Hi Mike and Andrew, This is an interesting discussion. What about *direct* cooling of the ESAS (East Siberian Arctic Shelf - which includes the East Siberian Sea), to try to reduce methane emissions? We have to consider all possible methods of reducing emissions here, since there is enough potential methane to multiply global warming by many times (at least 40 times from only 10% of potential methane by my calculation). There are signs that recent unprecedented warming of the sea has put the under-water permafrost in a critical condition, poised to trigger abrupt climate change at any moment [1]. We cannot afford to wait two or three years for geoengineering - the risk from this methane is too great.
BTW, Shakhova [1] describes the positive feedback as likely strong [2], whereas Wikipedia [3] describes it as weak [4]. I think the Wikipedia article needs updating! Best wishes, John [1] http://adsabs.harvard.edu/abs/2010EGUGA..1213027S [2] *Sustained release of methane to the atmosphere from thawing Arctic permafrost likely is a strong positive feedback to climate warming* [3] http://en.wikipedia.org/wiki/Arctic_methane_release [4] *This results in a weak positive feedback<http://en.wikipedia.org/wiki/Positive_feedback>effect, as methane <http://en.wikipedia.org/wiki/Methane> is itself a greenhouse gas<http://en.wikipedia.org/wiki/Greenhouse_gas>. The feedback is weak, however, because methane is well-mixed globally: the local release leads to a warming spread over the whole globe.* --- On Sun, Apr 17, 2011 at 3:37 AM, 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.
