Review of Larocca et al. 'Arctic glacier snowline altitudes rise 150 meters over the last four decades', The Cryosphere Discussions.

This paper uses satellite observations of Arctic glacier end of summer snowlines as a proxy for equilibrium line altitudes. Snowlines were mapped for 269 land-terminating glaciers from Landsat optical images between 1984 and 2022. Snow line altitudes were extracted from ASTER GDEM elevation information and then compared with field-based ELA measurements and ERA-5 reanalysis climate information. The authors relate their changes to summer warming, decreases in snowfall, and increases in rainfall. I liked the paper and think it will make a valuable contribution to the literature. The paper is substantive and rigorous, and both the quality of writing and figures is excellent. I had just a few questions and suggestions as I went through the manuscript and will list them here for inclusion by the authors into a revised manuscript.

- 37, worth differentiating here how many of these 42 are in the Arctic (not many).

- 40, there's another data source that is relevant but not mentioned here - longer term (multi decadal) records of glacier area (and sometimes) volume change from archival aerial stereophotogrammetry. Find and cite some of these studies.

- 54-55, this sentence would be better placed in the previous paragraph.

- 62, can you specify what is meant by 'glacier morpho-topographic variables' here, as it's a bit of an unwieldy term. I don't really know what it means but it seems important for it to be known at this crucial part of the manuscript. Probably worth a mention of the representivity of using land-terminating glaciers only too, given that the larger mass losses tend to be a tidewater terminating glaciers.

- Figure 1, I find the very light green shading difficult to see, can this be made a darker, more distinct colour? Likewise, the difference between a small black dot and a small pink dot with a thick black edge is also not distinct. What about solid black vs solid blue?

- Section 2.1, presumably an elevational range is important. Can you summarise the range of elevations over which these 269 glaciers lie (maybe ELA elevation). I would think you need a range of low, medium and higher elevation sites. If you do not have this, please justify why not.

- 97, sorry, I'm a bit unclear about this - you used a digitisation tool, yet digitised all SLs manually? Specify clearly what the tool was for, and what the tool did not do.

- 98, as ever with these remote sensing-based estimates of snow line / ELA, how do you account for the presence and influence of the superimposed ice zone? [note, I see that this is addresses in section 4.1]. And then further, why do you not differentiate between the snow line and the firn line which you may be able to distinguish in optical imagery in some years.

- 103-104, why do you include glaciers whose maximum altitude is higher than the snowline? With your sample size, I'm sure it would be straightforward to exclude all those glaciers with such low maximum elevations and include only those that allow the snowline to be measured every year. Inclusion of these glaciers is likely to bias your results in some way, so as an absolute minimum you need to account for this and discuss it.

- 109, will mean snowline elevations be affected by factors such as changing glacier hypsometry (as the snowline changes) and avalanching onto the glacier surface? These may be relevant at local scales. If you can quantify, do, otherwise mention as a potential source of uncertainty.

- Table 1, spectral range of bands (if different)?

- Figure 3, why no glaciers in Svalbard which surely is the most well studied of these regions? But Svalbard is in the Figure 4 plot?

- 128, Cite the RGI paper as well as the dataset (Pfeffer et al., 2014, doi: 10.3189/2014JoG13J176.

- 183, n=?

- 307, more could be said about the correlations between SLA and spring rainfall. I would expect spring rain to result in less snow due to melting from latent heat release and then enhanced rates of compaction and will likely lead to an earlier snow melt and then higher ELA.

- 378, It would worth attempting to quantify the error in the rate of SLA rise due to glacier thinning and include it here and in the main summary of results. Also, 'deflating' here and elsewhere is an odd word choice. Suggest 'thinning', or 'lowering'.

- Dowdeswell ref in main text not in the ref list, and Jiskoot ref in list not in the main text