Review of, ‘Tropical glaciers on Puncak Java (Irian Jaya/west Paupa, Indonesia) close to extinction by David Ibel and co-authors.

General comments:

Using a historical map and spaceborne satellite imagery, Ibel and others report on areal changes of small tropical glaciers in Indonesia. They show substantial retreat of these glaciers over the last 150 year with about 64% shrinkage since 2018. The data provided in this short report are certainly suitable for the Cryosphere, but I feel that the authors need to address a few major issues before the manuscript is suitable for publication. Below, I summarize those major points, and I also provide minor suggestions to improve the readability of the work.

Major comments:

• Uncertainty analysis – While I can appreciate that this contribution is submitted as a ‘brief communication’, this should not prevent the authors from reporting on the uncertainties in their data and overall reports. Glacier mapping is not perfect, even when the quality of imagery is good, and the mapper is experienced. Glacier areas (and rates of change) are reported with no uncertainties. The uncertainty in the map from 1850 CE must also be high, but it sounded like only three ‘landmarks’ were used geocoding (authors mention distortion and shifts). What translation was used? Three ground control points for the map would yield an extremely high RMSE unless a thin plate spline was used (which assumes no errors, but this really would be unrealistic anyway). I would recommend that the authors consult papers that describe how to complete an uncertainty analysis for glacier mapping (e.g. Granshaw and Fountain, 2006; Fountain et al., 2023).
• Attribution of loss – Why did the authors not attempt to attribute the observed area changes to climate drivers. The end of the discussion section points out a few possible factors which could explain these changes, but the reader is left wondering what the primary driver really is. They describe, for example, temperature changes between 1972-2000 but their data is mostly after 2000. It would be relatively easy to analyze temperature at the appropriate pressure level (they cite 550 hPa) from ERA5 over the period 1950-present for the closest grid point. Even a simple descriptive analysis may allow the authors to at least partition some of their results into climatic vs. non-climatic factors.
• Short history section is too long – While the length of this section might be fine for a full-size manuscript, I found this section to be perhaps too rich in details (e.g. do we really need to know names of past explorers for the data presented in the paper?). I would prefer to see more details that pertain to supporting the objectives of the paper and/or the reliability of the results (uncertainties). 

Minor points:

Line 11: not certain what authors imply by ‘accounts’

Line 13: change to ‘In 2024, glacier area was …’

Line 14: Strike ‘very’ – a vague qualifier unless you are talking about a definition (e.g. ‘very fine sand’ is defined by a size range).

Line 27: Use ‘First’, ‘Second,’ … rather than ‘Firstly’ – less wordy.

Line 73: Either refer to their position in terms of pressure level (e.g. 500-600 hPa) ,or actual elevation above sea level. Using both is confusing since they often don’t coincide.

Line 80: As described in the major comments, I would recommend that the authors at least consult reanalysis data for attribution (at least annual or warm-season temperature anomalies).

Line 88: Do we know these glaciers actual surge? Or do the authors mean ‘advance’ or ‘underwent expansion’?

Line 111: Uppercase ‘glacier’ after Maren. Formal names use ‘Glacier’. Same logic is Green Lake but Green and Blue lakes (lowercase when referring to plural).

Line 119: Strike ‘very’

Line 120: I think the convention for units is to use superscripts ‘no slash’) so m^{3} w.e. yr^{-1} throughout

Line 120 onward: The use of the term ‘mass balance’ when referring to mass (volume) change is confusing. If you don’t have surface area I suggest you use ‘mass change’.

Line 140-145: There are few details provided so it become difficult for a reader to agree with your interpretation as to the quality of the co-registration. Can you provide some more information to support this claim (RMSE, number of control points used, etc)?

Line 151: Strike ‘very’ and throughout paper.

Lines 145-160: As described in the major comments section, more information is required and some uncertainty estimates for the glacier mapping.

Lines 165: So if Permana et al., (2019) report on these glaciers, how do your extents compare to that work? This comparison would provide you with at least some assessment of the reliability of the mapping between these projects.

Line 190: Not a big deal, but deep blue typically used to demarcate water on maps. Can you simply use a given color with varied saturation levels ? Also, showing polylines is preferred rather than polygons as one can’t see examine imagery or present-day ice.

Line 208: You can’t assert that there was no period of growth especially between 1850 CE and late 1940s since you have no data. Statement needs revision.

Line 225: If you log right panel x axis, what year does area =0.0 km2? As described in major comments section, how has temperature (500 hPa pressure level) varied over this time? ERA5 goes back to the 1950s. You can download monthly data for seasonal, annual anomaly calculation.

Line 235: There is a logic gap here. The authors suggest that attribution is not possible given the lack of meteorological data yet in the introduction there is mention of glaciers like this being good indicators of global climate. The two last authors have used reanalysis in the past. Why not do a simple analysis to help attribute changes of these glaciers?

Tables and Figures:

Fig 1 (a and b) are quite pixelated for me. Can they be reproduced at a higher resolution?

Refs:

Granshaw, F. D., & Fountain, A. G. (2006). Glacier change (1958–1998) in the North Cascades National Park Complex, Washington, USA. Journal of Glaciology, 52(177), 251−256.

Fountain, A. G., Glenn, B., and Mcneil, C.: Inventory of glaciers and perennial snowfields of the conterminous USA, Earth Syst. Sci. Data, 15, 4077–4104, https://doi.org/10.5194/essd-15-4077-2023, 2023.