JUSTICE STEVENS delivered the opinion of the Court.
We granted certiorari to decide two questions of law.
Concluding that the Court of Appeals for the Ninth Circuit misapplied the National Environmental Policy Act of 1969 (NEPA), 83 Stat. 852, 42 U. S. C. § 4321 et seq., and gave inadequate deference to the Forest Service's interpretation of its own regulations, we reverse and remand for further proceedings.
The Forest Service is authorized by statute to manage the national forests for "outdoor recreation, range, timber, watershed, and wildlife and fish purposes." 74 Stat. 215, 16 U. S. C. § 528. See also 90 Stat. 2949, 16 U. S. C. § 1600 et seq. Pursuant to that authorization, the Forest Service has issued "special use" permits for the operation of approximately 170 Alpine and Nordic ski areas on federal lands. See H. R. Rep. No. 99-709, pt. 1, p. 2 (1986).
The Forest Service permit process involves three separate stages. The Forest Service first examines the general environmental and financial feasibility of a proposed project and decides whether to issue a special use permit. See 36 CFR § 251.54(f) (1988). Because that decision is a "major Federal action" within the meaning of NEPA, it must be preceded by the preparation of an Environmental Impact Statement (EIS). 42 U. S. C. § 4332. If the Service decides to issue a permit, it then proceeds to select a developer, formulate the basic terms of the arrangement with the selected party,
Sandy Butte is a 6,000-foot mountain located in the Okanogan National Forest in Okanogan County, Washington. At present Sandy Butte, like the Methow Valley it overlooks, is an unspoiled, sparsely populated area that the District Court characterized as "pristine." App. to Pet. for Cert. 20a. In 1968, Congress established the North Cascades National Park and directed the Secretaries of the Interior and Agriculture to agree on the designation of areas within, and adjacent to, the park for public uses, including ski areas. 82 Stat. 926, 930, 16 U. S. C. §§ 90, 90d-3. A 1970 study conducted by the Forest Service pursuant to this congressional directive identified Sandy Butte as having the highest potential of any site in the State of Washington for development as a major downhill ski resort.
In response to MRI's application, the Forest Service, in cooperation with state and county officials, prepared an EIS known as the Early Winters Alpine Winter Sports Study (Early Winters Study or Study). The stated purpose of the EIS was "to provide the information required to evaluate the potential for skiing at Early Winters" and "to assist in making a decision whether to issue a Special Use Permit for downhill skiing on all or a portion of approximately 3900 acres of National Forest System land." Early Winters Study 1. A draft of the Study was completed and circulated in 1982, but release of the final EIS was delayed as Congress considered including Sandy Butte in a proposed wilderness area. App. to Pet. for Cert. 26a. When the Washington State Wilderness Act of 1984 was passed, however, Sandy Butte was excluded from the wilderness designation,
The effects of the proposed development on air quality and wildlife received particular attention in the Study. In the chapter on "Environmental Consequences," the first subject discussed is air quality. As is true of other subjects, the discussion included an analysis of cumulative impacts over several
In its discussion of air-quality mitigation measures, the EIS identified actions that could be taken by the county government to mitigate the adverse effects of development, as well as those that the Forest Service itself could implement at the construction stage of the project. The Study suggested that Okanogan County develop an air quality management plan, requiring weatherization of new buildings, limiting the number of wood stoves and fireplaces, and adopting monitoring and enforcement measures.
