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Uncertainty and the basis for confidence in solar geoengineering research


Solar geoengineering is an emerging topic in climate-change discussions. To support future decisions on the deployment of this technology, society requires better estimates of its environmental impacts and limitations. As solar geoengineering has never been deployed, conclusions about its climatic effects are primarily obtained through models and natural analogues. As such, our confidence in projections of solar geoengineering, the basis for that confidence and how our confidence can be improved is limited. In this Perspective, we review our current understanding of uncertainty and risk in solar geoengineering via stratospheric aerosols. Using a risk-register framework, we illustrate key uncertainties, such as sub-grid-scale mixing or effects of stratospheric heating, investigations of which should be prioritized to transition the field to a mission-driven research agenda. We conclude with recommendations for possible avenues of research, including targeted model intercomparisons and appropriately governed small-scale field experiments.

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Fig. 1: Climatic effects and uncertainties associated with SAG.
Fig. 2: Contrast between QBO strength for SAG via equatorial SO2 injection and GLENS.
Fig. 3: Effectiveness of SAG strategies in achieving temperature targets.
Fig. 4: Schematic of a risk register.
Fig. 5: Uncertainty in climate responses to SAG.


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The authors thank D. Visioni for helpful comments on the manuscript. Support for B.K. was provided in part by the National Science Foundation through agreement CBET-1931641, the Indiana University Environmental Resilience Institute and the Prepared for Environmental Change Grand Challenge initiative. The Pacific Northwest National Laboratory is operated for the US Department of Energy by Battelle Memorial Institute under contract DE-AC05-76RL01830. Support for D.G.M. was provided by the Atkinson Center for a Sustainable Future at Cornell University and by the National Science Foundation through agreement CBET-1818759.

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Kravitz, B., MacMartin, D.G. Uncertainty and the basis for confidence in solar geoengineering research. Nat Rev Earth Environ 1, 64–75 (2020).

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