	I. Introduction

Congressional inaction on climate change has led various entities to pursue climate change measures off Capitol Hill. The principal focus of such suits has been to establish greenhouse gas (GHG) emissions and climate change impacts as a nuisance. For reasons discussed in this report, the prospects of this common law litigation are limited. Recently, the outlook for at least those cases based on the federal common law of nuisance and seeking injunctive relief has particularly dimmed. In American Electric Power Co., Inc. v. Connecticut , it held that in light of EPA's authority over GHG emissions as clarified in Massachusetts , federal common law in the climate change area is "displaced." That is, federal courts may not use federal common law to add their own judge-made GHG emission standards, whether or not EPA exercises its authority. Private nuisance actions are brought by the aggrieved landowner. II. In light of American Electric Power , however, one of these threshold issues—whether the federal common law of nuisance has been displaced—will likely prove the key one in future efforts to use federal common law to address climate change. Though the Supreme Court barred federal courts from developing a "general" common law 73 years ago (they should instead apply the substantive law of the state in which they sit), the Court has since clarified that in areas of national concern, such as interstate pollution, the articulation of federal common law by the federal courts is appropriate. Thus, the question arose early on in some of the climate change cases whether the federal CAA displaces judge-made law in the climate change area. (See Section III.A. Other, Now Less Important, Threshold Issues

The threshold issues made less important by American Electric Power in federal-common-law climate change litigation are, again, the standing issue and political question doctrine. As explicated by the Court, this constraint demands that a plaintiff in federal court demonstrate (1) actual or imminent injury that is concrete and particularized, and not speculative; (2) that the injury is or will be caused by the defendant; and (3) that the injury likely will be redressed by a favorable court decision. A suit seeking relief from climate change impacts may run into difficulty with each of the three constitutional standing requirements. American Electric Power

		A. Plaintiffs sought to require the electric utilities to abate their contribution to the nuisance of climate change by reducing their CO 2 emissions. If the merits of the state common law nuisance claims are reached (in American Electric Power or other litigation), which state's common law will apply? A provocative question now getting attention is whether American Electric Power displaces climate-change-based federal common law actions seeking monetary relief. In the (perhaps unlikely) event that such a law would be silent as to its intended impact on common law claims, it could be argued that elimination of EPA authority over GHGs also eliminates any displacement of federal common law. The others are Village of Kivalina v. ExxonMobil Corp. and Comer v. Murphy Oil USA , discussed here. In Village of Kivalina , an Inupiat Eskimo village on the northwest Alaska coast sued 24 oil and energy companies, claiming that the large quantities of GHGs they emit contribute to climate change. The suit seeks monetary damages. Owners of Gulf coast property damaged by Hurricane Katrina sued certain oil, coal, and chemical companies under state law. However, on May 27, 2011, the plaintiffs refiled the case (with minor modifications), creating a second opportunity for a ruling on whether American Electric Power applies to cases seeking damages. V. A New Common Law Theory Enters the Fray: Public Trust Doctrine

Since May 2011, the nuisance lawsuits above have been joined by a coordinated campaign of lawsuits and rulemaking petitions seeking to attack climate change by an entirely different common law theory: public trust doctrine.
Note: Despite this report being archived, the reader may find updated treatment of the topics covered herein in CRS Report R42613, Climate Change and Existing Law: A Survey of Legal Issues Past, Present, and Future, by [author name scrubbed]. See especially sections I, II.H., and III.A.
Congressional inaction on climate change has led concerned parties to explore other ways to address climate change—including lawsuits seeking to establish climate change impacts as a common law nuisance. The prospects for these common law suits are limited, however, owing in part to the unsuitability of private litigation for dealing with global problems like climate change. Recently, the outlook for federal common-law suits seeking injunctive relief vis-a-vis climate change became particularly dim. On June 20, 2011, the Supreme Court ruled in American Electric Power Co., Inc. v. Connecticut that given EPA's Clean Air Act authority over greenhouse gas (GHG) emissions—affirmed by the Court a few years ago—the federal common law of nuisance in the area of climate change is "displaced." Federal courts may not use federal common law to add their own judge-made GHG emission standards to those of EPA.
The displacement of federal common law by American Electric Power is only one of three threshold issues that have bedeviled lawsuits seeking to establish climate change as a common law nuisance. The standing inquiry requires a plaintiff in federal court to show actual or imminent injury caused by the defendant, and the likelihood that the injury will be redressed by the requested relief. Each of these factors can pose difficulties for the climate-change plaintiff. Similarly, the political question doctrine has led some courts to dismiss common-law climate change suits on the ground that the issue is better left with the political branches.
American Electric Power raises several questions. First, with federal common law displaced in the area of climate change, are state common law claims viable? Two threats to such claims are the possibility of preemption by the Clean Air Act (the sounder argument is against preemption), and the influence of the Supreme's Court's aversion to judge-made law in the climate change area so evident in American Electric Power. A second question is whether American Electric Power displaces climate-change-based federal common law actions when the remedy sought is monetary rather than injunctive. Finally, if Congress eliminates EPA authority over GHG emissions and is silent as to federal common law actions, does federal common law cease to be displaced so that such actions are again possible?
In addition to American Electric Power, there are two other active cases raising common law nuisance claims as to climate change. In Village of Kivalina v. ExxonMobil Corp., a coastal Eskimo village is suing energy companies alleging that their GHG emissions have contributed to shoreline erosion, requiring relocation of the village. In Comer v. Murphy Oil, Gulf coast landowners are suing energy and chemical companies asserting that their GHG emissions intensified Hurricane Katrina, adding to plaintiffs' property damage. Both cases raise the above-noted issue whether American Electric Power applies to actions seeking monetary damages.
A second common law theory recently has entered the fray. Since May 2011, either a suit or rulemaking petition has been filed in every state arguing that the respective state has a "public trust" duty to the atmosphere that requires it to address climate change.