Persistently rising atmospheric greenhouse gas concentrations challenge dominant Liberal hopes that science and multilateralism might deliver rational, global climate outcomes. Emerging Realist climate approaches that take power and national interests seriously have yet to explore Morgenthau’s concern that ‘scientism’ – exaggerated faith in scientific rationality to solve political problems – lead to disastrous underestimations of power and irrationality. Recently, Realists have mooted ‘solar geoengineering’ designs as a ‘lesser evil’ option to deliberately cool the Earth independently of emissions reductions. However, assessments of solar geoengineering prospects barely factor in Realist concerns, focusing instead on idealised scientific modeling of bio-physical effects and Liberal governance scenarios. To explore how geoengineering technoscience would be ‘translated’ into security assessments, geopolitical logics were elicited through interviews and group discussions with (mainly Arctic-oriented) national security professionals. Security experts reframe solar geoengineering in three significant ways: a) from a climate ‘global public good’ to a source of geopolitical leverage and disruption; b) from a risk reduction tool to a potential source of distrust and escalation; and c) from a knowledge-deficit problem solvable by more research, to a potential disinformation vector. This expands Realist scholarship on climate change and identifies serious risks to ongoing scientific and commercial pursuit of such technologies.