The Clean Air Act authorizes the Environmental Protection Agency to regulate power plants by setting a “standard of performance” for their emission of certain pollutants into the air. 84 Stat. 1683, 42 U. S. C. § 7411(a)(1). That standard may be different for new and existing plants, but in each case it must refect the “best system of emission reduction” that the Agency has determined to be “adequately demonstrated” for the particular category. §§ 7411(a)(1), (b)(1), (d). For existing plants, the States then implement that requirement by issuing rules restricting emissions from sources within their borders.
Since passage of the Act 50 years ago, EPA has exercised this authority by setting performance standards based on measures that would reduce pollution by causing plants to operate more cleanly. In 2015, however, EPA issued a new rule concluding that the “best system of emission reduction” for existing coal-fred power plants included a requirement that such facilities reduce their own production of electricity, or subsidize increased generation by natural gas, wind, or solar sources.
The question before us is whether this broader conception of EPA's authority is within the power granted to it by the Clean Air Act.
for Sen. Sheldon Whitehouse et al. by Erwin Chemerinsky. Briefs of amici curiae were fled in all cases for Apple Inc. et al. by Lisa S. Blatt and Matthew B. Nicholson; for the Claremont Institute's Center for Constitutional Jurisprudence by John C. Eastman and An thony T. Caso; for the Edison Electric Institute et al. by Thomas A. Loren- zen and Elizabeth B. Dawson; and for Scholars of Congressional Accountability by Ruth Greenwood and Theresa J. Lee.
Briefs of amici curiae were fled in No. 20–1530 for Doctors for Disaster Preparedness et al. by Andrew L. Schlafy; and for Julian Davis Mortenson by Elizabeth B. Wydra, Brianne J. Gorod, and Brian R. Frazelle.
Page Proof Pending Publication
I
A
The Clean Air Act establishes three main regulatory programs to control air pollution from stationary sources such as power plants. Clean Air Amendments of 1970, 84 Stat. 1676, 42 U. S. C. § 7401 et seq. One program is the New Source Performance Standards program of Section 111, at issue here. The other two are the National Ambient Air Quality Standards (NAAQS) program, set out in Sections 108 through 110 of the Act, 42 U. S. C. §§ 7408–7410, and the Hazardous Air Pollutants (HAP) program, set out in Section 112, § 7412. To understand the place and function of Section 111 in the statutory scheme, some background on the other two programs is in order.
The NAAQS program addresses air pollutants that “may reasonably be anticipated to endanger public health or welfare,” and “the presence of which in the ambient air results from numerous or diverse mobile or stationary sources.” § 7408(a)(1). After identifying such pollutants, EPA establishes a NAAQS for each. The NAAQS represents “the maximum airborne concentration of [the] pollutant that the public health can tolerate.” Whitman v. American Truck ing Assns., Inc., 531 U. S. 457, 465 (2001); see § 7409(b). EPA, though, does not choose which sources must reduce their pollution and by how much to meet the ambient pollution target. Instead, Section 110 of the Act leaves that task in the frst instance to the States, requiring each “to submit to [EPA] a plan designed to implement and maintain such standards within its boundaries.” Train v. Natural Re sources Defense Council, Inc., 421 U. S. 60, 65 (1975); § 7410. The second major program governing stationary sources is the HAP program. The HAP program primarily targets pollutants, other than those already covered by a NAAQS, that present “a threat of adverse human health effects,” including substances known or anticipated to be “carcinogenic, Page Proof Pending Publication mutagenic, teratogenic, neurotoxic,” or otherwise “acutely or chronically toxic.” § 7412(b)(2).
EPA's regulatory role with respect to these toxic pollutants is different in kind from its role in administering the NAAQS program. There, EPA is generally limited to determining the maximum safe amount of covered pollutants in the air. As to each hazardous pollutant, by contrast, the Agency must promulgate emissions standards for both new and existing major sources. § 7412(d)(1). Those standards must “require the maximum degree of reduction in emissions . . . that the [EPA] Administrator, taking into consideration the cost of achieving such emission reduction, and any non- air quality health and environmental impacts and energy requirements, determines is achievable . . . through application of measures, processes, methods, systems or techniques” of emission reduction. § 7412(d)(2). In other words, EPA must directly require all covered sources to reduce their emissions to a certain level. And it chooses that level by determining the “maximum degree of reduction” it considers “achievable” in practice by using the best existing technologies and methods. § 7412(d)(3).
Thus, in the parlance of environmental law, Section 112 directs the Agency to impose “technology-based standard[s] for hazardous emissions,” Alaska Dept. of Environmental Conservation v. EPA, 540 U. S. 461, 485, n. 12 (2004) (emphasis added). This sort of “ `technology-based' approach focuses upon the control technologies that are available to industrial entities and requires the agency to . . . ensur[e] that regulated frms adopt the appropriate cleanup technology.” T. McGarity, Media-Quality, Technology, and Cost-Beneft Balancing Strategies for Health and Environmental Regulation, 46 Law & Contemp. Prob. 159, 160 (Summer 1983) (McGarity). (Such “technologies” are not limited to literal technology, such as scrubbers; “[c]hanges in the design and operation” of the facility, or “in the way that employees perform their tasks,” are also available options. Id., at 163, n. 18.)
Page Proof Pending Publication The third air pollution control scheme is the New Source Performance Standards program of Section 111. § 7411.
That section directs EPA to list “categories of stationary sources” that it determines “cause[ ], or contribute[ ] signifcantly to, air pollution which may reasonably be anticipated to endanger public health or welfare.” § 7411(b)(1)(A). Under Section 111(b), the Agency must then promulgate for each category “Federal standards of performance for new sources,” § 7411(b)(1)(B). A “standard of performance” is one that “refects the degree of emission limitation achievable through the application of the best system of emission reduction which (taking into account the cost of achieving such reduction and any nonair quality health and environmental impact and energy requirements) the [EPA] Administrator determines has been adequately demonstrated.” § 7411(a)(1).
Thus, the statute directs EPA to (1) “determine[ ],” taking into account various factors, the “best system of emission reduction which . . . has been adequately demonstrated,” (2) ascertain the “degree of emission limitation achievable through the application” of that system, and (3) impose an emissions limit on new stationary sources that “refects” that amount. Ibid.; see also 80 Fed. Reg. 64538 (2015). Generally speaking, a source may achieve that emissions cap any way it chooses; the key is that its pollution be no more than the amount “achievable through the application of the best system of emission reduction . . . adequately demonstrated,” or the BSER. § 7411(a)(1); see § 7411(b)(5). EPA undertakes this analysis on a pollutant-by-pollutant basis, establishing different standards of performance with respect to different pollutants emitted from the same source category. See, e. g., 73 Fed. Reg. 35838 (2008); 42 Fed. Reg. 22510 (1977).
