International Court of Justice Advisory Opinion on Climate Change: A Game-Changer for the Vulnerable and a Just Transition?

This article was originally published in Medias24.

From wildfires scorching the Mediterranean region to devastating droughts afflicting Africa, recent years have been marked by massive loss and damage to communities and ecosystems, especially in poorer countries that contributed little to the climate crisis and are particularly vulnerable to its impacts—representing one of the gravest international injustices of the 21st century. 

In response to impacts in the Pacific, an initiative led by students from Pacific Island nations successfully advocated for Pacific Island governments to pursue an International Court of Justice Advisory Opinion (ICJ AO) on this existential planetary threat—in their words, “to take the world’s biggest problem to the world’s highest court.”

Brought together by the Government of Vanuatu, a cross-regional Core Group of States (which included Morocco and several other African countries) led a push that resulted in the successful adoption of a resolution at the UN General Assembly in 2023 (UNGA78). This resolution requested an ICJ AO on the obligations of states concerning climate change under international law and also the legal consequences for affected countries, peoples, and individuals. After nearly two years of deliberations, including written statements and oral hearings, the ICJ in July 2025 delivered its landmark advisory opinion, unequivocally outlining states' legal obligations under international law. 

Going beyond restating existing agreements on climate change, the ICJ delivered a powerful synthesis and exploration of obligations across mitigation, adaptation, and international cooperation, based on international law including but also looking beyond the UN Framework Convention on Climate Change (UNFCCC) and its Kyoto Protocol and Paris Agreement. Weaving in other relevant treaties and international human rights law, the Advisory Opinion solidifies the legal obligation to undertake climate action and international cooperation as part of the duty to prevent significant environmental harm and the duty to cooperate under customary international law. Crucially, the ICJ also confirms that general rules on state responsibility apply to breaches of these climate obligations—signaling a new era of accountability.

Obligations across Mitigation, Adaptation, and International Cooperation

An overarching takeaway from the ICJ AO is that states must act with “due diligence,” doing everything reasonable to achieve climate goals and prevent harm. This includes putting in place “regulatory mitigation mechanisms,” as well as adaptation measures to lessen impacts, in high-quality and ambitious Nationally Determined Contributions (NDCs) backed by domestic measures and policies, as well as international efforts in “cooperation, including in the fields of capacity building, transfers of finance and technology.” 

While all states have an obligation of due diligence (“erga omnes”), the degree of historical responsibility and how their NDCs and national actions may be judged will depend on factors such as historical contributions to cumulative GHG emissions, level of development, and national circumstances. The ICJ also considers the “multifactorial and evolutive character” of the principle of Common But Differentiated Responsibilities and Respective Capabilities (CBDR-RC), which entails implications for newly wealthy economies, while nevertheless upholding the special legal obligations on “developed countries” under the UNFCCC.

In terms of mitigation, failure of due diligence to protect the climate system from relevant emissions constitutes an “internationally wrongful act.” According to the ICJ, a state is responsible for its actions, and “internationally wrongful acts” by a state could include “fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences or the provision of fossil fuel subsidies” or failing to properly regulate emissions from “private actors under its jurisdiction.”

As for adaptation, the Advisory Opinion strongly affirms that climate adaptation is not an option but a legal obligation. It provides a basis for governments to be held legally accountable for their due diligence in adaptation planning, for their actions or inaction in “strengthening resilience”, and for their international cooperation, including the obligation of “developed countries” to support “developing countries” with adaptation costs. Per the UNFCCC, the Court recalls, legal accountability includes “matters of coastal zone management, water resources, and agriculture, and for the protection and rehabilitation of areas, particularly in Africa, affected by drought and desertification, as well as floods”. 

In addition, the Court confirms the “indispensable” role of international cooperation and financial assistance in addressing climate change and highlights the specific obligations of “developed countries” in this area in relation to climate change mitigation as well as adaptation costs. The Court explicitly recalls obligations to provide financial assistance under the UNFCCC’s Article 4 and the Paris Agreement’s Article 9.1, as well as other international law such as the UN Desertification Convention. This sets a clear legal expectation from the ICJ, strengthening the case for increasing provision of finance and improving transparency around it, further legitimizing the recent G77+China proposal at the UNFCCC 62nd Subsidiary Bodies meeting in June to adopt an agenda item on Article 9.1 addressing the provision of international public finance.  

When countries do not meet their climate obligations: Litigation, compensation, reparation?

According to the Court, if a state commits an “internationally wrongful act” related to climate change—meaning it breaks any of its identified legal duties—it becomes internationally responsible. The legal consequences of such an act could include several obligations, notably the duty to make full reparation for the damage caused through restitution and/or compensation. In addition, the Court recalls, financial compensation could include “indemnification for the impairment or loss of environmental goods and services in the period prior to recovery—and expenses incurred by injured States as a consequence of such damage.”

It is important to note that, per the Court, the obligation to make reparations is different from broader international climate finance obligations, which are about providing support for future and ongoing actions to mitigate or adapt to climate change, regardless of a specific wrongful actor. It is also distinct from the loss and damage mechanism under the Paris Agreement, which does not assign blame or legal responsibility for losses. 

Conclusions 

This ICJ Advisory Opinion breaks new ground for international law on climate change. Its significance is in the new political dynamics it will give rise to, in addition to new international lawsuits—though recent years have demonstrated that the limitations of international law require political efforts.

The Court situates the often-flouted commitments, declarations, and ambitions of states within the frame of international legal obligations, opening up a new world where states breaching their obligations can be held legally liable for their actions and inaction. Such litigation could ultimately compel countries to undertake the necessary emission reductions or provide material restitution and/or financial compensation for damages incurred by affected states. 

Concretely, countries in the Global South could use this legal opinion to pursue legal actions against those failing to uphold their climate duties, particularly those wealthier countries with significant historical emissions. This could include cases seeking compensation for climate-induced loss and damage, moving beyond the current voluntary mechanisms in place. 

Politically, this World Court opinion is very timely for countries in the Global South, including for African and Arab countries on the frontlines of climate impacts, given the current state of contestations in international climate politics within the UNFCCC process. This intervention offers much-needed reinforcement to the lacklustre state of international cooperation under the Paris Agreement, especially following COP29’s problematic process and inadequate outcome on the New Collective Quantified Goal (NCQG) on climate finance, as well as in the context of the 2025 NDC cycle. 

The Advisory Opinion could reshape the politics of international climate negotiations, potentially breaking longstanding deadlocks by virtue of a framework of legal obligations and the risk of liabilities for “wrongful acts,” both in international cooperation (e.g., provision of finance under Article 9.1) as well as national actions on mitigation and adaptation. Now is a fitting time for a reset of international climate politics on the basis of international justice, equity principles, human rights, and clearer pathways for legal action and accountability, especially ahead of COP30 and other multilateral fora. 

However, at the end of the day, the effectiveness of this Advisory Opinion hinges on the political will of states to uphold international law and respect their legal duties in good faith. As with the World Court’s provisional measures regarding the “Application of the Convention on the Prevention and Punishment of the Crime of Genocide in the Gaza Strip,” legal pronouncements alone are not enough but require a genuine political commitment to international law on the part of governments. 

Indeed, in its own conclusions, the ICJ holds that resolving an “existential problem of planetary proportions that imperils all forms of life” will require “human will and wisdom—at the individual, social, and political levels", expressing hope that "its conclusions will allow the law to inform and guide social and political action".