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

MacMartin, Douglas G.; Kravitz, Ben; Tilmes, Simone; Richter, Jadwiga H.; Mills, Michael J.; Lamarque, Jean‐François; Tribbia, Joseph; Vitt, Francis

doi:10.1002/2017jd026868

Cited by 131 publications

(186 citation statements)

References 52 publications

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“…This effort, also called system identification , began with the simulations described by Tilmes et al (), in which the injection parameter space was coarsely sampled via 10 year simulations involving different amounts of stratospheric SO 2 injection at different latitudes and altitudes. Tilmes et al () discuss the results from these simulations in greater detail, and MacMartin et al () discuss the linearity of these simulations and the ultimate selection of the degrees of freedom to be modified.…”

Section: Methodsmentioning

confidence: 99%

“…More specifically, these locations are at 30°S, 15°S, 15°N, and 30°N in latitude along 180° longitude at high altitude (approximately 5 km above the annual mean tropopause). MacMartin et al () discuss the details of why these four locations were chosen, but roughly summarizing, different combinations of injection in these four locations are capable of producing patterns of aerosol optical depth (AOD) that are constant ( ℓ 0 ), linear ( ℓ 1 ), and quadratic ( ℓ 2 ) with latitude. These three patterns are defined analogously to the definitions in equation , but with a different normalization so that at any latitude ψ ,

AOD (ψ) = ℓ_{0} + ℓ_{1} \sin (ψ) + ℓ_{2} (3 \overset{2}{\sin} (ψ) - 1) / 2

\begin{matrix} ℓ_{0} & = \frac{ξ_{0}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) d A \\ ℓ_{1} & = \frac{ξ_{1}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \sin ψ d A \\ ℓ_{2} & = \frac{ξ_{2}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \frac{1}{2} (3 \overset{2}{\sin} ψ - 1) d A \end{matrix}

where AOD is zonally averaged stratospheric sulfate aerosol optical depth.…”

Section: Methodsmentioning

confidence: 99%

“…These three patterns are defined analogously to the definitions in equation , but with a different normalization so that at any latitude ψ ,

AOD (ψ) = ℓ_{0} + ℓ_{1} \sin (ψ) + ℓ_{2} (3 \overset{2}{\sin} (ψ) - 1) / 2

\begin{matrix} ℓ_{0} & = \frac{ξ_{0}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) d A \\ ℓ_{1} & = \frac{ξ_{1}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \sin ψ d A \\ ℓ_{2} & = \frac{ξ_{2}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \frac{1}{2} (3 \overset{2}{\sin} ψ - 1) d A \end{matrix}

where AOD is zonally averaged stratospheric sulfate aerosol optical depth. In turn, MacMartin et al () demonstrate that these three patterns of AOD can produce somewhat controllable changes in T 0 , T 1 , and T 2 . The normalization factors are defined as

\begin{matrix} ξ_{0} & = \frac{1}{2} \int_{- π / 2}^{π / 2} d A = 1 \\ ξ_{1} & = \frac{1}{2} \int_{- π / 2}^{π / 2} \overset{2}{\sin} (ψ) d A = \frac{1}{3} \\ ξ_{2} & = \frac{1}{2} \int_{- π / 2}^{} \end{matrix}

…”

Section: Methodsmentioning

confidence: 99%

“…Here we provide the first demonstration of the ability to meet multiple simultaneous climate objectives in the presence of uncertainty with stratospheric sulfate aerosol geoengineering using a state‐of‐the‐art climate model. This manuscript is accompanied by several others (Mills et al, ; Richter et al, ; Tilmes et al, ; MacMartin et al, ) that have described many of the details that led to the ability to reach this point; we repeat the salient points from those manuscripts as necessary.…”

Section: Introductionmentioning

confidence: 99%

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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: Methodsmentioning

confidence: 99%

AOD (ψ) = ℓ_{0} + ℓ_{1} \sin (ψ) + ℓ_{2} (3 \overset{2}{\sin} (ψ) - 1) / 2

\begin{matrix} ℓ_{0} & = \frac{ξ_{0}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) d A \\ ℓ_{1} & = \frac{ξ_{1}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \sin ψ d A \\ ℓ_{2} & = \frac{ξ_{2}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \frac{1}{2} (3 \overset{2}{\sin} ψ - 1) d A \end{matrix}

where AOD is zonally averaged stratospheric sulfate aerosol optical depth.…”

Section: Methodsmentioning

confidence: 99%

“…These three patterns are defined analogously to the definitions in equation , but with a different normalization so that at any latitude ψ ,

