American Pick and Choose or Customary International Law?

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Since 2003, the United States (US) has been collecting, processing, and analyzing marine geophysical data to determine the outer limits of its continental shelf. Some 20 years later, on 19 December 2023, the US Department of State published the geographical coordinates that define its extended continental shelf (ECS), stating that:

‘The United States has determined its extended continental shelf limits in accordance with customary international law, as reflected in the relevant provisions of the 1982 United Nations Convention on the Law of the Sea, and the Scientific and Technical Guidelines of the Commission on the Limits of the Continental Shelf.’

The US has an inherent national interest in accurately identifying and declaring an ECS to other States in order to exercise its continental shelf rights with legal certainty under Article 77 UN Convention on the Law of the Sea (UNCLOS). The US delineation, which claims an ECS in the Arctic region, takes on even greater significance now that each of the other four Arctic States (i.e., Canada, Denmark in respect of Greenland, Norway, and Russia) has filed a submission with respect to an ECS in the Arctic ocean.

Although the US was among the States that participated in the Third Conference on the Law of the Sea, which resulted in the adoption of UNCLOS, it has not yet become a State party to the Convention. It is therefore uncertain whether the US, as a non-party, can rely on Article 76 UNCLOS in a way that obliges other States to accept the delineation of the outer limits of its CS as ‘final and binding’.

The US Position towards UNCLOS

At the conclusion of the Third Conference on the Law of the Sea, the outgoing Carter administration believed that the majority of UNCLOS articles aligned with the interests of the US and was willing to accept it in its entirety, including the regime for the deep seabed. In contrast, the Reagan administration opposed the ratification claiming that the provisions of Part XI on the deep seabed were inconsistent with US interests; however, it declared its acceptance of the provisions of UNCLOS, except for those contained in Part XI, as customary international law (CIL). All subsequent administrations, including the current one, have supported the US accession. Yet, Republican Senators have consistently rejected attempts to join UNCLOS due to concerns of a potential ‘loss of American sovereignty’ [for detailed analysis, see here, here, here, here, and here].

According to Article II, Section 2 of the US Constitution, the President is authorised to conclude international treaties by and with the advice and consent of the Senate, provided that two-thirds of the Senators present concur. Considering these stringent requirements and the unyielding position of the Republican Senators, it seems rather unrealistic that the US will ratify UNCLOS in the foreseeable future. Yet, more recently, on 29 April 2022, the US Legal Advisor addressed the UN General Assembly and reaffirmed the ‘US support for [UNCLOS]  and [its] continued regard for much of the Convention as reflective of customary international law.’

Status of Paras. 2 to 7 of Article 76 UNCLOS

The relevant provisions referred to by the US in its statement concerning its ECS are those contained in paras. 2 to 7 of Article 76 UNCLOS, which outline the methodology and process for a coastal State to determine the precise locations of the points defining the ECS. In accordance with Article 34 of the Vienna Convention on the Law of Treaties (VCLT) and the principle of pacta tertiis, UNCLOS creates rights and obligations only between its parties; no such rights and obligations are provided for between parties and non-parties. But, where CIL reflects the provisions of UNCLOS, it is binding on non-parties, such as the US, and on parties in their relations with non-parties. Therefore, the US would only be able to apply the criteria set out in paras. 2 to 7 of Article 76 UNCLOS to establish the outer limits of its continental shelf, if the latter could be acknowledged as CIL. In fact, the US acknowledged as early as 1987 that the delineation ‘provisions of Article 76 […] reflect [CIL] and that [it would] use these rules when [delineating] its continental shelf’, referring variously to paras. 1 to 7 [pp. 1878-9]. The US has been consistently firm in this position and has recently reaffirmed it.

Prior to considering the status of paras. 2 to 7, it should be noted that the definition of the continental shelf set out in para. 1 of Article 76 UNCLOS has been recognised as reflecting CIL by the International Court of Justice (ICJ) in its 2012 judgment on the Territorial and Maritime Dispute case [para. 118]. Yet, the Court refrained from determining the status of paras. 2 to 7 under CIL in its 2023 judgment on the Continental Shelf Delimitation case [para. 82], despite instructing the disputing parties to submit their arguments on this issue in the 2022 order [p. 565].

