Impacts on Agriculture from Surface Ozone and Ultraviolet Radiation Changes Due to Stratospheric Sulfate Injection

Solar radiation management using stratospheric aerosols has been proposed to reduce anthropogenic global warming. Studies have shown that its cooling effects, along with precipitation and solar radiation reduction, would influence agricultural production differently in different regions. However, surface ozone concentration and ultraviolet radiation (UV) changes have not been considered in any previous agriculture studies. Simulated solar radiation management impacts the ozone budget and the surface UV. We use the G4 Specified Stratospheric Aerosol (G4SSA) scenario, in which 8 Tg SO₂ is injected into the stratosphere each year from 2020 to 2069 to counteract warming from RCP6.0 forcing. Under G4SSA, surface ozone would decrease over agricultural regions compared with RCP6.0. Surface UV is calculated by the offline Tropospheric Ultraviolet and Visible (TUV) model, and it would slightly increase as a result of the balance between the aerosol blocking effect and stratospheric ozone depletion. We assess how surface ozone and UV changes under G4SSA impact agricultural production, and whether those changes are as important as cooling, precipitation, and total insolation changes. We use the crop model in the Community Land Model, version 5 (CLM5-crop) coupled with an ozone damage module and simulate rice, maize, spring wheat, soybean, cotton and sugarcane in current global planting regions. We perform two sets of crop simulations (with and without ozone damage) for G4SSA and for the global warming reference run RCP6.0. Agricultural practice (e.g., fertilizer usage and seeds) and planting areas are fixed in both runs. With the ozone damage module turned on, regional ozone concentration changes would alter stomatal conductance and the photosynthesis rate, and hence change crop production. With less ozone in most agriculture regions in G4SSA compared with RCP6.0, ozone changes show positive impacts on crop yields in most regions. However, the benefit from the direct cooling effect is larger than the crop production increases due to reduced surface ozone under G4SSA. The UV impact on crops is calculated with a statistical model from a review of previous literature, and the impact is small.