Sorry. Yes, you are right, your analysis of G3S addresses my concern.
Thanks for your response. On Sun, Mar 6, 2016 at 1:39 PM, Angus Ferraro <[email protected]> wrote: > Hi Ken, > > I agree, analysis of G1 and G2 would have strengthened the argument > somewhat. We did analyse the G3 and G3S HadGEM2-ES simulations and found a > statistically significant difference in temperature-independent > precipitation changes there. We could have done similar tests for G1 and G2 > with more models, of course. We also did some radiative transfer > calculations including the effect of the stratospheric aerosols, which gave > tropospheric heating changes consistent with the magnitude of precipitation > reduction we saw. We didn't explicitly consider pattern changes in > temperature, but the agreement between the radiative transfer results and > the GCM results suggests it's not a major effect. The agreement isn't > perfect, though, and we did rather neglect to discuss the possibility of > the pattern of temperature changes being a possible cause of this. > > We didn't really touch upon regional changes in precipitation. I find Cao > et al's results really useful because of their discussion of the regional > changes and the fact the regression approach does quite well in simulating > them. > > Cheers > > Angus > > On Sunday, 6 March 2016 17:27:12 UTC, kcaldeira wrote: >> >> It is not clear to me that Ferraro et al (2016) were able to exclude the >> possibility that some of these precipitation changes were associated with >> changes in the spatial pattern of near-surface air temperatures, and not >> due directly to the presence of aerosols. >> >> It would seem that to make a more compelling case, they would need to do >> the same analysis with G1 and G2, using solar dimming instead of aerosols, >> and show that their methodology did not project a similar a reduction in >> precipitation as a consequence of the reduction in solar intensity. >> >> I am not questioning the validity of their hypothesis, but rather the >> strength of evidence that they supply in support of their hypothesis. It is >> seems to me that their methods could yield similar results even if their >> hypothesis turns out to be wrong. (Forgive me if they did the same analysis >> using G1 and G2 and I somehow missed it.) >> >> --- >> >> Now that I have written this, I realize that Long Cao's paper from late >> last year is relevant to Ferraro et al's results. >> >> We looked at simulations that changes solar intensity and CO2 but did not >> use aerosols (see attached). >> >> http://onlinelibrary.wiley.com/doi/10.1002/2015JD023901/abstract >> >> Our analysis indicated that in our simulations a reduction in solar >> intensity (at constant temperature) would lead to a small statistically >> insignificant reduction in global mean precipitation but a statistically >> significant reduction in land runoff. >> >> Best, >> Ken >> >> _______________ >> Ken Caldeira >> >> Carnegie Institution for Science >> Dept of Global Ecology >> 260 Panama Street, Stanford, CA 94305 USA >> +1 650 704 7212 [email protected] >> website: http://dge.stanford.edu/labs/caldeiralab/ >> blog: http://kencaldeira.org >> @KenCaldeira >> >> My assistant is Dawn Ross <[email protected]>, with access to >> incoming emails. >> >> >> >> On Sun, Mar 6, 2016 at 4:40 AM, Stephen Salter <[email protected]> wrote: >> >>> Hi All >>> >>> The effects of reduced precipitation from stratospheric aerosols >>> identified by Farraro are there with marine cloud brightening but it also >>> has others. Making the sea cooler than the land makes stronger monsoons to >>> move more water to land. Making stronger winds over the sea makes for more >>> breaking waves and so more evaporation. Making smaller drops in clouds >>> over the sea reduces rainfall over the sea to leave more to fall further >>> inland. >>> >>> Bala and Caldeira in DOI 10.1007/s00382-010-0868-1 say that the overall >>> result of the conflicting effects could lead to increased river run off >>> with a contribution from reduced evaporation ashore. >>> >>> Nobody cares much about precipitation over sea except for people living >>> on small islands who might be more worried about rising sea levels. It is >>> possible to use the power in sea waves to do carbon-free desalination. >>> >>> Stephen >>> >>> >>> Emeritus Professor of Engineering Design. School of Engineering, >>> University of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland >>> [email protected], Tel +44 (0)131 650 5704, Cell 07795 203 195, >>> WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change >>> >>> On 06/03/2016 12:20, Andrew Lockley wrote: >>> >>> >>> >>> https://angusferraro.wordpress.com/2016/03/05/can-stratospheric-aerosols-directly-affect-global-precipitation/ >>> >>> Can stratospheric aerosols directly affect global precipitation? >>> >>> What is the effect of stratospheric aerosol geoengineering on global >>> precipitation? If we were to inject sulphate aerosol into the stratosphere >>> it would reflect some sunlight and cool the Earth, but the atmosphere’s >>> CO2 levels would remain high. This is important, because CO2 actually has >>> an effect on precipitation even when it doesn’t affect surface temperature. >>> In a recent paper with a summer student, I’ve shown the aerosols can >>> contribute a similar effect. >>> >>> Three climate models (CanESM2, HadGEM2-ES, MPI-ESM-LR) did simulations >>> of the future with and without geoengineering. The simulations with >>> stratospheric aerosols (G3 and G4) show greater temperature-independent >>> precipitation reductions than the simulations without them (RCP4.5 and G3S). >>> >>> Precipitation as energy flow >>> >>> Precipitation transfers energy from the Earth’s surface to its >>> atmosphere. It takes energy to evaporate water from the surface. Just as >>> evaporation of sweat from your skin cools you off by taking up heat from >>> your skin, evaporation from the Earth’s surface cools it through energy >>> transfer. Precipitation occurs when this water condenses out in the >>> atmosphere. Condensation releases the heat energy stored when the water >>> evaporated, warming