Dear John, > The arithmetic gives a frightening answer, which I expect is why you never > hear it and nobody publishes it.
Nature and Science love frightening results and would be happy to publish those if they are correct. But not if they contradict the evidence we have. You seem to imply that scientists only publish what they like or what people want to hear. I don’t see any evidence for that. If I had strong evidence for things being much worse, I would publish that tomorrow. Same if I could prove that climate change is a hoax. We are not “selling a dream to the media, politicians, environmentalists and the UN”, we publish and assess what the science and the data tell us. There are two main errors in your analysis: > The CO2 would only fall very slowly for the rest of the century, because of > CO2's long life in the atmosphere. Thus the forcing from nearly 500 ppm CO2 > would persist for the rest of the century. First, the initial decrease of CO2 isn’t that slow for zero emissions because the exchange with the surface ocean and land is fast. CO2 doesn’t have a single lifetime, and it’s the long tail that is slow. For a single pulse emission into the atmosphere, after 50 years only half remains in the air (Joos, doi:10.5194/acp-13-2793-2013, Fig. 1a). Second, other gases would also be reduced and some have shorter lifetimes. Even without going abruptly to zero, e.g. as in RCP2.6, the radiative forcing decreases after 2050. For zero emissions in 2050 the forcing would drop more. > Even if the warming rate remained at only 0.25C for the rest of century, > temperature would rise a further 1.25C to reach 3.2C above pre-industrial. That is simply wrong. There is no reason for the warming rate to remain the same if the forcing decreases. For *constant* forcing (today) the additional warming is about 0.5°C after 200 years (IPCC AR5 WG1 p.1103 bottom left). For 50 years it’s about half (Knutti, 2008 doi:10.1029/2007JD009473, Fig. 1b). That is for constant forcing, so obviously for *decreasing* forcing it’s even less. RCP2.6 temperature is constant after 2050, it doesn’t increase. As I said before, the climate system is complex, but conservation of energy is not. Look at the simple Q=F-lambda T discussed below: if forcing F is constant or even decreasing, then temperature T only increases a bit because heat uptake Q reduces, but in equilibrium T is proportional to F. So the assumptions that T would continue to increase at the same rate if F is decreasing violates conservation of energy. We are in the fortunate position to have dozens of simple and comprehensive climate models which have run such scenarios, and the models do incorporate all those timescales in the climate and carbon cycle, they include other gases, and the feedbacks. RCP2.6 has zero CO2 emissions around 2075 (IPCC AR5 WG1 Fig. TS.19, p. 94) and stays “likely” below 2°C relative to preindustrial (IPCC AR5 WG1 SPM p.20). Zero CO2 emissions in 2050 would result in less warming than that. Even if the models underestimate the Artic sea ice loss, that would not change those numbers a lot. The albedo feedback is only about a quarter of the total global feedback (IPCC AR4 WG1 Fig. 8.14, p.631). Even the models with the steepest sea ice decline do not support your analysis. No model is perfect, but I’d rather base my conclusions on the best possible representation of all processes, the best data, and a quantitative analysis, than on a naïve and wrong extrapolation of past trends. Climate change is a serious issue, but it doesn’t help if people go out with scary extrapolations that have no scientific basis. Best regards, Reto From: John Nissen [mailto:[email protected]] Sent: Mittwoch, 16. November 2016 11:45 To: Knutti Reto <[email protected]> Cc: Michael MacCracken <[email protected]>; David Lewis <[email protected]>; geoengineering <[email protected]>; Kevin Anderson <[email protected]>; [email protected]; Greg Rau <[email protected]>; Peter Wadhams <[email protected]>; Kevin Lister <[email protected]>; Sev Clarke <[email protected]>; Alan Gadian <[email protected]> Subject: Re: [geo] Negative Emissions: Arrows in the Quiver, Life Preserver, and/or Moral Hazard? Hello Knutti, The arithmetic gives a frightening answer, which I expect is why you never hear it and nobody publishes it. Suppose the CO2 level had got to 500 ppm by 2050, when net emissions reached zero. The CO2 would only fall very slowly for the rest of the century, because of CO2's long life in the atmosphere. Thus the forcing from nearly 500 ppm CO2 would persist for the rest