Written reply of Ecuador to the questions put by Judges Cleveland, Tladi, Aurescu and Charlesworth at the end of the hearing held on 13 December 2024

INTERNATIONAL COURT OF JUSTICE
OBLIGATIONS OF STATES IN RESPECT
OF CLIMATE CHANGE
(REQUEST FOR ADVISORY OPINION)
RESPONSE OF THE REPUBLIC OF ECUADOR TO THE QUESTIONS PUT BY
JUDGES CLEVELAND, TLADI, AURESCU AND CHARLESWORTH
20 DECEMBER 2024

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TABLE OF CONTENTS
Introduction………………………………………………………………………….1
Judge Cleveland’s Question…………………………………………………………1
Judge Tladi’s Question………………………………………………………………3
Judge Aurescu’s Question………………………………….......................................6
Judge Charlesworth’s Question……………………………………………………...7
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Introduction
1. The Republic of Ecuador (‘Ecuador’) hereby submits its response to the questions
posed by Judges Cleveland, Tladi, Aurescu, and Charlesworth at the closing of the oral hearing
of 13 December 20241, in accordance with the instructions provided by the letter of the
Registrar of the same date and by the President of the Court on 2 December 20242.
2. Ecuador welcomes this opportunity to clarify certain legal aspects of the law applicable
to the subject-matter of the present proceeding that may not have been fully apparent even after
lengthy written and oral submissions by States and international organizations participating in
this case. Each question put by the Judges is addressed below in turn, so as to assist the Court.
Judge Cleveland’s Question
3. Judge Cleveland asked:
“During these proceedings, a number of participants have referred to the production of
fossil fuels in the context of climate change, including with respect to subsidies. In your
view, what are the specific obligations under international law of States within whose
jurisdiction fossil fuels are produced to ensure protection of the climate system and
other parts of the environment from anthropogenic emissions of greenhouse gases, if
any?”
4. States within whose jurisdiction fossil fuels are produced have a particular position in
relation to the climate crisis, and consequently bear certain obligations that are specific to them,
while also considering the principles of equity and common but differentiated responsibilities
(‘CBDR’).
5. At the outset, States are obliged to adopt mitigation measures towards transitioning
away from fossil fuels in energy systems in a just, orderly and equitable manner. This
1 CR2024/54, pp. 39-40.
2 CR2024/35, p. 95.
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obligation derives from Article 4(1) and (2) of the Paris Agreement and customary international
law3, and is based on the best available science concerning mitigation pathways4.
6. A related obligation finds expression in Article 2(1)(c) of the Paris Agreement, which
refers to “[m]aking finance flows consistent with a pathway towards low greenhouse gas
emissions and climate-resilient development”. This obligation entails for States within whose
jurisdiction fossil fuels are produced that they must curtail their finance flows in support of the
production of fossil fuels, in particular by phasing out related subsidies. They may indeed do
so gradually – especially if they are developing countries whose economies are highly
dependent on income generated from fossil fuel production5 – but within a clear timeframe that
takes into consideration the evolving circumstances of the climate crisis. They may also
promote the use of transitional fuels in energy systems that are critical to a country’s energy
security6.
7. States within whose jurisdiction fossil fuels are produced must also increase finance
flows for low-emission renewable energy as part an effort to diversify their economies and
reduce their reliance on fossil fuels. They must not undermine such support by continuing at
the same time to direct significant finance flows towards the production of fossil fuels, as that
would be incompatible with both the letter and spirit of the climate change treaty regime.
8. Developed States within whose jurisdiction fossil fuels are produced are also under an
obligation to support developing countries, including through financing for clean energy
transitions.
9. Finally, States within whose jurisdiction fossil fuels are produced must cooperate in
promoting scientific, technological, technical, socio-economic, and other research, as well as
the transfer of technology, relating specificallty to clean energy transition technologies and
related climate adaptation efforts.
3 Written Statement of Ecuador, para. 3.30.
4 IPCC, Climate Change 2023: Synthesis Report. A Report of the Intergovernmental Panel on Climate Change.
Contribution of Working Groups I, II, and III to the Sixth Assessment Report of the IPCC (2023), p. 21.
