| 29 Sep 2025
Projecting the evolution of the Northern Patagonian Icefield until the year 2200
Abstract. The Northern Patagonian Icefield (NPI), Chile, is the second-largest ice mass in the Southern Hemisphere outside Antarctica and a major remnant of the Patagonian ice sheet from the Last Glacial Period. It is located in the Southern Andes, which is among the world's glacierized regions with the most negative specific mass balances. The NPI is a highly dynamic system, with high amounts of accumulation and ablation, and includes Glaciar San Rafael, the tidewater calving glacier closest to the equator.
Using the ice-sheet model SICOPOLIS, we reproduce the dynamical state and observed changes of the NPI in the early 21st century and project its evolution until 2200. Calving is represented by prescribing an additional mass loss for ocean-terminating grid cells (Glaciar San Rafael). A spin-up experiment generates an icefield comparable to conditions around the year 2000, which we then force with present-day and projected surface mass balance under climate scenarios SSP1-2.6 and SSP5-8.5.
In the committed mass loss run, the NPI stabilizes by 2100 at around 75 % of its current volume. Under climate change scenarios, mass loss accelerates from the mid-21st century and continues until 2200, despite assuming constant climate during the final century. The NPI exhibits a response time of approximately 100 years, highlighting the need for caution when interpreting current trends. By 2200, the remaining volume strongly depends on the emission pathway: 64 ± 10 % under SSP1-2.6 versus 32 ± 14 % under SSP5-8.5. These results confirm that for Patagonia, as found elsewhere, every fraction of a degree of warming matters.
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
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Review of Schaefer et al, The Cryosphere
Thank you for this opportunity to review this manuscript, and apologies for the tardy review.
General comments
Schaefer et al present a most welcome analysis of the future of the Northern Patagonian Icefield, a sensitive icefield of some import in Patagonia. The manuscript is clearly presented and provides a careful analysis of the future behaviour of the icefield.
I have some recommendations for improved clarity and to hopefully help elevate the manuscript.
My most significant comment is to do with the surface mass balance approximation of the icefield. The Andes have one of the most extreme climatic divides found worldwide (Sauter, 2020). The strong orographic influence on climate is evident in terrestrial observations. To what extent does downscaled climate data match observations? This needs a clear evaluation.
Specific comments
Bed topography – how does the bed topography compare with that provided by Millan et al. (2022)?
In line 136 insufficient detail is provided for the SMB model. How does this calculate SMB? This is important, as differences in SMB may explain the differences in these projections and others in the Discussion.
Line 138 – the ablation stakes and shallow firn cores are vague, and this evaluation needs more explanation.
Line 153 – how do these ice velocity measurements differ to Millan et al. (2022)?
The modelling workflow is provided clearly, but some more details are required in places.
Line 169 – I agree that the NPI in 2000 was likely not in equilibrium with climate, and there observational datasets of ice recession and thinning at this time that would support this statement.
Line 197-198 – to help the reader, clarify again the experiments run (SSPs, to what year, etc.).
Line 200 – it is not clear to me why the additional experiment forced by ECHAM5 A1B scenario is used. This is quite dated now and has been superseded by CMIP6. Also this is one model, whereas the CMIP6 is a multi model mean. I would recommend just removing this experiment as I don’t think it adds anything.
Line 202 – to help the reader, and improve usefulness for readers, I recommend also summarising the volume and area change as a % of the 2000 ice volume (or some other standard year).
Figure 8/9 – the ‘m’ in the colour bar is rotated. It would be easier to read if it were horizontal. Note the year of glacier outlines shown (2000?).
Clarify here why the experiments were run to 2200 and not 2300, when CMIP 6 extended model runs are available until 2300 CE (Eyring et al., 2016).
Line 204 – clarify here the total area loss in km2 and % change.
Overall I found the results section rather brief. I would add more details on glacier changes under the two different scenarios. Do glaciers remain calving by 2200 or are all on dry land, above sea level? What is the ice velocity?
Can you show the simulated surface mass balance on the icefields for the two different SSPs at different timescales (like the ice thickness figure).
Line 217 – more information on the SMB model used could also be helpful here. Was the SMB a temperature index model or something more complex, and could this explain the differences?
Line 221 – precipitation is crucial for the Patagonian icefield SMB (Sauter, 2020); any biases in the downscaled climate data would have a big effect, potentially larger than calving flux. This needs more careful evaluation.
Line 227 – could these differences also be explained because GlacierMIP2 (Marzeion et al., 2020) is forced by CMIP6 at a broader scale, with temperature index models used to calculate SMB at best. How much more (or less) reliable is the climate forcing data used here given the statistical downscaling?
Line 272 – I couldn’t see these results of % change in the results, don’t include new things in the conclusions and put these data in the results section too.
Table A1 – precipitation variation will also be very important, can you also provide this information in the table?
References used in this review.
Eyring, V., Bony, S., Meehl, G.A., Senior, C.A., Stevens, B., Stouffer, R.J., Taylor, K.E., 2016. Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev. 9, 1937-1958.
Marzeion, B., Hock, R., Anderson, B., Bliss, A., Champollion, N., Fujita, K., Huss, M., Immerzeel, W., Kraaijenbrink, P., Malles, J.-H., Maussion, F., Radić, V., Rounce, D.R., Sakai, A., Shannon, S., van de Wal, R., Zekollari, H., 2020. Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change. Earth's Future 8.
Millan, R., Mouginot, J., Rabatel, A., Morlighem, M., 2022. Ice velocity and thickness of the world’s glaciers. Nature Geoscience 15, 124-129.
Sauter, T., 2020. Revisiting extreme precipitation amounts over southern South America and implications for the Patagonian Icefields. HHydrol. Earth Syst. Sci. 24, 2003-2016.