For many years, questions about the future have been marginalised within the social sciences: asking how we might live in a post-fossil society, or what are the key decisions and events that could take us there, has been seen as outside of the disciplinary scope. In this paper – which takes as its point of departure the ‘speculative turn’ that is increasingly inspiring a range of works, from foresight scenarios to design fiction – we insist on the need to invent methods and practices which provide speculative spaces that allow such questions to be articulated. We use our own speculative initiative, ‘The Museum of Carbon Ruins’, to foreground a series of ethical questions that accompany such speculative endeavours, but which have so far been neglected in contemporary discussions. Working within a critical utopian modality, Carbon Ruins does not foreclose ethical possibilities, but allows citizens to grapple with, evaluate, amend and critique the post-fossil futures that official policy is striving towards.<br /><br />Key messages<br /><ul><li>A pioneering and reflective examination of the ethics of speculative methods in climate policy.</li><br /><li>Presents utopian modes as an analytical lens to turn on sociotechnical and/or climate imaginaries.</li><br /><li>Explores the Museum of Carbon Ruins, a unique co-productive climate communications initiative.</li><br /><li>Openly fictional futures strike a fairer discursive bargain than the masked utopias of ecomodernism.</li></ul>