Upon closer examination of the structure of Article 76 UNCLOS, a striking observation can be made with regard to the relationship of its paragraphs: Whereas para. 1 sets out the continental margin criterion, paras. 2 to 7 substantially modify it, rather than merely implementing it. Put differently, implementing paras. 2 to 7 may not always lead to continental shelf limits that extend to the ‘outer edge of the continental margin’ as mentioned in para. 1. This interrelationship was further acknowledged by the International Tribunal for the Law of the Sea (ITLOS) in its 2012 judgment on the Bay of Bengal case, where it held that para. 1 of Article 76 UNCLOS ‘should be understood in light of the subsequent provisions of the article defining the continental shelf and the continental margin’ [para. 437]. Due to this interrelationship between paras. 1 to 7, these provisions could be considered as an ‘indivisible regime’ and, consequently, Article 76 UNCLOS could be regarded in its entirety as constituting CIL. In its 2012 judgment on the Territorial and Maritime Disputes case, the ICJ relied on the concept of the ‘indivisible regime’ to conclude that the integrity of Article 121 UNCLOS qualifies as CIL [para. 139].

The interrelationship of the provisions of Article 76 UNCLOS is further reinforced by another consideration: If paragraph 1 were to be recognised as CIL, but the ensuing provisions were not, a non-party would be able to define its ECS on the basis of other criteria, while avoiding the restrictions imposed by the ensuing provisions. This is an assessment that has been put forward by a number of scholars, including Baumert [pp. 975-6] and Oxman [p. 411]. The latter argues that not accepting paras. 2 to 7 as CIL is an ‘audacious contention’, leading to a situation where the ‘status as a non-party [would] not only relieve [a non-party] of the duty to comply with the institutional provisions of the LOSC but [would] confer upon it the exceptional benefit of a continental shelf that is not limited by the detailed substantive criteria and constraints set forth in Article 76’ [fn. 52]. In his dissenting opinion appended to the 2023 judgment on the Delimitation of the Continental Shelf case, Judge Tomka alluded to the interrelationship of paras. 1 to 7, stating that ‘[t]here is no doubt […] that the other key provisions [i.e., paras. 2 to 7] defining the outer limits of the continental shelf beyond 200 nautical miles are also reflective of customary international law’ [para. 21]. This position was contradicted by other scholars, such as Suarez, Tanaka and Golitsyn. In 2008, Suarez argued that ‘there is a widely- accepted view that the continental shelf beyond 200 [nautical miles] is not part of customary international law’ [p. 181]. In 2012, Tanaka noted that ‘it would be difficult to argue that the continental shelf beyond 200 nautical miles is part of customary international law’ due to the lack of widespread State practice and opinio juris [p. 140]. According to Golitsyn, Article 76 ‘can hardly be viewed as a reflection of customary international law’ [pp. 401, 405].

It is therefore necessary to carefully assess whether, today, paras. 2 to 7 have attained the status of CIL. This requires the identification of the two constituent elements of CIL: a general State practice and the acceptance of that practice as law (opinio iuris). In view of the fact that UNCLOS has 168 States parties, it could be said that it ‘has given rise to a general practice that is accepted as law (opinio iuris), thus generating a new rule of [CIL]’ [p. 143]. To ascertain the element of opinio iuris, reference may be had to domestic laws, declarations, regulations, or other similar enactments of legislative or executive bodies constituting State practice. Some coastal states, including Brazil, Costa Rica, Namibia, and South Africa, have accepted all of paras. 2 to 7 through the adoption of statutory law. The enactments of the coastal States of Chile, Ecuador, Iceland, Madagascar, and Trinidad and Tobago employ one or more of the formulas (para. 4) or limitations (para. 5 and 6) of Article 76. Yet, as the International Law Commission (ILC) rightly noted in its 2018 Draft conclusions on the identification of customary international law, it must be demonstrated that States ‘engage in the practice not (solely) because of  the treaty obligation, but out of a conviction that the rule embodied in the treaty is or has become a rule of [CIL]’ [p. 144]. Consequently, the enactments of States parties to UNCLOS are hardly conclusive in determining whether Article 76 is part of CIL.