In its discussion of adverse effects on area wildlife, the EIS concluded that no endangered or threatened species would be affected by the proposed development and that the only impact on sensitive species was the probable loss of a pair of spotted owls and their progeny. Id., at 75. With regard to other wildlife, the Study considered the impact on 75 different
In a comment in response to the draft EIS, the Washington Department of Game voiced a special concern about potential losses to the State's largest migratory deer herd, which uses the Methow Valley as a critical winter range and as its migration route. Id., at Appendix D (letter of November 18, 1982). The state agency estimated that the total population of mule deer in the area most likely to be affected was "better than 30,000 animals" and that "the ultimate impact on the Methow deer herd could exceed a 50 percent reduction in numbers." Ibid. The agency asserted that "Okanogan County residents place a great deal of importance on the area's deer herd." Ibid. In addition, it explained that hunters had "harvested" 3,247 deer in the Methow Valley area in 1981, and that, since in 1980 hunters on average spent $1,980 for each deer killed in Washington, they had contributed over $6 million to the State's economy in 1981. Because the deer harvest is apparently proportional to the size of the herd, the state agency predicted that "Washington business can expect to lose over $3 million annually from reduced recreational opportunity." Ibid. The Forest Service's own analysis of the impact on the deer herd was more modest. It first concluded that the actual operation of the ski hill would have only a "minor" direct impact on the herd,
As was true of its discussion of air quality, the EIS also described both on-site and off-site mitigation measures. Among possible on-site mitigation possibilities, the Study recommended locating runs, ski lifts, and roads so as to minimize interference with wildlife, restricting access to selected roads during fawning season, and further examination of the effect of the development on mule deer migration routes.
Ultimately, the Early Winters Study recommended the issuance of a permit for development at the second highest level considered — a 16-lift ski area able to accommodate 8,200 skiers at one time. On July 5, 1984, the Regional Forester decided to issue a special use permit as recommended by the
Four organizations (respondents)
Thereafter, respondents brought this action under the Administrative Procedure Act, 5 U. S. C. §§ 701-706, to obtain judicial review of the Forest Service's decision. Their principal claim was that the Early Winters Study did not satisfy
Concluding that the Early Winters Study was inadequate as a matter of law, the Court of Appeals reversed. Methow Valley Citizens Council v. Regional Forester, 833 F.2d 810
The court found a similar defect in the EIS' treatment of air quality. Since the EIS made it clear that commercial development in the Methow Valley will result in violations of state air-quality standards unless effective mitigation measures are put in place by the local governments and the private developer, the Court of Appeals concluded that the Forest Service had an affirmative duty to "develop the necessary mitigation measures before the permit is granted." Id., at 819 (emphasis in original) (footnote omitted). The court held that this duty was imposed by both the Forest Service's own regulations and § 102 of NEPA. Ibid. It read the statute as imposing a substantive requirement that " `action be taken to mitigate the adverse effects of major federal actions.' " Ibid. (quoting Stop H-3 Assn. v. Brinegar, 389 F.Supp. 1102, 1111 (Haw. 1974), rev'd on other grounds, 533 F.2d 434 (CA9), cert. denied, 429 U.S. 999 (1976)). For this reason, it concluded that "an EIS must include a thorough discussion of measures to mitigate the adverse environmental impacts of a proposed action." 833 F. 2d, at 819. The Court of Appeals concluded by quoting this paragraph from an opinion it had just announced:
Section 101 of NEPA declares a broad national commitment to protecting and promoting environmental quality. 83 Stat. 852, 42 U. S. C. § 4331. To ensure that this commitment is "infused into the ongoing programs and actions of the Federal Government, the act also establishes some important `action-forcing' procedures." 115 Cong. Rec. 40416 (remarks of Sen. Jackson). See also S. Rep. No. 91-296, p. 19 (1969); Andrus v. Sierra Club, 442 U.S. 347, 350 (1979); Kleppe v. Sierra Club, 427 U.S. 390, 409, and n. 18 (1976). Section 102 thus, among other measures
The statutory requirement that a federal agency contemplating a major action prepare such an environmental impact statement serves NEPA's "action-forcing" purpose in two important respects. See Baltimore Gas & Electric Co. v. Natural Resources Defense Council, Inc., 462 U.S. 87, 97 (1983); Weinberger v. Catholic Action of Hawaii/Peace Education Project, 454 U.S. 139, 143 (1981). It ensures that the agency, in reaching its decision, will have available, and will carefully consider, detailed information concerning significant environmental impacts; it also guarantees that the relevant information will be made available to the larger audience that may also play a role in both the decisionmaking process and the implementation of that decision.
