Abstract
Because 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 mW 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.
Highlights
The Earth has been described as “a pale blue dot,” its albedo is low because the deep water covering two-thirds of its surface is as dark as a blacktop parking lot
As the hydrosphere stores most of the energy trapped by greenhouse gases, increasing surface albedo to reduce heat oceanic uptake is a potentially important way to counterbalance human-induced warming from landscape darkening and emission of black carbon and greenhouse gases
This paper considers issues relating to the creation and persistence of microbubbles and the potential for using reflective microbubble dispersions, to manage solar radiation uptake by locally brightening some of the > 300 million square kilometers of fresh and salt water that cover most of the Earth
Summary
The Earth has been described as “a pale blue dot,” its albedo is low because the deep water covering two-thirds of its surface is as dark as a blacktop parking lot. We calculate the scale of the injections that would be required for two potential applications of microbubble injection, one focused on reducing evaporation from reservoirs, cooling ponds and other water bodies as a step toward conserving water and improving energy efficiency, and the second on increasing ocean surface albedo in order to reduce planetary absorption of solar radiation. With 25% coverage by marine cloud cover, the hydrosols increased the global, top-of-the-atmosphere albedo by ~0.175 over the 70% of the world covered with water This increases the overall planetary albedo by 0.05, times the ratio of sea to land area, producing a global albedo gain of ~0.031, which in the model runs reduced global average surface temperature by ~ 2.7 K, an overall cooling greater than the warming induced by doubling the baseline CO2 concentration of 390 ppmv to 780 ppmv. Raising the albedo of rivers might be used to mitigate power plant thermal pollution, and brightening cooling ponds to reduce solar heating may likewise reduce power plant CO2 emission by increasing thermodynamic efficiency
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
