Comer v. Murphy Oil USA was a climate change lawsuit brought by Mississippi Gulf Coast property owners against dozens of oil, coal, utility, and chemical companies, alleging that the defendants’ greenhouse gas emissions intensified Hurricane Katrina and destroyed their homes. Filed weeks after Katrina in 2005 and refiled in 2011, the case ended in dismissal both times, once after an unprecedented loss of quorum at the Fifth Circuit erased a plaintiffs’ victory, and again on res judicata and preemption grounds. It remains one of the earliest and most closely studied attempts to hold fossil fuel producers liable in tort for climate-related harm.
Who Sued, and What They Alleged
Ned Comer, Brenda Comer, and roughly a dozen other coastal Mississippi property owners filed the original complaint on September 20, 2005, in the U.S. District Court for the Southern District of Mississippi. They alleged that the defendants ranked among the largest sources of greenhouse gases driving global warming, that the warming raised sea surface temperatures and sea levels, and that those conditions strengthened Katrina. The injuries they claimed included physical damage to homes, higher insurance premiums, diminished property values, loss of use from saltwater intrusion and habitat destruction, and debris and hazardous substances deposited on their land.1LSU Law. Comer v. Murphy Oil USA, Case No. 1:11-cv-00220-LG-RHW
The legal theories came from Mississippi common law: public nuisance, private nuisance, trespass, and negligence. The plaintiffs also initially pleaded unjust enrichment, fraudulent misrepresentation, civil conspiracy, and a declaratory judgment that federal law did not preempt their state tort claims.2Climate Case Chart. Comer v. Murphy Oil USA, Inc.
The defendant list was enormous. Murphy Oil USA was the lead name, but the roster grew to include ExxonMobil, Shell, Chevron, BP, ConocoPhillips, Hess, Anadarko, and Apache on the oil side; Peabody Energy, Arch Coal, Alpha Natural Resources, Massey Energy, CONSOL, and Westmoreland on the coal side; the Tennessee Valley Authority, Southern Company subsidiaries, AEP, Duke Energy, Entergy, Dominion, and Xcel among utilities; and DuPont, Dow Chemical, and Honeywell among chemical and industrial firms. One motion to dismiss was joined by 62 defendants.3vLex. Comer v. Murphy Oil USA, Inc.1LSU Law. Comer v. Murphy Oil USA, Case No. 1:11-cv-00220-LG-RHW
How the First Case Reached and Then Lost at the Fifth Circuit
The district court dismissed the original suit, holding that the plaintiffs lacked standing and that their claims presented a non-justiciable political question. They appealed.
On October 16, 2009, a three-judge Fifth Circuit panel reversed. Judges Dennis, Stewart, and Davis held the plaintiffs had standing to pursue their nuisance, trespass, and negligence claims. The panel concluded that plaintiffs did not need to show the defendants were the sole cause of their injuries, only that emissions were a contributing factor, and it drew on the Supreme Court’s 2007 decision in Massachusetts v. EPA for the plausibility of the emissions-warming link.4FindLaw. Comer v. Murphy Oil USA, No. 07-607565University of Houston Law Center. Comer v. Murphy Oil USA Panel Opinion The panel rejected the political question defense, reasoning that ordinary state common-law property claims are the sort of thing courts have always handled. It also dismissed the unjust enrichment, fraudulent misrepresentation, and civil conspiracy counts as generalized grievances that failed prudential standing. It was the first time a federal appeals court had allowed private tort-based climate nuisance claims against energy companies to proceed.6Federalist Society. Complaints About the Weather
The defendants petitioned for rehearing en banc. Nine of sixteen active Fifth Circuit judges voted 6–3 to rehear, and under circuit rules that order automatically vacated the panel opinion. The plaintiffs’ win was gone before the rehearing even happened.7Harvard Law Review. Fifth Circuit Leaves Panel Decision Vacated Upon Loss of En Banc Quorum
Then a further judge recused, dropping the eligible bench to eight. A quorum required nine. In May 2010, a five-judge majority issued a per curiam order dismissing the appeal entirely, leaving the panel decision vacated and the original district court dismissal standing.7Harvard Law Review. Fifth Circuit Leaves Panel Decision Vacated Upon Loss of En Banc Quorum The majority refused to bring in judges from other circuits, refused to invoke the “rule of necessity,” and refused to hold the case in abeyance until a new judge was confirmed. Judges Davis and Dennis dissented, with Dennis arguing that the eight remaining judges did constitute a quorum once recused judges were excluded from the count and that the rule of necessity should have preserved the plaintiffs’ right of appeal.8Liskow. Fifth Circuit Dismisses Appeal in Comer v. Murphy Oil USA
Rather than seek certiorari in the usual way, the plaintiffs asked the Supreme Court for a writ of mandamus ordering the Fifth Circuit to reinstate the appeal. The Court denied the petition without comment on January 10, 2011.9Climate Case Chart. Comer v. Murphy Oil USA, Inc.