Although the thrust of Section 111 focuses on emissions limits for new and modifed sources—as its title indicates— Page Proof Pending Publication the statute also authorizes regulation of certain pollutants from existing sources. Under Section 111(d), once EPA “has set new source standards addressing emissions of a particular pollutant under . . . section 111(b),” 80 Fed. Reg. 64711, it must then address emissions of that same pollutant by existing sources—but only if they are not already regulated under the NAAQS or HAP programs. § 7411(d)(1).
Existing power plants, for example, emit many pollutants covered by a NAAQS or HAP standard. Section 111(d) thus “operates as a gap-fller,” empowering EPA to regulate harmful emissions not already controlled under the Agency's other authorities. American Lung Assn. v. EPA, 985 F. 3d 914, 932 (CADC 2021).
Although the States set the actual rules governing existing power plants, EPA itself still retains the primary regulatory role in Section 111(d). The Agency, not the States, decides the amount of pollution reduction that must ultimately be achieved. It does so by again determining, as when setting the new source rules, “the best system of emission reduction . . . that has been adequately demonstrated for [existing covered] facilities.” 40 CFR § 60.22(b)(5) (2021); see also 80 Fed. Reg. 64664, and n. 1. The States then submit plans containing the emissions restrictions that they intend to adopt and enforce in order not to exceed the permissible level of pollution established by EPA. See §§ 60.23, 60.24; 42 U. S. C. § 7411(d)(1).
Refecting the ancillary nature of Section 111(d), EPA has used it only a handful of times since the enactment of the statute in 1970. See 80 Fed. Reg. 64703, and n. 275 (past regulations pertained to “four pollutants from fve source categories”). For instance, the Agency has established emissions limits on acid mist from sulfuric acid production, 41 Fed. Reg. 48706 (1976) (identifying “fber mist eliminator” technology as BSER); sulfde gases released by kraft pulp mills, 44 Fed. Reg. 29829 (1979) (determining BSER to be a combination of scrubbers, incineration, fltration systems, Page Proof Pending Publication and temperature control); and emissions of various harmful gases from municipal landflls, 61 Fed. Reg. 9907 (1996) (setting BSER as use of a fare to combust the gases). It was thus only a slight overstatement for one of the architects of the 1990 amendments to the Clean Air Act to refer to Section 111(d) as an “obscure, never-used section of the law.” Hearings on S. 300 et al. before the Subcommittee on Environmental Protection of the Senate Committee on Environment and Public Works, 100th Cong., 1st Sess., 13 (1987) (remarks of Sen. Durenberger).
B
Things changed in October 2015, when EPA promulgated two rules addressing carbon dioxide pollution from power plants—one for new plants under Section 111(b), the other for existing plants under Section 111(d). Both were premised on the Agency's earlier fnding that carbon dioxide is an “air pollutant” that “may reasonably be anticipated to endanger public health or welfare” by causing climate change. 80 Fed. Reg. 64530. Carbon dioxide is not subject to a NAAQS and has not been listed as a hazardous pollutant.
The frst rule announced by EPA established federal carbon emissions limits for new power plants of two varieties: fossil-fuel-fred electric steam generating units (mostly coal fred) and natural-gas-fred stationary combustion turbines. Id., at 64512. Following the statutory process set out above, the Agency determined the BSER for the two categories of sources. For steam generating units, for instance, EPA determined that the BSER was a combination of high- effciency production processes and carbon capture technology. See ibid. EPA then set the emissions limit based on the amount of carbon dioxide that a plant would emit with these technologies in place. Id., at 64513.
The second rule was triggered by the frst: Because EPA was now regulating carbon dioxide from new coal and gas plants, Section 111(d) required EPA to also address carbon emissions from existing coal and gas plants.
See Page Proof Pending Publication § 7411(d)(1). It did so through what it called the Clean Power Plan rule.
In that rule, EPA established “fnal emission guidelines for states to follow in developing plans” to regulate existing power plants within their borders. Id., at 64662. To arrive at the guideline limits, EPA did the same thing it does when imposing federal regulations on new sources: It identifed the BSER.
The BSER that the Agency selected for existing coal-fred power plants, however, was quite different from the BSER it had chosen for new sources. The BSER for existing plants included three types of measures, which the Agency called “building blocks.” Id., at 64667. The frst building block was “heat rate improvements” at coal-fred plants—essentially practices such plants could undertake to burn coal more effciently. Id., at 64727. But such improvements, EPA stated, would “lead to only small emission reductions,” because coal-fred power plants were already operating near optimum effciency. Ibid. On the Agency's view, “much larger emission reductions [were] needed from [coal-fred plants] to address climate change.” Ibid. So the Agency included two additional building blocks in its BSER, both of which involve what it called “generation shifting from higher-emitting to lower-emitting” producers of electricity. Id., at 64728. Building block two was a shift in electricity production from existing coal-fred power plants to natural-gas-fred plants. Ibid. Because natural gas plants produce “typically less than half as much” carbon dioxide per unit of electricity created as coal-fred plants, the Agency explained, “this generation shift [would] reduce[] CO2emissions.” Ibid. Building block three worked the same way, except that the shift was from both coal- and gas- fred plants to “new low- or zero-carbon generating capacity,” mainly wind and solar. Id., at 64729, 64748 (emphasis deleted). “Most of the CO2controls” in the rule came from the application of building blocks two and three. Id., at 64728. Page Proof Pending Publication The Agency identifed three ways in which a regulated plant operator could implement a shift in generation to cleaner sources. Id., at 64731. First, an operator could simply reduce the regulated plant's own production of electricity. Second, it could build a new natural gas plant, wind farm, or solar installation, or invest in someone else's existing facility and then increase generation there. Ibid. Finally, operators could purchase emission allowances or credits as part of a cap-and-trade regime. Id., at 64731–64732. Under such a scheme, sources that achieve a reduction in their emissions can sell a credit representing the value of that reduction to others, who are able to count it toward their own applicable emissions caps.
EPA explained that taking any of these steps would implement a sector-wide shift in electricity production from coal to natural gas and renewables. Id., at 64731. Given the integrated nature of the power grid, “adding electricity to the grid from one generator will result in the instantaneous reduction in generation from other generators,” and “reductions in generation from one generator lead to the instantaneous increase in generation” by others. Id., at 64769. So coal plants, whether by reducing their own production, subsidizing an increase in production by cleaner sources, or both, would cause a shift toward wind, solar, and natural gas.
