimination of U.S. LD, MD, and HD vehicle emissions on trends in GMST and GSLR.

\174\ Average annual observed CO2 concentrations in 2024 were 423 ppmv. Source: Trends in Atmospheric Carbon Dioxide (CO2) from: https://gml.noaa.gov/ccgg/trends/global.html.

\175\ Note that observed data do not exactly correspond with that modeled estimates, as the FaIR and BRICK modeling start in 1750 (or 1850) for estimation of both historical and future projected GHG concentrations, temperatures, and GSLR.

\176\ Uncertainties in GSLR parameters considered in BRICK, include but are not limited to sea level rise contributions from glaciers and ice caps and the Antarctica and Greenland ice sheets, as well as ocean thermal expansion. The calibration of the 10,000 parameter sets is described in: Rennert, K., Errickson, F., Prest, B.C. et al. Comprehensive evidence implies a higher social cost of CO2. Nature 610, 687-692 (2022). https://doi.org/10.1038/s41586-022-05224-9.

\177\ GMST observations in 2024 were 1.55 (1.42-1.68) [deg]C relative to 1850-1900 to present from https://wmo.int/publication-series/state-of-global-climate-2024. The uncertainty in observed temperatures is due to the uncertainty in temperature before 1900, due to the sparsity of observations during that period.

\178\ Observations of GSLR in 2024 are 22.5 cm relative to pre- industrial. Source: https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level.

In this analysis, we reviewed the projected impact on GMST and GSLR by applying two important qualifications. First, the projected impacts on GMST and GSLR are not themselves the adverse impacts on health and welfare relevant for purposes of the analysis. Rather, they are imperfect proxies for such adverse impacts, which we are assuming without accepting play a causal role in such adverse impacts. We did not apply a quantitative discount when analyzing the modeling performed for purposes of this final action. Nevertheless, it bears emphasis that the projected impacts on GMST and GSLR trends do not translate directly to adverse health and welfare impacts and do not account for additional factors, including adaptation and mitigation factors, that would necessarily inform such impacts. As discussed in section V.A of this preamble, the analytical difficulties, uncertainties, and multiple causal leaps involved in this exercise are themselves a reason to conclude that CAA section 202(a)(1) does not encompass emissions that can be said to lead to adverse health and welfare impacts only by constructing a global air pollution framework.

Second, the elimination of GHG emissions from all new and existing U.S. LD, MD, and HD vehicles substantially overestimates the impacts of the EPA's GHG emission standards. The standards apply only to “new” vehicles and engines, and fleet turnover (i.e., the transition from existing vehicles to new vehicles covered by the standards) generally takes more than 20 years.\179\ The most recent GHG emission standards finalized in 2024 phased in beginning in MY 2026 and increased in stringency through MY 2032 and beyond, meaning the full emissions reductions attributable to the standards would not be expected until well after 2052. Moreover, despite being the most stringent to date, the 2024 standards were projected to reduce GHG emissions by approximately 50 percent as compared to the preexisting standards for MY 2026 and beyond.\180\ The appropriate discount between the modeled scenario (the elimination of all GHG emissions from vehicles) and the reductions achieved in practice by EPA GHG emission standards (i.e., the difference between the scenario and the likely real-world scenario) turns on a variety of factors that are difficult to predict, including our regulatory decisions for MY 2032 and beyond, separate regulatory influences, and changes to the underlying economics, technologies, and consumer preferences. For illustrative purposes, we present below a scenario in which EPA GHG emission standards would eliminate an additional 50 percent of GHG emissions from LD, MD, and HD vehicles as compared to the baseline.

\179\ U.S. EPA. “Population and Activity of Onroad Vehicles in MOVES5” EPA-420-R-24-019, November 2024.

\180\ For MY 2032 and beyond new motor vehicles, the EPA projected that the 2024 GHG emission standards final rules would result in a 50 percent reduction in new LD vehicle CO2 emissions, a 41 percent reduction in new MD vehicle CO2 emissions, and a 25-60 percent reduction in new HD vehicle CO2 emissions (dependent on vehicle category). See 89 FR 27842, 27908-09 (Apr. 18, 2024); 89 FR 29440, 29451-52 (Apr. 22, 2024); 89 CFR 27914-915.

Under the 50 percent reduction scenario, retaining a GHG emission standards program for vehicles and engines would result in a 0.007 (0.005-0.009) [deg]C impact on projected GMST through 2050 and 0.019 (0.012-0.027) [deg]C impact on projected GMST through 2100. Retention would result in a 0.05 (0.03-0.053) cm impact on projected GSLR from 2027 to 2050 and 0.7 (0.20-2.39) cm impact on projected GSLR from 2027 to 2100. Again, this is an illustrative scenario and a rough estimate that pairs some analytic tools not intended for this purpose with other tools in the literature. As such, it cannot be assumed to translate with precision directly to specific adverse health or welfare impacts. Note, however, that these figures are themselves likely an overestimation of the actual predicted impact of GHG emission standards over the relevant time horizon because this illustrative 50 percent reduction scenario does not reflect what such standards would realistically achieve given technical and statutory constraints.

Whether viewed in terms of the complete elimination scenario or the illustrative 50 percent reduction scenario, these projections lead the EPA to determine that GHG emission standards under CAA section 202(a)(1) have no material impact (i.e., beyond a de minimis level) on the global climate change concerns relied upon in the Endangerment Finding to justify regulation. This determination leads us to two independent conclusions. First, as discussed in section V.A of this preamble, the futility of GHG emission standards under CAA section 202(a)(1) further supports that the best reading of the statute does not encompass global climate change concerns within the scope of the “air pollution” that Congress authorized and required the EPA to address. And second, as discussed in this section below, the futility of GHG emission standards under CAA section 202(a)(1) renders retaining such standards unreasonable given the certain and immense costs and other direct adverse impacts of the standards.

Under any reasonable understanding, the predicted impacts of eliminating all U.S. GHG emissions from vehicles and engines on GMST and GSLR are de minimis. Even without accounting for the difference between total elimination under the modeled scenario and emission control using GHG standards under the discounted scenario, the predicted impacts through 2100 (0.013 [deg]C as shown in Table 5) are below the

range of measurability for GMST and likewise for GSLR (1.4 cm as shown in Table 7).\181\ Additionally, as stated previously, GMST variability from 2016-2025 was 0.14 [deg]C, which is almost four times greater than the GMST change estimated in 2100 from eliminating all U.S. vehicle and engine GHG emissions.\182\

\181\ See National Oceanic and Atmospheric Administration (NOAA), National Centers for Environmental Information, Global Surface Temperature Anomalies-Methodology and Uncertainty, estimating uncertainty in annual global mean surface temperature of approximately 0.05 [deg]C since 1950, increasing to 0.1-0.2 [deg]C in the late 19th Century. Available at https://www.ncei.noaa.gov/access/monitoring/global-temperature-anomalies.

\182\ National Centers for Environmental Information, Climate at a Glance. NOAAGlobalTemp. Available at https://ncei.noaa.gov/access/monitoring/climate-at-a-glance/global/time-series/globe/land_ocean/tavg/ytd/12/1950-2025.

Once the figures are reduced to reflect the potential impact of EPA GHG emission standards, which only reduce, rather than eliminate, all GHG emissions from vehicles and engines for the reasons discussed above, the de minimis nature of the impact is even clearer. The reduced impact is approximately one percent of the model-projected change in GMST for 2050 and 2100.\183\ The reduced impact is much less than one percent of the change in GSLR modeled for 2050 and 2100. As discussed in section V.A of this preamble, Congress does not include de minimis concerns in general statutory language, and agencies need not address de minimis concerns where doing so would yield trivial value under the statutory scheme.\184\ The general instruction in CAA section 202(a)(1) to “prescribe . . . standards” for emissions that contribute to air pollution which may reasonably be anticipated to endanger public health or welfare does not override this background principle, and regulatory agencies and courts have consistently viewed impacts of one percent as de minimis and therefore not encompassed within general statutory language.\185\

\183\ For context, the Administrator relied in the Endangerment Finding on predictions that global temperature would increase from 1990 to 2100 between 1.8 to 4.0 [deg]C. 74 FR 66519.

\184\ See, e.g., UARG, 573 U.S. at 333; Ala. Power, 636 F.2d at 360-61.

