Stratospheric aerosol geoengineering: Sensitivity of global monsoon precipitation to the latitude of injections

Abstract:

Deliberate modification of planetary energy balance through the injection of sulfate aerosols into the stratosphere is one of the several proposed geoengineering methods to counter anthropogenic climate warming. Several previous studies have shown that this method can be effective in offsetting the global mean temperature changes, but there could be large residual and overcompensating regional changes. In this study, we analyze the impact of latitudinally varying stratosphere aerosol injection locations on the global monsoon precipitation.

The impact of varying the latitudinal position of aerosol injection on the monsoon precipitation in the RCP8.5 scenario is estimated by analyzing single point sulfate injection simulations from NCAR, where 12 Tg of SO₂ is injected each year into the stratosphere at 30°S, 15°S, equator, 15°N, and 30°N. We find that during the period 2043-2049, relative to RCP8.5, the hemispheric mean summer monsoon precipitation decreases in the hemisphere where aerosols are injected but increases in the opposite hemisphere. These changes can be up to ±10% depending on the latitude of injection. The precipitation changes are more prominent over regions such as India, where the summer monsoon precipitation decreases by about 21% and 29%, respectively, when aerosols are injected at 15°N for 30°N.

We find that the precipitation changes are associated with shifts in the location of the inter-tropical convergence zone (ITCZ). The sulfate injection causes more cooling in the hemisphere where it is injected, altering the interhemispheric temperature gradient. The energy deficit in the injection hemisphere, necessitates a heat transport across the equator and a shift in Hadley cells, causing a shift in the location of the ITCZ. Our study shows that adverse effects are likely for India when aerosols are injected at 15°N, though injection at this latitude has been shown to be more efficient in cooling the global climate.