Hello John, Given - I believe - that neither of us would chose to support the deployment of any SRM scheme unless and until: (1) it is globally accepted to be manifestly necessary, (2) a comprehensive examination of all possible adverse consequences of deployment (meteorological, climatological, hydrological, societal, chemical etc etc) has been conducted and deemed by some internationally agreed body to be non-existent or negligible, it is not realistic for us to envisage any adequately powerful SRM scheme to be deployed within an absolute minimum of 5 years and more likely 10. With those constraints in mind, I see no reason to assume that either of these schemes would be ready for deployment significantly earlier or later than the other. (I dont know on what basis you have made your judgement as to time-frames). What needs to happen is that a rigorous and comprehensive research assessment of all aspects of both schemes (and any other promising ones) should be adequately funded immediately. A decision re deployment cannot sensibly be made until all the above requirements have been met.
Limited-area field-testing designed to better understand the natural phenomena involved, to assess the SRM schemes and the technology under development are of course an important part of what is required. A little of this has already been conducted, in the case of both schemes, largely inadvertently. But the journey ahead remains a long one. Cheers, John. lat...@ucar.edu Quoting John Nissen <j...@cloudworld.co.uk>: Hi John, While I absolutely agree that a joint approach of stratospheric aerosols and marine cloud brightening would be ideal, I don't believe we have the luxury of time to wait until the latter is ready for deployment. There is a very fundamental difference of view between people in this group as to the severity of the situation in the Arctic, and hence the balancing of geoengineering risks against the risks of not geoengineering. I find myself at one end of the spectrum, believing that we are if anything verging on being too late to save catastrophe, with the sea ice imminent disappearance being a catalyst for the dual catastrophes of methane release and Greenland ice sheet disintegration. I suspect others in this group, perhaps Alan Robock may be an example, are at the other end of the spectrum, believing that there is not significant risk of reaching a tipping point in the Arctic for many decades, and hence emissions reductions should be given a chance to work. People at this end of the spectrum would consider the dangers of geoengineering are inevitably greater than those of not geoengineering. However, as David Keith has observed, the more scientists look at the dangers arising from excess CO2 in the atmosphere and global warming, the more worried they become. Many of us have been brought up to think of this world being created for our benefit, such that it will continue automatically to look after us, as a benign natural system. Interference with this system invites retribution - and geoengineering is seen as a dangerous interference. However there is much evidence that our civilisation has developed over the past 8000 years with the climate system precariously balanced between getting too hot (and sea level rising) and getting too cold (with sea level falling). There is the Ruddiman hypothesis, that mankind has emitted just the amount of greenhouse gases over this period to maintain the precise balance to allow civilisation to develop. Furthermore there have been no super-volcanoes (such as Toba) to upset this balance, although one or two are now overdue. Thus it is entirely by luck that our society has been able to develop - with coal and oil at hand to fuel our growth to 6 billion people, globally trading. There is absolutely no reason why this luck should continue. And we have now upset the balance by injecting a colossal pulse of CO2 into the atmosphere. If you start to look at geoengineering from this perspective, you see it as almost certainly the only way out of the mess we have got ourselves into. Certainly emissions reduction has no chance to avoid catastrophes arising in the Arctic, because of the time-scales involved. Since politicians are still being told that emissions reductions can save the day, I can only assume that their advisers do not have this perspective on the situation, and do not appreciate the degree of danger we might be in. Nobody wants to believe how dangerous the situation might be. We all prefer to turn a blind eye to the possibility that our whole civilisation could collapse. However Jared Diamond, who has looked into how past civilisations have collapsed, finds that we are doing all the wrong things. So I see SRM with stratospheric (or possibly tropospheric) aerosols as something we could do very quickly to stave off further retreat of Arctic sea ice, while we beaver away at getting the Salter ships afloat and wafting spray into marine clouds. If I am to feel reasonably safe for my children, the SRM with aerosols would be be started this year, to at least to establish an engineering solution that could be quickly scaled up. Cheers, John --- John Latham wrote: > * > * > * > * To:- > geoengineering@googlegroups.com,climateintervent...@googlegroups.com > > From:- john latham lat...@ucar.edu > > Hello All, > > Yesterday?s contributions from Alan Robock, Gregory Benford and > Kelly Wanser are very useful in highlighting a variety of important, > delicate and unresolved questions regarding geoengineering, > especially SRM ideas and polar ice cover. I agree with Kelly that > although Paul Crutzen?s stratospheric sulfur idea is the > long-standing front-runner amongst the SRM schemes and should > certainly be fully funded for comprehensive examination, the focus > on it as against other SRM schemes ? especially cloud whitening ? > has perhaps been somewhat excessive. > > Two independent recent papers, employing very different models, > indicate that ? subject to satisfactory resolution of each one of a > number of crucial questions regarding technological, cloud behavior > and adverse consequence issues, which may of course not be achieved > ? the cloud whitening scheme, deployed in a 2xCO2 atmosphere, could > maintain the sea-ice coverage at both poles (and also globally > averaged surface temperature) at approximately current values, > although the geographical distributions would be different from at > present. I attach a recently published paper by Rasch et al. which > gives more detail on some of this work. > > I agree with Kelly that should it ever be generally deemed that SRM > geoengineering was necessary, and if intensive research showed that > both above-mentioned schemes were technologically feasible, with no > unacceptable adverse consequences, then using them both in concert > may well be optimal, as more flexibility would thereby exist. > > Cheers, John. > > -- > John Latham > > lat...@ucar.edu & john.latha...@manchester.ac.uk > > Tel. 303-444-2429 (H) & 303-497-8182 (W) -- > You received this message because you are subscribed to the Google > Groups "geoengineering" group. > To post to this group, send email to > geoengineer...@googlegroups.com. > To unsubscribe from this group, send email to > geoengineering+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. -- John Latham lat...@ucar.edu & john.latha...@manchester.ac.uk Tel. 303-444-2429 (H) & 303-497-8182 (W) -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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