How geoengineering scenarios frame assumptions and create expectations

Geoengineering could remake environments and societies, and early governance can help to steer the development of technologies towards sustainable outcomes. In the absence of observational data, geoengineering research and discussions are increasingly informed by scenarios, which provide heuristic tools for 'envisioning' potential futures. Although designed for specific research goals, scenarios can have broader implications by influencing expectations about the societal role that emerging geoengineering technologies can play. Yet the design of geoengineering scenarios has gone largely unscrutinized. This study is a meta-analysis in which we evaluate geoengineering scenarios from the literature to identify emerging expectations and assess these in the context of sustainability science. We find that geoengineering scenarios can be classified into three types based on purpose and use: for scientific knowledge-building; as 'structured conversation' starters; or as exploratory research tools. The first category dominates the literature; these scenarios stem from physical science disciplines where scientific tradition dictates simplification and standardization, both of which may provide misleading images of the future and therefore hinder robust decision-making. In contrast, scenarios used as exploratory tools depict not one single image of why and how geoengineering might evolve, but many. Analysis of these exploratory scenarios reveal expectations that a geoengineered future may hinge on at least four key elements-the potential for a universal geoengineering agreement, public perceptions of geoengineering, technical controllability, and the severity of climate impacts. These elements were not studied in the scientific knowledge-building scenarios, suggesting the need for an additional category of scenarios. Aligning with concepts of sustainability science, new geoengineering scenario exercises would merge participatory practices of exploratory scenarios with deterministic practices of technical scientific scenarios.