PCLM-D-25-00435

Increased Mortality Risks of Winter Temperature Flips: A Growing Concern in Aging Society of Subtropical Climate Regions

PLOS Climate

Dear Dr. Ren,

Thank you for submitting your manuscript to PLOS Climate. After careful consideration, we feel that it has merit but does not fully meet PLOS Climate’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

EDITOR:

After careful consideration and thorough reviewing of the manuscrit, serious concerns have been raised by the reviewers, particularly on the methods and results, and these comments should be addressed before further consideration of the manuscript.

Please submit your revised manuscript by April 13, 2026. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at climate@plos.org. When you’re ready to submit your revision, log on to https://www.editorialmanager.com/pclm/ and select the ’Submissions Needing Revision’ folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A letter that responds to each point raised by the editor and reviewer(s). You should upload this letter as a separate file labeled ’Response to Reviewers’.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled ’Revised Manuscript with Track Changes’.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled ’Manuscript’.

Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

We look forward to receiving your revised manuscript.

Kind regards,

Noureddine Benkeblia, Dr. Sci., Dr. Agr.

Academic Editor

PLOS Climate

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Additional Editor Comments (if provided):

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Reviewers’ comments:

Reviewer’s Responses to Questions

-->Comments to the Author

1. Does this manuscript meet PLOS Climate’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.-->

Reviewer #1: Partly

Reviewer #2: Yes

Reviewer #3: Yes

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

Reviewer #1: I don’t know

Reviewer #2: Yes

Reviewer #3: Yes

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-->3. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. 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: Yes

Reviewer #2: Yes

Reviewer #3: No

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

PLOS Climate 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

Reviewer #3: 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: I thank the authors for their submission of “Increased Mortality Risks of Winter Temperature Flips: A Growing Concern in Aging Society of Subtropical Climate Regions”. I agree with the authors that rapid temperature flips are likely to have detrimental effects on human health, especially amongst the elderly, and that the impact is understudied and likely difficult to quantify. The approach authors take to quantifying temperature flips and the human health dataset are appropriate, with the limitations of both clearly discussed. However, my enthusiasm for the manuscript is severely diminished by the analysis and results linking temperature flips and human health outcomes. While it is possible that my concerns come from a lack of clarity around the precise methods, I cannot recommend this manuscript for publication without major changes to both the methods and results, including additional analysis.

Specific Concerns:

• The statistical models used for determining the health effects of temperature flip events and resulting methods are not entirely clear.

o The authors mention the use of “a smoothed relationship between expected mortality and the other factors were included”, but do not mention what the “other factors” are. What type of smooth was used (e.g., LOESS, spline)?

o It is unclear how long-term trends, seasonality, and day of week were accounted for. Are these fixed effects, non-linear smooths, or some other method (e.g., detrending)?

o As a quasi-Poisson model was used, I assume the response variable was daily mortality. Was the population size included as an offset?

o The authors say that they used a distributed lag nonlinear model with a maximum lag of 28 days. However, it is never discussed what the estimated lag time is. This has major implications for the interpretation of the results.

o Related to the point above, the authors mention sensitivity analysis comparing to a 21-day lag. Given that the statistical method estimates the lag, this is superfluous. If a 21-day lag was optimal, the method should converge on that value. Additionally, if that is a commonly used lag, as stated, citations should be included justifying it.

• There are several issues with the figures

o I believe the figures are misnumbered

o The figures are complex with multiple panels and a large amount of information, yet the captions are simple 1 sentence titles, making it difficult to interpret the figures.

o The low resolution of the figures make it difficult for me to judge their accuracy compared to written results.

• It is not entirely clear to me what precisely the values in Table 3 represent, making it impossible for me to judge the text descriptions and conclusions drawn from them.

o Are these adjusted relative rates after accounting for other characteristics (e.g., impact of starting temperature after accounting for magnitude, duration, and rate) or from univariate analysis?

o Are these rates relative to non-event mortality? This would be my expectation, however, lines 288-291 use the result to describe differences between events beginning at cold temperatures and events starting at warm temperatures.

• Why was the 75th percentile used to differentiate “high” events vs “low” events?

• In the paragraph beginning on line 369, the authors compare the relationship between temperature flips and prolonged exposure to low daily temperatures, stating that their results suggest temperature flips have an impact beyond absolute or percentile-defined low temperatures. However, they do not seem to explicitly test this, only if temperature flips show a significant relationship with morality rates.

o Given that temperature flips are likely followed by prolonged periods of low temperatures, and that the estimated lag period is not provided, prolonged periods of low temperature may provide a more appropriate explanation for the mortality. Periods of low temperature should be accounted for in the model or alternative models based on periods of low temperature should be developed to evaluate the relative impact.

