Ohio v. Environmental Protection Agency

AGENCY et al on applications for stay No. 23A349. Argued February 21, 2024—Decided June 27, 2024* The Clean Air Act envisions a collaborative effort between States and the federal government to regulate air quality. When the Environmental Protection Agency sets standards for common air pollutants, States must submit a State Implementation Plan, or SIP, providing for the “implementation, maintenance, and enforcement” of those standards in their jurisdictions. See 42 U. S. C. § 7410(a)(1). Because air currents can carry pollution across state borders, States must also design their plans with neighboring States in mind. Under the Act's “Good Neighbor Provision,” state plans must prohibit emissions “in amounts which will . . . contribute significantly to nonattainment in, or interfere with maintenance by, any other State” of the relevant air-quality standard. § 7410(a)(2)(D)(i)(I). Only if a SIP flails to satisfy the “applicable requirements” of the Act may EPA issue a Federal Implementation Plan, or FIP, for the noncompliant State that flails to correct the deficiencies in its SIP. §§ 7410(k)(3), (c)(1). In 2015, EPA revised its air-quality standards for ozone, thus triggering a requirement for States to submit new SIPs. Years later, EPA announced its intention to disapprove over 20 SIPs because the agency believed they had flailed to address adequately obligations under the Good Neighbor Provision. During the public comment period for the proposed SIP disapprovals, EPA issued a single proposed FIP to bind all those States. EPA designed its proposed FIP based on which emissions-control measures would maximize cost effectiveness in improving ozone levels downwind and on the assumption the FIP would apply to all covered States. Commenters warned that the proposed SIP disapprovals were flawed and that a failure to achieve all the SIP disapprovals as EPA envisioned would mean that EPA would need to reassess the measures necessary to maximize cost-effective ozone-level *Together with No. 23A350, Kinder Morgan, Inc., et al. v. Environmental Protection Agency et al., No. 23A351, American Forest & Paper Assn. et al. v. Environmental Protection Agency, et al., and No. 23A384, United States Steel Corp. v. Environmental Protection Agency et al., also on applications for stay.

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improvements in light of a different set of States. EPA proceeded to issue its final FIP without addressing this concern. Instead, EPA announced that its plan was severable: Should any jurisdiction drop out, the plan would continue to apply unchanged to the remaining jurisdictions. Ongoing litigation over the SIP disapprovals soon vindicated at least some of the commenters' concerns. Courts stayed 12 of the SIP disapprovals, which meant EPA could not apply its FIP to those States.

A number of the remaining States and industry groups challenged the FIP in the D. C. Circuit. They argued that EPA's decision to apply the FIP after so many other States had dropped out was “arbitrary” or “capricious,” and they asked the court to stay any effort to enforce the FIP against them while their appeal unfolded. The D. C. Circuit denied relief, and the parties renewed their request in this Court. Held: The applications for a stay are granted; enforcement of EPA's rule against the applicants shall be stayed pending the disposition of the applicants' petition for review in the D. C. Circuit and any petition for writ of certiorari, timely sought. Pp. 290–300. (a) When deciding an application for a stay, the Court asks (1) whether the applicant is likely to succeed on the merits, (2) whether it will suffer irreparable injury without a stay, (3) whether the stay will substantially injure the other parties interested in the proceedings, and (4) where the public interest lies. Nken v. Holder, 556 U. S. 418, 434. When States and other parties seek to stay the enforcement of a federal regulation against them, often “the harms and equities [will be] very weighty on both sides.” Labrador v. Poe, 601 U. S. –––, ––– (Kava-naugh, J., concurring in grant of stay). Because that is true here, resolution of applicants' stay requests ultimately turns on the first question: Who is likely to prevail at the end. See Nken , 556 U. S., at 434. Pp. 290–292. (b) Applicants are likely to prevail on their arbitrary-or-capricious claim. An agency action qualifies as “arbitrary” or “capricious” if it is not “reasonable and reasonably explained.” FCC v. Prometheus Radio Project, 592 U. S. 414, 423. Thus, the agency must offer “a satisfactory explanation for its action[,] including a rational connection between the facts found and the choice made,” and cannot simply ignore “an important aspect of the problem.” Motor Vehicle Mfrs. Assn. of United States, Inc. v. State Farm Mut. Automobile Ins. Co., 463 U. S. 29, 43. EPA's plan rested on an assumption that all the upwind States would adopt emissions-reduction measures up to a uniform level of costs to the point of diminishing returns. Commenters posed their concerns that if upwind States fell out of the planned FIP, the point at which emissions-control measures maximize cost-effective downwind air-quality im -

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provements might shift. To this question, EPA offered no reasoned response. As a result, the applicants are likely to prevail on their argument that EPA's final rule was not “reasonably explained,” Prometheus Radio Project, 592 U. S., at 423, and that it instead ignored “an important aspect of the problem” before it, State Farm Mut. Automobile Ins. Co., 463 U. S., at 43. Pp. 292–294.

(c) EPA's alternative arguments are unavailing. First, EPA argues that adding a “severability” provision to its final rule—i. e., providing the FIP would “continue to be implemented” without regard to the number of States remaining—responded to commenters' concerns. But EPA's response did not address those concerns so much as it side-stepped them. Nothing in the final rule's severability provision actually addressed whether and how measures found to maximize cost effectiveness in achieving downwind ozone air-quality improvements with the participation of all the upwind States remain so when many fewer States might be subject to the agency's plan. Second, EPA insists that no one raised that concern during the public comment period. The Act's “reasonable specificity” requirement, however, does not mean a party must rehearse the identical argument made before the agency. Here, EPA had notice of the objection, and its own statements and actions confirm the agency appreciated the concern. Third, EPA argues that applicants must return to EPA and file a motion asking it to reconsider its final rule before presenting their objection in court because the “grounds for [their] objection arose after the period for public comment.” § 7607(d)(7)(B). Nothing requires the applicants to return to EPA to raise (again) a concern EPA already had a chance to address. Pp. 294–298. Applications for stay granted. Gorsuch, J., delivered the opinion of the Court, in which Roberts, C. J., and Thomas, Alito , and Kavanaugh, JJ., joined. Barrett, J., filed a dissenting opinion, in which Sotomayor , Kagan, and Jackson, JJ., joined, post, p. 300.

Mathura J. Sridharan, Deputy Solicitor General of Ohio, argued the cause for state applicants in No. 23A349. With her on the application for stay and reply were Dave Yost, Attorney General, Zachery P . Keller, Deputy Solicitor General, Theodore E. Rokita, Attorney General of Indiana, James A. Barta, Deputy Solicitor General, Patrick Morri-sey, Attorney General of West Virginia, Lindsay S. See, So- Page Proof Pending Publication

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licitor General, and Michael Williams , Principal Deputy Solicitor General.

