In the last month, two federal courts of appeal have ruled on much-watched petitions for rehearing in climate change lawsuits. The decisions have set up a possible showdown on the viability of nuisance claims premised on damages allegedly caused by the effects of greenhouse gas emissions.

In Connecticut v. American Electric Power, the Court of Appeals for the Second Circuit rejected on March 5 requests both for rehearing by the original panel and for en banc review by the entire panel of circuit judges. The original panel's September 2009 decision resurrected lawsuits brought by New York City, several states, and private land trusts against electric utilities that allegedly emit 10 percent of America's man-made greenhouse gases. Premising their federal common law suit on alleged harms resulting from climate change, the plaintiffs seek an injunction forcing the utilities to cap and then reduce their greenhouse gas emissions.

The Second Circuit's decision came on the heels of a decision just a week earlier in the case of Comer v. Murphy Oil Co. There, the Fifth Circuit reached the opposite conclusion by vacating its original decision and agreeing to rehear that matter en banc. In the October 2009 Comer decision, the Fifth Circuit allowed a putative class of Gulf Coast residents and property owners to proceed with a suit against energy, fossil fuel, and chemical companies for Hurricane Katrina damage. Instead of an injunction, the Comer plaintiffs seek compensatory and punitive damages, contending that the defendants' combined greenhouse gas emissions increased global surface air and water temperatures, thus raising sea levels, thus compounding the storm, thus destroying plaintiffs' property. The original three-judge panel of the Fifth Circuit agreed with much of the Second Circuit's American Electric Power decision. However, the Fifth Circuit's decision to vacate its decision and rehear the case by the full panel of judges presents the distinct possibility that the Katrina claims will be dismissed, which could create a circuit court split. The en banc argument is set for the week of May 24, and the parties were ordered to file supplemental briefing.

The Second Circuit's rehearing denial in American Electric Power started running a 90-day clock within which the defendants may petition for review by the U.S. Supreme Court. The Second Circuit has already agreed to stay the return of the case to the district court (called a mandate), indicating that the defendants will indeed seek the Supreme Court's discretionary review.

Meanwhile on the West Coast, a third greenhouse gas nuisance suit, Native Village of Kivalina v. Exxonmobil Corp., is currently being briefed to the Court of Appeals for the Ninth Circuit. Expressly disagreeing with the Second Circuit's reasoning in American Electric Power, the Northern District of California in September 2009 dismissed the plaintiffs' federal nuisance claims for costs of future relocation that plaintiffs assert will be necessitated by global warming. "It is illogical to conclude," the district court held, "that the mere contribution of greenhouse gases into the atmosphere is sufficient to establish that a plaintiff's injury is fairly traceable to a defendant's conduct." The Alaskan native village is asking the Ninth Circuit to overturn that dismissal.

For more detail on the underlying opinions and their import, see Who's to Blame for Climate Change: Will a Jury Decide?