Summary report, 23 July 2025

The International Court of Justice (ICJ) released its much-awaited Advisory Opinion on States’ obligations with respect to climate change and the legal consequences for breaching these. It is the culmination of a two-year-long process that has seen record-breaking participation by States and international and regional organizations and strong engagement by legal scholars and civil society representatives from around the world. Judge Yuji Iwasawa, President of the Court, provided a summary of the Advisory Opinion in a public sitting, attended by Philemon Yang, President of the 79th session of the United Nations General Assembly (UNGA), and various State representatives. Civil society organizations held a livestream of the reading outside the Peace Palace in The Hague, the Netherlands, where the Court resides, and in various other cities.

The Advisory Opinion, which the Court adopted unanimously, underscores the role of the Intergovernmental Panel on Climate Change (IPCC) in providing best available science and considers the 1.5°C threshold to be the primary agreed temperature goal under the Paris Agreement on climate change, recalling that even a warming of 1.5°C is not considered safe. With regard to nationally determined contributions (NDCs) under the Paris Agreement, it emphasizes that:

• their content, which is key to assess compliance, is not entirely up to parties’ discretion;
• parties have to do their utmost to ensure their respective NDCs represent the highest possible ambition, with the exact standard depending on aspects such as the countries’ contribution to cumulative greenhouse gas (GHG) emissions and their level of development and national circumstances;
• NDCs must, when taken together, be capable of achieving the temperature goal and purposes of the Paris Agreement; and
• parties have an obligation to undertake best efforts to achieve their NDCs.

The Court clarified that States incur obligations beyond the climate treaties, notably stemming from human rights law and customary international law, regardless of whether a State is a party to the climate change treaties. This finding is significant in the light of possible withdrawal of certain countries from the climate treaties, as exemplified by the US’s withdrawal from the Paris Agreement.

The Advisory Opinion underscores that the failure of a State to take appropriate action to protect the climate system from GHG emissions—including those due to fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses, or the provision of fossil fuel subsidies—may constitute an internationally wrongful act which is attributable to that State. It also notes that a State may be considered responsible for not taking the necessary regulatory and legislative measures to limit the quantity of emissions released by private actors under its jurisdiction.

While the Court makes no pronouncement on the responsibility of individual States, which has to be assessed on a case-by-case basis, the Advisory Opinion lays out the remedies that are available, including non-repetition, restitution, and compensation.

The Advisory Opinion also highlights that:

• the human right to a clean, healthy, and sustainable environment is essential for the enjoyment of other human rights; and
• once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood, which is important for small island States whose territorial integrity is threatened by sea level rise.

Many consider the Advisory Opinion to be an historic achievement that sets the benchmark for climate action going forward. The Alliance of Small Island States (AOSIS), which are particularly vulnerable to climate change, welcomed it as “a global affirmation that climate harm is not just unjust, it is unlawful,” emphasizing they will carry it into “every negotiation, every courtroom, and every call for justice.” The Pacific island State of Vanuatu, who spearheaded the request for the Advisory Opinion, announced the preparation of a resolution to take back to the UNGA. Civil society representatives and environmental law experts lauded the outcome of the Court’s deliberations, underscoring it lays a path to climate justice, with human rights advocate Mary Robinson highlighting it “ushers in a new era of accountability for major emitters.”

This Briefing Note provides a brief history of the context of the proceedings, summarizes the Advisory Opinion and its appendices, and concludes with some take-aways and a preliminary outlook.

Brief History

International Court of Justice: The ICJ is the principal judicial organ of the United Nations. It was established by the United Nations Charter in 1945 and is the only court with both general and universal jurisdiction. In that sense, its role differs from that of specialist international tribunals, such as the International Tribunal on the Law of the Sea (ITLOS). The Court has a twofold role: first, to settle, in accordance with international law, legal disputes between States submitted to it by them; and, second, to give advisory opinions on legal matters referred to it by United Nations organs and specialized agencies.

The Court is composed of 15 judges. They are elected by the UNGA and the United Nations Security Council. Their term of office is nine years. In order to ensure institutional continuity, one-third of the Court is elected every three years. Once elected, the judges exercise their powers independently and impartially. Counsel speaking before the Court are appointed by the State or organization on whose behalf they speak. They are not required to possess the nationality of the State on behalf of which they appear, and are chosen from among those practitioners, professors of international law, and jurists of all countries who appear most qualified to present the views of the parties.

By interpreting international law and applying it to specific cases, the Court clarifies the substance of that law, and also contributes to its codification and progressive development. Judgments delivered by the Court in disputes between States are binding upon the parties concerned. Advisory opinions are non-binding. The United Nations organs and specialized agencies requesting the opinions can give effect to them or not, by whichever means they see fit. Since opening its doors in 1946, the Court has heard 195 cases, of which 30 are advisory opinions.

Key Developments with Regard to Climate Change: Eunice Newton Foote demonstrated the effects of carbon dioxide (CO2) on atmospheric temperatures as early as the mid-1800s, with subsequent research deepening humanity’s understanding of anthropogenic climate change and its variegated impacts. Building on the first World Climate Conference, held in 1979, the IPCC was established in 1988 to prepare a comprehensive review of the state of climate science, the social and economic impacts of climate change, and potential response strategies. With its first assessment report, published in 1990, the IPCC showed that the global average temperature had already increased as a result of anthropogenic GHG emissions, underlining climate change as a challenge with global consequences requiring international cooperation.

After the UNGA recognized climate change to be a common concern of humankind in Resolution 43/53 in 1988, the international political response to climate change began in 1992 with the adoption of the United Nations Framework Convention on Climate Change (UNFCCC). The Convention sets out the basic legal framework and principles for international climate change cooperation with the aim of stabilizing atmospheric concentrations of GHGs to avoid “dangerous anthropogenic interference with the climate system.”

In December 2015, parties to the UNFCCC adopted the Paris Agreement, which aims to limit the global average temperature increase to “well below” 2°C above pre-industrial levels, and pursue efforts to limit it to 1.5°C. It also aims to increase parties’ ability to adapt to the adverse impacts of climate change and make financial flows consistent with a pathway towards low-emission and climate-resilient development. Each party shall communicate, at five-year intervals, progressively more ambitious NDCs. Collective progress towards implementing the Agreement and reaching its objective is to be reviewed every five years through a Global Stocktake (GST).

The first GST concluded in 2023. It showed that parties are not on track to reach the Agreement’s objectives. The decision concluding the GST encourages parties to ensure their next NDCs are 1.5°C-aligned and contain ambitious, economy-wide emission reduction targets, covering all GHGs, sectors, and categories. The decision also calls on parties to contribute, in a nationally determined manner, to global efforts to transition away from fossil fuels in energy systems in a just, orderly, and equitable manner, accelerating action in this critical decade, so as to achieve net zero by 2050 in keeping with the science. The next round of NDCs is due in 2025. Recent negotiations raised doubts about the extent to which these will respond to the GST decision, especially with regard to fossil fuel transition.

ICJ Advisory Opinion on Climate Change: Recent years have seen an increase in climate-related court cases as well as deeper engagement from legal scholars and judicial bodies on matters related to the environment more generally. Stakeholders such as children, elderly women, and non-governmental organizations (NGOs) have turned to courts at the national and regional levels to bring about enhanced climate action. In 2022, the UNGA recognized the human right to a clean, healthy, and sustainable environment, and nature rights laws have been passed in various jurisdictions around the globe.

