How to Study Public International Law

Public International Law

Author: Dr. Bommuluri Bhavana Rao

Notes- LB-205 Public International Law syllabus

Nature and development of international law; sources; the relationship between international and municipal law; state responsibility; law of the sea; state jurisdiction; and sovereign, diplomatic, and consular immunity. It also prescribes foundational instruments including the UN Charter, the Statute of the International Court of Justice, the ICCPR, the ICESCR, the European Convention on Human Rights, UNCLOS, the 1994 Part XI Agreement, and India’s Maritime Zones Act.

Syllabus unit	Chapter
Nature and development of international law	Foundations; institutions; sanctions; third world perspectives
Sources of international law	Treaties, custom, general principles, subsidiary means, resolutions
Relationship between international and municipal law	Monism, dualism, treaty implementation, India-UK-US comparison
State responsibility	Attribution, breach, excuses, reparation, local remedies, ILC Articles
Law of the sea	Maritime zones, delimitation, seabed resources, India’s maritime law, ITLOS
State jurisdiction	Territoriality, nationality, extraterritoriality, universal jurisdiction, extradition, asylum
Immunities	Sovereign immunity; diplomatic and consular law; personal and functional immunities

Background

Public international law begins with the legal ordering of relations among states, but it does not end there. The UN Charter made sovereign equality, good-faith performance, peaceful settlement, and collective security foundational principles of the post-1945 legal order. Article 2 requires peaceful settlement of disputes and prohibits the threat or use of force inconsistent with the Charter; Chapter VII authorizes the Security Council to determine threats to the peace and to impose non-forcible and forcible measures; and Article 51 preserves the inherent right of individual and collective self-defence if an armed attack occurs. The Charter is not merely a political compact. It is the constitutional framework of contemporary public international law. 

The post-1945 order also widened the subject matter of international law. The Universal Declaration of Human Rights in 1948, followed by the ICCPR and the ICESCR in 1966, shifted the discipline away from an exclusively inter-State orientation toward a law that also protects persons. The Reparation for Injuries advisory opinion supplied the other great post-war move: the recognition that an international organization can possess international personality and capacity to bring claims in its own right. Together, these developments explain why the LB-205 syllabus appropriately treats states, international organizations, and individuals as part of one conceptual field. 

That widening did not erase the discipline’s asymmetries. A serious PIL course must also read the field through colonial history, decolonization, and Third World critiques. The advisory opinions in Western Sahara and Chagos show that self-determination and decolonization remain legally operative, not merely historical. They also remind us that the “universal” vocabulary of international law was often formed under unequal political conditions, and that anti-colonial struggles profoundly reshaped the law’s content, especially on territorial title, peoples’ rights, and institutional legitimacy. 

The sanctions and institutional dimension of the syllabus is equally well chosen. The Security Council’s sanctions system illustrates how international law can coerce without always resorting to armed force. Under Article 41, the Council may impose non-military measures; historically it has established 31 sanctions regimes, with 15 ongoing today, supported by sanctions committees, monitoring groups, and delisting mechanisms. Sanctions, however, do not operate in isolation; they sit alongside adjudication, treaty-body review, fact-finding, monitoring, and domestic implementation. Legal education should therefore treat “sanctions of international law” broadly, rather than reducing them to criminal or militarized enforcement alone. 

For example, a Security Council resolution imposes an asset freeze and travel ban on leaders of a non-state armed group operating across the territory of three States. One listed individual challenges the measure before a domestic court, arguing that the listing violated minimum procedural fairness. The question is not only whether the Council acted lawfully under Chapter VII, but also how domestic courts, due process expectations, and delisting procedures interact with binding UN obligations.

Why is it misleading to say that international law has no sanctions because it has no world police? How did the move from classic inter-State law to post-1945 institutional law alter the meaning of legal personality? In what ways do decolonization and Third World critiques reframe standard histories of international law?

Official texts and judgments for further reading. UN Charter; UDHR; ICCPR; ICESCR; Reparation for Injuries; Western Sahara; Chagos. 

I.                Sources of international law

The classic starting point remains Article 38 of the ICJ Statute, which identifies treaties, custom, general principles, and subsidiary means. The article is not a complete sociology of norm-production, but it remains the principal doctrinal map for legal argument. The modern task for everyone is to learn not only the list but also the method: how one proves a treaty rule, how one identifies custom, how one distinguishes general principles from policy, and how one uses resolutions and judicial decisions without confusing them with primary sources. 

