The ICJ’s Landmark Opinion: Climate Accountability for States and their Obligations in the Fight Against Climate Change

On 23 July 2025, the International Court of Justice (ICJ) delivered its Advisory Opinion on the Obligations of States in respect of Climate Change, marking a key moment in the intersection of international law and environmental protection. The General Assembly of the United Nations had previously adopted resolution 77/276 on 29 March 2023 which requested the ICJ to give an opinion to address two questions concerning the responsibilities that States have to mitigate climate change alongside the consequences of failing to do so. 

The Questions Before the ICJ

Two questions were raised with the ICJ by the General Assembly of the United Nations, seeking clarity as to:

1. The obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions.
2. The legal consequences for States that, through their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to:
   1. Other States and, in particular, small island developing States which are particularly vulnerable to the adverse effects of climate change; and
   2. Peoples and individuals of present and future generations affected by climate change.

Key Findings 

The ICJ’s opinion is notable not only for its content but also for its unanimous adoption. This is only the fifth instance of this occuring in the ICJ’s nearly 86-year history.

In answer to question (a) the ICJ:

• Affirmed that States which are party to climate change and environmental treaties are bound by their obligations under those treaties to protect the climate system and environment from anthropogenic greenhouse gas emissions.  
• Affirmed that such obligations on States are extended by customary international law which imposes duties upon them - including the prevention of significant harm to the environment by acting with due diligence and the duty to co-operate with each other in good faith to prevent such harm.
• Affirmed that States which are party to the United Nations Convention on the Law of the Sea have an obligation to protect and preserve the marine environment, including protection from the adverse effects of climate change.
• Confirmed that States have obligations under international human rights law to ensure the effective enjoyment of human rights through taking necessary measures to protect the climate system.

In answer to question (b) the ICJ considered that a breach by a State of the obligations identified in response to question (a) constituted an internationally wrongful act, with consequences of breach including the obligation to:

• Cease the wrongful acts or omissions (if continuing);
• Provide assurances and guarantees that the wrongful acts or omissions would not be repeated; and
• Provide full reparation to injured States, to include restitution, compensation and satisfaction in the event that a causal relationship can be established between the wrongful act and the injury suffered.

What does the ICJ’s Opinion Mean for the Future of Climate Governance?

The ICJ’s Advisory Opinion is vital in reaffirming that States have legal accountability for climate-related harm, with potential consequences for failure to comply. Furthermore, it potentially opens the door to future litigation, especially by vulnerable nations and affected communities.  For some states, the opinion may serve as a wakeup call, highlighting the requirement to align their domestic policies with their existing international obligations (set out in treaties, customary international law or human rights law).

While the ICJ opinion is non-binding, the legal and moral weight which is accorded to the opinion means that this is a significant development. Therefore, the opinion will become another important tool in the arsenal of vulnerable States and claimant groups in climate related negotiations and litigation. 

We were interested to note that, in addition to discussing greenhouse gas emissions, the ICJ concluded that conduct leading to production of greenhouse gases (such as the production or consumption of fossil fuels, granting fossil fuel exploration licenses or providing fossil fuel subsidies) could also constitute a “wrongful act”. In addition, the obligations identified by the ICJ are also deemed to include State’s duties to, “regulate activities of private actors as a matter of due diligence” – with failure to do so constituting a wrongful act. These measures collectively cast the net significantly wider when considering the responsibilities of States and whether they are meeting their climate obligations. 

This article was written by Fraser Campbell and Christopher Wenn.