As Congress has yet to enact a comprehensive legislative framework to address climate change, environmental advocates have increasingly turned to the judiciary to push for the regulation of greenhouse gas emissions. Some lawsuits have been brought against the federal government, but others have been brought against private entities under common law causes of action. This Note focuses on the state standing and separation of powers dynamics at play in this area of litigation, and considers recent arguments that states suing as parens patriae against private polluters should be entitled to a relaxed standing regime. It concludes that complex common law claims involve discrete separation of powers concerns that give rise to a dangerously unpredictable array of prudential justiciability limitations, and therefore proposes that state litigants invoke their sovereign interests in regulating environmentally harmful activities as the basis for standing in future climate litigation. Such interests present the types of concrete and particularized injuries that satisfy separation of powers concerns, and asserting standing on this basis reinforces federalism values by ensuring that states remain important ancillary enforcers of national environmental policies.