of the century. The current underlying trend rate of global warming is somewhere between 0.2C and 0.3C per decade, given that the average rate over the past 45 years was 0.18C per decade [1]. Taking 0.25C as a conservative average till 2050, and assuming we have had 1.1C global temperature rise since pre-industrial times, the global temperature would rise 0.85C by 2050 to reach 1.95C above pre-industrial. Even if the warming rate remained at only 0.25C for the rest of century, temperature would rise a further 1.25C to reach 3.2C above pre-industrial. Unfortunately leading climate scientists, in their efforts to get CO2 emission reduced, sold a dream to the media, politicians, environmentalists and the UN: that we can adapt to climate change providing net emissions are reduced to zero over the next few decades. According to this dream, the sea ice will last indefinitely, see the figure SPM.7(b) reproduced in Peter W’s book, page 89. Sea level will rise about half a metre this century: 44cm is the ‘best estimate’ in range 28cm to 61cm maximum according to AR5 [2]. There is no need for interventions, except possibly some "negative emissions" to achieve net zero emissions. We can make the planet safe for future generations. But it is a dream. The reality is that we need to reduce the net effect of climate forcing agents to zero, which includes restoring Arctic albedo. Saving the sea ice is crucial. We risk losing a critical element of the control of the planet’s climate system if we allow the Arctic Ocean to become seasonally free of sea ice, since it will probably be locked into this state indefinitely which could have catastrophic consequences for sea level rise, methane emissions and NH weather extremes. The Arctic has already warmed 7C according to Peter Carter. The most natural climate restoration CDR involves putting carbon into trees, soil and marine biomass. This simply involves improving forestry, agriculture and aquaculture practices on a massive scale. It is also returning the planet’s biosphere to a state before human population explosion when forests were cut down, soils denuded of carbon and marine biomass reduced. Surely this can only be good for the planet – and something positive that every environmentalist can work for. We can also use weathering of crushed olivine rocks on a large scale to neutralise CO2 and halt ocean acidification. This, together with local cooling, could save corals – even possibly the Great Barrier Reef. (Diatoms might help purify the water.) Who is standing in the way of this progress towards a safer planet? It is the scientists who continue to promote a dream: a totally unrealistic scenario of the future and a plan to get there. COP is just doing what seems to be required from this plan, though they know they cannot get to net zero emissions quickly enough with current pledges. And Trump now could throw a spanner in the COP works. However the plan is doomed, not because of Trump, but because it is based on a dream. We now need to focus on reality and how we can use CDR and albedo enhancement to restore the Earth System back to the Holocene norm, with potentially huge benefits for humanity and biodiversity. Kind Regards, John [1] https://www.theguardian.com/environment/2016/oct/03/global-temperature-climate-change-highest-115000-years [2] http://www.realclimate.org/index.php/archives/2013/10/sea-level-in-the-5th-ipcc-report/ On Tue, Nov 15, 2016 at 11:38 PM, Knutti Reto <[email protected]<mailto:[email protected]>> wrote: Dear John, > an embarrassment to IPCC, as it conflicts with their story that global > warming can be restricted to 2C or even 1.5C by getting net CO2 emissions to > zero. This is obviously not true from the physics, as I pointed out to you > and some other distinguished scientists a few days ago without challenge! > When net emissions fall to zero the rise in atmospheric CO2 flattens off but > the climate forcing remains, so temperature will continue rising. I wish I > was wrong about this, and we could halt temperature rise so easily. But, if > we are halt global warming we have to reduce the net forcing from all > radiative forcing agents, including Arctic albedo loss, to zero. I don’t deny the need for strong mitigation, but let’s try to inform decisions by the best possible science. Where is the evidence that zero CO2 emissions soon (say before 2050) would be insufficient to limit warming to 2°C. Please send me the papers or your analysis. I’d like to know what is “obviously not true from the physics”. If by “halt global warming” you