Dear Colleagues, Three posts are copied below from a thread from the recent NOAC meeting (that includes many more posts) that I've been asked to share to other "community" lists.
Best, Ron Dear Colleagues, My mistake in chat: Doug MacMartin was not a co-author, but did reply to John N on this issue. As this came up in today's NOAC meeting as well I'm taking the liberty of copying Doug's response below (and cc'ing him in the event that he is not on the NOAC list). Best, Ron Daniele Visioni wrote a paper on methane under SAI in 2017; https://acp.copernicus.org/articles/17/11209/2017/ Conclusions are a little hard to interpret from that paper, but yes, it’s understood that methane lifetime would go up relative to not injecting (not just from UV photolysis); that would then require more injection to compensate for the increased RF from CH4, Dan’s estimate when I’ve asked him is that that increase is of order 10% (so not negligible, but certainly not a “major” problem). I’d put this in the category of things that need more research to better quantify. Re UV, don’t forget that Sasha’s study was with GLENS, so with 4C of cooling from SAI (i.e., in a world in which we’d probably all be extinct if we didn’t have SAI). So a 1C cooling (which would still be a pretty big program) would be roughly ¼ of the UV impact. Also, given that strat ozone has a “super-recovery” under climate change, reductions in UV relative to that future world are still potentially increases relative to today (see, e.g., fig 3 in https://www.pnas.org/doi/10.1073/pnas.2202230119, which doesn’t have the UV plotted, but does have high latitude SH ozone (the SH being where the effect is larger than the NH); the scenarios that cool by ~1C have ozone levels in 2070 that are still higher than today. doug Dear Michael et al., I agree that no government yet has (to my knowledge) authorized the piloting and testing of initial SAI or any other form of direct climate cooling with potential global impact. The conventional wisdom appears to be that the risks are too great right now and that further research is necessary. However, I've yet to see a study that these "great risks" of initial piloting of deployment more than offset the clear and evident risks of not implementing global cooling as soon as possible, that rapid global cooling could mitigate. As far as i can tell current (mostly modeling) assessments of potential SAI risks of Ozone depletion, Monsoon interference, and increased Methane are all mixed and relatively moderate compared to the continued run toward the cliff that pathway that we are now on with a mitigation and draw down only approach. I think Doug MacMartin's post (that I copied earlier in this thread) covers some of the most recent research on potential *Methane depletion*. On *Monsoon interference*, as I recall (based on the podcast discussion of it here: https://podcasts.apple.com/us/podcast/single-hemisphere-srm-monsoons-bala/id1529459393?i=1000613339787) that this 2023 paper by Bala et al.: https://www.researchgate.net/publication/370468285_Quantification_of_tropical_monsoon_precipitation_changes_in_terms_of_interhemispheric_differences_in_stratospheric_sulfate_aerosol_optical_depth , concludes that unless SAI is applied at a high level and in a grossly asymmetric (relative to North and South Hemispheres) radical Monsoon interference is unlikely. On *Ozone depletion* here's some of the details on the decidedly mixed Montreal Protocol report on SAI (sent 5/17 to the usual lists): Below are key points the 2022 Montreal Protocol report's ( https://ozone.unep.org/system/files/documents/Scientific-Assessment-of-Ozone-Depletion-2022-Executive-Summary.pdf ) mixed assessment of SAI impact on ozone layer. The report focused on a spring injection of SAI in Antarctica (where the Ozone hole is largest) and found in model simulations, after 20 years of SAI sufficient to reduce global cooling by 0.5 C, loss of ozone in Antarctica in October similar to losses in the 1990s that if continued would delay ozone hole recovery by 25 to 50 years, but less loss if SAI is started later, and for larger applications enhancement of Ozone in the winter in NH mid-latitudes. Details from the ES Chap. 5, p. 21-22 report below: "Additional ozone depletion due to SAI is simulated in spring over Antarctica, with magnitudes dependent on the injection rate and timing. Simulations of strong SAI show an increase in total column ozone (TCO) in mid-lat- itudes (40–60°N) in the winter Northern Hemisphere. º For October over Antarctica, SAI simulations that achieve a global mean surface cooling of 0.5 °C in the first 20 years, show a reduction of TCO of around 58 ± 20 DU, assuming 2020–2040 halogen conditions. This reduc- tion brings TCO values close to the observed minimum in the 1990s. Less ozone loss would be expected for a later SAI start date, when halogen concentrations are project- ed to be lower. º Beyond the first 20 years, the continued application of strong SAI, to offset almost 5 °C of warming by 2100, re- duces Antarctic ozone in October by similar amounts (55 ± 20 DU) throughout the 21st century despite declining abundances of ozone-depleting substances (ODS). In this case, ozone hole recovery from ODSs is delayed by between 25 and 50 years. A peakshaving scenario po- tentially leads to less ozone depletion. º Under stronger SAI scenarios, ozone is significantly enhanced in NH mid-latitudes in winter owing to strato- spheric heating from injected sulfur, which leads to in- creased equator to poleward transport of ozone. º Ozone loss within the Arctic polar vortex has not yet been robustly quantified for SAI." Is anyone aware of any other risks that could rule out cautiously piloting SAI (for example in Polar regions per "the Cornell School" led by Doug)? Let me add that my understanding is that one of the problems with basing everything on modeling