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Solar geoengineering may not prevent strong warming from direct effects of CO₂ on stratocumulus cloud cover

Schneider, Tapio and Kaul, Colleen M. and Pressel, Kyle G. (2020) Solar geoengineering may not prevent strong warming from direct effects of CO₂ on stratocumulus cloud cover. Proceedings of the National Academy of Sciences of the United States of America, 117 (48). pp. 30179-30185. ISSN 0027-8424. PMCID PMC7720182. doi:10.1073/pnas.2003730117.

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Discussions of countering global warming with solar geoengineering assume that warming owing to rising greenhouse-gas concentrations can be compensated by artificially reducing the amount of sunlight Earth absorbs. However, solar geoengineering may not be fail-safe to prevent global warming because CO₂ can directly affect cloud cover: It reduces cloud cover by modulating the longwave radiative cooling within the atmosphere. This effect is not mitigated by solar geoengineering. Here, we use idealized high-resolution simulations of clouds to show that, even under a sustained solar geoengineering scenario with initially only modest warming, subtropical stratocumulus clouds gradually thin and may eventually break up into scattered cumulus clouds, at concentrations exceeding 1,700 parts per million (ppm). Because stratocumulus clouds cover large swaths of subtropical oceans and cool Earth by reflecting incident sunlight, their loss would trigger strong (about 5 K) global warming. Thus, the results highlight that, at least in this extreme and idealized scenario, solar geoengineering may not suffice to counter greenhouse-gas-driven global warming.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemCode CentralArticle
Schneider, Tapio0000-0001-5687-2287
Kaul, Colleen M.0000-0002-4462-0987
Pressel, Kyle G.0000-0002-4538-3055
Alternate Title:Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover
Additional Information:© 2020 National Academy of Sciences. Published under the PNAS license. Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved October 7, 2020 (received for review February 27, 2020). PNAS first published November 16, 2020. We thank Clare Singer for assistance with data processing. This research was made possible by the generosity of Eric and Wendy Schmidt by recommendation of the Schmidt Futures program, by Earthrise Alliance, Mountain Philanthropies, the Paul G. Allen Family Foundation, Charles Trimble, and NSF Grant AGS-1835860. The computations were performed on the California Institute of Technology’s (Caltech’s) High Performance Cluster, which is partially supported by a grant from the Gordon and Betty Moore Foundation. Part of this research was carried out at the Jet Propulsion Laboratory, Caltech, under a contract with NASA. C.M.K. and K.G.P. were at Caltech while carrying out this research. Data Availability: All data needed to evaluate the conclusions in the paper are present in the paper. The source code for the simulations is available at Author contributions: T.S. and C.M.K. designed research; T.S., C.M.K., and K.G.P. performed research; T.S., C.M.K., and K.G.P. analyzed data; and T.S. wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission.
Funding AgencyGrant Number
Eric and Wendy SchmidtUNSPECIFIED
Schmidt Futures ProgramUNSPECIFIED
Earthrise AllianceUNSPECIFIED
Mountain PhilanthropiesUNSPECIFIED
Paul G. Allen Family FoundationUNSPECIFIED
Charles TrimbleUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:global warming; geoengineering; cloud feedback
Issue or Number:48
PubMed Central ID:PMC7720182
Record Number:CaltechAUTHORS:20201117-081328944
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Official Citation:Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover Tapio Schneider, Colleen M. Kaul, Kyle G. Pressel Proceedings of the National Academy of Sciences Dec 2020, 117 (48) 30179-30185; DOI: 10.1073/pnas.2003730117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106693
Deposited By: Tony Diaz
Deposited On:17 Nov 2020 17:47
Last Modified:09 Feb 2022 20:16

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