Extending the range and reach of physically-based Greenland ice sheet sea-level projections

Goelzer, Heiko; Berends, Constantijn J.; Boberg, Fredrik; Durand, Gael; Edwards, Tamsin; Fettweis, Xavier; Gillet-Chaulet, Fabien; Glaude, Quentin; Huybrechts, Philippe; Le clec'h, Sébastien; Mottram, Ruth; Noël, Brice; Olesen, Martin; Rahlves, Charlotte; Rohmer, Jeremy; van den Broeke, Michiel; van de Wal, Roderik S. W.

doi:10.5194/egusphere-2025-3098

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https://doi.org/10.5194/egusphere-2025-3098

Preprints

26 Aug 2025

| 26 Aug 2025

Extending the range and reach of physically-based Greenland ice sheet sea-level projections

Heiko Goelzer, Constantijn J. Berends, Fredrik Boberg, Gael Durand, Tamsin Edwards, Xavier Fettweis, Fabien Gillet-Chaulet, Quentin Glaude, Philippe Huybrechts, Sébastien Le clec'h, Ruth Mottram, Brice Noël, Martin Olesen, Charlotte Rahlves, Jeremy Rohmer, Michiel van den Broeke, and Roderik S. W. van de Wal

Abstract. We present an ensemble of ice sheet model projections for the Greenland ice sheet (GrIS) that was produced as part of the European project PROTECT. The work makes use of ice sheet model (ISM) projections forced by high-resolution regional climate model (RCM) output and other climate model forcing, including a parameterisation for the retreat of marine-terminating outlet glaciers. The focus is on providing extended physically-based projections that improve our understanding of the range of GrIS future sea-level contributions and the inherent uncertainties over decadal to multi-centennial timescales. The experimental design builds on the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) protocol and extends it to more fully account for some of the uncertainties in sea-level projections. We include a wider range of CMIP6 climate model output, more climate change scenarios, several climate downscaling approaches, a wider range of sensitivity to ocean forcing and we extend projections schematically beyond the year 2100 up to year 2300, including idealised overshoot scenarios. GrIS sea-level rise contributions range from 16 to 353 mm in the year 2100 (relative to 2014), with strong dependency on the applied climate forcing. Contributions reach 49 to 3127 mm in 2300, indicative of large uncertainties and a potentially very large long-term response. We also extend the ISMIP6 forcing approach backwards over the historical period and successfully produce consistent simulations in both past and future for three of the four ISMs. The ensemble design of ISM experiments is geared towards the subsequent use of emulators to facilitate statistical interpretation of the results and produce probabilistic projections of the GrIS contribution to future sea-level rise.

Received: 01 Jul 2025 – Discussion started: 26 Aug 2025

Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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18 Dec 2025

Extending the range and reach of physically-based Greenland ice sheet sea-level projections

Heiko Goelzer, Constantijn J. Berends, Fredrik Boberg, Gael Durand, Tamsin L. Edwards, Xavier Fettweis, Fabien Gillet-Chaulet, Quentin Glaude, Philippe Huybrechts, Sébastien Le clec'h, Ruth Mottram, Brice Noël, Martin Olesen, Charlotte Rahlves, Jeremy Rohmer, Michiel van den Broeke, and Roderik S. W. van de Wal

The Cryosphere, 19, 6887–6906, https://doi.org/10.5194/tc-19-6887-2025,https://doi.org/10.5194/tc-19-6887-2025, 2025

Short summary

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-3098', Anonymous Referee #1, 25 Sep 2025
Goelzer et al. present the results from a multi-model ensemble of mass-loss/sea-level projections for the Greenland ice sheet, carried out under the PROTECT project. Compared to the Greenland projections for ISMIP6 (Goelzer et al. 2018, 2020), this study includes many improvements, notably (1) the projections begin from simulations that have run through the historical period, (2) global climate model output is downscaled by multiple RCMs, (3) the intermediate 4.5 scenario is included, and (4) some of the runs extends beyond the end of the century to 2300. Although there are fewer participating models than in ISMIP6, the other improvements make this study a valuable step forward. It is likely to be the most comprehensive set of Greenland sea-level projections available between now and when ISMIP7 results are published.
The paper is well organized and clearly written. It presents results in an accessible way without extraneous details. It’s possible to read the entire paper and come away with the key messages in an hour or two.
My main critique, which will be straightforward to address, is that some of the important results and conclusions do not appear in the Abstract or Section 5. Thus, busy readers (practitioners, for instance) won’t find the bottom-line results easily and might be left with questions. For example, the upper end of the 2300 range (3.1 m) is nearly half the total ice-sheet volume and is comparable to the most pessimistic projections for the West Antarctic Ice Sheet. However, this value assumes an extreme emissions scenario that arguably has a very low likelihood. Adding some caveats will reduce the chance that results will be misinterpreted.