In 2014, an advisory opinion of ITLOS confirmed that parties to the United Nations Convention on the Law of the Sea (UNCLOS) have to prevent, reduce, and control marine pollution from GHG emissions and protect and preserve the marine environment from climate change impacts and ocean acidification. In May 2025, the Inter-American Court of Human Rights delivered an advisory opinion, which affirmed the right to a healthy environment, noting it gives rise to the right to a healthy climate, and clarified, among other findings, that States have a duty to: take ambitious mitigation action based on the principles of progressivity, common but differentiated responsibilities, equity, prevention, and precaution; regulate corporate activities to that effect; and protect environmental defenders. Furthermore, a petition was filed in May 2025 for the African Court on Human and Peoples’ Rights to deliver an advisory opinion on the obligations of States with respect to the climate change crisis.

Building on a campaign by Pacific youth, the small island State of Vanuatu succeeded in gathering sufficient support for the UNGA to unanimously adopt Resolution 77/276 in 2023, requesting the ICJ to give an advisory opinion on the obligations of States with respect to climate change. Specifically, the UNGA requested the ICJ to clarify:

• the obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic emissions of GHGs for States and for present and future generations; and
• the legal consequences under these obligations for States where they, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to:
  • States, including, in particular, small island developing States (SIDS), which due to their geographical circumstances and level of development, are injured or specially affected by or are particularly vulnerable to the adverse effects of climate change; and
  • peoples and individuals of the present and future generations affected by the adverse effects of climate change.

All Member States are entitled to participate in ICJ proceedings. In addition, several international and regional organizations, including AOSIS, the Organization of the Petroleum Exporting Countries, and the International Union for the Conservation of Nature, were authorized to participate.

States and admitted organizations submitted a record-breaking 91 written statements and 62 written comments to inform the Court’s deliberations—more than in any other advisory proceeding before the Court. The ICJ also received submissions by various NGOs. The oral proceedings, which took place in December 2024, provided an opportunity for States and organizations to further elaborate on their written submissions or voice additional perspectives. Over the course of two weeks, 96 States and 11 international organizations presented oral statements at the Peace Palace, with a number of countries coming before the Court for the first time.

Statements touched upon the role of the UNFCCC, the Paris Agreement on climate change, and other environmental treaties, as well as human rights law, customary international law, and general principles of international law in defining the scope of States’ obligations. Speakers debated the point in time at which knowledge of the adverse impacts of GHG emissions gave rise to States’ duty of due diligence to prevent harm to the environment. They also diverged in their perspectives on the legal consequences of breaching those obligations, with some underscoring the UNFCCC’s and Paris Agreement’s facilitative, non-punitive approach to compliance—and others emphasizing obligations to cease wrongful acts and compensate for harm done under the customary rules of State responsibility.

After the hearings, 65 responses were submitted to the judges’ follow-up questions regarding: fossil fuel production, the interpretation of mitigation obligations under the Paris Agreement, the right to a healthy environment, and declarations related to State responsibility and liability for loss and damage.

For additional information about the Advisory Opinion, see: https://sdg.iisd.org/tag/icj-advisory-opinion/

Summary of the ICJ Advisory Opinion

On 23 July 2025, ICJ President Yuji Iwasawa provided a summary of the Advisory Opinion in a public sitting at the Peace Palace in The Hague, the Netherlands. This summary is reflected below, with the proviso that the complete Advisory Opinion is 140 pages long and contains additional elements, such as on obligations related to the ozone treaties, the Convention on Biological Diversity (CBD), and the United Nations Convention to Combat Desertification (UNCCD).

Scientific Background

The Court notes that the consequences of climate change are severe and far-reaching, affect both natural ecosystems and human populations, and underscore the urgent and existential threat posed by climate change. In its deliberations, the ICJ primarily relied on IPCC reports, which, participants in the proceedings agreed, constitute the best available science on the causes, nature, and consequences of climate change. The Court notes the equivalent definitions of the climate system provided by the IPCC and the UNFCCC, pointing to the totality of the atmosphere, hydrosphere, cryosphere, lithosphere, biosphere, and the interactions between them. Recalling IPCC findings, it highlights that risks and projected adverse impacts and related loss and damage from climate change will escalate with every increment of global warming and are higher for global warming of 1.5°C than at present, and even higher at 2°C of warming, noting that even a warming of 1.5°C is not considered safe for most nations, communities, ecosystems, and sectors.

Scope and Meaning of the UNGA’s Request

The Court considers that the relevant conduct for the purposes of these advisory proceedings is not limited to conduct that, itself, directly results in GHG emissions, but rather comprises all actions or omissions of States which result in the climate system and other parts of the environment being adversely affected by anthropogenic GHG emissions, encompassing the full range of human activities, including both consumption and production activities. The Court also formulated its Opinion in global terms, since GHG emissions are not territorially limited. It observes that while temporal issues related to the crystallization of States’ obligations may be particularly relevant for an in concreto assessment of the responsibility of States for breaches of obligations (assessment of the specific circumstances of an individual case), the present Opinion is not concerned with the invocation and determination of the responsibility of individual States or groups of States.

The ICJ highlights the intention behind the UNGA’s request as focused on the obligations incumbent upon States under the entire corpus of international law. The Court considers it is not requested to opine on the legal consequences, if any, for injuries arising out of acts not prohibited by international law. The Advisory Opinion also highlights the Court is not called upon to identify the legal responsibility of any particular State, but to establish the applicable legal framework of State responsibility, outlining in general terms the legal consequences flowing therefrom. It further notes that the responsibility of individual States or groups of States requires an in concreto assessment that must be undertaken on a case-by-case basis and that the Court does not prejudge the merits of any future claims that may be brought before courts or tribunals.

In terms of legal consequences with respect to certain categories of States that are particularly vulnerable, the Court notes that the application of the rules on State responsibility under customary international law does not differ depending on the category or status of an injured State. The Court considers that it is not called upon to determine any specific legal consequences with respect to particular injured States or groups of States. It nevertheless recognizes the unique situation faced by small island States and low-lying coastal States with regard to sea level rise and decides to address this issue in its consideration of legal obligations.

With regard to the legal consequences with respect to affected peoples and individuals of the present and future generations, the Court notes that whether individuals have any entitlement to invoke the legal responsibility of States, or to make a claim in a particular circumstance involving injury or harm arising from climate change, is dependent on the relevant primary obligations of States. It also notes that whether individuals are entitled to invoke a State’s responsibility depends not on the general rules of State responsibility, but on the specific legal instruments that create procedural and substantive rights and obligations governing the relationship between the States and the individuals concerned.

Applicable Law with Respect to States’ Obligations

The Court identifies “the most directly relevant applicable law” governing the questions at hand and determines whether any of those rules are excluded by virtue of the interpretative principle of lex specialis, that is the precedence of specific law. It points to the Charter of the United Nations, which provides that States shall act in accordance with the principle of good faith, including when addressing problems of common concern such as climate change. The Court observes that the UNFCCC, Kyoto Protocol, and Paris Agreement are the principal legal instruments regulating the international response to the global problem of climate change. It notes that the three instruments complement each other, with the UNFCCC establishing the ultimate objective, the basic principles, and general obligations of States, whereas the Kyoto Protocol and Paris Agreement respectively translate these basic principles and general obligations into a set of more specific interrelated obligations. In the view of the Court, UNCLOS, the ozone treaties, CBD, and UNCCD also form part of the most directly relevant applicable law. It expresses awareness that many other treaties are relevant for the international community’s efforts to address climate change, but decides to confine its examination to the most directly relevant applicable law.

