Introduction
The legal campaign to use international courts and tribunals to clarify states’ climate obligations under international law reached a historic milestone in 2024. The International Tribunal for the Law of the Sea (ITLOS) delivered its Advisory Opinion on Climate Change and International Law on 21 May 2024, holding that anthropogenic greenhouse gas emissions constitute “pollution of the marine environment” under UNCLOS, and that states parties therefore have specific, enforceable treaty obligations to reduce emissions that cause marine environment damage. Six months later, hearings began at the International Court of Justice on a request from the UN General Assembly for an Advisory Opinion on the obligations of states under international law in respect of climate change, a process initiated through UNGA Resolution A/77/276 of March 2023 driven by a coalition of Pacific Island states and champion the Vanuatu-led “Pacific Islands Students Fighting Climate Change” initiative.
These two proceedings represent a strategic judicial diplomacy campaign of remarkable sophistication: rather than litigating emissions disputes between specific states (which would face significant jurisdictional and causation problems), climate-vulnerable states and civil society actors have used the advisory opinion mechanism, which does not require adversarial standing between specific parties, to obtain authoritative international legal guidance on what international law requires. The opinions themselves, even as non-binding instruments in the strict formal sense, carry enormous persuasive authority and are expected to shape climate negotiations, domestic climate litigation, and the international community’s understanding of state responsibility for climate harm.
This article examines the legal framework for climate obligations under international law, the procedural and substantive features of the ITLOS and ICJ advisory opinion processes, the implications for state liability and reparations, India’s position as a major developing economy bearing significant climate impacts despite historically low per-capita emissions, and the lessons drawn from the Nuclear Weapons Advisory Opinion (1996).
Legal Framework
The international legal framework applicable to climate change obligations draws from several distinct bodies of law, and a central question in both the ITLOS and ICJ proceedings is how these bodies of law interact. The primary treaty regime is the UN Framework Convention on Climate Change (UNFCCC, 1992), its Kyoto Protocol (1997), and most significantly the Paris Agreement (2015), which commits states to holding global average temperature increase to well below two degrees Celsius above pre-industrial levels and pursuing efforts to limit it to 1.5 degrees Celsius. The Paris Agreement’s nationally determined contributions (NDCs) structure allows states to set their own emission reduction targets, creating a framework that is legally binding in procedural terms (states must communicate, update, and implement NDCs) but not in substantive terms (no specific reduction level is legally mandated at the international level).
Beyond the UNFCCC regime, multiple sources of international law create climate-relevant obligations. UNCLOS Articles 192 to 194 impose obligations on states to protect and preserve the marine environment and to prevent, reduce, and control pollution from any source, including pollution of the marine environment. The definition of “pollution of the marine environment” in UNCLOS Article 1(1)(4) includes the introduction of substances or energy that results in deleterious effects on living resources and marine life, human health, or marine activities. The central legal question before ITLOS was whether anthropogenic GHG emissions, which increase atmospheric CO2 concentrations, cause ocean acidification, coral bleaching, and sea level rise, constitute “pollution” within this definition.
General international law, particularly the Trail Smelter principle (derived from the 1941 US-Canada arbitration) and the ICJ’s Corfu Channel dictum, establishes the customary law obligation of states not to knowingly allow their territory to be used for acts contrary to the rights of other states. Applied to climate change, this principle supports the argument that states emitting GHGs at levels that cause transboundary damage to other states (including island states’ territorial inundation, coastal erosion, and agricultural disruption) violate their international obligations regardless of specific treaty commitments.
The ILC’s Articles on State Responsibility are relevant to the consequences of any breach: a state found to have violated its climate obligations would be required to cease the violation, offer assurances and guarantees of non-repetition, and make full reparation for injury caused. The reparation framework (restitution, compensation, satisfaction) applies. The causation challenge, connecting a specific state’s emissions to specific harm in another state, has long been considered the principal obstacle to climate liability claims.
The ITLOS Advisory Opinion (May 2024)
ITLOS issued its Advisory Opinion in Case No. 31 (Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law) on 21 May 2024. The Commission of Small Island States (COSIS), established by Antigua and Barbuda and Tuvalu in 2021 and subsequently joined by other small island states, submitted a request under Article 21 of the ITLOS Statute, which grants the Tribunal advisory jurisdiction at the request of any body authorised by the Agreement establishing ITLOS.
The Tribunal held, by a significant majority, that: (1) anthropogenic GHG emissions constitute “pollution of the marine environment” under UNCLOS Article 1(1)(4); (2) states parties have obligations under UNCLOS to take all necessary measures to prevent, reduce, and control marine environment pollution from GHG emissions, consistent with the best available science; (3) these obligations are obligations of conduct (requiring states to take serious and effective measures) rather than obligations of result (they do not mandate achieving a specific emissions level), but the threshold for compliance is higher than a purely procedural commitment; and (4) developing states have certain additional rights to receive assistance (capacity building, technology transfer, financing) from developed states in meeting their UNCLOS climate obligations.
