Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2019-21 Manuscript under review for journal Earth Syst. Dynam. Discussion started: 23 May 2019 c Author(s) 2019. CC BY 4.0 License. Climate System Response to Stratospheric Sulfate Aerosols: Sensitivity to Altitude of Aerosol Layer Krishnamohan Krishna-Pillai Sukumara-Pillai1, Govindasamy Bala1, and Long Cao2, Lei Duan2,3 and Ken Caldeira3 5 1 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India 2 Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, China 3 Department of Global Ecology, Carnegie Institution for Science, Stanford, CA 94305, USA Correspondence to: Krishnamohan Krishna-Pillai Sukumara-Pillai (
[email protected]) Abstract. Reduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested 10 as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer time. In this study, we isolate and assess the sensitivity to the altitude of the aerosol layer of stratospheric aerosol radiative forcing and the resulting climate change. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. 15 We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability and clouds, and consequently the effective radiative forcing.