In terms of applicable and relevant customary international law, the Court recalls its jurisprudence on the Legality of the Threat or Use of Nuclear Weapons, which affirmed that the duty to prevent significant harm to the environment is not confined to instances of direct cross-border harm and that it applies to global environmental concerns. The Court emphasizes that the duty to prevent significant harm to the environment therefore also applies with respect to the climate system and other parts of the environment.

The Court further highlights that the duty to prevent significant harm to the environment is an obligation to act with due diligence. Noting that determination of what is required by due diligence ultimately calls for an assessment in concreto, the Court underscores that this does not exclude the identification of a required standard of conduct at a general level, depending on the overall character of the risk to the part of the environment in question. The Court states this is particularly the case for climate change because the specific character of the risk of significant harm to the climate system is indisputably established, and climate change therefore poses a quintessentially universal risk to all States. The Court emphasizes the risk is of a general and urgent character, requiring the identification of a corresponding general standard of conduct, to be applied subject to the principle of common but differentiated responsibilities and respective capabilities (CBDR-RC). Under these circumstances, the Court recognizes that the standard of due diligence for preventing significant harm to the climate system is stringent, concluding that a heightened degree of vigilance and prevention is required.

The Court recalls the duty to cooperate lies at the core of the United Nations Charter and considers the duty of States to cooperate for the protection of the environment a rule whose customary character has been established. It notes the duty to cooperate:

• is intrinsically linked to the duty to prevent significant harm to the environment, because uncoordinated individual efforts by States may not lead to a meaningful result; and
• derives from the principle that the management of shared resources must be governed by the principle of good faith.

The Court concludes that the duty to cooperate for the protection of the environment can serve as a guiding principle for the interpretation of other rules.

The Court further considers that the core human rights treaties and the human rights recognized under customary international law form part of the most directly relevant applicable law—and that the principles of sustainable development, CBDR-RC, equity, intergenerational equity, the precautionary approach or principle, and the polluter-pays principle are applicable as guiding principles for the interpretation and application of the most directly relevant legal rules.

The Court considers that the argument that the climate change treaties constitute the only relevant applicable law cannot be upheld, including because it cannot find any actual inconsistency between the provisions of the climate change treaties and other rules and principles of international law. It therefore finds that the principle of lex specialis does not lead to a general exclusion by the climate change treaties of other rules of international law.

The Court emphasizes that this list of most directly relevant applicable law is without prejudice to other rules of international law that may also be relevant under various circumstances in the context of climate change. It notes that such rules may be found, for example, in international trade law, international investment law, and international humanitarian law.

Obligations of States under the Climate Treaties

The Court recalls that the precautionary approach or principle and the principles of CBDR-RC, sustainable development, equity, and intergenerational equity do not constitute standalone obligations within the climate treaty framework, but guide the interpretation of the treaty obligations. The Court further notes that, in interpreting their obligations under the climate change treaties, States need to have recourse to the relevant decisions of the governing bodies of these treaties. The Court further observes that in certain circumstances, the decisions of these bodies have certain legal effects, such as when they create legally binding obligations for the parties or when they constitute subsequent agreements under Article 31.3.a of the Vienna Convention on the Law of Treaties, insofar as they express agreement in substance between the parties regarding the interpretation of the relevant treaty.

On the relation between the UNFCCC, Kyoto Protocol, and Paris Agreement, the Court observes that it is only where the treaties are incompatible that the later-in-time obligation will supersede the earlier obligation, as per the lex posterior rule under customary international law. In the view of the Court, there is no incompatibility between the three climate change treaties; on the contrary, they are mutually supportive, with the Kyoto Protocol and Paris Agreement providing greater specification to the general obligations contained in the UNFCCC.

The Court notes that a key feature of the UNFCCC is the distinction it draws between “developed country Parties” and “developing country Parties,” which are subject to differing obligations and that this distinction is accomplished by providing for specific additional obligations for certain developed country parties and other parties listed in Annex I. It notes that the main obligations under the Framework Convention concerning mitigation are found in Article 4. It observes that certain obligations under Article 4.1, such as those related to national inventories, the formulation of national mitigation programmes, and the communication of information to the Conference of the Parties (COP), are obligations of result, while others are obligations of conduct because they do not require parties to bring about a particular result but rather use their best efforts. The Court further observes that Article 4.2 sets forth a number of distinct but interrelated obligations that are legally binding for Annex I parties. It underscores that obligations are legally binding upon the parties to which they pertain, regardless of whether they are of result or conduct, and that the distinction between obligations of conduct and obligations of result is not necessarily a strict one, stressing that breach of both types of obligations may result in State responsibility.

The Court notes that several provisions of the UNFCCC refer to legally binding obligations relating to adaptation, highlighting that Article 4.4 provides that Annex II parties shall assist the developing country parties that are particularly vulnerable to the adverse effects of climate change in meeting the costs of adaptation to those adverse effects. The Court further observes that the UNFCCC establishes an obligation for parties to cooperate in different areas, which is an obligation of conduct, the fulfilment of which is assessed against the standard of due diligence.

With regard to the Kyoto Protocol, the Court notes that the absence of a new commitment period does not deprive the Protocol of its legal effect and that its provisions may still serve as interpretative aids for the identification of obligations and for compliance assessment, noting that non-compliance with emission reduction commitments may constitute an internationally wrongful act.

With regard to the Paris Agreement, the Court notes that it provides for limiting the global average temperature increase to well below 2°C above pre-industrial levels as a goal and 1.5°C as an additional effort. However, the Court considers the 1.5°C threshold to be the parties’ primary agreed temperature goal for limiting the global average temperature increase under the Paris Agreement. In this context, the Court points to decisions by the COP serving as the Meeting of the Parties to the Paris Agreement (CMA) referencing the 1.5°C target, such as decision 1/CMA.5 on the first Global Stocktake, which, in the Court’s view, expresses agreement on the interpretation of the Paris Agreement’s temperature goal within the meaning of Article 31.3.a of the Vienna Convention on the Law of the Treaties. This, it adds, is consistent with Paris Agreement Article 4.1, which requires that mitigation measures be based on the “best available science.”

The Court notes that the principle of CBDR-RC featured in the UNFCCC has been formulated differently in the Paris Agreement through the addition of the phrase “in the light of different national circumstances.” In the view of the Court, the additional phrase does not change the core of the principle of CBDR-RC; rather, it adds nuance by recognizing that the status of a State as developed or developing is not static, but depends on an assessment of the State’s current circumstances.

The Court also notes that the Paris Agreement contains several obligations of conduct and obligations of result, which are mutually supportive, noting that compliance with obligations of conduct under the Paris Agreement is assessed on the basis of whether the party in question exercised due diligence and employed best efforts by using all the means at its disposal in the performance of that obligation.

With regard to mitigation, the Court notes that the Paris Agreement’s temperature goal constitutes, in addition to the Agreement’s object and purpose, the “context” relevant for the interpretation of other obligations, such as the mitigation obligations. It also notes that the Paris Agreement reinforces the obligations relating to the promotion and enhancement of carbon sinks and reservoirs set forth in UNFCCC Article 4.

The Court observes that the obligations to prepare, communicate, and maintain successive NDCs, and account for and register them are obligations of result, and failure to do so would constitute a breach of that obligation. It also highlights that the mere preparation, communication, and maintenance of successive NDCs is not sufficient as the content of the NDCs is equally relevant to determine compliance.

Pointing to Paris Agreement Article 4.3, the Court considers that the discretion of parties in the preparation of their NDCs is limited, emphasizing progression over time. It also notes that the content of a party’s NDCs must be capable of making an adequate contribution to the achievement of the temperature goal.