Catherine E. Stetson argued the cause for industry applicants in all cases. With her on the application for stay and reply in No. 23A350 were Ana M. Gutiérrez, Michael D. Miller, Brittany M. Pemberton, and Eric D. McArthur. Jonathan Y . Ellis, Allison D. Wood, Makram B. Jaber, Michael B. Schon, Mithun Mansinghani, David M. Flannery, and Kathy G. Beckett filed an application for stay and reply in No. 23A351. John D. Lazzaretti filed an application for stay and reply in No. 23A384.

Deputy Solicitor General Stewart argued the cause for federal respondents in all cases. Solicitor General Prelogar filed a response in opposition to the applications for stay in all cases.

Judith N. Vale, Deputy Solicitor General of New York, argued the cause for state respondents in all cases. With her on the briefs were Letitia James, Attorney General, Barbara D. Underwood, Solicitor General, Elizabeth A. Brody and Stephen J. Yanni, Assistant Solicitors General, and Morgan A. Costello and Claiborne E. Walthall, Assistant Attorneys General, and Sylvia Hinds-Radix, Corporation Counsel for New York City, and by the Attorneys General for their respective jurisdictions as follows: William Tong of Connecti-cut, Kathleen Jennings of Delaware, Brian L. Schwalb of the District of Columbia, Kwame Raoul of Illinois, Anthony G. Brown of Maryland, Andrea Joy Campbell of Massachusetts, Matthew J. Platkin of New Jersey, Michelle A. Henry of Pennsylvania, and Joshua L. Kaul of Wisconsin. Megan M. Herzog, Sean H. Donahue, David T. Goldberg, Vickie L. Patton, Shaun A. Goho, Neil Gormley, and Kathleen L. Riley filed a response in opposition to the applications for stay for public interest respondents in all cases.†

The Clean Air Act envisions States and the federal government working together to improve air quality. Under that law's terms, States bear “primary responsibility” for developing plans to achieve air-quality goals. 42 U. S. C. § 7401(a)(3). Should a State fail to prepare a legally compliant plan, however, the federal government may sometimes step in and assume that authority for itself. § 7410(c)(1). Here, the federal government announced its intention to reject over 20 States' plans for controlling ozone pollution. In their place, the government sought to impose a single, uniform federal plan. This litigation concerns whether, in adopting that plan, the federal government complied with the terms of the Act.

A

“The Clean Air Act regulates air quality through a federal-state collaboration.” EME Homer City Generation, L.P . v. EPA, 795 F. 3d 118, 124 (CADC 2015). Periodically, the Environmental Protection Agency (EPA) sets standards for common air pollutants, as necessary to “protect the public health.” §§ 7409(a)(1), (b)(1). Once EPA sets a new standard, the clock starts ticking: States have three years to design and submit a plan—called a State Implementation Plan, or SIP—providing for the “implementation, maintenance, and enforcement” of that standard in their jurisdictions. § 7410(a)(1); see EPA v. EME Homer City Generation, L. P ., 572 U. S. 489, 498 (2014). Under the Act, States decide how to measure ambient air quality. § 7410(a)(2)(B). States pick “emission limitations and other control measures.” § 7410(a)(2)(A). And States provide for the enforcement of their prescribed measures. § 7410(a)(2)(C).

At the same time, States must design these plans with their neighbors in mind. Because air currents can carry pollution across state borders, emissions in upwind States Page Proof Pending Publication

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Because the States bear “primary responsibility” for developing compliance plans, § 7401(a)(3), EPA has “no authority to question the wisdom of a State's choices of emission limitations.” Train v. Natural Resources Defense Council, Inc., 421 U. S. 60, 79 (1975). So long as a SIP satisfies the “applicable requirements” of the Act, including the Good Neighbor Provision, EPA “shall approve” it within 18 months of its submission. § 7410(k)(3); see §§ 7410(k)(1)(B), (k)(2). If, however, a SIP falls short, EPA “shall” issue a Federal Implementation Plan, or FIP, for the noncompliant State—that is, “unless” the State corrects the deficiencies in its SIP first. § 7410(c)(1); EME Homer , 572 U. S., at 498. EPA must also ensure States meet the new air-quality standard by a statutory deadline. See § 7511.

B

A layer of ozone in the atmosphere shields the world from the sun's radiation. See Natural Resources Defense Council v. EPA, 464 F. 3d 1, 3 (CADC 2006). But closer to earth, ozone can hurt more than it helps. Forming when sunlight interacts with a wide range of precursor pollutants, ground-level ozone can trigger and exacerbate health problems and damage vegetation. 80 Fed. Reg. 65299, 65302, 65370 (2015).

To mitigate those and other problems, in 2015 EPA revised its air-quality standards for ozone from 75 to 70 parts per billion. Id., at 65293–65294. That change triggered a requirement for States to submit new SIPs. Id., at 65437. Along the way, EPA issued a guidance document advising States that they had “flexibility” in choosing how to address their Good Neighbor obligations. See EPA, Memorandum, Page Proof Pending Publication

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For over two years, EPA did not act on the SIPs it received. See, e. g., 87 Fed. Reg. 9838, 9845–9851 (2022). Then, in February 2022, the agency announced its intention to disapprove 19 of them on the ground that the States submitting them had flailed to address adequately their obligations under the Good Neighbor Provision. 1 A few months later, the agency proposed disapproving four more SIPs. 2 Pursuant to the Act, the agency issued its proposed SIP disapprovals for public comment before fnalizing them. See § 7607(d)(3).

C

During that public comment period, the agency proposed a single FIP to bind all 23 States. 3 87 Fed. Reg. 20036,

In broad strokes, here is how EPA's proposed rule worked to eliminate a State's “significant contribution” to downwind ozone problems. First, the agency identified various emissions-control measures and, using nationwide data, calculated how much each typically costs to reduce a ton of nitrogen-oxide emissions. Id., at 20076; see, e. g., id., at 20077–20081. Next, the agency sought to predict how much each upwind State's nitrogen-oxide emissions would fall if emissions-producing facilities in the State adopted each measure. Id., at 20076; see, e. g., id., at 20088–20089; EPA, Ozone Transport Policy Analysis Proposed Rule TSD 22–23 (EPA–HQ–OAR–2021–0668, 2022) (Proposed Ozone Analysis). In making those predictions, EPA often considered data specific to the emissions-producing facilities in the State, and fed “unit-level and state-level” values into its calculations. See id., at 9–10, 13. Then, the agency estimated how much, on average, ozone levels would fall in downwind States with the adoption of each measure. 87 Fed. Reg . 20076; see, e. g., id., at 20092–20093, 20096–20097; Proposed Ozone Analysis 51–52. In making those estimations, too, EPA calibrated its modeling to each State's features, “deter-min[ing] the relationship between changes in emissions and changes in ozone contributions on a state-by-state . . . basis.” Id., at 33; see also id., at 40, 42. Page Proof Pending Publication