5 See also United Nations Framework Convention on Climate Change (‘UNFCCC`), Articles 4.8(h) and 4.10.
6 UNFCCC, Decision 1/CMA.5, Outcome of the first global stocktake (FCCC/PA/CMA/2023/16/Add.1, 13
December 2023, para. 29.
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Judge Tladi’s Question
10. Judge Tladi formulated the following question:
“In their written and oral pleadings, participants have generally engaged in an
interpretation of the various paragraphs of Article 4 of the Paris Agreement. Many
participants have, on the basis of this interpretation, come to the conclusion that, to the
extent that Article 4 imposes any obligations in respect of Nationally Determined
Contributions, these are procedural obligations. Participants coming to this conclusion
have, in general, relied on the ordinary meaning of the words, context and sometimes
some elements in Article 31 (3) of the Vienna Convention on the Law of Treaties. I
would like to know from the participants whether, according to them, “the object and
purpose” of the Paris Agreement, and the object and purpose of the climate change
treaty framework in general has any effect on this interpretation and if so, what effect
does it have?”
11. The UNFCCC and the Paris Agreement must be interpreted in accordance with the rules
of treaty interpretation laid down in Articles 31-33 of the Vienna Convention on the Law of
Treaties (‘VCLT’), which reflect customary international law7. The object and purpose of the
treaty is one of main elements of interpretation to be taken into account. As paragraph 1 of
Article 31 makes clear: “A treaty shall be interpreted in good faith in accordance with the
ordinary meaning to be given to the terms of the treaty in their context and in the light of its
object and purpose”8. Treaty interpretation is a “single combined operation” – all elements
should be considered to arrive at the meaning to given to a text, as appropriate9.
12. The Paris Agreement contains key obligations for States in respect of climate change,
not least in its Article 4, which addresses nationally determined contributions (‘NDCs’). Many
of those obligations may be considered “procedural”, as described by some participants in these
proceedings. This is notably the case of the obligation under paragraph 2 to prepare,
communicate and maintain successive NDC’s, which must be fulfilled in accordance with the
requirements laid down in other provisions of the same article.
7 Sovereignty over Pulau Ligitan and Pulau Sipadan (Indonesia/Malaysia), Judgment, I.C.J. Reports 2002, p. 625,
para. 37; Certain Questions of Mutual Assistance in Criminal Matters (Djibouti v. France), Judgment, I.C.J.
Reports 2008, p. 177, para. 153.
8 Emphasis added.
9 ILC, Draft conclusions on subsequent agreements and subsequent practice in relation to the interpretation of
treaties (2018), Conclusion 2(5).
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13. However, not all the obligations under Article 4 of the Paris Agreement are
“procedural” in nature. Notably, paragraph 2 of Article 4 provides that “Parties shall pursue
domestic mitigation measures, with the aim of achieving the objectives of [NDCs]”. The
ordinary meaning of this provision makes clear that States have a substantive obligation to
design, adopt and implement (“pursue”) mitigation measures at the domestic level to achieve
the goals of their NDCs.
14. This obligation is one of due diligence in that it does not require States to achieve a
particular result, but to make best efforts to obtain that result. Ecuador has already explained
elsewhere the standard that should be applied when assessing whether a due diligence
obligation has been properly fulfilled, including in the specific context of climate change10.
Similar conduct is required from States under the principle of prevention and the duty to protect
and preserve the marine environment under customary international law, and the obligation to
adopt and implement measures to prevent, reduce and control pollution of the marine
environment under UNCLOS.
15. The scope of Article 4 of the Paris Agreement is clarified by the object and purpose of
the Agreement, as well as that of the UNFCCC. Article 2 of the Paris Agreement states that its
aim is to “strengthen the global response to the threat of climate change, in the context of
sustainable development and efforts to eradicate poverty” 11. This must be done by holding the
increase of global average temperature to well below 1.5º-2º C above pre-industrial levels12;
increasing the ability to adapt to the adverse effects of climate change13; and providing
appropriate finance flows14; all while reflecting the principles of equity and CBDR15.
16. The object and purpose of the Paris Agreement is aimed at “enhancing the
implementation of the [UNFCCC], including its objective”16. Article 2 of the UNFCCC, for its
part, states that:
10 See, for example, Written Comments of Ecuador, para. 65, referring to the findings of the International Tribunal
for the Law of the Sea on this matter in the COSIS Advisory Opinion.
