General comments

The paper by Hoang et al. describes the implementation of the simple surface energy and mass balance model BESSI into the iLOVECLIM Earth system model. First, the performance of BESSI for the simulation of the present-day SMB over Greenland and Antarctica is compared with results of the regional climate model MAR. Then BESSI is driven by climate forcing from iLOVECLIM simulations to show how climate model biases affect the SMB and how the results compare to the insolation-temperature-melt (ITM) method used previously in iLOVECLIM. Finally, transient iLOVECLIM simulations of the last interglacial period are performed and climate fields are used to drive BESSI and estimate the evolution of the SMB and its different components over the time interval from 135 to 115 kyrBP. The results indicate that BESSI and the ITM produce different SMB evolutions for the Greenland ice sheet over this period of time. I have some major comments that should be addressed before this paper can be published in Climate of the Past.

The paper is rather technical, with a large part being dedicated to the description of the BESSI model (which is already described in detail in Born et al. 2018) and model evaluation for the present-day Greenland and Antarctic ice sheets. This part of the paper would actually better fit the scope of a journal like Geoscientific Model Development. However, I think that there is the potential to make the more scientific part of the paper more prominent to make the publication generally more interesting for readers of Climate of the Past. To make the paper more suitable for Climate of the Past, I would suggest a few changes:

• generally shift the focus of the paper towards the simulations of the LIG
• expand the introduction with some background information about what is known about the climate and ice sheet evolution (in particular Greenland) over the LIG, both from modeling studies and reconstructions (e.g. sea level)
• add a discussion of the implications of the simulated SMB for the Greenland ice sheet evolution over the LIG
• possibly move the Appendix B into the main paper, as the sensitivity analysis is scientifically interesting

BESSI is certainly more physically-based than the original ITM model, but as also acknowledged by the authors, this does not necessarily imply a more realistic representation of the SMB. Nevertheless, at several places in the text the authors make claims like:

• ‘The model also captures well the variation of SMB and its components during the LIG.’
• ‘For long-term simulations in paleo studies, BESSI has proved to be able to provide reliable data in a short time as it has a physical model setup and is computationally inexpensive. Particularly, in this work, BESSI-iLOVECLIM simulates well the SMB evolution during the LIG, following the change of the orbital configuration and carbon dioxide concentration.’

To justify statements like these, at the very least the simulated SMB should be compared with previous modelling studies (e.g. Sommers et al. 2021 but also some of the previous work by the authors themselves).

Simulated temperature (or more generally climate) changes over Greenland during the early phase of the LIG at a time when the GIS was probably similar to its present-day state could be compared with previous modelling studies (e.g. CMIP6 lig127k) and proxy data.

Finally, the English usage in this manuscript must be substantial improved to make the text easier to follow.

Minor comments

L. 1: ‘retreat-advanced’ -> ‘retreat-advance’

L. 8: ‘an’ -> ‘the’

L. 11: ITM not defined

L. 16: MaBP is not really a standard abbreviation, possibly use Myr BP or Ma instead?

L. 16: I wouldn’t call glacial cycles ‘events’

L. 36-39: maybe worth mentioning that some EMICs are using more sophisticated SMB schemes (e.g. Calov et al. 2005 and Willeit et al. 2024)

L. 44: ‘physically key’ -> ‘key physical’

L. 57: ‘a’ -> ‘the’

L. 66-67: repetition of ‘annual global mean temperature’

L. 67-68: the cited references do not support the statement that the LIG was globally 2°C warmer than the pre-industrial. Actually, I believe there is an agreement now that the global temperature change was small, with models indicating no significant change (Otto-Bliesner et al., 2021).

L. 68: retreat of glaciers has certainly little to do with global mean temperature changes

L. 127: ‘air temperature is transported to the surface’: I would rather say that it is assumed that the temperature of the snow/rain corresponds to the air temperature, right? Considering that precipitation is formed at higher altitudes above the ground where it is usually colder, is this a good approximation? Maybe also provide some details on how large this flux is under typical conditions.

L. 129-130: please specify the units for precip, particularly because it seems to be expressed in non-SI units of m(water equivalent)/s.

L. 130: why is 273.15 used here and not Ts as for snowfall?

L. 140-148: If I understand this correctly, as long as the mass of the top layer is below 500 kg/m2, BESSI includes only a single layer. Why is that? Considering that for typical snow densities of ~350 kg/m3 this means that a single layer can be ~1.5 meter thick, this implies that the model is not really resolving vertical gradients and processes in the snow pack.

L. 158: Eq. 12 doesn’t consider changes in the liquid water/snow storage in the layers, why?

L. 196: ( missing

L. 286: And how do you deal with the grid cells that are not covered by the iLOVECLIM land domain?

L. 291: ‘climate major pattern’ -> ‘major climate patterns’

L. 327-328: ITM is equally unrealistic, as it completely ignores the sublimation

L. 339-340: sentence unclear

L. 398: remove ‘possibly’

Why not integrate Fig. S1 into Fig. 2?

Fig. 6: Maybe worth specifying that ITM is also driven by iLOVECLIM climate output?

Fig. 6, 8, 11, 12: The colormap for the SMB is not color-blind-friendly.

Fig. 12: wrong units in caption

Table 2: The Melt from the ITM should rather be compared to the Runoff, as refreezing is implicitly accounted for in the ITM model.

References

Otto-Bliesner, B. L., Brady, E. C., Zhao, A., Brierley, C. M., Axford, Y., Capron, E., Govin, A., Hoffman, J. S., Isaacs, E., Kageyama, M., Scussolini, P., Tzedakis, P. C., Williams, C. J. R., Wolff, E., Abe-Ouchi, A., Braconnot, P., Ramos Buarque, S., Cao, J., De Vernal, A., Vittoria Guarino, M., Guo, C., Legrande, A. N., Lohmann, G., Meissner, K. J., Menviel, L., Morozova, P. A., Nisancioglu, K. H., O’Ishi, R., Mélia, D. S. Y., Shi, X., Sicard, M., Sime, L., Stepanek, C., Tomas, R., Volodin, E., Yeung, N. K. H., Zhang, Q., Zhang, Z., and Zheng, W.: Large-scale features of Last Interglacial climate: Results from evaluating the lig127k simulations for the Coupled Model Intercomparison Project (CMIP6)-Paleoclimate Modeling Intercomparison Project (PMIP4), Clim. Past, 17, 63–94, https://doi.org/10.5194/cp-17-63-2021, 2021.

Calov, R., Ganopolski, A., Claussen, M., Petoukhov, V., and Greve, R.: Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system, Clim. Dyn., 24, 545–561, https://doi.org/10.1007/s00382-005-0007-6, 2005.

Willeit, M., Calov, R., Talento, S., Greve, R., Bernales, J., Klemann, V., Bagge, M., and Ganopolski, A.: Glacial inception through rapid ice area increase driven by albedo and vegetation feedbacks, Clim. Past, 20, 597–623, https://doi.org/10.5194/cp-20-597-2024, 2024.

Sommers, A. N., Otto-Bliesner, B. L., Lipscomb, W. H., Lofverstrom, M., Shafer, S. L., Bartlein, P. J., Brady, E. C., Kluzek, E., Leguy, G., Thayer-Calder, K., and Tomas, R. A.: Retreat and Regrowth of the Greenland Ice Sheet During the Last Interglacial as Simulated by the CESM2-CISM2 Coupled Climate–Ice Sheet Model, Paleoceanogr. Paleoclimatology, 36, 1–19, https://doi.org/10.1029/2021PA004272, 2021.

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