Specific comments
l. 19: The Abstract does a good job of describing what was done, but it leaves out some key results. For example, one main result is that the projections are very sensitive to the climate scenario (as expected), moderately sensitive to the RCM choice, and relatively insensitive to the ice sheet model choice. The relatively high RCM sensitivity may be surprising for readers not familiar with Glaude et al. (2024). Also, I suggest stating the 2300 high-end value not only for the extended SSP5-8.5 scenario, but also for the projections with 2100 repeat forcing. Arguably, the repeat-forcing scenario is more realistic and thus more relevant for practitioners than the extended SSP5-8.5 scenario.
l. 55: This paragraph describes an important advance on ISMIP6, responding to the criticisms of Aschwanden et al. (2021). Are you able to say (not here, but later in the paper) how much difference this change makes, compared to initializations that do not include a historical simulation?
l. 95: Please state the equation that describes this parameterization.
l. 99: Can you say how the various percentile values of kappa were determined? In particular, how was the 5% value derived? The language suggests that there is a 5% probability that kappa is at least this high, but I suspect there are deep uncertainties here.
l. 229: The paper doesn’t say how well the 2015 initial ice-sheet geometries compare to observations (e.g., BedMachine ice thickness). I suggest adding a map-view figure showing (1) the observed ice thickness from BedMachine and (2) the thickness error at 2015 for one ensemble member for each ISM, perhaps indicating on each panel the rms thickness error over the ice-covered area.
Optionally, you could also add a graph or table comparing (for each ISM) the simulated mass change over the historical period to the estimated observed mass loss.
l. 236: The text cites O’Neill et al. (2021) for the 2300 scenario. This should be O’Neill et al. (2016). I suggest stating that the maximum CO₂ concentration for this scenario is about 2200 ppm (see Fig. 5b in that paper), roughly double the value at 2100. This explains the large differences in 2300 between the repeat-forcing experiments and those based on ScenarioMIP.
l. 255: “another problem on this timescale may be that the climate response to changing ice sheet geometry is not properly accounted for”. Isn’t this also true for the “natural extensions”? The IPSL and CESM2 extensions weren’t run with interactive ice sheets, so in neither case would the ESM simulate the climate response to changing ice sheet geometry. Or is there a subtlety I’m missing?
I want to suggest that the issues with schematic repeat forcing are not necessarily worse than those associated with CO₂ of 2200 ppm. Neither scenario is fully realistic, but the two approaches are complementary and are probably the best we can do with the CMIP6 output we have.
l. 323: Can you say why the SMB in RACMO is less negative for future projections than those in MAR and HIRHAM? This is discussed by Glaude et al. (2024), but it would be helpful to give a summary here.
Figure 6:
Please state in the caption that this is for 2100.

In panel c, I suggest showing the ranges separately for 8.5 repeat forcing and 8.5 extended forcing, since the former is arguably more plausible than the latter.

It would be helpful to use a different symbol for the CISM runs with extreme values of kappa – e.g., an open green circle instead of a closed green circle. This would confirm that the range of CISM results is close to that of the other ISMs when large kappa is excluded.