mean limit/stabilize warming at some level above preindustrial (e.g. 1.5 or 2°C), then your statement is simply wrong: net forcing does not need to be zero as I showed below. By definition net zero forcing implies zero warming in after sufficient time, because the forcing is defined as an anomaly from a reference temperature, typically preindustrial. Best regards, Reto Knutti From: John Nissen [mailto:[email protected]<mailto:[email protected]>] Sent: Dienstag, 15. November 2016 14:53 To: Michael MacCracken <[email protected]<mailto:[email protected]>> Cc: Knutti Reto <[email protected]<mailto:[email protected]>>; David Lewis <[email protected]<mailto:[email protected]>>; geoengineering <[email protected]<mailto:[email protected]>>; Kevin Anderson <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>; Greg Rau <[email protected]<mailto:[email protected]>>; Peter Wadhams <[email protected]<mailto:[email protected]>>; Kevin Lister <[email protected]<mailto:[email protected]>>; Sev Clarke <[email protected]<mailto:[email protected]>>; Alan Gadian <[email protected]<mailto:[email protected]>> Subject: Re: [geo] Negative Emissions: Arrows in the Quiver, Life Preserver, and/or Moral Hazard? [Please excuse if this arrives twice] Hi Mike, I suppose I might have expected you to loyally defend IPCC. But their position is untenable. On the sea ice, Peter Wadhams presented the death spiral to an audience of sea ice modelling experts at the Royal Society, and not a single person rose to say it is not happening. The exponential trend of sea ice volume decline has been followed until 2012, and even the subsequent volume estimates (which are tricky due to so much broken ice and surface slush) are within natural variability. Therefore on the precautionary principle we must act on the expectation of losing sea ice at the end of summer within a few years, despite what modellers might hope. Peter Wadhams points out in his book that the trend towards nearly ice-free conditions in September is "blindingly obvious" and he cannot understand why IPCC clings to models. "The trend in the PIOMAS data effectively gives us a drop-dead date of about 2020 for summer sea ice" [1]. As Kevin Lister points out, a rapid demise of sea ice would be an embarrassment to IPCC, as it conflicts with their story that global warming can be restricted to 2C or even 1.5C by getting net CO2 emissions to zero. This is obviously not true from the physics, as I pointed out to you and some other distinguished scientists a few days ago without challenge! When net emissions fall to zero the rise in atmospheric CO2 flattens off but the climate forcing remains, so temperature will continue rising. I wish I was wrong about this, and we could halt temperature rise so easily. But, if we are halt global warming we have to reduce the net forcing from all radiative forcing agents, including Arctic albedo loss, to zero. This means we have the huge challenge of reducing levels of CO2, methane and other greenhouse gases to their pre-industrial levels. And we have to restore Arctic albedo. When we have done all this, we will have saved the sea ice, halted sea level rise from Greenland ice melt and hopefully restored climate in the Northern Hemisphere, reducing the weather extremes to their old level. Thus we should be close to restoring the Earth System to the 'old norm' of the Holocene in which our civilisation developed and flourished. In the process we can actually improve food production, as I point out in the attached letter which I was hoping could be presented to COP22. Restoration is the only path to a safe future for our children and grand-children. It can be done. It must be done. Best wishes, John [1] Wadhams (2016) "A farewell to ice" page 88. On Tue, Nov 15, 2016 at 7:38 PM, Michael MacCracken <[email protected]<mailto:[email protected]>> wrote: Dear Knutti--Thank you for your note and full explanation. I have been trying to point out these misconceptions of John's for a number of years now. I hope your note will finally convince him. I have also been trying to convince him that the really significant drop in albedo leading to large amounts of additional solar absorbed comes when the fresh snow on ice melts (presumably in late spring), reducing the surface albedo from something like 70-80% to or order 20-30% and that the albedo effect of going from melting ice surface albedo to the albedo of open water (with Sun at low slant angle) will not lead to a catastrophic increase in the absorbed heat in the fall (though it may well set the situation