the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Sep 2025
Decoded Antarctic snow accumulation history reconciles observed and modeled trends in accumulation and large-scale warming patterns
Abstract. Ice-core reconstructions indicate that increased snow accumulation on the Antarctic Ice Sheet mitigated global sea level rise by ~11 mm during 1901–2000. However, in the most recent 40 years of more intense observation and warming, the trend in the Antarctic-wide accumulation rate has been negligible. We attribute these trends by evaluating Earth system model experiments in comparison with dynamically consistent reconstructions of surface climate. Single-forcing experiments reveal that rising concentrations of greenhouse gases (GHGs) have been the underlying driver of increased accumulation, yet acting alone would have caused twice the observed accumulation-related sea level mitigation during 1901–2000. Aerosol-driven cooling partially compensates this overprediction, but there is strong evidence for other processes at work. We hypothesize that high-latitude winds have been working together with ice-shelf meltwater fluxes to dampen Southern Ocean surface warming and suppress the GHG-driven accumulation increase since the initiation of West Antarctic ice shelf thinning in the mid-twentieth century. The wind pattern associated with strengthening of the Southern Hemisphere westerlies and deepening of the Amundsen Sea Low distributes accumulation unevenly across the continent in an orographic pattern that is consistent across models and the reconstructions. In reconstructions, these same wind and accumulation patterns are associated with muted surface warming across the eastern Pacific and Southern Ocean, a pattern not captured in climate projections including the all-forcings large ensemble studied here. However, the westerly wind history constrained by paleoclimate data assimilation largely reconciles differences between the model's ensemble-mean response and the observed world for both Antarctic-wide accumulation and large-scale warming patterns. Although the large ensemble simulates similar wind histories to the real one, its corresponding responses in SSTs and Antarctic-wide accumulation are decoupled from the wind. We discuss how this significant observation-model discrepancy, which has widespread implications for projecting regional climate change, likely arises from omitted meltwater forcing and/or resolution limitations. As a component of the sea level budget and a gauge of the magnitude and spatial pattern of climate change, Antarctic snow accumulation is a critical target for models to replicate.
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Status: final response (author comments only)
- CC1: 'Comment on egusphere-2025-3666', Jeffrey Radke, 12 Dec 2025
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RC1: 'Comment on egusphere-2025-3666', Yetang Wang, 24 Dec 2025
By integrating observations, reconstructions, and Earth system model experiments, this study provides a comprehensive insight into changes in Antarctic snow accumulation and its underlying physical mechanisms. The research indicates that increased greenhouse gases are the primary driver of enhanced Antarctic accumulation, but their effect is partially offset by the cooling influence of aerosols. Since the mid-20th century, the high-latitude wind field and meltwater from ice shelves have collectively suppressed Southern Ocean warming, significantly weakening the greenhouse gas-induced increase in accumulation. Both models and reconstructions consistently demonstrate that wind patterns associated with the strengthening of the westerlies and Amundsen Sea Low lead to uneven accumulation distribution across the Antarctica. Furthermore, the authors note that although the historical wind fields in large ensemble simulations align with observations, the corresponding SST and overall Antarctic accumulation responses appear decoupled from these wind field changes. This discrepancy may stem from unaccounted meltwater forcing and/or limitations in model resolution.
In summary, the authors have undertaken substantial work. These results are highly valuable for estimating the changes in Antarctic snow accumulation rates and their contribution to global sea-level rise, and will be of great interest to the communities reading Earth System Dynamics. Therefore, I recommend acceptance of this manuscript after minor revisions. Some of my suggestions are as follows:
- The introduction is logical and concise. However, the summary of recent snow accumulation studies could be enhanced, particularly with regard to the multi-source data employed and the novel conclusions.
- The authors should provide a brief introduction to the spatial patterns of Antarctic snow accumulation under different forcings or modes in the results section and compare their differences.
- In the Discussion, it would be highly beneficial to include a schematic diagram, such as a conceptual model illustrating the physical feedback chain linking "wind–meltwater–SST–snow accumulation". This diagram should include as many atmospheric and oceanic processes mentioned in the study as possible.
- Current understanding indicates that Antarctic climate change is strongly influenced by internal variability. Therefore, I suggest the authors enhance the mechanistic explanation regarding the impact of modes of climate variability on Antarctic snow accumulation rates, particularly the teleconnections originating from the tropical Pacific.
- The authors should add a significance testing when conducting trend analyses, such as Figures 4 and 7.
- I recommended to add citations or comparisons with results from other CMIP6 models in the discussion.
- Regarding readability of the figure, it is suggested that the authors increase the font size of text in certain figures to make them more noticeable to readers, as illustrated in Figure 3. Moreover, the representation of statistical significance (stippling) in Figure 5 is not sufficiently clear.