Figure 8: I found this figure confusing because there are experiments of the same type on both sides of the dashed lines, but it’s hard to compare them due to the different vertical scales. I suggest using a different color for each type of forcing: o2300, r2300, x2300, and e2200. Another possibility might be having a separate panel for each type (maybe combining e2200 with x2300), with a different vertical scale for the natural extensions.
l. 371: Please state the ranges for Goelzer et al. (2020) and Payne et al. (2021). It might be worth noting that the Payne et al. ranges are much larger than those in Goelzer et al., and similar to the ranges in this study, because of the high warming in some CMIP6 models compared to CMIP5.
l. 374: “A solid number” is vague; can you make this more quantitative?
Somewhere in the Discussion, I suggest commenting on the value of a “mini-MIP” like this one. Does it save time, without diminishing the results, to run just four models instead of a larger number? Other MIP groups might see this study as a template for efficiently updating projections between IPCC reports when resources are limited.
I also suggest stating that the lack of climate feedbacks (as would be present in an ESM with interactive ice sheets) is an important limitation of the study.
l. 411: Since some readers will skim the Abstract and then go straight to the Conclusions, I suggest adding a paragraph summarizing the main results. I think some redundancy with the Discussion is okay. For example:
Give the total GMSL ranges for the different scenarios and time frames.

Restate the result that under high forcing, the ESM choice is the largest contributor to the uncertainty, followed by RCM choice and ISM choice. The rather large sensitivity to RCM choice points to the need for better understanding of the downscaling.

You might add some thoughts on how ISMIP7 will build on this study.

Minor fixes
Please make sure there is a carriage return between each paragraph, or some other indication of a paragraph break.
For figures, put just the label (e.g., Figure 1) in boldface, instead of the entire caption.
l. 87 I think it’s more common to denote surface temperature by ‘TS’ than ‘ST’.
Table 1: Change “RCP5.8” to “RCP8.5” in the header.
l. 126: No hyphen in “grid cells”
l. 162: CO2 -> CO₂(also in l. 164)
l. 174: The units here are not formatted correctly.
l. 350: 6% (no space)
l. 356: Add a comma after “scenario SSP1-2.6” for clarity.
l. 423: I think a word is missing after “text”.
l. 427: “heigh” -> “height”
l. 454: “in function” -> “as a function”?
l. 459: The “/ 4” means that a quarter of the anomaly was applied? Maybe change the wording for clarity.
l. 460: “compared” -> “compared to”
l. 491: This is a sentence fragment; it needs a verb.
l. 495: Extraneous decimal point in “SSP5-.8.5”
Citation: https://doi.org/10.5194/egusphere-2025-3098-RC1
- AC1: 'Reply on RC2', Heiko Goelzer, 11 Oct 2025
  
  The supplement contains replies to both referees
  
  Citation: https://doi.org/10.5194/egusphere-2025-3098-AC1
RC2:
'Comment on egusphere-2025-3098', Anonymous Referee #2, 07 Oct 2025
The authors present results from a multi-model ensemble of future Greenland ice sheet projections carried out within the PROTECT project. This study includes several improvements compared to the ISMIP6 simulations, i.e., it includes different regional climate models for the downscaling (compared to just one in ISMIP6), the protocol has been extended over the historical period, and intermediate CO2 scenario runs have been included. The authors present ranges of potential sea level contributions with respect to the scenarios, regional climate models, and ice sheet models used. This study clearly adds nicely to the ISMIP6 results and comprises valuable results for assessing the potential behavior of the Greenland ice sheet under future warming and the uncertainties associated with it.
The paper is well structured and well written. The figures are of high quality and informative.

General comments:
I think it would be helpful for the reader to include additional figures regarding the initial ice sheet state and the climate forcing used. Time series of the global mean temperature would allow for assessing the effect of the ESM’s climate sensitivity on the ice sheet response. As one huge advantage of this study compared to ISMIP is the historical simulations, I think it would be helpful to include time series of the SMB for different models and/or a map of the initial ice sheet showing how well current observations of the ice sheet extent are captured by the ensemble.

The authors state the importance of emulators and that their model results are geared towards emulator use. However, I miss some more explanation of this. As I understand, the ensemble has been updated with additional experiments to meet the needs of emulators. Except for this, were there additional requirements for the model output to be met in order to facilitate the use of emulators?

