Although I was initially worried by Denis's point that arctic aerosols will capture some rays that would otherwise just pass tangentially through the stratosphere, I have now done some geometry and believe that this will only apply to about 0.2% of the incident sunlight on the Arctic at midsummer.
This is because the atmosphere is thin in comparison with the radius of the earth. This applies of course to all aerosols SO2 or SiO2. My main argument for suggesting silica (Greg's diatoms) is that we might be able to control particle size much more exactly. John Gorman ----- Original Message ----- From: <[email protected]> To: <[email protected]>; <[email protected]>; <[email protected]> Sent: Monday, May 11, 2009 4:33 PM Subject: [geo] Re: Balancing the pros and cons of geoengineering All: Bonnelle Denis is right that a detailed study of aerosol reflections needs doing. Someone may wish to use research time on it, but without any funding it's difficult to mount a determined attack on the many parameters that need varying. The issue of particle size demands some actual experiments, to see what happens to candidate aerosols at the actual altitudes considered. How much particle growth occurs, under what conditions of humidity, pressure, etc? What's the true fallout time vs altitude and particle size? There's a whole agenda here. I do wonder how much Lowell Wood and collaborators are doing on this, but Lowell is mum. Gregory Benford -----Original Message----- From: John Gorman <[email protected]> To: Bonnelle Denis <[email protected]>; [email protected] Sent: Mon, 11 May 2009 1:59 am Subject: [geo] Re: Balancing the pros and cons of geoengineering I have to admit I hadnt thought of that aspect of aerosols in the arctic. To Gregory Benfold -What do you think ? John Gorman ----- Original Message ----- From: Bonnelle Denis To: [email protected] ; [email protected] ; John Nissen ; [email protected] Sent: Monday, May 11, 2009 9:42 AM Subject: [geo] Re: Balancing the pros and cons of geoengineering Dear all, (please forgive me if the following geometrical arguments have already been discussed). The positive feedback (albedo, methane, etc.) rationale for focusing about the Arctic is doubtlessly great. But the geometry is not very favorable, especially if very tangential sun rays are concerned, which is more often the case near the poles than near the equator. The most dramatic case is the one of the most tangential rays which: 1 - without geoengineering - would have traveled horizontally through the stratosphere, unharmed, and which: 2 - would be diffracted by the silica, half upwards but also half downwards, giving their heat to the earth. Seen from the sun, the relevant cross-section is around 10 or 20 km (the considered stratospheric layer's thickness) multiplied by 2000 or 3000 km (the considered bow length). Such a result (several 10,000 km²) is not negligible when compared to the whole target cross-section (the same 2000 or 3000 km, multiplied by 300 or 400 km which is the width, seen from the sun, of the true useful target region). In addition, the effect in our x0,000 km² region will be more intense, as the rays which travel quite horizontally through the stratosphere will meet much more silica than those which make a larger angle with the horizontal. And even in the latter case (i.e., in all the target region, but mainly for sun rays which will reach the atmosphere with a quite small angle with the horizontal), an effect of the silica will be to increase the proportion of such rays which will be redirected towards the ground in a rather vertical direction, instead of coming quite tangentially (the blue sky will be brighter). Thus, various effects will have to be considered: lesser absorption in various layers of the atmosphere, lesser reflexion on the ocean surface, deeper penetration into the ocean, etc. It doesn't seem clear to me, whether such undesired effects will be lower than the desired fact that half of such diffracted rays will be redirected upwards, i.e. outwards of the earth climatic machine. Best regards, Denis Bonnelle. [email protected] De : [email protected] [mailto:[email protected]] De la part de John Gorman Envoyé : lundi 11 mai 2009 09:45 À : [email protected]; John Nissen; [email protected] Objet : [geo] Re: Balancing the pros and cons of geoengineering I am thinking of how to get funding for in-lab Evaluation of Tetra Ethyl Silicate Dissolved in Aviation Kerosene As a Means of 0D Distributing Stratospheric Aerosols for Geoenginering. The two points below are relevant to this discussion but a bit muddled as this is a rehash of my submission to the Royal Society 1)Possible Advantages of Silica. Particle size. At these submicron sizes it is the size of the particle which defines the wavelength of light which is reflected/diffracted. There have been several papers, which have pointed out the difficulty of controlling sulphuric acid droplet size and the problem of agglomeration of the droplets. (Papers include that by Tilmes/Robock in the Royal Society's Philosophical Transactions) It seems logical that the concentration of Tetra ethyl silicate in aviation fuel would define the size of silica particles produced on burning. If so, the particle size could be selected for maximum reduction in net radiation. There would then be less material and fewer particles/droplets for the same level of global cooling. 