Thus, special attention should be paid to the practice of non-parties, the practice of parties in relation to non-parties, and vice versa [p. 146]. In 1988, six years prior to the entry into force of UNCLOS, the States parties to the Antarctic Treaty agreed that the ‘continental shelf […] would be determined by reference to all the criteria and the rules embodied in paragraphs 1 to 7 of Article 76 of the [UNCLOS].’ The maritime boundary treaty between Ireland and the United Kingdom (UK) was drawn up on the basis of the detailed provisions of Article 76 and was concluded before the two States became parties to UNCLOS in 1988. In 2017, Cuba, which is a party to UNCLOS, entered into a maritime delimitation treaty with the United States relating to their respective continental shelves, relying on the provisions contained in paras. 2 to 7 of Article 76. Along with the US, Peru is another non-party, which considers paras. 2 to 7 as reflecting CIL; in its memorial to the ICJ in the Maritime Dispute case, the latter referred to ‘the customary rules codified in Article 76 of the 1982 Convention’ [para. 7.25]. In the recent contentious proceedings against Colombia (non-party), Nicaragua (party) has expressed the view that it considers the provisions of paras. 2 to 7 as part of the CIL [paras. 20, 21].

On the basis of these considerations, the conclusion can be drawn that paras. 2 to 7 of Article 76 are now an integral part of CIL.

Status of the Scientific and Technical Guidelines of the Commission on the Limitation of the Continental Shelf

In accordance with the provisions of Annex II to UNCLOS, the Commission on the Limitation of the Continental Shelf (CLCS) has issued Scientific and Technical Guidelines (Guidelines) to facilitate the preparation of submissions by coastal States. Although it is evident that these Guidelines do not per se constitute CIL, the ICJ found in its 2023 judgment on the Continental Shelf Delimitation case ‘that the practice of States before the CLCS is indicative of opinio iuris, even if such practice may have been motivated in part by considerations other than a sense of legal obligation’ [para. 77]. The ILC has also supported this view, noting that the ‘[c]onduct of [non-State] actors is not practice that contributes to the formation, or expression, of rules of customary international law, but may be relevant when assessing [State] practice’ [p. 37]. Consequently, to the extent that coastal States have adhered to the Guidelines in their submissions to the CLCS, their provisions can be considered as constituting CIL.

Non-Party Submission and Binding Force of the American Delineation?

According to para. 8 of Article 76 UNCLOS, the ‘limits of the shelf established by a coastal State on the basis of the [CLCS’s] recommendations shall be final and binding’. The binding force of such a delineation by a party or non-party may extend to all parties and non-parties, if para. 8 of Article 76 UNCLOS can be regarded to form part of CIL. Consequently, this would mean that a non-party could file a submission to CLCS.

In the past, the US took the position that due to its non-party status, it did not have access to CLCS [p. 10]. However, it appears that this position may have changed. In fact, the US has most recently published an executive summary in relation to its ECS, in which it states that:

‘The United States is also open to filing its submission package with the Commission as a non-Party to the Convention. This would be consistent with the Commission’s mandate to provide recommendations and advice to coastal States concerning the outer limits of the continental shelf and would support the rules-based system under the Convention for delineating the continental shelf and the seabed area beyond national jurisdiction.’

This statement indicates that the US considers para. 8 also to be reflective of CIL, thereby allowing it to institute a procedure before CLCS and confer binding force on its delineation. Yet, this position seems very questionable.

McDorman [pp. 303-4] and Pedrozo [pp. 152-3] argued that the Commission’s mandate does not prevent a non-party from using it. As of the end of 2023, coastal States have made 93 submissions to CLCS pursuant to para. 8 of Article 76 UNCLOS. As each of these was made by a coastal State that was a party to the Convention at the time of its submission, none provides clear support that para. 8 reflects CIL. Additionally, there is a lack of enactments and declarations by coastal States which would suggest that para. 8 is part of CIL. For lack of general State practice and opinio iuris, paragraph 8 does not appear to constitute CIL. Thus, non-parties do not have access to CLCS.  Elferink [p. 2], Wolfrum [p. 6], Baumert [p. 979], Mao, Li, Liu, and Zhang [pp. 7-8] share this view. It is also in line with the declarations and separate opinions of four judges, namely Donoghue, Mensah, Cot, and Robinson, who were involved in the 2012 Territorial and Maritime Dispute case. Donoghue noted that non-party ‘States have no duty to make submissions to the Commission’ [para. 28]. Mensah argued that ‘the obligations under Article 76, paragraphs 8 and 9, are “treaty obligations” that apply only as between States that have expressed their consent to be bound by the UNCLOS treaty’ [para. 8]. Cot observed that ‘[i]t is difficult to regard paragraph 8 as an expression of customary law[;] [t]he provision institutes a specific procedure which is not accessible to non-member States’ [paras. 19-20]. Robinson considered that ‘there can be no doubt that the provision in Article 76 (8) of UNCLOS establishes a procedure that is only open to States parties to UNCLOS’ [para. 11].

