Andrew, tyour remarks and Alan's reply suggest some confusion about two very different backascttering media. the material Aziz describes results from drying a surfactant laden ( hundreds of ppm ) salt water foam produced i literally in vitro in a food blender in which the cells are visible to the naked eye. and stable as styrofoam if kept dry--- both the salt and soluble polymers will redissolve on contact wit sea or rain water.
The microbubbles Caldera and I made and modeled are in contrast roughly a million times smaller the the Aziz foam cells, and, on a volume of contained air basis , about four orders of magnitude more efficient in backscattering solar energy. The question is therefore one of striking an empirical balance between long bubble life and small bubble size. The other point is that because microbubble hydrosls can double water albedo at part per million volume concentrations, which is to say parts per billion of brightened water mass, their impact on water chemistry and surface gas exchange is proportionately small- indeed microscopic. Hydrosols and floating foams can overlap in reflectivity, but are very different physically., especially because ( see figure in linked paper) micron sized bubbles do not rise as fast as the downflow of ordinary convection in the ocean mixed layer. On Friday, January 13, 2017 at 12:46:28 PM UTC-5, Andrew Lockley wrote: > > To summarise a short side thread between Alan and myself: > > Foams would potentially have a broad range of impacts, principally by > limiting gas exchange, eg: > * lower CO2 uptake (leading to higher atmos CO2,esp locally) > * reductions in NPP > * reduced DMS output (esp if bubbles don't burst), etc. > > Good opportunity for further study. > > Additionally, this reminds me a bit of the "plastic sheets in deserts" > idea, which turned out to be problematic > > A > > On 13 January 2017 at 13:15, Alan Robock <[email protected] > <javascript:>> wrote: > > 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: [email protected] > <javascript:> > > 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 > > > > -- > > You received this message because you are subscribed to the Google > Groups > > "geoengineering" group. > > To unsubscribe from this group and stop receiving emails from it, send > an > > email to [email protected] <javascript:>. > > To post to this group, send email to [email protected] > <javascript:>. > > Visit this group at https://groups.google.com/group/geoengineering. > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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