2)The most likely first application of a stratospheric aerosol sunscreen is that proposed by Gregory Benfold "Saving the Arctic". Combined with the aircraft distribution system, the proposal would be to spread the aerosol by aircraft flying between 40 and 60,000 ft. from the time of first Arctic daylight (April approximately) until late July approximately. Ideally for very long stratospheric life, aerosols need to be injected at about 80,000 ft. If they are only injected at 50,000 ft. they will fall out of the atmosphere in about three months. (Ken Caldera's lecture available on U tube). In this case that is exactly what we want so that they would fall out by the end of the Arctic summer and would not be present during the winter --. Most of the arguments that aerosols will damage the ozone layer assume that the aerosols are injected high in the stratosphere for long life. In this case most of the injection would not reach the ozone layer. In addition the aerosols would no longer be present in winter when the effect is greatest. It seems very likely that implementation of this type would succeed in "saving the Arctic". In particular the target would be to eliminate significant melting of the Greenland ice sheet or sudden loss of parts of it. The same principle could then be applied to Antarctica. The target should be zero sea level rise. If this could be achieved the saving in=2 0costs of construction, relocating populations and lives lost in flood disasters would be absolutely enormous. john Gorman ps this is a really good discussion -by everyone. ----- Original Message ----- From: Andrew Lockley To: John Nissen Cc: Alvia Gaskill ; [email protected] ; [email protected] ; [email protected] ; [email protected] ; [email protected] ; [email protected] ; [email protected] ; [email protected] Sent: Sunday, May 10, 2009 1:01 AM Subject: [geo] Re: Balancing the pros and cons of geoengineering Can't we modify the aerosol size, and deployment patterns, to make sure they fall out quickly and don't go anywhere near India? A 2009/5/9 John Nissen <[email protected]> Very good discussion. I'm trying to get a balance of pros (benefits B1-B7) and cons (specific fears S1-S21). What I'd like out of our discussion is some kind of risk assessment for the possible downside of a weaker monsoon, as this is considered the biggest risk in the regional effects (S1). And we could make this reasonably pessimistic, to be on the safe side - i.e. be cautious with the application of geoengineering. On the other hand, we might be able to reduce this risk, e.g. by neutralising sulphate aerosol; if there's a good chance of this working, then we can factor that into the calculation. Or the risk might be offset by a benefit in that region, e.g. improved summer water supply from Himalayan glaciers? So, what kind of impact would a weaker monsoon (ISM) have on India? What is the probability of stratospheric aerosols deployed in the Arctic would produce a weaker monsoon? Can this risk be significantly countered? Can it be significantly offset? Note that the risk on benefit side might be measured in terms of a risk, without geoengineering, of millions or even billions of lives being lost (especially if massive methane release adds several degrees of global warming, B4). Alternatively we could measure in GDP lost - current global GDP (aka GWP) is about $60 trillion I believe. Cheers, John ----- Original Message ----- From: "Alvia Gaskill" <[email protected]> To: <[email protected]>; <[email protected]> Cc: <[email protected]>; "Andrew Lockley" <[email protected]>; <[email protected]>; =2 0 <[email protected]>; <[email protected]>; <[email protected]>; <[email protected]>; <[email protected]> Sent: Saturday, May 09, 2009 4:50 PM Subject: Re: [geo] Re: Balancing the pros and cons of geoengineering Stephen makes a good point that leads to a more general one. If there are precipitation reductions associated with sunlight blocking schemes, consideration should also be given to mitigating these, analogous to the medications given to patients with Type II diabetes to combat the side effects of the primary drug. This is an oversimplification, but the way summer monsoons work is that in the summer the land gets warmer than the ocean faster, creating a low pressure area and this causes on shore flow as air moves from high to low presssure. For some reason, Laki caused this to be muted. There were no aerosols from Laki over India and it has been suggested there was a teleconnected response (see the paper Stephen attached) although in paleo climate the authors say the effects were direct, but don't give specifics. In the case of Pinatubo, both the land and sea were cooled by the aerosol and the land simply didn't heat up fast enough to generate the on sh ore flow. If the Arctic only aerosol geoengineering does cause a reduction in the ISM (Indian Summer Monsoon as there are other monsoons that affect India, but this is the most important one), use of the cloud whitening to restore at least some of the temperature differential should be considered. Likewise, in a global aerosol scheme, with a global aerosol spread similar to that of Pinatubo, the cloud whitening could also be used to create a temperature differential, but at some point it becomes a race to the bottom, with the land temperature simply too cool to initiate the low pressure area. In this case, reducing the depth of the aerosol layer over the land may be the most effective way to restore the dynamics. I previously suggested using ammonia released from either planes or balloons to react with the sulfate aerosol and drop them out as ammonium sulfate. This idea as well as Stephen's could be applied to other locations such as the Amazon, Eastern China and Africa where models indicate unacceptable reductions in precipitation are a result of either aerosol geoengineering or global warming. Of course, the ammonia wouldn't be of any value in a global warming/no aerosol scenario. I said in one the earliest=2 0papers I wrote on geoengineering that eventually we were going to have to learn how to manipulate the climate to our advantage. That includes both gross scale and fine tuning. In a related