Flawed Emergency Intervention: Slow Ocean Response to Abrupt Stratospheric Aerosol Injection

Given the possibility of irreversible, anthropogenic changes in the climate system, technologies such as solar radiation management (SRM) are sometimes framed as possible emergency interventions. However, little knowledge exists on the efficacy of such deployments. To fill in this gap, we perform Community Earth System Model 2 simulations of an intense warming scenario on which we impose gradual early-century SRM or rapid late-century cooling (an emergency intervention), both realized via stratospheric aerosol injection (SAI). While both scenarios cool Earth's surface, ocean responses differ drastically. Rapid cooling fails to release deep ocean heat content or restore an ailing North Atlantic deep convection but partially stabilizes the Atlantic meridional overturning circulation. In contrast, the early intervention effectively mitigates changes in all of these features. Our results suggest that slow ocean timescales impair the efficacy of some SAI emergency interventions. Stratospheric aerosol injection (SAI) is a promising, yet controversial proposal to mask the effects of anthropogenic climate change by releasing sunlight-reflecting particles into the atmosphere. Currently, many studies are focusing on the benefits of near future SAI deployments. We, however, investigate SAI as a late emergency intervention. To what extent can SAI still help if we continue to heat and destabilize the climate? In this study, we simulate the impacts of an abrupt, SAI cooling intervention deployed against the backdrop of a climate much hotter than today's. While SAI readily cools Earth's surface, it is challenged by a slow ocean response. Heat trapped below the ocean surface remains a contributor to sea-level rise and important currents weakened by climate change linger in ailing condition. In contrast, an earlier SAI intervention effectively mitigates changes in these features. Our findings re-emphasize the urgent need for climate action. If anthropogenic heating continues, even an intervention as powerful as SAI will encounter its limits. Efficacy of stratospheric aerosol injection (SAI) impaired by anthropogenic ocean heating Deep ocean heating, weakened Atlantic Meridional Overturning Circulation (AMOC) and collapsed North Atlantic deep convection only partially addressed by late SAI SAI decouples AMOC and global mean surface temperature, thereby inducing climate states not seen in purely greenhouse gas-forced scenarios