In this paper, we develop an analysis of public discourse on geoengineering. We examine in detail public responses to Solar Radiation Management (SRM) technologies, a class of geoengineering that proposes to intentionally reflect some of the incoming sunlight back into space with the effect of cooling the planet and thus counteracting anthropogenic climate change. SRM geoengineering is a distinctive technological issue that has the potential to reconfigure environments, societies, politics and ontologies in ways that are as yet poorly understood or conceptualised. We develop a methodology that aims to open up deliberation on SRM geoengineering, on the sort of world that its deployment would bring into being and on the factors that shape public responses. We find that geoengineering is acceptable only under very specific, and highly contingent, conditions. Given the implausibility of these conditions being realised in the real world, we set out implications for geoengineering governance. We argue that SRM geoengineering not only will in a sense be creating a world, but a particular kind of world, one with an increased likelihood of geopolitical conflict, a new condition of global experimentality, and major threats to democratic governance. This implies an important but challenging role for the social sciences.