the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Spatially heterogeneous effect of the climate warming on the Arctic land ice
Damien Maure
Christoph Kittel
Clara Lambin
Alison Delhasse
Xavier Fettweis
Abstract. Global warming has already substantially altered the Arctic cryosphere. Due to the Arctic warming amplification, the temperature is increasing more strongly leading to pervasive changes in this area. Recent years were notably marked by melt records over the Greenland Ice Sheet while other regions such as Svalbard seem to remain less influenced. This raises the question of the current state of the Greenland Ice Sheet and the various ice caps in the Arctic for which few studies are available. We here run the Regional Climate Model (RCM) Modèle Atmosphérique Régional (MAR) at a resolution of 6 km over 4 different domains covering all the Arctic grounded cryosphere to produce a unified Surface Mass Balance product from 1950 to present day. We also compare our results to large-scale indices to better understand the heterogeneity of the evolutions across the Arctic and their links to recent climate change. We find a sharp decrease of SMB over the western Arctic (Canada and Greenland), in relationship with the atmospheric blocking situations that have become more frequent in summer, resulting in a 41 % increase of the melt rate since 1950. This increase is not seen over the Russian Arctic and Svalbard permanent ice areas, where melt rates have increased by only 9 % on average, illustrating a heterogeneity in the Arctic SMB response to global warming.
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Damien Maure et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2023-7', Shawn Marshall, 26 Apr 2023
This is an interesting study, well-explained and with excellent Figures in support of the analysis and conclusions. I am not aware of a comparable study that considers the circum-Arctic mass balance with 'standardized' models. The emerging east-west patterns are interesting, systematic, and nicely explained, i.e., the conclusions are well supported by the model results and discussion. I support publication subject to clarification of a number of relatively minor considerations.
On a high level, it would be interesting to comment on the overall Arctic glacier (and Greenland) mass loss, focusing on the SMB (atmospheric climate signal) and the authors' sense of whether one can separate (i) the overall Arctic warming impact from (ii) the influence of atmospheric circulation anomalies. That is maybe like considering PC1 and PC2 in some kind of SMB pattern analysis, so perhaps that is another study. But I would welcome a short discussion from the authors on whether these are separable, how each contribution may be changing in time, and what that means for future decades - should we expect some persistence in this kind of atmospheric pattern (i.e., ridging over the western Arctic and Greenland)? Just discussion points.
l.18, "could modify the SMB" - I guess this is very clearly happening, beyond just conditional. Many prior studies show how changing T and P are modifying the SMB across Arctic ice caps, e.g. Huggonet et al. (2021), IPCC (2021) and references therein
l.23, "quick" is hard to define - seconds, minutes, months, years. Suggest being specific here, e.g., if you are referring to synoptic, seasonal, or interannual variability
l.28, see also Rajewicz and Marshall (2014) on this point. Not that this needs to be cited, but it directly assesses the anticyclonic circulation/ridging anomalies that are being discussed here, and notes how these strongly and simultaneously impact Arctic Canada and southern/western Greenland, of relevance to this manuscript. I would also note that this can be expected to be highly correlated with cool anonalies in the eastern subArctic, as ridging over the western Arctic and Greenland would typically be accompanied by a trough (cooler conditions) in the eastern North Atlantic and Eurasian sector of the Arctic
l.34, suggest rewording, "a unified estimate is still lacking"
l.39, "aims", plural
l.53, the 6 km resolution is high in some ways, for the size of the domain, but does not resolve many of the smaller ice masses, particularly in mountainous regions such as coastal Greenland and Baffin Island. On this particular point on l.53, omitting grid cells that are less than 50% ice covered, I worry if this might exclude a large amount of the ablation area of many of the glaciers and ice caps. This could cause a systematic underestimation of ablation, by excluding a lot of marginal ice area. It will be good to discuss this and even compare the captured ice area/hypsometry to what one would see at 1 km, for example.
l.66, “over the ocean”l.67, suggested rewording to "surface pressure, sea ice concentration, and sea surface temperature"
Figure 2, "annual time scale" - are these averaged for the decade? Please clarify in the caption
l.137-138, discussion of the lower interannual variability of the altimetry data. This would be helpful and interesting to compare with WGMS SMB data which is available for some of these regions (e.g., Artctic Canada, Iceland) - what does the interannual variability look like there? It would be very instructive to include a third box-whisker for the WGMS data where it is available, recognizing that it is not covering the full domain in any of these regions. Particularly around whether the modelled interannual variabiliy is realistic, and to compare SMB with SMB directly for all regions where this is possible.
l.151-152, "while this decrease is mainly driven by Greenland..." True, but this is mostly because Greenland dominates the total mass loss? vs. the % change being the driver, as argued here.
Figure 4, Please define RU and SF in the caption
l.156, "over Baffin Island" (no the, here and throughout)
l.157, Are these numbers right, for Baffin Island? Something is sending up red flags for me here. The glacierized area of Baffin Island is much less than Ellesmere, so the modelled runoff and mass loss from here seems out of proportion compared with Devon and Ellesmere. There are a lot of smaller ice masses that may not be well-captured at 6 km. This might make sense in the context of more negative specific mass balance rates here (average m/yr of thinning), but it would be helpful to discuss and present this for the different regions, based on the RGI glacier areas.
l.216, I don't think "desertic" is a word. Recommend just "dry" ?
l.248, "that those regions" - Do you mean the eastern Arctic? Be specific here.
