|I’m really glad to read that the authors have addressed most of the reviewers’ comments and I would like thank the authors for their efforts. There is still an important, major discussion lacking though on the downscaled SMB components for HIRHAM5 runs over Antarctica (see below), after which the paper would be ready for publication in my opinion. Although the SMB results are indeed in the range of other current estimates, this is not the case for individual SMB components, which suggests that good results are obtained for the wrong reasons. The high runoff rates for the downscaling of EC-EARTHv3 in Antarctica are of particular concern, and may have for instance strong consequences for risk assessment of ice shelves vulnerability. Please expand more on these values. More minor comments are reported below. |
L62-64: Please expand briefly in the text on the information brought by these evaluations about the performance of EC-EARTHv2&3 relative to others CMIP models.
L70-72: This is incorrect. Mass is lost by the ice sheet when the ice flows through the grounding line and becomes afloat. Since ice shelves are already floating terminations of glaciers, occurrence of melting below the ice shelves and/or thinning of ice shelves has an indirect consequence on mass loss through ice sheet dynamics (by triggering the retreat, acceleration and drawdown of marine-terminating glacier) but do not contribute directly to the mass balance in the way suggested here. Please rephrase.
L93: I know what you mean here, but strictly speaking this is another shortcut that could be avoided, as melt is not part of the SMB. If all melt refreezes, like in Antarctica, there is no direct link between surface ablation and melt. I suggest to replace with something like “leading to large meltwater runoff amounts” or equivalent.
L199-200: This is correct for the SMB, but as a result of a very different balance between its components.
L283-288: This is where I suggest that your results are in significant disagreement with the literature and here I would call for a more complete comparison with other state-of-the-art estimates of individual SMB components (see Lenaerts et al., 2016; van Wessem et al., 2018; Kittel et al., 2021). The average (1971-2000) ice-sheet integrated runoff values of the EC-EARTv3 downscaling of 854 Gt yr-1 with 593 yr-1 for the ice shelves (Table 2 in the revised manuscript) deserve particular attention. These numbers given for the present climate state are even higher than the average values projected for the end of the century under ssp585 for the warmest ESM in Kittel et al. (2021). More than 3000 Gt yr-1 of projected RU for the AIS by the end of the century is also very high. Moreover, I’m not sure it relates exclusively to a positive temperature bias in EC-EARTH since HIRHAM5 driven by ERA-I already yields high runoff rates (172 Gt yr-1 over the present period, which would correspond to the meltwater fluxes in other RCM estimates, i.e., implying that the whole melt amount runs off entirely). In this reference run, high runoff rates are partly compensated by high snowfall rates in the uppermost range of the whole RCM ensemble (Mottram et al., 2021). Please comment on all of this.
L364-366: The absence of uncertainties associated with your average values complicates a bit the comparison, but as far as I can read in Kittel et al. (2021) (their Table 1), the highest of the 4 future runoff anomalies amounts to 260 Gt yr-1 for the grounded ice, which differ by much more than 150 Gt yr-1 from the HIRHAM5_EC-EARTH3 future anomaly of 1094-261 = 833 Gt yr-1 reported here. Could you give more details on your calculation?
Kittel, C., Amory, C., Agosta, C., Jourdain, N. C., Hofer, S., Delhasse, A., Doutreloup, S., Huot, P.-V., Lang, C., Fichefet, T., and Fettweis, X.: Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet, The Cryosphere, 15, 1215–1236, https://doi.org/10.5194/tc-15-1215-2021, 2021.
Mottram, R., Hansen, N., Kittel, C., van Wessem, J. M., Agosta, C., Amory, C., Boberg, F., van de Berg, W. J., Fettweis, X., Gossart, A., van Lipzig, N. P. M., van Meijgaard, E., Orr, A., Phillips, T., Webster, S., Simonsen, S. B., and Souverijns, N.: What is the surface mass balance of Antarctica? An intercomparison of regional climate model estimates, The Cryosphere, 15, 3751–3784, https://doi.org/10.5194/tc-15-3751-2021, 2021.
Lenaerts, J.T.M., Vizcaino, M., Fyke, J. et al. Present-day and future Antarctic ice sheet climate and surface mass balance in the Community Earth System Model. Clim Dyn 47, 1367–1381 (2016). https://doi.org/10.1007/s00382-015-2907-4
van Wessem, J. M., van de Berg, W. J., Noël, B. P. Y., van Meijgaard, E., Amory, C., Birnbaum, G., Jakobs, C. L., Krüger, K., Lenaerts, J. T. M., Lhermitte, S., Ligtenberg, S. R. M., Medley, B., Reijmer, C. H., van Tricht, K., Trusel, L. D., van Ulft, L. H., Wouters, B., Wuite, J., and van den Broeke, M. R.: Modelling the climate and surface mass balance of polar ice sheets using RACMO2 – Part 2: Antarctica (1979–2016), The Cryosphere, 12, 1479–1498, https://doi.org/10.5194/tc-12-1479-2018, 2018.