Exergy and Demography: Present Scenarios and Future Projections

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript is interesting and in line with the overall scope of the Energies Journal. However, the following points should be checked and improved in order to provide a better version/relevance of the proposed work.

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Abstract/Introduction sections

The abstract section could have conclusions/key(s) message(s). In addition, the Introduction section could be more concise. Please be careful with the details about the selection criteria for the chosen countries and the storyline that you want to communicate.

It is suggested to avoid groups of references like [3,11,12,18,24]. If required, offer a brief description of each publication cited.

Improve the quality of the Figures. For instance, Fig. 1 shows incomplete information (i.e., imports, materials, etc.). In Figure 2, it is suggested to add a legend with the meaning Es Eout ENR MSG, … etc … Figure 2a to 2d should be Figure 3a to 3d. Figure 2d double-check the blue bars.

Methods/Materials Section: It is suggested to add a flowsheet covering the details of the main steps covered in Sections 3 and 4. 4.1.4–. Türkiye = (Turkey)

5–. DISCUSSION

Results and discussion (Illustrations): Currently, the structure and explanation are very limited. It is suggested to add a Supplementary Section to move part of the Figures and include a synthesized Table with the main findings. Thus, it should be more effective in the way data is presented and how there are discussed.

REFERENCES: 9 of 38 references belong to the author. It is suggested to check if all of the cited publications are necessary/required. For example, [24] E. Sciubba, 1998: A novel exergetic costing method for determining the optimal allocation of scarce resources, did not appear cited in the manuscript.

Author Response

please see attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review this fascinating and ambitious manuscript. The attempt to integrate exergy analysis with demographic structures represents a bold and intellectually stimulating contribution to the sustainability discourse. The conceptual framing—anchoring sustainability in thermodynamic principles rather than normative or monetary proxies—is both provocative and valuable. Especially noteworthy is the introduction of the “Degree of Sustainability” as a physically grounded metric, and the cross-national comparison that illustrates the model’s potential scope.

However, the manuscript, in its current form, requires significant improvement in several areas to meet the standards of scientific rigor and communicability.

1. The study relies heavily on data approximations and limited demographic-exergy datasets. While these constraints are acknowledged, their methodological consequences are not fully explored. Using averaged exergy factors and heuristic adjustments for countries with different economic structures risks producing misleading projections. A stronger empirical anchor—perhaps a detailed case study with reliable data—would greatly enhance the model's credibility.

2. The allocation of exergy by age group is one of the core innovations of the paper, but the methodological foundation is thin. The scarcity of age-specific consumption data and the extrapolation across cultural and economic contexts raise concerns about generalizability. Incorporating a clearer rationale, justification for age consumption factors, or at least bounding the uncertainty they introduce, would significantly strengthen the analysis.

3. The paper currently lacks any form of uncertainty analysis, sensitivity testing, or validation. This omission is particularly concerning given the quantitative nature of the model and the assumptions involved. Even a basic Monte Carlo simulation or scenario range analysis would help to convey the robustness (or limits) of the findings.

4. The tone of the manuscript occasionally leans into deterministic or absolute claims—particularly in suggesting that thermodynamic unsustainability invalidates all other sustainability metrics. While thermodynamics offers a powerful lens, a more balanced and interdisciplinary framing would acknowledge the roles of institutional, cultural, and economic systems in shaping energy behavior.

5. The structure of the manuscript could benefit from better organization and visual clarity. Several sections are overloaded with figures and tables that, while rich in content, are not always well-integrated into the narrative. A more synthetic presentation of key results—especially cross-country comparisons—would help guide the reader through the findings more effectively.

6. The policy implications, while compelling, would benefit from deeper engagement with existing literature in energy policy, demography, and development studies. The model’s outputs could be better contextualized through references to real-world planning scenarios, governance challenges, or existing energy transition frameworks.