The Refiled Case and Why It Was Dismissed
On May 27, 2011, the plaintiffs filed a nearly identical lawsuit, sometimes called Comer II, before Judge Louis Guirola Jr. in the Southern District of Mississippi.10Climate Case Chart. Comer v. Murphy Oil USA, Inc., Memorandum Opinion and Order
Judge Guirola dismissed the case on March 20, 2012, on multiple independent grounds. The court found the claims barred by res judicata and collateral estoppel because the new complaint was “nearly identical” to the 2005 lawsuit and that judgment had never been overturned. Beyond that, the court held the plaintiffs lacked Article III standing because their injuries were not fairly traceable to any particular defendant, the case presented a non-justiciable political question, the Clean Air Act preempted the claims, the statute of limitations had run, and proximate causation could not be shown.10Climate Case Chart. Comer v. Murphy Oil USA, Inc., Memorandum Opinion and Order
The preemption ruling leaned on a decision that had come down between Comer I and Comer II. In American Electric Power Co. v. Connecticut, decided in June 2011, the Supreme Court held 8–0 that the Clean Air Act displaces federal common-law nuisance claims aimed at reducing carbon dioxide emissions from power plants.11Justia. American Electric Power Co. v. Connecticut, 564 U.S. 410 The Comer plaintiffs argued their case was different because they sought money damages under state law, not a federal injunction. The district court disagreed.10Climate Case Chart. Comer v. Murphy Oil USA, Inc., Memorandum Opinion and Order
The Fifth Circuit affirmed on May 14, 2013, but on narrow grounds. It held that res judicata alone barred the claims and that “a federal court may not abrogate principles of res judicata out of equitable concerns,” and it declined to reach the Clean Air Act preemption question.2Climate Case Chart. Comer v. Murphy Oil USA, Inc. That ended the litigation.
The Causation Problem the Case Never Resolved
Underneath the procedural drama sat a hard evidentiary question that Comer never answered on the merits: how does a plaintiff prove that any particular company’s emissions caused a specific storm and specific damage? Defendants framed the burden as requiring plaintiffs to show what Katrina’s strength would have been without global warming, how much of each plaintiff’s damage traced to any difference in the storm’s strength, and how much traced to third-party failures like FEMA.1LSU Law. Comer v. Murphy Oil USA, Case No. 1:11-cv-00220-LG-RHW
The 2009 panel had sidestepped this at the pleading stage by separating the threshold “fairly traceable” test for standing from the merits question of proximate causation. Because the case never reached the merits, the deeper scientific questions were never litigated.5University of Houston Law Center. Comer v. Murphy Oil USA Panel Opinion In the years since, attribution science has advanced. Researchers now use probabilistic methods to estimate how much human-caused warming increased the likelihood or intensity of specific extreme weather events, and source attribution studies have traced roughly two-thirds of industrial-era carbon dioxide emissions to about 90 fossil fuel and cement producers. Whether courts will accept that evidence to establish causation in tort is still being tested.12Environmental Law Institute. Applying Attribution: Impacts Climate Attribution Science and Tort Litigation
Why the Case Still Matters
The vacated 2009 panel opinion carries no binding precedential weight, but it was the first federal appellate ruling to hold that private individuals could pursue tort claims against energy companies for climate-related harm. Its treatment of standing shaped how later lawyers framed emissions-and-injury pleadings.
The case also mapped the outer limits of tort law as a climate remedy. AEP v. Connecticut foreclosed federal common-law nuisance claims by holding that the Clean Air Act gave the EPA authority over carbon emissions and left no room for courts to fashion their own remedies.13Cornell Law Institute. American Electric Power Co. v. Connecticut, No. 10-174 The Ninth Circuit then extended that logic to bar damage claims as well as injunctions in Native Village of Kivalina v. ExxonMobil, brought by an Alaskan village facing climate-driven coastal erosion.14McGuireWoods. Death of Environmental Common Law Together those rulings closed out the first generation of federal climate nuisance suits.
The Supreme Court left open whether state tort claims survive Clean Air Act preemption. The current wave of climate litigation, brought largely by cities, counties, and state attorneys general in state courts, has moved onto that ground, often reframing claims as consumer fraud or state-law nuisance to avoid the displacement problem that ended Comer.