Shashank Pandey, the writer is a lawyer and former research fellow at Vidhi Centre for Legal Policy
On Wednesday, the International Court of Justice (ICJ) delivered its advisory opinion in response to the UN General Assembly’s request to clarify the obligations of states under international law with respect to the climate system. While the opinion addresses a wide range of issues, ranging from human rights to rising sea levels, the court identifies due diligence as the key legal standard that determines whether states have met their obligations to prevent harm from greenhouse gas (GHG) emissions.
In the complex architecture of treaty law, customary obligations, and evolving scientific knowledge, the concept of due diligence provides the clearest, enforceable test of lawful state conduct. Here, the focus will be on the due diligence standard because it is not only central to the court’s reasoning but also the most usable legal tool going forward to assess climate accountability.
Due diligence as a threshold for responsibility
The ICJ affirms that due diligence is a duty of conduct, not of result (para. 136). In climate terms, it means a state must do everything “reasonably available” within its means to avoid causing significant environmental harm, particularly from GHG emissions (para. 272-273). Importantly, the it characterises due diligence as stringent in the climate context (para. 280), reflecting the scale and urgency of the crisis.
Due diligence is not generic. It must be assessed in concreto, considering a state’s specific circumstances but with no room for inaction. This is where the ICJ’s contribution is significant—it unpacks due diligence into several components that now serve as benchmarks for measuring compliance.
The ICJ outlines three critical dimensions of due diligence—substantive obligations, procedural requirements, and context-sensitive application based on capacity and evolving science.
First, the ICJ explained that states need to adopt and enforce legal and policy frameworks that ensure “deep, rapid and sustained” reductions in emissions (para. 281). It is not enough to announce goals, states must also implement them through legislation, administrative controls, and monitoring. A failure to regulate major sectors like energy, transport, or land use will likely amount to a breach.
Second, a core component of due diligence, the precautionary principle, obliges states to take preventive measures even in the face of scientific uncertainty (para. 294). The existence of a plausible risk, such as an Intergovernmental Panel on Climate Change report indicating threats from high emissions, creates an immediate obligation to act. Waiting for conclusive evidence is no defence for state inaction.
And third, the procedural necessities like risk assessments, environmental impact assessments (EIAs), notification, and consultation are now binding obligations (paras. 295-299). These are not bureaucratic formalities. A failure to conduct proper EIAs or consult with affected states before undertaking a high-emission project constitutes a breach of due diligence. This procedural layer ensures decisions are informed by science, transparent, and accountable across borders.
Dynamic nature of due diligence
Acknowledging the principle of common but differentiated responsibilities, the court allows for variation in what is expected of states based on their capabilities (paras. 290-292). But crucially, it does not allow capacity limits to become a shield for inertia. Every state must take all reasonable measures it can. Simultaneously, high-capacity states are held to a higher standard and bear additional obligations to support others through financial assistance, technology transfer, and capacity-building (paras. 260-267).
Another critical feature of the court’s reasoning is its recognition that due diligence is not static. It evolves with scientific and technological advances (para. 284). What counts as “reasonable measures” today will shift as more effective tools become available. This embeds a dynamic standard into international law, forcing states to revise outdated policies and continuously adapt.
Ensuring compliant state climate actions
The ICJ’s articulation of due diligence turns an abstract idea into a structured legal test. While the opinion is non-binding, its authority lies in its persuasive value and clarification of customary law. It now provides a baseline against which both litigation and political accountability can be measured. For instance, if a state submits an unambitious nationally determined contribution or fails to execute it effectively, it can be challenged as falling short of the due diligence standard (paras. 250-254).
The ICJ then uses the due diligence metric to determine the broader framework of state responsibility (paras. 421-455). A breach of this standard can trigger obligations of cessation, guarantees of non-repetition, and reparation. In short, this is not symbolic law but rather lays the foundation for real legal consequences and will influence future climate litigation in courts.
The ICJ has done more than clarify obligations. It has operationalised them. By turning due diligence into a concrete, evolving, and enforceable standard, the ICJ has given states, courts, and affected communities a workable tool to assess climate conduct. The message is clear that environmental obligations are not aspirational but legal, measurable, and enforceable. In a fragmented international legal landscape, that clarity was long overdue.