up for an earlier melting of the snow surface in the spring, etc.). What would be really interesting to have is a graph of the amount of solar heat uptake at the surface over the warm season (I guess, as well, actually having a comparison of what the uptake is now with what it would be were there no sea ice). Best regards, Mike MacCracken On 11/15/16 2:18 PM, Knutti Reto wrote: Dear John, all As a coordinating lead author of IPCC AR5 WG1 (and someone how has done work on these topics) I’m surprised to read such comments. > Blunder 1. IPCC has ignored the increasing loss of Arctic albedo, which is > already contributing the equivalent of 30 ppm CO2 to the radiative budget, > i.e. a quarter of the forcing from CO2. […] The first blunder is symptomatic > of IPCC's treatment of the Arctic sea ice, where they refuse to accept the > observations that it is in a death spiral, preferring to rely on models of > proven inadequacy which predict that the sea ice will last for decades. You > can read all about it in Peter Wadhams' new book "A Fairwell to Ice". The change in albedo is part of every climate model as snow cover and sea ice change. Indeed some many models show smaller Arctic sea ice decline than observed. But the natural variability is very large (e.g. Kay 2011, Swart 2015, Screen 2013, 2016). There is no reason why short term trends could simply be extrapolated, and the predictions by Peter Wadhams of sea ice disappearing by today have not happened so far (https://www.theguardian.com/environment/2012/sep/17/arctic-collapse-sea-ice, http://www.independent.co.uk/environment/climate-change/arctic-could-become-ice-free-for-first-time-in-more-than-100000-years-claims-leading-scientist-a7065781.html). Maybe the models are missing something, but it’s just as plausible (and in most scientist’s view more likely) that the models are largely consistent with observations within natural variability. Many studies have used observations to recalibrate and weight models, and even IPCC has explicitly made projections for Arctic sea ice based on those models that best reproduce various aspects of sea ice (section 12.4.6.1). All of these studies indicate that using observations point to a somewhat steeper decline of Arctic sea ice (Boe 2009, Massonnet 2012, Mahlstein 2012, Wang 2013, Notz 2016), but not a “death spiral”. I’m not downplaying the strong changes in the Arctic, but the science suggests a fairly linear (and reversible) relationship between Arctic sea ice and temperature with large variability superimposed. In my view they do not support a “death spiral”. >Blunder 2. IPCC has ignored the warming effect of accumulated CO2. They say >that global temperature rise will be halted when net CO2 emissions have fallen >to zero, ignoring the effect of accumulated CO2 and other forcing agents in >the atmosphere.[…] The second blunder can be illustrated by AR5 WG1 figure >6-40 attached and available here [1]. The red curves are supposed to show the >effect if net emissions were to suddenly fall to zero at 2050, when CO2 has >reached about 500 ppm. The temperature (red curve in bottom diagram) should >continue to rise as a result of the forcing from 500 ppm CO2; but instead the >temperature flattens off as if the accumulated CO2 ceased to have a warming >effect! Of course CO2 continues to have an effect, but as emissions are set to zero the atmospheric concentration and therefore forcing decrease. >It is absolutely astonishing and frightening that such a fundamental mistake >can be made. Where is the evidence for a fundamental mistake? >If we want to halt global warming at any particular temperature, then we need >to bring net forcing down to zero by the time that temperature has been >reached. No, that is simply wrong. The forcing has to decrease to compensate the slowly decreasing ocean heat uptake, but it does not have to be zero at any time to limit warming, not even in equilibrium. The global energy balance is Q=F-lambda*T where Q is heat uptake, F is forcing, lambda is the inverse of climate sensitivity and T is warming (see Knutti and Hegerl 2008 for example). If today F~=2.3 Wm-2 and Q~=0.9 Wm-2 and we want to keep T constant and Q=0 towards equilibrium then F needs to decrease to about 2.3-0.9=1.4 Wm-2 on the timescale on which the ocean warms (decades to centuries), but not zero. Climate is complex, but conservation of energy isn’t. IPCC WG1 chapter 12 has an long discussion of the difference concepts of commitment warming (section 12.5.2) with plenty of references from different models going back