Doesn't lifetime depend massively on injection height & particle size? Size in turn depends on precursor, injection density, weather etc.
What is the latest thinking on the preferred precursor and injection conditions? Acid mist, SO2 or H2S? A On Mar 19, 2012 4:43 PM, "Mike MacCracken" <[email protected]> wrote: > 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" <[email protected]> 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, [email protected], 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: [email protected] > New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock > > 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" <[email protected]> < > mailto:[email protected] <[email protected]>> 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" <[email protected]> < > mailto:[email protected] <[email protected]>> > 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 [email protected] > 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 <[email protected]> > <mailto:[email protected] <[email protected]>> > 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 [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.