The Court emphasizes that because of the seriousness of the threat posed by climate change, the standard of due diligence to be applied in preparing the NDCs is stringent, meaning that each party has to do its utmost to ensure that the NDCs it puts forward represent its highest possible ambition in order to realize the objectives of the Paris Agreement. Consistent with the varying character of due diligence and CBDR-RC, the standard to be applied when assessing NDCs will vary, depending on historical contributions to cumulative GHG emissions, the level of development, and national circumstances.

The Court specifies that, when taken together, NDCs must be capable of achieving the temperature goal of limiting global warming to 1.5°C as well as the overall objective of stabilizing GHG concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.

The Court underlines the obligation for parties to pursue domestic mitigation measures in line with Paris Agreement Article 4.2, noting the obligation is substantive—and an obligation of conduct, not result. It considers that the standard of due diligence attached to the obligation to pursue domestic mitigation measures is stringent because the best available science indicates that impacts escalate with every increment of global warming.

With regard to adaptation, the Court considers that the fulfilment of obligations is to be assessed against a standard of due diligence and that parties must use their best efforts, in line with the best available science, with a view to enhancing adaptive capacity, strengthening resilience, and reducing vulnerability to climate change. The Court observes that the adaptation obligations under the Paris Agreement complement the mitigation obligations in preventing and reducing the harmful consequences of climate change.

The Court notes that States are free to select the means of cooperating, as long as such means are consistent with the obligations of good faith and due diligence. The Court further notes that the principal forms of cooperation prescribed by the Paris Agreement are financial assistance, technology transfer, and capacity building.

Obligations of States under Customary International Law

The Court notes that the duty to prevent significant harm to the environment also applies to the climate system, which is an integral and vitally important part of the environment that must be protected for present and future generations. It holds that States are subject to the duty to prevent significant harm either where no harm has yet been caused but the risk of future significant harm exists, or where some harm has already been caused and there is a risk of further significant harm. Citing ITLOS, the Court specifies that whether an activity constitutes a risk of significant harm depends on both the probability or foreseeability of the occurrence of harm—and its severity or magnitude. This, it states, should be determined by, among other factors, an assessment of the risk and level of harm combined. It emphasizes that the higher the probability and the seriousness of possible harm, the more demanding the required standard of conduct.

The Court is of the view that a risk of significant harm may also be present in situations where significant harm to the environment is caused by the cumulative effect of different acts undertaken by various States—and by private actors subject to their respective jurisdiction or control, even if it is difficult to identify a share of responsibility of any particular State. The Court underscores that States must assess the possible cumulative effects of their acts and the planned activities under their jurisdiction or control. It is the sum of all activities that contribute to anthropogenic GHG emissions over time, not a specific emitting activity, that produce the risk of significant harm to the climate system, the Court notes. This means that the risk associated with climate change is a consequence of a combination of activities by different States and that States need to avert the risk through a coordinated and cooperative response. The Court highlights that determination of significant harm must take into account the best available science. It notes that the question whether any specific harm, or risk of harm, to a State constitutes a relevant adverse effect of climate change must be assessed in concreto.

The Court finds that the diffuse and multifaceted nature of various forms of conduct that contribute to anthropogenic climate change does not preclude the application of the duty to prevent significant harm to the climate system and other parts of the environment.

The Court reaffirms that States must fulfil their duty to prevent significant harm to the environment by acting with due diligence. It notes that determination of what due diligence requires from a State in a particular situation depends on elements such as:

• the appropriateness of measures, including regulatory mitigation mechanisms that are designed to achieve the deep, rapid, and sustained reductions of GHG emissions that are necessary for the prevention of significant harm to the climate system, and adaptation measures;
• the availability of, and the need to acquire and analyze, scientific and technological information;
• current standards that may arise from binding and non-binding norms and may be reflected in COP decisions and in recommended technical norms and practices;
• States’ different capabilities, as reflected in CBDR-RC;
• the precautionary approach or principle, noting that States are required to take appropriate measures to prevent significant harm where reliable scientific evidence of a risk of significant harm exists and should not refrain from or delay taking actions of prevention in the face of scientific uncertainty; and
• procedural steps, including risk assessment, environmental impact assessment, notification, and consultation, which are particularly warranted when an activity significantly affects collective efforts to address harm to the climate system.

The Court emphasizes the importance of cooperation in the context of a resource shared by all States, and protection of the climate system requires sustained and continuous forms of cooperation. It notes that while States are not required to conclude treaties, they are required to make good faith efforts to arrive at appropriate forms of collective action. The Court recognizes that the duty to cooperate leaves States some discretion in determining the means for regulating their GHG emissions, but emphasizes that this discretion cannot serve as an excuse for States to refrain from cooperating with the required level of due diligence or to present their effort as an entirely voluntary contribution which cannot be subjected to scrutiny.

Regarding the relationship between obligations arising from treaties and from customary international law, the Court notes that when several norms bear on a single issue, they should be interpreted to give rise to a single set of compatible obligations. The Court also considers that the obligations arising from the climate change treaties, as interpreted in the Advisory Opinion and State practice in implementing them, inform the general customary obligations, just as the general customary obligations provide guidance for the interpretation of the climate change treaties.

The Court considers that, at the present stage, compliance in full and in good faith by a State with the climate change treaties suggests that this State substantially complies with the general customary duties to prevent significant environmental harm and to cooperate. However, the Court emphasizes that this does not mean that the customary obligations would be fulfilled simply by States complying with their obligations under the climate change treaties. It highlights that, while the treaties and customary international law inform each other, they establish independent obligations that do not necessarily overlap.

The Court further states that the customary obligations of any State not a party to one or more of the climate treaties at present find expression, at least in part, in the general practice of States, and emphasizes that customary obligations are the same for all States and exist independently regardless of whether a State is a party to the climate treaties. On this basis, the Court considers it possible that a non-party State which cooperates with the community of States parties to the three climate treaties in a way that is equivalent to that of a State party, may, in certain instances, be considered to fulfil its customary obligations through practice that comports with the required conduct under the climate treaties. The Court notes that if a non-party State does not cooperate in such a way, it has the full burden of demonstrating that its policies and practices are in conformity with its customary obligations.

Obligations of States under UNCLOS

Citing ITLOS, the Court notes that anthropogenic GHG emissions may be characterized as pollution of the marine environment within the meaning of UNCLOS, making Part XII of UNCLOS relevant to the questions before the ICJ. In the view of the Court, the obligation under UNCLOS Article 192 consists of a positive obligation to take measures to protect and preserve the marine environment and a negative obligation not to degrade it. It notes that the standard of due diligence to be applied when complying with the obligation to protect and preserve the marine environment is stringent.

The Court finds that under UNCLOS Article 194.1 States parties are under an obligation to take all necessary measures to reduce and control pollution, with the ultimate aim of preventing its occurrence altogether, although they are not required to ensure an immediate cessation of marine pollution caused by anthropogenic GHG emissions. The Court emphasizes that it is not necessarily sufficient for States parties to fulfil their obligations under the UNFCCC and Paris Agreement in order to satisfy the obligation laid down by Article 194.1. It considers that what constitutes a “necessary measure” within the meaning of that provision should be assessed according to objective criteria, taking into account the best available science, international rules and standards relating to climate change, and the available means and capabilities of the States concerned, including their different national circumstances.

Regarding the obligation to cooperate under UNCLOS Article 197, which is an obligation of conduct requiring States to act with due diligence, the Court considers that this obligation is of a continuing nature and it requires States parties, inter alia, to make ongoing efforts to formulate and elaborate rules and recommended practices. The Court notes that the adoption of treaties for the protection of the climate system, such as the UNFCCC or Paris Agreement, does not release States parties from this requirement under UNCLOS.