Having decided that the “best system of emission reduction . . . adequately demonstrated” was one that would reduce carbon pollution mostly by moving production to cleaner sources, EPA then set about determining “the degree of emission limitation achievable through the application” of that system. 42 U. S. C. § 7411(a)(1). The Agency recognized that—given the nature of generation shifting—it could choose from “a wide range of potential stringencies for the BSER.” 80 Fed. Reg. 64730. Put differently, in translating the BSER into an operational emissions limit, EPA could choose whether to require anything from a little generPage Proof Pending Publication Page Proof Pending Publication ation shifting to a great deal. The Agency settled on what it regarded as a “reasonable” amount of shift, which it based on modeling of how much more electricity both natural gas and renewable sources could supply without causing undue cost increases or reducing the overall power supply. Id., at 64797–64811. Based on these changes, EPA projected that by 2030, it would be feasible to have coal provide 27% of national electricity generation, down from 38% in 2014. Id., at 64665, 64694; see Dept. of Energy, U. S. Energy Information Admin., Monthly Energy Review (May 2015), Electricity Net Generation: Electric Power Sector, p. 106 (Table 7.2b).
From these signifcant projected reductions in generation, EPA developed a series of complex equations to “determine the emission performance rates” that States would be required to implement. 80 Fed. Reg. 64815. The calculations resulted in numerical emissions ceilings so strict that no existing coal plant would have been able to achieve them without engaging in one of the three means of shifting generation described above. Indeed, the emissions limit the Clean Power Plan established for existing power plants was actually stricter than the cap imposed by the simultaneously published standards for new plants. Compare id., at 64742, with id., at 64513.
The point, after all, was to compel the transfer of power generating capacity from existing sources to wind and solar. The White House stated that the Clean Power Plan would “drive a[n] . . . aggressive transformation in the domestic energy industry.” White House Fact Sheet, App. in Ameri can Lung Assn. v. EPA, No. 19–1140 etc. (CADC), p. 2076. EPA's own modeling concluded that the rule would entail billions of dollars in compliance costs (to be paid in the form of higher energy prices), require the retirement of dozens of coal-fred plants, and eliminate tens of thousands of jobs across various sectors. EPA, Regulatory Impact Analysis for the Clean Power Plan Final Rule 3–22, 3–30, 3–33, 6–24, 6–25 (2015).
The Energy Information Administration reached similar conclusions, projecting that the rule would cause retail electricity prices to remain persistently 10% higher in many States, and would reduce GDP by at least a trillion 2009 dollars by 2040. Dept. of Energy, Analysis of the Impacts of the Clean Power Plan 21, 63–64 (May 2015).
C
These projections were never tested, because the Clean Power Plan never went into effect. The same day that EPA promulgated the rule, dozens of parties (including 27 States) petitioned for review in the D. C. Circuit. After that court declined to enter a stay of the rule, the challengers sought the same relief from this Court. We granted a stay, preventing the rule from taking effect. West Virginia v. EPA, 577 U. S. 1126 (2016). The Court of Appeals later heard argument on the merits en banc. But before it could issue a decision, there was a change in Presidential administrations. The new administration requested that the litigation be held in abeyance so that EPA could reconsider the Clean Power Plan. The D. C. Circuit obliged, and later dismissed the petitions for review as moot.
EPA eventually repealed the rule in 2019, concluding that the Clean Power Plan had been “in excess of its statutory authority” under Section 111(d). 84 Fed. Reg. 32523 (2019). Specifcally, the Agency concluded that generation shifting should not have been considered as part of the BSER. The Agency interpreted Section 111 as “limit[ing] the BSER to those systems that can be put into operation at a building, structure, facility, or installation,” such as “add-on controls” and “inherently lower-emitting processes/practices/designs.” Id., at 32524. It then explained that the Clean Power Plan, rather than setting the standard “based on the application of equipment and practices at the level of an individual facility,” had instead based it on “a shift in the energy generation mix at the grid level,” id., at 32523—not the sort of measure that Page Proof Pending Publication has “a Potential for Application to an Individual Source.” Id., at 32524.
The Agency determined that “the interpretative question raised” by the Clean Power Plan—“i. e., whether a `system of emission reduction' can consist of generation-shifting measures”—fell under the “major question doctrine.” Id., at 32529. Under that doctrine, EPA explained, courts “expect Congress to speak clearly if it wishes to assign to an agency decisions of vast economic and political signifcance.” Ibid. (quoting Utility Air Regulatory Group v. EPA, 573 U. S. 302, 324 (2014) (internal quotation marks omitted)). The Agency concluded that the Clean Power Plan was such a decision, for a number of reasons. Its “generation-shifting scheme was projected to have billions of dollars of impact.” 84 Fed. Reg. 32529. “[N]o section 111 rule of the scores issued ha[d] ever been based on generation shifting.” Ibid. And that novel reading of the statute would empower EPA “to order the wholesale restructuring of any industrial sector” based only on its discretionary assessment of “such factors as `cost' and `feasibility.' ” Ibid. EPA argued that under the major questions doctrine, a clear statement was necessary to conclude that Congress intended to delegate authority “of this breadth to regulate a fundamental sector of the economy.” Ibid. It found none. “Indeed,” it concluded, given the text and structure of the statute, “Congress has directly spoken to this precise question and precluded” the use of measures such as generation shifting. Ibid. In the same rulemaking, the Agency replaced the Clean Power Plan by promulgating a different Section 111(d) regulation, known as the Affordable Clean Energy (ACE) Rule. Id., at 32532. Based on its view of what measures may permissibly make up the BSER, EPA determined that the best system would be akin to building block one of the Clean Power Plan: a combination of equipment upgrades and operating practices that would improve facilities' heat rates. Id., Page Proof Pending Publication at 32522, 32537. The ACE Rule determined that the application of its BSER measures would result in only small reductions in carbon dioxide emissions. Id., at 32561.
D
A number of States and private parties immediately fled petitions for review in the D. C. Circuit, challenging EPA's repeal of the Clean Power Plan and its enactment of the replacement ACE Rule. Other States and private entities— including petitioners here West Virginia, North Dakota, and Westmoreland Mining Holdings LLC—intervened to defend both actions.
