Substantially the same principles apply to actions that become moot on appeal as apply before judgment. E.g., Annot., What Circumstances Render Civil Case, or Issue Arising Therein, Moot So as to Preclude Supreme Court’s Consideration of Their Merits, 44 L.Ed.2d 745 (1975); Note, Mootness on Appeal in the Supreme Court, 83 Harv. L. Rev. 1672 (1970).
When an event occurs during an appeal, without the fault of the defendant, that renders it impossible for the court to grant effective relief to the plaintiff if the court should rule in favor of the plaintiff, the issue is moot and the appeal should normally be dismissed. Alvarez v. Smith, 558 U.S. 87, 89, 130 S.Ct. 576, 578, 175 L.Ed.2d 447, 451 (2009); United States v. Munsingwear, Inc., 340 U.S. 36, 39, 71 S.Ct. 104, 106, 95 L.Ed. 36, 41 (1950). Depending on circumstances, the trial court’s decree may be vacated before the dismissal. On vacatur or dismissal of the appeal, see U.S. Bancorp Mortgage Co. v. Bonner Mall Partnership, 513 U.S. 18, 26, 115 S.Ct. 386, 392, 130 L.Ed.2d 233, 242 (1994); NASD Dispute Resolution, Inc. v. Judicial Council of State of California, 488 F.3d 1065, 1068-69 (9th Cir.2007). An appellate court is less likely to struggle to avoid mootness when the appellant could have acted to avoid or diminish the mooting of the issues and failed to do so. E.g., Building a Better Redondo, Inc. v. City of Redondo Beach, 203 Cal.App.4th 852, 867, 137 Cal.Rptr.3d 622, 634 (2d Dist.2012) (“Appellants could have requested that the trial court stay enforcement of the writ or sought a writ of supersedeas had there been any issue of the judgment being enforced pending appeal, but they did not.”).
The grounds for avoiding mootness in the trial court may also be offered in opposition to dismissal for mootness on appeal. These include a significant issue remaining alive, general public interest in a recurring issue, and cessation that is only voluntary. The determination is discretionary, especially in state courts that do not face Article III limitations. For example, California law recognizes that, when “issues on appeal affect the general public interest and the future rights of the parties, and there is reasonable probability that the same questions will again be litigated and appealed, an appellate court may, although the appeal be subject to dismissal, nevertheless adjudicate the issues involved.” People v. West Coast Shows, Inc., 10 Cal.App.3d 462, 468, 89 Cal.Rptr. 290, 294–95 (1st Dist.1970); accord, DuBarry Int’l, Inc. v. Southwest Forest Industries, Inc., 231 Cal.App.3d 552, 556 n.2, 282 Cal.Rptr. 181, 183 n.2 (2d Dist.1991) (declining to find mootness despite settlement after oral arguments).
The appellate court can take additional evidence to determine if the matter has become moot on appeal, usually by remanding for a determination but occasionally by judicial notice. E.g., Vitek v. Jones, 436 U.S. 407, 98 S. Ct. 2276, 56 L. Ed. 2d 381 (1978); Indiana Employment Security Div. v. Burney, 409 U.S. 540 (1973). Mootness is one of the few issues on which appellate courts will take additional evidence with any frequency. Larner v. Los Angeles Doctors Hospital Associates, L.P., 168 Cal.App.4th 1291, 89 Cal.Rptr.3d 324 (2d Dist.2008) (judicial notice of settlement agreements); Cornblum v. Board of Supervisors, 110 Cal.App.3d 976, 981–82, 168 Cal.Rptr. 294, 297–98 (4th Dist.1980) (appellate and trial courts took judicial notice of records in parallel action whose judgment rendered this action moot). The appellate court may raise the question of mootness sua sponte. Medberry v. Crosby, 351 F.3d 1049, 1054 n.3 (11th Cir. 2003).
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