The Short-Term Cost of Greening the Global Fleet
Round 1
Reviewer 1 Report
Paper Title: The short-term cost of greening the global fleet.
The issue this paper deals with is of great interest for academics, regulators and above all the industry and its future.
The authors undertake a challenging task of treating a huge amount of heterogenous data (vessel types) and examine newbuilding cost, demolition income and vessel retrofitting cost from a financial perspective stressing the need for increasing availability of finance, if the sector is to achieve policy objectives.
Literature Review
It is exhaustive but not directly related to what the authors have set out to do. It would help if the authors provide some information on the available finances to the industry and ways through which the industry obtains financing.
Methodology
Even though I agree with the authors procedure in deriving estimates for the overall cost and subtract from it the demolition revenue I would like to see something more elaborate in estimating this cost other than simple linear regressions which have a considerable prediction error and the R squared is not appropriate for showing the fit. For example, I believe omitted variables bias is present and the method of estimation therefore should involve instruments.
Minor Concerns
p.81 English correction required
p.697 English correction required
p.706 English correction required
p.725 English correction required
Substantial revision of English expression is recommended
I believe that this paper is publishable and will substantially contribute to the issue under consideration
Author Response
"Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is an interesting paper which is publishable given the below recommendations are addressed.
Line 50 3.429 bn
Line 53 by 2026
Line 61 replace “chapter 3” with “section 3”
Line 63 replace “chapter 4” with “section 4”
Line 63 replace “chapter 5” with “section 5”
Line 63 replace “chapter” with “section”
Line 80 replace “Error! 80 Reference source not found..”
Line 110 replace “Error! 80 Reference source not found..”
Lines 119 – 122 Needs rephasing. Make two sentences. Question should be separated lines.
Line 135 clarify what are the needs stemming from carbon inventory emission levels.
Line 157 “Figure 3”
Line 207 replace “Error! 80 Reference source not found..”
Line 234 3.429 bn
Lines 244 add a line or two elaborating on what comes next. This way the section will end more smoothly and link better with the methodology section.
Line 247 “of the global fleet”
Line 266 “Figure 5”
Line 318 “Table 2”
Line 329 “Figure 6”
Line 333 replace “Table 1” with “Table 2”
Line 347 “Figure 7”
Line 357 “Figure 8”
Line 368 “Figure 9, a”
Line 369 “Figure 9, b”
Line 369 “Figure 9, c”
Line 374 “Figure 9, a”
Line 389 “(Figure 10)”
Line 414 replace “chapter” “with section”
Line 432 “(Figure 11)”
Line 436 “(Figure 12)”
Line 440 “(Table 3)”
Line 448 “Table 4”
Line 454 “Table 4”
Line 462 “Table 5”
Line 467 “Table 5”
Line 529 “Table 7”
Line 536 replace “chapter” “with section”
Line 540 “Table 8”
Line 544 replace “Table 2” with “Table 8”
Line 544 “See chapter 4.1. or parameter overview in Appendix A.” Needs clarification.
Line 546 clearly state in which section equations 2 to 5 are illustrated
Line 555 “Figure 13”
Line 563 replace “USD33.bn” with “USD33 bn”
Line 610 “Table 9”
Line 611 replace “Table 3” with “Table 9”
Line 624 “Table 10”
Line 625 replace “Table 4” with “Table 10”
Line 641 Is it “Figure 13”?
Line 624 delete “in chapter 5.1”
Line 643 “Figure 15”
Line 647 replace “Figure 4” with “Figure 15”
Line 651 (Figure 15, a and b)
Line 654 (Figure 15, a and c)
Line 655 (Table 11)
Line 657 replace “Table 5” with “Table 11”
Line 697 delete “chapter 2”
Lines 703 to 705 need to be rephrased or deleted
Line 706 delete “(see chapter 4.2)”
Line 708 delete “(see chapter 5)”
Section 4.2 can be omitted as results luck significant validity.
Section 4.4 need to be included in section 5 (Conclusions)
Conclusions are very weak and do not represent the extend of the work. Authors need to completely rewrite conclusions by addressing the below questions:
- Why is the paper of importance?
- What is gap is aims at addressing?
- What is methodology used?
- What are the key results?
- How are these results different or similar to previous works?
- What are the limitations of the study?
- Policy, social and industry implications
- Recommendations for future work
All Figures and Tables need to have a Source. If a Figure or Table comes from the authors then the source should be as follows: “Source: Authors”
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors’ work is very interesting and timely, given that, as also acknowledged by the authors, the decarbonization of international shipping is high on the political agenda, with a series of regulations having entered or planning to enter into force in the upcoming years.
The practicality of the 5-year time horizon considered by the authors can be questioned and thus this needs to be well explained early in the paper (now this is done in sub-section 4.4) so that readers develop a better understanding of the adopted approach and of the contribution this paper aims to make to the relevant literature – this should also be more clearly stated in the introduction.
In the policy outline part, the impact regional policy initiatives may have (e.g. at EU level) can be elaborated a bit more, discussing also complementarities or differences with IMO. The literature review part can also be further strengthened with an overview of research contributions also approaching cost considerations of the decarbonization of international shipping. The few insights provided in the introduction can fit into that part.
The methodological part is well-structured and adequately described. However, there are some concerns that need to be considered and clarified: (i) in table 2, where descriptive statistics are provided for the fleet taken into consideration, 1868 is stated as the min year of built with the maximum age being 152 years. I guess this is not right and thus the dataset should be re-checked, (ii) at the same table, 2023 is stated as the maximum year built. Doesn’t this belong to the orderbook? How the negative price stated in the age column is justified? Please clarify. (iii) at the same table, for the demolition part, the last column is not visible. (iv) the decision to use wind-assisted propulsion as an indicative technology benchmark should be better explained and justified. It’s not very clear on what grounds this decision was taken. (v) industry estimates are mentioned for estimating the installation cost of a Fletter Rotor. Is there any specific references to be inserted? As currently stated, it's a bit abstract (vi) the assumptions made for the other types of vessels should be also better explained (p. 17, lines 494-498). (vii) source of tables 6 and 7?
The results presented and the relevant discussion made are both very interesting. A small clarification should be provided on how the scenarios considered were built. Were they based on any consultation activity with relevant industry experts?
In the conclusions, the study’s policy implications should be better explained. Is there any specific recommendation to be made for informing IMO’s policy?
Some more specific (editing) comments are also listed below:
- Abstract - line 16: profits instead of ‘proceeds’?
- Introduction - line 29: “discussed in the literature and the relevant press”. Some indicative references may be provided here. Same at line 59 “many researchers are contributing on this aspect”
- Introduction - line 35: Which session? This can be specified
- Introduction - line 46: UNCTAD (2017) – no updated data on the new versions (2018-2020)? Please check.
- Introduction – line 54: a brief description of the approach Psaraftis and Kontovas followed, can be inserted here so that a better understanding is provided to readers
- 4, line 153: why there were reduced during that time? As a result of the global financial crisis and the impact on trade? This can be justified.
- In some places in the text there is an “Error” and the respective references are not included (e.g. p. 2, lines 80-81, etc.)
- Numbering of tables should be corrected. For some figures also (e.g. figure 10). Numbering of both tables and figures is not always consistent within the text.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
I have carefully reviewed the authors' responses and changes performed in the revised version of the manuscript. All of my comments have been successfully addressed, so I recommend the paper to be accepted for publication.
