PONE-D-24-18915Widespread loss of safe lake ice access in response to a warming climatePLOS ONE

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3. Thank you for stating the following financial disclosure:

“The Natural Sciences and Engineering Research Council Discovery Grant, the York University Research Chair programme, and ArcticNet provided funding to Sapna Sharma to support this research.

R. Iestyn Woolway was supported by a UKRI Natural Environment Research Council (NERC) Independent Research Fellowship [grant number NE/T011246/1].

Lei Huang was supported by the National Natural Science Foundation of China (No. 42201049) and the Second Tibetan Plateau Scientific Expedition and Research (STEP) (grant number 2019QZKK0202).”

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“We would like to thank the Arctic Mobilities team for extensive discussions over the past year, including Alison Cook, Jackie Dawson, Chris Derksen, Stephen Howell, and Lawrence Mudryk. We would also like to thank the Natural Sciences and Engineering Research Council Discovery Grant, the York University Research Chair programme, and ArcticNet to SS for providing funding to support this research. RIW was supported by a UKRI Natural Environment Research Council (NERC) Independent Research Fellowship [grant number NE/T011246/1]. Lei Huang was supported by the National Natural Science Foundation of China (No. 42201049) and the Second Tibetan Plateau Scientific Expedition and Research (STEP) (grant number 2019QZKK0202). The CESM2-LE simulations presented here have been conducted through a partnership between the Institute for Basic Sciences (IBS) Center for Climate Physics (ICCP) in South Korea and the Community Earth System Model (CESM) group at the National Center for Atmospheric Research (NCAR) in the United States, representing a broad collaborative effort between scientists from both centers. The simulations were conducted on the IBS/ICCP supercomputer “Aleph.”

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“The Natural Sciences and Engineering Research Council Discovery Grant, the York University Research Chair programme, and ArcticNet provided funding to Sapna Sharma to support this research.

R. Iestyn Woolway was supported by a UKRI Natural Environment Research Council (NERC) Independent Research Fellowship [grant number NE/T011246/1].

Lei Huang was supported by the National Natural Science Foundation of China (No. 42201049) and the Second Tibetan Plateau Scientific Expedition and Research (STEP) (grant number 2019QZKK0202).”

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Additional Editor Comments:

The manuscript has been reviewed by two anonymous reviewers. The study carry out a significant step forward in predicting lake ice safety in a warming climate, with important findings on how ice quality impacts safety and how warming affects the duration of safe and unsafe ice periods. However, some improvements are required such as terminology needs to be more precise, with clearer definitions for key terms. The abstract and introduction should provide more context and move detailed climatic information from the discussion to the introduction. Model validation should be expanded with more detailed statistical analysis and inclusion of validation figures in the main text. The results and discussion sections need deeper exploration of model predictions and drivers of variability. I hope the revision =will strengthen the quality, readability, precision, and validation.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: No

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: No

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This paper addresses an important and interesting problem: lake ice phenology and quality to better assess safe lake ice use during the formation and melt periods.

1) This paper described that “Lake ice on timing was validated against 328 lakes from the Global Lake and River Ice Phenology database with >20 years of data (20). The correlation coefficient r was 0.78 with a mean absolute error (MAE) of 11.7 days. Ice-off timing had an r = 0.94 with an MAE of 15.6 days from a sample of 322 lakes. Ice thickness was validated with records from 15 Canadian lakes with an r = 98 0.93”. (1) it needs to provide detailed information about spatio-temporal distribution of lake ice-on and ice-off timing and lake ice thickness. (2) The correlation coefficient r was 0.78 with a mean absolute error (MAE) of 11.7 days. Ice-off timing had an r = 0.94 with an MAE of 15.6 days from a sample of 322 lakes. There are a large uncertainties of research results like “… The transition period of unsafe ice increases by 4.97 ± 3.67 days in a 4 °C warmer world…”,” …The unsafe transition 33 period increases by an average of 19.8 ± 8.84 days and 8.75 ± 6.63 days…” according to MAE (Mean Absolute Error). How to proof the accuracy of results?

2) The introduction could be enhanced by adding relevant studies on the state of lake ice cover in the Northern Hemisphere, and even globally, under the background of climate warming. This would provide some research background support for this study.

3) It is recommended to add a discussion section about the prospects of the paper, discussing whether future research could propose opinions on regional lake ice safety based on ice thickness. For example, which areas have feasible ice safety and which do not.