many decades. There is even an FAQ 12.3 discussing that, and it also does discuss non-CO2 forcings. There are models which show some warming after zero CO2 emissions, and others that show some cooling, but in general these concepts of commitment warming are well understood. IPCC isn’t perfect, but it’s probably the best reviewed document on climate, with hundreds of scientist contributing. It seems rather unlikely that it would contain “fundamental mistakes”, and in my view the claims you made here have no scientific basis. Best regards, Reto Knutti, ETH Zurich http://www.iac.ethz.ch/people/knuttir Swart, Neil C., John C. Fyfe, Ed Hawkins, Jennifer E. Kay, and Alexandra Jahn. 2015. “Influence of Internal Variability on Arctic Sea-Ice Trends.” Nature Climate Change 5 (2). Nature Publishing Group: 86–89. doi:10.1038/nclimate2483. Kay, Jennifer E., Marika M. Holland, and Alexandra Jahn. 2011. “Inter-Annual to Multi-Decadal Arctic Sea Ice Extent Trends in a Warming World.” Geophysical Research Letters 38 (15): 2–7. doi:10.1029/2011GL048008. Screen, James a., Clara Deser, Ian Simmonds, and Robert Tomas. 2013. “Atmospheric Impacts of Arctic Sea-Ice Loss, 1979–2009: Separating Forced Change from Atmospheric Internal Variability.” Climate Dynamics 43 (1–2): 333–44. doi:10.1007/s00382-013-1830-9. Screen, James A., and Jennifer A. Francis. 2016. “Contribution of Sea-Ice Loss to Arctic Amplification Is Regulated by Pacific Ocean Decadal Variability.” Nature Climate Change 6 (9): 856–60. doi:10.1038/nclimate3011. Boé, Julien, Alex Hall, and Xin Qu. 2009. “September Sea-Ice Cover in the Arctic Ocean Projected to Vanish by 2100.” Nature Geoscience 2 (5). Nature Publishing Group: 341–43. doi:10.1038/ngeo467. Mahlstein, Irina, and Reto Knutti. 2012. “September Arctic Sea Ice Predicted to Disappear near 2°C Global Warming above Present.” Journal of Geophysical Research 117 (D6): 1–11. doi:10.1029/2011JD016709. Notz, Dirk, and Julienne Stroeve. 2016. “Observed Arctic Sea-Ice Loss Directly Follows Anthropogenic CO2 Emission.” Science, November, 1–9. doi:10.1126/science.aag2345. Overland, James E., and Muyin Wang. 2013. “When Will the Summer Arctic Be Nearly Sea Ice Free?” Geophysical Research Letters 40 (10): 2097–2101. doi:10.1002/grl.50316. Massonnet, F., T. Fichefet, H. Goosse, C. M. Bitz, G. Philippon-Berthier, M. M. Holland, and P.-Y. Barriat. 2012. “Constraining Projections of Summer Arctic Sea Ice.” The Cryosphere 6 (6): 1383–94. doi:10.5194/tc-6-1383-2012. Knutti, Reto, and Gabriele C. Hegerl. 2008. “The Equilibrium Sensitivity of the Earth’s Temperature to Radiation Changes.” Nature Geoscience 1 (11): 735–43. doi:10.1038/ngeo337. From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of John Nissen Sent: Montag, 14. November 2016 16:06 To: David Lewis <[email protected]><mailto:[email protected]> Cc: geoengineering <[email protected]><mailto:[email protected]>; Kevin Anderson <[email protected]><mailto:[email protected]>; [email protected]<mailto:[email protected]>; Greg Rau <[email protected]><mailto:[email protected]>; Peter Wadhams <[email protected]><mailto:[email protected]>; Kevin Lister <[email protected]><mailto:[email protected]>; Sev Clarke <[email protected]><mailto:[email protected]>; Alan Gadian <[email protected]><mailto:[email protected]> Subject: Re: [geo] Negative Emissions: Arrows in the Quiver, Life Preserver, and/or Moral Hazard? Dear David, I think Klaus et al have the voice of realism. Global warming is far more serious than we have been led to believe, and without several rapid interventions, we are heading for many degrees of global warming this century. IPCC are guilty of two colossal blunders in their projections of global warming. The effect has been to lull the international community into a false sense of security. Rapid interventions are now required to avoid a lethal combination of climate change, ocean acidification and rising sea levels. Here are the facts: Blunder 1. IPCC has ignored the increasing loss of Arctic albedo, which is already contributing the equivalent of 30 ppm CO2 to the radiative budget, i.e. a quarter of the forcing from CO2. Blunder 2. IPCC has ignored the warming effect of accumulated CO2. They say that global temperature rise will be halted when net CO2 emissions have fallen to zero, ignoring the effect of accumulated CO2 and other forcing agents in the atmosphere. The first blunder is symptomatic of IPCC's treatment of the Arctic sea ice, where they refuse to accept the observations that it is in a death spiral, preferring to rely on models of