issue, last year I posted a link from a group in the UK that was carrying out some 130 different models of aerosol geoengineering. It was a volunteer effort among universities. If they have done even a fraction of the modeling, this work should be taken into account in designing new studies such as Rutgers is proposing. Anyone have an update? You may recall also that we spent some time last year discussing the significance of the "little brown blotches" in absolute terms and now Ken also raises the issue of their resolution. http://en.wikipedia.org/wiki/Monsoon Monsoons are caused by the larger amplitude of the seasonal cycle of land temperature compared to that of nearby oceans. This differential warming happens because heat in the ocean is mixed vertically through a "mixed layer" that may be fifty meters deep, through the action of wind and buoyancy-generated turbulence, whereas the land surface conducts heat slowly, with the seasonal signal penetrating perhaps a meter or so. Additionally, the specific heat 20 capacity of liquid water is significantly higher than that of most materials that make up land. Together, these factors mean that the heat capacity of the layer participating in the seasonal cycle is much larger over the oceans than over land, with the consequence that the air over the land warms faster and reaches a higher temperature than the air over the ocean.[11] Heating of the air over the land reduces the air's density, creating an area of low pressure. This produces a wind blowing toward the land, bringing moist near-surface air from over the ocean. Rainfall is caused by the moist ocean air being lifted upwards by mountains, surface heating, convergence at the surface, divergence aloft, or from storm-produced outflows at the surface. However the lifting occurs, the air cools due to expansion, which in turn produces condensation. In winter, the land cools off quickly, but the ocean retains heat longer. The cold air over the land creates a high pressure area which produces a breeze from land to ocean.[11] Monsoons are similar to sea and land breezes, a term usually referring to the localized, diurnal (daily) cycle of circulation near coastlines, but they are much larger in scale, stronger and seasonal.[12] -- --- Original Message ----- From: "Stephen Salter" <[email protected]> To: <[email protected]> Cc: <[email protected]>; "Andrew Lockley" <[email protected]>; <[email protected]>; <[email protected]>; <[email protected]>; <[email protected]>; <[email protected]>; <[email protected]> Sent: Saturday, May 09, 2009 6:43 AM Subject: [geo] Re: Balancing the pros and cons of geoengineering Hi All The attached paper by Zickfeld et al shows, in figure 2, what might happen to the Indian Monsoon if we do nothing. Cooling the sea relative to the land should move things in the opposite direction. Stephen Emeritus Professor of Engineering Design School of Engineering and Electronics University of Edinburgh Mayfield Road Edinburgh EH9 3JL Scotland tel +44 131 650 5704 fax +44 131 650 5702 Mobile 07795 203 195 [email protected] http://www.see.ed.ac.uk/~shs Alan Robock wrote: Dear Ken, I agree. We need several models to do the same experiment so we can see how robust the ModelE results are. That is why we have proposed to the IPCC modeling groups to all do the same experiments so we can compare results. Nevertheless, observations after large volcanic eruptions, 0Aincluding 1783 Laki and 1991 Pinatubo, show exactly the same precip reductions as our calculations. Even if precip in the summer monsoon region goes down, how important is it for food production? It will be countered by increased CO2 and increased diffuse solar radiation, both of which should make plants grow more. We need people studying impacts of climate change on agriculture to take our scenarios and analyze them. Alan Alan Robock, Professor II Director, Meteorology Undergraduate Program Associate Director, Center for Environmental Prediction Department of Environmental Sciences Phone: +1-732-932-9800 x6222 Rutgers University Fax: +1-732-932-8644 14 College Farm Road E-mail: [email protected] New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock Ken Caldeira wrote: A few questions re claims about monsoons: 1. How well is the monsoon represented in the model's base state? Is this a model whose predictions about the monsoon are to be trusted? 2. Since the believability of climate model results for an y small region based on one model simulation is low, for some reasonably defined global metrics (e.g., rms error in temperature and precip, averaged over land surface, cf. Caldeira and Wood 2008) is the amount of mean climate change reduced by reasonable aerosol forcing? (I conjecture yes.) Alan is interpreting as significant his little brown blotches in the right side of Fig 7 in a model with 4 x 5 degree resolution (see attachment). How does the GISS ModelE do in the monsoon region? If you look at Fig 9 of Jiandong et al (attached), at least in cloud radiative forcing, GISS ModelE is one of the worst IPCC AR4 models in the monsoon region. So, while Alan may ultimately be proven right, it is a little premature to be implying that we know based on Alan's simulations how these aerosol schemes will affect the Indian monsoon. If you look at Caldeira and Wood (2008), we find that idealized Arctic solar reduction plus CO2, on average precipitation is increased relative to the 1xCO2 world. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected] <mailto:[email protected]>; [email protected] <mailto:[email protected]> http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 > -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. <BR --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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