Since none of those with the skills to do these calculations much more professionally seem to be jumping in quickly to take over the reigns, I'll try not to embarrass myself in giving initial crude answers to my own question from the other day, which follow:
I find that in a recent paper from MIT (Leibensperger, 2011), the localized RF from sulfate aerosol’s direct effect for the eastern US is estimated as -.3W/m2. Then, if we estimate for Twomey/Albrecht indirects, we can say roughly something like -.5W/m2 for the current eastern US sulfate forcing. What are the sulfur levels giving this RF? The basic NAAQS - annual average primary standard - is still unchanged from the 1970s. (http:// www.epa.gov/air/sulfurdioxide/), at 30ppb (about 80 micrograms/m3). But in actuality, average regional levels now only range from 1-6ppb across the US. There was apparently talk lately of introducing a new 5- minute standard for asthmatics, but it was not done, and I think we can all agree that a geoengineering approach could be designed to avoid spikes pretty well, so the annual average – of course, in our case, it would really be a three or four month average – is alone what matters here. So, let’s examine some actual current annual average local levels a bit. http://www.epa.gov/airtrends/sulfur.html I live now in New York City. The most complete reading here is from a midtown Manhattan monitor station, where as recently as 2003 SO2 seems to have been around 14ppb, but the data ends in 2007, by which time it had dropped to ~11ppb. I used to live rather close, it would seem, to that particular monitoring station back in the early 1990s, when the levels it read were closer to 20ppb, but let’s take something nearer the lower figure and be conservative. Either way, this area entails some of the highest readings in the eastern US for SO2 pollution that I found. Look at the interactive map's levels around the rest of the eastern US - they are really surprisingly low now almost everywhere. I was shocked when I looked at it (no wonder warming is ahead of the models! At least it suggests the termination effect won’t be too bad here in the US - we’ve already gone through much of it!). Within that 1-6ppb range, let’s say it’s an average of 3ppb? Now, then, is it not accurate to say that we should be able to go up to 3x or even 4x that -.5W/m2 without making any air that is worse than Manhattan's has been very recently? That is, if we aimed for ~12ppb level. Is this really so bad, so evil? I didn’t realize I was torturing myself by living here! I walk my dog almost daily in the one old growth section of the city (Inwood Hill Park), where there is plentiful lichen, moss, etc. Birds of all varieties seem healthy and in robust populations. A new species of leopard frog was just discovered here, as you might have read the other day. It is not pristine, but I found a crayfish walking around by a stream in Central Park. I have even had asthmatic friends who love living here, except in the heat of summer. Is this air I am breathing every day really so noxious and dangerous that you would not want to consider using it, in an almost completely unpopulated area moreover, even if thereby you could help stave off a potential arctic disaster? Really? Next, what are the levels of SO2 currently in Siberia? There is one former gulag site where there is today smelting and other industry that emits massive SO2, but that is far from the ESAS and otherwise the level seems to be very low. One recent paper I found (Lee et al, 2011), that aims to constrain SO2 global emission estimates by looking at ozone and other satellite data (OMI and SCIAMACHY), makes it appear in a map as though the area in question is extremely low, although it is not at all detailed. Thus, my supposition is that we could possibly get some –2W/m2, possibly half the local net forcing, without creating any air worse than New York City’s has been just in this past decade. Please correct me if that seems to be mistaken. The current modeled estimates for ESAS talik extent suggest about 3-5% of total area. Thus, to give an adequate buffer around this, to effectively cool incoming waters, etc, covering 10% of ESAS area = ~50,000 sq. miles. Now, maybe some of those with better expertise can figure the dispersal rates, column depth, etc, etc and estimate how just how much sulfur this would entail, that is, to emit enough S to cover ~50,000 sq. miles with about 12ppb SO2 for about four months per year, how much sulfur is that? Thanks much in advance for your answer, I appreciate it. Lastly, in terms of the addition of methane effects, I find that it would at best add only about .1W/m2, and possibly almost nothing measurable. Using a very rough methane RF (including all indirect effects, i.e., from Shindell et al, 2009) of 1000ppb=~1W/m2, then with an anomaly