The Court of Appeals consolidated all 12 petitions for review into one case. It then held that EPA's “repeal of the Clean Power Plan rested critically on a mistaken reading of the Clean Air Act”—namely, that generation shifting cannot be a “system of emission reduction” under Section 111. 985 F. 3d, at 995. To the contrary, the court concluded, the statute could reasonably be read to encompass generation shifting. As part of that analysis, the Court of Appeals concluded that the major questions doctrine did not apply, and thus rejected the need for a clear statement of congressional intent to delegate such power to EPA. Id., at 959–968.
Having found that EPA misunderstood the scope of its authority under the Clean Air Act, the Court vacated the Agency's repeal of the Clean Power Plan and remanded to the Agency for further consideration. Id., at 995. It also vacated and remanded the replacement rule, the ACE Rule, for the same reason. Ibid. The court's decision, handed down on January 19, 2021, was quickly followed by another change in Presidential administrations. One month later, EPA moved the Court of Appeals to partially stay the issuance of its mandate as it pertained to the Clean Power Plan. The Agency did so to ensure that the Clean Power Plan would not immediately go Page Proof Pending Publication Page Proof Pending Publication back into effect. Respondents' Motion for a Partial Stay of Issuance of the Mandate in American Lung Assn. v. EPA, No. 19–1140 etc. (CADC), p. 4. EPA believed that such a result would not make sense while it was in the process of considering whether to promulgate a new Section 111(d) rule. Ibid. No party opposed the motion, and the court accordingly stayed its vacatur of the Agency's repeal of the Clean Power Plan.
Westmoreland, The North American Coal Corporation, and the States defending the repeal of the Clean Power Plan all fled petitions for certiorari. We granted the petitions and consolidated the cases. 595 U. S. ––– (2021).
II
We frst consider the Government's contention that no petitioner has Article III standing to seek our review. Although most disputes over standing concern whether a plaintiff has satisfed the requirement when fling suit, “Article III demands that an actual controversy persist throughout all stages of litigation.” Hollingsworth v. Perry, 570 U. S. 693, 705 (2013) (internal quotation marks omitted). The requirement of standing “must be met by persons seeking appellate review, just as it must be met by persons appearing in courts of frst instance.” Arizonans for Offcial English v. Arizona, 520 U. S. 43, 64 (1997). In considering a litigant's standing to appeal, the question is whether it has experienced an injury “fairly traceable to the judgment below.” Food Marketing Institute v. Argus Leader Media, 588 U. S. –––, ––– (2019) (emphasis added; internal quotation marks omitted). If so, and a “favorable ruling” from the appellate court “would redress [that] injury,” then the appellant has a cognizable Article III stake. Ibid. Here, it is apparent that at least one group of petitioners— the state petitioners—are injured by the Court of Appeals' judgment. That judgment vacated “the ACE rule and its embedded repeal of the Clean Power Plan,” 985 F. 3d, at 995 (emphasis added), and accordingly purports to bring the Clean Power Plan back into legal effect. Thus, to the extent the Clean Power Plan harms the States, the D. C. Circuit's judgment inficts the same injury. And there can be “little question” that the rule does injure the States, since they are “the object of” its requirement that they more stringently regulate power plant emissions within their borders. Lujan v. Defenders of Wildlife, 504 U. S. 555, 561–562 (1992). The Government counters that “agency and judicial actions” subsequent to the court's entry of judgment have “eliminated any . . . possibility” of injury. Brief for Federal Respondents 16. First, after the decision, EPA informed the Court of Appeals that it does not intend to enforce the Clean Power Plan because it has decided to promulgate a new Section 111(d) rule. Second, on EPA's request, the lower court stayed the part of its judgment that vacated the repeal, pending that new rulemaking. “These circumstances,” says the Government, “have mooted the prior dispute as to the CPP Repeal Rule's legality.” Id., at 17 (emphasis added).
That Freudian slip, however, reveals the basic faw in the Government's argument: It is the doctrine of mootness, not standing, that addresses whether “an intervening circumstance [has] deprive[d] the plaintiff of a personal stake in the outcome of the lawsuit.” Genesis HealthCare Corp. v. Symczyk, 569 U. S. 66, 72 (2013) (internal quotation marks omitted); see also Friends of the Earth, Inc. v. Laidlaw En vironmental Services (TOC), Inc., 528 U. S. 167, 189–192 (2000). The distinction matters because the Government, not petitioners, bears the burden to establish that a once-live case has become moot. Id., at 189; Adarand Constructors, Inc. v. Slater, 528 U. S. 216, 222 (2000) (per curiam). That burden is “heavy” where, as here, “[t]he only conceivable basis for a fnding of mootness in th[e] case is [the respondent's] voluntary conduct.” Friends of the Earth, 528 U. S., at 189. Although the Government briefy argues that the lower court's stay of its mandate extinguished the conPage Proof Pending Publication Page Proof Pending Publication troversy, it cites no authority for that proposition, and it does not make sense: Lower courts frequently stay their mandates when notifed that the losing party intends to seek our certiorari review. So the Government's mootness argument boils down to its representation that EPA has no intention of enforcing the Clean Power Plan prior to promulgating a new Section 111(d) rule.
But “[v]oluntary cessation does not moot a case” unless it is “absolutely clear that the allegedly wrongful behavior could not reasonably be expected to recur.” Parents In volved in Community Schools v. Seattle School Dist. No. 1, 551 U. S. 701, 719 (2007). Here the Government “nowhere suggests that if this litigation is resolved in its favor it will not” reimpose emissions limits predicated on generation shifting; indeed, it “vigorously defends” the legality of such an approach. Ibid. We do not dismiss a case as moot in such circumstances. See City of Mesquite v. Aladdin's Cas tle, Inc., 455 U. S. 283, 288–289 (1982). The case thus remains justiciable, and we may turn to the merits.
III
A
In devising emissions limits for power plants, EPA frst “determines” the “best system of emission reduction” that— taking into account cost, health, and other factors—it fnds “has been adequately demonstrated.” 42 U. S. C. § 7411(a) (1). The Agency then quantifes “the degree of emission limitation achievable” if that best system were applied to the covered source. Ibid.; see also 80 Fed. Reg. 64719. The BSER, therefore, “is the central determination that the EPA must make in formulating [its emission] guidelines” under Section 111. Id., at 64723. The issue here is whether restructuring the Nation's overall mix of electricity generation, to transition from 38% coal to 27% coal by 2030, can be the “best system of emission reduction” within the meaning of Section 111.
