Hello Erica (and Ken, Stephen & Co), I wish, Erica, to add a little more information to the comments made by Stephen Salter and Ken Caldeira vis-a-vis your upcoming paper in Science News. Ken has confirmed Stephen's statement that a conclusion of the Bala, Caldeira et al paper is that - for the conditions examined - the rainfall over land at the CO2x2 point, with cloud seeding occurring, the rainfall over land is nowhere less than in the current (or control) CO2x1 situation, and is greater in some regions. Bala et al have provided a plausible physical / meteorological explanation for this result.
The current situation regarding the crucially important question of the impact of the cloud brightening scheme on rainfall over land is, as far as I know, as follows. Three GCM studies have been made, by three separate groups, using three different and well-regarded models. (1) Jones et al (2008) reported that cloud seeding could produce significant reductions of rainfall over northern South America. (2) Rasch et al. (2009) did not find rainfall reduction in this area, and did not find significant rainfall reduction over land. (3) Bala et al found no rainfall reduction over land, as described earlier. In addition to the differences between the three models, the most significant differences between the three studies seem to us to be the large differences in the fraction of oceanic suitable clouds seeded. In the case of the Jones at el study, this was very small. In the case of the Rasch et al study a wide range of intermediate fractions was employed. In the case of the Bala et al study - which is the most comprehensive of the three vis a vis rainfall changes over land - all suitable maritime clouds were seeded. We have recently initiated model-comparison studies which hopefully will tell us whether the differences in results are due to differences in the models or differences in the fraction (and location) of clouds seeded. At this stage the question as to whether or not the cloud brightening scheme would reduce significantly rainfall anywhere over land must remain an open question. No categoric statement can be made at this stage, in my view. We'd be most grateful, Erica, if it was possible for you to modify your article to take account of the points made by Stephen, Ken and me. If this is not possible at this late stage please could you advise us how best to publish a rebuttal of your statement on this one point in the next issue of your magazine. Thank you. My final point is that all three studies indicate that IF ALL outstanding technological, scientific and adverse ramification questions could be satisfactorily and positively resolved, the cloud brightening geoengineering technique could produce a globally averaged negative forcing which would roughly balance the positive forcing resulting from a doubling of atmospheric CO2 concentration. All Best Wishes, John. [email protected] Quoting Ken Caldeira <[email protected]>: > The paper under discussion is either in press or close to being in press at > Climate Dynamics with G Bala as first author. > > Because of Clausius-Claperyon, one expects precipitation to increase with > heating and decrease with cooling. So you would expect a CO2 induced warming > to increase precipitation and a cloud-whitening induced cooling to decrease > precipitation. > > Relative to the 2xCO2 case we do find that cloud whitening reduces > precipitation. However, it reduces it preferentially over the oceans, and > over land it does not reduce it as much as the CO2 increased it. So, in our > simulations with 2xCO2 and unrealistically large and uniform amounts of > marine cloud whitening, relative to the 1xCO2 case, there is a decrease in > precipitation over the oceans and an increase over land. > > Significantly, even though, relative to the 2xCO2 case there is a decrease > in precipitation over land, there is an even greater decrease in evaporation > over land, so on average soils are moister and there is an increase in > runoff. > > So, there does seem to be an error in Erika's story (which could have been > entirely the result of my having misspoken). > > > ___________________________________________________ > 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 > > > On Fri, May 28, 2010 at 8:51 AM, Stephen Salter <[email protected]> wrote: > >> Erika >> >> In your geoengineering article in Science news due out on 5 June you quote >> Ken Caldeira as saying that cloud brightening would decrease rainfall over >> land. Alan Robock has collected evidence to show that this has been observed >> in volcanic historical eruptions and it has been predicted for stratospheric >> aerosols. >> >> However a paper by Bala and others, including Caldeira, says the opposite >> is the case for cloud brightening. Their final paragraph reads >> >> /In summary, prior studies have suggested that offsetting global warming by >> reflecting sunlight to space would result in a drying of the continents. In >> contrast, our study indicates that reflecting sunlight to space by reducing >> cloud droplet size over the oceans could lead, on average, to a moistening >> of the continents. >> >> /The Bala paper is too big to attach to an email but you can download a >> copy from the root of the file below my signature. >> >> The difference is very important and your article could affect decisions on >> research funding. May I ask you to look into the matter? >> >> Stephen Salter >> / >> / >> >> Emeritus Professor of Engineering Design >> School of Engineering and Electronics >> University of Edinburgh >> Mayfield Road >> Edinburgh EH9 3JL >> Scotland >> tel +44 131 650 5704 >> fax +44 131 650 5702 >> Mobile 07795 203 195 >> [email protected] >> http://www.see.ed.ac.uk/~shs[1] <http://www.see.ed.ac.uk/%7Eshs> >> >> >> Erika Engelhaupt wrote: >> >>> >>> My feature story on geoengineering is out in the June 5 issue of Science >>> News, which you should be receiving a complimentary copy of in the mail. In >>> the meantime, here is a link to the online version, where you can also see >>> the illustration featured on our cover: >>> >>> >>> http://www.sciencenews.org/index/feature/activity/view/id/59391/title/Engineering_a_cooler_Earth >>> >>> (A better view of the cover is up on /Science News/’ Facebook site: >>> http://www.facebook.com/#!/photo.php?pid=4002108&id=35695491869<http://www.facebook.com/#%21/photo.php?pid=4002108&id=35695491869>< >>> http://www.facebook.com/#%21/photo.php?pid=4002108&id=35695491869> ) >>> >>> >>> /Science News/ is now also available on select Barnes & Noble and Borders >>> newsstands nationwide, although I’m not sure if they’ve received the new >>> issue quite yet. >>> >>> I hope you enjoy the story and find that I’ve balanced the issues >>> fairly—there was much more that I would have liked to have included if I’d >>> had more space. >>> >>> Best regards, >>> >>> Erika >>> >>> Erika Engelhaupt >>> >>> Deputy News Editor >>> >>> /Science News/// >>> >>> >> -- >> 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 >> "Climate Intervention" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]<climateintervention%[email protected]> >> . >> For more options, visit this group at >> http://groups.google.com/group/climateintervention?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. > > -- John Latham [email protected] & [email protected] Tel. 303-444-2429 (H) & 303-497-8182 (W) Links: ------ [1] http://www.see.ed.ac.uk/%7Eshs -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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