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On Apr 16, 2011, at 8:37 PM, Mike MacCracken <[email protected]> wrote: > Hi Andrew—On your objection about the biology of bright water, I’d like to > better understand your concern. How do you think the effect of the bubbles on > a clear day would compare to the effects of a thick cloud cover? Countering a > pretty significant increase in CO2 warming would require, if it could be > done, only a several percent increase in cloud cover [our roughly 50% cloud > cover contributes to reflection of 25% of solar radiation; if what we need to > do is get a 1.8% reduction in the solar constant where we have a 30% albedo, > which is the same as reducing absorbed radiation by about 4 W/m2, then what > we need is the equivalent of an increase in cloud cover from 50% to a bit > less than 53%, or something like that]. Are you suggesting that an increase > in cloud cover from 50 to 53% would have a devastating effect on marine > ecosystems? > > Let me try the calculation another rough, idealized way: If the 50% of clear > sky is responsible for increasing the global albedo from 25% to 30%, then, > allowing for say 10% atmospheric absorption of solar radiation going each way > (forget compounding effect), and two-thirds of this takes place over the 1/3 > of area that is land and ice (so average albedo of land is 4 times that of > ocean), then average ocean albedo is 6%. To then increase the global average > outgoing solar radiation, I calculate that the average ocean albedo has to go > from about 6% to a bit over 10%, which would reduce the available radiation > in the water from 94% to 90% of incoming solar radiation (accounting only for > the effect in clear sky region). > > While I realize that BrightWater envisions making the albedo a good bit > higher, this would mean that I would need to do less elsewhere. Given there > are large areas of the ocean where there is little biological activity due to > low nutrient levels, perhaps I could concentrate the water brightening in > those areas. So, let’s hypothesize that I aim to raise the ocean albedo from > 6% to 15% over the half of the ocean area with the lowest biological activity > (and I think the low biological activity areas are larger than the marine > stratus areas so the pattern of flux change would be less sharp than for the > Salter-Latham approach that can get a global counter-balancing. With bubble > lives limited, unlikely it would be a problem of bubbles drifting into > biologically active areas. > > Now, let’s think about combining the BrightWater and the Salter-Latham > approaches, giving us more even coverage—with the boats shooting up sea salt > sprays when below marine stratus and injecting bubbles when in clear skies, > so maybe half of the albedo effect proposed is needed by each approach. So, > maybe the amount of solar reaching the ocean goes down a couple of percent. > Are you really suggesting that this would devastate marine ecosystems—and > indeed be worse than reflecting a similar amount of radiation using a global > stratospheric aerosol layer? It is true that the combined approaches would be > concentrating their influence over the oceans as opposed to the global > stratospheric layer that spreads the effect over the globe, but the sulfate > aerosols are such inefficient backscatterers that one ends up with a quite > high proportion of forward scattered radiation. > > I am not saying there will not be effects—we’ll need a good bit of research > to get a sense of things—but, assuming that I have things properly estimated > (and I do agree accounting for Sun angle might well require another > adjustment), I do not see how one can rule out the Brightwater approach (on > its own or coupled with Salter-Latham) thinking that the impact on marine > ecosystems would be large and could not be minimized by choosing carefully > where one used the approach. > > Best, Mike MacCracken > > ******* > > > > So, given these > > > On 4/16/11 9:41 PM, "Andrew Lockley" <[email protected]> wrote: > > 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. -- 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.
