Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

[Andrew Lockley]

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

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.

[Govindasamy Bala]

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)." 

--
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 geoengineerin...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-04wbNfg0E3q_8GtwXay88n_2r%2BhzYfVfrNPjq9SpJd9pg%40mail.gmail.com.

--

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: gb...@iisc.ac.in; bala.gov@gmail.com
Web:http://dccc.iisc.ac.in/dr_govindasamy_bala_profile.html
-------------------------------------------------------------------

[Andrew Lockley]

Can you extrapolate to greater altitudes? 

[Douglas MacMartin]

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

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAD7fhV%3Dc5Q4XVod8rAide3VNOmN1uyPbp6B6TCRKij474F_Meg%40mail.gmail.com.

[Govindasamy Bala]

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

[Olivier Boucher]

Hi Bala,

this is a nice study. Have you tried to use radiative kernels to decompose the ERF (alike what we did in Boucher et al, GRL 2017, https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL074647) ? We also observed a compensation effect between the stratospheric heating and the stratospheric water vapour, but the latter wasn't so large, and we didn't inject very high.

Best regards,

Olivier

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAD7fhVnfGtvCzuWyf4j7v7jvpKUmMgvN_mvMYOCnDnr4R4AKKQ%40mail.gmail.com.

--

---

Latest article: Diversity of greenhouse gas emission drivers across European countries since the 2008 crisis

[Andrew Lockley]

If I understand from the email below , you used aerosols with no fall speed. Are experiments planned to simulate aerosol descent?

Andrew 

[Govindasamy Bala]

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......

[Andrew Lockley]

So what's your judgement on the ideal injection altitude?

Andrew 

[Govindasamy Bala]

Andrew,

Sedimentation effect works in the same direction as the effect we identified in our study. Therefore, higher the altitude of injection, the better. My judgement: 25 km would be good. 

[Andrew Lockley]

Is 26k less good than 25? 

[Govindasamy Bala]

26 km is probably not going to add any more benefit compared 25 km if you consider the effect identified in our paper but it is better when sedimentation effect is considered. More experiments with the NCAR WACCM model would be good to precisely nail this down.

[Andrew Lockley]

Considering all effects, what's your view on the ideal height?

Andrew 

[Stephen Salter]

Hi All

If higher altitudes give longer life and so lower spray quantities they also  give a slower frequency response, longer phase lag and a greater chance of being stuck with what you do not want such as reflecting energy back down during Arctic winters as pointed out by Jan-Egil Kristjansson.

Advocates for marine cloud brightening are pleased about the short life of spray to give a high frequency response and the ability to stop Arctic cooling in the autumn before, it too, works the wrong way.

Stephen

Emeritus Professor of Engineering Design. School of Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland S.Sa...@ed.ac.uk, Tel +44 (0)131 650 5704, Cell 07795 203 195, WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-04xNuvoL4t217_9MG8UCzfFG3-PXe%3DbX9Fmcx%2B69nKPkA%40mail.gmail.com.

[Douglas MacMartin]

I think it is clear that we don’t know that yet.  If you want my guess, it would be the same as Bala’s, that once you’re far enough from the tropopause there’s not that much benefit to going higher.  The answer will also depend on the latitude of injection.  One of a long list of questions that, if there were any appreciable funding, would not be fundamentally hard to answer.

[Douglas MacMartin]

Effect on the ozone layer will mostly be a function of the aerosol concentration (or rather, surface area), so scales similarly to the amount of reflected sunlight.  So injecting at lower altitude means (i) we need to put more in to get the same concentration, and (ii) we need a higher concentration to get the same cooling because we have to compensate for the higher stratospheric water vapour.  So if your goal is to maximize the ratio of cooling to ozone loss, we should probably still be injecting at higher altitude. 

 

(More complicated than that due to transport, so it is true that you could inject at a low enough altitude that the aerosols never make it to high latitudes (and don’t need to go that low; 16km is way too low to do anything useful in the tropics since it’s below the tropopause) then there’s less impact on ozone, and, if you inject enough, you could still get some tropical cooling, but then you screw up meridional temperature gradients.  And need a lot of injection.)

 

More broad answer is that yes, this is a more complicated optimization of different metrics, but for altitude they’re mostly going to point in the same direction.

 

(Also, IMHO, ozone loss has been way over-emphasized in terms of downsides… a big problem if you did a lot of cooling today, but probably not a big problem if you do a moderate amount of cooling in 20 years.)

