Russell, My comments below relate to your 'brightwater' proposal. Out of courtesy, I've removed the thread - so I'm not re-posting your comments without consent.
If bubble residency times are high, induced densities can be low. If residency times are low, you'll have to greatly increase local concentrations to cause a globally significant, persistent effect. I quote: "Seitz admitted that scaling it to cover an entire ocean would be technically difficult, not because of the energy<http://www.physorg.com/news189059955.html> requirement, which he said would be equivalent to about 1000 windmills, but because of the fact that the bubbles may not last long enough to effectively spread over large areas." The risk is, therefore, that very much greater local effects may be induced than is desirable, in order to create the necessary global cover. Not only might this affect primary productivity, but also more subtle biological events such as migration, navigation, feeding and breeding. Bioluminescence is likely to be a notable casualty. 'Hot spots' (or should that be cold spots) of concentrated treatment are therefore likely best avoided. The hot-spot effect is not unlike covering a forest in a dense blanket of fog, when the local weather never naturally causes such an effect. I would expect the ecosystem impacts to be very significant, or even catastrophic, especially if the treatment were persistent. Your video and images show the bubble plumes spreading laterally and vertically, rather like slicks. They also show a high optical density, far higher than I would regard as desirable in open ecosystems. Were the bubbles' residence time longer, the local concentrations could be relatively reduced, thus reducing the localised optical impact. Churning the bubbled water into untreated volumes would be desirable, and a towed streamer design with many small bubblers would be beneficial in this regard. Oil survey vessels use such a system, which I understand relies on hydrodynamic forces to distribute hydrophones over a wide track. The behaviour of microbubbles in high concentrations may be entirely different to that in lower concentrations - not least because of the limitations of locally available substances to dwell on the bubble surfaces. I think it would be extremely brave to make detailed predictions when such a large range of complex factors can affect the behaviour of the bubbles (to such an extent that the idea could easily be rendered impractical). Not only are optical effects a consideration, but you also need to consider the ecosystem impact of the surface physics and chemistry. If the microbubbles affect the movement or cycling of detritus and microorganisms, the ecosystem impact could be severe. I've also briefly looked over the maths you're proposing, and I'm not fully reassured by the calculations. I haven't checked the detail of the model you're using, but I'm concerned by the assertion that "The backscattering coefficient (bb) of hydrosols of micron-sized bubbles depends on the fraction of incident light that is intercepted and returned between 90º and 180º." - as, at high densities, there's a significant chance of rescattering of once-reflected light. I can't see how this has been accounted for in your model. Of further serious concern is your proposal to create 'icecaps' in the tropics. Such a localised cooling has the potential to strongly affect ocean overturning circulation, and could possibly induce an anoxic event. I don't think your modelling is robust enough to eliminate this possibility. Furthermore, by concentrating cooling in waterbodies, an intuitive analysis suggests that a reduction in evaporation will result. This has potentially major implications for terrestrial ecosystems and agriculture. Specific research in this regard is merited. I'm sure many of my criticisms have already been considered and discounted, so perhaps you can fill me in? Please don't get me wrong - I like your idea, and I want it to work. It's the most exciting new geoeng idea for a long time. But we need to be honest about the practical limitations of our predictive powers here, and the range of factors which need further study before we can start to hang our hats on these proposals. We also need to make sure that we don't unwittingly advocate a technique which could possibly cause a local or global environmental disaster. A -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
