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
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 <dgm...@cornell.edu
<mailto:dgm...@cornell.edu>> 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:*geoengineering@googlegroups.com
<mailto:geoengineering@googlegroups.com>
<geoengineering@googlegroups.com
<mailto:geoengineering@googlegroups.com>> *On Behalf Of
*Govindasamy Bala
*Sent:* Saturday, December 14, 2019 9:38 PM
*To:* Andrew Lockley <andrew.lock...@gmail.com
<mailto:andrew.lock...@gmail.com>>
*Cc:* geoengineering <geoengineering@googlegroups.com
<mailto:geoengineering@googlegroups.com>>
*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
<andrew.lock...@gmail.com <mailto:andrew.lock...@gmail.com>> 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.
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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 <mailto:gb...@iisc.ac.in>; bala.gov
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