The middle powers roar: Exploring a minilateral solar geoengineering deployment scenario

•Emergency framing of solar geoengineering may create challenges for political legitimacy.•Political considerations will affect technical designs of solar geoengineering deployment.•Scenario exercises can help anticipate future governance challenges and political developments. The prospect of solar geoengineering, which would entail reflecting a small fraction of incoming sunlight back to space to cool the planet, has been slowly but steadily rising on the climate policy agenda. Early research suggests that solar geoengineering could substantially reduce climate risks, but its development and potential use would be accompanied by an array of ecological and sociopolitical risks and governance challenges. Here we reflect on our participation in a solar geoengineering governance scenario exercise conducted at the 2019 International Summer School on Geoengineering Governance. In the scenario with which we engaged, a group of ‘middle powers’ intend to force the issue of solar geoengineering onto the international agenda after decades of deadlock and in the face of intensifying climate impacts. As participants in this exercise, we confronted a range of problems and issues we judged likely to arise. In this article, we discuss a number of these, including the manner in which political considerations are likely to influence the physical and technical aspects of deployment schemes, as well as ways in which emergency framing may undermine political legitimacy. These and other aspects of possible future deployment of solar geoengineering warrant additional targeted scenario analysis.