Disentangling the drivers of future Antarctic ice loss with a historically-calibrated ice-sheet model

Coulon, Violaine; Klose, Ann Kristin; Kittel, Christoph; Edwards, Tamsin; Turner, Fiona; Winkelmann, Ricarda; Pattyn, Frank

doi:https://doi.org/10.5194/egusphere-2023-1532

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https://doi.org/10.5194/egusphere-2023-1532

Preprints

27 Jul 2023

| 27 Jul 2023

Disentangling the drivers of future Antarctic ice loss with a historically-calibrated ice-sheet model

Violaine Coulon, Ann Kristin Klose, Christoph Kittel, Tamsin Edwards, Fiona Turner, Ricarda Winkelmann, and Frank Pattyn

Abstract. We use an observationally-calibrated ice-sheet model to investigate the future trajectory of the Antarctic ice sheet related to uncertainties in the future balance between sub-shelf melting and ice discharge on the one hand, and the surface mass balance on the other. Our ensemble of simulations, forced by a panel of CMIP6 climate models, suggests that the ocean will be the primary driver of short-term Antarctic mass loss, initiating ice loss in West Antarctica already during this century. The atmosphere initially plays a mitigating role through increased snowfall, leading to an Antarctic contribution to global mean sea-level rise by 2100 of 6 (-8 to 15) cm under a low-emission scenario and 5.5 (-10 to 16) cm under a very high-emission scenario. However, under the very high-emission pathway, the influence of the atmosphere shifts beyond the end of the century, becoming an amplifying driver of mass loss as the ice sheet's surface mass balance decreases. We show that this transition occurs when Antarctic near-surface warming exceeds a critical threshold of +7.5 °C, at which the increase in surface runoff outweighs the increase in snow accumulation, a signal that is amplified by the melt–elevation feedback. Therefore, under the very high-emission scenario, oceanic and atmospheric drivers are projected to result in a complete collapse of the West Antarctic ice sheet along with significant grounding-line retreat in the marine basins of the East Antarctic ice sheet, leading to a median global mean sea-level rise of 2.75 (6.95) m by 2300 (3000). Under a more sustainable socio-economic pathway, we find that the Antarctic ice sheet may still contribute to a median global mean sea-level rise of 0.62 (1.85) m by 2300 (3000). However, the rate of sea-level rise is significantly reduced as mass loss is likely to remain confined to the Amundsen Sea Embayment, where present-day climate conditions seem sufficient to commit to a continuous retreat of Thwaites Glacier.

Received: 06 Jul 2023 – Discussion started: 27 Jul 2023

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12 Feb 2024

Disentangling the drivers of future Antarctic ice loss with a historically calibrated ice-sheet model

Violaine Coulon, Ann Kristin Klose, Christoph Kittel, Tamsin Edwards, Fiona Turner, Ricarda Winkelmann, and Frank Pattyn

The Cryosphere, 18, 653–681, https://doi.org/10.5194/tc-18-653-2024,https://doi.org/10.5194/tc-18-653-2024, 2024

Short summary

Violaine Coulon, Ann Kristin Klose, Christoph Kittel, Tamsin Edwards, Fiona Turner, Ricarda Winkelmann, and Frank Pattyn

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-1532', Nicholas Golledge, 18 Aug 2023

This paper presents a suite of new ice sheet simulations for Antarctica, that explore a range of critical parameters where substantial uncertainty exists. By using an observationally-constrained starting point and a rigorous statistical framework for assessing ensemble members, the authors are able to disentangle the dominant drivers of ice sheet evolution both through time (out to year 3000), and across different sectors of the continent. Their results are consistent with previous findings, in terms of contributions to sea level, but the paper makes a significant advance through its rigorous and multi-parameter approach. The figures are extremely good - both informative and clear - and the text is very well written.

Overall I could find nothing of much substance to comment on. There is a typo ('adressing') at line 114, but this is I think the only one I found. At line 424 I thought maybe the Robel and Banwell paper could be mentioned - in terms of how meltwater ponds might localise. At line 481 I thought maybe a comment about model resolution could be made, and followed up in more detail in the model description Appendix. I for one am not going to argue that a model resolution of 16 km is insufficient for this kind of study - I think it is entirely pragmatic for an ensemble approach like this - but I know that there are others in the community who might like to see more justification for a 'low res' simulation, or at least some evidence that the GL tracks reliably.

But these are minor points. Overall I found this a fascinating and enjoyable paper to read, and it will almost certainly be of great value for future assessments of SLR.

Citation: https://doi.org/10.5194/egusphere-2023-1532-RC1
- AC1: 'Reply on RC1', Violaine Coulon, 20 Oct 2023
  
  Please see the attachment.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1532-AC1
RC2:
'Comment on egusphere-2023-1532', Daniel Martin, 20 Sep 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1532/egusphere-2023-1532-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-1532-RC2
- AC2: 'Reply on RC2', Violaine Coulon, 20 Oct 2023
  
  Please see the attachment.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1532-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-1532', Nicholas Golledge, 18 Aug 2023

This paper presents a suite of new ice sheet simulations for Antarctica, that explore a range of critical parameters where substantial uncertainty exists. By using an observationally-constrained starting point and a rigorous statistical framework for assessing ensemble members, the authors are able to disentangle the dominant drivers of ice sheet evolution both through time (out to year 3000), and across different sectors of the continent. Their results are consistent with previous findings, in terms of contributions to sea level, but the paper makes a significant advance through its rigorous and multi-parameter approach. The figures are extremely good - both informative and clear - and the text is very well written.

