Side Effects of Sulfur-Based Geoengineering Due To Absorptivity of Sulfate Aerosols

Sulfur-based stratospheric aerosol intervention (SAI) can cool the climate, but also heats the tropical lower stratosphere if done with injections at low latitudes. We explore the role of this heating in the climate response to SAI, by using mechanistic experiments that remove the effects of longwave absorption of sulfate aerosols above the tropopause. If longwave absorption by stratospheric aerosols is disabled, the heating of the tropical tropopause and most of the related side effects are strongly alleviated and the cooling per Tg-S injected is 40% bigger. Such side-effects include the poleward expansion of eddy-driven jets, acceleration of the stratospheric residual circulation, and delay of Antarctic ozone recovery. Our results add to other recent findings on SAI side effects and demonstrate that SAI scenarios with low-latitude injections of absorptive materials may result in atmospheric effects and regional climate changes that are comparable to those produced by the CO2 warming signal. We explore the effects of the injection of sulfur into the tropical stratosphere to lower global average temperatures from those projected under a high-emission greenhouse gas scenario to the levels of a mid-emission scenario. We found that some detrimental effects of this injection are of a similar magnitude to those from climate change itself in some regions. This includes a strong warming 15 km above the tropics, which alters large-scale weather patterns in the atmosphere. In comparison to the mid-emission scenario, we find enhanced surface warming in the polar regions and modification in regional precipitation patterns over land, therefore not completely alleviating the warming of the high-emission scenario in high northern latitudes. We show that the tropical stratospheric heating is responsible for a large portion of these side effects on tropospheric climate. Many side effects of sulfur-based stratospheric aerosol intervention are caused by heating of the tropical lower stratosphere Some regional patterns of change tied to atmospheric circulation can be of the same magnitude as those that are CO2-driven The absorptivity of the aerosol particles increases their lifetime but decreases their cooling efficiency per Tg-S per year by 40%