Simply by focusing the agency's attention on the environmental consequences of a proposed project, NEPA ensures that important effects will not be overlooked or underestimated only to be discovered after resources have been committed or the die otherwise cast. See ibid.; Kleppe, supra, at 409. Moreover, the strong precatory language of § 101 of the Act and the requirement that agencies prepare detailed impact statements inevitably bring pressure to bear on agencies "to respond to the needs of environmental quality." 115 Cong. Rec. 40425 (1969) (remarks of Sen. Muskie).
Publication of an EIS, both in draft and final form, also serves a larger informational role. It gives the public the assurance that the agency "has indeed considered environmental concerns in its decisionmaking process," Baltimore Gas & Electric Co., supra, at 97, and, perhaps more significantly, provides a springboard for public comment, see L. Caldwell, Science and the National Environmental Policy Act 72 (1982). Thus, in this case the final draft of the Early Winters Study reflects not only the work of the Forest Service itself, but also the critical views of the Washington State Department of Game, the Methow Valley Citizens Council, and
The sweeping policy goals announced in § 101 of NEPA are thus realized through a set of "action-forcing" procedures that require that agencies take a " `hard look' at environmental consequences," Kleppe, 427 U. S., at 410, n. 21 (citation omitted), and that provide for broad dissemination of relevant environmental information. Although these procedures are almost certain to affect the agency's substantive decision, it is now well settled that NEPA itself does not mandate particular results, but simply prescribes the necessary process. See Strycker's Bay Neighborhood Council, Inc. v. Karlen, 444 U.S. 223, 227-228 (1980) (per curiam); Vermont Yankee Nuclear Power Corp. v. Natural Resources Defense Council, Inc., 435 U.S. 519, 558 (1978). If the adverse environmental effects of the proposed action are adequately identified and evaluated, the agency is not constrained by NEPA from deciding that other values outweigh the environmental costs. See ibid.; Strycker's Bay Neighborhood Council, Inc., supra, at 227-228; Kleppe, supra, at 410, n. 21. In this
To be sure, one important ingredient of an EIS is the discussion of steps that can be taken to mitigate adverse environmental consequences.
There is a fundamental distinction, however, between a requirement that mitigation be discussed in sufficient detail to ensure that environmental consequences have been fairly evaluated, on the one hand, and a substantive requirement that a complete mitigation plan be actually formulated and adopted, on the other. In this case, the off-site effects on air quality and on the mule deer herd cannot be mitigated unless nonfederal government agencies take appropriate action. Since it is those state and local governmental bodies that have jurisdiction over the area in which the adverse effects need be addressed and since they have the authority to mitigate them, it would be incongruous to conclude that the Forest Service has no power to act until the local agencies have reached a final conclusion on what mitigating measures
We thus conclude that the Court of Appeals erred, first, in assuming that "NEPA requires that `action be taken to mitigate the adverse effects of major federal actions,' " 833 F. 2d, at 819 (quoting Stop H-3 Assn. v. Brinegar, 389 F. Supp., at 1111), and, second, in finding that this substantive requirement entails the further duty to include in every EIS "a detailed explanation of specific measures which will be employed to mitigate the adverse impacts of a proposed action," 833 F. 2d, at 819 (emphasis supplied).
The Court of Appeals also concluded that the Forest Service had an obligation to make a "worst case analysis" if it could not make a reasoned assessment of the impact of the Early Winters project on the mule deer herd. Such a "worst case analysis" was required at one time by CEQ regulations, but those regulations have since been amended. Moreover, although the prior regulations may well have expressed a permissible application of NEPA, the Act itself does not mandate that uncertainty in predicting environmental harms be addressed exclusively in this manner. Accordingly, we conclude that the Court of Appeals also erred in requiring the "worst case" study.