11 Paris Agreement, Article 2(1).
12 Paris Agreement, Article 2(1)(a).
13 Paris Agreement, Article 2(1)(b).
14 Paris Agreement, Article 2(1)(c).
15 Paris Agreement, Article 2(2).
16 Paris Agreement, Article 2(1).
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“The ultimate objective of this Convention and any related legal instruments that the
Conference of the Parties may adopt is to achieve, in accordance with the relevant
provisions of the Convention, stabilization of greenhouse gas concentrations in the
atmosphere at a level that would prevent dangerous anthropogenic interference with the
climate system. Such a level should be achieved within a time-frame sufficient to allow
ecosystems to adapt naturally to climate change, to ensure that food production is not
threatened and to enable economic development to proceed in a sustainable manner.”
17. Ecuador considers that the object and purpose of the UNFCCC and the Paris Agreement
inform the ordinary meaning of the provisions of Article 4 of the Paris Agreement. The
obligation to “pursue domestic mitigation measures”, for example, must be carried out in such
way that the greenhouse gas concentrations in the atmosphere are indeed stabilized, and the
global response to the threat of climate change is effectively strengthened. All States parties to
the UNFCCC and the Paris Agreement must pursue domestic mitigation measures, but the
obligation of developed countries with high historical emissions is more stringent in light of
the principles of equity and CBDR, expressly incorporated in the treaties to achieve an
equitable result when tackling climate change.
18. The object and purpose of the UNFCCC and the Paris Agreement must also be taken
into account when interpreting the obligation to prepare, communicate and maintain successive
NDCs, on the basis of which domestic mitigation measures are to be pursued. Some
participants argued during the proceedings that the implementation of this obligation is left to
the discretion of States, who alone can determine, for example, which mitigation measures are
necessary and in which time frame they may be implemented. Such a claim for unlimited
discretion is clearly at odds with the object and purpose of the UNFCCC and the Paris
Agreement. An NDC that does not reflect the level of ambition required by the treaty regime,
in light of the agreed standards and the best available science, would be in breach of the relevant
obligations. In the same vein, domestic mitigation measures pursued on the basis of NDCs that
are not compatible with the Paris Agreement would be contrary to international law as well.
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Judge Aurescu’s Question
19. Judge Aurescu asked:
“Some Participants have argued, during the written and/or oral stages of the
proceedings, that there exists the right to a clean, healthy and sustainable environment
in international law. Could you please develop what is, in your view, the legal content
of this right and its relation with the other human rights which you consider relevant
for this advisory opinion?”
20. Many participants in these proceedings indeed maintained that the right to a clean,
healthy and sustainable environment forms part of the corpus of general international law, be
it as a rule of customary international law or a general principle of law. The UN General
Assembly recently confirmed this, recognizing the right to a clean, healthy and sustainable
environment as a human right17. It did so while, inter alia, noting that “a vast majority of States
have recognized some form of the right to a clean, healthy and sustainable environment through
international agreements, their national constitutions, legislation laws or policies”18, and that
said right is “related to other rights and existing international law”19.
21. Determining the specific content of the right to a clean, healthy and sustainable
environment would require an assessment pursuant to the methodology for the identification
of rules of customary international law or general principles of law, as applicable. The content
of the right as a rule of customary international would necessitate showing the existence of
sufficient State practice accompanied by opinio juris. As regards general principles of law, one
would need to ascertain the existence of a principle common to the various legal systems of the
world and its transposition to the international legal system.
17 UN General Assembly resolution 76/300, 28 July 2022, para. 1.
18 Ibid., last preambular paragraph.
19 Ibid., para. 2.
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Judge Charlesworth’s Question
22. Judge Charlesworth asked:
In your understanding, what is the significance of the declarations made by some States
on becoming parties to the UNFCCC and the Paris Agreement to the effect that no
provision in these agreements may be interpreted as derogating from principles of
general international law or any claims or rights concerning compensation or liability
due to the adverse effects of climate change?”