there ranging from +100-200ppb, and a possible maximum 40% reduction emission rate from local wetlands – if the anomaly were completely caused by wetland emissions, which I very strongly doubt – then still at best one would only get -.1W/m2. So that factor would be very unlikely to be significant. Obviously, MCB could/should then be added to or combined with the above. Latham hasn’t responded, so maybe someone else could give a rough estimate of what the options might be to use them together and what those effects might be? I am, I confess, somewhat frustrated by some of the experts here excepting Mike – not in their expertise, which I always find impressive, but in their seeming inability, or perhaps unwillingness, to use such expertise more flexibly. John Nissen’s exchange with Latham a few days ago, with John’s poignant questions, I found almost painful to read, frankly (of course, I can appreciate that MCB deals with much the same complexities as CLAW, which after 800 papers is still mired in controversy – but maybe that only connotes that another 5 years of modeling still won’t alone resolve John's questions, but doing Lovelock’s version of what some have branded “improvisatory experimentation,” i.e., simply getting out into the field and making small prototypes and playing around variously with different parameters until you start to get what you are looking for, could be a better and quicker way to go?). As to the fundamental question of risk in dealing with tropospheric SO2, I think it’s probably safe to say that there is likely zero global-scale risk whatsoever to the proposed plan. The risks of a large-scale excursion of methane, if one took place, on the other hand, are without question extraordinary. I think that’s the kind of circumstance where you decide it’s best to act with relatively imperfect knowledge. None of us know what the probability of a large CH4 emission really is. And none will ever know what "might have been", whether we act or don’t act, had we taken the “other path.” That's what decision is all about. Nor do I imagine that anyone can really say whether what I am proposing would actually be effective, but as I just suggested for John's designs, one could always alter the parameters easily in real time. I think that in a larger context of fighting climate change altogether, what I'm suggesting also represents one possible “step 1” or “2” towards the lowest-possible-risk pathway forward, which is what everyone should be striving for, it seems to me. That is, the combination of a very large and rapid non-CO2 (CH4/BC) emissions program (please keep in mind, members of AMEG, that the recent Shindell paper had the good news that, if Asia is less important for Arctic BC forcing than some thought, it also means that a rather small number of northern European and Scandinavian countries can be quite important in reducing that arctic BC forcing – and therefore AMEG could and should ALSO be engaged in urgently requesting the UK government to be the spearhead for such a program, including more advanced diesel filters, etc) and at the same time, alongside it, some kind of small-scale, pinpointed geoengineering program like the one I am suggesting here, should, if done together, be able to push back strongly against the dissolution of the arctic as we know it for a while. Obviously that's hardly the end of the story, just steps 1 and 2, the first chapter. Then, along with steep declines in carbon emissions, the kind of SRM geoengineering that some here consider “serious” (both Revkin and Keith used that word in recent days seemingly to distinguish what they have in mind from what I am proposing), best pegged exclusively to lost aerosol loading (thus, no setting of any global “thermostat” as in Keith’s conundrum), which would then itself be pegged in its termination to subsequent CDR, through biochar, reforestation and other technologies like Keith’s artificial tress, etc. All that together creates, I think, the minimum-risk path ahead, five interlinked steps that might indeed have to be step-ordered. On what Fuller called a ‘Critical Path’, if you don’t follow the first steps first, you can forget about getting to the end of the process. If the patient stops breathing in the ambulance on the way to the emergency room for a quadruple bypass, you can kiss your elaborate surgery plans goodbye if you won’t be able to get them breathing again first. A big methane excursion could be like that patient stopping breathing, essentially ending all hope of moving to a political solution on emissions, and the dangers of that seems to be growing considerably. Again, no significant risks in this "step 1" treatment I propose, obvious huge risks in sitting by and watching the thing that is feared. all best, Nathan -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
