LASP Science Seminars

Various model experiments have been performed to identify the effects of stratospheric aerosol geoengineering (SAG). Most of these experiments did not target reaching surface temperatures that are required to limit impacts and the risk of global warming and for instance reaching tipping points. The Geoengineering Large Ensemble (GLENS) project performed model experiments using a feedback algorithm that identifies the needed amount of sulfur dioxide injections in the stratosphere at four predefined latitudes, 30^°N, 15^°N, 15^°S, and 30^°S, to reach three surface temperature targets close to present day: global mean temperature, and interhemispheric and pole-to-equator temperature gradients. These targets are designed to help reduce earlier identified side effects of SAG, including overcooling in the tropics, warming of high latitudes and large shifts in precipitation patterns.  However, the GLENS simulations are based on the business as usual future emission pathway and therefore require an increasing amount of sulfur injection with time. This would increase the risk of termination of the application. A more reasonable SAG model experiment, the so called “peak-shaving” experiment, has been proposed that limits global warming to 1.5^°C or 2.0^°C above 1850-1900 conditions, while following an overshoot scenario as the baseline scenario. In this seminar, I will present a new set of SAG model experiments that were performed with the Community Earth System Model Version 2 and using the Whole Atmosphere Community Climate Model Version 6, CESM2(WACCM6). These experiments are based on both, the CMIP6 overshoot scenario (SSP5-34-OS) and the high emission pathway scenario (SSP5-85). We use the feedback algorithm to limit global warming to 1.5^°C and 2.0^°C (for the overshoot case only) compared to 1850-1900 conditions. We find that some measures relevant to impacts on society and ecosystems more strongly depend on the defined temperature target (1.5^°C vs 2.0^°C), while others depend more strongly on the amount of carbon in the atmosphere or on the injection amount. Based on these finding, small or moderate applications of SAG in addition to strong mitigation efforts may help limit risks and side effects of global warming.