Dear Andrew
Thank you for your comments and for bringing our paper to the attention of the group. To answer your queries. 1. Our assumptions are based on the idea that if you inject at sensible locations, atmospheric currents will do most of the distribution for you, and by careful choice of location you can increase the likelihood that the particles will remain in the stratosphere for as long as possible. If you inject into the lower stratosphere at sub-tropical latitudes (10-20 deg, North or South) the Brewer Dobson circulation will naturally tend to take the particles up into the upper stratosphere and distribute them in latitude. If they are injected in the temperate zone (40-50 deg, N or S) the B-D circulation will keep them close to the tropopause, making it more likely that the particles will be folded into the troposphere, from which they will be washed out fairly quickly. Distribution in longitude will occur naturally because of the basic west to east airflow. 2. Aircraft and balloons both exist, but neither is optimised for aerosol delivery. You can get fighter jets that can fly at 20 km, but their payload is small and there would need to be extensive development to produce aircraft that could disperse 10 million tonnes of particles per annum at a reasonable cost. So a comparable development time for aircraft systems is not unreasonable. 3. Our figure for artillery systems is the number of barrels needed; I’m not sure I understand your distinction between the number of guns and the number of barrels. There has been very little work on the development of the large calibre weapons that would be needed since WW1. The construction of the barrels required very large capital investment and their construction was complex. They contained several layers of tubes, some being shrunk fit onto the inner layers and others being wire-wound under tension. Fabrication was complex and time-consuming. Gun wear was a major problem; the guns typically had a lifetime of about 300 firings before the hot gases eroded the linings, which meant a loss of accuracy and, more importantly from our point of view, a loss of pressure that reduced the range. So it is true that artillery has existed in the past, but a geoengineering application would require the building of new production facilities. The number of barrels needed is based on delivering 10 million tonnes of particles, and estimating the proportion of the shell weight that could be used for the product. 4. and 5. We accept that our cost and time figures are estimates, but to ascribe uncertainties would imply that we had more highly refined designs than we do. These figures are essentially ball-park estimates. However, we believe it is not unreasonable to point out, when considering the CFRP towers, for example, that they would require some 5000 years worth of carbon fibre production at the current rate. It would be pointless to define a figure for how long it would take to ramp up production to the required level, and even more pointless to define an uncertainty for that figure. Regards Chris Burgoyne On Sunday, August 12, 2012 2:23:22 AM UTC+1, andrewjlockley wrote: > > Chris, > > I'm sending a few thoughts on your recent paper to you and to the GE > list, as I'm interested to hear opinions on your (open access) paper > http://rsta.royalsocietypublishing.org/content/370/1974/4263.full > > It's always good to hear about the detailed engineering of delivery > systems, but from my initial reading of the work, there are a number > of issues which strike me as immediate points of concern (in no > particular order). > > 1) Use of possibly outdated models of injection latitudes and > longitudes. If I understand correctly, you suggest a longitude > dispersed system, and a latitude-concentrated one. This appears to > contradict other authors' arguments (e.g. Heckendorn, 2009; MacCracken > 2012) which seemingly suggest a regime broadly opposite to this > paper's. > 2) It seems strange to offer development times for aircraft the same > as for balloons, when one exists and the other doesn't. Even more > surprising when the aircraft currently exist in numbers which may be > sufficient to approximately do the job (as Alvia discussed a while ago > on this list). You also suggest that naval guns will take twice as > long to develop as balloons. Surely the existence of these guns, and > the production of similar guns in WWII, suggests a shorter timescale > than you suggest? > 3) You reference Blackstock (2009), which from memory suggest a far > lower number of guns. Why are your numbers so much higher? Are you > counting barrels or guns? > 4) You seem to offer cost comparisons for systems that have perhaps > not been optimized from an engineering perspective. Surely costs can > sometimes hinge on issues identifiable only with very detailed study, > similar to the one you set out for balloons. I'm left wondering > whether any potential difference in the reliability of the various > estimates could have been further stressed. > 5) You offer very specific development timescales for long-term > technology development projects. I think suggesting a 50 year > development horizon for a technology is maybe a bridge too far. > Perhaps this is hair-splitting, but I'd prefer to see 'can't be > estimated' or 'beyond the horizon', rather than a specific-sounding > but rather speculative '50 years'. > > It's good to have some hard engineering to debate. It would be great > to hear your views, and others', on this interesting paper. Hopefully > you'll be able to demolish a lot of my points, because it would be > great to have such a clear steer on the costs as your paper seems to > suggest. > > I look forward to your response. > > A > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To view this discussion on the web visit https://groups.google.com/d/msg/geoengineering/-/B_yF3LTk8Z8J. 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.
