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The Alien Tort Statute (ATS) provides that the district courts shall have original jurisdiction over any civil action by an alien for a tort only, committed in violation of the law of nations or a treaty of the United States. Several decisions have rejected environmental claims under the ATS because they read the ATS narrowly to protect only the most fundamental international human rights such as those prohibiting torture or war crimes and have been unwilling to accept broader claims to a right to life or a healthy environment. In 2002, in Sarei v. Rio Tinto PLC, the District Court for the Central District of California concluded that the United Nations Convention on the Law of the Sea (UNCLOS), which prohibits marine pollution affecting international waters, codified customary international law that may provide the basis of a claim under the ATS even though the United States has never ratified UNCLOS. The court, however, dismissed all of the plaintiffs' claims as presenting nonjusticiable political questions and alternatively dismissed the UNCLOS claim under the act of state doctrine and the doctrine of international comity. Even though it ultimately dismissed the case, the district court's decision in Sarei that UNCLOS constitutes customary international law cognizable under the ATS could enable plaintiffs to bring customary international law claims based on several MEAs that the United States has never ratified provided that a sufficiently large number of other nations have recognized that the agreement at issue implicates specific, universal and obligatory norms of international law.

In 2004, the Supreme Court in Sosa v. Alvarez-Machain held that federal courts should allow ATS suits based on principles of contemporary international law only if those norms have both wide acceptance and definite content comparable to those recognized as causes of action in 1789, especially piracy. In 2006, a divided panel of the Ninth Circuit affirmed the district court's decision that UNCLOS constitutes customary international law that is cognizable under the ATS because the Convention has been widely adopted. On April 12, 2007, however, in response to the defendant's petition for rehearing and for rehearing en banc, the three-judge panel withdrew its 2006 opinion and issued a superseding opinion. The majority did not decide whether the plaintiffs' substantive claims were valid, but did conclude that the allegations were sufficiently serious to warrant the exercise of federal jurisdiction. The Ninth Circuit reversed the district court's dismissal of all claims as nonjusticiable political questions and vacated the district court's dismissal of the UNCLOS claims on act of state and comity grounds, for reconsideration in light of its opinion.

On August 20, 2007, the Ninth Circuit ordered that the case be reheard by the en banc court. The order stated, "The three judge panel opinion shall not be cited as precedent by or to this court or any district court of the Ninth Circuit, except to the extent adopted by the en banc court." The Ninth Circuit's decision to grant a rehearing by the en banc court may reflect its concern about an overly broad interpretation by the three-judge panel opinion, although it is impossible to know until the Circuit issues its opinion in the case. On rehearing en banc, the Ninth Circuit should hold that the UNCLOS claim is not cognizable under the ATS because the content of UNCLOS is not as definite as the norms recognized in 1789.

Even under a broad interpretation of Sosa, most principles in international environmental agreements such as sustainable development are simply too vague to be enforceable. Courts should generally reject ATS suits based on general language or principles in MEAs because they do not possess a definite content comparable to those recognized in 1789 and thus fail to meet the Sosa standard. International courts and arbitration procedures are better suited to addressing transboundary pollution issues than American courts. Following Sosa, courts in ATS suits should usually recognize only serious human rights abuses such as torture as comparable to those recognized in 1789.