Like a tripartite juggernaut, all three branches of the U.S. federal government are actively grappling with climate change in kind: legislation from the U.S. Congress; regulation from the U.S. Environmental Protection Agency (EPA); and litigation in the judiciary all may come to bear on carbon emissions as a causal genesis of climate change. When all three branches of the federal government concurrently engage in questions of the same subject matter, interesting separation-of-powers concerns are implicated. In particular, climate change litigation has implicated the doctrine of displacement. Displacement has been raised as a procedural defense to suit under the federal common law of nuisance. Intuitively, a federal common-law cause of action for, say, pollution should be displaced whenever either of the other two branches has adequately dealt with the pollution problem. That is, requiring a defendant to comply with a court order when it is already in compliance with legislation or regulation on the matter would both be onerous for the defendant and would trammel on congressional or executive authority. Not only separation-of-powers principles but institutional competency concerns militate in favor of displacing federal common-law causes of action regarding subject matter with which either of the other two branches has already dealt. If the federal common law of public nuisance for carbon emissions is displaced by legislation from Congress or regulation from EPA, then carbon emitters have repose from federal common-law liability as long as they are in compliance with the legislative or regulative requirements. Unfortunately, the law of displacement, when applied to a case brought by states under the federal common law of public nuisance, is not nearly as straightforward as the foregoing sketch would suggest. What we might initially consider to be a narrow procedural issue is, upon further analysis, extremely thorny.