In 1977, President Carter directed that CEQ promulgate binding regulations implementing the procedural provisions of NEPA. Exec. Order No. 11991, 3 CFR 123 (1977 Comp.). Pursuant to this Presidential order, CEQ promulgated implementing regulations. Under § 1502.22 of these regulations — a provision which became known as the "worst case requirement" — CEQ provided that if certain information relevant to the agency's evaluation of the proposed action is either unavailable or too costly to obtain, the agency must include in the EIS a "worst case analysis and an indication of the probability or improbability of its occurrence." 40 CFR § 1502.22 (1985). In 1986, however, CEQ replaced the "worst case" requirement with a requirement that federal agencies, in the face of unavailable information concerning a reasonably foreseeable significant environmental consequence, prepare "a summary of existing credible scientific evidence which is relevant to evaluating the . . . adverse impacts" and prepare an "evaluation of such impacts based upon theoretical approaches or research methods generally accepted in the scientific community." 40 CFR § 1502.22(b) (1987). The amended regulation thus "retains the duty to describe the consequences of a remote, but potentially severe impact, but grounds the duty in evaluation of scientific opinion rather
The Court of Appeals recognized that the "worst case analysis" regulation has been superseded, yet held that "[t]his rescission . . . does not nullify the requirement . . . since the regulation was merely a codification of prior NEPA case law." 833 F. 2d, at 817, n. 11. This conclusion, however, is erroneous in a number of respects. Most notably, review of NEPA case law reveals that the regulation, in fact, was not a codification of prior judicial decisions. See Note, 86 Mich. L. Rev. 777, 798, 800-802, 813-814 (1988). The cases cited by the Court of Appeals ultimately rely on the Fifth Circuit's decision in Sierra Club v. Sigler, 695 F.2d 957 (1983). Sigler, however, simply recognized that the "worst case analysis" regulation codified the "judicially created principl[e]" that an EIS must "consider the probabilities of the occurrence of any environmental effects it discusses." Id., at 970-971. As CEQ recognized at the time it superseded the regulation, case law prior to the adoption of the "worst case analysis" provision did require agencies to describe environmental impacts even in the face of substantial uncertainty, but did not require that this obligation necessarily be met through the mechanism of a "worst case analysis." See 51 Fed. Reg. 15625 (1986). CEQ's abandonment of the "worst case analysis" provision, therefore, is not inconsistent with any previously established judicial interpretation of the statute.
Nor are we convinced that the new CEQ regulation is not controlling simply because it was preceded by a rule that was in some respects more demanding. In Andrus v. Sierra Club, 442 U. S., at 358, we held that CEQ regulations are entitled to substantial deference. In that case we recognized that although less deference may be in order in some cases in which the " `administrative guidelines' " conflict " `with earlier pronouncements of the agency,' " ibid. (quoting General Electric Co. v. Gilbert, 429 U.S. 125, 143 (1976)), substantial deference is nonetheless appropriate if there appears to have
The Court of Appeals also held that the Forest Service's failure to develop a complete mitigation plan violated the agency's own regulations. 833 F. 2d, at 814, n. 3, 819, and n. 14. Those regulations require that an application for a special use permit include "measures and plans for the protection and rehabilitation of the environment during construction, operation, maintenance, and termination of the project," 36 CFR § 251.54(e)(4) (1988), and that "[e]ach special use authorization . . . contain . . . [t]erms and conditions which will . . . minimize damage to scenic and esthetic values and fish and wildlife habitat and otherwise protect the environment," § 251.56(a)(1)(ii). Applying those regulations, the Court of Appeals concluded that "[s]ince the mitigation `plan' here at issue is so vague and undeveloped as to be wholly inadequate,. . . the Regional Forester's decision to grant the special use permit could be none other than arbitrary, capricious and an abuse of discretion." 833 F. 2d, at 814, n. 3. We disagree.
