Methane and the Warming Blame Game

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents a novel approach to attributing methane-induced warming to countries using cooperative game theory, specifically warming Shapley values. It addresses a critical gap in climate policy by providing a more accurate method for allocating historical responsibility for methane emissions, which are often underestimated by traditional methods. Here are some comments for improvement.

[1] Include a section discussing how policymakers could implement the Shapley value approach in international climate negotiations or national carbon budgeting.

[2] Provide more details on how the computational burden was managed (e.g., approximations, parallel processing) and potential simplifications for future applications.

[3] Explore the impact of emission data uncertainties (e.g., pre-1970 CH₄ estimates) on the results, possibly through sensitivity analyses.

[4] Provide a short discussion on how the results could inform equity principles (e.g., Common but Differentiated Responsibilities).

[5] Suggest applying the method to future scenarios (e.g., SSPs) or incorporating additional climate forcers (e.g., black carbon).

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors address a very interesting and novel issue. I would start my review ith the critique of the formal issues: There are grave issues in formatting! Fix them. Sources in square brackets are missing! The game-theoretical part is too short! It is not clear how the game theory relates to this research. The discussion part remind more introduction. Discuss there your results. We do not need a second introduction. 

The authors should embed the study into a broader context of energy transition and sustainability transitions. Refer to recent and underlying works in this field. Focus on the studies in the realm of environmental kuznets curve because you speak about nonlinearities. Refer to https://doi.org/10.1016/j.enpol.2013.07.131 and https://doi.org/10.1016/j.seps.2020.100936

Also, results are primarily given in millidegrees (m°C), which is technically accurate but hard for general audiences to interpret. Supplementing with % contributions or comparisons to national carbon budgets could improve clarity.

While some sections are dense, and there is room for clearer exposition and more normative discussion, the core methodology and findings are sound, novel, and relevant.

 

Author Response

Please see the attached document.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study quantifies the warming contributions of methane-emitting countries using a Simple Climate Model combined with cooperative game theory to allocate warming fairly via Shapley values. It reveals that the commonly used marginal “leave-one-out” method underestimates methane-induced warming by about 20%, due to methane's short atmospheric lifetime and nonlinear forcing relationships. The analysis spans major country groupings and highlights how methane's impact alters national warming responsibilities compared to CO2-focused assessments. The findings emphasize the importance of accurate methane attribution for equitable climate policy and suggest Shapley values as a robust tool for future allocation and mitigation planning.

 

1. Line 17, Introduction: “countries contributions” should be “countries' contributions” (possessive).
2. Line 19, Introduction: “responsibilites” typo; correct spelling is “responsibilities”.
3. Line 20, Introduction: “policymakers considerations” missing possessive apostrophe: “policymakers' considerations”.
4. Line 24, Introduction: “normative judgement” should be plural “judgements” for consistency or specify singular.
5. Line 35, Introduction: “simplifciation” typo; correct spelling is “simplification”.
6. Line 43, Introduction: “nonlinear” is sometimes written as “non-linear”; be consistent throughout the document.
7. Line 60, Data and Methods: “expressed relative the early industrial period” missing “to”: should be “expressed relative to the early industrial period”.
8. Line 136, Results: “Uncertainty in warming Shapley values is found by separate evaluation” should be “was found” (past tense).
9. Line 145, Results: “effect of LUC-CO2 estimates n these results” typo, should be “in these results”.
10. Line 185, Discussion: “Methane is a short-lived-climate-forcer (SLCF)” inconsistent hyphenation, should be “short-lived climate forcer”.
11. Line 197, Discussion: “It an extensively used approximate allocation method” missing verb “is”: “It is an extensively used...”
12. Line 204, Discussion: “The means that the warming impact.” should be “This means that the warming impact.”
13. The claim that TCRE cannot be applied to methane is made, but it doesn’t acknowledge alternative recent metrics fully.
14. The marginal or LOO method is said to underestimate warming, but the paper does not clearly define why this is problematic for policy implications.
15. The choice of the early industrial period baseline is assumed without discussing the potential variability or controversy over this baseline.
16. The “leave-one-in” method is described as overestimating warming but lacks an example or quantified explanation here.
17. The issue of computational feasibility is mentioned, but the impact of grouping countries rather than analyzing individually on the results is not discussed.
18. CEDS data omission of F-gases, though noted as 1%, could affect warming estimates especially for some countries, yet this uncertainty is downplayed.
19. The statement about aerosol masking is mentioned. However, lack sufficiently linked to how it affects uncertainties in methane warming specifically.
20. The discussion conflates methane lifetime with its warming impact, which may mislead readers about persistence and effect.
21. The critique of LOO as missing 23 m°C of warming is made but the policy relevance of this gap is not fully elaborated.
22. The statement “Methane present climate policy-makers with an acute set of challenges” is vague and not expanded.

Author Response

Please see the attached word document.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The author has substantially improved the manuscript. Almost all my comments have been satisfactorily addressed. Only my comment 2 has not been addressed. The author does not have to dive into the scholarship. A brief reference to these two papers would make clear that the author has scrutinized the pertinent literature from the broader lens of climate policy.

Author Response

I have integrated the two suggested references into the revised manuscript (in paragraph 3 of the introduction).

Thank you for your help and suggestions.

Reviewer 3 Report

Comments and Suggestions for Authors

Agreed with the revisions made by the authors. 

Author Response

Thank you for your insightful suggestions that have improved the manuscript.