• All project specific code should be made available

Reviewer #2: Scientific Review

1. Relevance and originality

The article addresses an emerging and underexplored issue: mortality effects associated with abrupt warm-to-cold temperature shifts during winter in ageing subtropical regions.

In contrast to the classical literature, which has primarily focused on:

absolute low temperatures,

cold waves,

diurnal temperature range or day-to-day temperature changes,

this study introduces and operationalises the concept of “warm-to-cold temperature flip events”, explicitly incorporating the dynamics, magnitude, and rate of cooling. This represents a novel conceptual and methodological contribution, adding substantial value to environmental epidemiology and public health research.

Editorial value: high and well aligned with the scope of PLOS Climate.

2. Scientific rationale and conceptual framework

The manuscript is well grounded in:

recent climate literature (thermal variability and atmospheric dynamics),

human cold physiology,

differential vulnerability in ageing populations.

The central hypothesis—that the speed and sequence of temperature change may be as important as, or more important than, absolute temperature thresholds—is well supported by both physiological mechanisms (vasoconstriction, sympathetic activation, inflammatory responses) and population-level adaptation in subtropical climates.

The approach avoids simplistic deterministic interpretations and is supported by a coherent dynamic framework, strengthening its biological plausibility.

3. Data and study design

Key strengths:

Use of very long meteorological time series (dating back to 1884) to characterise long-term trends.

Daily mortality data stratified by cause, age, and sex.

Focus on an extended winter period (November–March), appropriate for subtropical settings.

Stratification based on the official cold weather warning threshold, effectively linking scientific evidence with public policy relevance.

Limitations (appropriately acknowledged):

Reliance on a single representative meteorological station.

Exposure assessment based on outdoor temperature.

Exclusive focus on mortality outcomes (rather than morbidity).

These limitations are standard in studies of this type and are adequately discussed, without compromising internal validity.

4. Statistical methodology

The use of:

quasi-Poisson regression models,

Distributed Lag Non-Linear Models (DLNM),

adjustment for meteorological and air pollution confounders,

sensitivity analyses using alternative lag structures and event definitions,

is methodologically sound, appropriate, and well implemented.

The choice of a 28-day maximum lag is justified, and sensitivity analyses further support the robustness of the findings. From a reviewer’s perspective, no critical methodological weaknesses are identified.

5. Results

The results are:

internally consistent,

physiologically plausible,

aligned with previous findings while substantially extending existing evidence.

Key high-impact findings include:

A significant increase in total and cause-specific mortality risk.

Greater vulnerability among adults aged ≥75 years.

Elevated risks associated with rapid cooling events, even when official warning thresholds are not reached.

Clear evidence that the initial days of temperature flip events concentrate risk not captured by current warning systems.

Subgroup analyses further strengthen the credibility of these results.

6. Discussion and implications

The discussion is robust and well balanced:

Results are not overinterpreted.

Physiological mechanisms are appropriately integrated.

Findings are clearly contextualised within population adaptation and early warning system design.

The manuscript provides direct implications for early warning systems, suggesting that models relying solely on fixed temperature thresholds may be insufficient in contexts characterised by increasing thermal variability. This reinforces its applied relevance and policy significance, both of which are highly valued by PLOS Climate.

7. Overall scientific contribution

This manuscript:

Introduces a new analytical framework for assessing temperature-related health risks.

Provides robust evidence from a highly ageing subtropical city.

Is cautiously extrapolable to other subtropical regions worldwide.

Effectively links climate dynamics, health outcomes, and population ageing without oversimplification.

Overall contribution: clear, relevant, and suitable for publication.

8. Points for improvement (towards excellence)

To further strengthen the manuscript, the following refinements are suggested:

The Introduction may be overly technical at the outset. Reordering the section to foreground the public health and ageing dimensions before the climatic details would improve accessibility and narrative flow.

Although the “temperature flip” concept is well defined methodologically, its distinction from DTR, TCN, and temperature variability could be reinforced with a concise comparative statement.

A short paragraph on extrapolation to other subtropical cities (e.g. Latin America, Southeast Asia) would enhance generalisability.

Some sentences are long or repetitive; editorial language polishing would improve readability.

Overall recommendation: suitable for publication, subject to minor revisions.

