Tailoring Meridional and Seasonal Radiative Forcing by Sulfate Aerosol Solar Geoengineering

Dai, Zhen; Weisenstein, Debra K.; Keith, David W.

doi:10.1002/2017gl076472

Cited by 63 publications

(66 citation statements)

References 45 publications

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“…Aerosols prescribed in the stratosphere can cause local warming in the stratosphere by absorbing near-IR and terrestrial radiation (Stenchikov et al, 1998;Ferraro et al, 2011). This warming can lead to changes in the amount of water vapor in the stratosphere (Dessler et al, 2013) and the amount of high clouds by changing the tropospheric stability (Kuebbeler et al, 2012;Visioni et al, 2018). Boucher et al (2017) has shown that these fast adjustment processes can influence the effective radiative forcing of the climate system for sulfate aerosol injections.…”

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confidence: 99%

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

et al. 2019

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Reduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer. In this study, we isolate and assess the sensitivity of stratospheric aerosol radiative forcing and the resulting climate change to the altitude of the aerosol layer. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability, and clouds, and consequently the effective radiative forcing. We show that the magnitude of the effective radiative forcing is larger when aerosols are prescribed at higher altitudes and the differences in radiative forcing due to fast adjustment processes can account for a substantial part of the dependence of the amount of cooling on aerosol altitude. These altitude effects would be additional to dependences on aerosol microphysics, transport, and sedimentation, which are outside the scope of this study. The cooling effectiveness of stratospheric sulfate aerosols likely increases with the altitude of the aerosol layer both because aerosols higher in the stratosphere have larger effective radiative forcing and because they have higher stratospheric residence time; these two effects are likely to be of comparable importance.

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confidence: 99%

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

et al. 2019

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“…Either scenario creates a serious tradeoff between operational efficiency and costs on the one hand, and purported 'secrecy' on the other. Less efficiency for direct SAI deployment above the equator (Dai et al 2018) implies substantially more deployed payload for the same climate impact. More payload requires more or larger aircraft and more flights, making the program more easily detectable.…”

Section: Further Discussionmentioning

confidence: 99%

“…This is no verdict as to these four latitudes being optimal or definitive. It is a statement that, if forced to choose today, these four latitudes appear like a good starting point for discussions , Dai et al 2018. Note that while SAI latitudes matter, longitudes appear not to, as injections at any one longitude mix rapidly to all others.…”

Section: Stratospheric Aerosol Deployment Scenariomentioning

confidence: 99%

Stratospheric aerosol injection tactics and costs in the first 15 years of deployment

Smith

Wagner

2018

Environ. Res. Lett.

135

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We review the capabilities and costs of various lofting methods intended to deliver sulfates into the lower stratosphere. We lay out a future solar geoengineering deployment scenario of halving the increase in anthropogenic radiative forcing beginning 15 years hence, by deploying material to altitudes as high as ∼20 km. After surveying an exhaustive list of potential deployment techniques, we settle upon an aircraft-based delivery system. Unlike the one prior comprehensive study on the topic (McClellan et al 2012 Environ. Res. Lett. 7 034019), we conclude that no existing aircraft design-even with extensive modifications-can reasonably fulfill this mission. However, we also conclude that developing a new, purpose-built high-altitude tanker with substantial payload capabilities would neither be technologically difficult nor prohibitively expensive. We calculate early-year costs of ∼$1500 ton −1 of material deployed, resulting in average costs of ∼$2.25 billion yr −1 over the first 15 years of deployment. We further calculate the number of flights at ∼4000 in year one, linearly increasing by ∼4000 yr −1 . We conclude by arguing that, while cheap, such an aircraft-based program would unlikely be a secret, given the need for thousands of flights annually by airliner-sized aircraft operating from an international array of bases.

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“…[15][16][17][18][19][20] Typical average values of the neutral/ion ratio during daytime at mid-latitudes in the stratosphere is about 10 12 , and it is independent by the type of molecular species because cosmic rays ionize all neutral molecules in the stratosphere with a similar efficiency. [19] This low ion/neutral ratio can be counterbalanced by the fact that ion-molecule reactions are generally much faster than the neutral-neutral reactions (i. e. the neutral chemistry involved in the conversion of SO 2 into H 2 SO 4 takes approximately 30 days [21] ), and can heavily alter the total budget of important molecular species in the atmosphere. Hence, reactions involving the radical cation SO �þ 2 (all along the manuscript the radical symbol in SO �þ 2 will be omitted for the sake of simplicity), which can be produced in the stratosphere by ionizing radiation, should be considered in the chemistry models used when evaluating the climate impact of solar geoengineering involving sulfur dioxide as aerosol precursor.…”

Section: Introductionmentioning

confidence: 99%

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and Its Relevance in Solar Geoengineering Models

Satta¹,

Cartoni²,

Catone³

et al. 2019

Preprint

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In recent years solar geoengineering has been proposed as a promising strategy to contrast global warming induced by anthropogenic CO2 emissions. These technologies design to inject in the stratosphere massive amounts of molecular species, which can act as precursors for aerosol formation able to partially reflect sunlight. SO2 is one of these species. Since in the atmosphere several natural ionization sources, such as cosmic rays and corona discharge, are active, we have considered that SO2+ ions can be formed in the stratosphere in a significant amount after being injected by balloons or aircrafts. The SO2+ chemistry could play a role in the dynamics of aerosol formation as a cooling agent. We have studied theoretically and experimentally the reaction of SO2+, produced by tunable synchrotron radiation, with H2 leading to HSO2+ and H, the latter being involved in the ozone depletion by producing O2 and OH. This is an ionic possible alternative to OH formation during the nighttime, when the common sunlight process of OH generation cannot occur. In order to explain the experimental reactivity we propose a new non-thermal version of the Variational Transition State Theory. We provide analytic expressions for the temperature dependent rate coefficients, which should be tested in atmospheric kinetic models to fully explore the stratospheric solar geoengineering strategies.

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Tailoring Meridional and Seasonal Radiative Forcing by Sulfate Aerosol Solar Geoengineering

Cited by 63 publications

References 45 publications

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

Stratospheric aerosol injection tactics and costs in the first 15 years of deployment

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and Its Relevance in Solar Geoengineering Models

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