Design and Simulation of a Logistically Constrained High-Latitude, Low-Altitude Stratospheric Aerosol Injection Scenario in the Energy Exascale Earth System Model (E3SM)
The Arctic is warming faster than the rest of the globe, posing risks to climate tipping elements such as the collapse of the Greenland Ice Sheet, winter Arctic sea ice loss, weakening of the Atlantic Meridional Overturning Circulation, and permafrost collapse. Stratospheric Aerosol Injection (SAI) has shown potential to ameliorate these effects by reducing surface temperatures. Due to the potential for an asymmetric hemispheric response in precipitation, Arctic-only SAI is not recommended. Given the challenges associated with an Antarctic SAI program, including the lack of nearby large airports, however, we designed and simulated an Arctic-only logistically constrained SAI scenario, considering limitations imposed by factors affecting the planning, execution, and management of operations. Our scenario is constrained by aircraft development and delivery timelines. SAI deployment begins in 2032 and increases to a maximum annual injection of 6.7 TgSO2 by 2053 through 2070. The scenario is simulated in a modified version of the Energy Exascale Earth System Model (E3SMv2). Results indicate that Arctic-only SAI can reduce Northern Hemisphere temperatures and slow sea ice loss, though the early years of deployment may show limited cooling due to low ramp-in injection magnitudes. The Arctic-only SAI introduces minimal impact on Southern Hemisphere temperatures but significant shifts in the hydrologic cycle, particularly around the equator. Southern Hemisphere changes are low within the first two decades, suggesting that asymmetries in Arctic-only SAI deployment could be sustained without severe adverse climate impacts for the first couple of decades. These asymmetries matter given the challenges associated with an Antarctic SAI program. Our findings underscore the necessity of incorporating logistical constraints on deployment and the need for multi-model assessments in the evaluation of polar SAI scenarios. This approach would ensure a strong scientific understanding of polar SAI and facilitates policy and decision-maker understanding of the risks and benefits of SAI.