Integrating solar geoengineering into climate change scenarios

Abstract:

Purposely altering the Earth’s energy balance through solar geoengineering (or “solar radiation modification,” SRM) could counter anthropogenic climate change and associated risks, but has been marginalized in assessments and policy debates, mainly due to concerns about over-reliance, improper use, and other socio-political risks. Serious critical examination of its potential contributions, limitations, risks, and governance needs is essential, but will require both normalizing and scrutinizing it as a potential climate response. A feasible, effective, and early step toward such scrutiny would be to integrate solar geoengineering into the prominent scenarios – which we call “headline scenarios” – that are used in official climate-change assessments to coordinate analyses of potential climate futures and frame the communication of their principal results. Recent experience integrating carbon dioxide removal into scenarios suggests that such elevation of attention is likely to support needed investigation, not uncritical over-reliance. We identify specific aims for integration: to standardize and document scenarios to support and coordinate research; to support critical scrutiny of solar geoengineering by normalizing it as a possible response; and to inform near-term decisions. We also suggest principles for integration: specify potential implementation trajectories exogenously, not by optimization; represent those future uncertainties that are most important for near-term decisions; balance standardizing and coordinating subsequent analyses with encouraging exploration of diverse deployment types, impacts, and conditions; and limit the total number of scenarios. Although scenario development for assessments requires a collective deliberative process and presents challenges, we sketch three scenarios here as illustrations. These highlight the uncertainties most important for near-term decisions by framing three plausible extremes, one of ideally beneficial deployment and two of prominently identified potential failure modes.