 

doug

 

From: john gorman <gor...@waitrose.com>
Sent: Tuesday, December 17, 2019 9:39 AM
To: Douglas MacMartin <dgm...@cornell.edu>; Andrew Lockley <andrew....@gmail.com>; Govindasamy Bala <bala...@gmail.com>
Cc: geoengineering <geoengi...@googlegroups.com>; arctic...@googlegroups.com
Subject: RE: [geo] Climate system response to stratospheric sulfate aerosols:sensitivity to altitude of aerosol layer

 

I am surprised that this conversation has not mentioned the negative effect on the ozone layer. This would seem to be a reason for injecting at lower altitude eg 16 km or 55,000feet.

 

I see the fairly minor increase in quantity needed at lower altitude to be a reason for injecting at lower altitude considering the massive extra difficulty in injecting at the higher altitudes.

 

John gorman

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB08768544DB876F08A79BEDF18F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

 

[Douglas MacMartin]

I disagree with you about the “equator” part, I think we *know* that that is not the right answer. 

 

Might depend somewhat on whether your goal is purely to maximize global mean cooling, or to compensate for climate change.  Injecting some in each hemisphere but away from the equator gives a better tailoring of climate response to avoid the tropical overcooling and high-latitude undercooling that you get with equatorial injection, and at least in WACCM, for higher injection rates, is *more* effective per unit injection than equatorial injection because you aren’t constantly injecting into region of high aerosol concentrations in the tropical pipe, with associated increased coagulation rates.  So better from either perspective in that model.  (Oh, and then you also don’t mess with the QBO.)  See: Kravitz, B., D.G. MacMartin, S. Tilmes, J.H. Richter, M.J. Mills, W. Cheng, K. Dagon, A.S. Glanville, J.-F. Lamarque, I.R. Simpson, J.J. Tribbia, and F. Vitt, “Comparing surface and stratospheric impacts of geoengineering with different SO₂ injection strategies”, J. Geophysical Research A, 124, 2019. doi:10.1029/2019JD030329

 

So I actually think we do know the answer that you should not inject at the equator. 

 

(Or, rather, if you were only allowed to pick one latitude than the equator would be better than any other single latitude, but if you are willing to simultaneously inject into both hemispheres then you both require less injection and get better climate response.)

 

(As for altitude, we also know that injecting too high starts decreasing effectiveness, at least for sulfate, since it evaporates…)

 

From: Haywood, James <J.M.H...@exeter.ac.uk>
Sent: Tuesday, December 17, 2019 9:47 AM
To: Douglas MacMartin <dgm...@cornell.edu>; Andrew Lockley <andrew....@gmail.com>; Govindasamy Bala <bala...@gmail.com>
Cc: geoengineering <geoengi...@googlegroups.com>
Subject: Re: [geo] Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

 

Hi All,

 

Actually I do think we know this. The answer is high up and at the equator.

 

https://www.nature.com/articles/s41467-017-01606-0

 

This maximises the AOD and the global cooling without having the nasties associated with cooling one hemisphere with respect to the other (e.g. Sahelian drought and impacts on North Atlantic hurricanes). Figure 1 clearly shows the AOD being the most significant and the AOD shifting into both hemispheres.

 

 

Results look pretty similar with a more sophisticated (GLOMAP) scheme.

 

Best

 

Jim 

Impacts of hemispheric solar geoengineering on tropical cyclone frequency | Nature Communications Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known solar geoengineering ... www.nature.com

 

---

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB08768544DB876F08A79BEDF18F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

[Douglas MacMartin]

Agreed!

 

From: Haywood, James <J.M.H...@exeter.ac.uk>
Sent: Tuesday, December 17, 2019 10:13 AM
To: Douglas MacMartin <dgm...@cornell.edu>; Andrew Lockley <andrew....@gmail.com>; Govindasamy Bala <bala...@gmail.com>
Cc: geoengineering <geoengi...@googlegroups.com>
Subject: Re: [geo] Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

 

Hi All,

 

Agree with much of this, but if you had one point to choose and your aim was solely to cool the planet, it would be close to the equator and high up (a la Pinatubo). Of course, there are tailoring arguments as you mention, and I don't doubt that a more nuanced injection strategy would be more optimal.

 

Best

 

Jim

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB0876EE759BDE204DA76957348F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

[Haywood, James]

Hi All,

Agree with much of this, but if you had one point to choose and your aim was solely to cool the planet, it would be close to the equator and high up (a la Pinatubo). Of course, there are tailoring arguments as you mention, and I don't doubt that a more nuanced injection strategy would be more optimal.

