Hi Andrew‹On your objection about the biology of bright water, I¹d 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, let¹s 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, let¹s 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‹we¹ll 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.
