The ICJ Advisory Opinion and the Energy Transition Mandate
By Dr Mohammad Hazrati
Published on 14 August 2025
Finally, the long-awaited Advisory Opinion of the International Court of Justice (ICJ) on the obligations of States regarding climate change has been delivered. The Opinion exceeds expectations and can confidently be described as a turning point, not only in international climate change and environmental law but also in related fields such as international energy law. It is also expected to have a substantial and positive impact on climate action and the acceleration of energy transition initiatives.
The Advisory Opinion follows a request from the United Nations General Assembly (Resolution 77/276), initiated by a campaign led by Vanuatu and other small island developing States. The request posed two fundamental questions concerning the intersection of international environmental and human rights law, and the responsibilities of States:
- What are the obligations of States under international law to protect the climate system and environment from anthropogenic greenhouse gas emissions (GHG) for present and future generations?
- What are the legal consequences for States that have caused significant harm to the climate system, particularly for vulnerable countries and present or future communities affected by the adverse effects of climate change?
Although the ICJ’s Advisory Opinion is not legally binding, it carries great legal weight and moral authority. Such opinions often clarify and contribute to the development of international law, shape national legal frameworks, and influence future litigation. This historic Opinion joins two recent climate-related decisions by international bodies: the Inter-American Court of Human Rights and the International Tribunal for the Law of the Sea. While the Opinion contains numerous legal dimensions worthy of analysis, this reflection focuses primarily on its implications for the future of the energy transition.
In other words, although the Advisory Opinion clearly affirms States’ climate obligations, whether it specifically addresses the energy transition a specific aspect of general obligations and other climate actions, and what the defining characteristics or level of ambition of such a transition should be, remain to be seen. This blog post seeks to address these two questions.
A Clear Mandate for Energy Transition
My short answer to whether the Advisory Opinion addresses only general climate obligations or also specifically the energy transition is that it covers both—the energy transition as a specific aspect, along with broader climate obligations. Despite the belief that States are not under a specific legal obligation to reduce fossil fuel production or consumption and are instead free to adopt various emission and mitigation strategies, the Court considers fossil fuel production, consumption, exploration licenses, and subsidies as potential sources of internationally wrongful acts attributable to the State (para. 427).
In its discussion on attribution (paras. 425–432), the Court explains that in the context of State responsibility, attribution refers to the attachment of a given action or omission to a State under international law. Such attribution is a key element in establishing international responsibility and only conduct (acts or omissions) attributable to a State can give rise to an internationally wrongful act. It emphasises that the ‘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 licences, or the provision of fossil fuel subsidies—may constitute an internationally wrongful act which is attributable to that State’ (para. 427). This underscores the Court’s recognition that States could incur international responsibility for failing to take effective measures in the energy transition, particularly regarding fossil fuels. This interpretation establishes a basis for pursuing international litigation against States that expand their fossil fuel production or do not phase it out consistent with the 1.5°C temperature limit. Further support comes from the Joint Declaration by Judges Bhandari and Cleveland (para. 19), which states that obligations under the Paris Agreement, including the principles of progression and highest possible ambition in Article 4, require States’ Nationally Determined Contributions (NDCs) to address fossil fuel production, licensing, and subsidies in a manner consistent with achieving the 1.5°C goal. The significance of this development becomes even more apparent given that the Paris Agreement itself makes no mention of fossil fuels. Since the Court found that States’ obligations to protect the climate system and other parts of the environment from anthropogenic GHG emissions are erga omnes obligations (para. 440), all States have an interest in compliance. Therefore, any country, including those not directly harmed (para. 442), can bring a case against a fossil fuel–producing nation at the ICJ.
The Required Ambition and Pace of Transition
In the Opinion’s discussion of the obligations of State parties under the Paris Agreement, the Court observes 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 1.5°C as an additional effort, the 1.5°C temperature target has become the primary agreed-upon target for limiting the global average temperature increase under the Paris Agreement (para. 224). This shift is based on subsequent decisions adopted by the Conference of the Parties to the Paris Agreement, which reflect a common understanding of the interpretation of Articles 2 and 4, thereby constituting a “subsequent agreement” within the meaning of Article 31(3)(a) of the Vienna Convention on the Law of Treaties. The 1.5°C threshold has thus become the scientifically grounded and collectively endorsed benchmark under the Paris Agreement.
A 2021 study published in Nature explains how the 1.5°C target affects the energy transition and fossil fuel phase-out process. The study finds that to have a 50% chance of limiting global warming to 1.5°C, nearly 60% of oil and natural gas reserves, and 90% of coal reserves must remain unextracted by 2050. By comparison, under a 2°C carbon budget, about 35% of oil reserves would remain unextracted by 2050—25% less than the unextractable share required under the 1.5°C target.