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Immediately, commenters warned of a potential pitfall in the agency's approach. EPA had determined which emissions-control measures were cost effective at addressing downwind ozone levels based on an assumption that the FIP would apply to all covered States. But what happens if some or many of those States are not covered? As the commenters portrayed the SIPs, this was not an entirely speculative possibility. Many believed EPA's disapprovals of the SIPs were legally flawed. See, e. g., Comments of Missouri Dept. of Natural Resources 3 (June 17, 2022) (referencing “all the technical, legal, and procedural issues” with the proposed SIP disapproval); see also, e. g., Comments of Louisiana Dept. of Environmental Quality 1–3 (June 21, 2022); Comments of Texas Comm'n on Environmental Quality 2–4 (June 21, 2022); EPA, Response to Public Comments on Proposed Rule 9–11 (EPA–HQ–OAR–2021–0668). They added that EPA's FIP was “inextricably linked” to the SIP disapprovals. E . g., Comments of Missouri Dept. of Natural Resources, at 4. Without a SIP disapproval or missing SIP, after all, EPA could not include a State in its FIP. See, e. g.,

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As it happened, ongoing litigation over the SIP disapprovals soon seemed to vindicate at least some of the comment-

Despite those comments and developments, the agency proceeded to issue its final FIP. 88 Fed. Reg. 36654 (2023). 5 In response to the problem commenters raised, EPA adopted a severability provision stating that, should any jurisdiction drop out, its rule would “continue to be implemented as to any remaining jurisdictions.” Id., at 36693. But in doing so, EPA did not address whether or why the same emissions-control measures it mandated would continue to further the FIP's stated purpose of maximizing cost-effective air-quality improvement if fewer States remained in the plan.

D

After EPA issued its final FIP, litigation over the agency's SIP disapprovals continued. One court after another issued one stay after another. 6 Each new stay meant another State to which EPA could not apply its FIP. See § 7410(c)(1). Ultimately, EPA recognized that it could not

5 The final FIP covered 23 States. 88 Fed. Reg. 36654, 36656 (2023). That plan included Pennsylvania and Virginia, but EPA declined to cover Tennessee or Wyoming at the time, even though it had announced its intention to disapprove those States' SIPs. Ibid.; see also supra, at 285, and nn. 1–2. EPA has since proposed a plan for Tennessee and several other States. 89 Fed. Reg. 12666 (2024). 6 See, e. g., Order in No. 23–60069 (CA5, June 8, 2023) (Mississippi); Order in No. 23–682 (CA9, July 3, 2023) (Nevada); Order in No. 23–1776 (CA8, July 5, 2023) (Minnesota); Order in No. 23–3216 (CA6, July 25, 2023) (Kentucky); Order in No. 23–9520 etc. (CA10, July 27, 2023) (Utah and Oklahoma); Order in No. 23–11173 (CA11, Aug. 17, 2023) (Alabama); see also Order in No. 23–1418 (CA4, Aug. 10, 2023) (West Virginia, pending oral argument on preliminary motions to stay and to transfer); Order in No. 23–1418 (CA4, Jan. 10, 2024) (West Virginia, after oral argument and pending merits review of petition).

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A number of the remaining States and industry groups challenged the remnants of the FIP in the D. C. Circuit. They pointed to the Act's provisions authorizing a court to “reverse any . . . action” taken in connection with a FIP that is “arbitrary” or “capricious.” § 7607(d)(9)(A). And they argued that EPA's decision to apply the FIP to them even after so many other States had dropped out met that standard. As part of their challenge, they asked that court to stay any effort to enforce the FIP against them while their appeal unfolded. After that court denied relief, the applicants renewed their request here. The Court has received and reviewed over 400 pages of briefing and a voluminous record, held over an hour of oral argument on the applications, and engaged in months of postargument deliberations as we often do for the cases we hear.

Stay applications are nothing new. They seek a form of interim relief perhaps “as old as the judicial system of the nation.” Scripps-Howard Radio, Inc. v. FCC , 316 U. S. 4, 17 (1942). Like any other federal court faced with a stay request, we must provide the applicants with an answer—

In deciding whether to issue a stay, we apply the same “sound . . . principles” as other federal courts. Nken v. Holder, 556 U. S. 418, 434 (2009) (internal quotation marks omitted). Specifically, in this litigation, we ask (1) whether the applicant is likely to succeed on the merits, (2) whether it will suffer irreparable injury without a stay, (3) whether the stay will substantially injure the other parties interested in the proceedings, and (4) where the public interest lies. Ibid.; States' Application 13; Response in Opposition for Respondent EPA in No. 23A349 etc., p. 16 (EPA Response). 9

When States and other parties seek to stay the enforcement of a federal regulation against them, often “the harms and equities [will be] very weighty on both sides.” Labrador, 601 U. S., at ––– (opinion of Kavanaugh, J.). That is certainly the case here, for both sides have strong arguments with respect to the latter three Nken factors. On one side of the ledger, the federal government points to the air-quality benefits its FIP offers downwind States. EPA Response 48–50. On the other side, the States observe that a FIP issued unlawfully (as they contend this one was) necessarily impairs their sovereign interests in regulating their own industries and citizens—interests the Act expressly recognizes. See Part I–A, supra; States' Application 24–26; Maryland v. King , 567 U. S. 1301, 1303 (2012) (Roberts, C. J., in chambers). The States observe, too, that having to comply with the FIP during the pendency of this litigation risks placing them at a “competitive disadvantage” to their exempt peers. States' Application 21. The States and the private applicants also stress that complying with

9 Approaching the applications before us like any other stay request both accords with the Clean Air Act's text, see 42 U. S. C. § 7607(d), and usual practice in this field, see, e. g., Texas v. EPA, 829 F. 3d 405, 424 (CA5 2016); West Virginia v. EPA, 90 F. 4th 323, 331 (CA4 2024); In re Murray Energy Corp., 788 F. 3d 330, 335 (CADC 2015).

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Because each side has strong arguments about the harms they face and equities involved, our resolution of these stay requests ultimately turns on the merits and the question who is likely to prevail at the end of this litigation. See Nken, 556 U. S., at 434; Labrador , 601 U. S., at ––– (opinion of Kavanaugh, J.).

