Possibly. Note that Figure 4 from the paper is based on a model and not on actual measurements of radiative forcing. Since it is impossible to obtain cloud ice crystal samples from the 1970's, before leaded gasoline was phased out, one cannot say for certain that the large global negative forcing from the water deprived low level cirrus clouds would have occurred in the southern hemisphere. Leaded gasoline was only ended in Australia in 2002, so perhaps more recent field data can be used to address this uncertainty. All of the field data from the study was from European locations.
My guess is that the impact was much greater in the N. hemisphere, and taking a crude average while noting the Figure like all such figures is misleading with respect to surface area covered, the actual global impact was probably less than 0.4 W/M2, significant, but not enough to offset all or even half of the GHG forcing. Could one take advantage of the apparent increase in outgoing IR from such clouds today? Clearly, adding lead to the atmosphere is a non starter and I don't think it would be possible to do it anyway. The 50 nm diameter (radius?) particles in question were a very small fraction of a much larger universe of particles from burning of gasoline. Most of the lead from gasoline combustion ended up a few meters from the tailpipes of cars. So to duplicate this would require either a resumption of the burning of leaded gasoline, the burning of some kind of fuel containing lead just for this purpose (the scale would have to be much less and the lead content much higher, somewhat analogous to the idea behind enhancing sulfur in jet fuel) or to use some other material with similar properties. A specially engineered nano particle would seem the most likely choice, but since there are no such materials, this is not possible either. Phil Rasch presented a paper at the 2008 AGU meeting in which he proposed to increase cirrus clouds by adding water to them from aircraft. I may have the proposed mechanism wrong, but I think these were the more normal high level cirrus clouds and the objective was increased reflection of sunlight, not increased emission of IR. I had previously taken Cziczol to task for his uninformed comments about geoengineering in an interview Dan Whaley posted a short time ago. Looking through some of the other interviews, he made no mention of the geoengineering matter, so I assume that came about as a prompt from the journalist. My comments about Cziczol on this still stand. On May 18, 10:06 am, Ken Caldeira <[email protected]> wrote: > I thought this interesting not because adding lead to clouds is likely to be > a popular option, but because it suggests there may be scope for engineering > on the longwave side of the balance. > > Ken > > ---------------------------- > > Nature Geoscience 2, 333 - 336 (2009) > Published online: 19 April 2009 | doi:10.1038/ngeo499 > Inadvertent climate modification due to anthropogenic leadDaniel J. > Cziczo1<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a1> > ,2 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a2>, Olaf > Stetzer2 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a2>, > Annette > Worringen3<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a3>, > Martin Ebert3 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a3>, > Stephan > Weinbruch3<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a3>, > Michael > Kamphus4<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a4>, > Stephane J. > Gallavardin2<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a2> > ,4 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a4>, Joachim > Curtius4 > <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a4>,5<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a5>, > Stephan > Borrmann4<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a4> > ,6 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a6>, Karl D. > Froyd7 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a7>, > Stephan Mertes8<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a8>, > Ottmar Möhler9<http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a9>& > Ulrike Lohmann > 2 <http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html#a2> > > Aerosol particles can interact with water vapour in the atmosphere, > facilitating the condensation of water and the formation of clouds. At > temperatures below 273 K, a fraction of atmospheric particles act as sites > for ice-crystal formation. Atmospheric ice crystals—which are incorporated > into clouds that cover more than a third of the > globe1<http://www.nature.com/ngeo/journal/v2/n5/full/ngeo499.html#B1>—are > thought to initiate most of the terrestrial > precipitation2<http://www.nature.com/ngeo/journal/v2/n5/full/ngeo499.html#B2>. > Before the switch to unleaded fuel last century, the atmosphere contained > substantial quantities of particulate lead; whether this influenced > ice-crystal formation is not clear. Here, we combine field observations of > ice-crystal residues with laboratory measurements of artificial clouds, to > show that anthropogenic lead-containing particles are among the most > efficient ice-forming substances commonly found in the > atmosphere3<http://www.nature.com/ngeo/journal/v2/n5/full/ngeo499.html#B3>. > Using a global climate model, we estimate that up to 0.8 W m-2 more > long-wave radiation is emitted when 100% of ice-forming particles contain > lead, compared with when no particles contain lead. We suggest that > post-industrial emissions of particulate lead may have offset a proportion > of the warming attributed to greenhouse gases. > > http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo499.html > > see also:http://www.sciencedaily.com/releases/2009/05/090512093542.htm > > ___________________________________________________ > Ken Caldeira > > Carnegie Institution Dept of Global Ecology > 260 Panama Street, Stanford, CA 94305 USA > > [email protected]; > [email protected]http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab > +1 650 704 7212; fax: +1 650 462 5968 > > Cziczo_et_al_NatureGeo2009.pdf > 977KViewDownload --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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