It follows that the US as a non-party does not have access to the CLCS. Therefore, the American delineation is not binding nor final and has the same status as the outer limits of any other maritime zone: It remains for other States to assess the acceptability of such limits by reacting or not reacting.

It should be noted that CLCS has allowed the US, as a non-party, to submit communications regarding the submissions made by States parties to UNCLOS, as indeed it did for the submissions made by Russia and Canada. Thus, CLCS is not opposed to non-party participation. It remains to be seen if and how it will react to a non-party submission.

Concluding Remarks

The view that Article 76 in its entirety already fulfils the conditions for becoming a rule of CIL must be treated with great caution. Such a view obliterates the boundary between treaty law and customary law. Certainly, the determination of whether a provision of UNCLOS has the status of CIL cannot be arbitrarily based on the national interests of a State, but should rather depend on whether it fulfils the constituent elements of CIL.

As the US is not a party to UNCLOS, it must rely on CIL as the legal foundation for its continental shelf rights. Yet, to fully secure these rights, including establishing its outer limits with legal certainty, the most secure way for the US is to have access to Article 76 and the CLCS procedures as a party to UNCLOS.  This would provide the highest level of legal certainty and international recognition for the outer limits of its continental shelf, while also increasing international credibility. For the US, as the world’s leading maritime power, this is all the more crucial.

Since Raegan, US accession to UNCLOS has been on the agenda of every administration, but to no avail due to Senate gridlock. Nevertheless, these domestic issues must not lead to a practice whereby the US may simply declare certain provisions of UNCLOS to be CIL in order for them to apply in its case. The Senate does not consider accession to UNCLOS particularly advantageous, and this practice seems to be one of the reasons [p. 6]. However, allowing non-parties to pick and choose which provisions of UNCLOS they consider beneficial to their position and therefore applicable as rules of CIL would undermine the authority of UNCLOS. Becoming a State party, which is obligated to follow all UNCLOS provisions regardless of their benefit to national interests, would be of little use if such a practice were permitted.

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Naomi Burke says

January 17, 2024

Thank you, Khaled, for this very interesting analysis.
If paragraph 8 is not CIL, does it necessarily follow that non-parties do not have access to CLCS? Non-parties would not have an obligation to submit information to the CLCS but I see some merit in the argument that they are not prevented from doing so. On the other hand, there is potentially an argument to be made in relation to Article 4 of Annex II – if States Parties are obliged to submit at a minimum preliminary information within 10 years of the entry into force of the Convention for that State, is it fair to allow non-State parties to submit at any time?

Of course, if paragraph 8 is not CIL it can be said that State Parties are not obliged to recognise as final and binding the limits of the US shelf established on the basis of CLCS recommendations. But it may be in the interests of State Parties to do so, considering the protection of their joint interest in the resources of the Area. I agree that the best option would be for the US to ratify UNCLOS. But pending that ratification, I can see the benefit to States Parties in having the limits of the US shelf established in accordance with the CLCS procedure. (Query as to which is more likely to happen first, US ratification, or the CLCS getting through all of its pending submissions….)

Finally, I am curious as to what would happen if the US does make a submission to the CLCS. One could assume the CLCS might ask the UN Legal Counsel for advice – I’m sure they will be reading your post with great interest if that is the case.

Andrew Serdy says

January 17, 2024

I entirely agree with Naomi (hi!) regarding para 8. That leaves me with an observation and a question:
Even if paras 2 to 7 are not CIL (though para 3 at minimum surely is, since it defines what is meant by the term "continental margin" used in para 1 whose status as CIL was as you say confirmed in 2012), if the US is thinking of making a submission to the CLCS it could hardly do other than use the formulae of paras 4 to 7, as the CLCS itself has no mandate to consider anything else. Moreover, having maintained since 1987 that paras 2 to 7 are CIL, the US can no longer credibly argue to the contrary even though para 3 alone would, as you imply, allow it a broader continental shelf than under paras 4-7.
And the question: you say that all recent administrations have supported US accession to UNCLOS, but does that include Trump's? My impression during those years was that this was one of many international law questions best left unasked, in order not to lead the US to commit itself to an answer no one else would like.

