Hi Alan—Well, my mistake—I thought I got the 2-month number from your paper on this, but apparently not.
Mike On 3/19/12 1:12 PM, "Alan Robock" <rob...@envsci.rutgers.edu> wrote: > Dear Mike, > > The paper says: > > There is a clear seasonal cycle in the e-folding lifetime of > the stratospheric aerosols in the Arctic case ranging from > 2 to 4 months. The maximum lifetime occurs during boreal > summer with a minimum during boreal winter with the > formation of the polar vortex and higher rates of tropopause > folding. > > So 4 months is the correct number to use if you are looking at a ratio of > impact to mass of sulfur injections. > > > Alan > > [On sabbatical for current academic year. The best way to contact me > is by email, rob...@envsci.rutgers.edu, or at 732-881-1610 (cell).] > > Alan Robock, Professor II (Distinguished Professor) > Editor, Reviews of Geophysics > 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: rob...@envsci.rutgers.edu > New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock > > On 3/19/2012 9:42 AM, Mike MacCracken wrote: >> Re: [geo] Source on SRM causing warming Hi Alan—Well, I got the 2 months >> number from your paper—and used that. Interesting that a more detailed >> evaluation indicates that the lifetime in summer is longer. I think longer >> times than a week might well be possible in the troposphere by choosing >> injection times and meteorological conditions, so I’ll correct to ratio of 10 >> to 20 to 1 for stratosphere, but noting that there might not be a need for >> the aerosols to be there for 4 months, so the longer stratospheric time might >> be real, but not necessarily relevant. >> >> On the issue of the amount of pollution, a couple of comments. Aside from >> arguments over whether it is the sulfate or things with the sulfate causing >> the health effects that have been associated with sulfate from coal-fired >> power plants (for any sulfate injection it would be pure SO2 or whatever >> without all the other combustion products—or perhaps one might use sea salt >> or something else), due to past coal use in Europe and Soviet Union, we have >> a reasonable sense of what the impacts from sulfate might be. With summer >> only injections, one would avoid much of the acid deposition problem (shorter >> season, and not accumulating on snow and running off all at once). One would >> also be choosing emissions times to have air flows that carry the SO2/sulfate >> over the Arctic and not over the land. So, yes, will be some impacts, but can >> possibly be moderated to be less than, as your study suggested, the >> unintended side effects of stratospheric SO2. I am all for considering and >> comparing the full range of possible approaches (stratospheric, tropospheric, >> surface, etc.--separately and/or in combination). >> >> With some sense of what might be able to be done and the potential impacts, >> the next step is a comparative risk evaluation, as for all climate >> engineering. Without doing something, it is hard to see how the Arctic can be >> kept from very extensive thawing and loss of the climate that we have. With >> it, yes, some different types of impacts due to the engineering effort, but, >> assuming it works, a good deal less, or slowed climate impact on the Arctic, >> and if loss of glacier/ice sheet mass can be slowed (or reversed—as >> Caldeira-Wood study suggested), then a benefit to the global community. >> >> With some sense of relative risks of various choices, it becomes a political >> decision, with its many considerations. I happen to think that, if any >> climate engineering is to be considered, having a focused goal such as >> limiting polar warming and associated impacts would be more likely to be >> considered as a first step than jumping straight to a global >> counter-balancing approach, but that is just my opinion. In any case, rather >> than saying what is or is not acceptable, it seems to me our responsibility >> is to explore and evaluate options and then it is the governance system that >> decides about the tradeoffs of pollution versus un- (or under-) moderated >> Arctic change (and everything else). >> >> Mike >> >> >> On 3/19/12 12:03 PM, "Alan Robock" <rob...