As I’ve advocated a number of times in the past, I strongly believe that a formal global solicitation needs to be performed to help identify as many additional/new geoengineering options as possible. This could hopefully engage a wide participation from those outside of this group who otherwise wouldn't be able to share their insights. Since this is a global problem I believe it requires reaching outward to the global science and engineering community for potential solutions, and that not doing this is taking a risk we cannot afford. The following helps to explain why new concepts are crucially-needed.
“Can SRM save our bacon?” is question Andrew Lockley posed to the group recently. It’s a great question that deserves an honest answer. Based on what is known today, one answer could be “We simply don’t know yet- which is exactly why further research is so urgently needed!” However, a more honest answer would be, “We don’t yet have a solution. In fact, the solutions that we thought would be most likely to work are being shown to be less likely after closer consideration.” In other words, it seems that the confidence being placed on existing schemes is often over-stated. To support this, all one has to do is consider the real challenges with SO2 and MCB, the SRM solutions consistently shown in various reports and news articles as being most feasible to date. In fact, a comment from Eugene on the original post is what it seems most have concluded- “I would bet on upper atmosphere SO2 additions for cooling, since for sure it works and is relatively easy to implement” “FOR SURE IT WORKS”, and “easy to implement”. These are simply not true. In truth, we don’t know if SO2 injections can work effectively or what the side-effects would be for ozone or acid rain, and there is no proven way to deliver or disburse it properly. In David Keith’s recent paper ‘Photophoretic Levitation of Engineered Aerosols for Geoengineering’, he explains some of the limitations of SO2 including: “when aerosols are generated by continuous injection of SO2 the resulting size distribution tends to be substantially larger than optimal because most of the added sulfur is deposited on existing particles. This substantially limits the radiative forcing produced by large sulfur injections and can make it difficult to produce a radiative forcing sufficient to offset the radiative effect of a CO2 doubling.” So it appears that a closer look into SO2 is bringing its feasibility into serious question. I had read that direct injection of sulfuric acid is being considered as a replacement, but that likely has insurmountable problems with acid rain and ozone depletion. Now Dr. Keith is proposing photophoretic levitation, which seems highly theoretical. I hope it works, but it seems like much would be involved in determining true feasibility. In terms of marine cloud brightening (MCB), I’m afraid that some of the serious challenges with its feasibility may have been overlooked or have been possibly underappreciated. One of these is the issue of particle distribution (ironically much like SO2). In ‘H. Korhonen et al.: Enhancement of marine cloud albedo via controlled sea spray injections’, the conclusion is that even assuming the system sprays the “right” CCN’s, “We find that the wind speed dependence of the spray emissions, atmospheric transport and particle loss via deposition and precipitation scavenging lead to a spatially highly inhomogeneous CDNC. Therefore, generating nearly uniform cloud drop fields over large regions of the oceans, as has been assumed in earlier climate model studies, would be extremely challenging.” And in terms of the climate model results that are often referenced, “So far the effectiveness of sea spray geoengineering has been studied only with global scale models. However, the spatial resolution in these models is poor, so they cannot resolve the aerosol emissions, transport and activation on a scale of individual stratocumulus cloud cell. Because of this limitation, there is enormous scope for studying this problem using large eddy cloud resolving models where the issues related to the spreading and entrainment of the spray into the clouds, as well as cloud microphysics, can be studied in much more detail.” So if the Korhonen analysis is correct, the particle distribution for MCB would be “highly inhomogeneous”, greatly limiting the concept’s effectiveness vs an assumption of even particle distribution. Also, the spatial resolution of existing climate models is poor, so the conclusions drawn from these models should be treated with restraint. Finally, I hope I can be proven wrong on these MCB concerns, but they need to be seriously considered: The fundamental premise of the concept is for wind power from Flettner rotors to move the vessels fast enough so that underwater turbines (3m in diameter?) will spin to power both the spray system and Flettner rotors themselves. From an engineering-judgement standpoint (or just a typical sailor's experience), the turbines would likely create far too much drag to enable the vessels to exceed a slow forward crawl. Therefore the turbines wouldn't spin fast enough to create needed power for the spray system (a catch-22 problem). This could be determined on fairly short order by testing a ¼ scale working model. Other potential failure modes would include: 1. Developing a spray system that can create an adequate flow of ultra- fine salt particles (I realize that this is under development but don’t know the status) 2. Somehow ensuring the spray system doesn’t get clogged, even after weeks and months of drawing in raw sea water potentially with kelp, plastic debris etc. 3. Designing the vessels to withstand rough seas, large swells, and the possibility of being hit by large rogue waves. The current "artists conception" of the vessel design would likely be much too fragile for this. 4. Designing the vessels to prevent capsizing from high winds. Unlike sailboats, where sail size can be reduced to be very small during storms, the Flettner rotors will remain fully exposed during the strongest winds. This would create a tall healing moment, bringing their ability to avoid capsizing into serious question. This could be shown by testing a scaled down model in a wave tank. I hope questions like these can be answered (and some may already have), but regardless, research that’s been performed to date seems to indicate there’s a significant risk that SO2 injection and MCB may not work or won’t work effectively enough (especially in light of rising CO2 and methane levels). So to help ensure adequate mitigation capability exists, additional/new SRM options are urgently needed! -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. 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