Trade-offs of Solar Geoengineering and Mitigation under Climate Targets

Abstract. So far scientific analyses have mainly focused on the pros and cons of solar geoengineering or solar radiation management (SRM) as a climate policy option in mere isolation. Here we put SRM into the context of mitigation by a strictly temperature-target based approach. As a main innovation, we present a scheme by which the applicability regime of temperature targets is extended from mitigation-only to SRM-mitigation analyses. Hereby we explicitly account for a risk-risk comparison of SRM and global warming, while minimizing economic costs for complying with the 2 °C temperature target. To do so, we suggest precipitation guardrails that are compatible with the 2 °C target. Our analysis shows that the value system enshrined in the 2 °C target would be almost prohibitive for SRM, while still about half to nearly two-third of mitigation costs could be saved, depending on the choice of extra room for precipitation. In addition, assuming a climate sensitivity of 3 °C or more, in case of a delayed enough policy, a modest admixture of SRM to the policy portfolio might provide debatable trade-offs compared to a mitigation-only future. In addition, in our analysis for climate sensitivities higher than 4 °C, SRM will be an unavoidable policy tool to comply with the temperature targets.