When it comes to that question, the parties agree on the rules that guide our analysis. The applicants argue that a court is likely to hold EPA's final FIP “arbitrary” or “capricious” within the meaning of the Act and thus enjoin its enforcement against them. 42 U. S. C. § 7607(d)(9)(A); see, e. g., States' Application 15–16; Application for American Forest & Paper Association et al. 14; see also 5 U. S. C. § 706(2)(A). An agency action qualifies as “arbitrary” or “capricious” if it is not “reasonable and reasonably explained.” FCC v. Prometheus Radio Project, 592 U. S. 414, 423 (2021). In reviewing an agency's action under that standard, a court may not “ `substitute its judgment for that of the agency.' ” FCC v. Fox Television Stations, Inc., 556 U. S. 502, 513 (2009). But it must ensure, among other things, that the agency has offered “a satisfactory explanation for its action[,] including a rational connection between the facts found and the choice made.” Motor Vehicle Mfrs. Assn. of United States, Inc. v. State Farm Mut. Automobile Ins. Co ., 463 U. S. 29, 43 (1983) (internal quotation marks Page Proof Pending Publication

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We agree with the applicants that EPA's final FIP likely runs afoul of these long-settled standards. The problem stems from the way EPA chose to determine which emissions “contribute[d] significantly” to downwind States' difficulty meeting national ozone standards. 42 U. S. C. § 7410(a)(2)(D)(i)(I). Recall that EPA's plan rested on an assumption that all 23 upwind States would adopt emissions-reduction tools up to a “uniform” level of “costs” to the point of diminishing returns. 87 Fed. Reg. 20076, 20095; 88 Fed. Reg. 36661, 36683–36684, 36719; see Part I–C, supra. But as the applicants ask: What happens—as in fact did happen— when many of the upwind States fall out of the planned FIP and it may now cover only a fraction of the States and emissions EPA anticipated? See, e. g., States' Application 16–21; Application for American Forest & Paper Association et al. 14–15, 19–20. Does that affect the “knee in the curve,” or the point at which the remaining States might still “maxi-miz[e] cost-effectiv[e]” downwind ozone-level improvements? 87 Fed. Reg. 20055. As “the mix of states changes, . . . and their particular technologies and industries drop out with them,” might the point at which emissions-control measures maximize cost-effective downwind air-quality improvements also shift? Tr. of Oral Arg. 6.

Although commenters posed this concern to EPA during the notice and comment period, see Part I–C, supra, EPA offered no reasoned response. Indeed, at argument the government acknowledged that it could not represent with certainty whether the cost-effectiveness analysis it performed collectively for 23 States would yield the same results and command the same emissions-control measures if conducted for, say, just one State. Tr. of Oral Arg. 58–59. Perhaps there is some explanation why the number and identity of participating States does not affect what measures maximize cost-effective downwind air-quality improvements. But if Page Proof Pending Publication

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Resisting this conclusion, EPA advances three alternative arguments.

First, the government insists, the agency did offer a reasoned response to the applicants' concern, just not the one they hoped. When fnalizing its rule in response to public comments, the government represents, “the agency did consider whether the [FIP] could cogently be applied to a subset of the 23 covered States.” EPA Response 27; see also post, at 316–317 (Barrett, J., dissenting). And that consideration, the government stresses, led EPA to add a “severabil-ity” provision to its final rule in which the agency announced that the FIP would “ `continue to be implemented' ” without regard to the number of States remaining, even if just one State remained subject to its terms. EPA Response 27 (quoting 88 Fed. Reg. 36693). In support of its severability provision, EPA cited, among other things, its intent to address “ `important public health and environmental benefits' ” and encourage reliance by others “ `on th[e] final rule in their planning.' ” Ibid.

11 As the applicants conceded at oral argument, see Tr. of Oral Arg. 25– 26, EPA did not need to address every possible permutation when it sought to adopt a multi-State FIP. Our conclusion is narrower: When faced with comments like the ones it received, EPA needed to explain why it believed its rule would continue to offer cost-effective improvements in downwind air quality with only a subset of the States it originally intended to cover. To be sure, after this Court heard argument, EPA issued a document in which it sought to provide further explanations for the course it pursued. See 89 Fed. Reg. 23526 (2024). But the government has not suggested that we should consult this analysis in assessing the validity of the final rule. See Letter from E. Prelogar, Solicitor General, to S. Harris, Clerk of Court 1 (Mar. 28, 2024). Nor could it, since the Clean Air Act prevents us (and courts that may in the future assess the FIP's merits) from consulting explanations and information offered after the rule's promulgation. See 42 U. S. C. §§ 7607(d)(6)(C) (“The promulgated rule may not be based (in part or whole) on any information or data which has not been placed in the docket as of the date of such promulgation”), 7607(d)(7)(A) (restricting the “record for judicial review”). We therefore look to only “the grounds that the agency invoked when it” promulgated the FIP. Michigan v. EPA , 576 U. S. 743, 758 (2015). Should the applicants show the FIP was arbitrary or capricious on the existing record, as we have concluded is likely, the Clean Air Act entitles them to “revers[al]” of that rule's mandates on them. § 7607(d)(9)(A).

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We cannot agree. The Act's “reasonable specificity” requirement does not call for “a hair-splitting approach.” Appalachian Power Co. v. EPA, 135 F. 3d 791, 817 (CADC 1998). A party need not “rehears[e]” the identical argument made before the agency; it need only confirm that the government had “notice of [the] challenge” during the public comment period and a chance to consider “in substance, if not in form, the same objection now raised” in court. Id., at 818; see also, e. g., Bahr v. Regan, 6 F. 4th 1059, 1070 (CA9 2021).

Here, EPA had notice of the objection the applicants seek to press in court. Commenters alerted the agency that, should some States no longer participate in the plan, the agency would need to return to the drawing board and “conduct a new assessment and modeling of contribution” to determine what emissions-control measures maximized cost effectiveness in securing downwind ozone air-quality improvements. Comments of Air Stewardship Coalition, at 13–14; see also Part I–C, supra (noting examples of other comments). And, as we have just seen, EPA's own statements and actions confirm the agency appreciated that concern. In preparing the final rule in response to public comments, the agency emphatically insists, it “did consider whether the [r]ule could cogently be applied to a subset of the 23 covered States.” EPA Response 27. And as a result of that consideration, the agency observes, it opted to add a severability provision to its final rule. Ibid. By its own words and actions, then, the agency demonstrated that it was Page Proof Pending Publication

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Third, the government pursues one more argument in the alternative. As the agency sees it, the applicants must return to EPA and file a motion asking it to reconsider its final rule before presenting their objection in court. They must, the agency says, because the “grounds for [their] objection arose after the period for public comment.” § 7607(d)(7)(B); see EPA Response 20–21. As just discussed, however, EPA had the basis of the applicants' objection before it during the comment period. It chose to respond with a severability provision that in no way grappled with their concern. Nothing requires the applicants to return to EPA to raise (again) a concern EPA already had a chance to address.

