Andy Sorry but I do not find this an effective way to debate these topics, particularly in this case when I am responding to a summary that does not accurately reflect what I said. I would rather put the energy into writing a paper or discussing these topics in smaller groups. I would be very happy to chat more over the next couple days.
I do think there is some utility in this blog but I do not now look at it routinely. It may be that I am just old-fashioned, but I find that the 24-hour blogging culture tends to overemphasize emphasize spurious disagreement fueled by jumbled factoids in a way that makes it hard to identify substantive disagreements about facts and values. This is particularly true in a single-threaded format like this. But this may simply be my old-fashioned taste: many folks do contribute smart, relevant and thoughtful posts and are clearly having a lot of fun doing it. Cheers, David From: Andrew Lockley [mailto:[email protected]] Sent: Tuesday, August 6, 2013 10:38 AM To: Keith, David; geoengineering Subject: Response to D Keith lecture at Harvard David Below are a few questions and comments from your interesting lecture today. I'm copying to the Google group to invite wider comment on the important issues your raised. It would be great to hear any comments you have, if you are able to respond. Thanks A Ramp up You considered a linear and shallow ramp up of SRM intervention. This perhaps works particularly well for a linear climate response. Should we not instead be looking at more rapid temperature reductions, to reduce risks of crossing tipping points (Greenland, permafrost, etc)? Health impacts You assume quantifiable health impacts from particulate rain out. However, the aerosol rain out would be well distributed, with much occurring in depopulated areas. Are the health impacts of distributed particulates comparable to those from concentrated loading patterns (eg focussed on harbours and cities)? I assume the calculated risks were derived from these concentrated loading patterns. Will the health risks be reduced because rain out will likely mix with, or condensate, raindrops - hence diluting them to destruction. Delivery mechanism Previously you considered homogeneous condensation of H2SO4, and today you discussed in-situ high-altitude combustion of solid S to release SO2. In response to my verbal question, you stated that particle size distribution issues only kick in around 'a few' MT. However, having a constant delivery mechanism reduces the risk of 'nasty surprises' on switching, despite increased lofting costs in earlier stages. Is there an argument for 'starting as you mean to carry on'? Distribution pattern Particularly with high aerosol loads, there may be advantages to a temporally bound injection regime (when using precursor gases instead of direct particulate injection). This is due to the benefit of constrained particle growth. (See reference below) Does a potential requirement for a temporally-concentrated injection regime mean that the use of aircraft becomes problematic from a cost point of view? EG to do all the injection in a month per year, you'd likely need up to 12x as many aircraft. You also considered the spatial distribution pattern. A 30N to 30S injection regime may take advantage of the Brewer Dobson circulation. However, is there not a risk of particle size growth and rain out. See Heckendorn et al ( http://m.iopscience.iop.org/1748-9326/4/4/045108 ), who discussed particle growth, and I recall this paper may also have discussed spatial (vertical and latitude) and temporal distribution patterns, and advocated a more spatially varied injection regime. Smart particles You touched on the concept of 'smart particles'. Is there a risk that these can be weaponised to make a solar concentrator, capable of burning buildings on the ground? -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out.