Best

Jim

From: geoengi...@googlegroups.com <geoengi...@googlegroups.com> on behalf of Douglas MacMartin <dgm...@cornell.edu>

Sent: 17 December 2019 18:01

To: Haywood, James <J.M.H...@exeter.ac.uk>; Andrew Lockley <andrew....@gmail.com>; Govindasamy Bala <bala...@gmail.com>

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB0876EE759BDE204DA76957348F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

[Haywood, James]

Hi All,

Actually I do think we know this. The answer is high up and at the equator.

https://www.nature.com/articles/s41467-017-01606-0

This maximises the AOD and the global cooling without having the nasties associated with cooling one hemisphere with respect to the other (e.g. Sahelian drought and impacts on North Atlantic hurricanes). Figure 1 clearly shows the AOD being the most significant and the AOD shifting into both hemispheres.

Results look pretty similar with a more sophisticated (GLOMAP) scheme.

Best

Jim 

Impacts of hemispheric solar geoengineering on tropical cyclone frequency | Nature Communications Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known solar geoengineering ... www.nature.com

---

From: geoengi...@googlegroups.com <geoengi...@googlegroups.com> on behalf of Douglas MacMartin <dgm...@cornell.edu>
Sent: 17 December 2019 17:23

To: Andrew Lockley <andrew....@gmail.com>; Govindasamy Bala <bala...@gmail.com>
Cc: geoengineering <geoengi...@googlegroups.com>
Subject: RE: [geo] Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

 

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB08768544DB876F08A79BEDF18F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

[Keutsch, Frank N]

Hi,

I am with Doug on that the equator is not ideal. Also, I am with Doug on the ozone, if we stay on track with respect to emissions of halogen-containing substances. Not sure how big that "if" is but I am optimistic. My bigger concern is impact of stratospheric heating on dynamics etc. and so I look forward to seeing modeling studies investigating/minimizing this.

Frank

On Dec 17, 2019, at 1:01 PM, Douglas MacMartin <dgm...@cornell.edu> wrote:

I disagree with you about the “equator” part, I think we *know* that that is not the right answer. 

 

Might depend somewhat on whether your goal is purely to maximize global mean cooling, or to compensate for climate change.  Injecting some in each hemisphere but away from the equator gives a better tailoring of climate response to avoid the tropical overcooling and high-latitude undercooling that you get with equatorial injection, and at least in WACCM, for higher injection rates, is *more* effective per unit injection than equatorial injection because you aren’t constantly injecting into region of high aerosol concentrations in the tropical pipe, with associated increased coagulation rates.  So better from either perspective in that model.  (Oh, and then you also don’t mess with the QBO.)  See: Kravitz, B., D.G. MacMartin, S. Tilmes, J.H. Richter, M.J. Mills, W. Cheng, K. Dagon, A.S. Glanville, J.-F. Lamarque, I.R. Simpson, J.J. Tribbia, and F. Vitt, “Comparing surface and stratospheric impacts of geoengineering with different SO₂ injection strategies”, J. Geophysical Research A, 124, 2019. doi:10.1029/2019JD030329

 

So I actually think we do know the answer that you should not inject at the equator. 

 

(Or, rather, if you were only allowed to pick one latitude than the equator would be better than any other single latitude, but if you are willing to simultaneously inject into both hemispheres then you both require less injection and get better climate response.)

 

(As for altitude, we also know that injecting too high starts decreasing effectiveness, at least for sulfate, since it evaporates…)

 

From: Haywood, James <J.M.H...@exeter.ac.uk> 
Sent: Tuesday, December 17, 2019 9:47 AM
To: Douglas MacMartin <dgm...@cornell.edu>; Andrew Lockley <andrew....@gmail.com>; Govindasamy Bala <bala...@gmail.com>
Cc: geoengineering <geoengi...@googlegroups.com>
Subject: Re: [geo] Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

 

Hi All,

 

Actually I do think we know this. The answer is high up and at the equator.

 

https://www.nature.com/articles/s41467-017-01606-0

 

This maximises the AOD and the global cooling without having the nasties associated with cooling one hemisphere with respect to the other (e.g. Sahelian drought and impacts on North Atlantic hurricanes). Figure 1 clearly shows the AOD being the most significant and the AOD shifting into both hemispheres.

 

<image001.png>

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB0876EE759BDE204DA76957348F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

___________________________________________________________________________________________
Frank N. Keutsch
Stonington Professor of Engineering and Atmospheric Science

Harvard John A. Paulson School of Engineering and Applied Sciences 
Department of Chemistry and Chemical Biology
Harvard University
12 Oxford Street
Cambridge, MA 02138
USA

E-mail: keu...@seas.harvard.edu
Tel:+1-617-495-1878
___________________________________________________________________________________________

[john gorman]

I am surprised that this conversation has not mentioned the negative effect on the ozone layer. This would seem to be a reason for injecting at lower altitude eg 16 km or 55,000feet.

