The ICJ Advisory Opinion - Obligations of States on Climate Change: Part One - Obligations of Parties

In part two, I plan to present a summary of the portion of the seminar dealing with the second question,  what are the legal consequences under these obligations? I will also contextualize the AO from the standpoint of a developing country negotiator at the many COPs and Subsidiary Body meetings in which I have served as a national delegate over the years. Finally, in part three, I will cover the part of the seminar that examined the implications for Malaysia, and potential implications for the tone of COP30 in Belem, Brazil.

The “ICJ” or “Court” is the principal judicial organ of the United Nations (UN). It was established in June 1945 by the Charter of the United Nations, and its role is to settle, in accordance with international law, legal disputes submitted to it by States (often, highly contentious cases) and to give advisory opinions on legal questions referred to it by UN organs or agencies (in what are known as advisory proceedings). The Court is composed of 15 judges, who are elected for terms of office of 9 years by the UN General Assembly and the Security Council. When it receives a request for an advisory opinion, the Court will assemble all the facts, and can hold written and oral proceedings (similar to those in contentious cases). Advisory proceedings conclude with the delivery of the advisory opinion at a public sitting.

The legal nature of the Advisory Opinion (AO) delivered by the ICJ bears some explanation. Unlike a judicial ruling, which is a final, binding decision made by a court in a specific case, resolving a dispute between parties, or a declaratory judgment, which is a binding ruling that clarifies the legal rights and obligations of parties, but, unlike a judicial ruling, doesn't necessarily involve a specific dispute or require enforcement, an AO is a non-binding statement from a court or tribunal on a legal question, often requested by a government or international body. In this case, the UN General Assembly requested an advisory opinion of the ICJ on obligations of states regarding climate change. 

The Legal Question Posed

In 2019, a group of university students, who later became known as the Pacific Islands Students Fighting Climate Change (PISFCC), lobbied Tuvalu and Vanuatu to sponsor (co sponsored by other States, including Malaysia) a resolution before the UN General Assembly to request that the ICJ issue an advisory opinion on States' obligations for climate change under international law, and the legal consequences under these obligations. Specifically, the Court was asked: 

Having particular regard to the Charter of the United Nations, the International Covenant on Civil and Political Rights, the International Covenant on Economic, Social and Cultural Rights, the United Nations Framework Convention on Climate Change, the Paris Agreement, the United Nations Convention on the Law of the Sea, the duty of due diligence, the rights recognized in the Universal Declaration of Human Rights, the principle of prevention of significant harm to the environment and the duty to protect and preserve the marine environment;

(a) What are 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 greenhouse gases for States and for present and future generations?

(b) What are 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: 

i. States, including, in particular, small island developing States, 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?

ii. Peoples and individuals of the present and future generations affected by the adverse effects of climate change?

The Review Approach

The ICJ undertook a remarkably comprehensive review of the whole body of international law to determine the obligations of States in respect of climate change and the legal consequences of breaching those obligations. The Court first considered the sources of law, and concluded that the following were material to the case: 

• Treaties that concerned climate change,

• Other bilateral and multilateral treaties – Charter of the United Nations, the UN Convention on the Law of the Sea, other environmental treaties,

• Customary international law,

• International human rights law, and,

• Guiding principles, including on sustainable development, common but differentiated responsibilities and respective capabilities, equity, intergenerational equity, the precautionary principle, and the polluter pays principle

The pivotal question of Lex specialis

A key issue and a major flash point in the ICJ proceedings turned out to be the issue of Lex specialis, the rule that a specific law should take precedence over a more general law when both apply to the same situation. It essentially means that when two laws conflict, the more specific one should be applied. Among the States participating in the ICJ proceedings, two opposing perspectives of international law emerged. How the Court decided between these perspectives would have had a profound importance on the role international law itself. 

As might be expected, major emitter States argued that climate related obligations should only be those found within the climate treaties, and nowhere else. Relying on the principle of lex specialis, they advocated a narrow, atomistic interpretation of the climate treaties, while  rejecting the application of the both the State’s responsibility framework and the duty to prevent harm to the environment under customary international law.

In contrast, most other States, particularly small island States and other vulnerable and developing States, argued for a more robust role for customary international law in addressing complex and urgent global challenges like climate change. 

They pointed to the preambles of the UNFCCC and Paris Agreement that contain references to other rules and principles, indicating that the State parties to those treaties recognise that climate change is a problem for whose solution other rules and principles have a role to play. 

In this regard, the ICJ opined that States’ obligations in relation to climate change come not only from climate change treaties (UNFCCC, Kyoto Protocol and Paris Agreement) but also customary international law, including the duty to prevent significant harm to the environment. Hence, the entire body of customary international law remains relevant as a source of applicable law when determining “what are the obligations of States under international law to ensure the protection of the climate system and other parts of the environment”. This is interpreted to mean that while climate change treaties serve as the primary means by which States fulfil their general customary obligations, they are not the only sources of law. The Court explicitly stated that these treaties do not displace other rules and principles as lex specialis but rather coexist and inform each other within the broader international legal system. It follows, therefore, that from an operational standpoint, full and good faith compliance with climate treaties "suggests" substantial compliance with customary duties, but an independent assessment of customary law obligations must still be undertaken. The implications for this interpretation will be discussed further in part two of the three-part series.

States’ Obligations under Climate Change Treaties

The adoption of a temperature goal:

On the basis of the climate Change Treaties, the Court was of the view that while the Paris Agreement provides for limiting the global average temperature increase to well below 2°C above pre-industrial levels as a goal, and if possible, staying below 1.5°C as an additional effort, 1.5°C has become the scientifically based consensus target under the Paris Agreement. Hence, the ICJ considers the 1.5°C threshold to be the primary temperature goal.