Kevin Baumert says

January 17, 2024

Thank you, Khaled, for this thoughtful piece. There’s one part, however, that is not quite right, and it relates to observations made by Naomi and Andrew: the quote from the U.S. Executive Summary regarding the U.S. being “open” to filing as a non-party does not “indicate that the US considers para. 8 also to be reflective of CIL.” That’s not a position the U.S. has ever taken. If the U.S. considered para. 8 to be CIL, presumably the U.S. would have filed its submission with the CLCS, since para. 8 contains a legal obligation to do so. (“Information on the limits of the continental shelf beyond 200 nautical miles . . . shall be submitted by the coastal State . . . .”)

Rather, the legal inference to be drawn is that the U.S. considers a non-party submission to the CLCS to be legally permissible: it is neither required nor is it prohibited. I.e., just because para. 8 is not part of CIL does not mean there is a legal problem with a non-party sending information to the CLCS. (What the CLCS does with that information is a separate question pertaining to the CLCS’s mandate under the Convention.)

Accordingly, I don’t see any picking and choosing by the U.S. based on whether the provisions are “beneficial to their position”. As Khaled points out, paras. 1 to 7 are CIL whereas para 8 is not. The U.S. is following the former and not the latter. That said, the U.S. stated that it is open to following para. 8 (even though it is not required). For reasons explained well in this piece, that would seemingly be beneficial to all, not just the United States.

Arron Honniball says

January 17, 2024

Thanks for an interesting read Khaled!
Regardless of the question of whether Article 76(8) is CIL –for which I don't believe non-Parties could question lawfully established limits, or vice versa if non-Parties did garner CLCS recommendations– is the key not in the hands of the CLCS to determine if they will furnish their advisory function to non-Parties? I.e., not whether a coastal state submission is permissible, but whether it will be considered.
Naomi raises some further interesting questions to explore. The submission deadline disparity is somewhat further reflected on page 6 where a Contracting Party submission will be “upon [USA] accession to the Convention”; while a Non-Contracting Party submission is without reference to any applicable timeframe.
Finally, I would imagine the position of State Parties will be of great importance for the CLCS in considering whether recommendations are furnished. The USA appears to have understandably focused on asking neighbouring states with overlapping entitlements whether they would object to consideration by the CLCS. The Executive Summary cannot be taken as an exhaustive account (no objections are reported) but apparently “Canada has advised the United States that it would not object to the consideration of a U.S. submission by the Commission…The Bahamas has similarly advised the United States that it would not object to the consideration of a U.S. submission by the Commission” (p. 25).
Would a sensible middle ground be to have a non-contracting party submission requesting not to take any action for the time being until further Parties views garnered, or the state becomes a contracting party?

Khaled El Mahmoud says

January 17, 2024

Dear Naomi,

Thanks for raising these interesting questions.

I also find the argument that non-State parties are not obliged to make submissions, but are not legally prohibited from doing so, to be quite persuasive. However, it is unclear whether the CLCS would actually be authorised to consider such a non-party submission.

From a strictly legal and dogmatic perspective, I consider it difficult to see how it would be possible for the CLCS, a treaty body specifically established under UNCLOS, to consider the submission of a non-party. A State's entitlement to make a submission to the CLCS is based on its status as a party to UNCLOS. By the same logic, the authority of the CLCS to consider such a submission is also limited by UNCLOS and cannot be extended ratione personae beyond the scope of the treaty. In my view, to do otherwise would be tantamount to acting ulta vires.

Furthermore, even if one were to consider such submissions as possible and the CLCS as authorised to review them, the delineation could not be final and binding, as pointed out in your comment, since it would seem unconscionable for non-parties to be able to reap benefits of not ratifying UNCLOS. Non-parties cannot be granted additional rights which do not yet exist under CIL.

This begs the question: to what extent is a non-party submission beneficial?
Considering that other states can react to the delineation of non-parties as they would to the delineation of any other maritime zone outside of CLCS procedures, and that the recommendations of CLCS will not result in a delineation with final and binding effect, it can be said that there is no real advantage in non-party submissions.

Providing the possibility for non-parties to participate in the CLCS procedures by filing their communications in relation to the delineation of States parties appears to be sufficient to advance the international interest in the clarification of maritime boundaries.

I am more than happy to discuss this further if you are interested.


Khaled El Mahmoud says

January 17, 2024

Dear Andrew,

To the best of my knowledge, the Trump administration has not expressly voiced its support or opposition to the ratification of UNCLOS. Yet, it would appear that Secretary Pompeo's statement on the South China Sea contains what could be seen as an implicit endorsement of UNCLOS (for a complete analysis, cf.


