I'm not sure Dr Trenberth's comments accurately reflect the state of current knowledge.
>From my recollection of yesterday's webinar (https://youtu.be/YHKEEqYlJP4) , David Keith was particularly scathing about the persistence of this "drought" mythology. My personal understanding is that : * Hydrological cycle activity increases under warming, so any "drought" is relative to an artificial climate * Studies (eg http://iopscience.iop.org/article/10.1088/1748-9326/9/7/074013/meta) have shown that all regions benefit from solar geoengineering, in terms of restoring both temperature and precipitation * Temperature correction is slightly weaker than precipitation correction, so a full temperature correction would lead to over-drying. However, nobody is recommending that particular level of intervention, to my knowledge. It's therefore as absurd as saying "we can't use air-conditioning, as it can cause hypothermia". * "Drought" is a complex phenomenon, and stomata response to rising CO2, plus the increased amount of diffuse solar radiation may enhance yields and reduce evapotranspiration (Dagon & Schrag (2016): Evapotranspiration over land decreases under model simulations of solar geoengineering) A On 25 Mar 2017 16:22, "Stephen Salter" <[email protected]> wrote: > Dear Dr Trenberth > > You are quoted in The Guardian article of 24March by Arthur Neslan as > saying that cutting incoming solar radiation promotes drought. This is > supported by Jim Haywood at the UK Hadley centre with regard to volcanic > eruptions and presumably injections of stratospheric sulphur. However > other work by Jim and his colleagues on marine cloud brightening with sea > salt in the troposphere shows that effects are different and that > precipitation can be changed in BOTH directions depending on where it is > done. Their 2009 paper at doi:10.1029/2008JD011450 in figure 8f shows > that spray in the South Atlantic off Namibia would produce 0.4mm more a day > in South Sudan and surrounding drought stricken regions but also a > reduction of about 1 mm a day in the Amazon basin. > > The same result of 0.4 mm a day is shown in work from Max Planck by Ulrike > Niemeier et al. in doi:10.1002/2013JD020445 in the bottom row of figure 7. > > The same amount is reported from the Geomip project in doi: > 10.1002/jgrd.50856. > > Bala et al in 10.1007/s00382-010-0868-1 showed that spraying everywhere > by enough to offset double CO2 would reduce the global mean precipitation > by 1.3% but that this was offset by the reduction in evaporation which > increased river run off by 7%. > > All the climate modelling I have seen has used steady spraying throughout > the year. But given the short life of tropospheric aerosol and the speed > and agility of spray vessels it is reasonable to hope that with knowledge > of the phase of monsoons, el Nino and local observations we can deploy > fleets tactically and cherry pick places and seasons for spray operations > to get a win-win result. > > What we need is a seasonal everywhere-to-everywhere transfer function of > the climate system. It may be possible to borrow an idea used by > telecommunications engineers to use climate models with separate > pseudo-random sequences of the concentration of cloud condensation nuclei > followed by correlation with model results round the world. This has been > tried as part of a PhD thesis by Ben Parkes at Leeds. He was able to > confirm the Hadley Centre Amazon drying result but also that it could be > reversed by spray off the Aleutians. I would like to see a replication of > his work. Please let me know if you would like more information on the > method and put me in touch with anyone who could do it. > > I would also be grateful to see any climate model results of marine cloud > brightening which have not been published especially if they were not > steady all-year round ones. We also need to understand the difference > between mono-disperse spray and the wider spreads of diameters. The > Alterskjaer 2013 paper at doi10.1029/2012GL054286 suggests that a wide > spread of small nuclei might work in the warming direction. > > Figures from the papers should be below. > > > > > Best wishes > > Stephen Salter Emeritus Professor of Engineering Design School of > Engineering University of Edinburgh Mayfield Road Edinburgh EH9 3DW > +44 (0) 131 650 5704 <+44%20131%20650%205704> > > > On 24/03/2017 21:49, Andrew Lockley wrote: > > US scientists launch world's biggest solar geoengineering study > > https://www.theguardian.com/environment/2017/mar/24/us-scien > tists-launch-worlds-biggest-solar-geoengineering-study? > CMP=Share_AndroidApp_Gmail > > -- > 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 https://groups.google.com/group/geoengineering. > For more options, visit https://groups.google.com/d/optout. > > 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 > "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 https://groups.google.com/group/geoengineering. > For more options, visit https://groups.google.com/d/optout. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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