What are the ramifications of the ICJ's advisory opinion on States' obligations to address climate change?

In brief 

• The International Court of Justice's (ICJ) unanimous opinion on the Obligations of States in Respect of Climate Change provides a powerful legal foundation for demanding greater action from both governments and private actors. 
• A breach of any identified obligation to protect the climate system and wider environment from greenhouse gas (GHG) emissions may constitute an internationally wrongful act, potentially requiring full reparation to injured States. 
• Such potentially wrongful acts include fossil fuel production and consumption, the granting of fossil fuel exploration licenses, and the provision of fossil fuel subsidies, which deals a major blow to the oil and gas industry. 
• They also include States' failure to adopt adequate laws or regulations to limit the emissions of private actors in their jurisdictions, which provides an important counterweight to current deregulatory efforts, such as EU Omnibus legislation. 
• In reinforcing the growing global consensus on issues of causation and attribution, the ICJ opinion will likely embolden domestic litigants building strategic claims seeking damages from large greenhouse gas (GHG) emitters. 
• Although non-binding, the advisory opinion carries considerable weight under international law, and its implications should be considered carefully in corporate boardrooms as well as in the corridors of Government. 

Background 

The ICJ was called upon by the UN General Assembly to consider two questions: 

1. For the benefit of current and future generations, what are States' obligations under international law to ensure protection of the climate system and other parts of the environment from human-induced GHG emissions? 
2. Based on these obligations, what are the legal consequences for States that, by their acts or omissions, cause significant harm to current and future generations – particularly those who are especially vulnerable to, and disproportionately affected by, the adverse impacts of climate change? 

No fewer than 96 countries and 11 regional organisations participated in public hearings before the ICJ (the largest number in the court's history), with arguments broadly reflecting one of two positions: 

1. That States' obligations to address climate change stem exclusively from climate-specific treaties (e.g. the Paris Agreement) and should be interpreted narrowly, without reference to broader principles of international law  
2. That major emitters can be held legally responsible for adverse climate impacts and that other areas of international law (such as human rights law) also impose obligations to significantly accelerate meaningful climate action. 

In its long-awaited advisory opinion, published on 23 July 2025, the ICJ firmly rejected the former position, affirming that climate treaties must be interpreted in harmony with other rules and principles of international law. Although non-binding, this opinion carries considerable weight, particularly given the number of States participating in the proceedings and the unanimous opinion of the court. 

Key legal obligations identified 

Treaty law 

• The UNFCCC, Kyoto Protocol and Paris Agreement set binding obligations for States to mitigate GHG emissions, adapt to climate change and co-operate internationally. The Paris Agreement’s 1.5°C temperature goal is a binding legal target, and States must prepare, communicate, and maintain nationally determined contributions (NDCs) that are collectively capable of achieving it. The "mere formal preparation, communication and maintenance of successive NDCs is not sufficient to comply with" States' obligations to mitigate climate change.  
• Parties to the UN Convention on the Law of the Sea (UNCLOS) have obligations to protect and preserve the marine environment from climate change impacts, including GHG emissions as marine pollution, and to co-operate globally and regionally. 
• Obligations under other environmental treaties – such as the Ozone Layer Convention and Montreal Protocol, the Biodiversity Convention and the Desertification Convention - are relevant to climate protection. 

Customary international law 

• The duty to prevent significant harm to the environment applies to the climate system and requires States to act with due diligence to prevent significant harm arising from activities within their jurisdiction or control. The standard of due diligence is stringent, "on account of the fact that the best available science indicates that the '[r]isks and projected adverse impacts and related losses and damages from climate change escalate with every increment of global warming'." 
• The duty to co-operate for the protection of the environment is intrinsically linked to the duty to prevent significant harm, since uncoordinated individual efforts by States may not lead to meaningful results. It also derives from the shared interest in conserving and managing shared resources. 

International human rights law

• States have obligations to respect, protect, and ensure the enjoyment of human rights, which are impaired by climate change.  
• The right to a clean, healthy and sustainable environment is recognised as a human right, inherent in the enjoyment of other rights such as life, health and an adequate standard of living. 

Guiding principles 

• The principles of sustainable development, common but differentiated responsibilities and respective capabilities, equity (including intergenerational equity), and the precautionary approach guide the interpretation and application of the above obligations.  

