Steven I am in favor of serious research on both strat aerosols and sea salt CCN.
Your comments suggest that you already know the outcome of that research. You may of course be correct, and in many ways I hope you are. I, however, see less basis for certainty. A few facts that seem relevant: 1. All simulations of stratospheric aerosols of which I am aware do show an arctic cooling tendency and increase in sea ice extent. 2. There is little reason to doubt that 1 Wm^2 radiative global forcing could be produce by sulfate aerosols using well understood technologies. (That is not a claim about risks and side effects, just about basic capability.) 3. There are large uncertainties about the efficacy of sea salt CCN in producing radiative forcing. It will certainly work sometimes under some conditions, but we don't yet have a good quantitative understanding of extent of conditions in which it might work and therefore of the aggregate effectiveness. 4. There are advantages and disadvantages to the fact that the sea salt CCN is more patchy. Given this is seems to me hard to conclude that we know the answer yet. Yours, David -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Stephen Salter Sent: Sunday, March 18, 2012 10:52 AM To: [email protected] Cc: Ken Caldeira; Andrew Lockley; Geoengineering; [email protected] Subject: Re: [geo] Source on SRM causing warming 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]> 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]> >> 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 >>> > > -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. -- 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. -- 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.