Specific comments:
L28f: Given that a large share of the spread is due to different scenarios, it might be more informative to give the GMSL spread here scenario-specific.
L95: Please consider showing the function for the parametrization here.
L99: After reading Slater et al. (2019), it became clear to me what you mean by “can be expressed probabilistically and is sampled …”. However, I think it would be helpful to include the PDF here and indicate which values you take for your simulations.
L125: “GIMP DEM”: not mentioned earlier. Please explain the acronym.
Table 2: Please avoid the page break in the table.
L134: Should be Appendix A, I assume.
L247: Should be Appendix C, I assume.
L264: Should be Appendix C, I assume. Here, I hoped to see some time series of the forcing data, e.g., global mean air temperature.
Figure 5: Given the large spread of the CISM results, would it be possible to use different markers for the different retreat parametrizations?
L366: Should be “rightmost” instead of “leftmost”
Citation: https://doi.org/10.5194/egusphere-2025-3098-RC2
- AC1: 'Reply on RC2', Heiko Goelzer, 11 Oct 2025
  
  The supplement contains replies to both referees
  
  Citation: https://doi.org/10.5194/egusphere-2025-3098-AC1

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-3098', Anonymous Referee #1, 25 Sep 2025
Goelzer et al. present the results from a multi-model ensemble of mass-loss/sea-level projections for the Greenland ice sheet, carried out under the PROTECT project. Compared to the Greenland projections for ISMIP6 (Goelzer et al. 2018, 2020), this study includes many improvements, notably (1) the projections begin from simulations that have run through the historical period, (2) global climate model output is downscaled by multiple RCMs, (3) the intermediate 4.5 scenario is included, and (4) some of the runs extends beyond the end of the century to 2300. Although there are fewer participating models than in ISMIP6, the other improvements make this study a valuable step forward. It is likely to be the most comprehensive set of Greenland sea-level projections available between now and when ISMIP7 results are published.
The paper is well organized and clearly written. It presents results in an accessible way without extraneous details. It’s possible to read the entire paper and come away with the key messages in an hour or two.
My main critique, which will be straightforward to address, is that some of the important results and conclusions do not appear in the Abstract or Section 5. Thus, busy readers (practitioners, for instance) won’t find the bottom-line results easily and might be left with questions. For example, the upper end of the 2300 range (3.1 m) is nearly half the total ice-sheet volume and is comparable to the most pessimistic projections for the West Antarctic Ice Sheet. However, this value assumes an extreme emissions scenario that arguably has a very low likelihood. Adding some caveats will reduce the chance that results will be misinterpreted.

Specific comments
l. 19: The Abstract does a good job of describing what was done, but it leaves out some key results. For example, one main result is that the projections are very sensitive to the climate scenario (as expected), moderately sensitive to the RCM choice, and relatively insensitive to the ice sheet model choice. The relatively high RCM sensitivity may be surprising for readers not familiar with Glaude et al. (2024). Also, I suggest stating the 2300 high-end value not only for the extended SSP5-8.5 scenario, but also for the projections with 2100 repeat forcing. Arguably, the repeat-forcing scenario is more realistic and thus more relevant for practitioners than the extended SSP5-8.5 scenario.
l. 55: This paragraph describes an important advance on ISMIP6, responding to the criticisms of Aschwanden et al. (2021). Are you able to say (not here, but later in the paper) how much difference this change makes, compared to initializations that do not include a historical simulation?
l. 95: Please state the equation that describes this parameterization.
l. 99: Can you say how the various percentile values of kappa were determined? In particular, how was the 5% value derived? The language suggests that there is a 5% probability that kappa is at least this high, but I suspect there are deep uncertainties here.
l. 229: The paper doesn’t say how well the 2015 initial ice-sheet geometries compare to observations (e.g., BedMachine ice thickness). I suggest adding a map-view figure showing (1) the observed ice thickness from BedMachine and (2) the thickness error at 2015 for one ensemble member for each ISM, perhaps indicating on each panel the rms thickness error over the ice-covered area.
Optionally, you could also add a graph or table comparing (for each ISM) the simulated mass change over the historical period to the estimated observed mass loss.
l. 236: The text cites O’Neill et al. (2021) for the 2300 scenario. This should be O’Neill et al. (2016). I suggest stating that the maximum CO₂ concentration for this scenario is about 2200 ppm (see Fig. 5b in that paper), roughly double the value at 2100. This explains the large differences in 2300 between the repeat-forcing experiments and those based on ScenarioMIP.
l. 255: “another problem on this timescale may be that the climate response to changing ice sheet geometry is not properly accounted for”. Isn’t this also true for the “natural extensions”? The IPSL and CESM2 extensions weren’t run with interactive ice sheets, so in neither case would the ESM simulate the climate response to changing ice sheet geometry. Or is there a subtlety I’m missing?
I want to suggest that the issues with schematic repeat forcing are not necessarily worse than those associated with CO₂ of 2200 ppm. Neither scenario is fully realistic, but the two approaches are complementary and are probably the best we can do with the CMIP6 output we have.
l. 323: Can you say why the SMB in RACMO is less negative for future projections than those in MAR and HIRHAM? This is discussed by Glaude et al. (2024), but it would be helpful to give a summary here.
Figure 6:
Please state in the caption that this is for 2100.

