Review of 'Location location location: A carbon footprint calculator for transparent travel to COP27'

This is an interesting article that compares the carbon footprint of various options for travel to the upcoming COP in Egypt.  The article is timely, highly relevant and of importance in providing an evidence base to support decision making and counteract greenwashing.  I would recommend a few changes to the article before it is finalised.  Comments and suggestions are provided below.

My main comment is that the structure of the article is a bit unusual in that it does not follow the standard scientific format of introduction – methods – results – discussion – conclusions.  While the article loosely follows this layout, there is no dedicated methodology section.  Information on the methods is given in an appendix and in places throughout the main text, but I found it a bit disjointed, with queries often occurring that were then answered later in the text.  I would recommend preparing a dedicated methods section to appear after the introduction and to contain relevant information relating to the assumptions, boundaries and methods.  If the authors decide to keep the appendix, then I would still recommend a dedicated methods section that gives an overview of the steps and assumptions, and that points clearly to the appendix.  An algorithm or flow chart showing the steps and/or a diagram showing the boundaries of the analysis would be a useful addition.

The other main comment I have is regarding the mention of climate justice and related issues.  The abstract infers that the principles of climate justice were incorporated into the carbon footprint calculator, but I’m not sure that this has been done.  The conclusions section also raises the importance of supporting sustainable development and promoting equity and climate justice, but this hasn’t really been addressed in the main paper.  Due to the stated importance, I would suggest expanding on the topic in the main paper.  The topic is outside my main area of research, but as a suggestion you could look at this work which I undertook with colleagues on the principle of justice in the renewable energy area: https://doi.org/10.1016/j.jclepro.2021.129280.  It might give you some ideas.

A few minor comments are below:

• Figure 1.  I assume that this graph shows the results for train from London to e.g. Brussels and then a flight to Egypt.  Could you please clarify this in the figure title.
• For the equation that appears above Figure 3, could you please clarify what is meant by “route”?  Is this the part of the journey that does not involve flights, or is this the entire journey including both flights and other means of transport?
• The terms CO2, CO2e, CO2-eq and CO2-equivalent are used variously throughout the paper.  Please check that the terms are used consistently.  Should all values be in CO2e?  If results are mixed and reported in both CO2 and CO2e, then I would advise amending the calculations so that all values are reported in CO2e.
• In Figure 3, the red line indicates points equal to 30 kgCO2e/hr.  The text below the figure states that journeys “beneath this line are considered worthwhile by an individual within this threshold”.  I find this a bit confusing.  Why is this threshold assumed?  Please expand on this.
• In the section on indirect effects, the referencing is done by name and year in places rather than by number.  Please keep the referencing style consistent.
• Also in this section, the text recommends that users double the amount of carbon offsets they purchase.  The next sentence states that the carbon footprint of the flight should be multiplied by 4.5.  Please expand on this to fully explain the points being made here, as the text appears contradictory.
• Is copyright permission required for Figure 4?  I also wonder if the image is really needed for your paper.  It’s an interesting image, but it might be better to use the space for your own results.
• The conclusions section raises interesting points, but a few of the issues mentioned have not been covered in the main text.  Generally, in academic writing, there should be nothing new in the conclusions section.  Examples are the references to financial investment, which wasn’t investigated in this paper (but the text in the conclusions implies that it was), along with conflicts in the Middle East.  These are both important issues, so I would suggest including discussion in the paper to address them.  The conclusions section also refers to the carbon footprinting and offsetting already undertaken by the Egyptian government; again, I don’t think this is covered in the main text, but it would be useful for it to be included.
• In the appendix in the section under flights, please give the reference for the average taxi time and the approach used by BEIS.  How do your results compare to the values in BEIS?  Also in this section, please provide the references for the EEA equivalent, the ICAO calculator and the values reported by Boeing and Airbus (a reference is give in the table caption, but not in the text).
• The text immediately above Table 1 in the appendix states that fuel is converted to GWP “as described”.  Where is this described?
• I suggest numbering tables and figures that appear in the appendix using a different system than is use for those in the main text, e.g. Table 1 vs Table A1.  Check the journal guidelines, but table numbers and captions usually appear above the table rather than below.
• In the section on passenger cars, it appears that all vehicles were assumed to be hybrid or electric.  I think this is the first time this has been mentioned.  Please explicitly state the assumptions (as per the comments on a suggested methodology section above).
• In the main text above Figure 1, the text states that electricity in France is carbon cheap, while in the appendix the text states that the UK emissions factors were used for all journeys.  Were UK emissions factors used for cars and specific country emissions factors used for rail?  If this is the approach taken, is it reasonable (as it appears to be a bit inconsistent)?  Was all rail travel assumed to be electric?  While electric rail might be more common than diesel overall, is it more common for the long-distance journeys investigated here?  The text states that it was assumed that electricity consumption is dominated by passenger rail as opposed to freight.  Please explain the relevance of this assumption.  Why was the value of 0.8 used?
• Please explain the terms tier 1, tier 2 etc at first mention.

Overall, this was a very interesting article and I would be keen to see an updated version.