Taking the government's argument (much) further, the dissent posits that every “objection that [a] final rule was not reasonably explained” must be raised in a motion for reconsideration. Post, at 306 (internal quotation marks omitted; emphasis deleted). But there is a reason why the government does not go so far. The Clean Air Act opens the court-

With the government's theories unavailing, the dissent advances others of its own. It begins by suggesting that the problem the applicants raise was not “ ` important' ” enough to warrant a reasoned reply from the agency because the methodology EPA employed in its FIP “appear[s] not to depend on the number of covered States.” Post, at 311–316, 317–318. Then, coming at the same point from another direction, the dissent seeks to excuse the agency's lack of a reasoned reply as “harmless” given, again, “the apparent lack of connection between the number of States covered and the FIP's methodology.” Post, at 319.

The trouble is, if the government had arguments along these lines, it did not make them. It did not despite its ample resources and voluminous briefing. See supra, at 290. This Court “normally decline[s] to entertain” arguments “forfeited” by the parties. Kingdomware Technologies, Inc. v. United States, 579 U. S. 162, 173 (2016). And we see no persuasive reason to depart from that rule here. Page Proof Pending Publication

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The applications for a stay in Nos. 23A349, 23A350, 23A351, and 23A384 are granted. Enforcement of EPA's rule against the applicants shall be stayed pending the disposition of the applicants' petitions for review in the United States Court of Appeals for the D. C. Circuit and any petition for writ of certiorari, if such writ is timely sought. Should the petition for certiorari be denied, this order will terminate automatically. If the petition is granted, this order shall terminate upon the sending down of the judgment of this Court.

It is so ordered.

Justice Barrett, with whom Justice Sotomayor , Justice Kagan, and Justice Jackson join, dissenting.

The Court today enjoins the enforcement of a major Environmental Protection Agency rule based on an underdeveloped theory that is unlikely to succeed on the merits. In so doing, the Court grants emergency relief in a fact-intensive and highly technical case without fully engaging with both the relevant law and the voluminous record. While the Court suggests that the EPA flailed to explain itself suff-ciently in response to comments, this theory must surmount sizable procedural obstacles and contrary record evidence.

dissent posits, only nationwide data informed EPA's analysis, why would EPA say that, “for purposes of identifying the appropriate level of control,” it focused on “the 23 upwind states that were linked” to the downwind States, rather than, say, “all states in the contiguous U. S.”? Final Ozone Analysis 3 (footnote omitted). Why would EPA explain that its “findings regarding air quality improvement” downwind were a “central component” of picking the appropriate cost levels and so defining a State's significant contribution? 88 Fed. Reg. 36741. And why would EPA bother to “determine the relationship between changes in emissions and changes in ozone contributions on a state-by-state . . . basis” and “cali-brat[e]” that relationship “based on state-specific source apportionment”? Final Ozone Analysis 43. In asking these questions, we do not profess answers; we simply highlight further reasons for caution. Page Proof Pending Publication

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I

will start by setting the record straight with respect to some important background.

First, the Court downplays EPA's statutory role in ensur-ing that States meet air-quality standards. Ante , at 283– 284. The Clean Air Act directs EPA to “establish national ambient air quality standards (NAAQS) for pollutants at levels that will protect public health.” EPA v. EME Homer City Generation, L. P ., 572 U. S. 489, 498 (2014); see 42 U. S. C. §§ 7408, 7409. States must create State Implementation Plans (SIPs) to ensure that their air meets these standards. § 7410(a)(1). But States also face an externality problem: “Pollutants generated by upwind sources are often transported by air currents . . . to downwind States,” relieving upwind States “of the associated costs” and making it difficult for downwind States to “maintain satisfactory air quality.” EME , 572 U. S., at 496. So the Act's Good Neighbor Provision requires SIPs to “prohibi[t]” the State's emissions sources from “emitting any air pollutant in amounts which will . . . contribute significantly to nonattainment in, or interfere with maintenance by, any other State with respect to any [NAAQS].” § 7410(a)(2)(D)(i)(I).

Given the incentives of upwind States to underregulate the pollution they send downwind, the Act requires EPA to determine whether a State “has flailed to submit an adequate SIP.” EME , 572 U. S., at 498; see § 7410(c)(1). If a SIP does not prevent the State's polluters from significantly contributing to nonattainment in downwind States, EPA “shall” promulgate a Federal Implementation Plan (FIP) that does. § 7410(c)(1). And EPA must stop the State's significant contributions by the statutory deadline for the affected downwind States to achieve compliance. See Wis-consin v. EPA, 938 F. 3d 303, 313–314 (CADC 2019) (per

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Third, the Court claims that commenters on the proposed FIP warned that its emissions limits might change if it covered fewer States, but EPA flailed to respond. Ante , at 287– 289. Not exactly. As I will elaborate below, commenters merely criticized EPA's decision to propose a FIP before its SIP disapprovals were final. EPA responded that this se-quencing was “consistent with [its] past practice in [its] efforts to timely address good neighbor obligations”: Given the August 2024 deadline for certain States to comply with the 2015 ozone NAAQS, EPA was “obligated” to start the years-long process of promulgating a FIP so that one could be effective in time. EPA, Response to Public Comments on Proposed Rule 149–150 (EPA–HQ–OAR–2021–0668–1127, June 2023) (Response to Comments); see Wisconsin, 938 F. 3d, at 313–314.

Finally, the Court repeatedly characterizes the FIP as relying on an “assumption that [it] would apply to all covered States.” Ante , at 287; see ante, at 293. But try as it might, Page Proof Pending Publication

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On the contrary, as I will explain in Part II–B, the final rule and its supporting documents suggest that EPA's methodology for setting emissions limits did not depend on the number of States in the plan, but on nationwide data for the relevant industries—and the FIP contains many examples of emissions limits that EPA created using nationwide inputs. Moreover, EPA has now confirmed this interpretation. During this litigation, EPA received petitions seeking reconsideration of the FIP on the ground that it should not be implemented in just a subset of the original States. EPA Page Proof Pending Publication

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To obtain emergency relief, applicants must, at a minimum, show that they are likely to succeed on the merits, that they will be irreparably injured absent a stay, and that the balance of the equities flavors them. Nken v. Holder, 556 U. S. 418, 425–426 (2009). Moreover, we should grant relief only if we would be likely to grant certiorari were the applicants' case to come to us in the usual course. See Does 1–3 v. Mills, 595 U. S. –––, ––– (2021) (Barrett, J., concurring in denial of application for injunctive relief); Hollingsworth v. Perry, 558 U. S. 183, 190 (2010) (per curiam ). In my view, the applicants cannot satisfy the stay factors. Most signif-cantly, they have not shown a likelihood of success on the merits.

