Some simple math: Global sulfur emissions into troposphere are about 50 Mt-S per year and they have a direct radiative forcing of about -0.4 Wm^-2.
These same sulfate aerosols kill about 1 million people per year. Of course current emissions are concentrated where people are you the ratio of mortality to radiative forcing is larger than it would be if you were focused on radiative forcing with tropospheric sulfate. But it would still be big. Intercontinental transport of sulfate kills, see: http://meetings.copernicus.org/www.cosis.net/abstracts/EGU2007/05111/EGU2007-J-05111.pdf If you want to make 1Wm^-2 of forcing with sulfate aerosol in the troposphere you might need of order 50 Mt-S per year, whereas in the stratosphere you might be able to get away with just over 1 Mt-S per year. (see #127 at http://www.keith.seas.harvard.edu/geo.html). One might do some optimization, but the case here has been clear for a long time. We said some of this twenty years ago. See in the table in the following though many numbers now look out of date or wrong: David W. Keith and Hadi Dowlatabadi (1992). A Serious Look at Geoengineering. Eos, Transactions American Geophysical Union, 73: 289-293. (PDF)<http://www.keith.seas.harvard.edu/papers/09_Keith_1992_SeriousLookAtGeoeng_s.pdf> David From: [email protected] [mailto:[email protected]] On Behalf Of Govindasamy Bala Sent: Thursday, March 15, 2012 9:53 PM To: [email protected] Cc: geoengineering Subject: Re: [geo] tropospheric aerosol use "Climate changes" by Budyko, on page 244, discusses why tropospheric aerosols are not as effective as stratospheric aerosols for climate modification. 1) life time is only a couple of weeks 2) Particle size becomes too big quickly and hence not effective for scattering 3) Presence of clouds make them less effective 4) absorption by aerosols of near IR shortwave could partially cancel the cooling by scattering. Bala On Thu, Mar 15, 2012 at 9:53 PM, Nathan Currier <[email protected]<mailto:[email protected]>> wrote: Does anyone know of any published papers exploring the use of tropospheric aerosol use? cheers, Nathan -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]<mailto:[email protected]>. To unsubscribe from this group, send email to [email protected]<mailto:geoengineering%[email protected]>. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en. -- Best wishes, ------------------------------------------------------------------- Dr. G. Bala Associate Professor Center for Atmospheric and Oceanic Sciences Indian Institute of Science Bangalore - 560 012 India Tel: +91 80 2293 3428 +91 80 2293 2075 Fax: +91 80 2360 0865 +91 80 2293 3425 Email: [email protected]<mailto:[email protected]> bala.gov<http://bala.gov>@gmail.com<http://gmail.com> Web:http://caos.iisc.ernet.in/faculty/gbala/gbala.html ------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]<mailto:[email protected]>. To unsubscribe from this group, send email to [email protected]<mailto:[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.
