So what's your judgement on the ideal injection altitude? Andrew
On Mon, 16 Dec 2019, 10:36 Govindasamy Bala, <[email protected]> wrote: > Andrew, > Many modeling groups (e.g. Tilmes and others) have already performed > simulations that inject aerosols at different heights and thus have > included the sedimentation effects and many many other effects. These > studies simulate the NET effects and hence hard to interpret and quantify > the individual effects. The strength of our ESD paper is that it changes > only one variable and identifies its individual contribution to the total > problem. > > What we have learnt during the course is that there are too many variables > in the aerosol SRM problem (transport, location of injection, aerosol-cloud > interaction, aerosol-radiation interaction, aerosol micro physics and the > resulting size distribution of the aerosols, etc.) and the resulting > uncertainties could be too large. This is of course known to many of us for > a long time...... > > On Mon, Dec 16, 2019 at 3:41 PM Andrew Lockley <[email protected]> > wrote: > >> If I understand from the email below , you used aerosols with no fall >> speed. Are experiments planned to simulate aerosol descent? >> >> Andrew >> >> On Mon, 16 Dec 2019, 05:43 Govindasamy Bala, <[email protected]> wrote: >> >>> Andrews, >>> >>> We did not do experiments with aerosols above 22 km. It is likely that >>> the cooling effect will be larger when aerosols are at 25 km. Beyond that >>> it is likely that the additional cooling benefits disappear. We need more >>> experiments to confirm this. >>> >>> The sensitivity to height in our paper arises mainly because of the >>> increases in stratospheric water vapor (which partly offsets the cooling >>> efficiency of the aerosols) that is associated with the stratospheric >>> heating by the aerosols. This increase in stratospheric water vapor is >>> largest when the aerosols (and the heating) is close to the tropopause. >>> >>> In our paper, we have isolated the effect of just one factor. As Doug >>> has pointed out, the sedimentation effect would also lead to more cooling >>> if aerosols are injected at higher altitudes... >>> >>> Best, >>> Bala >>> >>> On Sun, Dec 15, 2019 at 9:05 PM Douglas MacMartin <[email protected]> >>> wrote: >>> >>>> This is a great study to understand the effectiveness per unit mass **in >>>> the stratosphere**. Also keep in mind that there’s an additional >>>> factor, that at lower altitudes it takes higher injection rates to achieve >>>> the same burden in the stratosphere (i.e., lower lifetime at lower injected >>>> altitude). >>>> >>>> >>>> >>>> If the only thing you cared about was cost, then since there are >>>> existing studies demonstrating that you can design an aircraft to get to >>>> ~20-21km, we roughly know that it could be done, but higher altitude >>>> injection means less total sulfur injected and hence smaller side effects, >>>> and should be better understood both on the modeling and implementation >>>> cost as the trade may well be worth it. >>>> >>>> >>>> >>>> doug >>>> >>>> >>>> >>>> *From:* [email protected] < >>>> [email protected]> *On Behalf Of *Govindasamy Bala >>>> *Sent:* Saturday, December 14, 2019 9:38 PM >>>> *To:* Andrew Lockley <[email protected]> >>>> *Cc:* geoengineering <[email protected]> >>>> *Subject:* Re: [geo] Climate system response to stratospheric sulfate >>>> aerosols: sensitivity to altitude of aerosol layer >>>> >>>> >>>> >>>> Dear Andrew, >>>> >>>> Thanks for the posting. The heights studied were 16, 19 and 22 km, >>>> height that are relevant to solar radiation modification problem.. The >>>> final paragraph in the paper is worth reading to get more quantitative >>>> information from this modeling study. >>>> >>>> >>>> >>>> "To summarize, for the same mass, the efficiency (defined >>>> >>>> as changes in surface temperature per Tg S) of volcanic >>>> aerosol is less when it is prescribed at lower altitudes in the >>>> stratosphere (Fig. 9). For example, in our simulations, there is >>>> a surface cooling of 0.44K for each teragram of sulfur placed >>>> in the stratosphere at about 16 km altitude (100 hPa). There >>>> is an additional surface cooling of 0.15K per Tg S when the >>>> prescribed altitude is increased from about 16 km to about >>>> 22 km (37 hPa)." >>>> >>>> >>>> >>>> On Sat, Dec 14, 2019 at 12:55 AM Andrew Lockley < >>>> [email protected]> wrote: >>>> >>>> Poster's note : this has significant implications for the engineering >>>> of delivery systems. I can't do the pressure altitude conversion in my >>>> head, but it's a lot higher than what's generally been planned for. We're >>>> gonna need a bigger boat. >>>> >>>> >>>> >>>> >>>> >>>> https://www.earth-syst-dynam.net/10/885/2019/ >>>> >>>> >>>> >>>> Climate system response to stratospheric sulfate aerosols: sensitivity >>>> to