The Early Winters Study made clear that on-site effects of the development will be minimal and will be easily mitigated. For example, the Study reported that "[i]mpacts from construction, maintenance and operation of the proposed `hill' development on National Forest land will not have a measurable effect on existing or future air quality," Early Winters Study 65, and that "[t]he effect development and operation of the ski hill would have on deer migration should be minor," id., at 76. Given the limited on-site effects of the proposed
The Court of Appeals' conclusion that the Early Winters Study's treatment of possible mitigation measures is inadequate apparently turns on the court's review of the proposed off-site measures. Although NEPA and CEQ regulations require detailed analysis of both on-site and off-site mitigation measures, see, e. g., 40 CFR § 1502.16(b) (1987), there is no basis for concluding that the Forest Service's own regulations must also be read in all cases to condition issuance of a special use permit on consideration (and implementation) of off-site mitigation measures. The Forest Service regulations were promulgated pursuant to a broad grant of authority "to permit the use and occupancy of suitable areas of land within the national forests . . . for the purpose of constructing or maintaining hotels, resorts, and any other structures or facilities necessary or desirable for recreation, public convenience, or safety," 16 U. S. C. § 497, and were not based on the more direct congressional concern for environmental quality embodied in NEPA.
In sum, we conclude that NEPA does not require a fully developed plan detailing what steps will be taken to mitigate adverse environmental impacts and does not require a "worst case analysis." In addition, we hold that the Forest Service has adopted a permissible interpretation of its own regulations. The judgment of the Court of Appeals is accordingly reversed, and the case is remanded for further proceedings consistent with this opinion.
It is so ordered.
JUSTICE BRENNAN, concurring.
I write separately to highlight the Court's observation that "one important ingredient of an EIS is the discussion of steps that can be taken to mitigate adverse environmental consequences." Ante, at 351.
"1. The County will initiate the formation of an Air Quality Control Authority or similar administrative structure pursuant to Washington State statutes.
"2. The County will develop an airshed management plan that incorporates strategies which will result in ambient air quality standards for the Methow Valley that are stricter than existing State standards. As part of the airshed management plan, the following mitigation measures will be considered:
" — Development of land use codes specifically addressing site development and project design directed at energy efficiency and air pollution control.
" — Requiring all new construction to be fully weatherized to reduce the need for supplemental heating sources (i. e., wood) beyond the central facilities heating needs.
" — Restricting the number of fireplaces and wood stoves. At a minimum, few fireplaces should be allowed in accommodations constructed for tourist use.
" — Encouraging the use of alternative, non-polluting energy sources.
" — Establishing a certification mechanism for wood stoves and fireplace inserts.
" — Establishing an air pollution monitoring system specifically designed to alert local residents to impending pollution episodes and to record long term changes in air quality levels. Such long term data will be used to evaluate the success or failure of the mitigation and impose more stringent measures if standards are violated.
" — Development of enforcement measures to assure that standards will be met." Early Winters Study 68-69.
"1. The Master Plan will require prompt revegetation of all disturbed areas and the mandatory application of dust control measures (e. g., rocking and oiling) on unpaved construction roads.
"2. The construction phase will follow established Forest Service/State of Washington smoke management practices identified in the Washington State Smoke Management Plan. The Master Plan will identify opportunities for utilization of waste wood, generated by the project, thereby minimizing open burning." Id., at 69.
"a) Locate runs, lifts, roads, and other facilities to minimize disturbance of blue grouse wintering areas (primarily ridgetops).
"b) Leave dead and defective trees standing in timbered areas where skier safety can be protected.
"c) Restrict activities and travel on selected roads during the fawning season (June).
"d) Locate new service roads away from water sources and fawning cover.
"e) Evaluate impact to mule deer migration routes in review of Master Plan.
