Climate engineering (geoengineering) is rising up the global policy agenda, partly because international divisions pose deep challenges to collective climate mitigation. However, geoengineering is similarly subject to clashing interests, knowledge‐traditions and geopolitics. Modelling and technical assessments of geoengineering are facilitated by assumptions of a single global planner (or some as yet unspecified rational governance), but the practicality of international governance remains mostly speculative. Using evidence gathered from state delegates, climate activists and modellers, we reveal three underlying and clashing ‘geofutures’: an idealised understanding of governable geoengineering that abstracts from technical and political realities; a situated understanding of geoengineering emphasising power hierarchies in world order; and a pragmatist precautionary understanding emerging in spaces of negotiation such as UN Environment Assembly (UNEA). Set in the wider historical context of climate politics, the failure to agree even to a study of geoengineering at UNEA indicates underlying obstacles to global rules and institutions for geoengineering posed by divergent interests and underlying epistemic and political differences. Technology assessments should recognise that geoengineering will not be exempt from international fractures; that deployment of geoengineering through imposition is a serious risk; and that contestations over geofutures pertain, not only to climate policy, but also the future of planetary order.
- Assessments of the feasibility and desirability of geoengineering technologies should never be based solely on knowledge produced under idealised conditions, (e.g. climate modelling or integrated climate and economic modelling).
- Assessments of technologies with global implications should factor in risks and complications generated by the international fragmentation of world politics and histories.
- Institutional designs for governing geoengineering should incorporate diverse and situated forms of knowledge as well as involve broad participation.
- Though they sometimes should be treated separately, an overarching governance framework for both CDR and solar radiation management (SRM) is needed to avoid deterrence of mitigation ('moral hazard').
- A governance process for geoengineering technologies, separate from climate governance, should be established at the United Nations Environment Programme (UNEP).