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 -- 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.