\185\ See, e.g., UARG, 573 U.S. at 333 (suggesting that an appropriate de minimis level of stationary source GHG emissions could be substantial in an absolute sense); EME Homer, 572 U.S. 489 (approving rule that did not require additional emissions reductions from States that contributed less than one percent to nonattainment in other States); In re Rail Freight Fuel Surcharge Antitrust Litig., 934 F.3d 619, 625 (D.C. Cir. 2019) (applying benchmark of five-to-six percent for the number of uninjured class members that destroy predominance in class certification context); CareFirst of Md., Inc. v. First Care, P.C., 434 F.3d 263, 268 (4th Cir. 2006) (survey showing two percent consumer confusion de minimis in the trademark context); Arent v. Shalala, 70 F.3d 610, 617 (D.C. Cir. 1995) (accepting 10 percent de minimis threshold in FDA compliance regulation).

Relevance to the best reading of CAA section 202(a)(1). In reaching this determination, we recognize that CAA section 202(a)(1) authorizes preventative regulation that need not fully ameliorate the identified harms. But in discussing the statute's preventative nature, the EPA and reviewing courts consistently understood that regulation must be capable of having at least a material impact on the identified danger.\186\ The background legal principles discussed in section V.A of this preamble support this reading of the statutory standard.

\186\ See, e.g., Ethyl Corp. v. EPA, 541 F.2d 1, 29-32 (D.C. Cir. 1976) (en banc) (approving standards for lead content in gasoline supported by finding that lead emissions from gasoline were a “significant source” of total environmental exposure “that was particularly suited to ready reduction”).

The futility determination reached in this final action is different in kind from the policy arguments previously addressed in Massachusetts and Coalition for Responsible Regulation, which focused on the cost-benefit balance of potential regulatory responses and general concerns about the most efficient way to regulate in response to global climate change concerns. Rather, we conclude that CAA section 202(a)(1) requires that emission standards be capable of having a material impact on the identified danger for the Administrator to conclude that the emissions “contribute” to air pollution that may “reasonably be anticipated” to endanger public health and welfare. If controlling or eliminating the emissions would not materially impact the identified danger, the emissions do not “contribute” to the air pollution. And because the emitted “air pollutant” and the “air pollution” are defined in this context as the “six well-mixed GHGs,” the air pollution cannot “reasonably be anticipated” as endangering health or welfare in the CAA section 202(a) context if controlling or eliminating all vehicle and engine emissions would have no impact. Put another way, the inability of GHG emission standards to have any material impact demonstrates that GHG emissions from new vehicles and engines do not contribute to air pollution that endangers public health or welfare. That determination is relevant to the findings required by CAA section 202(a)(1).

The EPA recognized in the Endangerment Finding that CAA section 202(a) incorporates de minimis principles, stating that the contribution of motor vehicle and engine GHG emissions to the “air pollution” must be more than trivial. See 74 FR 66506, 66509, 66542- 43. But we avoided consideration of this limitation in the remainder of the analysis by severing the endangerment and contribution findings from the analysis of responsive regulation. We asserted that requiring the Agency to show that control measures “would prevent at least a substantial part of the danger” would “be an unworkable interpretation, calling for EPA to project out the result of perhaps not one, but even several, future rulemakings stretching over perhaps a decade or decades.” 74 FR 66507-08. We further asserted that effectiveness would turn not only on CAA section 202(a) regulations, but also on “the larger context of the CAA and perhaps even the global context” based on our belief that all sources must “do their part” to avoid a collective action problem. 74 FR 66508. In this way, we deferred to future agency action any consideration whether regulation would have more than a de minimis impact. Upon reviewing multiple rounds of CAA section 202(a)(1) GHG emission standard rulemakings predicated on the Endangerment Finding, however, we acknowledge that the EPA never meaningfully returned to the question. Rather, we focused on estimates of GHG emission reductions and, in RIAs not relied upon to justify the standards, attempts to monetize such reductions using SCC methodology.\187\ That was not consistent with the best reading of the statute, which provides that the proper focus is not on the emissions themselves, but on the possible dangers to health or welfare.

\187\ See, e.g., 89 FR 29440, 29675 (Apr. 22, 2024) (2024 HD GHG Emission Standards Rule); 75 FR 25324 (May 7, 2010) (Tailpipe Rule).

Emission standards for criteria pollutants and air toxics have markedly different impacts, and a comparison to the GHG emission standards is illustrative.\188\ Unlike the GHG emission standards, the EPA's criteria pollutant and air toxic standards protect health and welfare by reducing emissions of air pollutants that have direct effects from local and regional exposure. Moreover, the standards achieve health and welfare benefits without relying on further action with respect to other sources (i.e., stationary sources) or

actions by other countries. Whether the EPA regulates criteria pollutant and air toxic emissions from power plants, for example, the CAA section 202(a) standards materially reduce the health and welfare impacts. Importantly, the risk-reduction benefits of those standards are material regardless whether other countries reduce emissions of the same pollutants.\189\

\188\ For example, approximately 45 percent of NOX, less than 10 percent of VOCs, and less than 10 percent of PM2.5 and PM10 in the United States come from the transportation sector. See https://www.epa.gov/transportation-air-pollution-and-climate-change/smog-soot-and-other-air-pollution-transportation.

\189\ To note, we acknowledge that criteria air pollution does come from other countries into the United States and the CAA allows for discounting those emissions when determining compliance with the NAAQS.

Independent basis for repealing GHG emission standards. Separate from the rescission of the Endangerment Finding, the EPA is finalizing the futility rationale as a standalone basis for repealing the GHG emission standards. Even if the CAA section 202(a)(1) authorized the Endangerment Finding as a standalone decision, it would be unreasonable and impermissible to retain a regulatory program that imposes immense costs while providing no material value in furtherance of a legitimate statutory objective. This alternative basis turns on the statutory language in CAA section 202(a) more generally, including the cost consideration requirements of CAA section 202(a)(2). As the Supreme Court explained in Michigan, agencies are bound to consider cost unless the statute expressly provides otherwise. Here, where the costs or regulation are certain and immense but the health and welfare value of regulation are uncertain and de minimis, it is unreasonable to maintain the GHG emissions program. For further discussion, see additional discussion in the sections of the preamble that follow and the Response to Comments document. 2. Summary of Comments and Responses and Updates to the Final Action

In response to the proposal, the Agency received a number of technical comments regarding the proposed futility basis, including comments on the impacts of total U.S. GHG emissions and U.S. motor vehicle GHG emissions to climate change effects. Multiple commenters provided projected changes in global CO2 concentrations and global surface temperature changes for the years 2050 and 2100 for a range of modeled scenarios. These scenarios included modeled changes from the elimination of all U.S. CO2, or elimination of all U.S. power sector CO2 emissions (which the commenter indicated was of similar magnitude to the emissions from motor vehicles), or the elimination of all U.S. motor vehicle GHG emissions. Other commenters cited to climate modeling the EPA included in the light-duty vehicle GHG 2010 standard setting final rule. In general, the commenters utilized the Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC) model, a model the EPA has used in the past. While the scenarios were not identical to the modeling described in section V.C.1 of this preamble which the EPA performed for this final action,\190\ the EPA finds that in general commenters who performed climate modeling projected changes in global surface temperature impacts similar to the EPA's modeling. As discussed in detail in section V.C.1 of this preamble, the EPA finds the modeled projected impacts from the complete elimination of GHG emissions from US on-road vehicles to be de minimis, and the impacts from potential EPA GHG standards for U.S on-road vehicles, which would not result in a complete elimination of GHG emissions, to be even smaller and thus also de minimis. The Response to Comments document summarizes the comments we received regarding climate modeling projections and our detailed responses.

\190\ See Memorandum to Docket EPA-HQ-OAR-2025-0194. “Technical Memo on: Temperature, CO2 Concentration, and Sea Level Rise Impacts of Greenhouse Gas Emissions from U.S. Motor Vehicles.”

VI. Additional Proposed Bases for Rescission of the Endangerment Finding and Repeal of GHG Emission Standards the Agency Is Not Finalizing at This Time

In this section, the EPA discusses the alternative bases for rescinding the 2009 Endangerment Finding and repealing associated new motor vehicle and engine GHG emission standards that we presented for comment at proposal but are not finalizing at this time. The discussion below is provided in the interests of transparency and public engagement and should not be understood as presenting any views or conclusions related to the bases for this final action set out in section V of this preamble. As explained below and noted where appropriate in the Response to Comments document, the comments received on these alternative proposed bases are out of scope of this final action given our predicate conclusions that we lacked statutory authority to issue the Endangerment Finding and cannot retain or prescribe GHG emission standards for new motor vehicles and engines in response to global climate change concerns under CAA section 202(a)(1) and, separately, that the futility of GHG emission standards in addressing global climate change concerns renders it unreasonable to retain the standards.

