A virtual global carbon price enabling engineers to drive essential and rapid decarbonization

Review
This Editor assessment review from the Editor-in-Chief aims to draw together the previous reviews of this revised submission and how the authors have so far responded. Also, it sets out some relatively small, detailed matters for clarification that would further improve the submission after the author's revision to the current version. These points deal mostly with the expressions used to calculate carbon prices and should be straightforward to address.

There have been two previous reviews of version 1 (https://doi.org/10.14324/111.444/000184.v1) from experts in the energy field. One review found the original submission lacked clarity in various respects: the submission needed to be strengthened in various ways, for example, with a clearer introduction and a Discussion section better linked to the main findings rather than containing suggestions for actions in the corporate sector. The other review found the submission made a potentially important contribution but that no reference to some main aspects of EU energy approaches, including those dealing with energy efficiency, and asked that these be included. Both reviewers felt the submission lacked some important contextual material. Given the nature of the submission - a new approach to costing infrastructure projects and a way to monitor progress towards net zero that might be widely adopted if generalised - both reviewers necessarily focused on the high-level strategic elements of the submission.

In my view, to make the higher-level amendments both reviewers suggest would entail providing a much more broad-ranging submission that would detract from the current focus, which is on the ways in which countries might move towards net zero through using a new way of pricing carbon in infrastructure projects. In my view, the submission is already complex enough and to address these points would entail a large review of the field and the submission is not a review of this kind - although one may be needed, as both reviewers imply.

The authors have addressed the remarks of the two reviewers in this revised version 2 (https://doi.org/10.14324/ucloepreprints.233.v2) about a lack of clarity in parts of the submission by improving the Introduction and expanding the Discussion section in a manner that provides an envelope for the carbon pricing work. The Introduction and Discussion now acknowledge the operational issues and professional challenges that engineers face worldwide and positions the submission in the high-level energy landscape that has been disrupted by the Russia-Ukraine conflict that has created such uncertainty that a high-level review article would not be practicable at this time. The carbon pricing elements of the submission now flow better as the text has been clarified, figure legends expanded and a lot of the detail placed in an information box (which will need careful positioning in any fully published version). I agree with the reviewers that that the paper juxtaposes operational and professional challenges with a new way of calculating and carbon prices that includes renewable themselves on the same footing as any other infrastructure project. This leads readers to judge whether the new approach to carbon pricing would help address the challenge that engineers face - but then readers of multi-disciplinary papers are best placed to make such a judgement and it might be considered wrong for the authors to go any further than they already have in suggesting actions that might be taken by countries or corporate bodies.

These improvements have enabled me to pick up a few points of detail that need to be corrected or clarified further.

These points are:

1. I cannot find any explanation in the main text as to what SIMPLE-CP and PREDICT-CP is. I can see they are both dealt with in the top left box in Fig 1. in terms of expressions being given to show how they are calculated. Inserting a sentence or two of explanation would help especially as the SIMPLE-CP seems to be defined in part by a term EXP which is not elsewhere explained.

2. I think the use of apparently different meanings of W etc is confusing:

a. Weff is defined in two different ways in the paper. In the legend to Fig 2. it is defined as the “The effective country weighting, Weff is (W x W*)0.5.” -- whereas in the earlier section on Calculating the Carbon Intensity Weighting (of an infrastructure project I think you mean) it is set out within the expression “y = SIMPLE-CP x Weff (or W for simplicity)”. In the second instance, which occurs first in the submission, the implication is that Weff is the equivalent of W. That means that the phrase “Weff is (W x W*)0.5” in the legend to Fig 2. would, as W is a short form of Weff, reads in full as “Weff is (Weff x W*)0.5”. That last expression doesn’t seem to me to make sense as Weff would then be itself multiplied by a factor all raised to an exponent. Please clarify the way the terms Weff and W are being used. If they are being used in different ways perhaps insert a sentence or two making that clear or change the letters being used to ensure clarity.

b. Perhaps this point falls if a. is dealt with suitably. In the section “Prioritizing infrastructure changes in the Developed World first”, the term W appears not as an “effective country weighting” (as in a. above) but as a “carbon inheritance”. If these two sets of words are equivalent and W is the same calculation term in both cases please make that clear in the text. If the use of W in the two instances is different then some different letter will be required in one place or the other or the use of Weff continuously in the relevant section.

c. This part of the text (same section as for b. above) does not seem to follow very well as W* is defined first as a simple ration Dc/Pc and then in the next sentence is redefined as the ration scaled: Here are the words used in the submission: “The second term, carbon liability (W*), we define as the cumulative carbon emissions D (= ΣC) of a country divided by its current population (Dc/Pc). That ratio is then scaled by the world’s cumulative emissions and population to obtain W*.” Perhaps this can be easily edited?

3. The sentence: “The relationship is strongest if consumption, rather than domestic-only emissions are included.” seems out of place and perhaps was meant to be included in the previous paragraph which discusses Fig 2. It would be worth making crystal clear which relationship is used for Fig 2. i.e. whether it is consumption or domestic-only based. This will make a big difference to interpretation so could be important for the reader to be left in no doubt about.

4. I note a reference is made in the legend to Fig 1. to 1860 cities. Could you please confirm that the country comparisons are just that and not city-to-city comparisons or an aggregate of city comparisons. If Fig 1. And Fig 2. have been prepared in that proxy city-based way please make that is clear in the text with an explanation as to why cities have been used as a proxy for countries.

5. Can anything more be said about the any of the proprietary software used to generate data for the study? Readers may be interested in it if they want to take up the approach or test reproducibility or sensitivity.

Declarations and potential conflicts of interest.
Professor Dan Osborn, Editor-in-Chief of UCL Open Environment, is affiliated to the same University as the corresponding Author (University College London, UK) but however does not possess any research or partnership conflicting interests with the corresponding Author. It is deemed that sufficient external peer review has been sought for this submission to ensure effective and proper peer review standards, in line with the journals peer review policies (https://journals.uclpress.co.uk/ucloe/site/journal-policies/).

Note:
This review refers to round 2 of peer review.

Review

Note:
This review refers to round 1 of peer review and may pertain to an earlier version of the document.

Review

Note:
This review refers to round 1 of peer review and may pertain to an earlier version of the document.