PCLM-D-22-00017

Emission reduction targets and outcomes of the Clean Development Mechanism (2005 – 2020)

PLOS Climate

Dear Dr. Lo,

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

No specific changes are strictly required for publication, but both reviewers made a number of constructive suggestions which appear manageable and would increase the value of the article. Since there are many suggestions, but none which appear very large or time-consuming, please provide a response to each in your rebuttal letter. If there are comments that you prefer not to address, you may simply note that. But acceptance of the manuscript is conditional on your making a clear effort to address most of the comments.

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We very much look forward to receiving your revised manuscript.

Kind regards,

Malcolm Fairbrother, Ph.D.

Academic Editor

PLOS Climate

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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: Yes

Reviewer #2: Yes

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

Reviewer #1: Yes

Reviewer #2: 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

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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

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5. Review Comments to the Author

Reviewer 1

I very much enjoyed reading this paper, and think it will make a significant contribution to the literature on the CDM, offsets, and importantly, discussions of the design of the SDM. I think the main challenge for the authors is to really "punch up" their contributions which I see as:

a) CDM underperforms according to its own criteria. If one takes into account critiques about additionality, this underperformance is likely greater.

b) Four emerging economies dominate in terms of benefits.

c) Problematic HFC projects have a large role in both the financing and the emissions reductions of CDM.

d) Economic benefits unevenly distributed -- suggesting that this is not the engine for "clean development" for the poorest nations (a point you already made).

I think there are a lot of important findings in here, so my comments are primarily meant to highlight what I think are some of the points that could be made more prominent, and enhance the contributions of the paper. There are a few questions / clarifications.

Questions / Comments / Recommendations for revision.

1 What’s the “official database” (p 3, L 61)

2 Emphasize that this is performance according to their own additionality criteria. Note that there are many critiques about whether the additionality baselines are inflated. Thus, there is a very plausible argument that the underperformance is underestimated.

3 I think there could be more framing in the intro / abstract about how these findings are very important because of the emerging offset market (i.e. SDM) under Article 6. Many of these patterns are likely to continue in the absence of significant institutional reform.

4 P 4, L 72-76: The timeframe of the paper is also important because it represents the “heyday” of the CDM right after entry into force of the KP.

5 Perhaps CDM projects and Emissions Reductions sections should go under Methods?

6 CDM projects should be retitled something more descriptive: CDM Projects Analyzed or Selecting the Sample or something like that.

7 The section titled “Emissions Reductions” should perhaps renamed Estimating Emissions Reductions? (Again, something more descriptive)

8 It would be interesting to know how many MRs were withdrawn. This tells us something about the robustness of the estimation process.

9 P 6, L141-50. May be worth describing in “laymen’s terms” a little more about reference price, spot price, and what this means in plainer language. For example – explain “monthly CER prices” and why they’re the best alternative to spot prices.

10 “Economic Contributions” heading could also be more descriptive. One suggestion: Does the CDM help developing countries economically? (Just a suggestion)

11 This sentence on p 7 needs better explanation: “Based on secondary market prices, this approach has a limitation of underestimating the value of ‘bi/multilateral’ CDM projects, which are seen as operating under a forward purchase agreement.” I am an expert on CDM and had difficulty understanding it.

12 P 7, L 188-189: This point about price volatility is important and could be further emphasized earlier in the paper.

13 Table 1: A brief definition of bi/multilateral projects would be helpful, and why this distinction is important. Why is the percentage column significant? What does it tell us about the nature / functioning of the CDM? Should we expect bi / multi projects to perform differently?

14 Figure 1: This is fantastic! Why are there negative CER units issued?

15 P10, L 268. Controversies surrounding HFC projects could be discussed more prominently. Note that the EU also stopped accepting these projects.

16 It also bears emphasis that the performance rate is heavily influenced by the presence of these very problematic projects.

17 It might also be useful to calculate what China’s emissions reductions look like in Figure 1 with and without HFC projects.

18 P 11, L 293: I don’t understand how you’re defining “higher performance” if not achieving reduction target. Can you explain a bit further?

19 I would also consider adding one sentence in the Abstract which highlights basic findings about the best and worst performing types of projects. This is very useful data for lots of people.

20 P 15, L 423-24: Also could be emphasized that China, India, South Korea and Brazil dominate the market AND get higher prices per CER much earlier in the paper. This is an important finding.

Reviewer 2

1 L53. Are ex-ante and ex-post the wrong way round?

2 L107. I think you could remark on the fact that in only 12 cases did the project underestimate the amount of carbon removed. What does that tell us? Perhaps you could make a reference to the literature on optimism bias in project management.

3 L108. What does this mean?

4 L126. Can you describe how and why you weight the performance rates (basically I think that you need to do this immediately after you first mention weighting).

5 L237. Where does the 2% discount come from?

6 L310. Many more (not much).

7 L332. What does over the year mean? Do you mean over time?

8 L346 Values?

9 L357 Ditto.

10 L431. To [an] uneven…

11 L474. I do not think that the mismatch raises question about cost-effectiveness per se.

12 L478. I do not think that the mismatch necessarily represents an inequitable outcome.

13 Figure 5 is confusing

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Reviewer #1: Yes: Jessica F. Green

Reviewer #2: No

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Emission reduction targets and outcomes of the Clean Development Mechanism (2005 – 2020)

PCLM-D-22-00017R1

Dear Dr. Lo,

We are pleased to inform you that your manuscript 'Emission reduction targets and outcomes of the Clean Development Mechanism (2005 – 2020)' 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.

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

Best regards,

Malcolm Fairbrother, Ph.D.

Academic Editor

PLOS Climate

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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

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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

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

Reviewer #1: Yes

**********

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

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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

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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 am satisfied with the revisions and think this will be an excellent publication.

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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: Yes: Jessica F. Green

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