proven inadequacy which predict that the sea ice will last for decades. You can read all about it in Peter Wadhams' new book "A Fairwell to Ice". The second blunder can be illustrated by AR5 WG1 figure 6-40 attached and available here [1]. The red curves are supposed to show the effect if net emissions were to suddenly fall to zero at 2050, when CO2 has reached about 500 ppm. The temperature (red curve in bottom diagram) should continue to rise as a result of the forcing from 500 ppm CO2; but instead the temperature flattens off as if the accumulated CO2 ceased to have a warming effect! It is absolutely astonishing and frightening that such a fundamental mistake can be made. If we want to halt global warming at any particular temperature, then we need to bring net forcing down to zero by the time that temperature has been reached. This involves bringing all GHGs down to their pre-industrial level and restoring Arctic albedo, unless their residual heating (positive forcing) is counteracted by an equal amount of cooling (negative forcing), e.g. from aerosols. CDR has to suck CO2 out of the atmosphere faster than it is being emitted into the atmosphere, in order to bring the level down from over 400 ppm to pre-industrial 280 ppm. Methane emissions have to be suppressed (including fugitive emissions from coal, oil and gas extraction) in order to bring the level down from 1850 ppb to pre-industrial 750 ppb. The retreat of sea ice has to be halted and then Arctic albedo has to be restored to its level of at least thirty years ago. Thus our best chance to halt global warming is through CO2 emissions reduction (better than already committed) combined with several immediate and aggressive interventions: CDR, methane emissions reduction, and rapid cooling of the Arctic. As Klaus Lackner et al say in their comment, CDR is indeed like throwing a lifebelt to a drowning person. We need to start CDR as quickly as we can, to be as certain as we can be to save the planet. In parallel we must suppress methane and cool the Arctic before we lose any more albedo from snow and sea ice retreat. The ultimate objective must be to restore the Earth System to Holocene conditions of climate stability, ocean alkalinity and sea level constancy. Cheers, John [1] http://www.ipcc.ch/report/graphics/images/Assessment%20Reports/AR5%20-%20WG1/Chapter%2006/thumbnail/Fig6-40.jpg On Mon, Nov 14, 2016 at 4:55 PM, David Lewis <[email protected]<mailto:[email protected]>> wrote: Anderson could maintain his stance as a voice for realism while adding his voice to those calling for research into all forms of geoengineering. He could compare the cost of reducing emissions to the current cost of removing them from the atmosphere, call for a vigorous program of further research, then state that it is still his opinion that civilization needs to urgently and fundamentally transform its social, economic, and political relations if it wants to continue to exist. Moral: Do not ignore or downplay potentially useful actions, especially if you have the time and resources to carefully evaluate them. ________________________________ From: Greg Rau <[email protected]<mailto:[email protected]>> To: Geoengineering <[email protected]<mailto:[email protected]>> Sent: Friday, November 11, 2016 4:50 PM Subject: [geo] Negative Emissions: Arrows in the Quiver, Life Preserver, and/or Moral Hazard? -- 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]<mailto:[email protected]>. To post to this group, send email to [email protected]<mailto:[email protected]>. Visit this group at https://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout . http://science.sciencemag.org/content/354/6313/714.1 GR: Disclaimer - I was a co-signer. -- 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]<mailto:[email protected]>. To post to this group, send email to [email protected]<mailto:[email protected]>. Visit this group at https://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. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To post to this group, send email to [email protected]<mailto:[email protected]>. Visit this group at https://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. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To post to this group, send email to [email protected]<mailto:[email protected]>. Visit this group at https://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. 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 https://groups.google.com/group/geoengineering. 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