In the proposal, the EPA described an alternative rationale for rescinding the 2009 Endangerment Finding and repealing associated GHG emission standards for new motor vehicles and engines. Under that alternative proposed basis, the EPA stated that even if CAA section 202(a)(1) could be read to authorize regulation of GHG emissions from new motor vehicles and engines in response to global climate change concerns, the Administrator would exercise his judgement differently today in light of intervening scientific developments and limitations and uncertainties in the record for the Endangerment Finding. Although the Administrator continues to harbor concerns regarding the scientific determinations underlying the Endangerment Finding, the EPA has decided not to finalize this scientific alternative rationale at this time. As explained in section V of this preamble, the EPA is rescinding the Endangerment Finding based on the best reading of CAA section 202(a)(1), under which the EPA concludes that Congress did not authorize the Agency to regulate GHG emissions from new motor vehicles and engines in response to global climate change, and, separately, is repealing the GHG emission standards for the additional reason that futility renders it unreasonable to retain the standards. These legal conclusions are sufficient to support rescission of the Endangerment Finding and repeal of the related GHG emission standards without the additional scientific basis set out at proposal.

As the EPA does not adopt or rely on the proposed scientific alternative rationale in this final action, the Agency does not need to, and is not legally required to, respond to comments that address that unfinalized alternative. Nevertheless, in the interest of transparency and to assist the public in understanding the outcome of this rulemaking, the EPA provides the following summary of major themes raised by commenters regarding the proposed scientific alternative rationale. The EPA offers this summary for informational purposes only. The EPA does not (and, given the bases on which it finalizes this action, cannot) in this rulemaking resolve the underlying scientific debates described below, does not issue a new or revised scientific determination under CAA section 202(a)(1), and does not adopt or endorse any particular assessment, study, or

comment as a statement of the Administrator's scientific judgement. The descriptions and responses that follow explain how the EPA has considered the comments in deciding not to finalize the scientific alternative rationale, but they are not necessary to, and do not form an independent basis for, the legal conclusions on which this final action rests. In light of the conclusions adopted in this final action with respect to the best reading of CAA section 202(a)(1) and the EPA's authority thereunder, we cannot resolve remaining uncertainty regarding these issues in this regulatory context.

Comments Asking the EPA to Characterize Whether the Science of Climate Change is “Settled”: Several commenters asked the EPA to state more clearly whether the Agency views the science of climate change as settled or unsettled. Some commenters urged the EPA to state that climate science remains unsettled, and that significant disagreement persists on key issues related to climate sensitivity, extreme events, and projected impacts. Others urged the EPA to state that the science is settled to the extent relevant to the Endangerment Finding and pointed to statements by scientific organizations and assessments that describe strong or “overwhelming” consensus regarding the reality of climate change and the influence of human activities.

Response: The Administrator continues to harbor concerns regarding the scientific analysis underpinning the Endangerment Finding. A core tenet of empirical science is that it is falsifiable--that it can always be updated or changed in light of new evidence. The scientific record contains analyses that regularly reveal new uncertainties, challenge old assumptions, propose new interpretations of evidence, and reach differing conclusions. Analyses also explicitly question the weight that policymakers should place on particular projections or impact estimates, due in part to this uncertainty. Commenters generally recognized that relevant data is being collected on a continuing basis and analyzed against prior projections but drew very different conclusions from such data. Similarly, commenters drew very different conclusions from statements by scientific organizations that the consensus on these issues is strong or “overwhelming,” which certain commenters took as evidence of certainty and others took as reason to question the underlying data and analyses. We recognize the importance of these issues and the importance placed on them by many commenters. In light of the bases adopted for this final action, however, the EPA lacks authority to resolve these issues here for regulatory purposes under CAA section 202(a)(1).

Comments Asserting That Intervening Science No Longer Supports the 2009 Endangerment Finding: Some commenters supported the proposal's description of scientific uncertainty and agreed that the current record does not support the assumptions and conclusions of the Endangerment Finding. These commenters argued that experience since 2009 revealed limitations in global and regional climate models, including differences between model projections and certain observational records and reanalysis in specific regions or time periods. These commenters stated that projections of temperature change, sea level rise, and some categories of extreme events span wide ranges, and they contend that those ranges reduce confidence in the magnitude and timing of risks that the Endangerment Finding associated with anthropogenic GHG emissions.

Additionally, one commenter, for example, provides that there is significant bias in climate methodology that was relied upon in the Endangerment Finding. That commenter specifically provides that “mainstream climate research” has relied on a triply biased methodology that runs overheated models with inflated emission scenarios and ignores or minimized adaptation. The result, according to that commenter, is exaggerating the physical impacts of GHG emissions and harmfulness of such impacts.

Commenters also focused on causation and scale. These commenters emphasized that climate change is a global phenomenon and argued that GHG emissions from U.S. mobile sources represent a de minimis share of global GHG emissions. In their view, the available science does not support a sufficiently direct and quantifiable link between incremental changes in GHG emissions from U.S. vehicles and specific public health or welfare harms in the U.S. These commenters claimed that the Endangerment Finding relied too heavily on modeled scenarios and synthesis reports and did not fully account for natural variability, observational uncertainty, and adaptive capacity.

Response: The EPA acknowledges that some commenters view intervening scientific literature and observational experience as weakening the basis they believe underlay the Endangerment Finding. We also acknowledge that questions related to model performance, regional patterns of change, internal variability, and the magnitude of projected impacts will continue to be examined. As provided in this section, the existence of these differing approaches and viewpoints confirms that climate science, including climate-impact assessments, remains an active field of research and assessment rather than a closed or static record. Researchers continue to refine observational datasets, develop and evaluate models, improve methods for detecting and attributing observed changes, and explore alternative ways to characterize uncertainty and risk. Assessment bodies periodically revisit and synthesize this evolving literature, and authors continue to publish analyses that emphasize different aspects of the evidence. The EPA therefore views the scientific record as dynamic and subject to ongoing refinement, and the Agency does not, in this final action, attempt to resolve the scientific or methodological debates reflected in that record. In light of the bases adopted for this final action, the EPA lacks authority to resolve these issues here for regulatory purposes under CAA section 202(a)(1).

Comments Asserting That Scientific Assessments Since 2009 Have Strengthened the Basis for the 2009 Endangerment Finding: Other commenters disagreed with the scientific discussion in the proposal and with the claim that intervening science no longer supports the Endangerment Finding. These commenters emphasized that, in their view, major assessment reports completed since 2009, including the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report and the Fifth National Climate Assessment (NCA5), describe that the climate system has warmed; that human activities, particularly GHG emissions, have contributed substantially to observed warming since the mid-twentieth century; and that climate change already affects a wide range of physical, ecological, social, and economic outcomes. Commenters pointed to NCA5's finding that climate change is affecting every U.S. region and multiple sectors, including health, agriculture, infrastructure, and ecosystems, and that risks increase with additional emissions. Commenters also cited reports from the National Academies of Sciences (NAS), such as Climate Change: Evidence and Causes, and a 2025 review of GHG emissions and U.S. climate, health, and welfare which they describe as concluding that multiple lines of evidence link anthropogenic GHG emissions to observed warming and associated risks.

These commenters argued that, taken together, these assessments indicate that the scientific basis for concluding that GHG emissions may reasonably be anticipated to endanger public health and welfare has strengthened since 2009, not weakened. These commenters contended that the proposal downplayed or mischaracterized these assessments by emphasizing selected uncertainties without giving sufficient weight to their central conclusions.

Response: The EPA acknowledges that many commenters relied on IPCC, NCA5, and NAS reports to argue that mainstream scientific assessments continue to support and, in their view, reinforce the types of conclusions that informed the Endangerment Finding. The EPA further acknowledges that these assessments describe several conclusions, including that human influence has warmed the climate system and that climate change poses a range of risks to people and the environment.

At the same time, the EPA recognizes that the scientific record does not consist of a single set of results, but instead reflects a range of analyses that place different weight on particular datasets, models, and impact estimates. Some studies and assessments rely more heavily on global climate model ensembles and long-term series of surface temperature, ocean heat content, and sea level, while others emphasize satellite records, reanalysis products, and shorter-term regional observations. Different authors make different methodological choices about how to treat internal climate variability, combine observational datasets, and evaluate model performance at global, regional, or local scales.

The literature includes a range of results with varied degrees of confidence regarding probabilistic outcomes, which in turn may affect the weight decision makers should place in particular projections and in the quantification of specific climate-related risks. Similarly, impact analyses and integrated assessments apply different assumptions when translating projected physical changes into estimates of effects on health, agriculture, infrastructure, ecosystems, and the broader economy. Those analyses vary in their assumptions about population, economic growth, land use, technical change, adaptation, and behavioral responses. Some studies emphasize the potential for adaptation and innovation to reduce harms; others highlight the potential for compounding effects, distributional consequences, or low-probability, high-impact outcomes. These choices can lead to different estimates of the magnitude, timing, and regional distribution of impacts, even when starting from similar underlying physical projections.

