the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Mar 2023
Analysis of the simulated feedbacks on large-scale ice sheets from ice-sheet climate interactions
Abstract. In study presented here we focus on the large climate-ice sheet feedbacks on global scales on time scales of 100,000 yrs. We conducted a series of idealised sensitivity experiments under CO2 and solar radiation reduction scenarios with the Globally Resolved Energy Balance - Ice Sheet Model v1.0 (GREB-ISM v1.0), to study the characteristics of five climate-ice sheet feedbacks, including albedo, snowfall, ice latent heat, topography and sea level feedbacks. We analysed the relative importance of each of these feedbacks on the ice sheet growth and on the climate system (surface temperature). The results indicate that the inclusion of ice sheets will delay the response to the external forcing and facilitate the climate cooling in the high latitude and altitude areas in the Northern Hemisphere, but also causes a small amount of warming elsewhere, due to the blocking of atmospheric heat transport. As for individual feedbacks, the albedo feedback is the most dominant positive feedback in favour of ice sheet build-up and cooler climates, whereas snowfall feedback is the greatest negative feedback that reduces the growth of ice sheets. The large ice latent heat required to melt ice allows to maintain ice sheets from one cold seasons to the next and therefore provides a positive feedback for ice sheet growth. The ice sheets impact on the topography is also a positive feedback but with smaller impact than the albedo feedback. The sea level change influences ice sheets by shifting their location, in particular allowing ice sheets growth in the Arctic Ocean, while reducing it over central north Asia.
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Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-370', Mario Krapp, 12 Apr 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-370/egusphere-2023-370-RC1-supplement.pdf
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AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
Dear Editor and referees,
we like to thank the two referees and editor for the time spend on reviewing this manuscript and for the many very helpful comments they provided. We think the referee comments have helped us to substantially improve the presentation of this work.
The attached file is our response letter with point-by-point reply.            Â
With best regards,
Zhiang Xie, Dietmar Dommenget
-
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
-
RC2: 'Comment on egusphere-2023-370', Anonymous Referee #2, 27 Apr 2023
This study uses a simplified coupled ice sheet-climate model to analyze feedback between large-scale ice sheets and the climate system. The climate part is a global energy balance model with an invariant wind field. The ice sheet model has four vertical layers and a positive degree day scheme to calculate the surface mass balance. One of the main findings is that the albedo feedback dominates ice growth. This is not groundbreaking in itself but I welcome the author's approach to take advantage of a computationally tool to systematically test the sensitivity of the ice-climate system.
The scope of the manuscript is interesting and well-suited for The Cryosphere (although to me Climate of the Past is an even better fit). My criticism focusses on the limitations of the GREB model and the extent to which they are tested and discussed in the manuscript. I think these aspects must be addressed before publication.1) It is difficult to understand to what degree the results depend on model limitations. If I understood correctly, GREB uses a prescribed and time-invariant wind field. This average field and (invariant) statistics about its variance are then used to prescribe moisture transport. This is a strong limitation as previous studies have found the dynamic response of, e.g., the stationary wave pattern (Löfverström and Liakka, 2016) or local circulation changes around ice sheets (Merz et al., 2014a,b) to be very important. Also, the ocean circulation in GREB cannot change, which is another strong limitation. I understand that testing the assumptions that went into making the efficient model can only be tested fully in a more complex model, but it should be possible to estimate some simplifications by adjusting model parameters within GREB. As an example, there must be a parameterization for meridional heat transport by the ocean that could be changed to approximate changes in the circulation. Such changes are believed to be essential for climate-ice sheet interactions on longer time scales. Similarly, the lack of a dynamic response of the atmosphere to the growth of the Laurentide ice sheet should be tested. How important are the feedbacks in the presence of this additional effect? This needs to be quantified.
2) Related to this first point, I would like to see a more detailed discussion of the merits that the author's approach holds. Why should simulations with a strongly simplified model be considered by journals and their readers? How can these simple models answer questions that more sophisticated models cannot? Does the manuscript in its present form really take advantage of the low computational cost of GREB-ISM? I do not think so as it appears to only present a handfull of simulations, each only representing a few hours of time on a regular single CPU. Why were not more changes in GHGs tested? Why not different changes in solar irradiation? Also, what does a 5% reduction in solar output mean for simulations that run over 100,000 years? Is this a constant offset? Does it have seasonality? GREB-ISM can, and maybe should, be used to do more comprehensive tests of Milankovitch forcing, including the importance of time scales (obliquity, precession, etc.).
Minor comments:
- The manuscript requires language editing. I think that running individual paragraphs through GPT or similar would probably solve 95% of the issues.line 138: "Atmospheric blocking" usually refers to a specific type of circulation anomaly, different from what is meant here.
line 179: Most (all?) of the processes described here cannot be addressed with GREB-ISM
figure 6: This only presents anomalies. How does the ice topography of FULL without perturbations look?
figure 10: The division by 10 for one of the columns must be immediately visible in the figure without the need to read the caption.
figure 12: What does "mm/dy" mean? Per day (d) or per year (yr)?
figure 14: I found this figure and the corresponding text difficult to follow and cannot say I am convinced.
figures in general: I think there is too many figures for the relatively straightforward point that the manuscript is trying to make.