Mark Seidenberg says

January 18, 2024

I have trying since 19 December 2023 announcements by both NOAA and the U. S. Department of State how the could make a claim to that area shown in the posted map,
since it would have to include a territorial sea baseline from the Plover Group (4 islands that existed in year 1850 to the north of Russian America that included Cooper and Martin islands) which is now to the north of Alaska.

It was on 1 August 1850 at
8:30 pm that the British Royal

Navy took formal possession of the Plover Group in the name of Queen Victoria.

During the night of 29 - 30 March 1867, William Hunter (2nd Assistant Secretary of State) informed the other drafter of the Alaska Treaty the UK was the sovereign of the Plover Group to the north of Russian America.

During meetings in The Hague, Netherlands between 13 March - 12 April 1930, Samuel Wittemure Boggs (Geographer of State) offer to conceded Machias Seal Island of the Western Seal Islands in Washington County, Maine to New Brundswick for a British concession of the Plover Group to the USA. The offer was made to William Eric Beckett (2nd Legal Advisor of the British Foreign Office) as am Imperial Question. Beckett agreed with Boggs that it was an Imperial Question, but rejected Boggs view that it could be handled other than by Treaty. So the British Foreign Office rejected the proposal of a territory swap.

In August 1938 Boggs tried it again with the Federal Government of Canada. That government also reject an island exchange. Boggs did not return to Ottawa until 31 March 1944.

Any ideas as to how the baseline of the territorial sea is drawn to the east of Plover Point, Alaska?

Andrew Serdy says

January 18, 2024

Dear Khaled
Thanks for the Pompeo pointer.
Further to your reply to Naomi, the CLCS not long after it came into existence posed to one of the early meetings of the States Parties the question of whether it could entertain submissions from non-parties to UNCLOS, only to receive the reply that the States Parties saw no need to answer the question until a concrete case arose, something that has only now come into prospect. It does show, though, that the CLCS is sensibly reticent to act unilaterally on a non-party's submission.
As to whether a non-party's outer limit on the basis of any CLCS recommendations it might receive is final and binding, in practice the answer would be yes even if formally it might be no. After all, the ex hypothesi concordance between the recommendations and the outer limit would mean that the submitting State would have applied the rules of paras 4 to 7 correctly in the Commission's view, so any party to seeking to challenge that would be facing an uphill battle. On the other hand, parties may be more likely to question whether non-parties' outer limits really are "on the basis of" the recommendations, which to date they have not done in respect of fellow parties, yet would be unable to use the Part XV dispute settlement mechanisms to that end.
Lastly, I am not convinced that the benefits of outer limits being final and binding runs all one way, in the submitting State's favour. The "binding" part yes, more or less, but the burden of the finality also falls on that State; it does not get a second chance to make a submission if new technologies or new scientific understandings postdating its completion of the Article 76 process indicate that its continental margin extends further than previously thought. That to my mind is a sufficiently balanced outcome to avoid being tarred as unconscionable.
Best wishes

Coalter Lathrop says

January 19, 2024

This is a great discussion. Thank you, Khaled, for kicking it off with your thorough analysis.

In the not unlikely event that the US does not accede to the Convention (possibly ever, unfortunately) and the Commission does not make recommendations, where might the US claim end up?

Would it be subject to perpetual and universal uncertainty or could it live (perhaps uncomfortably) in a web of bilateral relationships based in the "logic of opposability" (borrowing from E Bjorge's 2021 piece in BYIL)?

Although there is no obligation to do so, it seems that interested states could make their own assessments of the US claim (assuming the US is willing to share the whole of the "data and other material" on which the claimed limits are based), and respond or act accordingly thereby signalling agreement or objection. That is, individual states could step into the shoes of the Commission and "check the math".

With agreement (partial or total), the US claim (or part of it) may be opposable to the agreeing state(s) (only). With objection (tacit or express), the US claim would remain a non-opposable unilateral act with respect to objecting states.

I was struck by the number of current and former Commissioners who provided assistance on the US claim (14 from 14 different countries) [p 13 of the executive summary]. This, alone, says nothing about agreement at the state level, but it does point to the capacity of many states (from Malaysia to Mexico to Mozambique, from Scandinavia to the tip of South America) to undertake a rigorous assessment of the underlying scientific and technical data used by the US to assemble its claimed outer limit.

Ideally, the US accedes and the Commission provides recommendations, etc. That isn't where we are.

Second best, the Commission provides recommendations on a non-party submission.

Perhaps the above represents the third best outcome for the purposes of certainty and stability in a less-than-ideal world?