altitude of aerosol layer >>>> >>>> *Krishna-Pillai Sukumara-Pillai Krishnamohan et al. *Received: 01 May >>>> 2019 – Discussion started: 23 May 2019 – Revised: 24 Oct 2019 – Accepted: >>>> 08 Nov 2019 – Published: 13 Dec 2019 >>>> >>>> Abstract >>>> >>>> top <https://www.earth-syst-dynam.net/10/885/2019/#top> >>>> >>>> Reduction of surface temperatures of the planet by injecting sulfate >>>> aerosols in the stratosphere has been suggested as an option to reduce the >>>> amount of human-induced climate warming. Several previous studies have >>>> shown that for a specified amount of injection, aerosols injected at a >>>> higher altitude in the stratosphere would produce more cooling because >>>> aerosol sedimentation would take longer. In this study, we isolate and >>>> assess the sensitivity of stratospheric aerosol radiative forcing and the >>>> resulting climate change to the altitude of the aerosol layer. We study >>>> this by prescribing a specified amount of sulfate aerosols, of a size >>>> typical of what is produced by volcanoes, distributed uniformly at >>>> different levels in the stratosphere. We find that stratospheric sulfate >>>> aerosols are more effective in cooling climate when they reside higher in >>>> the stratosphere. We explain this sensitivity in terms of effective >>>> radiative forcing: volcanic aerosols heat the stratospheric layers where >>>> they reside, altering stratospheric water vapor content, tropospheric >>>> stability, and clouds, and consequently the effective radiative forcing. We >>>> show that the magnitude of the effective radiative forcing is larger when >>>> aerosols are prescribed at higher altitudes and the differences in >>>> radiative forcing due to fast adjustment processes can account for a >>>> substantial part of the dependence of the amount of cooling on aerosol >>>> altitude. These altitude effects would be additional to dependences on >>>> aerosol microphysics, transport, and sedimentation, which are outside the >>>> scope of this study. The cooling effectiveness of stratospheric sulfate >>>> aerosols likely increases with the altitude of the aerosol layer both >>>> because aerosols higher in the stratosphere have larger effective radiative >>>> forcing and because they have higher stratospheric residence time; these >>>> two effects are likely to be of comparable importance. >>>> >>>> -- >>>> 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 view this discussion on the web visit >>>> https://groups.google.com/d/msgid/geoengineering/CAJ3C-04wbNfg0E3q_8GtwXay88n_2r%2BhzYfVfrNPjq9SpJd9pg%40mail.gmail.com >>>> <https://groups.google.com/d/msgid/geoengineering/CAJ3C-04wbNfg0E3q_8GtwXay88n_2r%2BhzYfVfrNPjq9SpJd9pg%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> >>>> >>>> >>>> -- >>>> >>>> With Best Wishes, >>>> >>>> ------------------------------------------------------------------- >>>> G. Bala >>>> Professor >>>> Center for Atmospheric and Oceanic Sciences >>>> Indian Institute of Science >>>> Bangalore - 560 012 >>>> India >>>> >>>> Tel: +91 80 2293 3428; +91 80 2293 2505 >>>> Fax: +91 80 2360 0865; +91 80 2293 3425 >>>> Email: [email protected]; [email protected] >>>> Web:http://dccc.iisc.ac.in/dr_govindasamy_bala_profile.html >>>> ------------------------------------------------------------------- >>>> >>>> >>>> >>>> -- >>>> 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 view this discussion on the web visit >>>> https://groups.google.com/d/msgid/geoengineering/CAD7fhV%3Dc5Q4XVod8rAide3VNOmN1uyPbp6B6TCRKij474F_Meg%40mail.gmail.com >>>> <https://groups.google.com/d/msgid/geoengineering/CAD7fhV%3Dc5Q4XVod8rAide3VNOmN1uyPbp6B6TCRKij474F_Meg%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> >>> >>> -- >>> With Best Wishes, >>> >>> ------------------------------------------------------------------- >>> G. Bala >>> Professor >>> Center for Atmospheric and Oceanic Sciences >>> Indian Institute of Science >>> Bangalore - 560 012 >>> India >>> >>> Tel: +91 80 2293 3428; +91 80 2293 2505 >>> Fax: +91 80 2360 0865; +91 80 2293 3425 >>> Email: [email protected]; [email protected] >>> Web:http://dccc.iisc.ac.in/dr_govindasamy_bala_profile.html >>> ------------------------------------------------------------------- >>> >>> > > -- > With Best Wishes, > > ------------------------------------------------------------------- > G. Bala > Professor > Center for Atmospheric and Oceanic Sciences > Indian Institute of Science > Bangalore - 560 012 > India > > Tel: +91 80 2293 3428; +91 80 2293 2505 > Fax: +91 80 2360 0865; +91 80 2293 3425 > Email: [email protected]; [email protected] > Web:http://dccc.iisc.ac.in/dr_govindasamy_bala_profile.html > ------------------------------------------------------------------- > > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-0760p77LDACUHYxWHa_4JzyN8mB6NT4NoQ0WnEZ%3DoBL3g%40mail.gmail.com.