Legal consequences of breach 

State responsibility 

• General framework: a breach of any identified obligation constitutes an internationally wrongful act, entailing State responsibility under customary international law. The general rules of State responsibility apply unless specifically excluded by treaty, which is not the case for the climate change treaties. 
• Attribution and causation: the rules on attribution and causation are applicable, even in the complex context of climate change, involving multiple States and cumulative effects. Each injured State may invoke responsibility against any State that has committed a wrongful act resulting in damage. 
• "Erga omnes" character: obligations to protect the climate system are erga omnes (owed to the international community as a whole), allowing any State to invoke responsibility for breaches, not just those directly injured. 

Remedies 

• Duty of performance: the responsible State must continue to perform the breached obligation. 
• Cessation and non-repetition: if continuing, the State must cease the wrongful act and provide assurances against repetition if required. 
• Reparation: full reparation is required, which may include restitution, compensation, and satisfaction, provided a sufficiently direct and certain causal nexus is established between the wrongful act and the injury. 

Implications for private entities 

While the ICJ's advisory opinion focuses on the obligations of States in respect of tackling climate change, it is likely to have significant ramifications for private actors too.  

A major blow for the fossil fuel industry 

The Court explicitly states that "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." 

The ICJ opinion therefore supports the goals of the Fossil Fuel Non-Proliferation Treaty, strengthens legal arguments for ending fossil fuel subsidies, and could well act as a further spur for strategic anti-fossil fuel litigation. 

A counterweight to deregulatory pressure 

Additionally, the stringent due diligence obligation imposed on States to prevent significant harm not only requires sufficiently ambitious policies for dealing with climate change, but also the means to enforce them. In other words, governments can also be held responsible for failures to adopt adequate laws or regulations to limit the emissions of private actors in their jurisdiction. 

It will be interesting to see if/how this affirmation of States' legal duty to effectively regulate private actors will affect the current backlash against enhanced sustainability regulations, exemplified by EU omnibus legislation.  

A growing global consensus on causation 

A striking feature of the ICJ opinion is its consistency with recent rulings of domestic courts grappling with one of the knottiest questions of climate litigation – causation and attribution.  

Just over a month ago, in Luciano Lliuya v. RWE AG, the Higher Regional Court of Hamm confirmed that a company can, in principle, be liable for climate harm, in a manner reflective of its contribution to global emissions. In a significant win for private litigation against high emitters, the Court accepted that causation can be made out in claims brought against large corporate emitters for climate damages, stating that "in the case of multi-causal liability scenarios, a comparative consideration must always be made. It is not the mere amount of the causal contribution as such – e.g. 5% or 10% – that is the yardstick for materiality, but the amount in relation to other causal contributions." 

Previously, in Smith v. Fonterra Co-Operative Group Limited, ruling on a strike out application, the Supreme Court of New Zealand had also affirmed that causation may be made out in cases seeking to hold large polluters accountable for climate harms. 

The ICJ similarly rejected arguments that "causation is impossible to establish in the present context due to the diffuse nature of climate change." Rather, it held that "the standard of 'a sufficiently direct and certain causal nexus' between an alleged wrongful action or omission and the alleged damage is flexible enough to address the challenges arising in respect of the phenomenon of climate change." 

Consequently, the global consensus that the law can recognise a causal link between GHG emissions and consequent climate harm, is undoubtedly growing. The ICJ’s opinion is likely to significantly reinforce the efforts of domestic litigants who are building strategic claims seeking damages from large GHG emitters.  

How we can help 

There is an increasing disconnect between the scientific consensus on what is required for a just and sustainable future, and the outcomes being delivered by current policies and business strategies.  

For those looking to obtain justice for affected communities and drive systemic change, strategic litigation is a powerful tool for holding institutions to account. Our work in this space is distinguished by an unusual level of in-house capability in data science and global group actions management, as well as by strong relationships with litigation funders, philanthropists, crowdfunding organisations, NGOs and academics. 

For those seeking to drive necessary transformations within their organisations, we advise corporates and private interests on evolving sustainability risks and opportunities, and the governance and management best practices necessary to address them. Balancing compliance with strategic foresight, our interdisciplinary team of expert lawyers and sustainability professionals helps clients to assess where they are exposed to risk, to identify opportunities to strengthen resilience, and to transform with confidence. 

Visit our Mishcon Purpose pages to find out more.