Treaties are the most concrete source. The Vienna Convention on the Law of Treaties states the canonical rule of pacta sunt servanda in Article 26 and the corollary rule in Article 27 that a party may not invoke its internal law as justification for failure to perform a treaty. Treaty interpretation is then structured by the VCLT’s good-faith method, read in context and in light of object and purpose. In teaching, this means that treaty law is not just about ratification; it is about interpretation, reservations, subsequent practice, invalidity, and termination. 

Customary international law is methodologically harder. The ILC’s 2018 Conclusions on the Identification of Customary International Law reaffirm the two-element approach: a general practice accepted as law, or opinio juris. The North Sea Continental Shelf cases remain the cornerstone because the ICJ insisted that a treaty rule becomes custom only where practice is sufficiently extensive and virtually uniform and is accompanied by a sense of legal obligation. The Asylum case supplies the complementary lesson that a claimed regional or local custom must be shown by constant and uniform usage accepted as law. The Lotus case continues to matter because it dramatizes the permissive structure of jurisdictional reasoning: sovereignty gives regulatory space unless a prohibitive rule can be shown. 

General principles are not an invitation to free-form moral reasoning; they are legal principles sufficiently common to major municipal systems or inherent in adjudication itself, such as good faith, finality, responsibility for wrongful conduct, and procedural fairness. Judicial decisions and the writings of highly qualified publicists are subsidiary means for determining rules, not independent law-making powers. Yet in practice, judgments are indispensable because they discipline legal argument and make the evidence of custom, treaty interpretation, and general principles legible. 

General Assembly resolutions, Security Council resolutions, and advisory opinions occupy an intermediate space that we often misread. General Assembly resolutions are usually not binding by themselves, but they may crystallize or evidence opinio juris, shape institutional authority, and influence interpretation. The Nuclear Weapons advisory opinion illustrates how Assembly resolutions can matter to custom formation without automatically becoming custom. Security Council resolutions, by contrast, may be binding under the Charter framework, and Namibia remains a principal illustration of the legal consequences of Council action. Advisory opinions such as Western Sahara, Kosovo, and Chagos are formally non-binding, but they can be jurisprudentially decisive in institutional practice and persuasive across the wider system. 

Source	Core method of identification	Typical classroom mistake	Best doctrinal corrective
Treaties	Text, context, object and purpose, good faith	Treating signature as the end of analysis	Start with interpretation and domestic effect
Custom	General practice plus opinio juris	Confusing repetition with legality	Ask whether States acted from legal obligation
General principles	Comparative or systemic legal reasoning	Turning equity into free discretion	Tie the principle to adjudicative necessity or common legal traditions
Judicial decisions	Persuasive evidence and clarification	Treating one case as universal custom	Ask what source the court was applying
Resolutions and soft law	Context, institutional authority, normative pull	Assuming all resolutions bind equally	Distinguish evidence, interpretation, and binding Chapter VII measures

Let us take an example.  State A and State B have no fisheries treaty. State A claims there is now a customary rule prohibiting certain driftnets on the high seas because many Assembly resolutions condemn them and dozens of States have adopted domestic bans. State B replies that political support is not enough. One should separate State practice, opinio juris, treaty analogy, scientific evidence, and soft-law influence.

Why is Article 38 still central despite the growth of institutions and soft law? How do North Sea and the ILC Conclusions discipline claims about emerging custom? When can a UN resolution matter legally even if it is not binding in the same way as a treaty or a Chapter VII decision?

Official texts and judgments for further reading. ICJ Statute; VCLT; ILC Conclusions on Custom; Lotus; North Sea Continental Shelf; Asylum; Nuclear Weapons; Namibia. 

II.            International law and municipal law

The classical theories are familiar: monism imagines a unified legal order in which international and domestic norms form one hierarchy; dualism treats them as separate systems requiring transformation or incorporation. In practice, modern states rarely fit neatly into either ideal type. The real lawyer’s question is functional: when does a treaty or customary rule become judicially usable in a domestic court, and when is legislative intermediation required? The VCLT’s Article 27 settles one point at the international level: a State cannot justify treaty breach by invoking its internal law. But it does not tell a domestic court how nationally to rank treaty norms in its own constitutional system. 