In panel c, I suggest showing the ranges separately for 8.5 repeat forcing and 8.5 extended forcing, since the former is arguably more plausible than the latter.

It would be helpful to use a different symbol for the CISM runs with extreme values of kappa – e.g., an open green circle instead of a closed green circle. This would confirm that the range of CISM results is close to that of the other ISMs when large kappa is excluded.

Figure 8: I found this figure confusing because there are experiments of the same type on both sides of the dashed lines, but it’s hard to compare them due to the different vertical scales. I suggest using a different color for each type of forcing: o2300, r2300, x2300, and e2200. Another possibility might be having a separate panel for each type (maybe combining e2200 with x2300), with a different vertical scale for the natural extensions.
l. 371: Please state the ranges for Goelzer et al. (2020) and Payne et al. (2021). It might be worth noting that the Payne et al. ranges are much larger than those in Goelzer et al., and similar to the ranges in this study, because of the high warming in some CMIP6 models compared to CMIP5.
l. 374: “A solid number” is vague; can you make this more quantitative?
Somewhere in the Discussion, I suggest commenting on the value of a “mini-MIP” like this one. Does it save time, without diminishing the results, to run just four models instead of a larger number? Other MIP groups might see this study as a template for efficiently updating projections between IPCC reports when resources are limited.
I also suggest stating that the lack of climate feedbacks (as would be present in an ESM with interactive ice sheets) is an important limitation of the study.
l. 411: Since some readers will skim the Abstract and then go straight to the Conclusions, I suggest adding a paragraph summarizing the main results. I think some redundancy with the Discussion is okay. For example:
Give the total GMSL ranges for the different scenarios and time frames.

Restate the result that under high forcing, the ESM choice is the largest contributor to the uncertainty, followed by RCM choice and ISM choice. The rather large sensitivity to RCM choice points to the need for better understanding of the downscaling.

You might add some thoughts on how ISMIP7 will build on this study.

Minor fixes
Please make sure there is a carriage return between each paragraph, or some other indication of a paragraph break.
For figures, put just the label (e.g., Figure 1) in boldface, instead of the entire caption.
l. 87 I think it’s more common to denote surface temperature by ‘TS’ than ‘ST’.
Table 1: Change “RCP5.8” to “RCP8.5” in the header.
l. 126: No hyphen in “grid cells”
l. 162: CO2 -> CO₂(also in l. 164)
l. 174: The units here are not formatted correctly.
l. 350: 6% (no space)
l. 356: Add a comma after “scenario SSP1-2.6” for clarity.
l. 423: I think a word is missing after “text”.
l. 427: “heigh” -> “height”
l. 454: “in function” -> “as a function”?
l. 459: The “/ 4” means that a quarter of the anomaly was applied? Maybe change the wording for clarity.
l. 460: “compared” -> “compared to”
l. 491: This is a sentence fragment; it needs a verb.
l. 495: Extraneous decimal point in “SSP5-.8.5”
Citation: https://doi.org/10.5194/egusphere-2025-3098-RC1
- AC1: 'Reply on RC2', Heiko Goelzer, 11 Oct 2025
  
  The supplement contains replies to both referees
  
  Citation: https://doi.org/10.5194/egusphere-2025-3098-AC1
RC2:
'Comment on egusphere-2025-3098', Anonymous Referee #2, 07 Oct 2025
The authors present results from a multi-model ensemble of future Greenland ice sheet projections carried out within the PROTECT project. This study includes several improvements compared to the ISMIP6 simulations, i.e., it includes different regional climate models for the downscaling (compared to just one in ISMIP6), the protocol has been extended over the historical period, and intermediate CO2 scenario runs have been included. The authors present ranges of potential sea level contributions with respect to the scenarios, regional climate models, and ice sheet models used. This study clearly adds nicely to the ISMIP6 results and comprises valuable results for assessing the potential behavior of the Greenland ice sheet under future warming and the uncertainties associated with it.
The paper is well structured and well written. The figures are of high quality and informative.