This is an intellectually original and promising piece of research. With thorough revision—especially to strengthen data transparency, methodological robustness, and disciplinary integration—it has the potential to make a lasting contribution to the field. I encourage the author to continue developing this model with careful attention to empirical grounding and critical reflection

Author Response

please see attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Legenda to figure 3 >> Suggested: Legend to Figure 3
Figure 5: The Population Pyramid (Very bad resolution, improve the quality)
Figure 6: All figures adapted from [http24] >> Suggested: All figures adapted from [24]

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Figure numeration is wrong!
Figure 8a – Population Pyramids for Italy 2023 and 2050
Figure 8a – Population Pyramids for France 2024 and 2050

4.1.4 – Türkiye >> CHANGE to Turkey
Figure 10a-b-c: Türkiye >> CHANGE to Turkey

Figure 8 to Figure 15:

• Define (Mio)
• Unify information (data range)!

• The info for Kenya is based on data of 2020
• The info for Congo is based on data of 2021
• The info for Italy, India, Bangladesh are based on data of 2023
• The info for France, Romania, Turkey, China,  is based on data of 2024

REFERENCE: This is not the proper way to cite online resources, double-check!
[43] https://www.populationpyramid.net/world/2024/, accessed September 2024
[44] https://www.euractiv.com/section/politics/news/romania, accessed December 2024

Author Response

Legenda to figure 3 >> Suggested: Legend to Figure 3 Done
Figure 5: The Population Pyramid (Very bad resolution, improve the quality) The original picture is blurred, could not edit it
Figure 6: All figures adapted from [http24] >> Suggested: All figures adapted from [24] Done

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Figure numeration is wrong! fixed, thanks!
Figure 8a – Population Pyramids for Italy 2023 and 2050
Figure 8a – Population Pyramids for France 2024 and 2050

4.1.4 – Türkiye >> CHANGE to Turkey The turkish government has issued an official note in 2024 to recommend the use of  "Türkiye"
Figure 10a-b-c: Türkiye >> CHANGE to Turkey

Figure 8 to Figure 15:

• Define (Mio) Done
• Unify information (data range)! Cannot do: I took the latest officially available data for each Country

• The info for Kenya is based on data of 2020
• The info for Congo is based on data of 2021
• The info for Italy, India, Bangladesh are based on data of 2023
• The info for France, Romania, Turkey, China,  is based on data of 2024

REFERENCE: This is not the proper way to cite online resources, double-check! I used the APA recommended format
[43] https://www.populationpyramid.net/world/2024/, accessed September 2024
[44] https://www.euractiv.com/section/politics/news/romania, accessed December 2024

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Author,

Thank you again for your insightful feedback and for the substantive improvements already reflected in the revised manuscript. I apologize for the remaining gaps and appreciate the opportunity to address them. Below are detailed suggestions and clarifications to strengthen the paper further:

1. Empirical Anchor & Age-Consumption Factors
   Although Section 5.1 now flags the provisional nature of the HIC/MIC/LIC age-factor curves, readers still lack a clear sense of how sensitive the results are to those assumptions. To remedy this:

• Supplementary Table or Boxed Mini-Case: Introduce a short case study for one representative country (e.g., Italy) showing total exergy demand under three scenarios: baseline age-factors, all factors increased by 10 %, and all factors decreased by 10 %.
• Interpretation Paragraph: Immediately below the table, add 2–3 sentences explaining how a ±10 % shift translates into absolute exergy changes (e.g., “a 10 % upward shift in age-factors increases total exergy demand by X PJ, which corresponds to a Y % change in the Degree of Sustainability”).

2. Uncertainty Analysis & Sensitivity Testing
   The current manuscript still lacks quantitative uncertainty bounds. Even without full probabilistic modeling, please include:

• Two-Scenario Banner: A concise “Low-Factor” vs. “High-Factor” comparison in Section 5.1 (e.g., Figure X), showing exergy projections for 2030 and 2050 under both scenarios.
• Tornado Chart: A chart illustrating which age-factor bands (e.g., “0–14 yrs,” “15–64 yrs,” “65+ yrs”) exert the greatest influence on aggregate exergy demand. This visual will help readers see which demographic assumptions matter most.

