COP30: carbon cost of travel and accommodation in Belém from UK

Review
This review is for the manuscript titled ‘COP30: Carbon cost of travel and accommodation in Belem from UK’. The article presents valuable commentary of the emissions associated with delegates traveling from the UK to the highest-level event claiming to address the global climate crisis. The article is of value to the readership of the journal, and as such I am recommending the manuscript for publication with minor revisions.
There are two key areas that need attention and these are as follows: Firstly, as it is now 2026, the event (COP30) has taken place yet is presented as a future event in the article. I therefore recommend the language throughout the manuscript to be adjusted to reflect that the event is in the past (that is, with past tense). This may lead to some editing along the way based on the arguments presented, but it will improve the article overall.
Secondly, the main claim of the article is that it calculates emissions of delegates from the UK to the conference site in Belem, and includes air and accommodation emissions calculations. Overall, the key contributions of the article is not the calculator, as it was already developed, but the commentary on the COP30 event and associated emissions. As such, I strongly recommend that the article is framed not as a calculation but as a commentary on the event itself.
In terms of the calculations, the air travel calculator is relatively straightforward (although needs slightly more justification), however the cruise accommodation calculation is more of a commentary and hypothetical. While this is a valuable contribution in terms of the problematic nature of cruise accommodation for a climate event such as COP30, it is not quite results of a calculation per se, and thus should not be presented as definitive. Rather, I recommend this section be presented as an analysis and discussion of existing information, which better reflects the discussion in this section.
Aside from these two more significant adjustments, other comments are as follows:
Introduction:
Arguments in the introduction are set up well, articulating the unavoidable environmental impact associated with selecting a remote and difficult-to-reach destination such as Belem for a major intergovernmental climate crisis. Ensure to reference all claims in this section, for example (Paragraph 3, page 2, line 1: “the organisers consider the ships pragmatic” – this is a claim that needs a reference for support).
It would be useful to the reader to identify the aim of the paper at some point in the introduction section.

Methodolog and Results:
This section is explained reasonably well, however, some details would strengthen the paper overall.
Firstly, I checked the Barnsley et al. (2023) source for detailed information on the calculator, but all I could find was a web link to UCL’s climate hub and the calculator there. Perhaps provide a link to this calculator as well. This also means I was unable to find further detail about the methodology of the calculator and associated assumptions. Please include this in the Appendix at the very least, otherwise this work is not replicable and lacks validity.
There is a paragraph identifying that overland travel in Europe was excluded. This feels like it should sit in the methods rather than the results, as it is an assumption baked into the calculation (that European land transport is not significant in terms of total emissions per delegate and was thus omitted from final calculations).
Second paragraph in the results section on Cruise findings needs to be broken down as the ‘methods’ and discussion are muddled and difficult to follow. This large chunk of text covers the background, methods, some assumptions and the political context of onboard power supply, none of which belong in the results section. More detail unpacking Figure 4 would be great to see here, while the other comments, along with the remaining ‘results’ should be reframed as an ‘analysis’ based on existing work rather than a ‘calculation’ per se.
Conclusions:
This section overall lacks links to literature to support the claims made throughout. Adding more references to support arguments would also ground the work in the wider body of literature.
Finally, the limitations and future research directions are also lacking. Please add some context for limitations and future work.
I do hope the authors take on board the comments provided as much of the work is quite minor and is largely to do with the positioning of the contribution of the work. Otherwise, I wish the authors the best of luck with their future work in this important field.

Note:
This review refers to round 1 of peer review.

Review
I appreciate critical consideration of emissions associated with COP. The large carbon footprint of the conferences is known, and the paper does not provide significantly new insights, but it is nevertheless important to maintain the focus on conferences.

What I am missing, perhaps, is the general question whether it is necessary for 50,000 + people to travel to the COP, which should be an event in which policymakers come together to discuss climate policies. The paper takes for granted that the current setup, dominated by lobbyists, also attracting thousands of activists from all over the world, is necessary or even meaningful. There is a substantial academic critique of conferences that deserves to be mentioned.

Regarding cruise ships, the crucial question is from where these travelled to Belem. Most energy use is associated with sailing; in port, cruise ships will only use auxiliary engines for power production. Hence, the emission values used may be misleading, as these refer to a combination of sailing/in port fuel use. As you write, MSC Seaview and the Costa Diadema will be relying on onboard generators... resulting potentially in the emission of several dozen tons of CO2 daily". But several dozen ton are equivalent to just a few long-haul flights, if considering non-CO2 warming. This makes the cruise ship aspect less relevant.

I think that you make valid points, but the main question is not raised: Is it not paramount to a) find locations for COPs that minimise the average travel distance for delegates, and b) to cut down on the size of these conferences for reasons of accommodation and travel emission cuts, as well as the capacity of towns? (apart from the fact that lobbyists - industry or environmental - should be excluded from COP.)

Note:
This review refers to round 1 of peer review.