AOD (ψ) = ℓ_{0} + ℓ_{1} \sin (ψ) + ℓ_{2} (3 \overset{2}{\sin} (ψ) - 1) / 2

\begin{matrix} ℓ_{0} & = \frac{ξ_{0}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) d A \\ ℓ_{1} & = \frac{ξ_{1}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \sin ψ d A \\ ℓ_{2} & = \frac{ξ_{2}}{A} \int_{- π / 2}^{π / 2} AOD (ψ) \frac{1}{2} (3 \overset{2}{\sin} ψ - 1) d A \end{matrix}

\begin{matrix} ξ_{0} & = \frac{1}{2} \int_{- π / 2}^{π / 2} d A = 1 \\ ξ_{1} & = \frac{1}{2} \int_{- π / 2}^{π / 2} \overset{2}{\sin} (ψ) d A = \frac{1}{3} \\ ξ_{2} & = \frac{1}{2} \int_{- π / 2}^{} \end{matrix}

…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…Understanding the RF contribution of the UT ice perturbation in a SG scenario is particularly crucial if the scientific community wants to design experiments whose goal is to meet a given climate target, as proposed in Kravitz et al (2017) and MacMartin et al (2017).…”

mentioning

confidence: 99%

Upper tropospheric ice sensitivity to sulfate geoengineering

Visioni¹,

Pitari²,

Mancini³

2018

Preprint

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Abstract. Aside from the direct surface cooling sulfate geoengineering (SG) would produce, the investigation on possible sideeffects of this method is still ongoing, as for instance on upper tropospheric cirrus cloudiness. Goal of the present study is to better understand the SG thermo-dynamical effects on the homogeneous freezing ice formation process. This is done by comparing SG model simulations against a RCP4.5 reference case: in one case the aerosol-driven surface cooling is included and coupled to the stratospheric warming resulting from aerosol absorption of longwave radiation. In a second SG perturbed case, 5 surface temperatures are kept unchanged with respect to the reference RCP4.5 case. Surface cooling and lower stratospheric warming, together, tend to stabilize the atmosphere, thus decreasing turbulence and water vapor updraft velocities (-10% in our modeling study). The net effect is an induced cirrus thinning, which may then produce a significant indirect negative radiative forcing (RF). This would go in the same direction as the direct effect of solar radiation scattering by the aerosols, thus influencing the amount of sulfur needed to counteract the positive RF due to greenhouse gases. In our study, given a 8 Tg-SO 2 10 equatorial injection in the lower stratosphere, an all-sky net tropopause RF of -2.13 W/m 2 is calculated, of which -0.96 W/m 2 (45%) from the indirect effect on cirrus thinning (7.5% reduction in ice optical depth). When the surface cooling is ignored, the ice optical depth reduction is lowered to 5%, with an all-sky net tropopause RF of -1.45 W/m ). This highlights the importance of including all dynamical feedbacks of SG aerosols.

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Regional Climate Impacts of Stabilizing Global Warming at 1.5 K Using Solar Geoengineering

et al. 2018

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The 2015 Paris Agreement aims to limit global warming to well below 2 K above preindustrial levels, and to pursue efforts to limit global warming to 1.5 K, in order to avert dangerous climate change. However, current greenhouse gas emissions targets are more compatible with scenarios exhibiting end‐of‐century global warming of 2.6–3.1 K, in clear contradiction to the 1.5 K target. In this study, we use a global climate model to investigate the climatic impacts of using solar geoengineering by stratospheric aerosol injection to stabilize global‐mean temperature at 1.5 K for the duration of the 21st century against three scenarios spanning the range of plausible greenhouse gas mitigation pathways (RCP2.6, RCP4.5, and RCP8.5). In addition to stabilizing global mean temperature and offsetting both Arctic sea‐ice loss and thermosteric sea‐level rise, we find that solar geoengineering could effectively counteract enhancements to the frequency of extreme storms in the North Atlantic and heatwaves in Europe, but would be less effective at counteracting hydrological changes in the Amazon basin and North Atlantic storm track displacement. In summary, solar geoengineering may reduce global mean impacts but is an imperfect solution at the regional level, where the effects of climate change are experienced. Our results should galvanize research into the regionality of climate responses to solar geoengineering.

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

Cited by 131 publications

References 52 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

Upper tropospheric ice sensitivity to sulfate geoengineering

Regional Climate Impacts of Stabilizing Global Warming at 1.5 K Using Solar Geoengineering

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