The Court notes that States parties must therefore take their obligations under UNCLOS into account when implementing their obligations under the climate change treaties, other relevant environmental treaties, and customary international law, and vice versa.

Obligations of States in Relation to Sea Level Rise and Related Issues

The Court considers that the provisions of UNCLOS do not require States parties, in the context of physical changes resulting from climate change-related sea level rise, to update the charts or lists of geographical coordinates that show the baselines and outer limit lines of their maritime zones once they have been duly established. It considers that States parties to UNCLOS are under no obligation to update such charts or lists of geographical coordinates.

The Court notes that several participants in the proceedings argued that sea level rise poses a significant threat to the territorial integrity and thus to the very statehood of small island States and that, in the event of a complete loss of a State’s territory and displacement of its population, a strong presumption in favor of continued statehood should apply. The Court finds that, once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood.

Obligations of States under International Human Rights Law

The Court recalls that the environment is the foundation for human life, upon which the health and well-being of both present and future generations depend. It thus considers that the protection of the environment is a precondition for the enjoyment of human rights. The Court is of the view that the adverse effects of climate change may significantly impair the enjoyment of certain human rights, such as the rights to: life; health; an adequate standard of living, which encompasses access to food, water, and housing; and privacy, family, and home—as well as the rights of women, children, and Indigenous Peoples.

The Court considers that conditions resulting from climate change which are likely to endanger the lives of individuals may lead them to seek safety in another country or prevent them from returning to their own. In the view of the Court, States have obligations under the principle of non-refoulement, or no return, where there are substantial grounds for believing that there is a real risk of irreparable harm to the right to life if individuals are returned to their country of origin.

The Court is of the view that a clean, healthy, and sustainable environment is a precondition for the enjoyment of many human rights, such as the right to life, the right to health, and the right to an adequate standard of living, including access to water, food, and housing. It considers that the right to a clean, healthy, and sustainable environment results from the interdependence between human rights and the protection of the environment. Consequently, insofar as States parties to human rights treaties are required to guarantee the effective enjoyment of such rights, the Court considers it “difficult to see how these obligations can be fulfilled without at the same time ensuring the protection of the right to a clean, healthy and sustainable environment as a human right.” It concludes that, under international law, the human right to a clean, healthy, and sustainable environment is essential for the enjoyment of other human rights.

The Court recalls its earlier recognition of the applicability of human rights treaties when a State exercises jurisdiction outside its territory. In the context of the Advisory Opinion, the Court considers it does not need to determine the specific circumstances under which a State can be regarded as exercising its jurisdiction outside its own territory, since any such determination depends on the provisions of each treaty. The Court further emphasizes that the scope of human rights treaty law and that of customary law are distinct.

The Court finds that under international human rights law, States are required to take necessary measures to ensure the protection of the climate system and other parts of the environment, considering that the full enjoyment of human rights cannot be guaranteed without it.

The Court is also of the view that international human rights law, the climate treaties, and other relevant environmental treaties, as well as the relevant obligations under customary international law inform each other and that States must therefore take their obligations under international human rights law into account when implementing their other obligations and vice versa.

Legal Consequences Arising from States’ Acts and Omissions that Cause Significant Harm to the Climate System and Other Parts of the Environment

The Court considers its task is to identify the legal framework under which the conduct of States can be assessed in order to determine: whether a State, or a group of States, is responsible for a breach of its obligations pertaining to the protection of the climate system; whether a State or group of States can invoke the responsibility of another State or group of States in breach; and the remedies that are available to the injured State or States in case of such a breach.

It observes that participants in the advisory proceedings were divided in their views as to whether the general rules on State responsibility apply in the context of climate change or whether the legal consequences arising from a breach of States’ obligations are solely or primarily governed by the climate treaties. With regard to the question of applicability of the rules on State responsibility, the Court notes that: those rules do not vary with the nature of the wrongful act in question in the absence of a clearly expressed lex specialis; and, in order for the lex specialis maxim to apply, there must be some actual inconsistency or a discernible intention that one provision is to exclude the other.

The Court finds that the text, context, and object and purpose of the climate treaties do not support the proposition that the parties intended to exclude the general rules of State responsibility. In particular, the Court finds no evidence in Articles 8 (loss and damage) and 15 (compliance), or in the procedural mechanisms thereunder, of any discernible intention on the part of the parties to the Paris Agreement to derogate from the customary international law rules on State responsibility for breaches of treaty obligations. Therefore, the Court concludes that responsibility for breaches of obligations under the climate change treaties, and in relation to the loss and damage associated with the adverse effects of climate change, is to be determined by applying the well-established rules on State responsibility under customary international law.

The Court notes that the unprecedented nature and scale of harm resulting from climate change give rise to particular issues in relation to the application of the customary rules on State responsibility, chiefly questions relating to attribution and causation.

In considering the alleged difficulties in attributing actions or omissions to a State, the Court emphasizes at the outset that attribution is to be based on criteria determined by international law. In the Court’s view, the well-established rule of international law that the conduct of any organ of a State must be regarded as an act of that State is applicable in the context of climate change.

The Court emphasizes that failure of a State to take appropriate action to protect the climate system from GHG emissions—including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses, or the provision of fossil fuel subsidies—may constitute an internationally wrongful act, which is attributable to that State.

The judges observed that the obligations it has identified in its Advisory Opinion include the obligation of States to regulate the activities of private actors as a matter of due diligence. Therefore, attribution in this context involves attaching to a State its own actions or omissions that constitute a failure to exercise regulatory due diligence. The Court finds a State may thus be responsible where, for example, it has failed to exercise due diligence by not taking the necessary regulatory and legislative measures to limit the quantity of emissions caused by private actors under its jurisdiction.

The Court further notes that some participants in the advisory proceedings submitted that it is difficult to invoke responsibility in the context of climate change given that the wrongful conduct is cumulative in nature, involves different States over a period of time, and involves a plurality of States that cause injury to a plurality of injured States. In this respect, the Court observes that while climate change is caused by cumulative GHG emissions, it is scientifically possible to determine each State’s total contribution to global emissions, taking into account both historical and current emissions. It recalls that what constitutes a wrongful act is not the emissions in and of themselves but actions or omissions causing significant harm to the climate system, in breach of a State’s international obligations.

The Court acknowledges that the fact that multiple States have contributed to climate change may indeed increase the difficulty of determining whether and to what extent an individual State’s breach of an obligation has caused significant harm to the climate system. However, the Court considers that, in principle, the rules on State responsibility are capable of addressing a situation in which there exists a plurality of injured or responsible States.

Therefore, in the climate change context, the Court finds that:

• each injured State may separately invoke the responsibility of every State which has committed an internationally wrongful act resulting in damage to the climate system and other parts of the environment; and
• where several States are responsible for the same internationally wrongful act, the responsibility of each State may be invoked in relation to that act.

The Court observes that causation of damage is not a requirement for a determination of responsibility as such. It notes that causation or causality is a legal concept that plays a role in determining reparation and that, since reparation implies the existence of damage, causation must be established between a wrongful act and particular damage suffered by the injured State or, in the case of a breach of obligations under international human rights law, by the injured individuals.