Comments on Scientific Uncertainty, Assumptions, and What Remains Unknown: Commenters on both sides discussed the nature and implications of scientific uncertainty. Commenters who supported rescission on scientific grounds highlighted uncertainty in estimates of climate sensitivity, the representation of cloud and aerosol processes, regional precipitation changes, and how the frequency and intensity of specific extreme events may change in particular locations. These commenters argued that differences among observational datasets and model ensembles at certain scales make it difficult, in their view, to quantify reliably the magnitude of future climate change and associated impacts.

Other commenters agreed that uncertainties exist but emphasized that major assessments explicitly acknowledge and characterize these uncertainties while still reaching robust conclusions about several aspects of climate change. These commenters noted that the Global Change Research Act directs national assessments to discuss both scientific findings and scientific uncertainties, and argued that uncertainty often relates to the size, timing, or regional distribution of projected changes rather than the direction of change or the fundamental influence of GHG emissions on the climate system.

Commenters from multiple perspectives also discussed uncertainties and assumptions in the translation of physical climate changes to quantified health and welfare outcomes. These commenters observed that impact assessments must make assumptions about future population and economic growth, land use, technology, adaptation measures, and human behavior. Some commenters argued that such assumptions may overstate risks by underestimated adaptation and innovation. Others argued that the same assumptions may understate risks because they may not fully capture low-probability, high-impact outcomes, compounding effects, or distributional consequences.

Response: The EPA agrees that significant uncertain assumptions remain in the scientific record related to climate change and its impacts. Climate and impact modeling necessarily involve choices about emissions scenarios, socioeconomic pathways, and adaptation responses, as well as assumptions about processes within the climate system itself. The EPA also recognizes that different scientific bodies and authors may draw different inferences from the same underlying data when weighing these uncertainties. Major assessments, such as IPCC and NCA5, describe many of these uncertainties and present ranges of projected outcomes, while still expressing confidence in certain broad findings. Other analyses highlighted by commenters place relatively greater emphasis on the limits of current models and on the difficulty of quantifying net impacts.

Comments on Ongoing Scientific Debate and Future Assessments, Including a Possible 6th National Climate Assessment (NCA6): Several commenters asked the EPA to recognize explicitly that scientific research and debate about climate change will continue, regardless of the outcome of this rulemaking. These commenters pointed to ongoing work in universities, Federal and state agencies, and international institutions, and noted that the U.S. has historically produced periodic NCAs under the Global Change Research Act.

Some commenters referenced recent developments affecting Federal climate assessment activities, including actions that have affected contributors and online access to materials related to a future NCA6. These commenters argued that even if institutional arrangements change, scientific work on climate change will continue in peer reviewed literature and independent synthesis efforts. Some commenters urged the EPA to defer any change to the Endangerment Finding until after any new national or international assessment, while others argued that the existence of continuing debate and evolving research supports a decision not to rely on the Endangerment Finding.

In response, the EPA understands that scientific research and debate about climate change will continue during and after this Administration. Researchers will continue to publish new observations, attribution studies, model evaluations, and impact assessments. Domestic and international bodies may undertake additional synthesis efforts, including any future work related to a NCA6 or comparable report.

Comments on the EPA's use of the Proposed Scientific Alternative: Some commenters who opposed the proposed scientific alternative requested that if the EPA decides not to finalize that rationale, the Agency should make clear that the Agency is not relying on specific scientific critiques as a necessary or independent basis for rescinding the Endangerment Finding or

repealing vehicle GHG standards. These commenters expressed concern that references in the proposal could be misinterpreted as a new negative scientific judgement about climate change and its impacts. These commenters asked the EPA to clarify that the Agency is not issuing a new scientific determination under CAA section 202(a). Other commenters, including some who supported rescission on scientific grounds, urged the EPA to retain a version of the scientific alternative rationale in the final action to signal ongoing concerns about the treatment of uncertainty, model performance, and global versus domestic contributions to climate risk. These commenters argued that such a discussion would provide context for any future Agency considerations of climate-related issues, even if the EPA based this particular decision primarily on legal grounds.

Response: The EPA has considered these comments and, in this final action, is not finalizing the alternative climate science rationale and is not finalizing new findings by the Administrator with respect to global climate change concerns under CAA section 202(a)(1). The EPA does not rely on any specific critique of climate science as a necessary justification for this action. Given our conclusion that we lack legal authority to regulate in response to global climate change concerns under CAA section 202(a)(1), it would be unnecessary and inappropriate to resolve such questions in this regulatory context. The EPA includes this section to summarize major scientific themes commenters raised and to acknowledge that scientific research and debate about climate change will continue. This discussion does not endorse or reject any particular assessment, study, or comment letter in the docket with respect to assertions regarding global climate change science and has limited its responses to the bases being finalized in this final action. The EPA's conclusion in this final action is limited to the legal determination that CAA section 202(a) does not provide the authority to regulate GHG emissions from new motor vehicles or new motor vehicle engines for the purpose of addressing global climate change concerns, irrespective of how ongoing scientific debates are ultimately resolved.

B. There Is No Requisite Technology for Light- and Medium-Duty Vehicles That Meaningfully Addresses the Identified Dangers of the Six “Well- Mixed” GHGs

As stated in section V.C of this preamble, even if all GHG emissions were eliminated from all LD, MD and HD vehicles and engines, it would have a de minimis impact on public health or welfare. Therefore, there is no requisite control technology for LD and MD vehicles and engines that would meaningfully address the potential public health or welfare impacts since there is no technology that would completely eliminate all GHG emissions from vehicles.

However, due to the EPA's lack of authority under CAA section 202(a), the EPA does not believe that it is necessary to finalize this alternative basis for repeal. To note, as it relates to setting standards under CAA section 202(a)(2), the EPA must take into account requisite technology, giving appropriate consideration to the cost of compliance.

We therefore believe it is more appropriate to consider whether there is any “requisite technology” that could meet the statutory requirements when establishing standards than under this regulatory action.

In the proposal, the Agency described alternative bases that the Administrator could consider as rationale for the proposed repeal of the GHG standards. One of them was the negative impact that higher vehicle prices (from the GHG standards) may have on delaying the purchase of safer and lower emitting vehicles. In the proposal, the Agency noted that complying with GHG emission standards often requires manufacturers to design and install new and more expensive technologies, thereby increasing the price of new vehicles and reducing consumer demand. More expensive new vehicles are cost prohibitive for some consumers, and those consumers are likely to turn to the used vehicle market or continue using an older vehicle rather than purchase a new vehicle. The Agency stated in the proposal that all other things being equal, an increase in the price of new vehicles can result in consumers keeping their vehicles for longer periods, delaying the purchase of new vehicles, and decreasing the rate at which old vehicles in the national fleet are replaced by new vehicles (i.e., fleet turnover). Contrary to the goals of the EPA's GHG emission standards and the intended purpose of CAA section 202(a), a delay in fleet turnover can negatively impact air quality because older vehicles tend to emit higher levels of air pollutants, including criteria pollutants and hazardous air pollutants, regulated by the EPA.\191\ Slowing fleet turnover is of particular concern with respect to the EPA's 2024 GHG Emission Standards Rules because of the large increase in vehicle technology costs which will likely lead to large increases in purchase prices, and the impact battery electric and fuel cell vehicle technologies will have on purchasing decisions of consumers (for light- , medium-, and heavy-duty vehicle buyers). Increased prices and some consumers rejecting battery electric and fuel cell vehicle technologies may lead consumers to hold on to their existing vehicles longer. Vehicles are more likely to emit less air pollution with each subsequent model year because of improvements in technology, ordinary wear and tear that decreases the effectiveness of installed technology, and greater stringency in more recent regulations for criteria pollutants and hazardous air pollutants.\192\ The Agency requested comment on this proposed alternative basis for the repeal of the vehicle and engine GHG standards.

\191\ A discussion of the impact of higher vehicle prices on slowing fleet turnover and thus increasing emissions can be found at 85 FR 24186 and 25039.

\192\ See 90 FR 36313.

