Re: [geo] Re: cloud seeding - need for research - ja

[John Nissen]

Hi John, I saw some research somewhere that said that global cloud cover had decreased over the past decades, contributing slightly to global warming.  But I can't find it now.  Do you know about it?  Could it be due to black carbon?  Here's an extract from a Hansen essay: 'Black carbon aerosols cause a positive climate forcing that is very uncertain in magnitude, but we estimate that it is probably of the order of 0.5 to 1 Watt per square meter on global average. It causes warming in several ways: by absorbing sunlight, by warming the lower layer of the atmosphere and thus reducing cloud cover, by making clouds slightly "dirty", and by darkening snow and sea ice surfaces when it is deposited there.' (http://www.giss.nasa.gov/research/features/200111_altscenario/discussion.html) Perhaps more importantly, do we know what is happening in the Arctic?  I believe it was expected that cloud cover would increase significantly over coming decades - which would reduce the effectiveness of any stratospheric aerosol geoengineering.  (I'm copying this to Jeff Ridley who might know the answer.) Whilst cloud cover has a cooling effect in Arctic summer, I assume it would have a heating effect in winter.  How do these effects balance out?  Has anybody done the calculations? Cheers, John --- John Latham wrote: Hello Mike et al, I agree entirely with you Mike that seeding can cause ice fogs to disperse. Also electrostatic droplet seeding could help dissipate warm fogs. I should have more carefully indicated that I was focusing on seeding of  clouds containing ice, and particularly mixed-phase clouds. Cheers,      John. Quoting Mike MacCracken <mmacc...@comcast.net>: > With one exception, I agree with John. The exception is that I think it has > been demonstrated that one can clear an ice fog with seeding, and this has > been done to open airports, etc.--not to generate precipitation (in any > form). > > I would add that the water vapor content of air and clouds above Greenland > is likely so low that one could not be likely to get a significant buildup > of snow. Whether one could seed storms or change sea surface temperatures in > surrounding areas in a way that would lead to greater likelihood of storms > depositing snow on Greenland (or Antarctica, etc.) has not, to my knowledge, > been looked at at all. > > Mike > > > On 12/16/09 4:00 AM, "John Latham" <john.latha...@manchester.ac.uk> wrote: > >> Hello Neil, Andrew et al. >> >> Cloud seeding (principally to make rain) has had a long and highly chequered >> history in the 60 years since Vonnegut, Schaefer & Langmuir did their >> pioneering work. Many studies since then were contaminated by commercial >> interests. There is no essentially no consensus as to whether and under what >> circumstances it will work. This is especially true for clouds that contain >> ice. Whether seeding will enhance, reduce or have negligible effect on such >> clouds depends on: atmospheric stability, cloud-base temperature, updraught >> speed, presence or absence of conditions in which natural secondary can >> function, level and location etc etc. I think there is good reason to feel >> sceptical of studies reporting quantitative estimates of changes induced by >> seeding. My view is that - as with several geoengineering schemes - what is >> urgently required is well-controlled , comprehensive field experiments. Only >> then will it be possible to establish whether cloud seeding might, on a >> regional scale, be important vis-a-vis climate change. >> >> Cheers,   John. >> >> >> ******************************** >> >> Quoting Neil Farbstein <pro...@att.net>: >> >>> > I'm glad we agree. Small cloud seeding experiments over Greenland >>> > should be practical.  