Glacier evolution in high-mountain Asia under stratospheric  sulfate aerosol injection geoengineering

Zhao, Liyun; Yang, Yi; Cheng, Wei; Ji, Duoying; Moore, John C.

doi:https://doi.org/10.5194/acp-17-6547-2017

Articles | Volume 17, issue 11

https://doi.org/10.5194/acp-17-6547-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

The Geoengineering Model Intercomparison Project (GeoMIP):...

https://doi.org/10.5194/acp-17-6547-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 11

Research article

|

02 Jun 2017

Research article |

| 02 Jun 2017

Glacier evolution in high-mountain Asia under stratospheric sulfate aerosol injection geoengineering

Liyun Zhao, Yi Yang, Wei Cheng, Duoying Ji, and John C. Moore

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Final revised paper (published on 02 Jun 2017)
Preprint (discussion started on 30 Sep 2016)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review', Anonymous Referee #1, 17 Oct 2016
- AC1: 'reply to Anonymous Referee #1', Liyun Zhao, 09 Mar 2017
RC2: 'Review', Anonymous Referee #2, 02 Dec 2016
- AC2: 'reply to Anonymous Referee #2', Liyun Zhao, 09 Mar 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Liyun Zhao on behalf of the Authors (09 Mar 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Mar 2017) by Ben Kravitz

RR by Anonymous Referee #1 (20 Mar 2017)

Suggestions for revision or reasons for rejection

The authors have addressed my comments very well. However, I have a number of concerns about new material in the paper.

General comments

An altitude precipitation lapse-rate of 3%/100m is introduced with no explanation, no justification and no citations. I’m unfamiliar with this term and a quick literature search didn’t enlighten me. If this is to be used it needs to be properly explained, justified and cited for those unfamiliar with this approach to be convinced of its validity.

It is great that the authors have included precipitation in their analysis but I was still left somewhat in the dark about what difference it had made. I suggest two changes to address this:
1) The old results are presented at the end of section 3 but it seems as if this ought to have been left for section 5 where a quantitative comparison of the two approaches could have been usefully presented.
2) It would be great to have the role of precipitation change explicitly addressed in the abstract or conclusion. A paragraph buried in the middle of section 5.1 explains that the widely reported reduction in mean precipitation expected for solar geoengineering is unlikely to be as important as the temperature-driven shift from solid to liquid precip for forcing Himalayan glacier change. It would be great to see this important piece of context brought out more prominently.

HadGEM2-ES’ G4 run is excluded from the glacier analysis as the mass loss is far lower than the other models. This is not a principled reason to exclude it and one should be given or else HadGEM2-ES’ G4 experiment should be retained. Such a reason ought to be formulated in terms of the properties of the model, its implementation of the G4 experiment, or its climate features. This reason should also be consistent with keeping the G3 run from this model.
The anomalous rapid growth of Tibetan glaciers in experiment G3 and in the initial years of G4 is not explained. Is it the case that this model predicts the rapid growth of these glaciers under current conditions? If so, is that consistent with observations?

Specific comments

L29 – The “sudden temperature rise” reported is calculated over a 20 year period, this should be rephrased.
L58 – “glacier responses to geoengineering scenarios has been limited to…” The start of this sentence needs some work.
L127 – This explanation of the terms could be clearer; I’d suggest either using a list or the “respectively” form rather than a combination of both.
L177 – The phrasing of this is a little off. The design of experiment G3 should be explained. It is no accident that there is no net change in radiative forcing, that was part of the experimental design.
L181 – I would have liked to see a table of the global-mean or Himalayan-mean temperature change for each model and for each experiment here. This would be a useful reference point for some of the comparisons discussed.
Eqns 7 and 8 – what does the letter i refer to and what are the listed numbers in reference to?
L252 – “These three choices lead to a range of about 2.5mm of global sea level in glacier volume loss at 2050.” What is the context for this figure?
L275-278 – “…with data regional…” other way around?
Figure 2 and others – “downscaled AND BIAS-CORRECTED”
Figure 3 – The axis labels on this figure need to be changed to be clearer how different panel C and D are. Panel D shows only solid precipitation and not precipitation as a casual glance would suggest. In addition, is the “across model spread” the full range or is it the standard deviation?
L390 and throughout – how are these rates calculated? Are these mean rates, peak rates or rates for a specific decade?
L530 – “11.1, 12.5….” – add comma
L559 – Your results do not have “smaller uncertainties” as yours are not a full measure of uncertainty.
L584 – add “respectively” following the glacier retreat figures or else rephrase the sentence.

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ED: Reconsider after minor revisions (Editor review) (12 Apr 2017) by Ben Kravitz

AR by Liyun Zhao on behalf of the Authors (20 Apr 2017)

ED: Publish as is (21 Apr 2017) by Ben Kravitz

AR by Liyun Zhao on behalf of the Authors (26 Apr 2017)

Short summary

We find stratospheric sulfate aerosol injection geoengineering, G3, can slow shrinkage of high-mountain Asia glaciers by about 50 % by 2069 relative to losses from RCP8.5. The reduction in mean precipitation expected for solar geoengineering is less important than the temperature-driven shift from solid to liquid precipitation for forcing Himalayan glacier change. The termination of geoengineering in 2069 leads to temperature rise of 1.3 °C and corresponding increase in glacier volume loss rate.