"f) Design and harvest nearby, off-site timber sales to retain adequate travel corridors, foraging, roosting, and nesting sites for spotted owls.
"g) Protect other likely migration routes between summer and winter habitats for spotted owls.
"h) Restrict other activities within the spotted owls home range.
"i) Springs and riparian areas in the permit area will be protected as water sources and wildlife habitat. . . ." Id., at 16-17.
The Study further noted that additional mitigation opportunities might result from review of the master plan. Id., at 77.
" Limit development on deer winter range and along migration routes through rezoning options, tax incentives and other means.
"Since loss of winter range and disruption of migration routes are primarily concerns which will cause declines in deer numbers, protection of vital portions will be assured prior to a ski hill development. Rezoning is essential and will occur, to include County rezoning options such as:
"(a) The Methow Review District which is currently applied to obtain certain densities, open space, and design.
"(b) Other optional zone districts such as Conservation Districts which are available for amending existing zoning and protecting environmentally sensitive lands.
"Other measures are probably needed, and which could occur, include:
"(c) Conservation Easements between private individuals and trust agencies (e. g., Washington Department of Game) should be encouraged. Benefits would occur to both the landowner in the form of tax breaks, and the wildlife resource in the form of undeveloped, status quo habitat.
"(d) Acquisition of certain land tracts essential to migrating deer may be needed to insure continued passage. These lands would be administered by a wildlife management agency (e. g., Washington Department of Game).
" Minimize potential road kills of deer and other wildlife by use of warning signs, speed limits, and roadway design where wildlife crossings and high speed driving occur. Responsibility rests with the appropriate agency's road department (i. e., County, State, Federal) in the Methow Valley.
" Protect wildlife from free-ranging dogs through County ordinances that are enforceable.
" Through zoning, discourage development in riparian areas." Id., at 77-78.
"(a) Avoiding the impact altogether by not taking a certain action or parts of an action.
"(b) Minimizing impacts by limiting the degree or magnitude of the action and its implementation.
"(c) Rectifying the impact by repairing, rehabilitating, or restoring the affected environment.
"(d) Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action.
"(e) Compensating for the impact by replacing or providing substitute resources or environments." 40 CFR § 1508.20 (1987).
"[T]he MOU offers no assurance whatsoever that the vague mitigation objectives it features — performance of almost all of which would be the responsibility of third parties to the permit process — would ever in fact be achieved or even that effective measures would ever be designed (let alone implemented), if the Early Winters development were to proceed. Cf. Preservation Coalition [v. Pierce, 667 F.2d 851, 860 (CA9 1982)] (`Since many of the "mitigations" proposed by the agency were . . . potential actions to be taken by [third parties] reliance on them . . . was improper')." Methow Valley Citizens Council v. Regional Forester, 833 F.2d 810, 819-820 (CA9 1987).
Because NEPA imposes no substantive requirement that mitigation measures actually be taken, it should not be read to require agencies to obtain an assurance that third parties will implement particular measures.
"Many respondents to the Council's Advance Notice of Proposed Rule-making pointed to the limitless nature of the inquiry established by this requirement; that is, one can always conjure up a worse `worst case' by adding an additional variable to a hypothetical scenario. Experts in the field of risk analysis and perception stated that the `worst case analysis' lacks defensible rationale or procedures, and that the current regulatory language stands `without any discernible link to the disciplines that have devoted so much thought and effort toward developing rational ways to cope with problems of uncertainty. It is, therefore, not surprising that no one knows how to do a worst case analysis . . .', Slovic, P., February 1, 1985, Response to ANPRM.
"Moreover, in the institutional context of litigation over EIS(s) the `worst case' rule has proved counterproductive, because it has led to agencies being required to devote substantial time and resources to preparation of analyses which are not considered useful to decisionmakers and divert the EIS process from its intended purpose." 50 Fed. Reg. 32236 (1985).