Bright water: hydrosols, water conservation and climate change

Abstract

The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters. AbstractBecause air-water and water-air interfaces are equally refractive, cloud droplets and microbubbles dispersed in bodies of water reflect sunlight in much the same way. The lifetime of sunlight-reflecting microbubbles, and hence the scale on which they may be applied, depends on Stokes Law and the influence of ambient or added surfactants. Small bubbles backscatter light more efficiently than large ones, opening the possibility of using highly dilute micron-radius hydrosols to substantially brighten surface waters. Such microbubbles can noticeably increase water surface reflectivity, even at volume fractions of parts per million and such loadings can be created at an energy cost as low as J m -2 to initiate and milliwatts m -2 to sustain. Increasing water albedo in this way can reduce solar energy absorption by as much as 100 W m -2 , potentially reducing equilibrium temperatures of standing water bodies by several Kelvins. While aerosols injected into the stratosphere tend to alter climate globally, hydrosols can be used to modulate surface albedo, locally and reversibly, without risk of degrading the ozone layer or altering the color of the sky. The low energy cost of microbubbles suggests a new approach to solar radiation management in water conservation and geoengineering: Don't dim the Sun; Brighten the water.

Climate response to imposed solar radiation reductions in high latitudes

“…First, the tropospheric albedo could be increased by re-creating the tropospheric haze layer present during the late 20th century as a result of the sulfur dioxide emissions from power plants in Europe, Russia, and North America; while it would likely best be done by other means, such an aerosol increment would be expected to reduce solar radiation reaching the surface, as may have been happening since at least the 1980s (Valero et al, 1984). Second, surface albedo could be increased by injecting microbubbles (Seitz, 2011) into open water areas such as leads; this could be used to reduce absorption of solar radiation, especially in limited areas that might constrain bubble spread.…”

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

“…The broad idea of microbubble deployment as a form of SRM is explored by Seitz (2010). Here we only examine the potential benefits and risks of such a scheme, and do not advocate deployment of any form of geoengineering regardless of its present feasibility.…”

“…Here we only examine the potential benefits and risks of such a scheme, and do not advocate deployment of any form of geoengineering regardless of its present feasibility. Robock (2011) has cautioned against the potential implications of ocean albedo modification as presented by Seitz (2010).…”

L'ingénierie climatique face au réchauffement climatique : solution d'avenir ou fuite en avant ?

“…En principe, on pourrait augmenter l'albédo de la planète en injectant de petites particules dans la stratosphère (Crutzen, 2006 ;Keith 2010), en ensemençant les nuages bas au-dessus des océans (Latham, 1990 ;Salter et al, 2008) avec des particules de sels marins, ou encore en augmentant la réflectivité des surfaces continentales (Hamwey, 2007 ;Akbari et al, 2009 ;Ridgwell et al, 2009 ;Irvine et al, 2011) ou des océans (Evans et al, 2010 ;Seitz, 2011), comme illustré sur la figure 3. Le degré de maturité de ces projets d'ingénierie climatique est très variable.…”

“…Pour finir notre tour d'horizon des techniques qui ont été proposées, il faut nous tourner de nouveau vers l'océan. Rendre l'océan plus brillant, comme l'ont suggéré Evans et al (2010) ou Seitz (2011), offre un potentiel de refroidissement considé-rable, de par la surface de l'océan global et sa faible réflectivité naturelle, mais les moyens d'y parvenir semblent a priori irréalistes (fabrication de mousse à la surface de l'océan par injection d'air sous la surface ou par largage de grandes quantités de particules ou de bouées flottantes réfléchis-santes dans l'océan).…”