23. Upon joining the UNFCCC and the Paris Agreement, eleven States made declarations,
which have not encountered opposition by other States20. For the UNFCCC, Tuvalu’s
declaration is representative:
“The Government of Tuvalu declares its understanding that signature of the Convention
shall in no way constitute a renunciation of any rights under international law
concerning state responsibility for the adverse effects of climate change, and that no
provisions in the Convention can be interpreted as derogating from the principles of
general international law”.
24. For the Paris Agreement, the declaration of the Cook Islands is representative:
“The Government of the Cook Islands declares its understanding that acceptance of the
Paris Agreement and its application shall in no way constitute a renunciation of any
rights under international law concerning State responsibility for the adverse effects of
climate change and that no provision in the Paris Agreement can be interpreted as
derogating from principles of general international law or any claims or rights
concerning compensation due to the impacts of climate change.
The Government of the Cook Islands further declares that, in light of the best available
scientific information and assessment on climate change and its impacts, it considers
the emissions reduction obligations in the aforesaid Paris Agreement to be inadequate
to prevent a global temperature stabilisation level at or above 1.5 degrees Celsius
relative to pre-industrial levels and as a consequence, such emissions will have severe
implications for our national interests”.
20 A total of thirteen declarations were made by eleven States, with some States making declarations for both
treaties. As regards the UNFCCC, declarations were made by Fiji, Kiribati, Nauru, Papua New Guinea, and
Tuvalu. For the Paris Agreement, declarations were made by the Cook Islands, the Marshall Islands, Micronesia
(Federated States of), Nauru, Niue, Solomon Islands, Tuvalu, and Vanuatu. Nauru and Tuvalu made declarations
for both treaties.
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25. The declarations, made at the time of the conclusion21 of the treaties and consistently
formulated to preserve existing rights and obligations under international law, qualify as
permissible interpretive declarations governed by the law of treaties.
26. They do not, like reservations22, seek to “exclude or modify the legal effect” of treaty
provisions23, but rather to “specify or clarify the meaning or scope” of the UNFCCC and the
Paris Agreement, specifically as regards their relationship with other rules of international
law24. When “interpreted in good faith in accordance with the ordinary meaning to be given to
its terms, with a view to identifying therefrom the intention of its author, in light of the treaty
to which it refers”, their purpose is clear25. Moreover, as the International Law Commission
(‘ILC’) clarified, when a treaty prohibits reservations, as both the UNFCCC and the Paris
Agreement do26, unilateral statements should be presumed not to constitute reservations27.
27. The declarations confirm the conclusion of the vast majority of participants in these
proceedings that the UNFCCC and the Paris Agreement do not constitute lex specialis and do
not displace other rules of international law that may be applicable in the context of climate
change. As Ecuador explained in its submissions, while these treaties contain specific
provisions addressing climate change mitigation, adaptation, cooperation, and loss and
damage, they do not displace or supersede the applicability of other relevant rules, including
those derived from customary international law, general principles of law, and other treaty
regimes, such as UNCLOS and human rights treaties, as well as the law of state responsibility.
The relationship between the climate change treaty regime and other rules of international law
must be assessed on a case-by-case basis, taking into account the specific content and scope of
the rule in question, including its object and purpose28.
21 While the term ‘conclusion’ of a treaty is not clearly defined in the VCLT, for interpretative declarations the
most appropriate meaning is a contextual and pragmatic one. The term should be understood broadly as
encompassing the entire process of joining a treaty, including signature, ratification, and accession. See R.
Gardiner, Treaty Interpretation, 2nd ed. (OUP, 2017), pp. 234-235.
22 ILC, Guide to Practice on Reservations to Treaties (2011), Guideline 1.3.3.
23 Ibid., Guideline 1.1
24 Ibid., Guideline 1.2.
25 Ibid., Guideline 1.3.1.
26 The UNFCCC and the Paris Agreement prohibit reservations in Article 24 and Article 27 respectively.
27 ILC, Guide to Practice on Reservations to Treaties (2011), Guideline 1.3.3.
28 Written Comments of Ecuador, para. 18.
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28. For the avoidance of any doubt, Ecuador reiterates that the above conclusion obtains
irrespective of the interpretative declarations, based on the general rules of interpretation and
conflict of norms. Absent these declarations, there would still be no basis in the UNFCCC and
the Paris Agreement themselves or elsewhere for concluding that they displace other norms of
international law altogether. The relationship between the various rules of international law
relating to climate change remain informed by complementarity and mutual supportiveness29.