In addition, with respect to mitigation obligations under the Paris Agreement, the Court holds that the level of ambition reflected in a party’s NDCs is not left entirely to its discretion (paras. 237–249). Instead, States are required to exercise due diligence and ensure that their NDCs are capable of fulfilling their obligations under the Agreement. Given the severity of the climate crisis, the Court emphasises that the standard of due diligence to be applied in preparing NDCs is particularly stringent. Each party must do its utmost to ensure that its NDC represents its highest possible ambition in order to achieve the objectives of the Agreement. The stringent due diligence obligations to implement such NDCs require States to adopt and enforce regulations aimed at reducing global dependence on fossil fuels, including phasing out their production and use and transitioning to cleaner energy sources in a manner consistent with achieving the 1.5°C temperature goal (see the Joint Declaration of Judges Bhandari and Cleveland). However, the principle of common but differentiated responsibilities and respective capabilities, recognised by the Court as guiding the implementation of obligations under climate change treaties (paras. 148–151), requires that States with greater resources and technical capacity transition more rapidly and assist other States. Accordingly, energy transition strategies are expected not only to aim for the 1.5°C target as their central objective but also to reflect the highest possible level of ambition that each State can achieve, based on its capacities, responsibilities, and national circumstances.
Coherence with Broader International Law
The next point concerns the concept of a “just transition.” Although the Advisory Opinion does not explicitly use this term, its reasoning suggests the concept is implicitly present. Specifically, the Court’s discussion on lex specialis—noting that when several rules apply to a single issue, they should be interpreted as far as possible to create a coherent and compatible set of obligations (para. 165)—reflects an approach that supports balancing different legal principles, which aligns with the idea of a just transition.
The Court ultimately found no actual inconsistency between the provisions of the climate change treaties and other relevant rules of international law in addressing Question (a). It also observed that since the Preambles of the United Nations Framework Convention on Climate Change and the Paris Agreement both contain references to other rules and principles, State parties to these treaties have thereby recognised that climate change is a problem whose solution involves multiple legal frameworks and principles (para. 168).
Thus, by placing human rights as a core concept and the centre of the energy transition, this reasoning strongly supports the importance of the just transition concept. One possible interpretation of these Statements is that, in implementing their climate change obligations, including energy transition programs, States are required to respect and not violate their other international law obligations, including those under international human rights law. Moreover, the Court explicitly recognises that the principles of sustainable development, common but differentiated responsibilities and respective capabilities, equity, intergenerational equity, and the precautionary approach serve as guiding principles for interpreting and applying the most directly relevant legal rules. Consequently, States must take these principles into account when designing and implementing policies and measures to fulfil their climate change commitments, including energy transition programs. Again, considering the principle of common but differentiated responsibilities and respective capabilities, together with the principle of equity, the obligation to transition away from fossil fuel dependence applies to all States. However, those with greater resources and technical capabilities are obliged to adopt deeper and faster targets than States with lesser capabilities (see the Joint Declaration of Judges Bhandari and Cleveland).
Regulating Private Actors
The Opinion also considers the role of private actors. Since private companies can play a significant role in the energy transition, either as accelerators or as obstacles, one might argue that their conduct, resulting in GHG emissions, is not attributable to States and therefore does not engage State responsibility (see, for instance, Written Statement of the Kingdom of Saudi Arabia, para. 6.7). This argument could have real implications for how governments engage with the private sector in energy transition programs, particularly in deciding whether to rely on voluntary standards or to impose binding regulatory measures.
However, the Court observes that while private conduct is not attributable to States, a State may still be responsible if, for example, it fails to exercise due diligence by not adopting the necessary regulatory and legislative measures to limit the quantity of emissions caused by private actors under its jurisdiction. The Court stresses that effective regulation, including legislative and administrative action, is essential. This extends the responsibility for the energy transition beyond State-owned enterprises to the broader private sector, moving beyond voluntary actions by private companies and affirming the obligation of States to ensure that all actors align with climate goals.
Conclusion
This Advisory Opinion is poised to shape the future trajectory not only of international climate and environmental law and governance, but also of energy law, by clearly identifying fossil fuel activities as a probable source of an internationally wrongful acts attributable to the State. As stated in the opening line of the Joint Declaration by Judges Bhandari and Cleveland:
Climate change treaties and customary international law require all States to phase out fossil fuel production and use and transition to clean energy—[the] Court recognises that obligations to protect the climate system encompass fossil fuel production, licensing, and subsidies.
The advisory opinion also offers important guidance on defining the pace, level of ambition, scope, and key features of the energy transition, including the imperative of ensuring a just transition. Among its key implications is the affirmation of the centrality of the energy transition in achieving the 1.5°C target.
The Opinion is expected to influence both the tone and substance of the upcoming COP negotiations in November, potentially prompting more assertive and unambiguous commitments to phase out fossil fuels and helping to resolve the ongoing debate over their inclusion in the final COP declaration. By clarifying States’ obligations and reinforcing accountability, the Opinion may serve as both a legal and moral compass guiding international cooperation and domestic climate and energy policy in the years ahead.
Dr Mohammad Hazrati is Senior Research Fellow at the Centre for International Law, National University of Singapore, specialising in energy, environmental, and climate change law and policy, with a particular focus on the energy transition.