20.01.2020

# New Publications

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Krishnamohan, K. S.; et al. (2020): The Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere

Krishnamohan, K. S.; Bala, Govindasamy; Cao, Long; Duan, Lei; Caldeira, Ken (2020): The Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere. In Earth's Future. DOI: 10.1029/2019EF001326.

"We show that stratospheric sulfate aerosols, for a given mass of sulfates, cause more cooling when prescribed at the lower levels of the stratosphere because of hygroscopic growth. The larger relative humidity in the lower stratosphere causes an increase in the aerosol size through hygroscopic growth which leads to a larger scattering efficiency."

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14.01.2020

# New Publications

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Kravitz, Ben; MacMartin, Douglas G. (2020): Uncertainty and the basis for confidence in solar geoengineering research

Kravitz, Ben; MacMartin, Douglas G. (2020): Uncertainty and the basis for confidence in solar geoengineering research. In Nat Rev Earth Environ 1 (1), pp. 64–75. DOI: 10.1038/s43017-019-0004-7.

"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."

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23.12.2019

# Media

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MIT Technology Review: The US government has approved funds for geoengineering research

"The program includes assessments of “solar climate interventions,” including “proposals to inject material [into the stratosphere] to affect climate.”"

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16.12.2019

# New Publications

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Krishnamohan, Krishna-Pillai Sukumara-Pillai; et al. (2019): Climate System Response to Stratospheric Sulfate Aerosols: Sensitivity to Altitude of Aerosol Layer

Krishnamohan, Krishna-Pillai Sukumara-Pillai, Govindasamy Bala, Long Cao, Lei Duan, and Ken Caldeira (2019): Climate System Response to Stratospheric Sulfate Aerosols: Sensitivity to Altitude of Aerosol Layer. Earth System Dynamics 10 (4): 885–900. https://doi.org/https://doi.org/10.5194/esd-10-885-2019.

‌"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."

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09.12.2019

# New Publications

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Simpson, I.R.; et al. (2019): The Regional Hydroclimate Response to Stratospheric Sulfate Geoengineering and the Role of Stratospheric Heating

Simpson, I. R.; Tilmes, S.; Richter, J. H.; Kravitz, B.; MacMartin, D. G.; Mills, M. J. et al. (2019): The Regional Hydroclimate Response to Stratospheric Sulfate Geoengineering and the Role of Stratospheric Heating. In Journal of Geophysical Research: Atmospheres 124. DOI: 10.1029/2019JD031093.

"Here, a 20‐member ensemble of simulations with the Community Earth System Model with the Whole Atmosphere Community Climate Model as its atmospheric component is used to investigate the projected hydroclimate changes that occur when greenhouse gas‐driven warming, under a high emissions scenario, is offset with stratospheric aerosol geoengineering."

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11.11.2019

# New Publications

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Schroeder, C.; et al (2019): “Stratospheric Aerosol Injection as a Deep Reinforcement Learning Problem

Schroeder, Christian, and Thomas Hornigold. 2019. “Stratospheric Aerosol Injection as a Deep Reinforcement Learning Problem.” ArXiv.Org. 2019. https://arxiv.org/abs/1905.07366v1.

‌"We suggest treating SAI as a high-dimensional control problem, with policies trained according to a context-sensitive reward function within the Deep Reinforcement Learning (DRL) paradigm. In order to facilitate training in simulation, we suggest to emulate HadCM3, a widely used General Circulation Model, using deep learning techniques. We believe this is the first application of DRL to the climate sciences."

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30.09.2019

# Media

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Neue Zürcher Zeitung: We led the planet and its stable, mild climate into a new geological epoch: the Anthropocene

German newspaper article about Paul Crutzen and his ozone research.

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17.09.2019

# New Publications

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Halstead, John (2018): Stratospheric aerosol injection research and existential risk

Halstead, John (2018): Stratospheric aerosol injection research and existential risk. In Futures 102, pp. 63–77. DOI: 10.1016/j.futures.2018.03.004.

"This paper discusses whether Stratospheric Aerosol Injection (SAI) should be researched, on the controversial ethical assumption that reducing existential risk is overwhelmingly morally important. On the one hand, SAI could eliminate the environmental existential risks of climate change (arguably around a 1% chance of catastrophe), and reduce the risks of interstate conflict associated with extreme warming."

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26.05.2018

# New Publications

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Tilmes, Simone; et al. (2018): CESM1(WACCM) Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) Project

Tilmes, Simone; Richter, Jadwiga H.; Kravitz, Ben; MacMartin, Douglas G.; Mills, Michael J.; Simpson, Isla R. et al. (2018): CESM1(WACCM) Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) Project. In Bulletin of the American Meteorological Society. DOI: 10.1175/BAMS-D-17-0267.1.

"This paper describes the stratospheric aerosol geoengineering large ensemble (GLENS) project, which promotes the use of a unique model dataset, performed with the Community Earth System Model, with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM1(WACCM)), to investigate global and regional impacts of geoengineering. The performed simulations were designed to achieve multiple simultaneous climate goals, by strategically placing sulfur injections at four different locations in the stratosphere, unlike many earlier studies that targeted globally averaged surface temperature by placing injections in regions at or around the equator."

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11.05.2018

# New Publications

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Richter, Jadwiga H.; et al. (2018): Stratospheric response in the first geoengineering simulation meeting multiple surface climate objectives

Richter, Jadwiga H.; Tilmes, Simone; Glanville, Anne A.; Kravitz, Ben; MacMartin, Douglas G.; Mills, Michael J. et al. (2018): Stratospheric response in the first geoengineering simulation meeting multiple surface climate objectives. In J. Geophys. Res. Atmos. DOI: 10.1029/2018JD028285.

"We describe here changes in stratospheric dynamics and chemistry in a first century‐long sulfate aerosol geoengineering simulation in which the mean surface temperature and the inter‐hemispheric and equator‐to‐pole surface temperature gradients were kept near their 2020 levels despite the RCP8.5 emission scenario. Simulations were carried out with the Community Earth System Model, version 1 with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM1 (WACCM)) coupled to a feedback algorithm controlling the magnitude of sulfur dioxide (SO2) injections at four injection latitudes."

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