l.264, I think that here and throughout, this should be Novaya Zemlya. Nova Zembla is an island in the Canadian Arctic, near Baffin Island, but is not what the authors are referring to, I thinkl.268, Fig. 9a
l.269, "has been -62 Gt/yr"
Citation: https://doi.org/10.5194/tc-2023-7-RC1 -
RC2: 'Comment on tc-2023-7', Anonymous Referee #2, 01 May 2023
The manuscript by Maure et al. describe surface mass balance simulated using the regional climate model MAR at a 6-km resolution for glaciers in Canada, Greenland, Iceland, Svalbard and the Russian Arctic, as well as the Greenland Ice Sheet. The simulation covers the period from 1950 to 2020. Model results are validated against weather station observations and stake data. The main finding is that differences in regional mass balance, with more negative SMB in the western Arctic, can be explained by atmospheric blocking situations that affect SMB in Greenland and Canada, but less in Svalbard and the Russian Arctic. These findings are important and novel and given that the results were produced with the same model gives confidence in their robustness. Overall, I find that the manuscript is well written and logically structured. The figures are also of sufficient quality. I do have some moderate to major concerns that are further detailed below and which I would like to see addressed. My main concerns regard a lack of comparison with available data and limited comparison with other studies. For example, for Svalbard the agreement of simulated SMB with other studies seems rather poor, and none of the available stake data were used for calibration or validation (unlike in other studies). I suggest to add more comparisons with region-specific studies and/or available (stake) observations. Main advantages of validation against stake data, compared to validation against geodetic measurements, are that 1) also large tide-water glaciers can be included, and 2) that temporal variability and trends of surface mass balance can be validated. This is relevant because the presented SMB results, trends and differences between regions form the basis for the main conclusions.
Specific comments:
Title: Please consider removing "the" before "climate warming"
L2-3: Svalbard experienced record melt in summer 2022.
L11: The 9% increase in melt is much lower than other studies have shown for Svalbard (e.g. Östby et al. 2017, Van Pelt et al. 2019, Noël et al. 2021). This should at least have been acknowledged since other studies focusing on individual regions did more efforts to calibrate their models against available data (primarily stake data).
L18-19: Remove brackets around "i.e. the Greenland ... perificial glaciers".
L20-21: To be complete also mass fluxes by condensation/riming should be considered in the SMB.
L22-23: Remove brackets around "Note that ... Cogley et al. (2010)"
L31-32: Changes in SMB in Svalbard were maybe not as large as e.g. in the Canadian Arctic, but they were still significant. See Schuler et al. (2020; doi: 10.3389/feart.2020.00156) and references therein. Except Lang et al. 2015 all other modelling studies found significant negative mass balance trends.
L60-63: A 6-km spatial resolution is a reasonable choice given the large simulation domain. It could be acknowledged here though that a lack of topographic detail affects calculation of surface mass balance in areas with strong topographic variations, particularly through impacts on local precipitation, wind drift, temperature, insolation and shading.
L73-76: It is unfortunate that no stake data were used in this study for a region like Svalbard, whereas they are readily available. Comparing only against geodetic mass balance for land-terminating glaciers gives a somewhat biased assessment (since large tidewater glaciers and ice caps are excluded). And more importantly, the geodetic data do not allow for validation of temporal variability and trends of SMB, which would have been possible with stake data.
Table 1: It would have been great to see a comparison of linear trends (particularly in T2m) as well.
L109-111: Why use data corrected to sea level when raw data exist too?
L112-113: Is the negative bias of >3 degrees C for Svalbard also a result of a sea level correction? If not, such a temperature could have a pronounced impact on melt in summer.
Figure 2: Pressure is maybe not the most crucial parameter to validate here, as it has hardly any impact on mass balance calculations. On the other hand, precipitation is important but not validated at all. For example, stake winter balance data could have given an indication on potential biases of snowfall during the cold season.
Section 3.2: I appreciate the use of geodetic MB observations for validation. There are however some drawbacks too. Besides that only land-terminating glaciers can be compared it also does not enable comparison of temporal mass balance variability and trends. This would have been possible when (also) stake data would have been used for comparison. It is particularly important in this study which draws conclusions on differences in mass balance and trends between regions.
Figure 3: Two things are interesting here: 1) the larger spread in model results per region than the geodetic observations show, 2) the stronger region to region variability in the model than in the observations. This would be an interesting discussion point, that I think should be added in the Discussion session.
L156-162: It would be more robust to calculate a (linear) trend based on all results since 1950. Now the significance drops because of the use of a selection of data. The results may also be biased a bit by excluding a relatively cold period 1970-1990 in many Arctic regions.
Table 2 caption: "averaged" --> "averages"
L168-173: Here it would have been good to include comparisons with other (region-specific) studies (e.g. Schuler et al. 2020 for Svalbard). This would help because the validation against the geodetic data does not give any insight in reliability of simulated surface mass balance trends.
L195-196: Lang et al. (2015), which also uses the MAR model, is the only study out of many in recent years that also simulated stable mass balance. This discrepancy with other literature should be acknowledged.
L206: "more icy" --> "colder"
L210-212: See also my earlier comment. It is somewhat biased to compare 1950-1970 to 2000-2020 and not 1975-1995 to 2000-2020, or 1950-1985 to 1985-2020. By the way, why the 5-year gaps? Please note that the increase of SMB after 2000 for Svalbard does not agree with the consensus results by Schuler et al. (2020).
L248: "lower" --> "smaller"
L250-254: The frontal ablation dataset for Northern Hemisphere tidewater glaciers by Kochtitzky et al (2022; doi: 10.1038/s41467-022-33231-x) could have been of use here.
Citation: https://doi.org/10.5194/tc-2023-7-RC2
Damien Maure et al.
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