India’s practice is best taught as pragmatic constitutional accommodation. (Berubari, Jolly George Varghese, Gramophone Company, Vellore, Vishaka, and Puttaswamy). Taken together, those cases support three broad propositions. First, treaties that alter rights, liabilities, or territory ordinarily require municipal implementation. Second, courts may read constitutional and statutory provisions, where possible, consistently with international obligations. Third, international human rights and environmental norms can significantly shape domestic constitutional reasoning when there is no direct statutory contradiction. The official record for Vellore shows the Supreme Court’s centrality in domesticating precaution and polluter-pays reasoning, while Puttaswamy demonstrates the modern Court’s willingness to situate privacy within a wider constitutional and international rights discourse. Later Supreme Court decisions have also continued to cite Gramophone Company and Vishaka as leading authorities on the use of international law in interpretation.  

Comparative practice

A.   In the United States, modern doctrine distinguishes between self-executing and non-self-executing treaties, a distinction highlighted in the official materials around Medellín v. Texas.

B.   In the United Kingdom, the better pedagogical point is not to overstate theory but to show how PIL questions still reach domestic courts through immunity, foreign act of state, human rights, and legislative interpretation; the UK Supreme Court’s materials in Belhaj and Reyes make that plain.

C.   The “relationship doctrine” is not a purely constitutional puzzle. It shapes extradition, sanctions implementation, human-rights litigation, environmental regulation, and the reception of international judgments. 

Illustrative hypothetical. India ratifies a new treaty on transboundary digital surveillance but Parliament has not yet enacted implementing legislation. A petitioner argues that Indian courts should nevertheless read Article 21 and data-protection statutes in conformity with the treaty. A second petitioner argues that the treaty cannot be used at all absent legislation. The classroom task is to test both arguments against the logic of Vishaka, Puttaswamy, and Article 27 of the VCLT.

Is Article 27 of the VCLT a rule for international responsibility, a rule for domestic courts, or both? What is the doctrinal difference between using international law as an interpretive aid and giving it direct domestic force? Why does India’s practice resist simple classification as wholly monist or wholly dualist?

Official texts and judgments for further reading. VCLT Articles 26 and 27; India’s syllabus cases on reception; Vellore; Puttaswamy; UK Supreme Court materials in Belhaj and Reyes; U.S. Supreme Court materials in Medellín. 

III.         Subjects, Jurisdiction, Immunities, and Responsibility

States, international organizations, individuals, and corporations

States remain the primary subjects of international law because the Charter is built on the sovereign equality of Members and because States remain the principal makers, addressees, and enforcers of rules. Recognition, succession, and responsibility therefore remain central doctrinal questions. But the category of “subject” is no longer exhausted by statehood. The Reparation for Injuries opinion held that the United Nations possesses international personality and may bring claims in its own right, while the modern human-rights and criminal-law regime recognizes individuals not merely as objects of state action but as holders of rights and, in some fields, bearers of direct international responsibility. 

Corporations occupy an ambiguous middle ground. They are not “subjects” in the same plenary way as States, but they plainly participate in international legal processes. Barcelona Traction remains essential for explaining corporate nationality and the limits of shareholder protection through diplomatic protection. At the same time, current institutional practice shows that corporations and investors regularly appear in international dispute settlement, especially in ICSID and PCA proceedings. The lesson is that subjectivity is functional and sectoral, some entities have only the capacities given to them by specific regimes. 

Illustrative hypothetical. A multinational enterprise incorporated in State A, controlled by shareholders from State B, and operating in State C alleges expropriation and environmental mistreatment. Which entities can appear internationally, and on what legal basis: State A, State B, the corporation, the shareholders, or affected individuals?

What did Reparation for Injuries actually decide about international personality? Does recognition create statehood, acknowledge it, or sometimes do both? Why is it more accurate to speak of “capacities under international law” than of fixed yes-or-no subject status?

Official texts and judgments for further reading. UN Charter Articles 2 and 4; Reparation for Injuries; Kosovo; Western Sahara; Chagos; Barcelona Traction; ICC and human-rights instruments. 