4) It is suggested to divide the methods and results sections into paragraphs, such as making the methods the second section (2. Methods, 2.1, 2.2, 2.3, etc.), to make the research process clearer and easier for readers to understand. Adding a graphical abstract would be even better.

Reviewer #2: This manuscript presents a model study of lake ice phenology and quality changes associated with warmer air temperatures. It represents a critical step forward toward predicting the safety of lake ice in a warmer world. The model predictions indicate that in addition to shorter ice cover periods, the period from unsafe ice to safe ice is lengthening. An important result is that ice quality can be the dominant determinant of ice safety. However, I find that some of the terms could be defined more precisely, and model validation could be improved.

General comments:

Abstract:

- Please include a brief explanation of how ice quality impacts ice safety.

- Please describe briefly the analysis to contextualize the changes in the transition period. For example, the scope of the analysis is unclear; how many lakes (or grid cells with lakes) were modelled?

- The language is vague in places: ‘up to 35 days longer in a warming world’. What does ‘a warming world’ mean quantitatively?

Introduction:

- I miss a paragraph explaining the formation and properties of black versus white ice. Why is white ice considered less safe?

- I also miss a paragraph briefly describing the anticipated or ongoing climatic changes that affect lake ice formation, such as rising winter air temperatures, changing wind speed and a shift in the type and the amount of precipitation. OK, I see now that some of this information is included in the Discussion (L276-289). I would recommend moving this paragraph to the introduction.

Methods:

- If I understand correctly, the authors used the CESM2-LE + LISSS model to obtain predictions of ice thickness at various climate warming scenarios, and then computed the length of the ‘unsafe’ and ‘safe’ ice periods based on ice thickness recommendations from the MDNR and the assumption that the ice is either 100% black ice, 50% black ice and 50% white ice, or 100% white ice.

- Outcomes of statistical tests should include the analysis and the sample size (e.g. L96, r = 0.92).

- Why is the Pearson correlation coefficient (r) used here and not the coefficient of determination (r2), which is usually used to determine model fit?

- The model validation could be expanded upon. For example, you can have a high coefficient of determination, but a significant deviation from the 1:1 line. I suggest that figures showing the model validation be included in the main text. I would also suggest that the authors look for a larger and more representative lake ice thickness dataset to validate the model.

Results

- A key part of the results is a comparison between modelled transition times from ice formation to ‘safe’ ice for both black ice and white ice. How realistic is the immediate formation of white ice after ice-on, given what we know about the formation process of white ice? For example, does the model predict more freeze-thaw cycles at the start of the season? If it is not a realistic scenario, is it useful?

- The regional distribution of transition times is not mentioned in the results, but it appears that some regions are transitioning to longer ‘safe’ ice seasons, correct?

Discussion

- The discussion seems to be a combination of introduction and results. I’d like to see a deeper exploration as to why the model predicts the shifts in the transition times (Fig. 2) and what variable(s) determine(s) their global distribution (Fig. 3). Some of this information should be in the model results. For example, are the number of freeze-thaw cycles increasing? Is the decline in the ice growth rate due to the direct influence of warmer air temperatures or also indirect effects, such as increasing precipitation as snow (insulation) or rain (melt)?

- Figure 2 is not discussed in much detail. What are the drivers of the spatial variability in transition period trends?

Specific comments:

L29: doesn’t the safe ice thickness depend on the ratio of black and white ice?

L31-33. ‘4.97 ± 3.67 days’ given the confidence interval (standard deviation?) it may be more appropriate to use one decimal here.

L36. ‘increase the risk of drowning’. Is this substantiated?

L37-38: ‘when black ice transitions to white ice conditions’. Doesn’t this usually happen at the end of winter?

L50: only North America?

L57: what is meant by ‘stable’?

L62. Here or earlier, please provide a working definition of ‘safe ice’ (e.g. safe for one person to walk on, 5 cm for black ice and 10 cm for white ice) – with a reference (e.g. ref. 7 or Gold 1971).

L97-98: why were only 15 lakes used to validate lake ice thickness?

L102: What does ‘weaker’ mean here? Barrette (ref. 21) estimated the flexural strength of ice, which is proportional, but not identical to load-bearing strength. However, their results roughly correspond to those of Gold 1971, who found that the load-bearing capacity of white ice was about 50% that of black ice based on documented ice failure under vehicular loads.