The Court holds that applicants are likely to succeed on a claim that the Good Neighbor Plan is “arbitrary” or “capricious.” 42 U. S. C. § 7607(d)(9). The “arbitrary-and -capricious standard requires that agency action” be both “[1] reasonable and [2] reasonably explained.” FCC v. Prometheus Radio Project, 592 U. S. 414, 423 (2021). The Court's theory is that EPA did not “ `reasonably explai[n]' ” “why Page Proof Pending Publication

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The Clean Air Act imposes a procedural bar on the challenges that a plaintiff can bring in court: Only objections that were “raised with reasonable specificity during the period for public comment . . . may be raised during judicial review.” § 7607(d)(7)(B). If it was “impracticable to raise such objection within such time or if the grounds for such objection arose after the period for public comment,” the challenger may petition for reconsideration of the rule and can obtain judicial review only if EPA refuses. Ibid. While EPA has now separately denied petitions for reconsideration of the Good Neighbor Plan, this case came to us directly; we are assessing applicants' likelihood of success in challenging the plan itself, not the denial of reconsideration. So the procedural bar on objections not raised in the comments presents a significant obstacle—in two ways. Page Proof Pending Publication

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The D. C. Circuit, on remand in EME Homer , considered a similar objection that EPA had “violated the Clean Air Act's notice and comment requirements”: EPA had “signif-cantly amend[ed] the Rule between the proposed and final versions without providing additional opportunity for notice and comment.” 795 F. 3d, at 137. But because this procedural objection could not have been raised during the comment period, “the only appropriate path for petitioners” under § 7607(d)(7)(B) was to raise it “through an initial petition for reconsideration to EPA.” Ibid. So the D. C. Circuit lacked “authority at th[at] time to reach this question.” Ibid. While such “logical outgrowth” challenges typically are cognizable under the Administrative Procedure Act, see Shell Oil Co. v. EPA, 950 F. 2d 741, 747 (CADC 1991), the Clean Air Act channels these challenges through reconsideration proceedings. This Court's failure-to-explain objection may face the same problem: It is not judicially reviewable in its current posture. 1

1 The Court offers a feeble response to this application of § 7607(d)(7)(B)'s procedural bar. Ante , at 297–298. It simply quotes § 7607(d)(7)(B) and asserts without support that it means that a plaintiff “need not go back to the agency and insist on an explanation a second time.” Ante , at 298. The Court flails to engage with the logic of this argument: The objection that the final rule did not contain sufficient explanation was not and could not have

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Another collection of the Court's inapposite comments relates to the inclusion of specific sources, emissions controls, and industries in the proposed plan—not States. See ante, at 288, n. 4. For example, one commenter argued that the “cost effectiveness of the requirement to employ SNCR will be highly variable, and is unlikely to meet EPA expectations in even the most optimistic case.” Comments of Indiana Municipal Power Agency 9 (June 20, 2022). That is a challenge to EPA's endorsement of a particular emissions-control technology; it says nothing about the FIP's dependence on a particular number of States. See also, e. g., Comments of Lower Colorado River Authority 21–22 (June 21, 2022).

been raised during the comment period, so it must be raised in a petition for reconsideration. EME Homer , 795 F. 3d, at 137. The Court claims that its theory is different from the logical-outgrowth challenge the D. C. Circuit considered in EME Homer . Ante , at 298. But the Court ignores the fact that its failure-to-explain challenge and logical-outgrowth challenges are both “objection[s] to the notice and comment process itself” that depend on the content of the final rule. EME Homer , 795 F. 3d, at 137. Even if the public raised an “important problem . . . during the comment period,” ante, at 298, the Court's basis for enjoining the FIP's enforcement is not that the alleged problem is real, but that the final rule did not address it. Page Proof Pending Publication

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The closest comment that the Court can find—which it quotes repeatedly—is one sentence that obliquely refers to some “new assessment and modeling of contribution” that EPA might need to perform. Comments of Air Stewardship Coalition 13–14 (June 21, 2022). The Court dresses up this comment by characterizing it as a warning about what might happen “[i]f the FIP did not wind up applying to all 23 States” and responding to the concern that a “different set of States might mean that the `knee in the curve' would shift” and change the cost-effective “emissions-control meas-

The commenter's actual objection was to EPA's sequencing of its actions—proposing a FIP before it finalized its SIP disapprovals. The commenter titled this section “EPA Step Two Screening is Premised on the Premature Disapproval of 19 Upwind States['] Good Neighbor SIPs.” Air Stewardship Comments 13 (boldface omitted). And the relevant sentence reads in full:

“The proposed FIP essentially prejudges the outcome of those pending SIP actions and, in the event EPA takes a different action on those SIPs than contemplated in this proposal, it would be required to conduct a new assessment and modeling of contribution and subject those findings to public comment.” Id., at 14.

This sentence says nothing about what would be required if after EPA finalizes its SIP disapprovals and issues a final FIP, some States drop out of the plan. Nor does it suggest that the plan's cost-effectiveness thresholds or emissions controls would change with a different number of States. Nor is it clear what the comment means by its bare reference to a “new assessment and modeling of contribution”: Would EPA be required to perform a new evaluation of which upwind States cause pollution in downwind States? A new analysis of how much pollution each source must eliminate? A new assessment of the plan's impact on downwind States?

It is therefore difficult to see how this comment raised with “reasonable specificity” the objection that the removal of some States from the final plan would invalidate EPA's cost-effectiveness thresholds and chosen emissions-control measures.4 That is not how EPA understood it. EPA char-

In sum, § 7607(d)(7)(B)'s procedural bar likely forecloses both the failure-to-explain objection that the Court credits and any substantive challenge to the reasonableness of applying the FIP to a subset of the originally covered States.

Even if applicants clear § 7607(d)(7)(B)'s procedural bar, they face an uphill battle on the merits. To prevail on the Court's theory, applicants must show that EPA's actions were “arbitrary” or “capricious.” §§ 7607(d)(9)(A), (D). “The scope of review under the `arbitrary and capricious' standard is narrow and a court is not to substitute its judgment for that of the agency.” State Farm, 463 U. S., at 43. A rule is arbitrary and capricious if the agency “entirely flailed to consider an important aspect of the problem.” Ibid. (emphasis added). But we will “ `uphold a decision of less than ideal clarity if the agency's path may reasonably be discerned.' ” Ibid. (quoting Bowman Transp., Inc. v. Arkansas-Best Freight System, Inc., 419 U. S. 281, 286 (1974)). Given the explanations and state-agnostic methodology apparent in the final rule and its supporting documentation—and the paucity of comments specifically raising the issue—EPA may well have done enough to justify its plan's severability.

