The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2

Lohmann, Ulrike; Neubauer, David

doi:https://doi.org/10.5194/acp-18-8807-2018

Articles | Volume 18, issue 12

https://doi.org/10.5194/acp-18-8807-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

BACCHUS – Impact of Biogenic versus Anthropogenic emissions...

https://doi.org/10.5194/acp-18-8807-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 12

Research article

|

22 Jun 2018

Research article |

| 22 Jun 2018

The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2

Ulrike Lohmann and David Neubauer

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Final revised paper (published on 22 Jun 2018)
Preprint (discussion started on 14 Feb 2018)

Interactive discussion

Status: closed

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

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RC1: 'Review of "The importance of mixed-phase clouds for climate sensitivity in the global aerosol-climate model ECHAM6-HAM2"', Anonymous Referee #1, 01 Mar 2018
- AC2: 'Response to reviewer 1', Ulrike Lohmann, 04 May 2018
RC2: 'Review of The importance of mixed-phase clouds for climate sensitivity in the global aerosol-climate model ECHAM6-HAM2', Anonymous Referee #2, 07 Mar 2018
- AC4: 'Response to reviewer 2', Ulrike Lohmann, 04 May 2018
RC3: 'Review of Lohmann & Neubauer', Anonymous Referee #3, 18 Mar 2018
- AC5: 'Response to reviewer 3', Ulrike Lohmann, 04 May 2018
SC1: 'Paper recently published in GRL', Alejandro Bodas-Salcedo, 28 Mar 2018
- AC1: 'Response to comment', Ulrike Lohmann, 09 Apr 2018

Peer-review completion

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

AR by Ulrike Lohmann on behalf of the Authors (05 May 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 May 2018) by Holger Tost

RR by Anonymous Referee #1 (21 May 2018)

RR by Trude Storelvmo (01 Jun 2018)

Suggestions for revision or reasons for rejection

The authors have addressed many of my previous comments/concerns, and the manuscript is improved over the previous version. A few issues remain, which are listed below. The manuscript should be suitable for publication once these are addressed.

1) Abstract, minor comment: The first two sentences state well-established facts that do not really belong in an abstract. The abstract is also quite long. The abstract could just begin with the 3rd sentence “How clouds change in a warmer climate…”
2) Abstract, Line 11: There is nothing in this paper that contradicts Tan et al., so I recommend rewriting this statement. Rather, the study seems to suggest that only severe underestimations (as in the CESM model) of supercooled liquid would significantly suppress climate sensitivity, so I would rather emphasise the novelty of that finding instead of presenting the findings as a contradiction to Tan et al. when they are really not
3) Abstract, Line 11-12: There is no support in the paper for this hypothesis, the way it is stated. The simulations do not show that the supercooled liquid fraction is not important.
4) Abstract, Lines 19 -21: Without a calculation of the non-cloud feedbacks the study is incomplete - conclusions regarding the importance of various cloud feedback can only be drawn if other feedbacks that are, to various degrees, compensating for the cloud feedbacks are also analysed.
5) Page 3, Line 32-35: Tan, Storelvmo and Zelinka (2018) showed that this is not the case, so I suggest removing these sentences.
6) Page 7, Line 30-31: This requires some additional explanation. Why is this necessary, and could this impact the simulated cloud feedbacks and climate sensitivity in ALL_LIQ? ALL_LIQ is by design unrealistic, so why is an unrealistic ice crystal number a concern here? Could you show zonal mean ice crystal number concentrations, perhaps as supplementary information?
7) Page 15: My previous comment remains: simulations HET and NOCONV are different from the other simulations not mainly because of their cloud phase, but for other reasons. Arguably, switching off convection (NOCONV) is a pretty fundamental change, and its impact on cloud phase would NOT be the most important one. Likewise, the nucleation mechanism in cirrus mainly changes aspects of the simulations OTHER THAN cloud phase. I’m not saying these aren’t interesting simulations, but they don't belong in a paper that focuses on the link between cloud phase and climate sensitivity. You need to compare simulations that are designed to be different in their cloud phase ONLY.
8) Page 23, line 11-13: You need to understand this better. Calculations of the the non-cloud feedbacks are much easier to perform than the decomposition of the cloud feedback that you already performed, and they do not require any special output, so it should be doable and would add a lot to the paper. The impression will otherwise be that you didn’t follow through in your analysis and therefore do not fully understand what’s going on in the simulations.

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ED: Publish subject to minor revisions (review by editor) (01 Jun 2018) by Holger Tost

AR by Ulrike Lohmann on behalf of the Authors (09 Jun 2018) Author's response Manuscript

ED: Publish as is (11 Jun 2018) by Holger Tost

AR by Ulrike Lohmann on behalf of the Authors (12 Jun 2018)

Short summary

The climate is warming, at the current rate so much so that the 2 ºC target is likely to be exceeded. Uncertainty remains as to when the 2 ºC of warming will be reached. One factor contributing to this uncertainty is how clouds change in the warmer climate. While previously most emphasis was placed on how low clouds change in the warmer climate, here we investigate the importance of mixed-phase and ice clouds.