Bridging the Attribution Gap: How the 2025 ICJ Advisory Opinion Redefined Responsibilities of States in Climate Litigation

For many years, international climate change litigation has been paralyzed by the nagging problem of the ‘attribution gap’. Under classical international law, state responsibility requires a direct and unbroken causal chain running from a state’s wrongful act to a specific, localized harm. That requirement has proved almost impossible to establish issues related to global climate change.

How can a small island nation demonstrate in court that a specific heatwave or coastal inundation was caused directly by the historical greenhouse gas (GHG) emissions of a particular industrialized country, rather than by the collective emissions of the whole world over a century?

However, the landmark Advisory Opinion delivered by the International Court of Justice (ICJ) on July 23, 2025, has fundamentally altered this landscape. The ICJ has effectively tried to bridge the ‘attribution gap’ by clarifying the role of stringent due diligence in assessing state responsibility, rather than relying solely on strict, localized causation. This article argues that the Court’s opinion has shifted the burden of proof in climate litigation allowing vulnerable states to invoke international responsibility without waiting for perfect scientific attribution.

The Challenge of Causation and Attribution

To understand the gravity of the ICJ’s intervention, we must first understand the structure of climate attribution science. In modern climate litigation, attribution theory in general is separated into three main areas: climate attribution (identification of the agents behind global warming), source attribution (quantifying the share of specific entities or states in global emissions), and impact attribution (quantifying the extent to which human-induced climate change affected an extreme weather event).

Historically, the gap between source and impact attribution has been weaponized by defendant states and fossil fuel majors. Even when a state’s historical emissions can be quantified (source), defendants argue that, given present scientific understanding, it is impossible to attribute a specific flood in South Asia or a hurricane in the Caribbean (impact) to them because of the indivisible nature of the atmosphere. This rigid and inflexible adherence to the traditional tort-like causation has often allowed large polluters to escape international legal accountability.

The catastrophic glacial flood in Nepal in August 2026 vividly exemplifies the attribution dilemma. The scientific analysis so far has identified human-induced warming as a factor in the conditions leading to glacier destabilization in the Himalayas. But the challenge of converting that scientific evidence into legal liability remains far more complex. Even so, Nepal would still struggle to prove that a specific state’s contribution to global emissions caused the individual harm suffered by the claimants, rather than merely showing that climate change increased the underlying risk. The World Weather Attribution review highlights the scientific dimension of this issue, while the ICJ Opinion provides the legal track for assessing state obligations and responsibility.

Stringent Due Diligence: The 2025 ICJ Shift

July 2025 ICJ Advisory Opinion (++Please hyperlink the advisory opinion++) was able to navigate this deadlock elegantly. Instead of trying to rewrite the laws of physics or scientific probability, the Court reshaped the legal standard of state conduct. The Court held unanimously that the set of treaties forming the global climate regime i.e. the UN Framework Convention on Climate Change (UNFCCC) (++Please hyperlink the convention++) and the Paris Agreement (++Please hyperlink the agreement++), are to be read together with customary international law, in line with “systemic integration”.

The Court affirmed a crucial duty that customary international law (Please hyperlink the source of recognition of this duty as customary law) places on every State, namely the duty to prevent severe environmental harm. It added that although customary international law imposes a standard of stringent due diligence for the prevention of significant environmental harm, it does not require proof that emissions from one State have caused identifiable harm in another. In other words, a state can be held internationally accountable only on the grounds of its failure to take regulatory, legislative, and enforcement measures to limit GHG emissions from public and private actors within its jurisdiction. The ICJ explicitly noted that a state’s failure to act, or to proactively realize the targets already outlined in its Nationally Determined Contributions (NDCs), amounts to a breach of international law.

Separating Procedural Breach from Causation

The major analytical shift here lies in the fact that the state’s responsibility is triggered by a procedural failure to act with due diligence, not just by the physical manifestation of harm itself. By democratizing legal standing, the ICJ treated climate protection duties as erga omnes obligations, that is universal obligations owed to the international community in their totality.

Here, a state vulnerable to climate change does not have to demonstrate that a particular ton of carbon emitted by a developed country was responsible for its rising sea levels. Rather, the vulnerable state can invoke the responsibility of the high-emitting state on the grounds that it violated an erga omnes duty of stringent due diligence by, for example, continually licensing vast fossil fuel extraction projects or failing to regulate the polluting companies.

This effectively removes the need for perfect impact attribution in the very first phase of establishing legal liability. While the science behind impact attribution will still be highly important in the reparation phase, where courts must quantify how much a state should pay for specific damages, it is no longer a strict obstacle to declaring that an internationally wrongful act has occurred.

Conclusion

The 2025 ICJ Advisory Opinion does not magically solve the climate crisis, nor does it render the complex science of climate attribution irrelevant. When developing countries seek reparations for rebuilding after particular disasters, courts will still require rigorous scientific modeling to quantify those damages. Nonetheless, what the Court has done is a major historic achievement in harmonizing international law with the physical realities of the atmospheric crisis.

By recognizing that the global climate system cannot be artificially confined into isolated, bilateral disputes between two countries, the ICJ has found that failing to exercise stringent due diligence through concrete, feasible domestic climate policies are itself an  international legal violation. For the first time, the attribution gap no longer constitutes an absolute shield against state responsibility. This gives climate-vulnerable states and civil society a voice to challenge high-emitting nations in legal tribunals today, forcing them to account not just for the historical damage they have already caused but also for the preventive actions they are currently failing to take.