To begin, the rule and its supporting documents arguably make clear that EPA's methodology for calculating cost-effectiveness thresholds and imposing emissions controls did not depend on the number of covered States. The rule applied EPA's longstanding “4-step interstate transport framework” to create emissions limits that will prevent NO x sources in upwind States from significantly contributing to ozone pollution in downwind States. 88 Fed. Reg. 36659; see 42 U. S. C. § 7410(a)(2)(D). Under that framework, EPA (1) identifies “downwind receptors that are expected to have problems attaining or maintaining the NAAQS”; (2) identi-fies which upwind States are “ `link[ed]' ” to those downwind receptors because they contribute at least 1% of a receptor's ozone; (3) determines which NO x sources in the linked upwind States “significantly contribute” to downwind nonattainment or interference; and (4) implements emissions lim-Page Proof Pending Publication

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Here is how EPA explains that methodology. A source “significantly contributes” to downwind pollution if there are cost-effective measures it could implement to reduce its emissions: It must halt those emissions that can be eliminated at a cost “under the cost threshold set by the Agency” for sources in that industry. EME , 572 U. S., at 518 (upholding this approach). So the “ `amount' of pollution” that sources must eliminate is “that amount . . . in excess of the emissions control strategies the EPA has deemed cost effective.” 88 Fed. Reg. 36676. EPA calculates for each type of source a “uniform level of NO x emissions control stringency” expressed as a “cost per ton of emissions reduction.” Id., at 36719. This cost-effectiveness threshold is based on the point “at which further emissions mitigation strategies become excessively costly on a per-ton basis while also delivering far fewer additional emissions reductions.” Id., at 36683 (describing this “ `knee in the curve' ” analysis). The plan requires sources in each covered State to reduce their emissions accordingly.6

7 EPA ultimately selected (based on nationwide data) a cost threshold of $1,800 per ton of NO x reduction that would apply in earlier years, and a cost threshold of $11,000 per ton that would apply in later years. 88 Fed. Reg. 36749, 36846. These cost thresholds corresponded to the cost of different emissions-control measures: For example, EGUs can “[r]etro-f[t] state-of-the-art combustion controls” and “[o]ptimiz[e] idled SCRs” for less than $1,800 per ton, and they can “[i]nstal[l new] SCR[s]” for less than $11,000 per ton. Ozone Transport Policy Analysis Final Rule TSD 5 (EPA–HQ–OAR–2021–0668–1080, Mar. 2023) (Final Ozone Analysis). EPA then calculated each State's emissions budget based on the assumption that the State's EGUs would implement the emissions-reductions strategies that cost less than the chosen thresholds. See n. 6, supra; 88 Fed. Reg. 36762; Final Ozone Analysis 6, 9. Given the likelihood that

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The Court, perhaps recognizing the problem that the FIP's seemingly state-agnostic methodology poses for its theory, throws at the wall a cherry-picked assortment of EPA state-

EPA selected cost thresholds based on nationwide data, each State's budget would be the same even if the FIP covered different States. 8 While EPA's methodology with respect to other industrial sources (non-EGUs) was more complicated, it also seems to have relied on nationwide data. EPA chose a “$7,500 marginal cost-per-ton threshold,” 88 Fed. Reg. 36740, which corresponded to the point of diminishing returns (the “knee in the curve”) when EPA assessed the impact of emissions controls in the highest impact industries and in “all industries” on the total “[o]zone [s]eason NOx [r]eductio[n]” potential, Technical Memorandum, Screening Assessment of Potential Emissions Reductions, Air Quality Impacts, and Costs From Non-EGU Emissions Units for 2026, p. 4 (EPA–HQ–OAR– 2021–0668–0150, Feb. 2022) (boldface omitted). This figure thus appears to have been determined based on industry-wide cost and emissions data rather than state-specific calculations. So too with the specific emissions limits EPA decided could be implemented for less than that cost. See, e. g., 88 Fed. Reg. 36825 (“EPA based the proposed emissions limits for cement kilns on the types of limits being met across the nation”). Page Proof Pending Publication

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EPA's analysis confirmed that its chosen emissions limits would not result in overcontrol if they were implemented in the States originally covered by the FIP. 88 Fed. Reg. 36741. Importantly, implementing the FIP “in fewer upwind states does not (and cannot possibly) result in overcon-trol” given that “there was no overcontrol even when more states, making more emission reductions, were included.” Denial 22. So the fact that EPA used state-specific data in Page Proof Pending Publication

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Thus, EPA generally characterized the FIP's emissions limits as dependent on nationwide data, not on any particular set of States.9 Confirming this interpretation, the final rule contemplates its application to a different number of States. It recognizes that “states may replace FlIPs with SIPs if EPA approves them,” and several sections explain how States may exit this FIP. 88 Fed. Reg. 36753, 36838–36843. And the rule's severability provision explains that EPA views the plan as “severable along . . . state and/or tribal jurisdictional lines.” Id., at 36693.

Moreover, EPA justified the FIP's severability: EPA “must address good neighbor obligations as expeditiously as practicable and by no later than the next applicable attainment date”; severability serves “important public health and environmental benefits” and ensures that stakeholders can “rely on this final rule in their planning.” Ibid. These rationales align with EPA's response to critics of its decision to propose a FIP before fnalizing its SIP disapprovals: Quickly proposing a FIP—just like keeping the FIP in place even if some States drop out—“is a reasonable and prudent means

Given these justifications and the state-agnostic methodology apparent in the final rule, EPA's “ `path may reasonably be discerned.' ” State Farm, 463 U. S., at 43. The FIP's cost thresholds and emissions limits did not depend in any significant way on the number of States included, so the drawbacks of severability were minimal. On the other hand, severability was necessary so that EPA could fulfill, to the greatest extent possible, its statutory obligation to eliminate the significant ozone contributions of upwind States and reduce harmful pollution in downwind States in time to meet the attainment deadlines. See Response to Comments 150 (noting the August 2024 ozone-NAAQS attainment deadline). If the FIP were not severable, EPA would have to go back to the drawing board for all States whenever a single State is removed—thwarting its mission for little reason.10

Finally, it is unlikely that EPA's response to comments evinces a “fail[ure] to consider an important aspect of the problem.” State Farm, 463 U. S., at 43 (emphasis added). An agency must respond to “ `relevant' and `significant' public comments,” and that requirement is not “particularly demanding”; the “agency need not respond at all to comments that are `purely speculative and do not disclose the factual or policy basis on which they rest.' ” Public Citizen, Inc. v.