Citation: https://doi.org/10.5194/egusphere-2025-3666-RC1 -
RC2: 'Comment on egusphere-2025-3666', Anonymous Referee #2, 29 Mar 2026
This article analyses ensembles of model simulations to show that the increase in snow accumulation over Antarctica induced by greenhouse gas emissions has been dampen by aerosol emissions and by changes in winds and ice sheet meltwater release. There is a huge amount of work behind this article, with the comparison of several multi-member ensembles of climate simulations. It is an important piece of work that bridges a gap towards the attribution of the total mass change of the Antarctic ice sheet, and that helps understand limitations of the CMIP models. However, several sections of this manuscript are difficult to follow. In my opinion, major revisions would therefore be needed to make this article suitable for publication.
Major comments:
I acknowledge that this article is not easy to write due to the large variety of analysed simulations. However, there is room for improvement, and I find the manuscript difficult to read in many sections. First, the information on the experiments is difficult to find, with some in section 2, some in Appendix, some in the results section (e.g., CESM1-AIS-meltwater), and some in other articles. My recommendation would be to put everything in the Method section. Second, the description of the results is sometimes long and difficult to follow, with some numbers difficult to relate the associated figure or experiment, and a lack of introductory sentences in each section to explain the aim of the following result description (while reading, the readers do not know where these long descriptions are leading them). A short paragraph describing the overall approach at the beginning of section 3 would also help.
My second major concern is that at several places, the reasoning is difficult to follow because of a lack of description of the experimental design, and/or because some numbers are not clearly sourced. These issues are listed in the detailed comments below.
My third major comment is that the authors seem to consider wind and meltwater changes at the same level as changes in greenhouse gases and aerosols. For example, they conclude that “winds have been working together with ice sheet and ice shelf meltwater fluxes to dampen Southern Ocean surface warming and suppress the GHG-driven snow accumulation increase”. Unlike GHG and aerosols, winds and SSTs are not external forcings, they are variables of the climate system. They are affected by GHG and aerosols among others and are also part of the internal variability. Technically, prescribed meltwater may be considered as external forcing, although it is only external due to the absence of interactive ice sheet in the model, and should in theory respond to GHG, aerosols, etc. I think that better introducing all these concepts in the manuscript would make the analysis easier to follow and the results more robust.
Detailed comments:Abstract, L. 28-29: I found it awkward to describe the role of GHG and aerosols, then to mention that there are other processes and describe the role of winds and freshwater. Changes in winds and freshwater do both emerge from emissions of GHG and aerosols (and internal variability, ozone, …), so I would not present them as “other processes at work”.
L. 65: The units seem wrong, Gt yr-1 is equivalent to mm yr-1, not to mm. This number is also misleading because the net SMB is not per se equivalent to sea-level rise, it is only the anomalies that lead to sea level rise.
L. 113-114: This is unclear. Rainfall is also an accumulation term (it fills firn porosity), i.e., a positive term in the surface mass balance, not only snowfall. Is rainfall included in the accumulation term or not?
L. 170-172: I would like some more explanations about the TPACE and "everything else" (EE) ensembles, and why the role of stratospheric ozone depletion and recovery cannot be isolated with these experiments (if it is important for this article, if not, it could be removed). Why isn’t stratospheric ozone investigated in a similar way as GHG and aerosols? Stratospheric ozone is part of the usual Detection–Attribution protocol.
Appendix A / section 3.4: The only information that are provided about CESM1-AIS-meltwater are in section 3.4 (a bit late compared to the method description), and only consists of “The meltwater experiment was designed to represent the spatial pattern of freshwater fluxes from ice shelf basal melt, with the total magnitude of these fluxes set to 2000 Gt yr-1 ”. I think that more information should be provided about this:
• Is the freshwater injected at the ocean surface? Along the front of unresolved ice shelf cavities?
• Why only mentioning ice shelf basal melt rates given that more than half of the current Antarctic mass discharge ends up as iceberg melting?
• Please compare the 2000 Gt yr-1 to recent estimates, e.g., those in Coulon et al. (2024, their Tab. 1).
• Is there some kind of correction in CESM ensuring that any SMB anomaly is reinjected into the ocean to conserve the ocean mass (e.g., Schmidt et al., 2025, their Fig. 10)? If so, it is worth mentioning it because any increase in SMB will lead to an increase in freshwater release in addition to the additional 2000 Gt yr-1.L. 201: “to form the prior” may not be meaningful for readers who have not read O’Connor et al. (2021), please expend a little.
Fig. 3 is not perfectly clear to me. Does each marker represent the mean temperature of a given year in 1901-2000 (X-axis) and the surface accumulation from 1901 to that year (Y-axis in panel a)? In a context of global warming, wouldn’t there be a good correlation between anything that accumulates in time and global temperature? Wouldn’t it be more relevant to plot the global annual mean temperature vs annual mean accumulation (in Gt/yr)?
