The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

Stap, Lennert B.; van de Wal, Roderik S. W.; de Boer, Bas; Bintanja, Richard; Lourens, Lucas J.

doi:https://doi.org/10.5194/cp-13-1243-2017

Articles | Volume 13, issue 9

https://doi.org/10.5194/cp-13-1243-2017

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

https://doi.org/10.5194/cp-13-1243-2017

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

Articles | Volume 13, issue 9

Research article

|

25 Sep 2017

Research article |

| 25 Sep 2017

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

Lennert B. Stap, Roderik S. W. van de Wal, Bas de Boer, Richard Bintanja, and Lucas J. Lourens

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Final revised paper (published on 25 Sep 2017)
Supplement to the final revised paper
Preprint (discussion started on 08 Nov 2016)

Interactive discussion

Status: closed

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

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RC1: 'Review of ‘The influence of ice sheets on the climate during the past 38 million years‘ by Stap et al.', Anonymous Referee #1, 19 Jan 2017
RC2: 'Review of the paper entitled “The influence of ice sheets on the climate during the past 38 million years” by Lennert B. Stap et al.', Anonymous Referee #2, 27 Jan 2017
AC1: 'Author's response (to both reviewers)', Lennert Stap, 24 Feb 2017

Peer-review completion

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

ED: Reconsider after major revisions (16 Mar 2017) by Zhengtang Guo

AR by Lennert Stap on behalf of the Authors (26 Apr 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Apr 2017) by Zhengtang Guo

RR by Anonymous Referee #1 (22 May 2017)

RR by Anonymous Referee #3 (08 Jun 2017)

Suggestions for revision or reasons for rejection

Review of revised manuscript cp-2016-109 "The influence of ice sheets on temperature during the past 38 million years "

After reading of the authors’ response and the revised manuscript, in my view there are some issues with that manuscript that still remain, which warrant a minor revision before it is suitable for publication.

General comments:

The authors' effort to address the first set of comments from the reviewers is appreciated, and in my opinion the revisions have improved the manuscript. The study should aid in the understanding and interpretation of the long term climate - ice sheet interaction in the transient simulations, which also sets a reference simulation for more sophisticated models. The scope of the new version of the paper, as the revised title and abstract state, is properly addressed. The overall structure of the paper is substantially improved. The introduction now includes useful discussion of complex climate model simulations on shorter time scales. The equations of the model are added so the paper is easier to read.

Sec3:
1. Hysteresis
This is the section that reviewer#2 holds strong objection, while reviewer#1 also wants the authors to clarify. I agree with the authors that these experiments are potentially interesting and provide valuable information for the research community, but some concerns (see below minor comments) still need to be addressed.

2. pCO2 reconstruction
As reviewer#2 points out that a drawback of the study is extending the simulation to the late Eocene (38 Ma) but completely ignoring the role of tectonics on CO2 in the model. I see the authors make this limitation clearer and show more quantified results of their simulated pCO2 compared with available proxies in the revised manuscript (in new Sec 3.3). In my view, more sophisticated model and setup are necessary to fully address such a caveat in the future studies.

Sec 4:
The ice-albedo feedback and the surface-height-temperature feedback are compared, and they have potentially interesting implications for the interpretation of ENSO proxy data. The overall argument under three CO2 scenarios (low CO2 -> strong NH ice-sheet and temperature change, albedo feedback more important; intermediate CO2 -> little melt NH ice-sheet and no deglaciation of Antarctica, minor temperature change; high CO2 -> strong SH ice-sheet and temperature change, elevation feedback more important) is fairly convincing.

Minor comments:

As suggested by reviewer#1, it is curious that a hysteresis behavior occurs when excluding overturning. For completeness the authors should at least list previous studies that has a similar feature but due to overturning (e.g. Zhang et al., 2014). Furthermore, after the discussion that roles out the possibility of coupled ice-sheet, coupled ocean overturning and sea ice and snow cover, the authors argue at the end of Sec 3.1 that ‘this means that the hysteresis is inherent to the core of the climate model: the parameterisation of vertical and horizontal energy transfer in the ocean and atmosphere’, but the conjecture is not really convincing. More evidences should be provided.

Also in the conclusion section it would be better for the authors not to simply list the conclusion as in the abstract, but to strengthen the connection between them (e.g. what’s the implication of hysteresis and pCO2 caveat in Sec 3 that potentially influence the conclusion in Sec 4), and to more convincingly demonstrate that those materials in Sec 3 are crucial to comprehensively understand the target of the study.

Editorial comments:

A few words and phrases (especially in the revised part) need to proof read as the English is not correct, e.g. P8L15, P8L26.

Refs
Zhang, X., Lohmann, G., Knorr, G., & Purcell, C. (2014). Abrupt glacial climate shifts controlled by ice sheet changes. Nature, 512(7514), 290-294.