Applicants face one more impediment: the Clean Air Act's stringent harmless-error rule. A court “reviewing alleged procedural errors . . . may invalidate [an EPA] rule only if the errors were so serious and related to matters of such central relevance to the rule that there is a substantial likelihood that the rule would have been significantly changed if such errors had not been made.” § 7607(d)(8) (emphasis added). This provision appears “tailor-made to undo” any “rigid presumption of vacatur” that might apply in other con-

The alleged error here plausibly is subject to § 7607(d)(8)'s harmless-error rule. As explained above, the Court does not suggest that it is substantively “[un]reasonable” to apply the FIP to fewer States, only that EPA did not “reasonably explai[n]” the FIP's severability in response to comments. Prometheus, 592 U. S., at 423. That is arguably an “alleged procedural error” within the meaning of § 7607(d)(8). In fact, the Act contemplates that at least some “arbitrary or capricious” challenges allege failures to “observ[e] . . . procedure required by law,” and such challenges may only succeed if § 7607(d)(8)'s “condition is . . . met.” § 7607(d)(9)(D).

If the Act's harmless-error rule applies, applicants are unlikely to prevail. Given the apparent lack of connection between the number of States covered and the FIP's methodology for determining cost thresholds and emissions limits, it is difficult to imagine a “substantial” likelihood that the rule would have been “significantly” different had EPA just responded more thoroughly. In fact, applicants seem to have conceded as much. See Tr. of Oral Arg. 6 (“[W]ith full candor to the Court, [the cost threshold] could be the same or even be more expensive”); id., at 9 (“I can't tell you what that looks like, whether there is a difference in the obligations or not”). And EPA, the Court says, had “notice” of the alleged concern that the cost thresholds might change with different States. Ante , at 296. Yet EPA still chose to make the FIP severable because of its statutory obligation to reduce downwind pollution—an obligation it repeatedly referenced. See, e. g., 88 Fed. Reg. 36693; Response to Comments 149–151. Would that same EPA have “significantly changed” the FIP had it just explained more thoroughly why the plan did not depend on the States covered? 12 And on top of all this,

* * *

With little to say in response to the FIP's apparent state-agnostic methodology for setting emissions limits and the Clean Air Act's stringent harmless-error rule, the Court resorts to raising forfeiture. Ante , at 298–299. But it is the Court that goes out of its way to develop a failure-to-explain theory largely absent from applicants' briefs. One can search diligently in the hundreds of pages of applicants' opening briefs for the Court's theory—that EPA flailed to explain in its final rule why the FIP's cost-effectiveness thresholds for imposing emissions limits do not shift with a different mix of States—and be left wondering where the Court found it. That theory appears not to have crystal-

require the Government to show that the rule would be the same; it is most naturally read to require the challenger to demonstrate a “substantial likelihood that the rule would have been significantly changed if such errors had not been made.” (Emphasis added.) And though § 7607(d)(9)(A) appears to allow reversal of “ `any' ” arbitrary or capricious “ `action,' ” ante, at 299, § 7607(d)(8)'s more specific harmless-error rule and § 7607(d)(9)(D)'s more specific requirements for reversal based on arbitrary or capricious procedural errors would seem to control.

Given that applicants' theory has evolved throughout the course of this litigation, we can hardly fault EPA for failing to raise every potentially meritorious defense in its response brief. That is particularly true given the compressed briefing schedule in this litigation's emergency posture: The Court gave EPA less than two weeks to respond to multiple applications raising a host of general and industry-specific technical challenges, filed less than a week earlier. Even still, EPA raised § 7607(d)(7)(B)'s procedural bar. Brief for Respondents 19. And on the merits, EPA expressly argued that the FIP's “viability and validity do not depend on the number of jurisdictions it covers”; the “Rule need not apply to any minimum number of States in order to operate coherently.” Id., at 24. EPA could also have demonstrated how the FIP's state-agnostic methodology for selecting cost thresholds was apparent in the final rule. But EPA cannot have forfeited that more specific point because applicants did not raise it to begin with.

Because EPA did not forfeit these responses to the merits of applicants' arbitrary-or-capricious challenge, there is no need to consider whether a departure from our typical approach to forfeited arguments is justified. See ante, at 298– 299. It remains applicants' burden to show that the FIP's alleged dependence on the covered States likely was an “important” problem that EPA “entirely flailed to consider.” State Farm, 463 U. S., at 43. And that is on top of their burden to overcome § 7607(d)(7)(B)'s procedural bar and the lack of “significant,” specific comments raising this issue. § 7607(d)(6)(B). Page Proof Pending Publication

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Given the emergency posture of this litigation, my views on the merits of the failure-to-explain objection and the application of the Clean Air Act's procedural bar and harmless-error rule are tentative. But even a tentative adverse conclusion can undermine applicants' likelihood of success. And applicants, to prevail, must run the table; they face the daunting task of surmounting all of these significant obstacles. They are unlikely to succeed.

The Court, seizing on a barely briefed failure-to-explain theory, grants relief anyway. It enjoins the Good Neighbor Plan's enforcement against any state or industry applicant pending review in the D. C. Circuit and any petition for certiorari. Ante , at 300. Given the number of companies included and the timelines for review, the Court's injunction leaves large swaths of upwind States free to keep contribut-ing significantly to their downwind neighbors' ozone problems for the next several years—even though the temporarily stayed SIP disapprovals may all be upheld and the FIP may yet cover all the original States. The Court justifies Page Proof Pending Publication

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Our emergency docket requires us to evaluate quickly the merits of applications without the benefit of full briefing and reasoned lower court opinions. See Does, 595 U. S., at ––– (opinion of Barrett, J.). Given those limitations, we should proceed all the more cautiously in cases like this one with voluminous, technical records and thorny legal questions. I

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The attached opinion has been revised to refect the usual publication and citation style of the United States Reports. The revised pagination makes available the official United States Reports citation in advance of publication. The syllabus has been prepared by the Reporter of Decisions for the convenience of the reader and constitutes no part of the opinion of the Court. A list of counsel who argued or filed briefs in this case, and who were members of the bar of this Court at the time this case was argued, has been inserted following the syllabus. Other revisions may include adjustments to formatting, captions, citation form, and any errant punctuation. The following additional edits were made: p. 284, line 13 from bottom: “National” is replaced with “Natural” p. 286, line 8: “family of” is inserted before “ozone”; “nitrous oxide” is replaced with “nitrogen oxides” p. 286, line 9: “nitrous oxide” is replaced with “nitrogen-oxide“ p. 286, line 18: “nitrous” is replaced with “nitrogen” p. 286, line 20: “nitrous” is replaced with “nitrogen” p. 288, n. 4, line 7: “nitrous oxide” is replaced with “nitrogen-oxide” p. 308, line 18: “might” is replaced with “would” p. 310, line 12: “might” is replaced with “would”

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