The Court recalls its previously stated view that the fact that the damage was the result of concurrent causes is not sufficient to exempt States from the obligation to make reparation. The Court considers that the existing legal standard for establishing causation, which has been developed in the jurisprudence of the Court, is capable of being applied to the establishment of causation between the internationally wrongful act of States’ non-compliance with obligations to protect the climate system from harm caused by anthropogenic GHG emissions—and the damage suffered by States as a result of such a wrongful act. The Court is of the view that the standard of “a sufficiently direct and certain causal nexus” between an alleged wrongful action or omission and the alleged damage is flexible enough to address the challenges arising with respect to the phenomenon of climate change.

In terms of the operation of this legal standard in the climate change context, the Court observes that causation involves two distinct elements: whether a given climatic event or trend can be attributed to anthropogenic climate change; and to what extent the damage caused by climate change can be attributed to a particular State or group of States. The Court notes that while the second element must be established in concreto with respect to specific claims brought by States, the first element may in many cases be addressed by recourse to science.

The Court underscores that scientific evidence establishes that significant harm to the climate system and other parts of the environment has been caused as a result of anthropogenic GHG emissions. It concludes that, while the causal link between the wrongful acts or omissions of a State and the harm arising from climate change is more tenuous than in the case of local sources of pollution, this does not mean that the identification of a causal link is impossible in the climate change context. It merely means that the causal link must be established in each case through an in concreto assessment, the Court finds.

The Court further finds that all States have a common interest in the protection of global environmental commons like the atmosphere and the high seas. Consequently, it notes, States’ obligations pertaining to the protection of the climate system and other parts of the environment from anthropogenic GHG emissions, in particular the obligation to prevent significant transboundary harm under customary international law, are obligations erga omnes, that is universally owed to all. The Court recalls that the UNFCCC and Paris Agreement acknowledge that climate change is a common concern of humankind requiring a global response. As such, the Court notes, the obligations of States under these treaties are obligations erga omnes partes, that is owed to all other parties to the same treaty. As a result, all States parties have a legal interest in the protection of the main mitigation obligations set forth in the climate change treaties and may invoke the responsibility of other States for failing to fulfil them.

The Court notes it cannot, in the context of these advisory proceedings, specify precisely what consequences are entailed by the commission of an internationally wrongful act of breaching obligations to protect the climate system from the anthropogenic GHG emissions since such consequences depend on the specific breach in question and on the nature of the particular harm.

However, the Court also notes that breaches of States’ obligations may give rise to the “entire panoply” of legal consequences provided for under the law of State responsibility, including: obligations of cessation and non-repetition, which are consequences that apply irrespective of the existence of harm; and the consequences requiring full reparation, including restitution, compensation, and/or satisfaction. The Court also underscores that breaches of States’ obligations do not affect the continued duty of the responsible State to perform the obligation breached.

The Court recalls that, under customary international law, a State responsible for an internationally wrongful act is under an obligation to cease that act if it is continuing and if the breached obligation is still in force. In this context, the Court is of the view that the obligation to put an end to the wrongful act may require a State to revoke all administrative, legislative, and other measures that constitute an internationally wrongful act of that State. It further notes that the duty of cessation may also require States to employ all means at their disposal to reduce their GHG emissions and take other measures in a manner, and to the extent, that ensures compliance with their obligations. Additionally, in appropriate circumstances, a responsible State could be required to offer appropriate assurances and guarantees of non-repetition.

The Court recalls that the appropriate nature and quantum of reparations cannot be assessed in the abstract and depends on the circumstances of a particular case. It observes that the remedy of restitution, which involves the re-establishment of the situation that existed before the wrongful act was committed, may prove difficult or unfeasible in the case of environmental harm, since such harm is often not easily reversible. Nonetheless, the Court considers that, in the circumstances of climate change caused by emissions of GHGs, restitution may take the form of reconstructing damaged or destroyed infrastructure and restoring ecosystems and biodiversity. It notes that whether or not these special forms of restitution are appropriate as reparation for damage suffered by States in relation to climate change is to be determined on a case-by-case basis.

The Court finds that, in the event that restitution should prove to be materially impossible, responsible States have an obligation to compensate. The Court considered that it is within the scope of this Opinion to consider whether compensation could be owed for significant harm caused by climate change, if a sufficiently direct and certain causal nexus can be shown between the wrongful acts of one or more States and the resulting harm. It notes that in the climate change context, reparations in the form of compensation may be difficult to calculate, as there is usually a degree of uncertainty with respect to the exact extent of the damage caused.

The Court further notes that whether satisfaction is warranted for a violation by a State or States of obligations regarding the emission of GHGs, and what form that satisfaction could take, will depend on the nature and circumstances of the breach.

Operative Clause of the Advisory Opinion

The Court,

• unanimously, finds that it has jurisdiction to give the Advisory Opinion requested;
• unanimously, decides to comply with the request for an Advisory Opinion;
• unanimously, is of the opinion that the climate treaties set forth binding obligations for States parties to ensure the protection of the climate system and other parts of the environment from anthropogenic GHG emissions, including that:
  • States parties to the UNFCCC have an obligation to adopt measures with a view to contributing to the mitigation of GHG emissions and adapting to climate change;
  • Annex I parties have additional obligations to take the lead in combating climate change by limiting their GHG emissions and enhancing their GHG sinks and reservoirs;
  • States parties to the UNFCCC have a duty to cooperate with each other in order to achieve the underlying objective of the Convention;
  • States parties to the Kyoto Protocol must comply with applicable provisions of the Protocol;
  • States parties to the Paris Agreement have an obligation to act with due diligence in taking measures in accordance with CBDR-RC capable of making an adequate contribution to achieving the temperature goal set out in the Agreement;
  • States parties to the Paris Agreement have an obligation to prepare, communicate, and maintain successive and progressive NDCs which, inter alia, when taken together, are capable of achieving the temperature goal of limiting global warming to 1.5°C above pre-industrial levels;
  • States parties to the Paris Agreement have an obligation to pursue measures which are capable of achieving the objectives set out in their successive NDCs; and
  • States parties to the Paris Agreement have obligations of adaptation and cooperation, including through technology and financial transfers, which must be performed in good faith;
• unanimously, is of the opinion that customary international law sets forth obligations for States to ensure the protection of the climate system and other parts of the environment from anthropogenic GHG emissions, including:
  • States have a duty to prevent significant harm to the environment by acting with due diligence and to use all means at their disposal to prevent activities carried out within their jurisdiction or control from causing significant harm to the climate system and other parts of the environment, in accordance with CBDR-RC; and
  • States have a duty to cooperate with each other in good faith to prevent significant harm to the climate system and other parts of the environment, which requires sustained and continuous forms of cooperation by States when taking measures to prevent such harm;
• unanimously, is of the opinion that States parties to the Vienna Convention for the Protection of the Ozone Layer and to the Montreal Protocol on Substances that Deplete the Ozone Layer and its Kigali Amendment, CBD, and UNCCD have obligations under these treaties to ensure the protection of the climate system and other parts of the environment from anthropogenic GHG emissions;
• unanimously, is of the opinion that States parties to UNCLOS have an obligation to adopt measures to protect and preserve the marine environment, including from the adverse effects of climate change and to cooperate in good faith;
• unanimously, is of the opinion that States have obligations under international human rights law to respect and ensure the effective enjoyment of human rights by taking necessary measures to protect the climate system and other parts of the environment; and
• unanimously, is of the opinion that a breach by a State of any obligations constitutes an internationally wrongful act entailing the responsibility of that State. The responsible State is under a continuing duty to perform the obligation breached. The legal consequences resulting from the commission of an internationally wrongful act may include the obligations of:
  • cessation of the wrongful actions or omissions, if they are continuing;
  • providing assurances and guarantees of non-repetition of wrongful actions or omissions, if circumstances so require; and
  • full reparation to injured States in the form of restitution, compensation, and satisfaction, provided that the general conditions of the law of State responsibility are met, including that a sufficiently direct and certain causal nexus can be shown between the wrongful act and injury.

