[Preprint] Deploying Solar Radiation Modification to limit warming under a current climate policy scenario results in a multi-century commitment

[Geoeng Info]

https://esd.copernicus.org/preprints/esd-2022-17/

Deploying Solar Radiation Modification to limit warming under a current climate policy scenario results in a multi-century commitment

Susanne Baur, Alexander Nauels, and Carl-Friedrich Schleussner

Abstract. 

A growing body of literature investigates the effects of Solar Radiation Modification (SRM) on global and regional climates. Previous studies have mainly focused on potentials and side-effects of SRM with little attention given to potential deployment timescales. Here, we look at a scenario that fails to achieve 1.5 °C-compatible mitigation and instead relies on SRM and Carbon Dioxide Removal (CDR) to avoid temperature rises above the threshold. Assuming SRM removes the incentive to increase mitigation beyond the currently pledged level of ambition, we assess SRM deployment lengths under three illustrative emission scenarios that follow current climate policy and are continued with varying assumptions about net-negative CDR (-11.5, -10 and -5 GtCO2yr-1). Under these assumptions, SRM would need to be deployed for around 245–315 years. We find only minor effects of SRM on the global net carbon flux decades after cessation. In total, around 976–1344 GtCO2 would need to be removed by CDR, much more than in so-called high-overshoot 1.5 °C scenarios. Our study points towards an additional risk of SRM that so far has received limited attention: Initialization and commitment to SRM would happen under the assumption that CDR can be scaled up sufficiently to allow SRM to be phased out again. In our scenarios, SRM would come with very long legacies of deployment, implying centennial commitments of costs, risks and negative side effects of SRM and CDR combined.