Shortwave radiative forcing, rapid adjustment, and feedback to the surface by sulfate geoengineering: analysis of the Geoengineering Model Intercomparison Project G4 scenario

Kashimura, Hiroki; Abe, Manabu; Watanabe, Shingo; Sekiya, Takashi; Ji, Duoying; Moore, John C.; Cole, Jason N. S.; Kravitz, Ben

doi:https://doi.org/10.5194/acp-17-3339-2017

Articles | Volume 17, issue 5

https://doi.org/10.5194/acp-17-3339-2017

© 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-17-3339-2017

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

Articles | Volume 17, issue 5

Research article

|

08 Mar 2017

Research article |

| 08 Mar 2017

Shortwave radiative forcing, rapid adjustment, and feedback to the surface by sulfate geoengineering: analysis of the Geoengineering Model Intercomparison Project G4 scenario

Hiroki Kashimura, Manabu Abe, Shingo Watanabe, Takashi Sekiya, Duoying Ji, John C. Moore, Jason N. S. Cole, and Ben Kravitz

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Final revised paper (published on 08 Mar 2017)
Supplement to the final revised paper
Preprint (discussion started on 09 Aug 2016)

Interactive discussion

Status: closed

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

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RC1: 'Review on Kashimura et al. (2016)', Anonymous Referee #1, 15 Aug 2016
- AC1: 'Reply to Referee #1', Hiroki Kashimura, 28 Nov 2016
RC2: 'Review', Aaron Donohoe, 23 Aug 2016
- AC2: 'Reply to Referee #2, Dr. Aaron Donohoe', Hiroki Kashimura, 28 Nov 2016

Peer-review completion

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

AR by Hiroki Kashimura on behalf of the Authors (28 Nov 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (06 Dec 2016) by Ulrike Lohmann

RR by Aaron Donohoe (20 Dec 2016)

RR by Anonymous Referee #3 (16 Jan 2017)

Suggestions for revision or reasons for rejection

The paper estimates the shortwave (SW) radiative forcing at the surface from the injection of sulfur in to the stratosphere. Their method is applied to the GeoMIP G4 models where 5 Mt SO2 is injected annually in a transient RCP4.5 scenario. A single layer model for SW radiative transfer is used to calculate the forcing of the aerosol layer, rapid adjustments and reactions from changes in water vapor, cloud amount, and surface albedo. The simple model is a simplification but it allows to differentiate between different effects and provide useful information relevant to human activities and interests and the assumptions made are clearly stated. The paper will be a valuable addition to current literature on the subject after some minor revisions.

A number of scatter plots are included in the analysis where means over 3 decades are used. These single values should be split into decadal means such that you have three values to base the analysis on instead of one. This will not only provide more data points for the regression, but also indicate more clearly the steadiness of the differences in climates over this period of the simulations.

Throughout the manuscript there is content that belongs only in the figure captions and not in the main text. E.g. “(shown by red symbols)” and similar is unnecessary in the main text; more interesting to read about the meaning of the results in the figures than color coding etc.

You should make some concluding remark on what your findings imply for human activities at the surface, as this is your initial motivation for the paper, and put your findings into a wider context.

Detailed comments are attached in the referee report.

Referee Report: PDF

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ED: Reconsider after minor revisions (Editor review) (16 Jan 2017) by Ulrike Lohmann

AR by Hiroki Kashimura on behalf of the Authors (26 Jan 2017) Author's response Manuscript

ED: Reconsider after minor revisions (Editor review) (03 Feb 2017) by Ulrike Lohmann

AR by Hiroki Kashimura on behalf of the Authors (09 Feb 2017) Author's response Manuscript

ED: Publish as is (10 Feb 2017) by Ulrike Lohmann

AR by Hiroki Kashimura on behalf of the Authors (13 Feb 2017)

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Short summary

This study analyses shortwave radiation (SW) in the G4 experiment of the Geoengineering Model Intercomparison Project. G4 involves stratospheric injection of 5 Tg yr⁻¹ of SO₂ against the RCP4.5 scenario. The global mean forcing of the sulphate geoengineering has an inter-model variablity of −3.6 to −1.6 W m⁻², implying a high uncertainty in modelled processes of sulfate aerosols. Changes in water vapour and cloud amounts due to the SO₂ injection weaken the forcing at the surface by around 50 %.