The Agency notes that since the publication of the EPA proposal, NHTSA issued a proposal to change the CAFE standards for certain model years of vehicles after determining that previous rulemakings inappropriately considered alternative fuel technologies and the availability of compliance credits, which is prohibited pursuant to 49 U.S.C. 32902(h). In their proposal,

NHTSA evaluated its statutory factors in light of current circumstances and tentatively concluded that the existing standards exceed those that are maximum feasible. In addition, NHTSA conducted detailed modeling of the impact of various levels of fuel economy standards on new vehicle purchases and the impact on the in-use vehicle fleet.\193\ NHTSA's proposal finds that more stringent fuel economy standards lead to higher vehicle prices, which in turn reduce vehicle fleet turnover.\194\ NHTSA also finds that newer vehicles are safer than older vehicles (both for the driver/occupants of the newer vehicles and for safety of the in-use fleet overall). NHTSA also finds that newer vehicles generally emit lower emissions of certain criteria pollutants, depending upon the model year of the vehicle. In addition, in their proposal, NHTSA evaluated its statutory factors in light of current circumstances and tentatively concluded that the existing standards exceed those that are maximum feasible. The Agency received substantial supportive and adverse comments on this proposed alternative rationale for repeal of the GHG standards. Several comments included technical assessments and modeling to support the commenters' views.

\193\ National Highway Traffic Safety Administration. “Draft Technical Support Document The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule III for Model Years 2022 to 2031 Passenger Cars and Light Trucks.” December 2025. Chapter 4.3.

\194\ A discussion of the impact of higher vehicle prices on slowing fleet turnover can be found at 85 FR 24626 (Apr. 30, 2020).

As discussed elsewhere in this preamble, the Agency is repealing the GHG standards because we do not have authority to establish such standards under the CAA. The EPA is not basing the repeal on the proposed alternative rationale described in this section (section VI.D of this preamble). For this reason, the Agency has not responded to the comments received on this alternative rationale from the proposal.

Nevertheless, the Agency does believe that when establishing or revising emission standards under CAA section 202(a), the Administrator may consider the impacts of emission standards on safety, and in some cases is required to do so, such as standards established under CAA section 202(a)(3)(A).

As discussed in sections III, IV, and VI of this preamble, the EPA is repealing all GHG emission standards for LD vehicles, MD vehicles, HD vehicles, and HD engines. This includes emission standards for the subset of four of the six “well-mixed GHGs” whose elevated concentrations in the upper atmosphere the Endangerment Finding identified as the “air pollution” in question that are actually emitted by such vehicles and engines--CO2, N2O, methane, and HFCs--as well as the compliance provisions for the GHG standards. These changes apply to all MYs of vehicles and engines, including MYs that have completed manufacture prior to the effective date of the final action.

This final action increases flexibility for vehicle manufacturers. Manufacturers will have no vehicle technology-mix constraints that arise from the EPA GHG standards and will be free to produce a range of technologies, including gasoline, diesel, alternative fuels, and plug- in electric vehicles. Thus, we do not anticipate material compliance difficulties on the part of manufacturers in response to this final action.

In section VII.A of this preamble, we discuss the anticipated impacts of repealing GHG emission standards under CAA section 202(a)(1) on the overall regulatory scheme for parties currently subject to the standards. As explained in this preamble section and elsewhere in this preamble, we did not reopen for comment or substantively revise any emission standards for criteria pollutants or hazardous air pollutants, nor did we reopen or substantively revise any regulatory provisions related to NHTSA's CAFE standards or the EPA's role in administering EPCA and EISA. This final action also does not impact Federal preemption for motor vehicle and engine emission standards under CAA section 209(a) or under EPCA and EISA, including with respect to GHGs. Regardless, whether we prescribe standards for GHG emissions from new motor vehicles or engines, CAA section 209(a) continues to apply by its own force to preempt State laws, regulations, and causes of action that adopt or attempt to enforce any standard relating to the control of emissions from new motor vehicles or engines.

In section VII.B of this preamble, we describe regulatory amendments related to the LD and MD vehicle program. In section VII.C of this preamble, we describe regulatory amendments related to the HD engine and vehicle program. A memorandum submitted to the docket includes redline text highlighting changes to the regulations.\195\

\195\ Memorandum to Docket EPA-HQ-OAR-2025-0194, “Redline Version of EPA's Final Regulations for the Rescission of the Greenhouse Gas Endangerment Finding and Motor Vehicle Greenhouse Gas Emission Standards Under the Clean Air Act.” February 2026.

The EPA's engine and vehicle programs are codified in Title 40 of the CFR. Specifically, the standard-setting parts for light- and medium-duty vehicles are located in 40 CFR part 85 and 86. The standard-setting part for HD engines is located in 40 CFR part 1036 and the standard-setting part for HD vehicles is 40 CFR part 1037. Each standard-setting part includes regulations describing emission standards and related requirements and compliance provisions for certifying engines or vehicles. Consistent with the proposed rule and explained in this preamble section and elsewhere in this preamble, the EPA is retaining measurement procedures, reporting requirements, and credit provisions for the LD program necessary for demonstrating compliance with NHTSA's CAFE standards and the EPA's fuel economy labeling program to meet our statutory obligations under EPCA and EISA. In response to comments on the proposed rule, we are revising the proposed approach for HD engines and vehicles subject to NHTSA's fuel- consumption standards to similarly retain measurement procedures and reporting requirements that are necessary for demonstrating compliance with NHTSA's standards.

Further, as explained in this section and elsewhere in this preamble, we did not reopen for comment and are not substantively revising emission standards or compliance provisions related to criteria pollutant exhaust emissions (i.e., NOX, HC, PM, and CO), air toxic emissions, or evaporative and refueling emissions.\196\ We may consider those issues, as appropriate, in future rulemakings.

\196\ In this rulemaking, NOX, HC, PM, and CO are sometimes described collectively as “criteria pollutants” because they are either criteria pollutants under the CAA or precursors to the criteria pollutants ozone and PM.

The repeal in this final action is limited to the regulatory provisions for GHG emission standards found in 40 CFR parts 85, 86, 1036, and 1037, with minor conforming adjustments to unrelated emission standards for new motor vehicles and engines in 40 CFR parts 600 and 1039. As detailed in sections VII.B and VII.C of this preamble, this final action does not revise emission standards for criteria pollutants or air toxics. The EPA may reconsider and propose to revise the regulatory provisions for those programs in a separate rulemaking action.

Similarly, we did not reopen for comment or propose to revise regulatory provisions necessary for NHTSA's CAFE standards or the EPA's co-administration of EPCA and EISA.

For this reason, the repealed provisions in this final action do not impact Federal preemption under EPCA, as amended by EISA, related to fuel economy standards. EPCA provides that when “an average fuel economy standard prescribed under this chapter is in effect, a state or a political subdivision of a state may not adopt or enforce a law or regulation related to fuel economy standards or average fuel economy standards for automobiles covered by an average fuel economy standard under this chapter” \197\ unless the standards are identical or apply only to vehicles obtained for the use of the state or political subdivision.\198\ We reiterate that the EPA did not reopen this issue in this rulemaking, as we did not propose to revise regulatory provisions necessary for NHTSA's CAFE standards or the EPA's co- administration of EPCA and EISA. In providing this information for better clarity on the scope of the final action, the EPA notes that we are not here “undertak[ing] a serious, substantive reconsideration of the existing” position. Growth Energy v. EPA, 5 F.4th 1, 21 (D.C. Cir. 2021).

\197\ 49 U.S.C. 32919(a).

\198\ 49 U.S.C. 32919(b)-(c).

The repealed provisions in this final action also do not impact Federal preemption under CAA section 209(a), which provides that “[n]o State or any political subdivision thereof shall adopt or attempt to enforce any standard relating to the control of emissions from new motor vehicles or new motor vehicle engines subject to this part,” including “certification,” “inspection” or “approval” requirements “relating to the control of emissions from” such vehicles or engines.\199\ Because new motor vehicles and engines that have been subject to GHG emission standards remain subject to Title II of the CAA, the statute would by its own force continue to preempt “any” State or local law, regulation, or cause of action that adopts or attempts to enforce “any standard relating to the control of emissions.” Relatedly, the CAA continues to preempt Federal common-law claims for vehicle and engine emissions because Congress adopted a standard for when such emissions rise to the level of regulatory concern and “delegated to EPA the decision whether and how to regulate” such emissions. Am. Elec. Power, 564 U.S. at 426. The CAA also continues to preempt state common-law claims and statutes that seek to regulate out-of-state emissions, independently of CAA section 209(a)'s express preemption provision for mobile-source emissions. See City of New York v. Chevron Corp., 993 F.3d 81, 98-100 (2d Cir. 2021); cf. Int'l Paper Co. v. Ouellette, 479 U.S. 481, 492 (1987). We retain our authority to prescribe emission standards for any air pollutant that, in the Administrator's judgment, causes or contributes to air pollution that may reasonably be anticipated to endanger public health or welfare. See the Response to Comments document for more detailed comment summaries and responses.

\199\ 42 U.S.C. 7543(a).

