Dear Colleagues, An outstanding and extremely informative interview with Doug MacMartin IMO on SAI (with some comments on MCB) shared recently by Andrew (thank you!):
https://www.youtube.com/live/_JBLMsXNmhs?si=3qoDl1RNLS4zb_zc who has also asked and posted in the geoengineering google group a number of important follow up questions (that I've taken the liberty of copying below this post.) A few observations that in some ways repeat what many of us have been saying repeatedly: 1) As Doug (and many others - see for example transcription of Ted Parsons - advisor to the Climate Overshoot Commission comment shared by Robert T) and many others have pointed out, the key problem with SAI (as far as we can tell at this point) appears to be political, or social science rather than natural science based. After all, volcanoes have been doing this throughout geological time with mostly (at least in human time frames) non-catastrophic impact. 2) Of course ideally we would have perfect democratic participatory global governance in place before we begin to pilot-test high leverage Direct Climate Cooling (DCC) ( https://drive.google.com/file/d/1jt-8OF7ncW71bEPqCDfJS5trr4-Nm4FJ/view?usp=sharing) deployment, but if we wait for perfect global governance before deploying we're allowing and risking (possibly very harmful) climate catastrophe (that we might possibly be able to reduce or prevent) to continue (one proposal for possibly "squaring the circle on this" here: 3) I thought the roughly 20 to 1 tradeoff (highlighted by Dan) between the harmful to humans and nature cooling sulfate aerosols we've been inadvertently emitting in the troposphere for decades, and roughly 5% of these we would need to put up in the stratosphere (where they would also have much less harmful impact on life on earth) to cool is a particularly good communications "hook". We've been in effect conducting very harmful and inefficient "geoengineering" for decades that we're now puting into "reverse termination shock" (see: https://drive.google.com/file/d/1R9Kg3d1DozwuxPIjyLWljb9Lld_pJCVm/view - that is reportedly/hopefully now on the IMO MEPC meeting agenda). See also HPAC discussions with Doug ( https://drive.google.com/file/d/1EyMvarUBlzon4GNyZlOYrSzSQYpD_m_a/view) and David Keith (https://muse.ai/vt/6mt51H5-Dr-David-Keith). 4) One quibble with Doug. Last I checked Make Sunsets was able to measure how high up their balloons lofted, were using helium not hydrogen filled balloons and to the best of my knowledge had roughly accurate (for mid-latitude SAI) sulfate aerosol cooling impact estimates ( https://makesunsets.com/blogs/news/calculating-cooling ). The problem with Make Sunsets is that it is not "scalable" politically or technologically (and I think MS agrees with this), but the effort has I think (following PT Barnum "any publicity is good publicity") had important political protest/awareness generating impact - see HPAC Make Sunsets interview ( https://muse.ai/v/AW112ix-Make-Sunsets). (As a (radical) economist I appear to often be pointing out to many of my more natural science and technology oriented colleagues the importance of looking at political-economic, not just natural science, constraints and affects.). Best, Ron PS - Make Sunsets' (MS) hydrogen balloon proposal raises important questions (MS refers to Make Sunsets) as noted by Andrew: "1) MS release lifting gas alongside S-compounds 2) MS plan to use H2 3) H2 is an indirect GHG, GWP100 is ~11 https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1067144/atmospheric-implications-of-increased-hydrogen-use.pdf https://www.nature.com/articles/s43247-023-00857-8 4) stratospheric H2 decomposes to H2O, a GHG I'm unclear on the following A) does the indirect GWP100 of H2 increase if it's directly released into the stratosphere? Common sense suggests so, but I can't see figures anywhere B) if stratospheric wetting is a problem, why isn't jet exhaust a problem? It's very wet - C8H18 + 12 1/2O2 => 8CO2 + 9H2O. So in thin air ~1/3 of the engine oxygen intake ends up as water. This applies to both commercial and geoengineering flights. C) is the above effect enough to net off the SAI? It doesn't seem so, SO2 is a very strong negative forcing agent in the stratosphere." I'd welcome comments Andrew Lockley" -- 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 geoengineering+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAPhUB9D%3Dfu2Rcbc6qMat%3DX7aOeHPHK9GtnvVTEgFob6%2ByaTVWA%40mail.gmail.com.
