The G4Foam Experiment: Global climate impacts of regional ocean albedo modification

doi:10.5194/acp-17-595-2017

Title: The G4Foam Experiment: Global climate impacts of regional ocean albedo modification

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Abstract

Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150%) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6Wm ^-2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0,more »« less

Authors:

^[1];

^[1]; Xia, Lili ^[1];

^[1];

^[2]

Rutgers Univ., New Brunswick, NJ (United States)
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Publication Date:: Thu Jan 12 00:00:00 EST 2017

Research Org.:: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:: USDOE

OSTI Identifier:: 1349159

Report Number(s):: PNNL-SA-122915
Journal ID: ISSN 1680-7324

Grant/Contract Number:: AC05-76RL01830

Resource Type:: Journal Article: Accepted Manuscript

Journal Name:: Atmospheric Chemistry and Physics (Online)

Additional Journal Information:: Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 17; Journal Issue: 1; Journal ID: ISSN 1680-7324

Publisher:: European Geosciences Union

Country of Publication:: United States

Language:: English

Subject:: 54 ENVIRONMENTAL SCIENCES

Citation Formats


                    Gabriel, Corey J., Robock, Alan, Xia, Lili, Zambri, Brian, and Kravitz, Ben. The G4Foam Experiment: Global climate impacts of regional ocean albedo modification.  United States: N. p., 2017. 
        Web.  doi:10.5194/acp-17-595-2017.

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                    Gabriel, Corey J., Robock, Alan, Xia, Lili, Zambri, Brian, & Kravitz, Ben. The G4Foam Experiment: Global climate impacts of regional ocean albedo modification.  United States.  doi:10.5194/acp-17-595-2017.

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                    Gabriel, Corey J., Robock, Alan, Xia, Lili, Zambri, Brian, and Kravitz, Ben. Thu .  
        "The G4Foam Experiment: Global climate impacts of regional ocean albedo modification".  United States.  
        doi:10.5194/acp-17-595-2017.  https://www.osti.gov/servlets/purl/1349159.

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@article{osti_1349159,

  title        = {The G4Foam Experiment: Global climate impacts of regional ocean albedo modification},

  author       = {Gabriel, Corey J. and Robock, Alan and Xia, Lili and Zambri, Brian and Kravitz, Ben},

  abstractNote = {Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150%) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6Wm-2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30°N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June–July–August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of -1.5 W m-2 is amplified through a series of positive cloud feedbacks, in which more shortwave radiation is reflected. Finally, the precipitation response is primarily the result of the intensification of the southern Hadley cell, as its mean position migrates northward and away from the Equator in response to the asymmetric cooling.},

  doi          = {10.5194/acp-17-595-2017},

  journal      = {Atmospheric Chemistry and Physics (Online)},

  number       = 1,

  volume       = 17,

  place        = {United States},

  year         = {Thu Jan 12 00:00:00 EST 2017},

  month        = {Thu Jan 12 00:00:00 EST 2017}

}

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DOI: 10.5194/acp-17-595-2017

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