The EPA's engine and vehicle programs are codified in Title 40 of the CFR. Specifically, the standard-setting parts for light- and medium-duty vehicles are located in 40 CFR parts 85 and 86. The standard-setting part for HD engines is located in 40 CFR part 1036 and the standard-setting part for HD vehicles is 40 CFR part 1037. Each standard-setting part includes regulations describing emission standards and related requirements and compliance provisions for certifying engines or vehicles.

Section VII.B.1 of this preamble provides background on the EPA's LD and MD vehicle GHG emission programs. In general, through a series of rulemakings beginning with MY 2010 for LD vehicles and MY 2014 for MD vehicles, the EPA increased the stringency of the GHG standards for these vehicles over time, in particular the CO2 standard. The remainder of section VII.B of this preamble summarizes the comments received, and describes the changes to the LD and MD vehicle GHG regulations after considering those comments. 1. Background on the Light- and Medium-Duty Vehicle GHG Program

In 2010, the EPA relied on the Endangerment Finding to adopt the first GHG emission standards for passenger cars and light trucks for MYs 2012 through 2016 in a joint rulemaking with NHTSA.\200\ In 2012, the EPA and NHTSA adopted another set of GHG standards (issued by the EPA) and fuel economy standards (issued by NHTSA) for passenger cars and light trucks for MYs 2017 and later in a joint rulemaking.\201\ In 2020, the EPA and NHTSA revised the standards that had previously been adopted and extended them for MYs 2021 through 2026.\202\ In 2021, we further revised GHG standards for passenger cars and light trucks for MYs 2023 through 2026.\203\ For MD vehicles, we initially adopted GHG standards as part of the Phase 1 and Phase 2 HD GHG standards. In 2024, we adopted new standards for passenger cars, light trucks, and MD vehicles starting in MY 2027, effectively combining standards that had previously been maintained separately.\204\

\200\ 75 FR 25324 (May 7, 2010).

\201\ 77 FR 62624 (Oct. 15, 2012).

\202\ 85 FR 24174 (Apr. 30, 2020).

\203\ 86 FR 74434 (Dec. 30, 2021).

\204\ 89 FR 27842 (Apr. 18, 2024).

The EPA has also taken various actions to comply with statutory obligations under EPCA and EISA. Enacted in 1975, EPCA requires NHTSA to establish a regulatory program for motor vehicle fuel economy (now known as CAFE standards) and requires the EPA to establish measurement procedures, data collection procedures, and rules for calculating average fuel economy values in support of NHTSA's CAFE standards. In 2007, Congress amended EPCA by enacting EISA, which required continuing increases in the stringency of CAFE standards for passenger cars and light trucks through MY 2020. EISA also authorized new fuel consumption standards for MD vehicles and HD engines and vehicles.\205\ Those standards, and the EPA's HD engine and vehicle GHG programs, are detailed in section VII.C of this preamble.

\205\ 49 U.S.C. 32902(k).

To comply with EPCA and EISA, the EPA adopted regulations for fuel economy measurements, calculations, and reporting under 40 CFR part 600. The regulation at 40 CFR part 600 now includes additional provisions for measuring, calculating, and reporting fuel consumption values for MD vehicles. This regulatory structure was designed to maximize efficiency within the Federal government and minimize the burden on the engine and vehicle manufacturers by centralizing data submission. We share information with NHTSA as needed to support implementation of NHTSA's fuel economy and consumption standards. 2. Summary of Comments and Updates to the Light- and Medium-Duty Programs

Most comments related to GHG standards for LD and MD vehicles were focused on the proposed rescission of the Endangerment Finding and repeal of the GHG standards. Manufacturers suggested in comments that the EPA establish or determine that the model

year 2027 and later GHG standards in 40 CFR 86.1818-12 and 86.1819-14 are not appropriate, even if those standards are removed in this final action. The commenters suggested making such a determination to prevent future rulemaking action that would simply restore the standards as originally adopted. The EPA is removing the GHG emission standards for the reasons described in sections II, IV, and VI of this preamble. Because we are finalizing the conclusion that the EPA lacks authority to prescribe GHG emission standards in response to global climate change concerns under CAA section 202(a)(1), we are not putting in place alternative GHG emission standards.

Commenters also correctly identified several additional amendments to remove detailed regulatory provisions that become obsolete in the absence of GHG standards. We have amended the regulation to incorporate the suggested amendments as noted in the following section VII.B.3 of this preamble. See the Response to Comments document for more detailed summaries of and responses to comments related to specific LD and MD vehicle GHG regulations. 3. Changes to the Light- and Medium-Duty Vehicle GHG Regulations

The EPA's LD and MD vehicle emission regulations are spread across three CFR parts. 40 CFR part 85 includes various general compliance provisions for both criteria pollutant and GHG emissions. Many of those criteria pollutant provisions apply equally to highway motorcycles (but not for GHG emissions, as there are no EPA GHG requirements under 40 CFR part 85 for motorcycles). 40 CFR part 86 includes emission standards and certification provisions for both criteria pollutant and GHG emissions. 40 CFR part 600 includes measurement and reporting procedures related to fuel economy and GHG standards and to fuel economy labeling.

In the following preamble subsections, we describe the changes in this final action to remove and amend specific portions of each of these regulatory parts. The general approach is to remove the MY 2012 and later GHG emission standards for passenger cars and light trucks and the MY 2014 and later GHG emission standards for MD vehicles. We are also removing the testing and reporting requirements associated with the GHG emission standards. In keeping with our obligations under EPCA, as noted in section VII.B.1 of this preamble, we are not removing the testing and reporting requirements related to CAFE standards for passenger cars and light trucks. We are similarly preserving the testing and reporting provisions related to NHTSA's fuel-consumption standards for MD vehicles. a. 40 CFR Part 85--Compliance Provisions for Light- and Medium-Duty Vehicles

This final action amends 40 CFR part 85 to remove all references to GHG emission standards and related provisions while retaining provisions that support our criteria pollutant emission program. In this preamble subsection, we describe several amendments that are necessary to remove GHG-related provisions from 40 CFR part 85 while ensuring that criteria pollutant emission standards are not substantively impacted. Table 8 provides a summary of amendments to 40 CFR part 85. [GRAPHIC] [TIFF OMITTED] TR18FE26.010

The regulations at 40 CFR part 85, subpart F, provide an exemption from the general tampering prohibition for clean alternative fuel conversions. Specifically, the regulations describe how anyone modifying an in-use vehicle to run a different fuel can demonstrate that the fuel conversion maintains a level of emission control that qualifies them for an exemption from the tampering prohibition. This exemption generally allows for modifying vehicles already certified to emission standards in a way that does not cause the modified vehicle to exceed the emission standards that apply for the certified vehicle. The demonstration applies for both criteria and GHG emissions. We are amending 40 CFR 85.525 by removing the requirement to demonstrate compliance with GHG emissions. Program requirements related to criteria exhaust, evaporative, and refueling emissions and onboard diagnostics remain unchanged.

The regulation at 40 CFR 85.1515 describes the standards that apply for Independent Commercial Importers in their practice of importing used vehicles. We are only removing the provision that disallowed generation and use of GHG emission credits. We note further that the regulation requires Independent Commercial Importers to meet all the standards that apply under 40 CFR part 86. With the other changes described in this action, the removal of GHG standards from 40 CFR part 86, subpart S, applies equally to imported vehicles. Imported vehicles continue to be subject to criteria exhaust, evaporative, and refueling emission standards and requirements for onboard diagnostics as specified in 40 CFR part 86, subpart S.

We are revising the recall-related instructions for remedial plans and consumer notification in 40 CFR 85.1803 and 85.1805 to remove a reference to 40 CFR 86.1865-12(j)(3), which we are removing in this action. The referenced paragraph relates to recall provisions for vehicles that do not comply with GHG standards. We are also revising definitions of “Emission-related defect” and “Voluntary emissions recall” in 40 CFR 85.1902 where those definitions describe how manufacturers must report GHG-related defects differently than defects related to criteria pollutant emission standards.

Finally, we proposed to amend the warranty provisions for specified major emission control components in 40 CFR 85.2103 by removing the reference to batteries serving as a Renewable Energy Storage System (RESS) for electric vehicles and plug-in hybrid electric vehicles, along with all components needed to charge the system, store energy, and transmit power to move the vehicle. Some commenters supported this proposed change. Other commenters noted that RESS provisions are not limited to greenhouse gas emissions and that the Agency specifically connected the warranty provisions to its nonmethane organic gases and oxides of nitrogen (NMOG+NOX) standards in the 2024 LD and MD Multi-Pollutant Emission Standards Rule.\206\ Considering the connection to the EPA criteria pollutant program, which is out of scope of this rulemaking, we are not taking final action at this time on the proposal to remove batteries serving as a RESS for electric vehicles and plug-in hybrid electric vehicles from the list of specified major emission control components in 40 CFR 85.2103(d)(1). We may consider revisions in a future criteria pollutant rule. Note that we are nevertheless finalizing the proposed change to remove 40 CFR 85.2103(d)(3), which established the newly required battery monitor as the basis for making battery-related warranty claims; since we are removing the requirement to install these dashboard-mounted battery monitors in this rulemaking, warranty implementation will necessarily proceed without the benefit of information from the battery monitor.

