Interhemispheric effect of global geography on  Earth's climate response to orbital forcing

Roychowdhury, Rajarshi; DeConto, Robert

doi:https://doi.org/10.5194/cp-15-377-2019

Articles | Volume 15, issue 1

https://doi.org/10.5194/cp-15-377-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/cp-15-377-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 1

Research article

|

26 Feb 2019

Research article |

| 26 Feb 2019

Interhemispheric effect of global geography on Earth's climate response to orbital forcing

Rajarshi Roychowdhury and Robert DeConto

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Final revised paper (published on 26 Feb 2019)
Preprint (discussion started on 08 Jun 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review', Anonymous Referee #1, 29 Jun 2017
- AC1: 'Response to Anonymous Referee #1', Rajarshi Roychowdhury, 02 Nov 2017
RC2: 'Review #2', Anonymous Referee #2, 11 Jul 2017
- AC2: 'Response to Anonymous Referee #2', Rajarshi Roychowdhury, 03 Nov 2017

Peer-review completion

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

ED: Reconsider after major revisions (24 Nov 2017) by Pascale Braconnot

AR by Rajarshi Roychowdhury on behalf of the Authors (07 Feb 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Mar 2018) by Pascale Braconnot

RR by Anonymous Referee #3 (09 Apr 2018)

Suggestions for revision or reasons for rejection

The editor gave me the very specific and difficult mission to assess to what extent the authors responded to the issues raised by the reviewers.

The authors made significant efforts to attempt to respond to the requests of the reviewers. They must be praised for that. Nevertheless this does not seem fully satisfactory to me since some of the important requests are rejected as 'irrelevant' (which I can partially understand) or worse, the additional parts add more confusion. The section about the clouds, the liquid water content, atmospheric pressure, snow cover and sea ice should inform the reader about the feedbacks but this is not really the case. Firstly, the analysis is almost exclusively limited to correlations and, on the other hand, it lacks an explanation of what the variables really are (is it annual average, seasonal, other?) and what is the physics behind the correlation.

The authors wrote themselves that a ‘true discussion’ of the role of asymmetry would involve simulations at every possible orbital configuration, including all possible eccentricity values’. And it really puzzles me because they have only 6 experiments, all with the same eccentricity. We are really far from covering the whole field of orbital parameters (and I understand that it is impossible for a GCM). However, what is done here is probably statistically not significant. Moreover, ‘statistical methods’ (latin hypercube) are very efficient to identify the set of variables that would be more representative for the full ranges of combinations although, even a carefully designed set of experiments would mean too many experiments.

The idea of studying the importance of the continent / ocean configuration is indeed very relevant but I am not convinced and remain very puzzled by this paper and the additional explanation provided, and I therefore join referee # 2 (in his initial review). I feel that the corrections made are 'cosmetic' but do not really answer the basic questions.

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RR by Anonymous Referee #2 (09 May 2018)

ED: Reconsider after major revisions (13 May 2018) by Pascale Braconnot

AR by Rajarshi Roychowdhury on behalf of the Authors (26 Oct 2018) Manuscript

ED: Referee Nomination & Report Request started (15 Nov 2018) by Pascale Braconnot

RR by Anonymous Referee #3 (27 Nov 2018)

Suggestions for revision or reasons for rejection

I thank the authors for providing a point by point response to the reviewer’s comments. I noted that their work should be considered as a first/preliminary step. I also acknowledge that the purpose of the paper is descriptive, and does not intend to provide any detailed dynamical analysis. The authors recognized and claimed the use of one single climate model, with its strengths and weaknesses, as well as the of a limited number of simulations.
This being said, I have a major comment regarding the data availability section. This section is missing in the manuscript (see https://www.climate-of-the-past.net/about/data_policy.html and https://www.climate-of-the-past.net/for_authors/manuscript_preparation.html ).

Moreover, data must be archived.
Input data: To my best knowledge there are few input data in this study, except the GHGs and the LSX Configuration. Reference AND citation to these data should probably be included (and can certainly easily be included).
Output data:
If the model outputs for all the simulations are archived and publicly available, this should be mentioned.
In any case the data used to support the conclusion of the paper (almost all the data plotted in the figures) must be archived and made publicly available. A citation should be attached to these data.

I also have a set of minor comments.
Fig1: All the curves are annual mean. Is it correct? This should be specified
GCM: Does this stand for Global Climate Model or General Circulation Model? What is the difference between both?
L 133: What does geography mean in this context? A reference may be useful.
L 150: Summer insolation is obviously NOT symmetric across both Hemisphere according to Figure 3a. It remains still unclear what is the difference between insolation and energy in this context.
L 227: Why is it ‘Northern and austral summers’ and not ‘boreal and Southern summers’? I would have expected ‘Northern and Southern summers’ or ‘boreal and austral summers’. What is the difference?
L 239: ‘The forcing (summer energy (J)) calculated at the top of the atmosphere is symmetric across both hemispheres (Figure 5a)’. According to the figure, it seems rather anti-symmetric or asymmetric.
L 258: The section numbering should be checked throughout.

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RR by Anonymous Referee #2 (21 Dec 2018)

ED: Publish subject to minor revisions (review by editor) (29 Dec 2018) by Pascale Braconnot

AR by Rajarshi Roychowdhury on behalf of the Authors (09 Jan 2019) Author's response Manuscript

ED: Publish as is (18 Jan 2019) by Pascale Braconnot

AR by Rajarshi Roychowdhury on behalf of the Authors (25 Jan 2019)

Short summary

The climate response of the Earth to orbital forcing shows a distinct hemispheric asymmetry, and one of the reasons can be ascribed to the unequal distribution of land in the Northern Hemisphere and Southern Hemisphere. We show that a land asymmetry effect (LAE) exists, and that it can be quantified. By using a GCM with a unique geographic setup, we illustrate that there are far-field influences of global geography that moderate or accentuate the Earth's response to orbital forcing.