@envsci.rutgers.edu> wrote: >> >> >>> Dear Mike, >>> >>> I don't know how you do this 6 to 1 calculation. We found that the >>> e-folding time for stratospheric aerosols in the Arctic s 2-4 months, with 4 >>> months in the summer, the relevant time. (see >>> http://climate.envsci.rutgers.edu/pdf/2008JD010050small.pdf ) If we compare >>> this to the lifetime of tropospheric aerosols, on week, and add a week to >>> the 4 months for their tropospheric time, the ratio is 130 days to 7 days, >>> which is 19 to 1, not 6 to 1. Furthermore, the health effects of additional >>> tropospheric pollution are not acceptable, in my opinion. >>> >>> >>> Alan >>> >>> [On sabbatical for current academic year. The best way to contact me >>> is by email, rob...@envsci.rutgers.edu, or at 732-881-1610 (cell).] >>> >>> Alan Robock, Professor II (Distinguished Professor) >>> Editor, Reviews of Geophysics >>> 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: rob...@envsci.rutgers.edu >>> New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock >>> <http://envsci.rutgers.edu/%7Erobock> >>> >>> On 3/18/2012 5:49 PM, Mike MacCracken wrote: >>> >>>> >>>> Hi Stephen--My wording must have been confusing. >>>> >>>> For stratospheric injections at low latitudes, the lifetime is 1-2 years. >>>> The aerosols do move poleward and are carried into the troposphere in mid >>>> and high latitudes. This is one approach to trying to limit global climate >>>> change, and, as David Keith says, studies indicate that these cool the >>>> polar >>>> regions, though perhaps not in the stratosphere. >>>> >>>> Your cloud brightening approach is also to limit global warming. I'd also >>>> suggest that we could offset some of the global warming by sulfate >>>> aerosols >>>> out over vast ocean areas instead of sulfate's present dominance over, >>>> now, >>>> southeastern Asia, China, etc.--so keeping or modestly enhancing the >>>> present >>>> cooling offset. [And reducing cirrus may also be a viable approach.] >>>> >>>> A third approach is to cool the poles (and this might be good for regional >>>> purposes alone), but cooling also pulls heat out of lower latitudes and >>>> helps to cool them somewhat. The Caldeira-Wood shows it works conceptually >>>> (they reduced solar constant) and Robock et al. injected SO2 into >>>> stratosphere to do (but the full year injection of SO2/SO4 likely spread >>>> some to lower latitudes and the monsoons were affected). One thing Robock >>>> et >>>> al. found was that the lifetime of sulfate in the polar stratosphere is >>>> about two months, and so that means that the potential 100 to 1 advantage >>>> of >>>> stratospheric sulfate is not valid, and we're down to 6 to 1 compared to >>>> surface-based approaches such as CCN or microbubbles to cool incoming >>>> waters, sulfate or something similar over Arctic area, surface brightening >>>> by microbubbles, etc.--noting that such approaches are only needed (and >>>> effective) for the few months per year when the Sun is well up in the >>>> sky. >>>> >>>> As David Keith also says, there is a lot of research to be done to >>>> determine >>>> which approaches or alone or in different variants might work, or be >>>> effective or ineffective and have unintended consequences, much less how >>>> such an approach or set of approaches might be integrated with mitigation, >>>> adaptation, suffering, etc. >>>> >>>> Best, Mike MacCracken >>>> >>>> >>>> >>>> >>>> >>>> >>>> On 3/18/12 12:52 PM, "Stephen Salter" <s.sal...@ed.ac.uk> >>>> <mailto:s.sal...