“It is a fundamental canon of statutory construction that the words of a statute must be read in their context and with a view to their place in the overall statutory scheme.” Davis v. Michigan Dept. of Treasury, 489 U. S. 803, 809 (1989). Where the statute at issue is one that confers authority upon an administrative agency, that inquiry must be “shaped, at least in some measure, by the nature of the question presented”—whether Congress in fact meant to confer the power the agency has asserted. FDA v. Brown & Wil liamson Tobacco Corp., 529 U. S. 120, 159 (2000). In the ordinary case, that context has no great effect on the appropriate analysis. Nonetheless, our precedent teaches that there are “extraordinary cases” that call for a different approach—cases in which the “history and the breadth of the authority that [the agency] has asserted,” and the “economic and political signifcance” of that assertion, provide a “reason to hesitate before concluding that Congress” meant to confer such authority. Id., at 159–160.
Such cases have arisen from all corners of the administrative state. In Brown & Williamson, for instance, the Food and Drug Administration claimed that its authority over “drugs” and “devices” included the power to regulate, and even ban, tobacco products. Id., at 126–127. We rejected that “expansive construction of the statute,” concluding that “Congress could not have intended to delegate” such a sweeping and consequential authority “in so cryptic a fashion.” Id., at 160. In Alabama Assn. of Realtors v. Depart ment of Health and Human Servs., 594 U. S. –––, ––– (2021) (per curiam), we concluded that the Centers for Disease Control and Prevention could not, under its authority to adopt measures “necessary to prevent the . . . spread of” disease, institute a nationwide eviction moratorium in response to the COVID–19 pandemic. We found the statute's language a “wafer-thin reed” on which to rest such a measure, given “the sheer scope of the CDC's claimed authority,” its “unprecedented” nature, and the fact that Congress had Page Proof Pending Publication Page Proof Pending Publication failed to extend the moratorium after previously having done so. Id., at ––– – –––.
Our decision in Utility Air addressed another question regarding EPA's authority—namely, whether EPA could construe the term “air pollutant,” in a specifc provision of the Clean Air Act, to cover greenhouse gases. 573 U. S., at 310. Despite its textual plausibility, we noted that the Agency's interpretation would have given it permitting authority over millions of small sources, such as hotels and offce buildings, that had never before been subject to such requirements. Id., at 310, 324. We declined to uphold EPA's claim of “unheralded” regulatory power over “a signifcant portion of the American economy.” Id., at 324. In Gonzales v. Oregon, 546 U. S. 243 (2006), we confronted the Attorney General's assertion that he could rescind the license of any physician who prescribed a controlled substance for assisted suicide, even in a State where such action was legal. The Attorney General argued that this came within his statutory power to revoke licenses where he found them “inconsistent with the public interest,” 21 U. S. C. §823(f). We considered the “idea that Congress gave [him] such broad and unusual authority through an implicit delegation . . . not sustainable.” 546 U. S., at 267. Similar considerations informed our recent decision invalidating the Occupational Safety and Health Administration's mandate that “84 million Americans . . . either obtain a COVID–19 vaccine or undergo weekly medical testing at their own expense.” National Federa tion of Independent Business v. Occupational Safety and Health Administration, 595 U. S. 109, 117 (2022) (per cu riam). We found it “telling that OSHA, in its half century of existence,” had never relied on its authority to regulate occupational hazards to impose such a remarkable measure. Id., at 119.
All of these regulatory assertions had a colorable textual basis. And yet, in each case, given the various circumstances, “common sense as to the manner in which Congress [would have been] likely to delegate” such power to the agency at issue, Brown & Williamson, 529 U. S., at 133, made it very unlikely that Congress had actually done so. Extraordinary grants of regulatory authority are rarely accomplished through “modest words,” “vague terms,” or “subtle device[s].” Whitman, 531 U. S., at 468. Nor does Congress typically use oblique or elliptical language to empower an agency to make a “radical or fundamental change” to a statutory scheme. MCI Telecommunications Corp. v. American Telephone & Telegraph Co., 512 U. S. 218, 229 (1994). Agencies have only those powers given to them by Congress, and “enabling legislation” is generally not an “open book to which the agency [may] add pages and change the plot line.” E. Gellhorn & P. Verkuil, Controlling Chevron-Based Delegations, 20 Cardozo L. Rev. 989, 1011 (1999). We presume that “Congress intends to make major policy decisions itself, not leave those decisions to agencies.” United States Telecom Assn. v. FCC, 855 F. 3d 381, 419 (CADC 2017) (Kavanaugh, J., dissenting from denial of rehearing en banc).
Thus, in certain extraordinary cases, both separation of powers principles and a practical understanding of legislative intent make us “reluctant to read into ambiguous statutory text” the delegation claimed to be lurking there. Util ity Air, 573 U. S., at 324.
To convince us otherwise, something more than a merely plausible textual basis for the agency action is necessary. The agency instead must point to “clear congressional authorization” for the power it claims. Ibid. The dissent criticizes us for “announc[ing] the arrival” of this major questions doctrine, and argues that each of the decisions just cited simply followed our “ordinary method” of “normal statutory interpretation,” post, at 764, 766 (opinion of Kagan, J.). But in what the dissent calls the “key case” in this area, Brown & Williamson, post, at 767, the Court could not have been clearer: “In extraordinary cases . . . Page Proof Pending Publication Page Proof Pending Publication there may be reason to hesitate” before accepting a reading of a statute that would, under more “ordinary” circumstances, be upheld. 529 U. S., at 159. Or, as we put it more recently, we “typically greet” assertions of “extravagant statutory power over the national economy” with “skepticism.” Utility Air, 573 U. S., at 324. The dissent attempts to ft the analysis in these cases within routine statutory interpretation, but the bottom line—a requirement of “clear congressional authorization,” ibid.—confrms that the approach under the major questions doctrine is distinct.
As for the major questions doctrine “label[ ],” post, at 764, it took hold because it refers to an identifable body of law that has developed over a series of signifcant cases all addressing a particular and recurring problem: agencies asserting highly consequential power beyond what Congress could reasonably be understood to have granted. Scholars and jurists have recognized the common threads between those decisions. So have we. See Utility Air, 573 U. S., at 324 (citing Brown & Williamson and MCI); King v. Burwell, 576 U. S. 473, 486 (2015) (citing Utility Air, Brown & William son, and Gonzales).
B
Under our precedents, this is a major questions case. In arguing that Section 111(d) empowers it to substantially restructure the American energy market, EPA “claim[ed] to discover in a long-extant statute an unheralded power” representing a “transformative expansion in [its] regulatory authority.” Utility Air, 573 U. S., at 324. It located that newfound power in the vague language of an “ancillary provision[ ]” of the Act, Whitman, 531 U. S., at 468, one that was designed to function as a gap fller and had rarely been used in the preceding decades. And the Agency's discovery allowed it to adopt a regulatory program that Congress had conspicuously and repeatedly declined to enact itself. Brown & Williamson, 529 U. S., at 159–160; Gonzales, 546 U. S., at 267–268; Alabama Assn., 594 U. S., at –––, –––. Given these circumstances, there is every reason to “hesitate before concluding that Congress” meant to confer on EPA the authority it claims under Section 111(d). Brown & Wil liamson, 529 U. S., at 159–160.
