With the report this week that Bill Gates has disbursed the first tranche ($300,000) of an estimated $5 million he’s allocated to climate geoengineering to a project that seeks to enhance cloud albedo through sea spray injections, the focus is front and center on this potential geoengineering scheme. Several researchers, most prominently John Latham and Stephen Salter, have hypothesized that emitting sea water droplets into maritime clouds will result in a fraction of such particles be transported to cloud altitude, where they will act as cloud condensation nuclei, increasing cloud droplet number concentration and increasing cloud albedo, thus exerting a negative forcing effect large enough to compensate for positive forcing expected to be associated with a doubling of atmospheric carbon dioxide concentrations. Salter has proposed deploying remote-controlled, wind-powered vessels capable of generating (via turbines dragged through the water) the electricity required to create a mist of seawater and loft it 1,000 meters into the atmosphere.
However, a recent study in the journal Atmospheric, Chemistry, and Physics (open access) demonstrates the technological challenges that lie ahead with this solar radiation management approach, H. Korhonen, et al., Enhancement of Marine Cloud Albedo via Controlled Sea Spray Injections: A Global Model Study of the Influence of Emission Rates, Microphysics and Transport, 10 Atmospheric, Chemistry & Physics 735-761 (2010). The study used a global aerosol model to simulate the potential impacts of artificial sea spray injection on cloud albedo.
The key findings from the study are as follows:
- It would prove “extremely challenging” to spray particles homogeneously without deploying a very large number of vessels; inhomogenous spraying would produce localized high concentrations of sea spray particles and cloud drops, leading to a different microphysical evolution that wouldn’t substantially increase cloud albedo. Many factors could thwart homogeneous dispersion, including wind speed, atmospheric transport and particle loss as a consequence of deposition and precipitation scavenging;
- In the study’s simulation, there is a relatively small increase of cloud drop number concentration, and even a decrease in some areas;
- The spatial resolution of the global scale models that have been used to study the effectiveness of sea spray engineering to date is poor; thus they are incapable of resolving criterial factors, including aerosol emissions, transport and activation activation on the scale of individual stratocumulus clouds. This dictates further study, including the use of large eddy cloud resolving models.
Geoengineering schemes clearly remain in their infancy, and as this study indicates, one would rely on them as a silver bullet to address climate change at the Earth’s peril.
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