Gabriel, Corey J., Alan Robock, Lili Xia, Brian Zambri, and Ben Kravitz,
2017: The G4Foam experiment: Global climate impacts of regional ocean
albedo modification. /Atmos. Chem. Phys.,/ *17*, 595-613,
doi:10.5194/acp-17-595-2017.
http://www.atmos-chem-phys.net/17/595/2017/
*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
+6 W m^−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. 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.
--
Alan
Alan Robock, Distinguished Professor
Editor, Reviews of Geophysics
Department of Environmental Sciences Phone: +1-848-932-5751
Rutgers University Fax: +1-732-932-8644
14 College Farm Road E-mail: rob...@envsci.rutgers.edu
New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock
☮ http://twitter.com/AlanRobock
Watch my 18 min TEDx talk at http://www.youtube.com/watch?v=qsrEk1oZ-54
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