Hi Ken,
We tried to write some down in our Earth’s Future piece last year, at least for stratospheric aerosols MacMartin, D. G., B. Kravitz, J.C.S. Long, and P.J. Rasch, “Geoengineering with stratospheric aerosols: what do we not know after a decade of research?” Earth’s Future, 4, 543-548, 2016. doi: 10.1002/2016EF000418 <http://onlinelibrary.wiley.com/doi/10.1002/2016EF000418/epdf> I agree with some of what has been said, that some of the biggest/hardest questions are on the societal side rather than climate science side, but I don’t think very many people would agree to deployment based on what we currently know on the climate science (I sure wouldn’t). I’d say what we know is simply that it is plausible that a limited deployment of solar geoengineering in addition to (as opposed to an alternative to) could reduce climate damages for most, and research has yet to identify any “showstoppers”. We know that using solar geoengineering to move global mean temperature all the way back to preindustrial will overcompensate some variables and is almost certainly not a reasonable balance of risk, but something like 3C --> 1.5C *might* be less risk (with appropriate caveating of aggregation, i.e., risk for whom) than allowing the climate to warm to 3C. We know we can achieve at least a few W/m2 of negative RF. There’s a lot of things we don’t know for stratospheric aerosols (and even more for MCB or cirrus thinning), including stratospheric processes (microphysics, chemistry, dynamics) and how the climate responds differently to that RF in contrast to GHG forcing. It would be valuable as a community to start trying to better quantify which uncertainties are most important to resolve, how significant they might be on our ability as a society to make informed decisions, and what modeling/observation/perturbative field tests might help resolve them (including how resolvable some uncertainty might be. Just to pick one random one, is the range of possible unknown impact of sedimenting aerosols on cirrus significant enough that it would affect our conclusions about impacts of a deployment? If so, what would we need to do to understand that, how long would that take, how much would that cost… Personally I’d like to talk to everyone at the GRC next week to get their expert opinions on these types of questions (as well as everyone who isn’t at the GRC). One thing I would like to push back on is the extent of “unknown unknowns”… of course one can’t (by definition) bound that, but given the natural analogs, is the possibility of these really significant in comparison with the known knowns and known unknowns of never considering geoengineering? See you in a few days, doug From: geoengineering@googlegroups.com [mailto:geoengineering@googlegroups.com] On Behalf Of Eric Durbrow Sent: Thursday, July 20, 2017 2:20 AM To: geoengineering <geoengineering@googlegroups.com> Subject: Re: [geo] Help: What do we know and what don't we know about solar geoengineering? Possible bullet points • It is virtually impossible to use SRM as an effective weapon. • However, some countries may see it as a weapon esp if deployed unilaterally. On 19 July 2017 at 9:41:57 , Klaus Lackner (klaus.lack...@asu.edu <mailto:klaus.lack...@asu.edu> ) wrote: What are the most important things we know about solar geo-engineering? * It can be done, it is comparatively cheap, but probably not as cheap as people think * It will cool the planet, but it will not simply cancel out greenhouse gas additions * There is more than one way of doing it, some are more reversible than others * It is no substitute for balancing the carbon budget * It acts fast, but needs constant maintenance What are the most important things we don’t know about solar geo-engineering * Who decides * Who pays for the unintended side effects * What are the unintended side effects for different methods under consideration * Benefit – risk analysis over time From: <kcalde...@gmail.com <mailto:kcalde...@gmail.com> > on behalf of Ken Caldeira <kcalde...@carnegiescience.edu <mailto:kcalde...@carnegiescience.edu> > Reply-To: "kcalde...@gmail.com <mailto:kcalde...@gmail.com> " <kcalde...@gmail.com <mailto:kcalde...@gmail.com> > Date: Wednesday, July 19, 2017 at 07:48 To: Geoengineering <Geoengineering@googlegroups.com <mailto:Geoengineering@googlegroups.com> > Subject: [geo] Help: What do we know and what don't we know about solar geoengineering? Folks, This Sunday evening, I am supposed to help kick off a discussion about what we know and what we don't know about solar geoengineering. https://www.grc.org/programs.aspx?id=17348 <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.grc.org_programs.aspx-3Fid-3D17348&d=DwMFaQ&c=l45AxH-kUV29SRQusp9vYR0n1GycN4_2jInuKy6zbqQ&r=hFjA8A8KwwhQx5qilpfIleTL0XYVr_fckT8DnwIEWlQ&m=fgPmqux2N1LODT1cufk_CJiAKTZhRHIqK_n9LouQzTo&s=kUPAtZyNn31QnhDsOVyKJMJGsHpEG9CEKV8lyxPkMS8&e=> It would be helpful if some people on this group could attempt to answer these questions: 1. What are the most important things we know about solar geoengineering? 2. What are the most important things we don't know about solar geoengineering? I would appreciate it if you could put your answers in the form of bullet points and not write essays. It would also help if you could cite a key relevant paper or two. Thanks, Ken Ken Caldeira Carnegie Institution for Science Dept of Global Ecology 260 Panama St Stanford CA 94305 USA +1 650 704 7212 http://CarnegieEnergyInnovation.org <https://urldefense.proofpoint.com/v2/url?u=http-3A__CarnegieEnergyInnovation.org&d=DwMFaQ&c=l45AxH-kUV29SRQusp9vYR0n1GycN4_2jInuKy6zbqQ&r=hFjA8A8KwwhQx5qilpfIleTL0XYVr_fckT8DnwIEWlQ&m=fgPmqux2N1LODT1cufk_CJiAKTZhRHIqK_n9LouQzTo&s=xTFR7pKw61rTex4OWOy9-gvMgRffknI8JWsUfksXA9U&e=> http://dge.stanford.edu/labs/caldeiralab <https://urldefense.proofpoint.com/v2/url?u=http-3A__dge.stanford.edu_labs_caldeiralab&d=DwMFaQ&c=l45AxH-kUV29SRQusp9vYR0n1GycN4_2jInuKy6zbqQ&r=hFjA8A8KwwhQx5qilpfIleTL0XYVr_fckT8DnwIEWlQ&m=fgPmqux2N1LODT1cufk_CJiAKTZhRHIqK_n9LouQzTo&s=1ImkopEb-MSF21XBDO0gH_GUlkaeWWtZ_0jEOLfQGKI&e=> Assistant, with access to incoming emails: Jess Barker jbar...@carnegiescience.edu <mailto:jbar...@carnegiescience.edu> -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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