Reflections of the Court on the Proceedings

The Court recalls that it has been suggested that these advisory proceedings are unlike any that have previously come before the Court. At the same time, it notes that the questions put to it by the UNGA are legal ones, and that the Court, as a court of law, can do no more than address the questions put to it through and within the limits of its judicial function—the Court’s assigned role in the international legal order. However, the Court notes that the questions posed by the UNGA represent more than a legal problem: they concern an existential problem of planetary proportions that imperils all forms of life and the very health of our planet.

The Court highlights that international law, whose authority has been invoked by the UNGA, has an important but ultimately limited role in resolving this problem. It emphasizes that a complete solution to this daunting, and self-inflicted, problem requires the contribution of all fields of human knowledge—law, science, economics, or any other. The Court notes that, above all, a lasting and satisfactory solution requires human will and wisdom—at the individual, social, and political levels—to change our habits, comforts, and current way of life in order to secure a future for ourselves and those who are yet to come.

Finally, the Court considers that, through this Advisory Opinion, it participates in the activities of the United Nations and the international community represented in that body, with the hope that its conclusions will allow the law to inform and guide social and political action to address the ongoing climate crisis.

Appendices to the Advisory Opinion

The Rules of the Court foresee that any judge who so desires may attach an individual opinion to an advisory opinion of the Court, whether dissenting from the majority or not, and a judge who wishes to record concurrence or dissent without stating reasons may do so in the form of a declaration (Article 107.3). While the Advisory Opinion and all its operative clauses were adopted unanimously, the judges appended several separate opinions and declarations. These are summarized below to provide further insights into the Court’s deliberations.

Vice-President Sebutinde appended a separate opinion, expressing that the Advisory Opinion:

• did not give much attention to least developed countries (LDCs) and SIDS, future generations, particularly vulnerable communities such as Indigenous Peoples, and the imbalance between major polluters and those whose GHG emissions are negligible;
• could have better articulated the right to self-determination and presumption of continued statehood in the context of sea level rise, CBDR-RC with respect to States obligations, and examples of appropriate reparation; and
• could have omitted matters related to the determination of State responsibility, attribution, and causation, noting these would need to be addressed in the context of contentious proceedings.

Judge Tomka appended a declaration on continued statehood in the context of sea level rise, noting that the Court had not been asked by the UNGA to pronounce itself on the matter and that, once it had decided to nevertheless address it, the Court should have provided a more rigorous answer.

Judge Yusuf appended a separate opinion, expressing disappointment with “the excessively formalistic approach” adopted by the Court, emphasizing, among others:

• disparities in historical and current contributions to climate change and the distinct responsibilities States bear, as well as the specific considerations to which SIDS and LDCs should be given;
• the Court should not only have addressed the legal consequences of internationally wrongful acts, but also the legal consequences of injuries arising out of conduct not prohibited by international law, recalling that the development of a distinct regime of international liability was driven by the recognition that the consequences of environmental harm may not be adequately addressed through the framework of State responsibility for internationally wrongful acts; and
• surprise at the Court’s inability to “make up its mind” on the formulation of a normative concept such as the “precautionary principle,” noting the Advisory Opinion uses the formulation “precautionary approach or principle” when it “could have at least” stayed with the formulation “precautionary approach” previously used by the Court.

Judge Xue appended a separate opinion on: how the principles of sustainable development and CBDR-RC guide the interpretations of obligations under the climate treaties, including with regard to changing unsustainable patterns of production and consumption and the due diligence standard to be applied to NDCs.

Judge Bhandari appended a separate opinion, noting the polluter-pays principle was insufficiently addressed and the normative status of the right to a clean, healthy, and sustainable environment could have been better articulated, and providing suggestions with regard to cessation, restitution, compensation, and satisfaction.

Judges Bhandari and Cleveland appended a joint declaration, noting the Court could have been “more forceful” in addressing fossil fuel production, the granting of fossil fuel exploration licenses, and the provision of fossil fuel subsidies, and emphasizing, among others, that:

• the obligations of States under the climate treaties and customary international law include phasing out of fossil fuel dependency, including by directly taking into account, and redressing, the downstream consequences of production, licensing, and subsidy activities;
• States with greater resources and technical capabilities are obliged to transition away from fossil fuel production and dependency with deeper and faster targets than States with lesser capabilities, and developed States with greater capabilities are required to provide financial and technological assistance to help developing States with lesser capabilities transition away from fossil fuels; and
• CBDR-RC does not exempt any State from measures that are necessary, consistent with their capabilities and national circumstances, to fulfil the objectives of the climate change treaties and stringent due diligence obligations.

Judge Nolte appended a declaration, among others:

• expressing skepticism as to whether fixed quantitative mitigation obligations, as primary obligations, can be derived from the general customary duty to prevent significant harm to the environment alone, noting that parties to the Paris Agreement have agreed that, for the time being, their collective efforts are not to be pursued through general fixed quantitative commitments as under the Kyoto Protocol;
• stating that the Court should have addressed the potential difficulties related to legal consequences of breaches of obligations “more openly” to avoid raising “false hopes” that climate litigation can supplement the mechanisms of financial transfers and the remedies for loss and damage contained in the climate change treaties; and
• cautioning that litigation as a surrogate form of climate policy risks having a counterproductive effect, and States may shy away from accepting new treaty obligations or maintaining procedures that could subject them to unpredictable legal consequences and challenge the distributive implications of court decisions and the very legitimacy of courts.

Judge Charlesworth appended a separate opinion on:

• the relationship between the obligation of prevention and the precautionary principle;
• the substantive and procedural features of the right to a clean and healthy environment; and
• States’ particular obligation to protect the human rights of vulnerable groups, such as Indigenous Peoples, women, children, people with disability, and people experiencing intersecting forms of discrimination, noting this requires close attention to the potentially discriminatory effects of measures taken to respond to climate change.

Judge Cleveland appended a declaration emphasizing: obligations with respect to the preservation and enhancement of carbon sinks and reservoirs; obligations to assess, report on, and mitigate harms resulting from armed conflict and other military activities; and that the interpretation of investment instruments must be informed by States’ obligations with respect to climate change under international law.

Judges Charlesworth, Brant, Cleveland, and Aurescu appended a joint declaration on the relationship between customary international law and treaty law with respect to climate change, emphasizing that the Court’s Advisory Opinion unequivocally rejects the argument that the climate change treaties constitute lex specialis in their relation to other rules of international law.

Judge Aurescu appended a separate opinion, emphasizing that the Court’s Advisory Opinion is “excessively and unnecessarily cautious and minimalist” on the issues of: sea level rise, including with regard to confirming continued statehood and matters related to non-refoulement such as temporary residence permits and measures against arbitrary detention; and the right to a clean, healthy, and sustainable environment.

Judge Tladi appended a declaration highlighting:

• what led to the Court’s conclusion that the 1.5°C is seen as the primary temperature goal of the Paris Agreement;
• the Court’s reflection on the right to a clean and healthy environment;
• the determination that parties to the Paris Agreement do not have an unfettered discretion to determine the content of their NDCs;
• that the sufficiency of the NDCs cannot be subject to the determination of the submitting State;
• it may be the case that full and good faith compliance with the Paris Agreement and its temperature goal may not amount to compliance with customary international law obligations, as this may be insufficient to protect the global system; and
• implications of the characterization of certain obligations relating to common spaces as obligations erga omnes or obligations erga omnes partes.