Prior to 2015, EPA had always set emissions limits under Section 111 based on the application of measures that would reduce pollution by causing the regulated source to operate more cleanly. See, e. g., 41 Fed. Reg. 48706 (requiring “degree of control achievable through the application of fber mist eliminators”); see also supra, at 710–711. It had never devised a cap by looking to a “system” that would reduce pollution simply by “shifting” polluting activity “from dirtier to cleaner sources.” 80 Fed. Reg. 64726; see id., at 64738 (“[O]ur traditional interpretation . . . has allowed regulated entities to produce as much of a particular good as they desire provided that they do so through an appropriately clean (or low-emitting) process.”). And as Justice Frankfurter has noted, “just as established practice may shed light on the extent of power conveyed by general statutory language, so the want of assertion of power by those who presumably would be alert to exercise it, is equally signifcant in determining whether such power was actually conferred.” FTC v. Bunte Brothers, Inc., 312 U. S. 349, 352 (1941).
The Government quibbles with this description of the history of Section 111(d), pointing to one rule that it says relied upon a cap-and-trade mechanism to reduce emissions. See 70 Fed. Reg. 28616 (2005) (Mercury Rule). The legality of that choice was controversial at the time and was never addressed by a court. See New Jersey v. EPA, 517 F. 3d 574 (CADC 2008) (vacating on other grounds). Even assuming the Rule was valid, though, it still does not help the Government. In that regulation, EPA set the actual “emission cap”—i. e., the limit on emissions that sources would be required to meet—“based on the level of [mercury] emissions reductions that w[ould] be achievable by” the use of “technologies [that could be] installed and operational on a nationPage Proof Pending Publication wide basis” in the relevant timeframe—namely, wet scrubbers. 70 Fed. Reg. 28620–28621. In other words, EPA set the cap based on the application of particular controls, and regulated sources could have complied by installing them. By contrast, and by design, there is no control a coal plant operator can deploy to attain the emissions limits established by the Clean Power Plan. See supra, at 714–715. The Mercury Rule, therefore, is no precedent for the Clean Power Plan. To the contrary, it was one more entry in an unbroken list of prior Section 111 rules that devised the enforceable emissions limit by determining the best control mechanisms available for the source.1 This consistent understanding of “system[s] of emission reduction” tracked the seemingly universal view, as stated by EPA in its inaugural Section 111(d) rulemaking, that “Congress intended a technology-based approach” to regulation in that Section. 40 Fed. Reg. 53343 (1975); see id., at 53341 (“degree of control to be refected in EPA's emission guidelines” will be based on “application of best adequately demonstrated control technology”).2 A technology-based stand1The dissent cites other ostensible precedents, see post, at 776–777, but they are also inapposite. A few allowed cap-and-trade or similar averaging measures as compliance mechanisms, like the Mercury Rule. See, e. g., 60 Fed. Reg. 65402 (1995). The others were not Section 111 rules. 2 See McGarity 165 (EPA promulgates “technology-based new source performance standards that require the implementation of the `best available demonstrated' technology”); P. McCubbin, The Risk in Technology- Based Standards, 16 Duke Env. L. & Pol'y Forum 1, 46, n. 180 (2005) (Section 111 standards “are another set of technology-based standards”); W. Wagner, The Triumph of Technology-Based Standards, 2000 U. Ill. L. Rev. 83, 84, n. 4 (“Technology-based standards made their initial appearance” in “Section 111 of the Clean Air Act,” which “requires the EPA to set technology-based emission limitations”).
The dissent points to a 1977 amendment to Section 111 as evidence that the 1970 Congress did not intend for EPA to establish this sort of source- specifc standard. Post, at 762–763. But it is clear that the 1977 amendment was merely intended to prohibit power plants from adopting one specifc kind of at-the-source measure—a switch from burning high-sulfur Page Proof Pending Publication ard, recall, is one that focuses on improving the emissions performance of individual sources. EPA “commonly referred to” the “level of control” required as a “best demonstrated technology (BDT)” standard, 73 Fed. Reg. 34073, and consistently applied it as such. E. g., 61 Fed. Reg. 9907 (declaring “BDT” to be “a well-designed and well-operated gas collection system and . . . a control device capable of reducing [harmful gases] in the collected gas by 98 weight-percent.”). Indeed, EPA nodded to this history in the Clean Power Plan itself, describing the sort of “systems of emission reduction” it had always before selected—“effciency improvements, fuel-switching,” and “add-on controls”—as “more traditional air pollution control measures.” 80 Fed. Reg. 64765, 64784. The Agency noted that it had “considered” such measures as potential systems of emission reduction for carbon dioxide, ibid., including a measure it ultimately adopted as a “component” of the BSER, namely, heat rate improvements. Id., at 64727.
But, the Agency explained, in order to “control[ ] CO2from affected [plants] at levels . . . necessary to mitigate the dangers presented by climate change,” it could not base the emissions limit on “measures that improve effciency at the power plants.” Id., at 64728. “The quantity of emissions reductions resulting from the application of these measures” would have been “too small.” Id., at 64727. Instead, to attain the necessary “critical CO2reductions,” EPA adopted what it called a “broader, forward-thinking approach to the design” of Section 111 regulations. Id., at 64703. Rather than focus on improving the performance of individual sources, it would “improve the overall power system by lowering the carbon intensity of power generation.” Ibid. (emphasis added). And it would do that by forcing a shift coal to low-sulfur coal—and was not intended or understood to change the basic, source-focused regulatory approach. See Wisconsin Elec. Power Co. v. Reilly, 893 F. 2d 901, 919 (CA7 1990) (explaining the history); B. Ackerman & W. Hassler, Clean Coal/Dirty Air (1981) (same). Page Proof Pending Publication throughout the power grid from one type of energy source to another. In the words of the then-EPA Administrator, the rule was “not about pollution control” so much as it was “an investment opportunity” for States, especially “investments in renewables and clean energy.” Oversight Hearing on EPA's Proposed Carbon Pollution Standards for Existing Power Plants before the Senate Committee on Environment and Public Works, 113th Cong., 2d Sess., p. 33 (2014).
