Geoengineering Large Ensemble Project

The Stratospheric Aerosol Geoengineering Large Ensemble project is a 20-member ensemble of stratospheric sulfate aerosol geoengineering simulations between 2020-2099 and a 20-member ensemble of control simulations over a reference period between 2010-2030 using the NCAR Community Earth System Model with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM1 WACCM) described in Mills et al., 2017. The goal of the geoengineering simulations was to maintain not only global mean surface temperature, but also interhemispheric and equator-to-pole surface temperature gradients at 2020 values under a RCP8.5 greenhouse gas scenario. To reach these climate objectives, a feedback-control strategy was employed to manage uncertainty and variability in the climate system by optimizing annual injections at four different locations in the stratosphere, namely at 30°N, 30°S, 15°N and 15°S. This feedback strategy was developed based on several independent single point sulfur injection experiments aimed at identifying the relationships between injection location and surface temperature response (Tilmes et al., 2017, MacMartin et al., 2017, Richter et al., 2017), which was then applied to a single-member simulation (Kravitz et al., 2017). The Stratospheric Aerosol Geoengineering Large Ensemble has been performed the same way as the earlier single-member simulation, only using a newer version of the land model than in Kravitz et al. (2017). The results of these simulations can be used to identify robust regional and seasonal climate change, extremes, and variability as the result of strategically performed geoengineering and to identify reasonable limits of stratospheric aerosol engineering. We hope for large community involvement in analyzing these experiments.

Both control and geoengineering simulations follow the same RCP8.5 pathway. The control simulations were performed over the reference period between 2010 and 2030. Three of these members were continued through at least 2097. The geoengineering simulations were branched from each of the 20 control simulations in 2020. Sulfur injections using the feedback-control algorithm were applied to each of the 20 members separately to keep the global temperature and hemispheric temperature gradients at 2020 conditions. All 20 members of these simulations continued until 2099. Further details of the simulations are described in Tilmes et al. (2018).

All the data from these simulations are available to the community which can be found in the sidebar links of this page.