We should give this some thought and modeling. >>> > Can you do that at your lab? Google satellite pictures and weather >>> > satellites can locate clouds that are likely targets to seed; The >>> > bigger clouds in the places that are most strategic. >>> > An international organization or groups of industrialized nations can >>> > pay the local residents or the greenland government subsidies for >>> > participating in the cloud seeding program. >>> > >>> > On Dec 15, 8:27 pm, Andrew Lockley <andrew.lock...@gmail.com> wrote: >>>> >> For clarity, the main reason my for suggesting cloud seeding is that it >>>> can >>>> >> be used to build up greenland to a height where the air temperature is >>>> low >>>> >> enough to sustain the ice sheet.  The could potentially reverse the >>>> >> catastrophic Greenland tipping point - which will unleash >>>> several metres > of >>>> >> sea level rise over a few hundred years.  Game over for London, Venice, >>>> >> Florida, New York, etc. if that happens.   Worth a bit of jet fuel or a >>>> few >>>> >> rockets to prevent that, I'd argue. >>>> >> >>>> >> A >>>> >> >>>> >> 2009/12/15 Neil Farbstein <pro...@att.net> >>>> >> >>>> >> >>>> >> >>>>> >> > I suggested the same cloud seeding strategy a month ago. Somebody >>>>> >> > authoritative said that the biggest snowfall  recorded over the >>>>> >> > alaskan arctic caused the biggest melt water recorded during the >>>>> >> > spring. That's anecdotal evidence but I dropped the idea of >>>>> working on >>>>> >> > that anyway. >>>> >> >>>>> >> > There wont be a melt water problem if clouds are seeded over large >>>>> >> > parts of the gulfstream to cool it and the winds that blow off it. >>>> >> >>>>> >> > On Dec 15, 5:47 am, Andrew Lockley <andrew.lock...@gmail.com> wrote: >>>>>> >> > > I note the use of cloud seeding by the Chinese, and its >>>> >> unexpected effect >>>>> >> > in >>>>>> >> > > causing huge snowfalls in Beijing.  It seems that there may be >>>> >> two useful >>>>>> >> > > geoengineering approaches with this technique, and I'd be >>>>>> interested in >>>>>> >> > > hearing comments. >>>> >> >>>>>> >> > > 1) Rebuild ice - by inducing snowfalls over Greenland, >>>> >> Antarctica and the >>>>>> >> > > Arctic, it would perhaps be possible to maintain ice.  In >>>>>> Greenland, >>>>> >> > where >>>>>> >> > > the height of the ice cap is critical, this would seem a >>>>>> particularly >>>>>> >> > > appealing prospect. >>>>>> >> > > 2) Albedo modification - Fresh snow is whiter than old snow, >>>>>> especially >>>>> >> > in >>>>>> >> > > polluted areas.  Is the albedo change worth pursuing?  My >>>>>> guess is > not. >>>>>> >> > >  HOWEVER, I suspect that triggering significant autumn and spring >>>>> >> > snowfalls >>>>>> >> > > in permafrost regions, we could potentially significantly modify >>>>>> albedo. >>>> >> >>>>>> >> > > I invite comments. >>>> >> >>>>>> >> > > A >>>> >> >>>>> >> > -- >>>> >> >>>>> >> > You received this message because you are subscribed to the Google >>>>> Groups >>>>> >> > "geoengineering" group. >>>>> >> > To post to this group, send email to >>>>> geoengineering@googlegroups.com. >>>>> >> > To unsubscribe from this group, send email to >>>>> >> > >>>> >> >>>> geoengineering+unsubscr...@googlegroups.com<geoengineering%2bunsubscr...@go­ >>>> oglegroups.com> >>>>> >> > . >>>>> >> > For more options, visit this group at >>>>> >> >http://groups.google.com/group/geoengineering?hl=en.- Hide >>>>> quoted text > - >>>> >> >>>> >> - Show quoted text - >>> > >>> > -- >>> > >>> > You received this message because you are subscribed to the Google >>> > Groups "geoengineering" group. >>> > To post to this group, send email to geoengineering@googlegroups.com. >>> > To unsubscribe from this group, send email to >>> > geoengineering+unsubscr...@googlegroups.com. >>> > For more options, visit this group at >>> > http://groups.google.com/group/geoengineering?hl=en. >>> > >>> > >>> > >> >> >> >> > > -- John Latham lat...@ucar.edu   &    john.latha...@manchester.ac.uk Tel. 303-444-2429 (H)    &  303-497-8182 (W) -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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