14.06.2017

# New Publications

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Lauvset, Siv K.; et al. (2017): Climate engineering and the ocean. Effects on biogeochemistry and primary production

Lauvset, Siv K.; Tjiputra, Jerry; Muri, Helene (2017): Climate engineering and the ocean. Effects on biogeochemistry and primary production. In: Biogeosciences Discuss., S. 1–36. DOI: 10.5194/bg-2017-235

"Here we use an Earth System Model with interactive biogeochemistry to project future ocean biogeochemistry impacts from large-scale deployment of three different radiation management (RM) climate engineering (also known as geoengineering) methods: stratospheric aerosol injection (SAI), marine sky brightening (MSB), and cirrus cloud thinning (CCT). We apply RM such that the change in radiative forcing in the RCP8.5 emission scenario is reduced to the change in radiative forcing in the RCP4.5 scenario. The resulting global mean sea surface temperatures in the RM experiments are comparable to those in RCP4.5, but there are regional differences."

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02.02.2017

# New Publications

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Kärcher, Bernd (2017): Cirrus Clouds and Their Response to Anthropogenic Activities

Kärcher, Bernd (2017): Cirrus Clouds and Their Response to Anthropogenic Activities. In: Curr Clim Change Rep. DOI: 10.1007/s40641-017-0060-3.

"This review assesses recent observational and modeling evidence of how anthropogenic activities might affect cirrus. Changes in physical properties and chemical composition of liquid aerosol particles will unlikely affect cirrus significantly, but anthropogenic influences may occur through changes in heterogeneous ice nuclei."

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19.11.2016

# New Publications

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Quaas, Johannes; et al. (2016): Regional climate engineering by radiation management: Prerequisites and prospects

Quaas, Johannes; Quaas, Martin F.; Boucher, Olivier; Rickels, Wilfried (2016): Regional climate engineering by radiation management: Prerequisites and prospects. In Earth’s Future. DOI 10.1002/2016EF000440.

"In this paper, we discuss the idea that RM can be differentiated and scaled in several dimensions with potential objectives being to influence a certain climate parameter in a specific region. Some short-lived climate forcers (e.g., tropospheric aerosols) exhibit strong geographical and temporal variability, potentially leading to limited- area climate responses. Marine cloud brightening and thinning or dissolution of cirrus clouds could be operated at a rather local scale."

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11.07.2016

# Media

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CSCS: Can cirrus cloud seeding help to “save” the climate? (press release)

Press release on Gasparini, Blaž; Lohmann, Ulrike (2016). "The interaction of cirrus clouds with radiation is a complex one, which depends on the concentration of ice crystals, their size, as well as on properties such as the temperature of the cloud and the underlying surface, and solar insolation.  Model calculations indicate their radiative effect accounts for about 5 Watts per square meter in global average. “Were one to eliminate all cirrus clouds, that would immediately counteract a CO2 doubling which adds a ‘warming’ impact of 3.7 Watts per square meter”, says atmospheric physicist Ulrike Lohmann of ETH Zurich. This is what makes cirrus clouds a potential target for geoengineering methods."

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11.07.2016

# New Publications

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Gasparini, Blaž; Lohmann, Ulrike (2016): Why cirrus cloud seeding cannot substantially cool the planet

Gasparini, Blaž; Lohmann, Ulrike (2016): Why cirrus cloud seeding cannot substantially cool the planet. In J. Geophys. Res. Atmos. 121 (9), pp. 4877–4893. DOI 10.1002/2015JD024666.

"The net warming effect of cirrus clouds has driven part of the geoengineering research toward the idea of decreasing their occurrence frequency by seeding them with efficient ice nucleating particles. We study responses of cirrus clouds to simplified global seeding strategies in terms of their radiative fluxes with the help of the ECHAM-HAM general circulation model. Our cirrus scheme takes into account the competition between homogeneous and heterogeneous freezing, preexisting ice crystals, and the full spectrum of updraft velocities."

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27.05.2016

# Media

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Inverse: The Crazy Plan to Zap Clouds with Lasers to Stop Climate Change

Media response to Matthews, M.; et al. (2016). "With the right kind of technology, it's possible."

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27.05.2016

# New Publications

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Matthews, M.; et al. (2016): Laser vaporization of cirrus-like ice particles with secondary ice multiplication

Matthews, M.; Pomel, F.; Wender, C.; Kiselev, A.; Duft, D.; Kasparian, J. et al. (2016): Laser vaporization of cirrus-like ice particles with secondary ice multiplication. In Science Advances 2 (5), e1501912-e1501912. DOI 10.1126/sciadv.1501912.

"We investigate the interaction of ultrashort laser filaments with individual 90-μm ice particles, representative of cirrus particles. The ice particles fragment under laser illumination. By monitoring the evolution of the corresponding ice/vapor system at up to 140,000 frames per second over 30 ms, we conclude that a shockwave vaporization supersaturates the neighboring region relative to ice, allowing the nucleation and growth of new ice particles, supported by laser-induced plasma photochemistry."

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13.04.2016

# New Publications

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Kärcher, B. (2016): The importance of contrail ice formation for mitigating the climate impact of aviation

Kärcher, B. (2016): The importance of contrail ice formation for mitigating the climate impact of aviation. In J. Geophys. Res. Atmos., pp. n/a-n/a. DOI 10.1002/2015JD024696.

CE relevant study on cirrus cloud reduction. "The improved scientific understanding of initial ice formation processes allows atmospheric effects of mitigation options related to contrail cirrus to be investigated in unprecedented detail, especially those associated with the use of alternative aviation fuels. This study will enable a leap forward toward more reliable simulations addressing global climatic effects of contrail-induced cloudiness."

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29.11.2015

# New Publications

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Kristjánsson, Jón Egill; et al. (2015): The hydrological cycle response to cirrus cloud thinning

Kristjánsson, Jón Egill; Muri, Helene; Schmidt, Hauke (2015): The hydrological cycle response to cirrus cloud thinning. In Geophys. Res. Lett., pp. n/a-n/a. DOI: 10.1002/2015GL066795 

"Using a global climate model, we investigate the hydrological cycle response to ‘cirrus cloud thinning (CCT)’, which is a proposed climate engineering technique that seeks to enhance outgoing longwave radiation. Investigations of the ‘fast response’ in experiments with fixed sea surface temperatures reveal that CCT causes a significant enhancement of the latent heat flux and precipitation. This is due to enhanced radiative cooling of the troposphere, which is opposite to the effect of increased CO2 concentrations."

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12.10.2015

# New Publications

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Penner, Joyce E.; et al. (2015): Can cirrus cloud seeding be used for geoengineering?

Penner, Joyce E.; Zhou, Cheng; Liu, Xiaohong (2015): Can cirrus cloud seeding be used for geoengineering? In Geophys. Res. Lett., pp. n/a-n/a. DOI: 10.1002/2015GL065992 

"Here we use an updated version of the Community Atmosphere Model version 5 (CAM5) and re-evaluate whether seeding is a viable mechanism for cooling. We explore different model set-ups (with and without secondary organic aerosols acting as heterogeneous ice nuclei). None of the updated versions of the CAM5 model lead to a significant amount of negative climate forcing, and hence do not lead to cooling."

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