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RR by Anonymous Referee #4 (21 Jun 2017)

RR by Anonymous Referee #2 (03 Jul 2017)

Suggestions for revision or reasons for rejection

"The influence of ice sheets on the climate during the past 38 million years"
Author(s): Lennert B. Stap, Roderik S. W. van de Wal, Bas de Boer, Richard Bintanja, and Lucas J. Lourens

I was indeed very busy these last two months and, because I raised major criticism in my first review and also because the authors provided an improved manuscript, it took me some time to reconsider this manuscript. Therefore, I apologize for this long delay.

General comments:
A very good point when reviewing a CP paper is that the different reviews of the paper are published and therefore are available to the readers. I did not change my mind concerning this paper. Indeed, as I said in my first review, this is an interesting, but limited step towards capturing ice sheet impact on climate evolution. Interesting, because it is using a simplified tool that enables the author to explore ice sheets and climate evolution since 38 Ma but limited, because the comparison with real evolution of climate due to the use of EBM for climate and 1D ice sheet model for ice sheets that only allow for a very theoretical approach. Moreover, even if the structure of the paper has been improved, I think that a first step using realistic CO2 reconstructions would have been a very interesting exercise, rather than reconstructing CO2, which is anyway a very difficult exercise. The authors now answer to my major comments concerning the weakness of their introduction in terms of comparison with previous studies. Also, as requested by the first reviewer, they added more information, included equations on their model and clarified their experimental design and comparison to CO2 reconstruction. They did not convince me on some aspects (see detailed review below) but I nevertheless consider that, with all the limitations they already included and, accounting for suggestions and remarks below, this paper may be published in Climate of the Past.

Detailed comments:
title: I think the title should refer to the fact it is a modeling study. Therefore, I would suggest "Influence of ice sheets on the climate during the past 38 million years inferred from a simple coupled ice sheet/climate model". This point is crucial for me, because, due to many major simplifications in this approach, the results are very theoretical, compared to the real climate evolution.
Methodology:
This part has been clearly improved due to both reviewer comments. Nevertheless, I think that, because the authors have a simple tool, that enables them to perform many simulations accounting for different CO2 scenarios, it would have been very interesting to prescribe reconstructed CO2 evolutions from different proxies to explore ice-sheet and climate evolution. Especially, to analyze the Antarctica inception, as simulated in the different scenarios, (e.g. when it occurred, and for which CO2 level, without any tuning). Nevertheless, I agree that they use a consistent approach, but tuning parameters, without understanding where are the bias and caveat of this method.
I am not sure I fully understand for instance why they have to tune the CO2 value for inception to the one from Pollard and Deconto and what are the consequences of this tuning.

Discussion:
In the discussion, the authors argue on the impact of ice sheets variability on climate for high and low CO2. It is a very consistent, but theoretical analysis, when compared to real climate evolution for many reasons, some are related to the fact that it is only the radiative forcing and not the dynamics that is considered here.

On the other hand, rapid dynamics change of the ice sheets may have important consequences on tropical atmospheric circulation (see for instance Mulitza 2008 for Heinrich events and African monsoon) that may change drastically our view on the variability of the ice sheet and its impact during cold and warm phases.

Comments on figures:
Fig 4: Please specify that the red curve is the new reference. The x axis title should be (Myears).
Fig 4A: the new ref systematically underestimates the values usually accounted for this period, after mis-M2 (~3.3 Ma) and till 3.0 Ma, for this warm period, PLIOMIP simulations take a value of 405 ppm (Haywood 2012), significantly larger than the new reference results (300 ppm).
Fig 4b: For MMCO, the CO2 are overestimated, with respect to the data.
Fig 4c: In this case, the new reference results are lower than the data. This figure illustrates the interest of providing simulations with consistent proxy reconstruction (alkenone, boron, stomates) rather than computed CO2, which is either overestimating or underestimating these reconstructions and moreover did not capture correctly all the processes for this geological time span.
Fig. 5: It would be very interesting to make several plots rather than only one with the three computed parameters to compare also the sea level evolution and the temperatures to data. For instance, 5a could be delta O18 and CO2 and 5b could be sea level evolution computed and compared to data and 5c temperature computed and compared to data.

Best Regard,

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ED: Publish subject to minor revisions (review by Editor) (11 Jul 2017) by Zhengtang Guo

AR by Lennert Stap on behalf of the Authors (21 Aug 2017) Author's response Manuscript

ED: Publish as is (23 Aug 2017) by Zhengtang Guo

AR by Lennert Stap on behalf of the Authors (23 Aug 2017) Author's response Manuscript

Short summary

We show the results of transient simulations with a coupled climate–ice sheet model over the past 38 million years. The CO₂ forcing of the model is inversely obtained from a benthic δ¹⁸O stack. These simulations enable us to study the influence of ice sheet variability on climate change on long timescales. We find that ice sheet–climate interaction strongly enhances Earth system sensitivity and polar amplification.