\206\ 89 FR 27965 (Apr. 18, 2024).

b. 40 CFR Part 86--Emission Standards and Certification Requirements for Light- and Medium-Duty Vehicles

In general, we are amending 40 CFR part 86 to remove all GHG emission standards, references to such standards, and related provisions while retaining provisions that support our criteria pollutant emission program. In this preamble subsection, we describe several amendments that are necessary to remove GHG-related provisions from 40 CFR part 86 while ensuring that criteria pollutant emission standards are not substantively impacted. Table 9 provides a summary of the amendments to 40 CFR part 86. [GRAPHIC] [TIFF OMITTED] TR18FE26.011

We are amending the list of materials incorporated by reference in 40 CFR 86.1 by removing material that is referenced only in regulations that we are removing in this final action.

We are amending the applicability statements in 40 CFR 86.1801-12 by removing references to GHG standards and related compliance provisions. We are also removing the instruction related to work factor for vehicles above 14,000 pounds gross vehicle weight rating (GVWR) at 40 CFR 86.1801-12(a)(3) since that is meaningful only in the context of GHG standards. We adopted the work-factor provision in a 2016 final rule as a means of limiting the extent to which manufacturers would certify those larger HD vehicles in test groups along with chassis- certified MD vehicles.\207\ Removing the instruction to calculate GHG standards based on a work factor appropriate for MD vehicles, without other compensating changes, could lead to a greater number of HD vehicles certified as MD vehicles. The work-factor provision was adopted as a means of addressing competing concerns from different manufacturers. As a result, we are limiting this provision to HD vehicles with a maximum value of 19,500 pounds GVWR. We believe this limitation is the best way to maintain a consistent approach for certifying affected vehicles.

\207\ 81 FR 73478 (Oct. 25, 2016).

We are amending the definitions in 40 CFR 86.1803-01 by removing several defined terms that are used only in regulatory provisions that we are removing in this final action. This includes removing the definition of “configuration”; while this definition is no longer needed, we are retaining the slightly different definition of “vehicle configuration,” since that definition is needed to support standards related to criteria pollutants. We are accordingly amending several references across 40 CFR part 86, subpart S, to change from a generic reference to “configuration” and replace it with the specific reference to “vehicle configuration.” We are also amending 40 CFR 86.1803-01 by adding a definition for “work factor” that is consistent with the definition that is embedded in 40 CFR 86.1819-14. We adopted the definition of “work factor” in 40 CFR 86.1819-14 primarily as a means of accounting for specific vehicle characteristics in establishing GHG emission standards for MD vehicles. We are removing all of 40 CFR 86.1819-14 as described below. However, we are keeping the definition of work factor to support the definition

of “medium-duty passenger vehicle,” which relies on the work factor concept to categorize vehicles for applying criteria pollutant emission standards.

We are amending 40 CFR 86.1803-01 and 86.1809-12 by removing references to the air conditioning efficiency test as part of the consideration for determining what is a defeat device. We are eliminating the air conditioning efficiency test from the EPA certification program because it has been used only to generate GHG credits. Note that we are not removing the air conditioning efficiency credit provisions and measurement procedures from 40 CFR 86.1868-12 and 1066.845, which are used by manufacturers for compliance with fuel economy standards as described in 40 CFR 600.510-12(c)(3). If in the future NHTSA changes the fuel economy standards to no longer reference air conditioning efficiency credits, we intend to remove those provisions from 40 CFR 600.513 if they become obsolete.

We are amending useful life specifications in 40 CFR 86.1805-12 and 86.1805-17 by removing references to useful life for GHG standards. Useful life for all criteria exhaust, evaporative, and refueling emission standards and onboard diagnostics remain unchanged.

In response to public comments, we are amending 40 CFR 86.1806-27 to clarify we are excluding certain information items identified in 13 CCR 1968.2 because they are related to GHG emission standards.

We are amending labeling requirements in 40 CFR 86.1807-01 by removing the requirement for battery electric vehicles (BEVs) and plug- in hybrid electric vehicles (PHEVs) to identify monitor family and battery durability family on the vehicle emission control information label. We are removing the battery monitoring and battery durability requirements in 40 CFR 86.1815-27 and therefore no longer need to include this family information as part of the certification process.

We are amending 40 CFR 86.1810-09(f)(2) by removing references to GHG emission standards. Manufacturer requirements to comply with altitude-related demonstration requirements for vehicles subject to the cold temperature standards for nonmethane hydrocarbon emissions remain unchanged.

We are amending 40 CFR 86.1810-17(j) by removing references to GHG emission standards. Small-volume manufacturers that modify a vehicle already certified by a different company must continue to meet other requirements as specified, such as those related to criteria exhaust, evaporative, and refueling emissions and onboard diagnostics.

We are amending 40 CFR 86.1811-17, 86.1811-27, and 86.1816-18 by removing references to GHG emission standards. We are not otherwise changing these sections, which establish criteria exhaust emission standards for LD and MD vehicles.

We are removing 40 CFR 86.1815-27, as proposed. We adopted this section to establish battery monitoring and battery durability requirements for BEVs and PHEVs. Since the earliest battery monitoring and battery durability requirements were scheduled to start in MY 2027, removing those requirements involves no immediate transition to discontinue compliance for certified vehicles.

We are removing 40 CFR 86.1818-12 and 86.1819-14. These sections described the GHG standards and implementing provisions for MY 2010 and later LD vehicles and for MY 2014 and later MD vehicles. We are discontinuing the requirement to demonstrate compliance with these GHG standards and note that this discontinuation applies as of the effective date of the final action. Manufacturers need not amend existing certificates for ongoing production for the current MY. Manufacturers will in any case not need to submit credit reports at the end of the current MY to demonstrate compliance with the fleet average CO2 standards.

We are amending test group specifications in 40 CFR 86.1823-08 by removing durability demonstration requirements related to GHG emission standards.

We are amending the provisions for establishing test groups in 40 CFR 86.1827-01 by removing the reference to CO2 emission standards.

We are amending testing specifications in 40 CFR 86.1829-15 by removing references to battery durability requirements and GHG emission standards, except where needed to account for emission measurements related to fuel economy labeling.

We are amending the compliance provisions 40 CFR 86.1835-01, 86.1838-01, 86.1841-01, 86.1848-10, and 86.1854-12 by removing references to GHG emission standards.

We are removing the description of battery monitor families and battery durability families and other GHG-related items from the reporting requirements in 40 CFR 86.1844-01.

We are amending carryover testing provisions in 40 CFR 86.1839-01 by removing references to accuracy requirements for battery monitoring for electric vehicles (EVs), which included battery electric vehicles and fuel cell electric vehicles, and PHEVs.

We are amending instructions for the application for certification in 40 CFR 86.1844-01 by removing references to refrigerant leakage rates and GHG emission standards.

We are amending in-use testing requirements in 40 CFR 86.1845-04 and 86.1846-01 by removing references to testing GHG emissions and testing related to battery monitor accuracy and battery durability for EVs and PHEVs. We are also amending 40 CFR 86.1845-04 by changing the nomenclature for the reference brake-specific CO2 emission rate needed to perform calculations related to in-use testing for engines certified under 40 CFR 1036.635 for use in vehicles with high towing capacity.

We are removing requirements for battery durability testing and other GHG-related provisions in 40 CFR 86.1847-01 and 86.1848-10.

We are amending the credit provisions for criteria exhaust and evaporative emissions in 40 CFR 86.1861-17 by referencing the credit provisions in 40 CFR part 1036, subpart H, instead of 40 CFR part 1037, subpart H. We are removing several credit provisions in 40 CFR part 1037, subpart H, in this rule because they were needed only in relation to the GHG standards in 40 CFR part 1037, which we are removing in this rule. The referenced credit provisions in 40 CFR part 1037, subpart H, are equivalent to the analogous credit provisions in 40 CFR part 1036, subpart H. While the final action preserves some credit-related provisions in 40 CFR part 1037 in support of NHTSA's fuel consumption standards, we are finalizing as proposed the updated references to 40 CFR part 1036 to ensure the complete subpart of the EPA averaging, banking, and trading provisions can continue to apply under 40 CFR 86.1861-17. We are also amending 40 CFR 86.1861-17 by removing a reference to 40 CFR 86.1865-12(j)(3), which we are removing in this action.