@ed.ac.uk> wrote: >>>> >>>> >>>> >>>>> >>>>> Mike >>>>> >>>>> I had thought that the plan was stratospheric aerosol to be released at >>>>> low latitudes and would slowly migrate to the poles where is would >>>>> gracefully descend. If you can be sure that it will all have gone in 10 >>>>> days then my concerns vanish. But if the air cannot get through the >>>>> water surface how can the aerosol it carries get there? It will form a >>>>> blanket even if it is a very low one. >>>>> >>>>> A short life would mean that we do not have to worry about methane >>>>> release. But can we do enough to cool the rest of the planet? Perhaps >>>>> Jon Egil can tell us about blanket lifetime. >>>>> >>>>> Stephen >>>>> >>>>> Mike MacCracken wrote: >>>>> >>>>> >>>>>> >>>>>> The Robock et al simulations of an Arctic injection found that the >>>>>> lifetime >>>>>> of particles in the lower Arctic stratosphere was only two months. In >>>>>> that >>>>>> one would only need particles up during the sunlit season (say three >>>>>> months, >>>>>> for only really helps after the sea ice surface has melted and the sun >>>>>> is >>>>>> high in the sky). During the relatively calm weather of Arctic summer, >>>>>> the >>>>>> lifetime of tropospheric sulfate, for example‹and quite possibly sea >>>>>> salt >>>>>> CCN--emitted above the inversion is likely 10 days or so. It is not at >>>>>> all >>>>>> clear to me that the 6 to 1 or so lifetime advantage of the lower >>>>>> stratosphere is really worth the effort to loft the aerosols. >>>>>> >>>>>> And on the temperature rise in the polar stratosphere, I would hope any >>>>>> calculation of the effects of the sulfate/dust injection only put it in >>>>>> during the sunlit season‹obviously, there would be no effect on solar >>>>>> radiation during the polar night, so, with a two month lifetime of >>>>>> aerosols >>>>>> there, it makes absolutely no sense to be lofting anything for about two >>>>>> thirds of the year. And so likely no effect on winter temperatures >>>>>> (although >>>>>> warming the coldest part of the polar winter stratosphere might well >>>>>> help to >>>>>> prevent an ozone hole from forming). >>>>>> >>>>>> So, I think a tropospheric brightening approach is likely the better >>>>>> option. >>>>>> Whether it can be done with just CCN or might also need sulfate seems to >>>>>> me >>>>>> worth investigating (what one needs may well be not just cloud >>>>>> brightening, >>>>>> but also clear sky aerosol loading). >>>>>> >>>>>> Best, Mike >>>>>> >>>>>> ***** >>>>>> >>>>>> On 3/17/12 8:41 PM, "Ken Caldeira" <kcalde...@carnegie.stanford.edu> >>>>>> <mailto:kcalde...@carnegie.stanford.edu> wrote: >>>>>> >>>>>> >>>>>> >>>>>> >>>>>>> >>>>>>> That is just misleading. The third attachment is a top-of-atmosphere >>>>>>> radiation balance on the email I am responding to shows shortwave >>>>>>> radiation. >>>>>>> >>>>>>> The attached figure shows the corresponding temperature field from the >>>>>>> same >>>>>>> simulation for the same time period. Note Arctic cooling. >>>>>>> >>>>>>> Also, we should not focus on individual regional blobs of color in an >>>>>>> average >>>>>>> of a single decade from a single simulation. >>>>>>> >>>>>>> The paper these figures came from is here: >>>>>>> http://www.atmos-chem-phys.net/10/5999/2010/acp-10-5999-2010.pdf >>>>>>> >>>>>>> _______________ >>>>>>> Ken Caldeira >>>>>>> >>>>>>> Carnegie Institution Dept of Global Ecology >>>>>>> 260 Panama Street, Stanford, CA 94305 USA >>>>>>> +1 650 704 7212 kcalde...@carnegie.stanford.edu >>>>>>> http://dge.stanford.edu/labs/caldeiralab @kencaldeira >>>>>>> >>>>>>> YouTube: >>>>>>> <http://www.youtube.com/watch?v=a9LaYCbYCxo> Climate change and the >>>>>>> transition from coal to low-carbon electricity >>>>>>> <http://www.youtube.com/watch?v=a9LaYCbYCxo> >>>>>>> Crop yields in a geoengineered climate >>>>>>> <http://www.youtube.com/watch?v=-0LCXNoIu-c> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Sat, Mar 17, 2012 at 1:31 PM, Andrew Lockley >>>>>>> <and...@andrewlockley.com> <mailto:and...@andrewlockley.com> >>>>>>> wrote: >>>>>>> >>>>>>> >>>>>>> Hi Here are some model outputs which Stephen sent me. These appear to show localized arctic warming in geoengineering simulations. This could be due to winter effects. I assume this is the source for the controversial figure in the BBC quote A >>>>>>> >>>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>>> >>>> >>>> >>>> >>>> >>>> >>> >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To post to this group, send email to geoengineering@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. >> > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. 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