29. While interpretive declarations cannot alter treaty obligations or override the parties’
common intent, they can nevertheless inform and influence the subsequent interpretation
process.
30. In this connection, the ILC has emphasised the importance of considering the reaction
of States to such declarations in assessing their weight. It clarified that, contrary to reservations,
approval of or opposition to an interpretative declaration “shall not be presumed”30 and that
“[a]n approval of an interpretative declaration shall not be inferred from the mere silence of a
State or an international organization”31. However, approval or opposition may be “inferred in
exceptional cases from the conduct of States”32.
31. The declarations referred to by Judge Charlesworth may represent such an exceptional
case. They address a central and critically important issue: the relationship between the
UNFCCC framework and established rules of general international law.
32. The declarations made upon joining the UNFCCC and reiterated when concluding the
Paris Agreement reaffirm that the climate regime does not constitute lex specialis and does not
displace other rules of international law that may be applicable in the context of climate change.
The consistent repetition of the declarations by States that are particularly vulnerable to the
adverse effects of climate change, the complete absence of contemporary or subsequent
objections to the declarations, and the clear significance of the issue at stake, are evidence of
29 Written Comments of Ecuador, para. 17.
30 ILC, Guide to Practice on Reservations to Treaties (2011), Guideline 2.9.8(1).
31 Ibid., Guideline 2.9.9.
32 Ibid., Guideline 2.9.8(2).
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acquiescence33. Had States disagreed with the declarations’ premise, they would have raised
objections – indeed they had ample opportunity to do so.
33. It bears noting that the threshold for assessing acquiescence to interpretative
declarations must be distinguished from the higher threshold that applies when a State seeks to
establish specific bilateral obligations through silence, as was the case in Obligation to
Negotiate Access to the Pacific Ocean. In that case, the question was whether an obligation
could be established, inter alia, on the basis of acquiescence to statements claiming the
existence of the obligation34. While an exacting standard may apply where it is alleged that
declarations would have required a response to prevent an obligation from arising, the same
need not apply where declarations are merely confirmatory of the continued operation of
general international law alongside treaty commitments.
34. This understanding is also supported by the arguments advanced by a majority of States
before the Court, which align with the declarations, despite these States having neither
endorsed nor opposed the declarations at the time they were made.
35. Irrespective of whether individual States explicitly or implicitly approved them, the ILC
confirmed that declarations may be considered as elements of treaty interpretation35. They do
not automatically qualify as context under Article 31(2)(b) or as subsequent agreements or
practice under Article 31(3) of the VCLT unless other parties demonstrably acquiesce, either
explicitly or implicitly, to their relevance for the interpretation of the treaty. However, they
may be relied upon as supplementary means of interpretation under Article 32.
36. The weight and persuasive force accorded to declarations under Article 32 of the VCLT
depend on their ability to shed light on a common understanding shared by the parties to the
33 Decision regarding delimitation of the border between Eritrea and Ethiopia, 13 April 2002, RIAA Vol. XXV,
p. 111, para. 3.9 (“In each case the ingredients are the same: an act, course of conduct or omission by or under the
authority of one party indicative of its view of the content of the applicable legal rule—whether of treaty or
customary origin; the knowledge, actual or reasonably to be inferred, of the other party, of such conduct or
omission; and a failure by the latter party within a reasonable time to reject, or dissociate itself from, the position
taken by the first”), referring to Case concerning the Temple of Preah Vihear (Cambodia v. Thailand), Merits,
Judgment of 15 June 1962, I.C.J. Reports 1962, p. 6.
34 Obligation to Negotiate Access to the Pacific Ocean (Bolivia v. Chile), Judgment, I.C.J. Reports 2018., pp.
52-54, paras. 149-152.
35 ILC, Guide to Practice on Reservations to Treaties (2011), Guideline 4.7.1.
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treaty36. In this specific case, the consistency of the declarations, the lack of opposition to them,
and the arguments made by a majority of States before the Court are evidence of a shared
understanding that the UNFCCC and the Paris Agreement do not displace other rules of
international law.
36 The Iron Rhine (Ijzeren Rijn), Award, 24 May 2005, RIAA, vol. XXVII, p. 63, para. 48.