This view of EPA's authority was not only unprecedented; it also effected a “fundamental revision of the statute, changing it from [one sort of] scheme of . . . regulation” into an entirely different kind. MCI, 512 U. S., at 231. Under the Agency's prior view of Section 111, its role was limited to ensuring the effcient pollution performance of each individual regulated source. Under that paradigm, if a source was already operating at that level, there was nothing more for EPA to do. Under its newly “discover[ed]” authority, Util ity Air, 573 U. S., at 324, however, EPA can demand much greater reductions in emissions based on a very different kind of policy judgment: that it would be “best” if coal made up a much smaller share of national electricity generation. And on this view of EPA's authority, it could go further, perhaps forcing coal plants to “shift” away virtually all of their generation—i. e., to cease making power altogether.3 The Government attempts to downplay the magnitude of this “unprecedented power over American industry.” In dustrial Union Dept., AFL–CIO v. American Petroleum In stitute, 448 U. S. 607, 645 (1980) (plurality opinion). The 3The dissent suggests that EPA could bring about the same result by, for example, simply requiring coal plants to become natural gas plants, and that this would ft within the prior regulatory approach of effciency- improving, at-the-source measures. Post, at 775. Of course, EPA has never ordered anything remotely like that, and we doubt it could. Section 111(d) empowers EPA to guide States in “establish[ing] standards of performance” for “existing source[s],” § 7411(d)(1), not to direct existing sources to effectively cease to exist.
Page Proof Pending Publication amount of generation shifting ordered, it argues, must be “adequately demonstrated” and “best” in light of the statutory factors of “cost,” “nonair quality health and environmental impact,” and “energy requirements.” 42 U. S. C. § 7411(a)(1). EPA therefore must limit the magnitude of generation shift it demands to a level that will not be “exorbitantly costly” or “threaten the reliability of the grid.” Brief for Federal Respondents 42.
But this argument does not so much limit the breadth of the Government's claimed authority as reveal it. On EPA's view of Section 111(d), Congress implicitly tasked it, and it alone, with balancing the many vital considerations of national policy implicated in deciding how Americans will get their energy. EPA decides, for instance, how much of a switch from coal to natural gas is practically feasible by 2020, 2025, and 2030 before the grid collapses, and how high energy prices can go as a result before they become unreasonably “exorbitant.”
There is little reason to think Congress assigned such decisions to the Agency. For one thing, as EPA itself admitted when requesting special funding, “Understand[ing] and project[ing] system-wide . . . trends in areas such as electricity transmission, distribution, and storage” requires “technical and policy expertise not traditionally needed in EPA regulatory development.” EPA, Fiscal Year 2016: Justifcation of Appropriation Estimates for the Committee on Appropriations 213 (2015) (emphasis added). “When [an] agency has no comparative expertise” in making certain policy judgments, we have said, “Congress presumably would not” task it with doing so. Kisor v. Wilkie, 588 U. S. –––, ––– (2019); see also Gonzales, 546 U. S., at 266–267.
We also fnd it “highly unlikely that Congress would leave” to “agency discretion” the decision of how much coal-based generation there should be over the coming decades. MCI, 512 U. S., at 231; see also Brown & Williamson, 529 U. S., at 160 (“We are confdent that Congress could not have inPage Proof Pending Publication Page Proof Pending Publication tended to delegate a decision of such economic and political signifcance to an agency in so cryptic a fashion.”). The basic and consequential tradeoffs involved in such a choice are ones that Congress would likely have intended for itself. See W. Eskridge, Interpreting Law: A Primer on How To Read Statutes and the Constitution 288 (2016) (“Even if Congress has delegated an agency general rulemaking or adjudicatory power, judges presume that Congress does not delegate its authority to settle or amend major social and economic policy decisions.”). Congress certainly has not conferred a like authority upon EPA anywhere else in the Clean Air Act. The last place one would expect to fnd it is in the previously little-used backwater of Section 111(d). The dissent contends that there is nothing surprising about EPA dictating the optimal mix of energy sources nationwide, since that sort of mandate will reduce air pollution from power plants, which is EPA's bread and butter. Post, at 771–773. But that does not follow. Forbidding evictions may slow the spread of disease, but the CDC's ordering such a measure certainly “raise[s] an eyebrow.” Post, at 770. We would not expect the Department of Homeland Security to make trade or foreign policy even though doing so could decrease illegal immigration. And no one would consider generation shifting a “tool” in OSHA's “toolbox,” post, at 772, even though reducing generation at coal plants would reduce workplace illness and injury from coal dust.
The dissent also cites our decision in American Elec.
Power Co. v. Connecticut, 564 U. S. 410 (2011). Post, at 771. The question there, however, was whether Congress wanted district court judges to decide, under unwritten federal nuisance law, “whether and how to regulate carbon-dioxide emissions from powerplants.” 564 U. S., at 426. We answered no, given the existence of Section 111(d). But we said nothing about the ways in which Congress intended EPA to exercise its power under that provision. And it is doubtful we had in mind that it would claim the authority to require a large shift from coal to natural gas, wind, and solar. After all, EPA had never regulated in that manner, despite having issued many prior rules governing power plants under Section 111. See, e. g., 71 Fed. Reg. 9866 (2006); 70 Fed. Reg. 28616; 44 Fed. Reg. 33580; 36 Fed. Reg. 24875 (1971).4 Finally, we cannot ignore that the regulatory writ EPA newly uncovered conveniently enabled it to enact a program that, long after the dangers posed by greenhouse gas emissions “had become well known, Congress considered and rejected” multiple times. Brown & Williamson, 529 U. S., at 144; see also Alabama Assn., 594 U. S., at –––; Bunte Broth ers, 312 U. S., at 352 (lack of authority not previously exercised “reinforced by [agency's] unsuccessful attempt . . . to secure from Congress an express grant of [the challenged] authority”). At bottom, the Clean Power Plan essentially adopted a cap-and-trade scheme, or set of state cap-andtrade schemes, for carbon. See 80 Fed. Reg. 64734 (“Emissions trading is . . . an integral part of our BSER analysis.”). Congress, however, has consistently rejected proposals to amend the Clean Air Act to create such a program. See, e. g., American Clean Energy and Security Act of 2009, H. R. 2454, 111th Cong., 1st Sess.; Clean Energy Jobs and American Power Act, S. 1733, 111th Cong., 1st Sess. (2009). It has 4According to the dissent, “EPA is always controlling the mix of energy sources” under Section 111 because all of the Agency's rules impose some costs on regulated plants, and therefore (all else equal) cause those plants to lose some share of the electricity market. Post, at 773. But there is an obvious difference between (1) issuing a rule that may end up causing an incidental loss of coal's market share, and (2) simply announcing what the market share of coal, natural gas, wind, and solar must be, and then requiring plants to reduce operations or subsidize their competitors to get there. No one has ever thought that the Clean Power Plan was just business as usual. See American Lung Assn. v. EPA, 985 F. 3d 914, 1000 (CADC 2021) (Walker, J., dissenting) (“Leaders of the environmental movement considered the rule `groundbreaking,' called its announcement `historic,' and labeled it a `critically important catalyst.' ” (footnotes omitted)).
