It is argued that science actually increases ignorance and uncertainty, or at least the awareness of them, by rendering unknown unknowns into known unknowns. Writing specifically on geoengineering, G. Winter describes the current situation as one of “conscious ignorance” in which it is possible to know, even before research is conducted, that sufficient knowledge to justify the risk of using stratospheric aerosols can never be gained; that ignorance can be known in advance of research to be “irreducible”. The rhetorical deployment of ignorance in the case for solar geoengineering seems quite straightforward: conducting some research is the only way to reduce ignorance about the technology. However, the case against solar geoengineering research seems to be two-fold. Ignorance is a binding constraint – “we simply cannot know” – and ignorance is a source of virtue – “it saves us from folly”.