General comments:
I think it would be helpful for the reader to include additional figures regarding the initial ice sheet state and the climate forcing used. Time series of the global mean temperature would allow for assessing the effect of the ESM’s climate sensitivity on the ice sheet response. As one huge advantage of this study compared to ISMIP is the historical simulations, I think it would be helpful to include time series of the SMB for different models and/or a map of the initial ice sheet showing how well current observations of the ice sheet extent are captured by the ensemble.

The authors state the importance of emulators and that their model results are geared towards emulator use. However, I miss some more explanation of this. As I understand, the ensemble has been updated with additional experiments to meet the needs of emulators. Except for this, were there additional requirements for the model output to be met in order to facilitate the use of emulators?

Specific comments:
L28f: Given that a large share of the spread is due to different scenarios, it might be more informative to give the GMSL spread here scenario-specific.
L95: Please consider showing the function for the parametrization here.
L99: After reading Slater et al. (2019), it became clear to me what you mean by “can be expressed probabilistically and is sampled …”. However, I think it would be helpful to include the PDF here and indicate which values you take for your simulations.
L125: “GIMP DEM”: not mentioned earlier. Please explain the acronym.
Table 2: Please avoid the page break in the table.
L134: Should be Appendix A, I assume.
L247: Should be Appendix C, I assume.
L264: Should be Appendix C, I assume. Here, I hoped to see some time series of the forcing data, e.g., global mean air temperature.
Figure 5: Given the large spread of the CISM results, would it be possible to use different markers for the different retreat parametrizations?
L366: Should be “rightmost” instead of “leftmost”
Citation: https://doi.org/10.5194/egusphere-2025-3098-RC2
- AC1: 'Reply on RC2', Heiko Goelzer, 11 Oct 2025
  
  The supplement contains replies to both referees
  
  Citation: https://doi.org/10.5194/egusphere-2025-3098-AC1

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) (03 Nov 2025) by Alexander Robinson

AR by Heiko Goelzer on behalf of the Authors (27 Nov 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (28 Nov 2025) by Alexander Robinson

To the authors,

Overall, the manuscript is in good shape and has addressed the comments of the reviewers well. Nonetheless, there are several minor improvements to be made. Two relatively general comments are given here:

- Section 2.6 and Appendix A are both a bit strangely introduced in this text, and I think Section 2.6 doesn't belong where it is. Mainly the phrases "Data request for ice sheet model output" and "The requested data" are a bit strange, as this section is intended to describe the data that is available and has been produced in this study right? There has not been a request from someone yet, or the request already happened internally within the group of contributors. Maybe reformulate to "Data availability" and "Data from this study consists of ...". More broadly, I would change current Appendix A to A.1, and move Section 2.6 to Appendix A.2. Reformulate without the phrase "request" anywhere, or make it clear that this relates to the internal requests within your consortium, it is not a current request to the community.

- Second, in regards to possible future work with this ensemble using an emulator, in this work I think it is appropriate to avoid referring to a concrete emulator or study, as none was described here. There are a few comments along these lines below.

Along with these general comments, please find additional specific comments for minor revisions below. I look forward to a revised version of the manuscript.

Best regards,
Alex

Specific comments

L19-23: These first three sentences are a bit redundant and confusing. Is the study presenting the projections or making use of them? I recommend revising for clarity here.