and limited lab and atmospheric testing is that atmospheric systems are so complex that it would be impossible to definitively (at a 95% confidence level) rule out all potential adverse unintended consequences. The best way to "test" appears to be thus to conduct limited pilots that gradually scale up and adjust and modify as more real time data is obtained. We are after all talking about mimicking (in a more gradual and deliberative way) the millions of tons of sulfur aerosol that has been injected into the stratosphere by volcanoes naturally for as long as we've been on this planet and much longer! This is not after all "nuclear radiation" but "natural" sulfur aerosols! This is not to say of course that modeling and other research should not continue, it's just the idea that purely researching without testing deployment for another 10 years or so (as David Keith opined in HPAC discussion) before then potentially going "all in" for deployment if global conditions become very extreme is a good strategy? I of course defer to Doug, Michael MacCracken and others are much more knowledgeable about all this than myself - but per Mike M's view (I believe - if you see this Mike please correct me if I'm misinterpreting!) it is a terrible mistake for policy to determined based on "scientific criteria" (like less than 5% risk). Rather, policy should be based on reducing catastrophic risk (even if it's low possibility) like crossing tipping points that we are much greater risk of crossing as we warm above 1.5 and 2.0 etc. Doug, I don't know if you're of the same view, but I certainly agree with everything in your most recent post on this thread (that I just saw!). Needless to say, I welcome further evidence and discussion on any of these points! Best, Ron Dear Michael et al., Agreed that anything impacting the globe has the potential to cause discontent and conflict. Unfortunately though, we’re in a situation that can only be solved globally. (In fact, I believe that one of the key reasons that the heavy lift to achieve timely and massive GHG reduction and draw down has unfortunately failed is due to the collapse of the Kyoto Protocol mandatory cap and trade regime and its replacement with a voluntary NDC regime: https://www.cpegonline.org/post/our-two-climate-crises-challenge.) So we have to find a way to implement a global cooling solution (that will probably have to be complemented early on and later by many more global and local cooling efforts using different methods: https://pdfhost.io/v/pR4xEbZzO_The_Case_for_Urgent_Direct_Climate_Cooling040223). I think part of the block against SAI that you (and many others) are expressing is due to a "big bang" conceptualization (do a lot of research and then proceed to rapid global implementation) that in my (and Mike MacCracken and I think Doug MacMartin and "the Cornell School" of SAI) is not a good way to think about implementation. *Rather, I think (I believe following MacCracken and "the Cornell School) a more realistic and advisable method is to start very gradually with pilot SAI baby steps in the poles* (lower tropopause) in the spring and so that it will fall out in the fall (aerosols likely to fall-out more quickly within months rather than years in the poles) that would increase albedo in the most important sun lit summer months and not obstruct long-wave release in the dark winter months. This would hopefully reduce critical Arctic sea ice melting and "Polar Amplification" that is a key source of jet stream meandering and slowing and recent extreme climate events (See Greta (ed) 2022 section 2.6 by Jennifer Francis for recent direct evidence - endnotes and references at: https://theclimatebook.org/en-us/). It has recently occurred to me that a good model for this kind of collaboration might be the international space station that includes the work of a large group of nations. (From Wikipedia: NASA (United States), Roscosmos (Russia) and the European Space Agency are the major partners of the space station and contribute most of the funding; other partners are the Japanese Aerospace Exploration Agency and the Canadian Space Agency). This could start small over the poles with a near term goal of reducing global extreme climate events, build trust, transparency, and grow in partners though include mostly countries with the resources and capabilities to contribute on which the rest of the world would be happy to 'free ride' especially if there were clear reductions in climate catastrophes. As the initial focus would be the poles I think the potential for opposition and conflict would be reduced. As this "International Global Direct Climate Cooling Agency" gained more trust, confidence, and partnerships, from countries around the world it could (if the SAI was working and beneficial) gradually expand to global coverage. (From Wikipedia again: the ISS has been described as the most expensive single item <https://en.wikipedia.org/wiki/Lists_of_most_expensive_items_by_category> ever constructed.[82] <https://en.wikipedia.org/wiki/International_Space_Station_programme#cite_note-84> As of 2010, the total cost was US$150 billion. This includes NASA's budget of $58.7 billion ($89.73 billion in 2021 dollars) for the station from 1985 to 2015, Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station, estimated at $1.4 billion each, or $50.4 billion in total. Assuming 20,000 person-days of use from 2000 to 2015 by two- to six-person crews, each person-day would cost $7.5 million, less than half the inflation-adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.[83] <https://en.wikipedia.org/wiki/International_Space_Station_programme#cite_note-International_Space_Station_lafleur20100308-85> ) Feedback on this is most welcome! Best, Ron -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAPhUB9C8z7eqa2WBcX9ELdVTj%2BNrP2DFouPUiXH_JuP0b1epfA%40mail.gmail.com.