Take-aways and Preliminary Outlook

As Judge Tladi notes, the subject matter of this Advisory Opinion concerns one of the most consequential issues in the history of the Court, even more consequential than the issue of nuclear weapons, which was described as relating to the survival of the human species. This Opinion speaks to the future of our planet, and “all of humanity and the natural world suffer” if it is harmed, emphasizes Judge Bhandari. It is therefore especially significant that the Court’s reply to the UNGA’s questions is unanimous, “a rarity in the history of the Court’s advisory jurisprudence,” with many also lauding the robustness of the Advisory Opinion that draws from a variety of legal sources.

The Court interpreted the “tapestry of States’ obligations” under international law, providing a clear legal benchmark against which to assess climate action. Crucially, it rejected some high-emitting countries’ argument of the preeminence of the climate treaties in defining obligations and consequences for failing to live up to them. The Court underscored that States incur climate-related obligations under, among others, customary international law, human rights treaties, and various other environmental treaties. This means that, on the one hand, compliance under the climate treaties is not necessarily sufficient to ensure compliance with other climate-related obligations, and, on the other hand, that States that are non-parties to the climate treaties are not freed from meaningfully engaging in climate action. The Court emphasized that all States have the duty to prevent significant harm to the environment and to cooperate to that effect, especially considering the climate system is a resource shared by all.

The Court’s interpretation of obligations under the Paris Agreement also breaks with the idea that it is a “largely toothless tool” that gives total discretion to parties with regard to the content of their nationally determined contributions (NDCs)—the key vehicle for the mitigation of greenhouse gas (GHG) emissions. This perspective is often brought forward in the climate change negotiations, raising doubts about many countries’ intention to follow up on the outcome of the first Global Stocktake under the Paris Agreement, especially with regard to transitioning away from fossil fuels.

The Court’s Advisory Opinion clarifies that parties do not, in fact, have unfettered discretion: they have to do “their utmost” to ensure their respective NDCs represent “the highest possible ambition.” It also clarifies that the standard of due diligence against which to assess these efforts depends on aspects such as a country’s contribution to cumulative GHG emissions and its level of development and national circumstances, in line with the principle of common but differentiated responsibilities and respective capabilities.

The Advisory Opinion is firmly grounded in science. Building on the work of the Intergovernmental Panel on Climate Change, which, the Court emphasizes, provides best available science, the judges underscored that: climate impacts jeopardize the enjoyment of human rights, including the right to life; even a global warming of 1.5°C is not considered safe; and every increment of warming matters. Against this background, and pointing to decisions adopted by the governing body of the Paris Agreement, the Court considers the 1.5°C threshold to be the primary agreed temperature goal under the Paris Agreement, as opposed to 2°C. It further emphasizes that NDCs must, when taken together, be capable of achieving the temperature goal and purposes of the Agreement, as well as the overall objective of the United Nations Framework Convention on Climate Change (UNFCCC) to stabilize GHG concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. The latter provision is key, considering that even full and good faith compliance with the Paris Agreement and its temperature goal may be insufficient to protect the climate system, meaning that States may still breach obligations under customary international law to prevent harm to the environment.

The Advisory Opinion underscores that what constitutes appropriate measures, including with regard to States’ obligation under the United Nations Convention on the Law of the Sea (UNCLOS) to protect the marine environment from the impacts of GHG emissions, depends on best available science, and that States are to take this into account in their actions. Notably, the Court pointed to fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses, and the provision of fossil fuel subsidies as examples of what may constitute the failure of a State to take appropriate action. It emphasized that parties have an obligation to undertake best efforts to achieve their NDCs, noting that a State may be considered responsible for not taking the necessary regulatory and legislative measures to limit the quantity of emissions released by private actors under its jurisdiction.

During the proceedings, some participants argued that the non-punitive and collaborative compliance mechanisms under the UNFCCC and Paris Agreement is the appropriate framework for addressing legal consequences. The Court refuted this by clarifying that breaches of States’ obligations may give rise to the “entire panoply” of legal consequences provided for under the law of State responsibility, including obligations of cessation, non-repetition, restitution, compensation, and/or satisfaction.

The Court emphasized that that each injured State may separately invoke the responsibility of every State which has committed an internationally wrongful act resulting in damage to the climate system and other parts of the environment, noting it is scientifically possible to determine each State’s total contribution to global emissions, taking into account both historical and current emissions. With regard to the obligation of reparation, the Court regarded the standard of “a sufficiently direct and certain causal nexus” between an alleged wrongful action or omission and the alleged damage flexible enough to address the challenges arising with respect to the phenomenon of climate change, noting the causal link must be established for each specific case.

In their immediate reaction to the Advisory Opinion, many stakeholders underscored it ends the “era of impunity” for major emitters. A follow-up to the ICJ Advisory Opinion can be expected at various levels and in various forms. The Pacific island of Vanuatu, which spearheaded the request for the Advisory Opinion, already announced the preparation of a resolution for the UNGA to respond to the Court’s work. It will require significant diplomatic engagement to ensure the international community not only takes note of the Advisory Opinion but fosters the implementation of its findings.

For now, it remains unclear how the Court’s clarifications will affect multilateral negotiations, such as at the upcoming Climate Change Conference in Belém, Brazil, which is less than fourth month away, or the negotiations towards a global plastic treaty (considering plastics are typically made from fossil fuels). However, the Advisory Opinion comes just in time to give new momentum to the development of ambitious NDCs, at least those that have yet to be finalized. The Court’s clarifications will undoubtedly inform the assessment of the new round of NDCs, due in 2025, yet the question remains whether there will be a space to reflect on these in the negotiations—something that was still up for debate at 2025 June Climate Meetings. Discussions on whether countries are living up to their due diligence obligations may also be spurred in the context of the negotiations with regard to adaptation and cooperation in the form of finance, technology transfer, and capacity building. Some cautioned that the Advisory Opinion may add to the difficulty of reaching consensus in the negotiations, also considering the weight given by the Court to decisions of the climate treaties’ governing bodies with respect to treaty interpretation.

Another question is who will now formally invoke States’ responsibility for failing to fulfil their obligations. Small island States are prime candidates to take the initiative. The human rights community more broadly is also mobilizing to leverage the Court’s assessment and open the door for various rights holders to hold large emitters accountable and enforce the right to a clean, healthy, and sustainable environment. In providing a clear legal benchmark on a variety of climate-related issues, the Advisory Opinion is expected to inform jurisprudence of courts worldwide, including with regard to questions of compensation.

The Court also sends a clear signal to the private sector of what lies ahead if governments take their obligations seriously, as did the advisory opinion of the Inter-American Court of Human Rights, which provided even further detail as to how States should regulate corporate actors with respect to climate change. The Advisory Opinion may, for example, have an impact on international investment disputes related to fossil fuel extraction.

The following months and years will show whether and how countries and stakeholders will give effect to the Advisory Opinion and which means they will see fit to do so. We can also expect more in-depth reflections on where the Opinion falls short, with the different judges’ separate opinions and declarations already providing a good indication, such as with regard to the specific consideration of least developed countries, small island developing States, and future generations. Whatever the direction forthcoming analyses take, the proceedings have already bolstered the hope of frontline communities, who have seen their concerns raised before the world’s highest court through the testimonies of numerous representatives of particularly vulnerable countries. They underscored youth’s driving force and showcased a new generation of legal scholars working to ensure that international law is in the service of all, not the few.