The significance of the ITLOS Opinion lies in its translation of abstract climate commitments into specific legal obligations grounded in a binding, universal treaty. UNCLOS has 168 parties, and the Opinion’s interpretation of UNCLOS creates climate obligations for all of them as a matter of treaty law, not merely as aspirational policy. The Opinion specifically addressed the science-law interface: it held that states’ obligations must be assessed against the best available science, meaning that the IPCC’s findings constitute the relevant scientific standard for compliance assessment. This grounding in IPCC science gives the opinion both authority and updating capacity as scientific understanding of climate impacts develops.
The ICJ Advisory Opinion Process
The UN General Assembly Resolution A/77/276, adopted in March 2023 on the initiative of Vanuatu and a coalition of Pacific and other climate-vulnerable states, requested the ICJ to provide an Advisory Opinion on two questions: (1) what obligations do states have under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic GHG emissions; and (2) what are the legal consequences under these obligations for states which, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, particularly for Small Island Developing States and developing countries in general?
The ICJ conducted its oral hearings in December 2024 and January 2025, with an unprecedented number of states and international organisations making submissions: over one hundred states filed written statements, and dozens participated in oral hearings. This breadth of engagement reflects both the importance of the issue and the utility of advisory opinions as a vehicle for comprehensive multilateral input on international law questions.
The ICJ’s Advisory Opinion is expected in 2025 or early 2026. The key legal questions the Court must address include: (1) what sources of international law are relevant, and how do they interact (UNFCCC, Paris Agreement, UNCLOS, customary law, human rights treaties); (2) whether obligations with respect to GHG emissions are obligations of conduct or of result; (3) what causation standard is applicable for establishing state responsibility for climate harm; and (4) what reparation, if any, is owed to states harmed by others’ emissions.
The causation question is the most legally complex. International law requires a causal link between a wrongful act and the harm for which compensation is sought. For climate change, the scientific concept of “attribution science” (probabilistic attribution of specific weather events or gradual harms to particular emissions sources or temperature increases) has advanced dramatically, but translating this into a legal causation standard that can attribute specific harm in Small Island Developing States to the emissions of specific states requires judgments about contribution, foreseeability, and the threshold of de minimis contributions.
Comparison with the Nuclear Weapons Advisory Opinion (1996)
The Nuclear Weapons Advisory Opinion is the most instructive precedent for understanding the ICJ climate advisory opinion’s likely structure and limitations. In 1996, the ICJ addressed the question of whether the threat or use of nuclear weapons is permitted under international law. The Court reached a remarkably ambiguous conclusion: it was unable to conclude definitively that nuclear weapons use is legal or illegal in all circumstances, but it held that any use of nuclear weapons would have to comply with IHL requirements and that the use of nuclear weapons would “generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law.” The Court unanimously agreed that states have an obligation to pursue in good faith nuclear disarmament negotiations.
The Nuclear Weapons Opinion illustrates several dynamics likely relevant to the climate opinion: (a) advisory opinions can articulate important legal principles without fully resolving the political controversy; (b) the ICJ is reluctant to reach absolute conclusions that would effectively govern state policy in areas of deep geopolitical sensitivity; (c) the unanimous or near-unanimous holding on an obligation to negotiate in good faith provides normative authority even when substantive legal conclusions are hedged. For climate, an analogous outcome might involve the Court holding that states have obligations of conduct (to pursue climate action in good faith, consistent with the best available science and the Paris Agreement framework) while hedging on the precise remedial consequences.
Contemporary Issues and Analysis
The advisory opinion strategy pursued by COSIS and the Vanuatu coalition is legally innovative because it sidesteps the most difficult obstacles to direct climate litigation between states: the need to establish specific bilateral jurisdiction, the attribution of specific harm, and the standing of claimant states to sue particular respondents. Advisory opinions are available to the ICJ on any legal question submitted by an authorised body; they apply to all states, not just litigants; and they carry the moral and persuasive authority of the Court without requiring a claimant to prove damages suffered.
The strategy also builds on a broader ecosystem of climate litigation. By 2024, over two thousand climate-related legal cases had been filed in domestic courts globally, and several landmark decisions had been issued: the Dutch Supreme Court’s Urgenda judgment (2019, confirming the government’s obligation to reduce emissions sufficiently to protect human rights); the German Constitutional Court’s Neubauer judgment (2021, holding that insufficient climate action violated future generations’ constitutional rights); and the European Court of Human Rights’ Verein KlimaSeniorinnen judgment (2024, finding that Switzerland violated the Convention by failing to take adequate measures to protect the applicants’ right to life against climate change risks). An ICJ advisory opinion endorsing broad state obligations would amplify and reinforce this domestic litigation wave.