 

I see the fairly minor increase in quantity needed at lower altitude to be a reason for injecting at lower altitude considering the massive extra difficulty in injecting at the higher altitudes.

 

John gorman

 

 

From: Douglas MacMartin
Sent: 17 December 2019 17:24
To: Andrew Lockley; Govindasamy Bala
Cc: geoengineering

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/DM5PR04MB08768544DB876F08A79BEDF18F500%40DM5PR04MB0876.namprd04.prod.outlook.com.

 

[Simone Tilmes]

Hi Everyone,

I am catching up with some of the discussion now. We had a couple papers that looked into the effects of ozone and one is attached. Any injections of participles in the stratosphere will impact ozone and in particular using sulfates and doing this will still lead to substantial ozone loss in mid- to high latitudes by ~2050 and less afterwards. We still have to explore the effects of other particles. I am just working on a paper (and had an AGU poster) comparing high (25km) low (20km) and EQ to 4 injection location applications. Hope to get a paper submitted early 2020, but in general, different methods result in reductions of polar ozone due to different reasons depending on the particle distribution and sizes. Dynamical changes also play a large role in particular if large amounts of sulfur are injected which can even lead to an increase of ozone, which is also not beneficial regarding impacts. Eq injections also cause a more pronounced strengthening of the polar vortex which causes more ozone loss. All of these questions need a much more in depth evaluation with different models and I hope that more modelers will work on this. We are planning some experiments for the next phase of the Chemistry-Climate-Modeling Initiative on this topic, and if you are interested, please let me know.

Cheers, Simone

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/5df9129e.1c69fb81.d7ebb.238bSMTPIN_ADDED_MISSING%40gmr-mx.google.com.

--

Simone Tilmes,
Atmospheric  Chemistry, Observations & Modeling Lab
National Center for Atmospheric Research
PO Box 3000
Boulder, Colorado  80307-3000
303-497-1445
303-497-1400 (fax)
til...@ucar.edu

[Simone Tilmes]

Hi John,

just to your comment, injecting in 16km in the tropics is not in the stratosphere, so that will not be efficient, but injecting outside the tropics would very likely require a much larger injection amount. Using 20km vs 25km altitudes is leading to a 50% increase in injection rate (see a Figure from a paper I am writing, showing SO4 burden per year (top) and SO4 burden vs injection rate, comparing GLENS: injections at 25km in 30N,15N, 30S, 15S, Low: injections at 20km in 30N,15N, 30S, 15S, EQ: injections at the equator, 110L: 25km injections with a model that has a higher vertical resolution),

Cheers, Simone

On Wed, Dec 18, 2019 at 2:55 AM john gorman <gor...@waitrose.com> wrote:

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/5df9129e.1c69fb81.d7ebb.238bSMTPIN_ADDED_MISSING%40gmr-mx.google.com.

[john gorman]

Thanks for these graphs etc. When the world suddenly realises that this is necessary, (and which disaster/flood /fire triggers this)  lots of decisions will suddenly have to be made. My guess is that we  will have to start with existing aircraft ie lower injection. Too much time will have been lost to go for any form of ideal.

 

I will work through your graphs in more detail.

 

Thanks

 

Joh gorman

 

 

From: Simone Tilmes
Sent: 18 December 2019 14:20
To: gor...@waitrose.com
Cc: dgm...@cornell.edu; Andrew Lockley; Govindasamy Bala; geoengineering; arctic...@googlegroups.com
Subject: Re: [geo] Climate system response to stratospheric sulfateaerosols:sensitivity to altitude of aerosol layer

 

Hi John,

just to your comment, injecting in 16km in the tropics is not in the stratosphere, so that will not be efficient, but injecting outside the tropics would very likely require a much larger injection amount. Using 20km vs 25km altitudes is leading to a 50% increase in injection rate (see a Figure from a paper I am writing, showing SO4 burden per year (top) and SO4 burden vs injection rate, comparing GLENS: injections at 25km in 30N,15N, 30S, 15S, Low: injections at 20km in 30N,15N, 30S, 15S, EQ: injections at the equator, 110L: 25km injections with a model that has a higher vertical resolution),

 

Cheers, Simone

 

[Andrew Lockley]

We can already do SRM with F15-E zoom climbers, so low altitude injection is not necessary. It would also be ineffective.

Development times for planes aren't far off international decision making times, so there's not necessarily a big rush - certainly not to the point of doing a bad program 

Andrew 

To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/5dfb2bb5.1c69fb81.43faf.0a8fSMTPIN_ADDED_MISSING%40gmr-mx.google.com.