We are removing 40 CFR 86.1865-12, which described the emission credit provisions related to the fleet average GHG standards. See the discussion related to 40 CFR 86.1818-12 and 86.1819-14 for the transition to discontinued GHG standards for the MY currently in production for the year when the final action is effective. More specifically, we will no longer recognize manufacturers' positive or negative GHG credit balances as of the effective date of the final action. Note also that we are removing 40 CFR 86.1865-12(j)(3), which describes recall provisions for

vehicles that do not comply with GHG standards. We recognize that a credit-based approach to recall is no longer appropriate without a GHG credit program. In the context of NMOG+NOX standards, recall would involve identifying and correcting a vehicle defect to bring vehicles into compliance with standards. Accordingly, we are removing the provisions describing a credit-based remedy for noncompliance.

We are removing 40 CFR 86.1866-12, 86.1867-12, and 86.1867-31. These sections describe GHG credit programs for advanced technology and air conditioning leakage that served only in relation to the GHG standards that we are removing in this action.

We are amending the credit provisions for air conditioning efficiency and for off-cycle technologies in 40 CFR 86.1868-12 and 86.1869-12 by removing references to the fleet average GHG standards and adjusting the description to clarify that these credit provisions continue to serve as inputs for calculating fuel consumption improvement values and average fuel economy for LD program vehicles under 40 CFR 600.510-12. Note that the 2024 LD and MD Multi-Pollutant Emission Standards Rule included several changes to narrow the availability of air conditioning efficiency and off-cycle credits; those changes continue to apply in the context of fuel consumption improvement values and average fuel economy.\208\

\208\ 89 FR 27842 (Apr. 18, 2024).

We are removing 40 CFR 86.1870-12, which described a GHG credit program for full-size pickup trucks with hybrid technology. Those GHG credits were also used for calculating fuel consumption improvement values and average fuel economy for LD program vehicles under 40 CFR 600.510-12. However, we amended those credit provisions in the 2021 final rule to establish MY 2024 as the last year that manufacturers could generate those credits.\209\ Because those credits are already discontinued for purposes of demonstrating compliance with EPA emission standards, manufacturers can no longer use those provisions to create fuel consumption improvement values under 40 CFR part 600.

\209\ 86 FR 74434 (Dec. 30, 2021).

c. 40 CFR part 600--Requirements Related to Fuel Economy for Light- and Medium-Duty Vehicles

In general, we are amending 40 CFR part 600 to remove all references to GHG emission standards and related provisions while retaining provisions that support compliance with CAFE standards and fuel economy labeling for passenger cars and light trucks. In the remainder of this preamble subsection, we describe several amendments needed to remove GHG-related provisions from 40 CFR part 600 without affecting provisions related to CAFE standards and fuel economy labeling. Table 10 provides a summary of the regulations we are either removing from or amending in 40 CFR part 600. [GRAPHIC] [TIFF OMITTED] TR18FE26.012

We are amending the applicability statements in 40 CFR 600.001 by removing references to carbon-related exhaust emissions and fleet average CO2 standards. We are also revising the reference in 40 CFR 600.001(a) to MD vehicles because the testing and reporting provisions remain only to support fuel-consumption standards that apply under 49 CFR part 535. Testing provisions will remain to describe (1) how passenger automobiles and light trucks (including MD passenger vehicles) must meet fuel economy standards, (2) how manufacturers must prepare fuel economy labels for those vehicles, and (3) how MD vehicles must meet fuel-consumption standards.

We are amending the definitions in 40 CFR 600.002 by removing the reference to fleet average CO2 standards. We are also amending several definitions related to MD vehicles to preserve content referenced in 40 CFR 86.1819-14, which we are removing in this final action. We are amending these definitions to support NHTSA's implementation of fuel-consumption standards for MD vehicles.

We are amending the definition of Medium-Duty Passenger Vehicle (MDPVFE) for purposes of fuel economy testing and reporting in 40 CFR 600.002 to align with the clarified definition published by NHTSA at 49 CFR 523.2 (89 FR 52945, June 24, 2024). Aligning these definitions is necessary to ensure the EPA's test procedures are properly applied to vehicles covered by fuel economy standards and labeling requirements.

As described for 40 CFR 86.1803-01, we are amending several references across 40 CFR part 600 to change from a generic reference to “configuration” and replace it with the specific reference to “vehicle configuration.”

We are amending the information requirements in 40 CFR 600.006 through 600.010 by removing references to carbon-related exhaust emissions, GHG

emission standards, and reporting GHG-related information generally.

We are amending the testing overview in 40 CFR 600.101 and 600.111- 08 by removing references to carbon-related exhaust emissions and fleet average CO2 emissions.

We are amending the emission calculations in 40 CFR 600.113-12 by removing references to carbon-related exhaust emissions and other GHG emissions.

We are amending the interim testing provisions in 40 CFR 600.117 by removing paragraph (a)(5) since we are discontinuing GHG testing with in-use vehicles under 40 CFR 86.1845-04. We are also revising paragraphs (a)(6) and (b) to clarify that manufacturers do not adjust measured fuel economy values to account for fuel effects, whether they test with E0 or E10 gasoline.

We are amending the testing, calculation, and reporting specifications in 40 CFR 600.116-12, 600.507-12, 600.509-12, and 600.510-12 by removing references to carbon-related exhaust emissions. We are also removing GHG-specific utility factors in 40 CFR 600.116-12. We note that calculations related to off-cycle credits in 40 CFR 600.510-12(c)(3)(ii) continue to rely on carbon-related exhaust emissions as specified in 40 CFR 86.1869-12.

We are amending the reporting requirements in 40 CFR 600.512-12 by removing references to carbon-related exhaust emissions. This includes amending 40 CFR 600.512-12(c)(5)(i) to explain that the purpose for performing the calculations in 40 CFR 600.510-12(c)(3) is to support credit calculations for fuel economy improvement factors, rather than demonstrating compliance with the fleet average standard for carbon- related exhaust emissions. We are moving the existing reporting requirement for emission credits related to fuel consumption improvement values from 40 CFR 86.1865-12(l)(2)(iii), which we are removing in this final action, to 40 CFR 600.512-12(c)(3) to preserve the existing provisions needed for fuel economy reporting. We are also removing the reporting requirements in 40 CFR 600.514-12, which are solely related to GHG emissions.

This section VII.C includes background on the EPA's HD GHG emission program and describes changes to the engine-based GHG regulations and the vehicle-based GHG regulations we are finalizing after considering comments. 1. Background on the Heavy-Duty Engine and Vehicle GHG Program

The EPA promulgated new GHG emission standards for HD engines and vehicles in three separate rulemakings. In 2011, the EPA established the first GHG standards for MY 2014 and later HD engines and vehicles in an action titled “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles” (HD GHG Phase 1).\210\ In 2016, the EPA set new GHG standards for MY 2021 and later HD engines and vehicles in an action titled “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles--Phase 2” (HD GHG Phase 2).\211\ Most recently, in 2024, the EPA finalized the 2024 HD GHG Emission Standards Rule, which set new CO2 emission standards for MY 2032 and later HD vehicles that phase in starting as early MY 2027 for certain vehicle categories.\212\ The phase-in revises MY 2027 GHG standards that were established previously under the EPA's HD GHG Phase 2 rulemaking.\213\

\210\ 76 FR 57106 (Sept. 15, 2011).

\211\ 81 FR 73478 (Oct. 25, 2016).

\212\ See 89 FR 29559-61 (Apr. 22, 2024).

\213\ 89 FR 29440 (Apr. 22, 2024).

The EPA and NHTSA jointly issued the HD GHG Phase 1 and HD GHG Phase 2 rulemakings covering HD GHG emission and fuel efficiency standards. The EPA set GHG emission standards under CAA section 202(a), and NHTSA set fuel consumption standards under EISA.\214\ The EPA and NHTSA programs were harmonized through MY 2026; however, NHTSA did not adopt changes in fuel consumption standards corresponding to the EPA's HD GHG Phase 3 standards. As a result, the CO2 emission and fuel consumption standards diverged in MY 2027 and later.

\214\ 49 U.S.C. 32902(k).

The EPA's regulations include the test procedures along with a certification and compliance program, which is led by the EPA. As noted previously, this regulatory structure was designed to maximize efficiency within the Federal government and minimize the burden on the engine and vehicle manufacturers by centralizing data submission. Manufacturers submit data and information to the EPA and the EPA, in turn, shares information with NHTSA as needed to support NHTSA's implementation of its fuel consumption standards.\215\

\215\ See 49 CFR 535.8; 40 CFR 1036.755 and 1037.755.