Dear AlanThank you for the paper and also for including a mention of cloud brightening. The presence or absence of ship tracks may be misleading.
As you can see from the 20 bar grey scale which should be below, the minimum contrast detectable by eye for sharp edged rectangles is three or four bars or 15 to 20% while the albedo change we need to reverse 1.6 watts per square damage since preindustrial times is only 0.47%. The fact that cloud brightening can work in both directions with some places giving cooling of 100 watts per square metre is very promising provided that we can tell where the good places, stop doing it in the bad places and make the change-over quickly. While this might need a new satellite instrument we may also be able to fit cloud-type sensors on each spray vessel.
I would much prefer an air conditioning system which allows local control in both directions with rapid adjustment and low phase shift. This is like a car with agile response to movements of the steering wheel as opposed to one which you buy with all direction changes burnt into a read-only memory based on road maps two years out of date.
Did you get a paper I did some time ago on detecting very small contrast changes?
Please let me know if you would like any other designs of grey scale. Stephen On 05/05/2013 13:39, Alan Robock wrote:
Robock, Alan, Douglas G. MacMartin, Riley Duren, and Matthew W. Christensen, 2013: Studying geoengineering with natural and anthropogenic analogs. /Climatic Change/, doi:10.1007/s10584-013-0777-5, published online.*Abstract.* Solar radiation management (SRM) has been proposed as a possible option for offsetting some anthropogenic radiative forcing, with the goal of reducing some of the associated climatic changes. There are clearly significant uncertainties associated with SRM, and even small-scale experiments that might reduce uncertainty would carry some risk. However, there are also natural and anthropogenic analogs to SRM, such as volcanic eruptions in the case of stratospheric aerosol injection and ship tracks in the case of marine cloud albedo modification. It is essential to understand what we can learn from these analogs in order to validate models, particularly because of the problematic nature of outdoor experiments. It is also important to understand what we cannot learn, as this might better focus attention on what risks would need to be solely examined by numerical models. Stratospheric conditions following a major volcanic eruption, for example, are not the same as those to be expected from intentional geoengineering, both because of confounding effects of volcanic ash and the differences between continuous and impulsive injection of material into the stratosphere. Nonetheless, better data would help validate models; we thus recommend an appropriate plan be developed to better monitor the next large volcanic eruption. Similarly, more could be learned about cloud albedo modification from careful study not only of ship tracks, but of ship and other aerosol emission sources in cloud regimes beyond the narrow conditions under which ship tracks form; this would benefit fromimproved satellite observing capabilities. See attachment. -- Alan Robock Alan Robock, Distinguished Professor Editor, Reviews of Geophysics Director, Meteorology Undergraduate Program Associate Director, Center for Environmental Prediction Department of Environmental Sciences Phone: +1-848-932-5751 Rutgers University Fax: +1-732-932-8644 14 College Farm Road E-mail:[email protected] New Brunswick, NJ 08901-8551 USAhttp://envsci.rutgers.edu/~robock http://twitter.com/AlanRobock --You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
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