How important are future marine and shipping aerosol emissions in a warming Arctic summer and autumn?

Gilgen, Anina; Huang, Wan Ting Katty; Ickes, Luisa; Neubauer, David; Lohmann, Ulrike

doi:https://doi.org/10.5194/acp-18-10521-2018

Articles | Volume 18, issue 14

https://doi.org/10.5194/acp-18-10521-2018

© 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-18-10521-2018

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

Articles | Volume 18, issue 14

Research article

|

24 Jul 2018

Research article |

| 24 Jul 2018

How important are future marine and shipping aerosol emissions in a warming Arctic summer and autumn?

Anina Gilgen, Wan Ting Katty Huang, Luisa Ickes, David Neubauer, and Ulrike Lohmann

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Final revised paper (published on 24 Jul 2018)
Supplement to the final revised paper
Preprint (discussion started on 09 Nov 2017)

Interactive discussion

Status: closed

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

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RC1: 'Review of «How important are future marine and shipping aerosol emissions in warming Arctic summer and autumn?” by Anina Gilgen et al.', Anonymous Referee #1, 06 Dec 2017
- AC1: 'Response to referee 1', Anina Gilgen, 11 May 2018
RC2: 'Interactive comment on "How important are future marine and shipping aerosol emissions in warming Arctic summer and autumn?" by Anina Gilgen et al.', Anonymous Referee #2, 28 Dec 2017
- AC2: 'Response to referee 2', Anina Gilgen, 11 May 2018
RC3: 'How credible are the simulations?', Anonymous Referee #3, 30 Dec 2017
- AC3: 'Response to referee 3', Anina Gilgen, 11 May 2018
AC4: 'New paper version', Anina Gilgen, 11 May 2018
AC5: 'Track-changes', Anina Gilgen, 11 May 2018
AC6: 'Supplementary Material', Anina Gilgen, 11 May 2018

Peer-review completion

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

AR by Anina Gilgen on behalf of the Authors (11 May 2018) Manuscript

ED: Referee Nomination & Report Request started (25 May 2018) by Holger Tost

RR by Anonymous Referee #3 (05 Jun 2018)

Suggestions for revision or reasons for rejection

The authors decided to only rather superficially address my comments. They invested some effort in adding comparison to data as Supplementary material, but the discussion and interpretation of their results remains unaffected. Similarly, in terms of comparison to other models, only the global mean sea salt emissions are put into context of one previously-published model study. The fact that their model is an outlier is not taken into further consideration. Both results are used to declare their results as “uncertain”. To respond to my proposition that the acting processes should be investigated in detail, the authors added two tables with mean numbers, without discussing these further.

Below I provide some more comments on the responses to my main concerns. In conclusion, I believe there is little use for another review. Even if I am quite disappointed by the replies, and indeed by the study itself, I believe only little improvement can be expected if one insisted on proper replies to the suggestions.

Observations: The authors provide now some comparison of their model to observational data. With respect to the aerosol, the results seem awkward. A low bias of 200 – 300 % is quoted with respect to aerosol optical depth. In turn, in comparison to surface data, a factor of 2 overestimation is reported. This might imply problems with vertical and/or horizontal transport in the model for the Arctic, which puts the aerosol results simulated by the model into question. A side note: “recent long-term surface observations” is a funny formulation. The ice water path bias is correctly discussed, and with regard to liquid clouds as well as the radiation balance, I also concur with the author’s conclusion that the model performs almost satisfactorily.
It is peculiar opinion that “model biases do not imply that the simulated changes are necessarily wrong”. It certainly does not help build confidence that they are right. Any demonstration that the simulated changes are trustworthy of course would be welcome. I do not see how the quoted paragraph (“Heterogeneous freezing...”) relates to the model evaluation discussion.

In my opinion, the model evaluation substantially improved, but a meaningful discussion of the results shown in the Supplementary material is missing. The authors merely superficially summarize the result of substantial model deficiencies, without discussing the implications for the interpretation of their simulation results.

Model context: The context of the model used by the authors with other model simulations also now improved a bit, but is still not very advanced. It is strange that the authors are not aware of the CMIP5 model capabilities. E.g. Ekman (JGR 2014) list half of the models as ones with interactive aerosol. The fact that the model the authors use is even in the global mean lower than any of the other models does not add confidence to the simulations. But why do the authors not look at Arctic data alone? After all, this is the region of interest.

Minimum CDNC: It is necessary that the authors quantify the “occasionally hit” (not necessary for the subtropics, but for the Arctic. What is the percentage of cloudy-sky situations in which the CDNC actually should be lower?

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ED: Publish subject to minor revisions (review by editor) (07 Jun 2018) by Holger Tost

AR by Anina Gilgen on behalf of the Authors (22 Jun 2018) Author's response Manuscript

ED: Publish as is (02 Jul 2018) by Holger Tost

AR by Anina Gilgen on behalf of the Authors (12 Jul 2018)

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Short summary

Aerosol emissions in Arctic summer and autumn are expected to increase in the future because of sea ice retreat. Using a global aerosol–climate model, we quantify the impact of increased aerosol emissions from the ocean and from Arctic shipping in the year 2050. The influence on radiation of both aerosols and clouds is analysed. Mainly driven by changes in surface albedo, the cooling effect of marine aerosols and clouds will increase. Future ship emissions might have a small net cooling effect.