India’s Position
India’s position in the ICJ advisory opinion proceedings reflects the complexity of a country that is simultaneously one of the world’s largest emitters (third globally in absolute terms) and one of the world’s most climate-vulnerable countries (subject to intensifying monsoon variability, sea level rise threatening coastal populations and the Sundarbans, and increasing heatwave frequency and intensity), while also being a developing country with hundreds of millions of people still lacking access to reliable energy and a historical per-capita emissions contribution far below that of developed countries.
India submitted written observations in the ICJ proceedings emphasising the principle of Common But Differentiated Responsibilities and Respective Capabilities (CBDR-RC), enshrined in the UNFCCC, which affirms that all states have obligations in respect of climate change but that developed countries, which contributed most to the accumulation of GHGs in the atmosphere through their historical industrialisation, bear primary responsibility and must lead in mitigation and finance. India argued that the advisory opinion should affirm CBDR-RC as a principle of customary international law, not merely a treaty provision, and should confirm that developing countries’ obligations are calibrated according to their capabilities and historical contributions.
India also resisted any framing of the advisory opinion that would impose identical obligations on all states regardless of historical responsibility, and has been alert to the risk that climate litigation could be weaponised against developing countries investing in the energy infrastructure needed for their development. India’s domestic climate commitments (the NDC updated in 2022 targeting 45% reduction in emissions intensity of GDP by 2030, 50% of cumulative electric power installed capacity from non-fossil fuel sources by 2030) are, India argues, ambitious and adequate given its development stage.
India’s advocacy for climate finance from developed countries to support developing-country adaptation and mitigation is central to its international climate diplomacy. The “Loss and Damage” mechanism established at COP27 (Sharm el-Sheikh, 2022) and operationalised at COP28 (Dubai, 2023) provides a financial mechanism for addressing the irreversible harms of climate change in vulnerable countries, a development India supported as consistent with the equity principles it champions.
Practical and Policy Implications
An ICJ advisory opinion affirming broad state obligations with respect to climate change, particularly if it endorses a causal connection between high-emitting states and harm to climate-vulnerable states, could catalyse a wave of inter-state claims before international tribunals. Pacific Island states have already indicated that they may bring claims against major emitting states before the ICJ or ITLOS following the advisory opinions. The causation obstacles remain significant, but the development of attribution science, which can now probabilistically connect specific quantities of emissions to specific temperature increases and consequent harms, provides a technical foundation for such claims that did not exist a decade ago.
For the international climate finance system, advisory opinions confirming that states have legal obligations (not merely political commitments) to provide finance for adaptation and loss and damage in vulnerable countries could strengthen the legal basis for claims against inadequate climate finance provision.
Suggestions and Reforms
The international legal climate framework would benefit from several reforms informed by the advisory opinion proceedings. First, the Paris Agreement should be supplemented by a protocol establishing legally binding minimum mitigation commitments for major emitting states (the top twenty emitters account for approximately eighty percent of global emissions), with a dispute settlement mechanism that allows affected states to challenge inadequate NDCs before an independent body.
Second, the Loss and Damage mechanism established at COP27/28 should be given a legal foundation in a binding treaty that specifies both developed-country contributions and the criteria for allocation of funds, transforming what is currently a political arrangement into an enforceable legal obligation.
Third, the ICJ should be encouraged by states parties to develop a specific climate chamber or fast-track procedure for climate-related advisory requests and interstate cases, given the urgency and complexity of climate litigation.
India should use its platform in international forums to advocate for both the equity principles (CBDR-RC and historical responsibility) and the development of effective financing mechanisms, while demonstrating domestic ambition on climate through continued renewable energy expansion and energy efficiency improvements that give India credibility as a constructive actor rather than a defender of the status quo.
Conclusion
The ITLOS Advisory Opinion of May 2024 and the pending ICJ Advisory Opinion on climate obligations mark a turning point in the legal treatment of climate change. For most of international law’s history, climate change has been treated as a political problem to be managed through negotiated treaties rather than a legal problem of state responsibility for wrongful acts. The advisory opinion strategy transforms this framing: it seeks authoritative judicial confirmation that states’ GHG emissions generate legal obligations, that insufficient action constitutes an internationally wrongful act, and that injured states have legal remedies. Whether this legal transformation will accelerate the mitigation and adaptation action that climate science demands is uncertain: legal norms are necessary but insufficient without political will. What the advisory opinions achieve is the removal of the excuse that international law is silent on the question. The law, it turns out, has clear things to say about climate obligations; the challenge is now holding states to them.