L108: please add that the ice quality gradients are based on assumptions/scenarios of 100% black ice, 50% black ice and 50% white ice, and 100% white ice.

L110: why is 2 cm used as the threshold for ice formation, and not >0 cm?

L112: What load (e.g. a person, or a car) do these safety recommendations apply to?

L117: Why these temperatures? Do they correspond to specific climate warming scenarios?

L119: were some grid cells excluded from the analysis? These could be grid cells without lakes or without freezing days. If so, please describe the selection procedure.

L121-122: Please provide a (supplementary) table showing the outcomes of all your statistical tests, including the test statistic and the sample size.

L121-122: ‘Shaprio-Wilks’ -> ‘Shapiro-Wilks’

L121-122: why is the Shapiro-Wilks test done when the other statistical tests are non-parametric (i.e. do not require the assumption of a particular distribution)?

L124: ‘Kurskal-Wallis’ -> ‘Kruskal-Wallis’

L124: conventionally (and arbitrarily), p < 0.05 is used. Why this threshold?

L126: ‘Kalmogorov-Smirnov’ -> ‘Kolmogorov-Smirnov (KS)’

L128: is this a two-sample comparison or a multiple comparison? If the latter, it is necessary to adjust p for the false discovery rate using the Benjamini-Hochberg or equivalent procedure.

L162-163: please define the uncertainty estimates (SD, 95% confidence interval) and the sample size (n = …).

L165-166: suggests changing ‘(≥10 cm, ≥15 cm, and ≥20 cm)’ to ‘(≥10 cm, ≥15 cm, and ≥20 cm, depending on assumed ice quality)’.

L179: Table 1, please include the outcome of the statistical test indicating whether or not each mean is significantly different from 0 at a specified confidence level (e.g. p = 0.05), or show the p-values.

L193: mention that you are talking about 100% black ice here.

L219: Figure 3 caption. when mentioning p-values it is customary to also name the statistical test and the sample size.

L233-244: this reads as part of the introduction. No results are discussed here as far as I can tell.

L232: ‘forecast’ is a term not usually applied to short-term rather than long-term model predictions. ‘Project’ or ‘Predict’ may be more appropriate here.

L245: suggest changing ‘forecasted’ to ‘projected’.

L246: did you mean ‘the primary mechanism through which we understand changes in ice phenology and duration…’?

L248: ‘some of the most recent long-term trends’: what is meant here? Trends since the year 2000?

L252: please provide a bit more context for these previous studies. ‘ice thickness declines’; ice thickness varies over the season, so is this the mean ice thickness? A 1C rise in air temperature; is this the annual mean air temperature? And did these previous studies cover the same lakes/area as this study?

L252: days C−1 -> days °C−1

L253: ‘projections forecast’: please see my previous comment on the use of ‘forecast’.

L257-258: which scenarios are compared here? (e.g. historical formation of black ice vs a future formation of white ice at 4°C).

L260: 9 days earlier. Do you mean ‘9 days before ice-off’ compared to ‘4 days before ice-off historically’? If so, again, which scenario is this prediction associated with? Also, this is a result which should be in the ‘Results’ section.

L276-289: this paragraph should be in the introduction. No results are discussed here.

L290: please provide references for the statements ‘rising winter and spring air temperatures’ and ‘increasing proportions of white ice’.

L299: this was already stated on L297.

L304-305: is the 29 days an average for all the lakes at 4 °C? If so, is this the same modelling approach with the same lakes (i.e. are the results comparable)?

L310: can the cumulative distributions be shown in a (supplementary) figure?

L317: ‘increasingly unpredictable ice safety’. This is an important result. Could this be quantified? E.g. compare the standard deviation of the transition period length (not the anomaly) between historic and warming scenarios and see if it increases.

L346: this paragraph is a combination of methods and results. Please restructure.

L392: ‘which some individuals may fail to take into account’. This is unscientific speculation, please remove.

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Reviewer #1: Yes: Yusufujiang Rusuli

Reviewer #2: No

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Widespread loss of safe lake ice access in response to a warming climate

PONE-D-24-18915R1

Dear Dr. Culpepper,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Sher Muhammad, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

The revision has improved the quality of the manuscript, I recommend it for publication. The authors are also suggested to made the data available including the validation data.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: No

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: I appreciate the effort by the authors to address all comments. The manuscript reads much clearer now.

Please ensure that the model calibration data (ice thickness measurements from 71 lakes) are also available; I did not see this in the data availability statement.

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Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: No

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