It is plausible that the impacts of climate change will render certain nation-states uninhabitable before the close of the century. While this may be the fate of a small number of those nation-states most vulnerable to climate change, its implications for the evolution of statehood and international law in a “post-climate” regime is potentially seismic. I argue that to respond to the phenomenon of landless nationstates, international law could accommodate an entirely new category of international actors. I introduce the Nation Ex-Situ. Ex-situ nationhood is a status that allows for the continued existence of a sovereign state, afforded all of the rights and benefits of sovereignty amongst the family of states, in perpetuity. In practice this would require the creation of a government framework that could exercise authority over a diffuse people. I elaborate on earlier calls to use a political trusteeship system to provide the framework for an analogous structure. I seek to accomplish two quite different but intimately related tasks: first, to define and justify the recognition of deterritorialized nation-states, and, second, to explain the trusteeship arrangement that will undergird the ex-situ nation. In doing so, I introduce the notion of a post-climate era, in which the very structure of human systems—be they legal, economic, or socio-political—are irrevocably changed and ever-changing.