Throughout the manuscript: numbers could be provided only in sea level equivalent, providing both Gt and mm SLE everywhere does not improve the readability.
L. 264: “has a mass gain of 6079 Gt”. Add “from 1900 to 2000”.
L. 265-268: I had to read these two sentences several times to try to figure out what was the meaning and the point of these sentences.
L. 269-270: It is ok to make such a statement here, but the statistical significance of the difference between two means is not only based on the standard deviations, it is also based on the number of years and/or ensemble members used to calculate the mean (see, e.g., two-sample t-test).
L. 270-272: please help the reader to see where these numbers are from (which panel? which experiment?).
L. 327-337: add a sentence at the beginning to explain what you’re doing with a single member. How was member #40 identified as the best member? Was the selection done in an objective way, i.e., based on some metrics?
Section 3.2: Are these results robust if the second-best member is used instead of member #40? Even for a perfect model, it seems impossible to get a perfect match with all observations for a member out of only 50. So how much are the conclusions based on the specific characteristics of member #40?
L. 437:439: The sentence “Negative accumulation trends occur in Wilkes Land, where the thinning Totten Glacier is located and in West Antarctica over the thinning Thwaites and Pine Island glaciers” might suggest that the accumulation trend explains the mass loss of these glaciers, but the increase in grounding line discharge is by far the leading driver of their mass loss (e.g., Rignot et al., 2013).
Section 3.4: please comment on the realism of the meltwater perturbation in these experiments. If it is over or under estimated, what would a more realistic perturbation induce?
Title of section 3.4: why “hidden”? Is it more hidden than any other of the investigated effects?
L. 531-536: This is very unclear. First, it needs to be understandable without having to read Dong et al. (2022a). Then, in which figure, experiment or analysis is the trend multiplied by five? And why five and how is this quantitatively linked to the evolution of Pine Island and Thwaites ice shelves in the mid 20th century? From the caption of Fig. 9b, I understand that a trend over a decade is extended to 50 years, is it just that a trend estimated over 10 years is applied to 50 years or is the slope of the trend multiplied by five? Please expand and reformulate.
L. 601-602: The internal variability in the CESM model may be weaker than the natural variability of the real world, as suggested by Casado et al. (2023) for a bunch of CMIP6 models. How would this affect the conclusions of this article?
L. 657-660: I am sorry but I would need further explanations to understand this: “As diagnosed by Simpson et al. (2023), positive ice-albedo feedbacks in [AAER] act on a cold pre-industrial background state, leading to strong cooling. These feedbacks are not as pronounced in [CESM2-LE] in which aerosols are introduced only after the climate has warmed somewhat due to increasing greenhouse gases. The strong cooling in [AAER] is artificial …”.
L. 683: correct “20250”.
Section 4.4: what about the effect of stratospheric ozone recovery in the projections to 2050?
L. 692-697: Specify that surface melting and runoff only become important beyond 2050 (e.g., Kittel et al., 2021; Jourdain et al., 2025).
L. 759-760: How does “the snow accumulation history” show that there is causality?
L. 787-788: “The CESM2's ensemble-mean version of accumulation increase would have been a welcome addition to the ice sheet's mass”. What do the authors mean here?
Additional referencesCasado, M., Hébert, R., Faranda, D. and Landais, A. (2023). The quandary of detecting the signature of climate change in Antarctica. Nature Climate Change, 13(10), 1082-1088.
Coulon, V., De Rydt, J., Gregov, T., Qin, Q. and Pattyn, F. (2024). Future freshwater fluxes from the Antarctic ice sheet. Geophysical Research Letters, 51(23), e2024GL111250.
Jourdain, N. C., Amory, C., Kittel, C. and Durand, G. (2025). Changes in Antarctic surface conditions and potential for ice shelf hydrofracturing from 1850 to 2200. The Cryosphere, 19(4), 1641-1674.
Kittel, C., Amory, C., Agosta, C., Jourdain, N. C., Hofer, S., Delhasse, A. and others (2021). Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet. The Cryosphere, 15(3), 1215-1236.
Rignot, E., Jacobs, S., Mouginot, J. and Scheuchl, B. (2013). Ice-shelf melting around Antarctica. Science, 341(6143), 266-270.
Citation: https://doi.org/10.5194/egusphere-2025-3666-RC2
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This paper presents a comprehensive and carefully executed analysis of Antarctic snow accumulation that meaningfully reconciles observations, reconstructions, and Earth system model behavior. The study is well written, logically structured, and grounded in a strong physical interpretation of circulation, SST patterns, and forcing attribution. The integration of large ensembles, observation-constrained experiments, and paleoclimate data assimilation is phenomenal, and the results offer important insights with clear implications for sea-level projections and climate model evaluation.
Overall, this is a valuable and impactful contribution to the field.