Geoengineering with stratospheric aerosols: What do we not know after a decade of research?

MacMartin, Douglas G.; Kravitz, Ben; Long, Jane C.; Rasch, Philip J.

doi:10.1002/2016ef000418

Cited by 44 publications

(45 citation statements)

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“…This aims at mimicking the aerosol layer created by large volcanic eruptions, which is known to cause global cooling (e.g., Robock, ). If geoengineering is to be considered as a potential response to addressing climate change, its effects, potentials, and limitations need to be quantified, particularly in comparison to other methods of addressing climate change, including mitigation of greenhouse gas emissions, adaptation to climate change, or carbon dioxide removal (e.g., MacMartin et al, ; Tilmes et al, ). Put simply, society needs to know what geoengineering can do and what it cannot do.…”

Section: Introductionmentioning

confidence: 99%

First Simulations of Designing Stratospheric Sulfate Aerosol Geoengineering to Meet Multiple Simultaneous Climate Objectives

et al. 2017

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We describe the first simulations of stratospheric sulfate aerosol geoengineering using multiple injection locations to meet multiple simultaneous surface temperature objectives. Simulations were performed using CESM1(WACCM), a coupled atmosphere‐ocean general circulation model with fully interactive stratospheric chemistry, dynamics (including an internally generated quasi‐biennial oscillation), and a sophisticated treatment of sulfate aerosol formation, microphysical growth, and deposition. The objectives are defined as maintaining three temperature features at their 2020 levels against a background of the RCP8.5 scenario over the period 2020–2099. These objectives are met using a feedback mechanism in which the rate of sulfur dioxide injection at each of the four locations is adjusted independently every year of simulation. Even in the presence of uncertainties, nonlinearities, and variability, the objectives are met, predominantly by SO2 injection at 30°N and 30°S. By the last year of simulation, the feedback algorithm calls for a total injection rate of 51 Tg SO2 per year. The injections are not in the tropics, which results in a greater degree of linearity of the surface climate response with injection amount than has been found in many previous studies using injection at the equator. Because the objectives are defined in terms of annual mean temperature, the required geongineering results in “overcooling” during summer and “undercooling” during winter. The hydrological cycle is also suppressed as compared to the reference values corresponding to the year 2020. The demonstration we describe in this study is an important step toward understanding what geoengineering can do and what it cannot do.

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Section: Introductionmentioning

confidence: 99%

First Simulations of Designing Stratospheric Sulfate Aerosol Geoengineering to Meet Multiple Simultaneous Climate Objectives

et al. 2017

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“…Here we consider, for the first time, whether simultaneous injection of stratospheric SO 2 at multiple different latitudes can be used to obtain multiple independent degrees of freedom of the spatial pattern of AOD, and in turn if these lead to multiple independent degrees of freedom of the spatial pattern of surface air temperature. The amplitude and spatial pattern of AOD that results from injection at any given latitude depends on a complex interplay of factors (MacMartin et al, ; Pitari et al, ), and thus, it is not immediately clear what spatial patterns of AOD are actually achievable given the constraints imposed by stratospheric circulation, nor whether the (nonlinear) interactions between injections at different latitudes preclude useful design. Injecting SO 2 leads to sulfate aerosols through oxidation, followed by nucleation, condensation, and coagulation; these microphysical processes affect the resulting size distribution (English et al, ; Heckendorn et al, ; Pierce et al, ), which affects both lifetime (through sedimentation) and AOD for a given sulfate mass.…”

Section: Introductionmentioning

confidence: 99%

The Climate Response to Stratospheric Aerosol Geoengineering Can Be Tailored Using Multiple Injection Locations

et al. 2017

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By injecting different amounts of SO2 at multiple different latitudes, the spatial pattern of aerosol optical depth (AOD) can be partially controlled. This leads to the ability to influence the climate response to geoengineering with stratospheric aerosols, providing the potential for design. We use simulations from the fully coupled whole‐atmosphere chemistry climate model CESM1(WACCM) to demonstrate that by appropriately combining injection at just four different locations, 30°S, 15°S, 15°N, and 30°N, then three spatial degrees of freedom of AOD can be achieved: an approximately spatially uniform AOD distribution, the relative difference in AOD between Northern and Southern Hemispheres, and the relative AOD in high versus low latitudes. For forcing levels that yield 1–2°C cooling, the AOD and surface temperature response are sufficiently linear in this model so that the response to different combinations of injection at different latitudes can be estimated from single‐latitude injection simulations; nonlinearities associated with both aerosol growth and changes to stratospheric circulation will be increasingly important at higher forcing levels. Optimized injection at multiple locations is predicted to improve compensation of CO2‐forced climate change relative to a case using only equatorial aerosol injection (which overcools the tropics relative to high latitudes). The additional degrees of freedom can be used, for example, to balance the interhemispheric temperature gradient and the equator to pole temperature gradient in addition to the global mean temperature. Further research is needed to better quantify the impacts of these strategies on changes to long‐term temperature, precipitation, and other climate parameters.

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“…Recent reviews of scientific studies and open questions regarding solar geoengineering (e.g. Irvine et al, 2016;MacMartin et al, 2016) highlighted again the need for accurate stratospheric aerosol models. These research interests motivate the introduction of a versatile stratospheric aerosol model within the IPSL Climate Model (IPSL-CM) and its atmospheric component LMDZ.…”

Section: Introductionmentioning

confidence: 99%

The Sectional Stratospheric Sulfate Aerosol module (S3A-v1) within the LMDZ general circulation model: description and evaluation against stratospheric aerosol observations

et al. 2017

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Abstract. Stratospheric aerosols play an important role in the climate system by affecting the Earth's radiative budget as well as atmospheric chemistry, and the capabilities to simulate them interactively within global models are continuously improving. It is important to represent accurately both aerosol microphysical and atmospheric dynamical processes because together they affect the size distribution and the residence time of the aerosol particles in the stratosphere. The newly developed LMDZ-S3A model presented in this article uses a sectional approach for sulfate particles in the stratosphere and includes the relevant microphysical processes. It allows full interaction between aerosol radiative effects (e.g. radiative heating) and atmospheric dynamics, including e.g. an internally generated quasi-biennial oscillation (QBO) in the stratosphere. Sulfur chemistry is semi-prescribed via climatological lifetimes. LMDZ-S3A reasonably reproduces aerosol observations in periods of low (background) and high (volcanic) stratospheric sulfate loading, but tends to overestimate the number of small particles and to underestimate the number of large particles. Thus, it may serve as a tool to study the climate impacts of volcanic eruptions, as well as the deliberate anthropogenic injection of aerosols into the stratosphere, which has been proposed as a method of geoengineering to abate global warming.

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Geoengineering with stratospheric aerosols: What do we not know after a decade of research?

Cited by 44 publications

References 50 publications

First Simulations of Designing Stratospheric Sulfate Aerosol Geoengineering to Meet Multiple Simultaneous Climate Objectives

First Simulations of Designing Stratospheric Sulfate Aerosol Geoengineering to Meet Multiple Simultaneous Climate Objectives

The Climate Response to Stratospheric Aerosol Geoengineering Can Be Tailored Using Multiple Injection Locations

The Sectional Stratospheric Sulfate Aerosol module (S3A-v1) within the LMDZ general circulation model: description and evaluation against stratospheric aerosol observations

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