IV.          Jurisdiction, extradition, asylum, and immunities

Jurisdiction is best explained through the tension between sovereignty and restraint. The Lotus case is still the canonical starting point because it portrays international law as permitting State action unless a prohibitive rule is shown. From there, one should move to the better-organized contemporary categories: territorial jurisdiction, nationality jurisdiction, protective and passive personality theories, universal jurisdiction, and various forms of extraterritorial regulation.

Jurisdiction becomes practically urgent where a State seeks custody over persons or conduct with cross-border links. 

Asylum and extradition reveal the limits of unilateralism. In Asylum case, the Court rejected Colombia’s claim because the alleged regional custom had not been proved by constant and uniform usage accepted as law. India’s Extradition Act, 1962, remains the basic statutory framework for the surrender of fugitives in Indian law. For consular access, LaGrand and Jadhav are now indispensable, both demonstrate that the Vienna Convention on Consular Relations creates concrete procedural obligations, and that failures of notification and access can have judicial consequences at the ICJ. 

Immunity cuts across all of this. Arrest Warrant case tells the distinction between substantive responsibility for international crimes and procedural immunity from the criminal jurisdiction of foreign states for certain incumbent senior officials. Jurisdictional Immunities of the State confirms that state immunity is a procedural rule protecting sovereign equality in domestic courts even amid serious allegations, unless a recognized exception applies. Diplomatic and consular law must then be understood through the concrete failures and remedies seen in Tehran Hostages, LaGrand, and Jadhav.

Modern national decisions such as Reyes and Belhaj are valuable because they show how domestic courts handle diplomatic immunity, state immunity, and foreign act-of-state reasoning where grave rights claims are pleaded in ordinary litigation. 

Doctrine	Core idea	Leading authority
Territorial jurisdiction	Primary basis of jurisdiction over acts and effects in territory	Lotus
Regional or local custom	Requires constant and uniform usage accepted as law	Asylum
Consular notification and access	Procedural rights of detained foreign nationals	LaGrand, Jadhav
Personal immunity	Incumbent senior officials may enjoy immunity from foreign criminal process	Arrest Warrant
State immunity	Procedural immunity of the State in foreign domestic courts	Jurisdictional Immunities

The table synthesizes the doctrinal structure reflected in the official case pages and summaries. 

Illustrative hypothetical. A foreign defence minister visits State X. While there, prosecutors in State X seek an arrest warrant for war crimes allegedly committed years earlier in the minister’s home State. At the same time, the minister’s official vehicle collides with a civilian, and a domestic tort suit is filed. One should analyze criminal jurisdiction, personal immunity, state immunity, and the distinction between official and private acts.

What does Lotus still teach after the expansion of treaty regulation? Why is universal jurisdiction conceptually distinct from immunity? Are LaGrand and Jadhav better understood as human-rights cases, consular-law cases, or federalism/implementation cases?

Official texts and judgments for further reading. Lotus; Asylum; India’s Extradition Act, 1962; Arrest Warrant; Jurisdictional Immunities; Tehran Hostages; LaGrand; Jadhav; Reyes; Belhaj. 

V.             State responsibility

The modern law of state responsibility is anchored in the ILC’s Articles on Responsibility of States for Internationally Wrongful Acts, adopted in 2001 and widely treated as the organizing framework of the field. The essential structure is simple but enormously productive: there must be conduct attributable to the State, a breach of an international obligation, and no valid circumstance precluding wrongfulness. Once responsibility is established, secondary rules govern cessation, assurances of non-repetition, reparation, invocation, and in some cases aggravated legal consequences. 

Attribution and breach are best explained through cases. Corfu Channel is fundamental for due diligence and the obligation not knowingly to allow one’s territory to be used for acts contrary to the rights of other States. Tehran Hostages demonstrates both direct State responsibility and a State’s responsibility for adopting and endorsing conduct initially carried out by private actors. Nicaragua remains central on the distinction between prohibited intervention, use of force, and the lawfulness of self-defence, while also offering a disciplined model of fact-law separation. LaGrand illustrates that procedural treaty obligations can ground responsibility just as much as classical territorial wrongs. 

Reparation is the natural sequel. The classic forms remain restitution, compensation, satisfaction, and assurances or guarantees of non-repetition. Recent ICJ practice shows that reparations are not theoretical. In the 2022 reparations judgment in Armed Activities on the Territory of the Congo, the Court engaged in a detailed remedial assessment. In environmental injury cases, the reparations phase now often turns on valuation methodology, ecological damage, uncertainty, and evidentiary approximation. Barcelona Traction should also be mentioned here because it links responsibility to diplomatic protection and to the distinction between obligations owed to a particular State and obligations owed to the international community more broadly. 