Page Proof Pending Publication also declined to enact similar measures, such as a carbon tax. See, e. g., Climate Protection Act of 2013, S. 332, 113th Cong., 1st Sess.; Save Our Climate Act of 2011, H. R. 3242, 112th Cong., 1st Sess. “The importance of the issue,” along with the fact that the same basic scheme EPA adopted “has been the subject of an earnest and profound debate across the country, . . . makes the oblique form of the claimed delegation all the more suspect.” Gonzales, 546 U. S., at 267–268 (internal quotation marks omitted).
C
Given these circumstances, our precedent counsels skepticism toward EPA's claim that Section 111 empowers it to devise carbon emissions caps based on a generation shifting approach. To overcome that skepticism, the Government must—under the major questions doctrine—point to “clear congressional authorization” to regulate in that manner. Utility Air, 573 U. S., at 324.
All the Government can offer, however, is the Agency's authority to establish emissions caps at a level refecting “the application of the best system of emission reduction . . . adequately demonstrated.” 42 U. S. C. § 7411(a)(1). As a matter of “defnitional possibilities,” FCC v. AT&T Inc., 562 U. S. 397, 407 (2011), generation shifting can be described as a “system”—“an aggregation or assemblage of objects united by some form of regular interaction,” Brief for Federal Respondents 31—capable of reducing emissions. But of course almost anything could constitute such a “system”; shorn of all context, the word is an empty vessel. Such a vague statutory grant is not close to the sort of clear authorization required by our precedents.
The Government, echoed by the other respondents, looks to other provisions of the Clean Air Act for support. It points out that the Act elsewhere uses the word “system” or “similar words” to describe cap-and-trade schemes or other sector-wide mechanisms for reducing pollution. Ibid. The Page Proof Pending Publication Acid Rain program set out in Title IV of the Act establishes a cap-and-trade scheme for reducing sulfur dioxide emissions, which the statute refers to as an “emission allocation and transfer system.” § 7651(b) (emphasis added). And Section 110 of the NAAQS program specifes that “marketable permits” and “auctions of emissions rights” qualify as “control measures, means, or techniques” that States may adopt in their state implementation plans in order “to meet the applicable requirements of” a NAAQS. §7410(a)(2)(A). If the word “system” or similar words like “technique” or “means” can encompass cap-and-trade, the Government maintains, why not in Section 111?
But just because a cap-and-trade “system” can be used to reduce emissions does not mean that it is the kind of “system of emission reduction” referred to in Section 111. Indeed, the Government's examples demonstrate why it is not.
First, unlike Section 111, the Acid Rain and NAAQS programs contemplate trading systems as a means of complying with an already established emissions limit, set either directly by Congress (as with Acid Rain, see 42 U. S. C. § 7651c) or by reference to the safe concentration of the pollutant in the ambient air (as with the NAAQS). In Section 111, by contrast, it is EPA's job to come up with the cap itself: the “numerical limit on emissions” that States must apply to each source. 80 Fed. Reg. 64768. We doubt that Congress directed the Agency to set an emissions cap at the level “which refects the degree of emission limitation achievable through the application of [a cap-and-trade] system,” § 7411(a)(1), for that degree is indeterminate. It is one thing for Congress to authorize regulated sources to use trading to comply with a preset cap, or a cap that must be based on some scientifc, objective criterion, such as the NAAQS. It is quite another to simply authorize EPA to set the cap itself wherever the Agency sees ft.
Second, Congress added the above authorizations for the use of emissions trading programs in 1990, simultaneous with Page Proof Pending Publication amending Section 111 to its present form. At the time, capand-trade was a novel and highly touted concept. The Acid Rain program was “the nation's frst-ever emissions trading program.” L. Heinzerling & R. Steinzor, A Perfect Storm: Mercury and the Bush Administration, 34 Env. L. Rep. 10297, 10309 (2004). And Congress went out of its way to amend the NAAQS statute to make absolutely clear that the “measures, means, [and] techniques” States could use to meet the NAAQS included cap-and-trade. § 7410(a)(2)(A). Yet “not a peep was heard from Congress about the possibility that a trading regime could be installed under § 111.” Id., at 10309.
Finally, the Government notes that other parts of the Clean Air Act, past and present, have “explicitly limited the permissible components of a particular `system' ” of emission reduction in some regard. Brief for Federal Respondents 32. For instance, a separate section of the statute empowers EPA to require the “degree of reduction achievable through the retroft application of the best system of contin uous emission reduction.” § 7651f(b)(2) (emphasis added). The comparatively unadorned use of the phrase “best system of emission reduction” in Section 111, the Government urges, “suggest[s] a conscious congressional” choice not to limit the measures that may constitute the BSER to those applicable at or to an individual source. Id., at 32.
These arguments, however, concern an interpretive question that is not at issue. We have no occasion to decide whether the statutory phrase “system of emission reduction” refers exclusively to measures that improve the pollution performance of individual sources, such that all other actions are ineligible to qualify as the BSER. To be sure, it is pertinent to our analysis that EPA has acted consistent with such a limitation for the frst four decades of the statute's existence. But the only interpretive question before us, and the only one we answer, is more narrow: whether the “best sysPage Proof Pending Publication tem of emission reduction” identifed by EPA in the Clean Power Plan was within the authority granted to the Agency in Section 111(d) of the Clean Air Act. For the reasons given, the answer is no.5 * * * Capping carbon dioxide emissions at a level that will force a nationwide transition away from the use of coal to generate electricity may be a sensible “solution to the crisis of the day.” New York v. United States, 505 U. S. 144, 187 (1992). But it is not plausible that Congress gave EPA the authority to adopt on its own such a regulatory scheme in Section 111(d). A decision of such magnitude and consequence rests with Congress itself, or an agency acting pursuant to a clear delegation from that representative body. The judgment of the Court of Appeals for the District of Columbia Circuit is reversed, and the cases are remanded for further proceedings consistent with this opinion.
It is so ordered.