the atmosphere. Globally, precipitation transfers >>> about 78 Watts per square metreof energy from the surface to the >>> atmosphere. Multiplying that by global surface area that’s a total energy >>> transfer of about 40 petajoules (that’s 40 with 15 zeros after it) of >>> energy every second! To put that in a bit of context, it’s about 40% of the >>> amount of energy the Sun transfers to the Earth’s surface. >>> >>> If precipitation changes, that’s the same as saying the atmospheric >>> energy balance changes. If we warm the atmosphere up, it is able to radiate >>> more energy (following the Stefan-Boltzmann law). To balance that, more >>> energy needs to go into the atmosphere. This happens through precipitation >>> changes. >>> >>> Direct effects of gases on precipitation >>> >>> Now imagine we change the amount of CO2 in the atmosphere. This >>> decreases the amount of energy the atmosphere emits to space, meaning the >>> atmosphere has more energy coming in than out. To restore balance the >>> atmospheric heating from precipitation goes down. This means that the >>> global precipitation response to global warming from increasing CO2 has two >>> opposing components: a temperature-independent effect of the CO2, which >>> decreases precipitation, and a temperature-dependent effect which arises >>> from the warming the CO2 subsequently causes. In the long run the >>> temperature-dependent effect is larger. Global warming will increase global >>> precipitation – although there could be local increases or decreases. >>> >>> But what happens if we do geoengineering? Say we get rid of the >>> temperature-dependent part using aerosols to reduce incoming solar >>> radiation. The temperature-independent effect of CO2 remains and global >>> precipitation will go down. >>> >>> Detecting the effect of stratospheric aerosol >>> >>> CO2 isn’t the only thing that has a temperature-independent effect. Any >>> substance that modifies the energy balance of the atmosphere has one. In >>> our newstudy, we ask whether stratospheric sulphate aerosol has a >>> detectable effect on global precipitation. Theoretically it makes sense, >>> but it is difficult to detect because usually there are >>> temperature-dependent effects obscuring it. >>> >>> We used a common method to remove the temperature-dependent effect. We >>> calculated the precipitation change for a given surface temperature change >>> from a separate simulation, then used this to remove the >>> temperature-dependent effect in climate model simulations of the future. We >>> did this for future scenarios with and without geoengineering. >>> >>> As expected, we found a temperature-independent influence which reduced >>> precipitation. Importantly, this effect was bigger when geoengineering >>> aerosols were present in the stratosphere. This was detectable in three >>> different climate models. The figure above shows this. The >>> non-geoengineered ‘RCP4.5’ simulation shows a precipitation decline when >>> the temperature effect is removed. This comes mainly from the CO2. The >>> ‘G3’ and ‘G4’ geoengineering simulations (blue and green lines) have an >>> even greater decline. The aerosol is acting to decrease precipitation >>> further. >>> >>> How does aerosol affect precipitation? >>> >>> The temperature-independent effect wasn’t present when geoengineering >>> was done by ‘dimming the Sun’. The ‘G3S’ simulation (orange lines in the >>> figure) does this, and it has a similar precipitation change to RCP4.5. So >>> what causes the precipitation reduction when stratospheric aerosols are >>> used? We calculated the effect of the aerosol on the energy budget of the >>> troposphere (where the precipitation occurs). We separated this in two: the >>> aerosol itself, and the stratospheric warming that occurs because of the >>> effect of the aerosol on the stratosphere’s energy budget. >>> >>> Black bars show the temperature-independent precipitation changes >>> simulated by the models. Orange bars show our calculation of the effect of >>> the stratospheric warming. Green bars show our calculation of effect of the >>> aerosol itself. Grey bars show our calculation of the total effect, which >>> is very close to the actual simulated result. >>> >>> We found the main effect was from the aerosol itself. The aerosol’s main >>> effect is to reduce incoming solar radiation and cool the surface. But we >>> showed it also interferes a little with the radiation escaping to space, >>> and this alters the energy balance of the troposphere. The precipitation >>> has to respond to these energy balance changes. >>> >>> This effect is not huge. We had to use many model simulations of the >>> 21st Century to detect it above the ‘noise’ of internal variability. In the >>> real world we only have one ‘simulation’, so this implies the >>> temperature-independent effect of stratospheric aerosol on precipitation >>> would not be detectable in real-world moderate geoengineering scenario. >>> This also means climate model simulations not including the effects of the >>> aerosol could capture much of the effects of geoengineering on the global >>> hydrological cycle. >>> >>> This effect could be more important under certain circumstances. If >>> geoengineering was more extreme, with more aerosol injected for longer, >>> precipitation would decrease more. But, based on these results, the main >>> effect of geoengineering on precipitation is that the temperature-dependent >>> changes are minimised. This means the temperature-independent effect of >>> increasing CO2 concentrations is unmasked, reducing precipitation. >>> >>> Take a look at the paper for more details – it’s open access! >>> >>> Ferraro, A. J., & Griffiths, H. G. (2016). Quantifying the >>> temperature-independent effect of stratospheric aerosol geoengineering on >>> global-mean precipitation in a multi- model ensemble. Environmental >>> Research Letters, 11, 034012. doi:10.1088/1748-9326/11/3/034012. >>> -- >>> 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. >>> 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. 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.