Jus cogens(peremtory norms)

The ILC’s 2022 text on peremptory norms notes the link between serious breaches of peremptory norms and obligations erga omnes, and it states that circumstances precluding wrongfulness cannot justify non-conformity with obligations arising from jus cogens. This helps one see responsibility not as a narrow bilateral dispute technique, but as part of the public order dimension of the international legal system. 

Illustrative hypothetical. State A’s cyber units secretly support a proxy group that disables the hospital network and port-management systems of State B. State A denies operational control but publicly praises the attackers and refuses to investigate. The class should test attribution, breach, due diligence, countermeasures, and reparation.

Why does the law of state responsibility distinguish primary from secondary rules? How do Tehran Hostages and Corfu Channel differ as models of attribution or due diligence? What is gained, analytically, by treating reparation as a separate stage rather than as part of breach?

Official texts and judgments for further reading. ILC Articles on State Responsibility; Corfu Channel; Tehran Hostages; Nicaragua; LaGrand; Armed Activities on the Territory of the Congo; ILC text on jus cogens. 

VI.          Peace, Security, Human Rights, Humanitarian Law, and International Criminal Law

Use of force, self-defence, and collective security

The legal architecture of force begins with the Charter. Article 2(4) prohibits the threat or use of force; Article 39 empowers the Security Council to determine threats to the peace, breaches of the peace, or acts of aggression; Article 41 authorizes non-military measures; and Article 51 preserves self-defence if an armed attack occurs, while requiring reporting to the Security Council and preserving the Council’s overriding competence. Any serious discussion of force must therefore begin from the presumption of prohibition, not from an assumption of sovereign freedom. 

The Nicaragua case remains the indispensable judicial exposition because it distinguishes the gravest forms of force from lesser frontier incidents, ties collective self-defence to actual armed attack and request, and resists attempts to smuggle interventionist policies into the legal category of self-defence. The Nuclear Weapons advisory opinion, though not a comprehensive code, adds two essential propositions: any threat or use of force must comply with the Charter, and any use of force must also satisfy the rules of international humanitarian law. These cases show one should keep three questions in mind: was there force, was there lawful authority, and were the means and methods lawful? 

Collective security should be observed institutionally, not abstractly. The Security Council’s sanctions practice demonstrates the range of Article 41 measures, from asset freezes and travel bans to arms embargoes and commodity restrictions. Today’s 15 ongoing sanctions regimes show that sanctions have become an ordinary legal technology of peace and security governance. But sanctions also generate due-process questions, implementation burdens, and domestic constitutional challenges, all of which belong in a serious PIL classroom. 

Illustrative hypothetical. State C invokes collective self-defence on behalf of State D after a series of cyber intrusions disables air-traffic systems and emergency services in D. No kinetic attack occurs, and attribution remains contested. We should ask what counts as an “armed attack,” what evidence is needed, whether anticipatory arguments are being smuggled in, and how proportionality and necessity would operate if force were used in response.

Does Article 51 codify, preserve, or limit an older inherent right? Why is the Security Council’s sanctions practice central to the law on force even when no armed action is authorized? Can an unlawful use of force ever be lawful in its methods under IHL, or are the questions conceptually distinct?

Official texts and judgments for further reading. UN Charter Articles 2, 39, 41 and 51; Nicaragua; Nuclear Weapons. 

VII.       Dispute Settlement

The Charter’s Article 33 framework and the ICJ’s own materials on its history and function make an important point - peaceful settlement is plural, not monopolized by courts. Negotiation, inquiry, mediation, conciliation, arbitration, judicial settlement, and recourse to regional agencies all remain valid methods. The ICJ’s jurisdiction in contentious cases depends on State consent, whether by special agreement, compromissory clause, or optional-clause declaration; advisory jurisdiction is structurally different because it serves institutional clarification rather than inter-State consent in the same way. One should therefore learn forum-selection as part of substantive law. 

