Stratospheric controlled perturbation experiment: a small-scale experiment to improve understanding of the risks of solar geoengineering

Dykema, J. A.; Keith, David W.; Anderson, James G.; Weisenstein, Debra K.

doi:10.1098/rsta.2014.0059

Cited by 87 publications

(62 citation statements)

References 101 publications

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“…In addition to reversing ozone loss caused by historical chlorofluorocarbon emissions, the injection of alkalis may provide a method to counter the steady growth of stratospheric NO x caused by anthropogenic N 2 O emissions (24). Laboratory and small-scale field experiments (using <1 kg of materials) (25) are, however, essential to reduce uncertainties in heterogeneous reaction rates and photochemistry of mixed salt aerosol, which are critical to predicting stratospheric ozone loss rates.…”

Section: Discussionmentioning

confidence: 99%

Stratospheric solar geoengineering without ozone loss

Keith

Weisenstein

Dykema

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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136

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Injecting sulfate aerosol into the stratosphere, the most frequently analyzed proposal for solar geoengineering, may reduce some climate risks, but it would also entail new risks, including ozone loss and heating of the lower tropical stratosphere, which, in turn, would increase water vapor concentration causing additional ozone loss and surface warming. We propose a method for stratospheric aerosol climate modification that uses a solid aerosol composed of alkaline metal salts that will convert hydrogen halides and nitric and sulfuric acids into stable salts to enable stratospheric geoengineering while reducing or reversing ozone depletion. Rather than minimizing reactive effects by reducing surface area using high refractive index materials, this method tailors the chemical reactivity. Specifically, we calculate that injection of calcite (CaCO3) aerosol particles might reduce net radiative forcing while simultaneously increasing column ozone toward its preanthropogenic baseline. A radiative forcing of −1 W⋅m−2, for example, might be achieved with a simultaneous 3.8% increase in column ozone using 2.1 Tg⋅y−1 of 275-nm radius calcite aerosol. Moreover, the radiative heating of the lower stratosphere would be roughly 10-fold less than if that same radiative forcing had been produced using sulfate aerosol. Although solar geoengineering cannot substitute for emissions cuts, it may supplement them by reducing some of the risks of climate change. Further research on this and similar methods could lead to reductions in risks and improved efficacy of solar geoengineering methods.

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Section: Discussionmentioning

confidence: 99%

Stratospheric solar geoengineering without ozone loss

Keith

Weisenstein

Dykema

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

136

131

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“…Stratospheric sulfate injection (SSI) is the most discussed form of geoengineering and, given the current state of research, the most feasible (Dykema et al, 2014;Keith et al, 2014). Implementation of the G4Foam regional ocean albedo modification scheme could be considered with or without concurrent SSI.…”

Section: Introductionmentioning

confidence: 99%

The G4Foam Experiment: global climate impacts of regional ocean albedo modification

et al. 2017

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Abstract. Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150 %) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6 W m −2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30 • N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June-July-August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of −1.5 W m −2 is amplified through a series of positive cloud feedbacks, in which more shortwave radiation is reflected. The precipitation response is primarily the result of the intensification of the southern Hadley cell, as its mean position migrates northward and away from the Equator in response to the asymmetric cooling.

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“…To ascertain the effectiveness of some medical treatment we ultimately have to test it on its intended subjects. A similar lesson, I suspect, holds for geoengineering: ascertaining geoengineering's effects (intended or otherwise), effectiveness, and necessary engineering features, requires field experiments (Keith et al 2014, Dykema et al 2014. On the extreme, Robock et al claim that full deployment is required to test geoengineering technology (2010) (although see MacMynowski et al (2011)).…”

Section: Epistemic Challenges To Geoengineeringmentioning

confidence: 99%

Geoengineering tensions

Currie¹

2018

Futures

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There has been much discussion of the moral, legal and prudential implications of geoengineering, and of governance structures for both the research and deployment of such technologies. However, insufficient attention has been paid to how such measures might affect geoengineering in terms of the incentive structures which underwrite scientific progress. There is a tension between the features that make science productive, and the need to govern geoengineering research, which has thus far gone underappreciated. I emphasize how geoengineering research requires governance which reaches beyond science's traditional boundaries, and moreover requires knowledge which itself reaches beyond what we traditionally expect scientists to know about. How we govern emerging technologies should be sensitive to the incentive structures which drive science.

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Stratospheric controlled perturbation experiment: a small-scale experiment to improve understanding of the risks of solar geoengineering

Cited by 87 publications

References 101 publications

Stratospheric solar geoengineering without ozone loss

Stratospheric solar geoengineering without ozone loss

The G4Foam Experiment: global climate impacts of regional ocean albedo modification

Geoengineering tensions

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