Multi-Model Simulation of Solar Geoengineering Indicates Avoidable Destabilization of the West Antarctic Ice Sheet

Heat transported in Circumpolar Deep Water is driving the break-up of ice shelves in the Amundsen Sea sector of Antarctica, that has been simulated to be unavoidable under all plausible greenhouse gas scenarios. However, Solar geoengineering scenarios remain largely unexplored. Solar geoengineering changes global thermal radiative balance, and atmospheric and oceanic transportation pathways. We simulate stratospheric aerosol injection (SAI) designed to reduce global mean temperatures from those under the unmitigated SSP5-8.5 scenario to those under the SSP2-4.5 scenario with six CMIP6-class Earth System Models. These consistently show intensified Antarctic polar vortex and sub-polar westerlies, which mitigates changes to easterly winds along the Amundsen Sea continental shelf compared with greenhouse gas scenarios. The models show significantly cooler Amundsen Sea waters and lower heat content at 300-600 m under SAI than with either solar dimming or the SSP5-8.5 unmitigated greenhouse gas scenarios. However, the heat content increases under all scenarios compared with present day suggesting that although vulnerable ice shelves would continue to thin, the rate would be lower for SAI even with SSP5-8.5 specified greenhouse gases, than for the moderate (SSP2-4.5) scenario. The simulations here use solar geoengineering designed to meet global temperature targets; interventions targeted at preserving the frozen high latitudes have also been proposed that might be expected to produce bigger local effects, but potentially deleterious impacts elsewhere. Considering the huge disruptions to society of ice sheet collapse, more research on avoiding them by intervention technology is a moral imperative. The Amundsen Sea sector of Antarctica is important because major ice sheet outlet glaciers are at, or close to, the tipping point threshold when greenhouse gas concentrations become irrelevant to their fate. Multi-meter sea level rises are essentially inevitable once past this tipping point, forcing hundreds of millions of people to relocate (mainly in the Global South), and costing around $40 billion per year per meter of sea level rise through the rest of the century in coastal defense systems. Hence any methods that may avoid ice sheet collapse should be researched. In this article we use 6 state of the art earth system models to simulate putting aerosols into the stratosphere (mimicking volcanic eruptions), might affect the heat carried by the oceans to the vulnerable glaciers in the Amundsen Sea. The stratospheric aerosols change the winds that drive warm deep water toward the glaciers, lowering the expected melting compared with the no greenhouse gas mitigation scenario, and even the lowered emissions pledged by the international community. This result contrasts with earlier work suggesting the ice sheets were doomed and encourages more sophisticated climate system interventions scenarios targeted toward to high latitudes. We simulate the effect of stratospheric aerosol injection (SAI) and greenhouse gas scenarios on ocean heat flow in the Amundsen Sea SAI impacts stratospheric winds that propagate into ocean circulation changes that reduce heat flow to the ice edge Researching ideas, that can complement mitigation, may provide alternatives to avoid crossing damaging social tipping points