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

Peter J Irvine,David W Keith

doi:10.1088/1748-9326/ab76de

Peter J Irvine, David W Keith

Open Access

https://doi.org/10.1088/1748-9326/ab76de

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Abstract

Stratospheric aerosol geoengineering is a proposal to artificially thicken the layer of reflective aerosols in the stratosphere and it is hoped that this may offer a means of reducing average climate changes. However, previous work has shown that it could not perfectly offset the effects of climate change and there is a concern that it may worsen climate impacts in some regions. One approach to evaluating this concern is to test whether the absolute magnitude of climate change at each location is significantly increased (exacerbated) or decreased (moderated) relative to the period just preceding deployment. In prior work it was found that halving warming with an idealized solar constant reduction would substantially reduce climate change overall, exacerbating change in a small fraction of places. Here, we test if this result holds for a more realistic representation of stratospheric aerosol geoengineering using the data from the geoengineering large ensemble (GLENS). Using a linearized scaling of GLENS we find that halving warming with stratospheric aerosols moderates important climate hazards in almost all regions. Only 1.3% of land area sees exacerbation of change in water availability, and regions that are exacerbated see wetting not drying contradicting the common assumption that solar geoengineering leads to drying in general. These results suggest that halving warming with stratospheric aerosol geoengineering could potentially reduce key climate hazards substantially while avoiding some problems associated with fully offsetting warming.

Highlights

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
For P − E, the distribution of climate anomalies is similar for Half-geoengineering large ensemble (GLENS) and Full-GLENS, both of which are narrower than RCP8.5, suggesting limited improvement beyond halving warming (figure 1(c))
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

Summary

Introduction

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. The effects of stratospheric aerosol geoengineering necessarily depend on how it would be deployed, on choices about the spatial distribution and magnitude of the radiative forcing (Keith 2013, Kravitz et al 2016). There are sideeffects of stratospheric aerosol geoengineering such as ozone loss and air pollution that are expected to grow as the scale of deployment grows (Crutzen 2006, Eastham et al 2018). For these reasons, several authors have suggested that deploying stratospheric aerosol geoengineering to limit warming rather than halt it would reduce climate risks without introducing some of the problems seen for larger scale deployments (Jones et al 2018, Keith and MacMartin 2015)

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