Literature (if not yet included in the manuscript):
Merz et al. 2014b: https://doi.org/10.1002/2014JD021940Merz et al. 2014a: https://doi.org/10.5194/cp-10-1221-2014
Citation: https://doi.org/10.5194/egusphere-2023-370-RC2 -
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
Dear Editor and referees,
we like to thank the two referees and editor for the time spend on reviewing this manuscript and for the many very helpful comments they provided. We think the referee comments have helped us to substantially improve the presentation of this work.
The attached file is our response letter with point-by-point reply.            Â
With best regards,
Zhiang Xie, Dietmar Dommenget
-
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
- AC2: 'Manuscript with trace tracking', Zhiang Xie, 03 Jul 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-370', Mario Krapp, 12 Apr 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-370/egusphere-2023-370-RC1-supplement.pdf
-
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
Dear Editor and referees,
we like to thank the two referees and editor for the time spend on reviewing this manuscript and for the many very helpful comments they provided. We think the referee comments have helped us to substantially improve the presentation of this work.
The attached file is our response letter with point-by-point reply.            Â
With best regards,
Zhiang Xie, Dietmar Dommenget
-
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
-
RC2: 'Comment on egusphere-2023-370', Anonymous Referee #2, 27 Apr 2023
This study uses a simplified coupled ice sheet-climate model to analyze feedback between large-scale ice sheets and the climate system. The climate part is a global energy balance model with an invariant wind field. The ice sheet model has four vertical layers and a positive degree day scheme to calculate the surface mass balance. One of the main findings is that the albedo feedback dominates ice growth. This is not groundbreaking in itself but I welcome the author's approach to take advantage of a computationally tool to systematically test the sensitivity of the ice-climate system.
The scope of the manuscript is interesting and well-suited for The Cryosphere (although to me Climate of the Past is an even better fit). My criticism focusses on the limitations of the GREB model and the extent to which they are tested and discussed in the manuscript. I think these aspects must be addressed before publication.1) It is difficult to understand to what degree the results depend on model limitations. If I understood correctly, GREB uses a prescribed and time-invariant wind field. This average field and (invariant) statistics about its variance are then used to prescribe moisture transport. This is a strong limitation as previous studies have found the dynamic response of, e.g., the stationary wave pattern (Löfverström and Liakka, 2016) or local circulation changes around ice sheets (Merz et al., 2014a,b) to be very important. Also, the ocean circulation in GREB cannot change, which is another strong limitation. I understand that testing the assumptions that went into making the efficient model can only be tested fully in a more complex model, but it should be possible to estimate some simplifications by adjusting model parameters within GREB. As an example, there must be a parameterization for meridional heat transport by the ocean that could be changed to approximate changes in the circulation. Such changes are believed to be essential for climate-ice sheet interactions on longer time scales. Similarly, the lack of a dynamic response of the atmosphere to the growth of the Laurentide ice sheet should be tested. How important are the feedbacks in the presence of this additional effect? This needs to be quantified.
2) Related to this first point, I would like to see a more detailed discussion of the merits that the author's approach holds. Why should simulations with a strongly simplified model be considered by journals and their readers? How can these simple models answer questions that more sophisticated models cannot? Does the manuscript in its present form really take advantage of the low computational cost of GREB-ISM? I do not think so as it appears to only present a handfull of simulations, each only representing a few hours of time on a regular single CPU. Why were not more changes in GHGs tested? Why not different changes in solar irradiation? Also, what does a 5% reduction in solar output mean for simulations that run over 100,000 years? Is this a constant offset? Does it have seasonality? GREB-ISM can, and maybe should, be used to do more comprehensive tests of Milankovitch forcing, including the importance of time scales (obliquity, precession, etc.).
Minor comments:
- The manuscript requires language editing. I think that running individual paragraphs through GPT or similar would probably solve 95% of the issues.line 138: "Atmospheric blocking" usually refers to a specific type of circulation anomaly, different from what is meant here.
line 179: Most (all?) of the processes described here cannot be addressed with GREB-ISM
figure 6: This only presents anomalies. How does the ice topography of FULL without perturbations look?
figure 10: The division by 10 for one of the columns must be immediately visible in the figure without the need to read the caption.
figure 12: What does "mm/dy" mean? Per day (d) or per year (yr)?
figure 14: I found this figure and the corresponding text difficult to follow and cannot say I am convinced.
figures in general: I think there is too many figures for the relatively straightforward point that the manuscript is trying to make.
Literature (if not yet included in the manuscript):
Merz et al. 2014b: https://doi.org/10.1002/2014JD021940Merz et al. 2014a: https://doi.org/10.5194/cp-10-1221-2014
Citation: https://doi.org/10.5194/egusphere-2023-370-RC2 -
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
Dear Editor and referees,
we like to thank the two referees and editor for the time spend on reviewing this manuscript and for the many very helpful comments they provided. We think the referee comments have helped us to substantially improve the presentation of this work.
The attached file is our response letter with point-by-point reply.            Â
With best regards,
Zhiang Xie, Dietmar Dommenget
-
AC1: 'Reply to RC1 and RC2', Zhiang Xie, 03 Jul 2023
- AC2: 'Manuscript with trace tracking', Zhiang Xie, 03 Jul 2023
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