Halving warming with stratospheric aerosol geoengineering moderates policy-relevant climate hazards: IOPscience

Stratospheric aerosol geoengineering, a proposal to add reflective aerosols to the stratosphere, might reduce the risks of climate change if used in combination with emissions cuts, carbon removal, and adaptation. Engineering assessments consistently find that lifting the required mass of material to the lower tropical stratosphere could be accomplished with commercially available aircraft technologies at a cost of a few billion dollars per million tons. And, the distribution of at least some aerosol precursors (such as SO₂) appears technically feasible (McClellan et al 2012, Smith and Wagner 2018, Bingaman et al 2020). Setting aside governance, which is likely the greatest challenge, the most salient technical question is whether these methods could reduce the overall magnitude of climate change without worsening impacts in some regions. That is, would stratospheric aerosol geoengineering create strong climate inequalities producing winners and losers?

We found that stratospheric aerosol geoengineering deployed to halve warming might substantially reduce the overall magnitude of climate change, while exacerbating hydrological change in only a small fraction of places. Deployed to offset all warming, stratospheric aerosol geoengineering in the Full-GLENS simulation overshoots on global-mean hydrological change, turning the intensification of the hydrological cycle under unabated climate change into a weakening. In Full-GLENS most regions see local hydrological change moderated, though some experience a substantial overshoot and a change in sign, and some see the hydrological impacts of climate change exacerbated. In Half-GLENS, regions which would have seen an overshoot instead see the effects of climate change more effectively offset, without experiencing a change in sign and only a few regions see exacerbation of any climate variable.