Reviewer #3: Data availability: The data used for the study should be deposited in a stable repository, rather than simply referring to external websites which may change their data access policies. Further, it would help greatly to include transformed and processed data (such as determinations of which days count as flip events), rather than simply providing the initial data inputs).

line 57 - "adaptation" is biological? behavioral? social? This claim should have a citation.

lines 101-102 - citation?

lines 102-105 - this very broad claim is unsupported.

141: can you provide the values for these averages and deviations?

142: what is the threshold for "cold"?

151: explain what "better represents" refers to

153-154: global warming has increased greatly over the past 30 years; is this "long-term" trend accounted for?

158: should the second equation be a difference rather than a sum?

268: why is the result for influenza so much higher than the others?

268: could you perform the analysis with a cause of mortality such as cancer, which is not expected to be very temperature dependent, to demonstrate that your methods would not show an increased ratio?

269-272: is it the case that the drop is more important than the absolute minimum temperature? how much of the effects are explained by the low final temperature, regardless of the initial temperature? in other words, is it the case that a drop from 15 to 12 degrees would lead to more excess mortality than a drop from 12.5 to 11 (smaller difference, but lower low)?

does the mortality refer to only deaths that happen on that day? wouldn’t it take a few days for influenza to lead to death? How would this death be attributed to a temperature drop if it occurs two weeks after the drop itself took place?

I would expect that health impacts result not only from low temperatures, but also on whether high temperatures during the day provide intermittent relief. Does your study differentiate between these two types of drops, where one drop has constant low temperatures while the other has decreasing low temperatures but with elevated high temperatures?

why might mortality be greater for females?

how would the proposed changes to a weather warming system identify a temperature flip? what would be the cutoff values that the authors propose, based on their data?

469: this seems like a large limitation. How does the general temperature data from this location compare to data from others? Depending on many architectural and environmental factors, some parts of the city could be easily heated during the day, while others would have lower temperatures persist; some parts of the city would be warmer depending on solar absorption/reflection, etc. Is the one data source you chose sufficiently representative?

470: this also seems like a large limitation, especially since no citations or statistics were given about the extent of heating, insulation, behavioral adaptations, etc. that define exposure.

Figures, especially Figure 1 and Figure 4, have extremely blurry text and are almost impossible to read, so I cannot give sufficient feedback on them.

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Reviewer #1: No

Reviewer #2: Yes:Carlos Barboza Pizard

Reviewer #3: No

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Increased Mortality Risks of Winter Temperature Flips: A Growing Concern in Aging Society of Subtropical Climate Regions

PCLM-D-25-00435R1

Dear Dr. Ren,

We are pleased to inform you that your manuscript ’Increased Mortality Risks of Winter Temperature Flips: A Growing Concern in Aging Society of Subtropical Climate Regions’ has been provisionally accepted for publication in PLOS Climate.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow-up email from a member of our team.

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact climate@plos.org.

Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Climate.

Best regards,

Noureddine Benkeblia, Dr. Sci., Dr. Agr.

Academic Editor

PLOS Climate

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Additional Editor Comments (if provided):

Reviewer Comments (if any, and for reference):

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 #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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-->2. Does this manuscript meet PLOS Climate’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.-->

Reviewer #1: Yes

Reviewer #2: Yes

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

Reviewer #1: Yes

Reviewer #2: Yes

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-->4. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. 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: Yes

Reviewer #2: Yes

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

PLOS Climate 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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-->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 #1: I thank the authors for their thoughtful and thorough revisions. I am overall very satisfied with the state of the manuscript. I do have minor suggestions for the authors:

On Line 231: You state that the sensitivity analysis "yielded similar results". This should either be left for the results or a reference to the supplemental information should be provided.

On line 239: it should be an "increased" or "increasing" frequency

The sentence beginning on line 438 is a strong generalization that should either be removed or supported with a citation.

Reviewer #2: Recommendation: Accept with minor revisions.

Justification

The revised manuscript demonstrates substantial improvement in methodological transparency, data availability, and scientific framing compared with the original submission. The study provides novel insights into the health impacts of abrupt temperature transitions in subtropical climates and presents robust evidence of increased mortality risks associated with warm-to-cold temperature flips. While some limitations remain, they are acknowledged by the authors and do not undermine the validity of the analysis. The manuscript therefore meets the scientific standards required for publication in a peer-reviewed climate-health journal.

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-->7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

Do you want your identity to be public for this peer review? If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.-->

Reviewer #1: No

Reviewer #2: Yes:Carlos Barboza Pizard

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