Radiative and climate impacts of a large volcanic eruption during  stratospheric sulfur geoengineering

Laakso, A.; Kokkola, H.; Partanen, A.-I.; Niemeier, U.; Timmreck, C.; Lehtinen, K. E. J.; Hakkarainen, H.; Korhonen, H.

doi:https://doi.org/10.5194/acp-16-305-2016

Articles | Volume 16, issue 1

https://doi.org/10.5194/acp-16-305-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-16-305-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 1

Research article

|

18 Jan 2016

Research article |

| 18 Jan 2016

Radiative and climate impacts of a large volcanic eruption during stratospheric sulfur geoengineering

A. Laakso, H. Kokkola, A.-I. Partanen, U. Niemeier, C. Timmreck, K. E. J. Lehtinen, H. Hakkarainen, and H. Korhonen

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Final revised paper (published on 18 Jan 2016)
Preprint (discussion started on 12 Aug 2015)

Interactive discussion

Status: closed

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

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- Supplement

RC C6659: 'Review of «Radiative and climate impacts of a large volcanic eruption during stratospheric sulfur geoengineering»', Anonymous Referee #3, 08 Sep 2015
- AC C9408: 'Response to Anonymous Referee #3', Anton Laakso, 17 Nov 2015
RC C6707: 'Review', Anonymous Referee #2, 09 Sep 2015
- AC C9407: 'Response to Anonymous Referee #2', Anton Laakso, 17 Nov 2015
RC C6768: 'A good study on SRM geoengineering', Anonymous Referee #1, 10 Sep 2015
- AC C9406: 'Response to Anonymous Referee #1', Anton Laakso, 17 Nov 2015

Peer-review completion

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

AR by Anton Laakso on behalf of the Authors (19 Nov 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Nov 2015) by Jens-Uwe Grooß

RR by Anonymous Referee #2 (15 Dec 2015)

Suggestions for revision or reasons for rejection

The authors have improved the manuscript based on the 1st round of reviewer’s comments, and I appreciate the author’s efforts in editing their work.

There are still some instances where I find the text not clear in regards to whether the study addresses the impact *of* a volcanic eruption, or the climate impacts to be expected after a volcanic eruption with other sets of external forcing change scenarios. The difference is important. The potential for misunderstanding can be decreased with some fairly minor text modifications, which I suggest in the specific comments below.

In the abstract (line 29) and elsewhere, the authors state that the maximum increase in radiative forcing is 30% smaller for an eruption in an SRM world, compared to within a non-SRM world. This is probably the major quantitative result of the study, and I had some difficulty understanding the origin of this number based on Figure 2b, where the difference between SRM Cont and the SRM + Volc sum seems to be much smaller than this. After some thought, I see that the difference (~2 W/m**2) is compared to the anomalous SW forcing, which is around 6 W/m**2, rather than the total SW forcing in the two cases, which is 12 W/m**2. This could be made clearer to the reader.

Specific comments:
P1.l23: Since the experiments explore also climate responses to changes in SRM, and not just the impacts of volcanic eruptions, I suggest changing the text here to: “study the radiative and climate changes occurring after volcanic eruptions during different SMR scenarios.”

P1.l25: same as above, suggest: “climate changes occurring after the eruption”

P1.l29: global radiative forcing

P2.l7: “concurrent” is ambiguous, do you the continuous SRM? Is there a missing “than” in this sentence?

P2.l8: again, since it’s not just the eruption that leads to these changes, I suggest: “In this simulation, only about 1/3 of the global ensemble-mean cooling occurs after the eruption, compared to that occurring after an eruption…”

P4.l23: This text sounds like it would suggest that studies of volcanic aerosol using ECHAM-HAM are severely flawed. It would be very nice to shortly acknowledge the other methods that have been used to address the difficulty posed by the course mode in other studies (e.g., Niemeier et al., 2009) just so a reader doesn’t get the impression that those studies have missed something completely.

p6.l8: typo in “Aquila”

p6.l25: “does not be” -> is not

p7.l23: “this has been seen”

p10.l7: “somewhat” is a gross understatement, there is a factor of two difference between the two!

P10.l7: please state what quantity these observations measure.

P10.l15: “Reliable” is maybe not the best word choice. The comparison with observations suggests a large model error, but perhaps those observations have large uncertainties? Without a fuller comparison, say with other model results, it’s quite difficult to say whether these simulations are realistic, or at least consistent with prior studies.

P10.l21-23: I don't believe this argument. Almost all sulfur is in the tropics over this time frame, where OH should be uniform. And why couldn't the peak in SH burden 5 months after the eruption have something to do with the timescale of cross-equator transport?

P15.l22: The 33% difference is not directly readable from the plot. Is this based on averaging the temperature anomalies over the 3 years and differencing? It would be nice to state the 3-year average T anomalies in the text. With the ensembles, you can also quote the uncertainty ranges of those mean differences, to be able to see if the average response for SRM Cont is significantly different than that for Volc.

P21.l5: “impacts of a volcanic eruption” should be changed to something like: “climate responses to be expected after a volcanic eruption”.

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ED: Reconsider after minor revisions (Editor review) (15 Dec 2015) by Jens-Uwe Grooß

AR by Anton Laakso on behalf of the Authors (21 Dec 2015) Author's response Manuscript

ED: Publish as is (22 Dec 2015) by Jens-Uwe Grooß

Short summary

We have studied the impacts of a volcanic eruption during solar radiation management (SRM) using an aerosol-climate model ECHAM5-HAM-SALSA and an Earth system model MPI-ESM. A volcanic eruption during stratospheric sulfur geoengineering would lead to larger particles and smaller amount of new particles than if an volcano erupts in normal atmospheric conditions. Thus, volcanic eruption during SRM would lead to only a small additional cooling which would last for a significantly shorter period.