Last glacial inception trajectories for the Northern Hemisphere from coupled ice and climate modelling

Bahadory, Taimaz; Tarasov, Lev; Andres, Heather

doi:https://doi.org/10.5194/cp-17-397-2021

Articles | Volume 17, issue 1

https://doi.org/10.5194/cp-17-397-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/cp-17-397-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 1

Research article

|

15 Feb 2021

Research article |

| 15 Feb 2021

Last glacial inception trajectories for the Northern Hemisphere from coupled ice and climate modelling

Taimaz Bahadory, Lev Tarasov, and Heather Andres

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Final revised paper (published on 15 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 27 Jan 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Discussion', John Andrews, 30 Mar 2020
- AC1: 'Response to reviews by Andre Ganopolski and John Andrews', Lev Tarasov, 16 Jun 2020
RC2: 'Review', Andrey Ganopolski, 31 Mar 2020
- AC1: 'Response to reviews by Andre Ganopolski and John Andrews', Lev Tarasov, 16 Jun 2020

Peer-review completion

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

ED: Reconsider after major revisions (18 Jun 2020) by Steven Phipps

AR by Lev Tarasov on behalf of the Authors (18 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Oct 2020) by Steven Phipps

RR by Andrey Ganopolski (17 Nov 2020)

Suggestions for revision or reasons for rejection

I appreciate the efforts which the authors made to respond to my criticism and suggestions and in general, I am satisfied with their response. However, I still have two remarks on the revised manuscript.

1) In response to my criticism that in the introduction the authors do not cite previous works on modelling of glacial inception (nothing personal – all my relevant papers have been cited in the manuscript by Bahadory et al.), the authors responded “ that most of the "25 modeling papers" cited in Calov et al. (2005) used what we judge to be “poor model/experimental configuration/designs and obtained poor results in large discord with paleo proxy constraints ...” Since many more papers on this subject have been published after Calov et al. (2005), the authors obviously consider all of them also to be “poor”. I do not believe that such attitude (unfortunately, not unusual) when previous publications considered to be obsolete and not worth mentioning just because they were based on the “wrong” models. However, only thanks to these earlier studies, we now can do some things better than it was possible 15 or 20 years ago and this is why the earlier efforts deserve at least to be acknowledged. After all, do the authors believe that their own study is problems-free and their results are in perfect agreement with paleo proxy constraints?

2) In my first review, I suggested that the modeled east-west asymmetry in the North American ice sheet distribution is not consistent with paleoclimate reconstructions and is caused by temperature biases of the LOVECLIM model. Following my recommendation, the authors now show (Fig. 14) modeled summer temperature biases and discuss their potential implications for modelling of glacial inception in section 3.1.2 (“Labrador and eastern NA remain ice-free, likely due to warm model biases in this region”) and 4.1 (“... temperature biases ... may have inhibited glaciation over Hudson Bay and northern Quebec”). However, in section 4.5, the authors continue to insist that (“except for Alaska”) their modelling results are consistent with paleoclimate reconstructions. To this end, the authors dismiss MIS5d reconstruction by Batchelor et al. (2018) as unreliable and claim that what Clark et al. (1993) wrote in their paper about the initialisation of glaciation in Keewatin and Quebec contradicts to their own figure (Fig. 19) which shows the opposite. Although the authors are much closer to Quebec than me, I would insist that their reading of Fig. 19 in Clark et al. (1993) is mistaken. Clark et al. (1993) wrote ”Following the last interglaciation, the Laurentide Ice Sheet first developed during Oxygen-Isotope Stage 5 over Keewatin, Quebec and Baffin Island” on the same page where they discuss Fig. 19. This is why I doubt that the text and Fig. 19 contradict each other. In fact, Fig. 19 only suggests that ice sheet was absent in the most southern part of Quebec during MIS5 which does not contract, for example, Batchelor’s MIS5d reconstruction. In any case, whatever the reliability of paleoclimate reconstructions of MIS5 North America ice sheet is, the Fig. 14 in the revised Bahadory et al. manuscript shows that their modelling results in the north-eastern part of North America are not trustworthy. Indeed, the figure shows summer temperature biases over Keewatin and Quebec of more than +10C (!). Since, according to model simulations, climate response to changes in orbital forcing at 116ka was only half of that, this area in the model remains much warmer during glacial inception than it is in reality even at present. This, of course, completely preclude ice sheet formation in eastern Canada. As I made it clear in my previous review, I have no intention to give advice to the authors which modelling approach they should use. However, I would now add to the list of publications which applied temperature biases corrections, the recent paper by Choudhury et al. (2020) and I believe this paper reinforces my concern about the impact of strong summer temperature biases in LOVECLIM on simulation of glacial inception.

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ED: Publish subject to minor revisions (review by editor) (24 Nov 2020) by Steven Phipps

AR by Lev Tarasov on behalf of the Authors (18 Dec 2020) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (21 Dec 2020) by Steven Phipps

Short summary

We present an ensemble of last glacial inception simulations using a fully coupled ice–climate model for the Northern Hemisphere. The ensemble largely captures inferred ice volume changes within proxy uncertainties. Notable features include an ice bridge across Davis Strait and between Greenland and Iceland. Via an equilibrium climate response experiment, we also demonstrate the potential value of fully coupled ice–climate modelling of last glacial inception to constrain future climate change.