The obligation to Mitigate GHG emissions:

The Court identified Annex I Parties (developed countries) as the Parties required to take the lead in limiting GHG emissions and enhancing GHG sinks and reservoirs, aiming to return combined emissions and removals to 1990 levels. In this context, the Paris Agreement reinforces actions to conserve and enhance sinks, like forests, as a primary lever alongside emission reduction.

The obligation to develop, communicate and implement Nationally Determined Contributions (NDCs):

With respect to NDCs, the core of the Paris Agreement, the ICJ noted that the Agreement obligates Parties to prepare, communicate, and maintain successive NDCs that represent a progression beyond previous ones and reflect their highest possible ambition, reflecting its common but differentiated responsibilities and respective capabilities, in the light of different national circumstances.

Although Art. 4, para. 2 of the Paris Agreement does not specify the content of the NDCs, it does not state that parties have an unfettered discretion in their preparation (as some States have sought to argue in these proceedings). In contrast, Art. 4, para. 3 of the Paris Agreement indicates that a party’s NDCs must become more demanding over time. Because in Art. 2, para. 1(a), there is an obligation to hold the increase in global average temperature to below 1.5°C. The existence of such standards in setting NDCs is also informed by the UNFCCC, which requires developed countries to take mitigation measures, and by the customary duty to prevent significant harm to the environment, which requires States to exercise due diligence, including with respect to activities such as setting NDCs.

A party’s obligations regarding its ambition in its NDCs, when interpreted in the context of the customary international law obligation to prevent significant harm to the environment, means that the contents of the party’s NDCs must be capable of making an adequate contribution to the achievement of the 1.5°C temperature goal. This places limitations on the discretion Parties have in the preparation of their NDCs. They are obliged to exercise due diligence and ensure their NDCs fulfil their obligations under the Paris Agreement. However, consistent with the varying character of due diligence and the principle of common but different responsibilities and respective capabilities, the standard of due diligence to be applied when assessing NCCs will vary depending, among others, on historical contributions to GHG emissions, the level of development and national circumstances of the party in question.

Obligations on the Production and Consumption of Fossil Fuels

The ICJ considered that the material scope of its inquiry encompasses the full range of human activities that contribute to climate change as a result of GHG emissions, including both consumption and production activities. In this regard, activities such as fossil fuel production, licensing, and subsidisation, and their cumulative and downstream effects, are central to mitigation obligations. The deeper implications of this obligation will be discussed in part three of the series, in the section covering the implications for Malaysia as an oil and gas producing nation.

The Obligation to Implement Adaptation Measures

The ICJ noted that under the UNFCCC, adapting to the adverse effects of climate change is, along with mitigation, a major area of action for parties. The ICJ further noted that the Paris Agreement aims to increase parties' ability to adapt to climate change impacts and foster climate resilience, and in light of these aims, Parties are encouraged to formulate and implement national adaptation plans and build resilience of socio-economic and ecological systems.

States’ Obligations under Customary International Law

Duty to Prevent Significant Harm to the Environment

The Court opined that States have an existing customary duty to prevent significant harm to the environment – even when no harm has yet been caused but the risk of future significant harm exists, or where some harm has already been caused and there exists a risk of further significant harm. Further, the Court explained that States must fulfil their duty to prevent significant harm to the environment by acting with due diligence. Because due diligence is a standard of conduct whose content in a specific situation is derived from various elements, including the circumstances of the State concerned, and which may evolve over time, the Court determined that the standard of due diligence for preventing significant harm to the climate system should be regarded as stringent.

Duty to Cooperate

The ICJ noted that the duty to co-operate takes on a special importance in the context of the need to reach a collective temperature goal, and is therefore, a duty founded on the recognition of the interdependences of States. The Court therefore saw cooperation, not as a matter of choice for States but as a pressing need and a legal obligation. In particular, they noted that States have a duty to co-operate, through financial assistance, technology transfer, and capacity-building, to help developing countries with their mitigation and adaptation obligations.

States’ Obligations under Human Rights Law 

Duty to Protect Human Rights

Finally, with respect to the issue of human rights, the Court viewed the adverse effects of climate change as potentially impairing the effective enjoyment of human rights. Noting that more than one hundred States have enshrined the right to a clean, healthy and sustainable environment in their constitutions or domestic laws, and the UN General Assembly’s resolution 78/300 of 28 July 2022 that recognised the right to a clean, healthy and sustainable environment as a human right, the Court concluded that under international law, the human right to a clean, healthy and sustainable environment is essential for the enjoyment of other human rights. 

This concludes part one of a three-part series on the the ICJs landmark advisory opinion on “the obligations of states with respect to climate change”. Part two will summarise the portion of the seminar dealing with the second question to the ICJ: What are the legal consequences under these obligations? In part two, I will also contextualize the AO from the standpoint of a developing country negotiator at the many COPs and Subsidiary Body meetings in which I have served as a national delegate over the years. Finally, in part three, I will cover the part of the seminar that examined the implications for Malaysia, and discuss the potential implications of the ICJ AO for the tone of the COP30 negotiations in Belem, Brazil.

Acknowledgement:

I would like to acknowledge the efforts and contribution of Mr. Kiu Jia Yaw and his excellent team at Kiu&Co for convening the Seminar entitled: The ICJ Advisory Opinion on Climate Change and What it Means for Malaysia, held at the Asian Institute of Chartered Bankers (AICB) on the 19th of August, 2025, on which this three-part series is based. Thank you Mr. Kiu. Your views and insights on the ICJ AO, and your clear and detailed explanations of the issues are deeply appreciated.