3. Balanced Thermodynamic Framing
   Some language remains overly deterministic. To soften absolute claims while retaining your core argument:

• Revised Phrasing: Replace statements such as “thermodynamic unsustainability invalidates all other metrics” with “thermodynamic constraints establish necessary—but not alone sufficient—criteria for sustainable development.”
• Contextual Sentence: Add a brief note acknowledging that social, institutional, and economic factors also shape real-world outcomes:

“While exergy availability underpins the physical feasibility of societal progress, factors such as governance quality, social equity, and technological innovation modulate how effectively societies convert thermodynamic potential into inclusive development.”

4. Figure Streamlining & Narrative Integration
   The manuscript still presents over twenty individual figures, many of which share similar layouts and are not immediately discussed. To improve flow:

• Combine Related Charts: Merge exergy vs. demographic trend graphs into a single multi-panel figure (e.g., panels a–c for three countries) with unified axis scales and consistent color coding.
• Immediate Lead-Ins: Ensure that every figure is introduced within two sentences of its appearance. For example:

“Figure 4 (panels a–c) illustrates how exergy demand and population age profiles co-evolve in HICs, MICs, and LICs.”

• Key Takeaway Boxes: After each major figure block, insert a 2–3-sentence “Key takeaway” explaining policy or demographic significance (e.g., “In Country A, the rapid aging of the population will reduce per-capita exergy availability by Z %, underscoring the need for efficiency improvements”).

5. Policy Implications & Literature Engagement
   Section 5.2 currently reads as general commentary. To ground it in existing frameworks:

• Targeted Citations: Reference the IEA’s Net Zero by 2050 Roadmap and the IPCC SR15 report, briefly summarizing their top-down assumptions.
• Complementary Role: Add a paragraph explaining how your bottom-up exergy-age model can refine those scenarios—for example, by revealing which demographic segments pose the greatest strain on future energy systems, thereby guiding more nuanced policy interventions.

6. “Three Pillars” Diagram Removal & Social Metrics Integration
   Given the detailed textual treatment of social, technical, and environmental linkages, the standalone “three pillars” graphic can now be omitted. In its place:

• Descriptive Schematic (Text-Only): Embed a concise description in the Introduction:

“Our framework situates economic, social, and environmental sustainability on a thermodynamic foundation by mapping exergy availability against indicators such as GDP per capita, Gini coefficient, and CO₂ emissions. In future work, one could translate, for instance, the Gini coefficient into an ‘exergy inequality index’ to harmonize social equity measures with thermodynamic constraints.”

• Footnote on Composite Index: Consider a brief footnote or endnote outlining how a composite sustainability index might weight DS alongside a social equity exergy proxy.

Additionally, several of the more repetitive country‐specific exergy–demography charts—while still valuable for completeness—do not add materially new insights beyond the main multi‐panel composites. I propose relocating these individual country figures (formerly Figs. 5–8) into a Supplementary Information section. This streamlines the main text, keeps the core narrative focused, and still makes all detailed outputs available for readers who wish to explore each case in depth.

Implementing these detailed revisions will directly address the remaining concerns, enhance methodological transparency, and ensure that the figures and narrative work in concert to guide the reader. Thank you again for your invaluable guidance and patience as I refine this manuscript.

Sincerely,

Author Response

Sincere thanks to Reviewer 2 for her/his extended comments. But I am afraid to say that the suggested "improvements" are on the one side unlikely to improve the paper, and on the other hand they would require a lot of work... to fix a very scanty database! As I tried to explain in my previous rebuttals, a sensitivity analysis is worthless since the data in reff. 1, 10, 12, 18, 19 are not only non-homogeneous, but also refer to different social situations and to different time periods. Again, I would very much like to be able to generate more reliable age-exergy factors, but this is impossible at the current state of the literature on the subject.

All other requests in principle hinge on this problem. 

Thanks again for the time invested in this review

enrico sciubba