Overall I could find nothing of much substance to comment on. There is a typo ('adressing') at line 114, but this is I think the only one I found. At line 424 I thought maybe the Robel and Banwell paper could be mentioned - in terms of how meltwater ponds might localise. At line 481 I thought maybe a comment about model resolution could be made, and followed up in more detail in the model description Appendix. I for one am not going to argue that a model resolution of 16 km is insufficient for this kind of study - I think it is entirely pragmatic for an ensemble approach like this - but I know that there are others in the community who might like to see more justification for a 'low res' simulation, or at least some evidence that the GL tracks reliably.

But these are minor points. Overall I found this a fascinating and enjoyable paper to read, and it will almost certainly be of great value for future assessments of SLR.

Citation: https://doi.org/10.5194/egusphere-2023-1532-RC1
- AC1: 'Reply on RC1', Violaine Coulon, 20 Oct 2023
  
  Please see the attachment.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1532-AC1
RC2:
'Comment on egusphere-2023-1532', Daniel Martin, 20 Sep 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1532/egusphere-2023-1532-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-1532-RC2
- AC2: 'Reply on RC2', Violaine Coulon, 20 Oct 2023
  
  Please see the attachment.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1532-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to minor revisions (review by editor) (06 Nov 2023) by Jan De Rydt

AR by Violaine Coulon on behalf of the Authors (07 Nov 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (28 Nov 2023) by Jan De Rydt

Dear Dr Coulon and co-authors,

Thank you for providing an updated manuscript with tracked changes in reply to the reviewer comments. Both reviewers requested minor changes, in particular 1) a justification for the use of 16km grid resolution and some evidence to show accuracy of this approach (R#1 and R#2), and 2) some additional discussion about the possible implications of a constant mantle viscosity (#R2). Whilst I think the second point and all other minor comments have been addressed in the revised manuscript, I was hoping to see a more in-depth discussion on the first point. You argue that the model can reliably simulate grounding line movement based on results for the MISMIP+ experiment. However, these simulations were done with 1, 2 and 4km resolution, which is a much higher resolution than the 16km used here, and results are obtained for a highly idealized geometry. Cornford et al. (2016) argue very strongly that convergence tests should be done on a case by case basis, and ideally I would like to see something done along those lines for your Antarctic setup. Would you be able to do a convergence test for 1 ensemble member of your Antarctica-wide setup with, e.g. 4, 8 and 16km resolution and running for a few 100 years? I appreciate this might be computationally prohibitive, in which case you might be able to demonstrate mesh convergence in a regional setup, e.g. for the Amundsen Sea, which I believe is available in KORI? If that’s also unfeasible, is it possible to include results from simulations with 8km (and 16km?) in the MISOMIP+ plot, with the understanding that this might be very crude given the 80km width of the domain? At the very least, please refer to Cornford et al. (2016) and Reese et al. (2018) in your discussions to raise awareness of the potential pitfalls of using coarse resolution and the grounding line flux condition.

All the best,
Jan De Rydt - editor

References
-------------
Cornford, S., Martin, D., Lee, V., Payne, A., & Ng, E. (2016). Adaptive mesh refinement versus subgrid friction interpolation in simulations of Antarctic ice dynamics. Annals of Glaciology, 57(73), 1-9. doi:10.1017/aog.2016.13

Reese, R., Winkelmann, R., and Gudmundsson, G. H.: Grounding-line flux formula applied as a flux condition in numerical simulations fails for buttressed Antarctic ice streams, The Cryosphere, 12, 3229–3242, https://doi.org/10.5194/tc-12-3229-2018, 2018

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AR by Violaine Coulon on behalf of the Authors (11 Dec 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (13 Dec 2023) by Jan De Rydt

AR by Violaine Coulon on behalf of the Authors (19 Dec 2023) Manuscript

Journal article(s) based on this preprint

12 Feb 2024

Disentangling the drivers of future Antarctic ice loss with a historically calibrated ice-sheet model

Violaine Coulon, Ann Kristin Klose, Christoph Kittel, Tamsin Edwards, Fiona Turner, Ricarda Winkelmann, and Frank Pattyn

The Cryosphere, 18, 653–681, https://doi.org/10.5194/tc-18-653-2024,https://doi.org/10.5194/tc-18-653-2024, 2024

Short summary

Violaine Coulon, Ann Kristin Klose, Christoph Kittel, Tamsin Edwards, Fiona Turner, Ricarda Winkelmann, and Frank Pattyn

Supplement

https://doi.org/10.5194/egusphere-2023-1532-supplement

Violaine Coulon, Ann Kristin Klose, Christoph Kittel, Tamsin Edwards, Fiona Turner, Ricarda Winkelmann, and Frank Pattyn

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We present new projections of the evolution of the Antarctic ice sheet until the end of the millennium, calibrated with observations. We show that the ocean will be the main trigger of future ice loss. As temperatures continue to rise, the atmosphere's role may shift from mitigating to amplifying Antarctic mass loss already by the end of the century. For high-emission scenarios, this may lead to substantial sea-level rise. Adopting sustainable practices would however reduce the rate of ice loss.


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