Great point, Nathan. However, you're ignoring an additional issue. Warming of the tropopause means it's easier for water to convect or fold in to the stratosphere. This is a potentially serious problem, and one I put on the list of unknowns already.
Bulk air movements also bring more methane into the stratosphere, which ultimately end up as water. My view is that we need urgent improvements in our ability to monitor and model the tropopause, if we are to have a hope of making SRM predictable and safe. A On 10 Aug 2014 04:39, "Nathan Currier" <[email protected]> wrote: > One very widespread geoengineering 'meme' concerns stratospheric SRM and > Pinatubo. One reads about it continuously - "like Pinatubo," we will “cool > the planet” through stratospheric aerosols. How real is this? Pinatubo > clearly cooled the planet *initially*, but are we sure – really sure – that > it > cooled the planet at all temporal scales? When you turn on a conventional > coal plant, it, too, “cools the planet”, if you care to look only at the > initial response. > > There is no discussion, as far as I remember, on the causes of the > increased stratospheric water vapor changes in Solomon et al 2010 that I > brought up recently at this group, a paper suggesting considerable climate > warming from increased stratospheric H2O. In the attached paper, there’s > discussion of how volcanic eruptions might impact stratospheric water > vapor, causing a pulse of increased water vapor over 5-10 years. Although > the volcano injects water vapor itself, its initial impact is actually to > *dry* the stratosphere, since the SO2 reaction uses up so much water > vapor, meaning that the much longer pulsed increase must come from > perturbations in the stratospheric chemistry/climate itself. One question I > wonder about is how intrinsically tied to the sulfur itself these H2O > pulses might be, perhaps because of changes in methane oxidation, of the > kind I was hypothesizing before? In the paper, the modeled increased > forcing of roughly +.1w/m2 might seem modest, compared to the initial > large negative forcing of –3w/m2 or so, but one lasts a year, the other > possibly a decade, and how accurate are these modeled estimates? It is > clearly far easier to recognize the sudden cooling from the eruption when > it takes place, than a slight warming signal persisting through a much > longer period of time in an already warming climate system. Yet clearly > this is vital to understand if anyone is going to be doing useful > geoengineering based on this. > > It’s interesting that in the Solomon the water vapor increase is noted to > have gone into a considerable decline around 2000-2003, around a decade > after Pinatubo. Further, it is important to note that the complex dynamics > leading to these entangled positive and negative forcings from a single > pulse will almost certainly be shifted by the sheer act of continuous > prolongation inherent in geoengineering, so the constant Pinatubo meme > becomes a little....empty? > > Cheers, Nathan > > On Tuesday, August 5, 2014 2:38:34 PM UTC-4, kcaldeira wrote: >> >> Folks, >> >> I am supposed to give a keynote talk at CEC14 in two weeks. For this >> talk, I would like to try to develop a list of oft-cited memes that many >> assume are established facts, but which may not in fact be true. >> >> I am thinking of things like: "With solar geoengineering, there will be >> winners and losers." "Termination risk is an important reason not to engage >> in solar geoengineering." "Solar geoengineering will cause widespread >> drying." >> >> I don't want to discuss all of these things here but simply to develop a >> list. You could help me by sending an email answering the questions: >> >> 2a. What memes are out there which many "experts" regard as >> well-established facts but which in fact might not be correct? >> >> 2b. Why do you suspect the correctness of that meme? >> >> 2c. (optional) Can you provide a citation or a link to where someone is >> assuming the meme is true? >> >> Thoughtful responses would be most appreciated. If you want to start >> discussion about a meme, please do so in a separate thread so that this >> thread can be easily used to develop a list. >> >> Thanks, >> >> Ken >> >> _______________ >> Ken Caldeira >> >> Carnegie Institution for Science >> Dept of Global Ecology >> 260 Panama Street, Stanford, CA 94305 USA >> +1 650 704 7212 [email protected] >> http://dge.stanford.edu/labs/caldeiralab >> https://twitter.com/KenCaldeira >> >> Assistant: Dawn Ross <[email protected]> >> >> -- > 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/d/optout. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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