Eoin Jackson

On Wednesday this week, the International court of Justice (ICJ) released its landmark Advisory Opinion on states’ obligations in respect of climate change. An Advisory Opinion is a non-binding opinion provided by the ICJ which clarifies existing relevant elements and principles of international law with regard to addressing climate change and serves as a useful tool for activists seeking to pressure states to take greater climate action. 

In a pivotal moment for climate justice, the court recognised that obligations under international law to address climate change are not solely derived from climate-specific treaties like the Paris Agreement but also arise from a multiplicity of other international law sources and principles. This opinion provides a powerful normative signal, reinforcing the case for ambitious national climate targets aligned with the best available climate science and potentially helping climate-vulnerable countries push for fairer outcomes in international negotiations, including demands for reparations for climate harm.

Questions before the court

The court was asked by the UN General Assembly to consider two questions (1) the nature and extent of states’ obligations under international law to address climate change and (2) based on these obligations, the nature and extent of any legal consequences for major polluters for their role in causing and exacerbating climate harm.

During written and oral submissions, Global North and Global South states were divided on these questions. Many wealthy nations argued that obligations to address climate change were derived solely from climate-specific treaties like the Paris Agreement, and, as such, there could be no legal consequences for climate harm arising from other sources of international law. On the other hand, climate-vulnerable nations and in particular the small-island-developing-states argued that major polluters should face legal consequences for climate harm, and that other areas of international law, such as international human rights law, also impose obligations on states to take climate action.

The findings of the advisory opinion

In a decisive victory for the Global South, the court confirmed that states obligations to address climate change are not just confined to the climate treaties, but are also derived from customary international law, key environmental treaties (e.g. the UN Convention on the Law of the Sea) as well as international human rights law treaties. In particular, the court set out that all parties to the Paris Agreement must take climate measures which reflect their “highest possible ambition”, in accordance with the best available climate science and other considerations like intergenerational equity and the principle of common but differentiated responsibilities. Additionally, the court confirmed that obligations also exist under customary international law for states to protect the climate system, including a need for states to undertake “stringent due diligence” with regard to taking measures to prevent climate harm. These measures complement existing climate obligations under the climate-treaty system, placing further pressure on states to increase climate ambition.

The court’s recognition of the intersection between international human rights law also offers some further opportunities for climate activists. The court’s acknowledgment that the right to a healthy environment is a precondition to the exercise of all other human rights opens the door for further rights-based climate cases. We have already seen this at the international level in cases like Daniel Billy vs. Australia before the UN Human Rights Committee (where Australia was found to have violated the rights of Torres Strait Islanders due to its insufficient action on climate change). Confirmation of the intersection between climate change and human rights law and the particular importance placed by the court on the right to a healthy environment is likely to spur on similar efforts.

The court’s approach to the international environmental law obligation to refrain from acts of transboundary harm is likely to be the most significant consequence of the opinion. The court found that, in certain circumstances, if a state breaches its climate-related legal obligations, it commits an internationally wrongful act and therefore can be held responsible for adverse consequences associated with this act. In this regard, the court noted that “failure of a state to take appropriate increased 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.” [427] Additionally, a state’s failure to adequately regulate private actors to reduce greenhouse gas emissions may also lead to the state being held responsible for this failure to undertake necessary due diligence obligations.

If a state is found responsible for breaching its climate-related obligations, the court affirms that it must: (1) cease the wrongful conduct if it is ongoing; (2) provide guarantees of non-repetition where necessary; and (3) make full reparation to affected states—whether through restitution, compensation, or satisfaction—provided a clear causal link exists between the wrongful act and the harm caused. Notably, the court’s explicit reference to the role of fossil fuels in climate harm, alongside its recognition of the potential for reparations, opens a crucial door for climate-vulnerable states to demand significantly greater loss-and-damage funding for the havoc long wrought by industrialised nations on their people and ecosystems.

The court concluded by underscoring the gravity of the moment – it stated that “the questions posed by the General Assembly 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”. It called for urgent, collective action by all states, affirming that climate justice is not merely a moral aspiration, but a legal and political imperative.

Next steps following the advisory opinion

The next steps for the climate justice movement will be transforming the guidance of the Advisory Opinion into tangible legal and political outcomes. This will likely include greater calls for loss-and-damage funding at COP30, further efforts to pursue climate litigation and continued pressure on policymakers to ensure that all states are taking ambitious science-led climate action. The opinion is a milestone in the international response to climate change and should be carefully analysed by lawyers and policymakers alike to fully grasp its far-reaching implications for the global pursuit of climate justice.

Eoin Jackson is a PhD candidate at the London School of Economics (LSE) and Irish rapporteur at the Sabin Center for Climate Change Law.