Nevertheless, in recognition of the fact that in some cases FERC "is required under NEPA to give some environmental consideration of nonjurisdictional facilities," FERC has developed a four-factor balancing test "to determine whether there is sufficient federal control over a project to warrant environmental analysis." Nat'l Comm. for the New River v. FERC, 373 F.3d 1323, 1333 (D.C. Cir. 2004). Under the test, FERC considers

" Id. at 373, 109 S.Ct. 1851. Rather, "a supplemental EIS must be prepared" only when a new action will affect the quality of the environment "in a significant manner or to a significant extent not already considered." Id. at 374, 109 S.Ct. 1851 ; see also Nat'l Comm. for the New River, Inc. v. FERC , 373 F.3d 1323, 1330 (D.C. Cir. 2004) (explaining that a supplemental impact statement is "only required where new information provides a seriously different picture of the environmental landscape" (quoting City of Olmsted Falls v. Fed. Aviation Admin. , 292 F.3d 261, 274 (D.C. Cir. 2002) )); Davis v. Latschar , 202 F.3d 359, 369 (D.C. Cir. 2000) (requiring a supplemental impact statement only for "changes that cause effects which are significantly different from those already studied"). And because an agency's decision whether to prepare a supplemental EIS requires "substantial agency expertise," courts must defer to the agency's "informed discretion."

NCNR is an environmental group devoted to protecting the New River, which travels northward from North Carolina through southwest Virginia. NCNR fought the initial certification as an intervenor and lost. FERC denied a request for stay and rehearing, 102 FERC ¶ 61,225 (2003), and this Court affirmed. See Nat'l Comm. for the New River, Inc. v. FERC, 373 F.3d 1323, 1325 (D.C. Cir. 2004) (holding that FERC's certification was not arbitrary and capricious). The pipeline has been operational since late 2003.

When we review an EIS prepared under NEPA, our "role is ‘simply to ensure that the agency has adequately considered and disclosed the environmental impact of its actions and that its decision is not arbitrary or capricious.’ " Nat'l Comm. for the New River v. FERC , 373 F.3d 1323, 1327 (D.C. Cir. 2004) (quoting Baltimore Gas & Elec. v. NRDC , 462 U.S. 87, 97–98, 103 S.Ct. 2246, 76 L.Ed.2d 437 (1983) ). We must "ensure that the agency took a ‘hard look’ at the environmental consequences of its decision to go forward with the project."

Rather, a SEIS must be prepared only where new information "provides a seriously different picture of the environmental landscape." Nat'l Comm. for the New River v. FERC , 373 F.3d 1323, 1330 (D.C. Cir. 2004) (emphasis added).So understood, regardless of whether the CEQ or FTA regulation applies, FTA and Maryland reasonably explained why the Friends' Metrorail information does not require preparation of a SEIS. Not only does that information not adversely affect the Purple Line's environmental impact in an absolute sense—the construction and operational footprint would remain the same—neither does it have relative environmental or transportation effects that would alter Maryland's selection of light rail over bus rapid transit or other alternatives. FTA determined that the Metrorail information offered no basis to distinguish the alternatives on environmental grounds: Each alternative "would have similar alignment characteristics" and thus similar "impacts on parks, wetlands, historic properties, residential and business properties, and other environmentally sensitive sites.

ExxonMobil Gas Mktg. Co. v. FERC, 297 F.3d 1071, 1083 (D.C.Cir.2002). Because the grant or denial of a Section 7 certificate of public convenience and necessity is a matter “peculiarly within the discretion of the Commission,” Okla. Natural Gas Co. v. Fed. Power Comm'n, 257 F.2d 634, 639 (D.C.Cir.1958), this court does not “substitute its judgment for that of the Commission,” Nat'l Comm. for the New River v. FERC, 373 F.3d 1323, 1327 (D.C.Cir.2004). Moreover, “[w]hen considering FERC's evaluation of ‘scientific data within its technical expertise,’ we afford FERC ‘an extreme degree of deference.’ ”

In so doing, we “cannot substitute [our] judgment for that of the Commission.” Nat'l Comm. for the New River, Inc. v. FERC, 373 F.3d 1323, 1327 (D.C.Cir.2004). All the while, we remain mindful that “[t]he grant [ ] or denial of a certificate of public convenience and necessity is a matter peculiarly within the discretion of the Commission.”

Rather, "if the new information shows that the remaining action will affect the quality of the environment ‘in a significant manner or to a significant extent not already considered,’ " a supplemental must be prepared. Nat'l Comm. for the New River v. FERC , 373 F.3d 1323, 1330 (D.C. Cir. 2004) (quoting Marsh , 490 U.S. at 374, 109 S.Ct. 1851 ). In addition, the D.C. Circuit has instructed that a supplement "is only required where new information ‘provides a seriously different picture of the environmental landscape.’ "

Although this obligation is not triggered "every time new information comes to light," an agency must prepare an SEIS whenever "new information provides a seriously different picture of the environmental landscape." Id. at 373, 109 S.Ct. 1851 ; Nat'l Comm. for the New River v. F . E . R . C . , 373 F.3d 1323, 1330 (D.C. Cir. 2004) (citation omitted); City of Olmsted Falls v. F . A . A . , 292 F.3d 261, 274 (D.C. Cir. 2002). Like other APA challenges, courts review an agency's decision to undertake or forego an SEIS under the arbitrary and capricious standard.

“An environmental impact statement is reviewed to ensure that the agency took a hard look at the environmental consequences of its decision to go forward with the project.” Nat'l Comm. for the New River v. F.E.R.C., 373 F.3d 1323, 1327 (D.C.Cir.2004) (citations omitted). “When an agency is evaluating scientific data within its technical expertise, an extreme degree of deference to the agency is warranted.”