L22: The focus is on providing → Here we provide

L25: Consider deleting "some of the"

L53: ice sheet scale → ice-sheet scale

L56: ice sheet projections → ice-sheet projections [etc, check throughout]

L69: it requires statistical tools → statistical tools are needed

L96 (equation): I am a strong proponent of following mathematical notation conventions in equations, which means e.g. 1 letter per variable, subscripts, etc. I would suggest reformulating this equation in this way. For example, I believe $a(x,y,t) = a_\mathrm{ref}(x,y)+a_\mathrm{anom}(x,y,t)+\frac{da}{dz}(x,y,t) \cdot \Delta z(t)$ would a clearer way to write this equation. Greve and Blatter (2009) use "a" for the accumulation-ablation term (ie, SMB), or Cuffey and Patterson (2010) use "b" for balance. I realize you may want to keep consistency with e.g. ISMIP6 and past work, so I would not consider a change mandatory. But I think it would improve readability here and then throughout the text.

L106: kappa → κ

L145: in familiar format → in a familiar format

L245-246: "one statistical downscaling method" ← Earlier it was stated that this would be considered as an RCM (L117-118). Make sure to frame this consistently throughout the paper. Perhaps the statement can be rephrased on L117-118 to simply say it can be considered similar in capability to an RCM in terms of the forcing it provides, if you want to continue to refer to it separately.

L256: to continue downscaling → of further downscaling of [or] of continuing to downscale

L287: from the beginning a modelling strategy → a modelling strategy from the beginning

L302: choices to cover → choices, intended to cover

FIgure 6: There is an inconsistency between Figs. 5 & 6, namely that in Fig. 5 it is clear that the VUB-GISM simulations gives higher and indeed the maximum SLCs by 2100, but in Fig. 6, NORCE-CISM is systematically higher and represents the maximum. I understand this is because Fig. 5 shows a particular subset. Would it be possible to add something to Fig. 6, to identify those simulations that were plotted in Fig. 5? Perhaps a vertical grey line behind each symbol that is associated with Fig. 5?

L334-335: I would suggest listing the (a), (b), ... before the item, so (a) ISMs, (b) RCMs, (c) scenarios and (d) CMIP iterations. This is more usual and eases readability. Or better, remove, the (a), (b), ... entirely, since this really about the figure, right? This ordering information is contained within the caption of the Figure itself.

L371: climate forcing. → climate forcing,

Figure 9: This figure should be improved significantly. Currently it relies heavily on the long programmatic x-labels to inform the reader of what they are looking at. First I would suggest, keeping one shared y-axis throughout. But rather have the lower 1/3 of the axis spaced evenly from 0-250 mm, then the upper 2/3 of the axis could show values from 250-3000mm. Then I would include some kind of light shading grouping the experiments together, as far as I can see, this is first by scenario, so groups of [ssp585-o2300, ssp126-r2300, ssp245-r2300, rcp85/ssp585-r2300, ssp585-x2300, ssp585-e220], with the latter group set to one side since it is further distinguished from the others. The shaded bands could have text labels directly or a corresponding legend. Then the x-labels could simply be comprised of the climate model and the choice of regional downscaling. This would be one solution to improve this figure.

L398: less ISMs → using a subset of ISMs

L398: due to additional → due to the incorporation of additional

L402: the subsequent → possible future

L415: is dominating → dominates

L419: we have explored here in addition → we have additionally explore here

L430: source of uncertainty → source of uncertainty on this timescale

L432: going to 2300 → going to 2300 or even beyond

L437-439: This sentence needs to be revised. Consider reordering the sentence, something like "Combined, these results indicate that modifications to the ISMIP6 forcing protocols and new methods to account for a changing ice sheet geometry are needed for robust standalone ice sheet simulations well beyond year 2100".

L443: provide the emulator → provide an emulator

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AR by Heiko Goelzer on behalf of the Authors (01 Dec 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (01 Dec 2025) by Alexander Robinson

AR by Heiko Goelzer on behalf of the Authors (11 Dec 2025) Manuscript

Journal article(s) based on this preprint

18 Dec 2025

Extending the range and reach of physically-based Greenland ice sheet sea-level projections

The Cryosphere, 19, 6887–6906, https://doi.org/10.5194/tc-19-6887-2025,https://doi.org/10.5194/tc-19-6887-2025, 2025

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We present an ensemble of ice sheet model projections for the Greenland ice sheet. The focus is on providing projections that improve our understanding of the range future sea-level rise and the inherent uncertainties over the next 100 to 300 years. Compared to earlier work we more fully account for some of the uncertainties in sea-level projections. We include a wider range of climate model output, more climate change scenarios and we extend projections schematically up to year 2300.


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