ITLOS has both contentious and advisory jurisdiction and has received 33 cases to date. The PCA, a treaty-based intergovernmental organization established in 1899, now services an unusually diverse portfolio: inter-State arbitration, treaty-based investment disputes, contract disputes involving States, and other proceedings. These institutions matter because PIL is no longer litigated only in one court. Procedural design, applicable law, confidentiality, enforcement, and technical specialization all vary forum by forum. 

Regional courts add another layer. The ECHR’s annual report and statistical system illustrate a highly institutionalized rights court. The Inter-American Court and African Court likewise show that regional judicialization is not merely derivative of Europe. For instructors, the practical lesson is that “Public International Law” should not be taught as if the ICJ were the only judicial voice that matters. The analytical lesson is that tribunals often cross-reference each other’s reasoning, creating a dense and evolving network of persuasive authority. 

Illustrative hypothetical. Two coastal States dispute detention of a foreign-flag vessel, alleged environmental harms, and investor losses under a concession agreement. The class should identify which issues could go to the ICJ, ITLOS, PCA, or ICSID, and which legal or strategic features would influence the choice.

Why is forum selection a substantive legal issue rather than merely a procedural one? How does State consent operate differently in contentious and advisory proceedings? When should a PIL lawyer prefer arbitration to adjudication, or a regional court to a global one?

Official texts and judgments for further reading. UN Charter Article 33; ICJ jurisdiction materials; ITLOS case page; PCA case statistics; ECHR annual report; regional court case portals. 

VIII.    The law of the sea

UNCLOS structures maritime zones, coastal-state rights, navigation freedoms, marine environmental obligations, delimitation rules, seabed governance, and dispute settlement. The UNCLOS, the 1994 Part XI Agreement, and India’s 1976 Maritime Zones Act makes plain that one is expected to connect treaty law, institutional design, and Indian statutory implementation. India Code confirms the 1976 Act’s scope and structure, including sections on territorial waters, the contiguous zone, the continental shelf, the EEZ, historic waters, and maritime boundaries.  

Delimitation jurisprudence should be learnt historically and comparatively. North Sea Continental Shelf remains essential for method and equity in delimitation reasoning. The Bangladesh/Myanmar case before ITLOS and the Bay of Bengal arbitration between Bangladesh and India show how modern tribunals operationalize delimitation in highly technical settings. 

Maritime Delimitation in the Indian Ocean (Somalia v. Kenya) demonstrates that delimitation remains a live, politically sensitive field of adjudication rather than a settled cartographic science. The Bay of Bengal and Enrica Lexie proceedings are especially useful because they connect PIL doctrine to India’s own maritime practice and litigation experience. 

The law of the sea is also where institutional innovation becomes visible. ITLOS’s first case was M/V Saiga, and the Tribunal’s official materials still present it as the starting point of its jurisprudence. The Seabed Disputes Chamber’s 2011 advisory opinion on sponsoring State obligations under Part XI remains foundational for the “common heritage of mankind” and due-diligence obligations relating to activities in the Area. Most dramatically, the 2024 ITLOS climate advisory opinion held that anthropogenic greenhouse gas emissions into the atmosphere can constitute “pollution of the marine environment” within UNCLOS, treated the relevant obligations as stringent obligations of due diligence, and specified duties of regulation, enforcement, cooperation, monitoring, and support for vulnerable developing States. That opinion belongs in every modern PIL course because it shows how UNCLOS has become a major climate-law instrument as well as a law-of-the-sea treaty. 

Illustrative hypothetical. State X authorizes deep-seabed exploratory activity through a private corporation it sponsors. Meanwhile, its land-based coal policies and ship registry generate large greenhouse-gas emissions with marine effects. One should ask how different parts of UNCLOS organize responsibility for seabed activities, atmospheric pollution affecting the sea, flag-State enforcement, and cooperation duties.

Why is the law of the sea an unusually good field for learning the interaction of treaty text, technical fact, and equitable reasoning? How has ITLOS changed the practical operation of UNCLOS? Does the 2024 climate advisory opinion show adaptation of old treaty language to new environmental realities, or judicial overreach? Defend your answer.

Official texts and judgments for further reading. UNCLOS and the 1994 Part XI Agreement; India’s Maritime Zones Act; North Sea Continental Shelf; Bangladesh/Myanmar; Bay of Bengal arbitration; Somalia v. Kenya; M/V Saiga; Seabed Disputes Chamber Advisory Opinion; ITLOS 2024 climate advisory opinion.