Rising temperatures, rising duties: legal obligations of states on climate change
The ICJ clarified States’ obligations on climate change: a historic moment for environmental law and global accountability.
On the 23rd of July 2025, the International Court of Justice (ICJ) rendered a long-awaited advisory opinion on the legal obligations of States with respect to climate change. This historic ruling, requested by the United Nations General Assembly in March 2023 through a resolution sponsored by 132 States, marks a milestone in the intersection between international environmental law and human rights. The opinion was adopted unanimously – only the fifth time in the 80-years long activity of the ICJ.
These proceedings followed a growing trend of climate-related cases at international and domestic levels and they reflected increasing demands from civil society, youth movements, and vulnerable nations for clarity and accountability in global climate governance. The Court was asked to clarify the obligations of States to protect the climate system for present and future generations, and to assess the legal consequences for States that have caused significant harm to the environment.
Although not legally binding for States, the ICJ’s opinion is binding for UN bodies, carries substantial legal and political weight, and is expected to influence future litigation, treaty interpretation, and climate diplomacy. The relevance of this opinion is demonstrated by the relevant participation in the proceedings: 96 States and 11 International Organizations presented oral statements, the highest number in history. Additionally, some of the States most affected by climate change – such as Barbados or Micronesia – appeared before the Court for their very first time.
I. The Legal Basis of Climate Obligations
The ICJ identified several sources of legal obligations concerning climate change, inter alia: the Charter of the United Nations, the United Nations Framework Convention on Climate Change, the Paris Agreement, the core human rights treaties, and customary international law. While the Court acknowledged that specific emissions targets fall within the remit of domestic and treaty-based negotiation, it emphasized the existence of binding duties to prevent significant transboundary harm, cooperate in good faith, and protect human rights affected by climate degradation.
The Court held that the contention – raised among others by the EU, the UK, and China – that climate change treaties constituted the only body of law applicable to the matter could not be sustained. It found that the principle of lex specialis did not mean that those treaties automatically excluded or displaced the application of other rules of international law in a general manner.
Notably, the Court reaffirmed the customary obligation of States to ensure that activities within their jurisdiction do not cause damage to other States or areas beyond national jurisdiction. This principle, long established in international law, gains new salience when applied to climate change, given its inherently global and cumulative effects. The ICJ also pointed to the customary duty to cooperate with each other in good faith to prevent significant harm to the climate system and other parts of the environment. This is relevant because it underlines how States that are not Parties to the environmental and climate change treaties are not excused from the duty to prevent significant harm to the environment; meaning that countries such as the United States – and those who may follow its steps – deciding to denounce the treaties can still be held accountable.
II. Human Rights and Intergenerational Equity
One of the most forward-looking aspects of the advisory opinion lies in its recognition of climate change as a human rights issue. The ICJ found that States have obligations to respect and protect human rights that are adversely affected by climate change, including the rights to life, health, water, food, and adequate housing. Moreover, it affirmed that every person has a right to a ‘clean, healthy and sustainable environment’.
Additionally, the Court considered that all States have a common interest in the protection of global environmental commons like the atmosphere and the high seas. Hence, States’ obligations on the protection of the climate system are obligations erga omnes. Drawing on jurisprudence from regional human rights courts and UN treaty bodies, the Court concluded that these obligations are especially acute in relation to vulnerable populations and Small Island Developing States (SIDS). In this regard, another conclusion appears fundamental: the Court held that even if an entire landmass disappeared and its people got displaced, the State should still be presumed to continue as a sovereign entity. Similarly, the ICJ affirmed that States do not have any obligation to update charts or lists of geographical co-ordinates due to sea-level rise, meaning that rights of States over their maritime zones remain protected.
Furthermore, the Court underscored the concept of intergenerational equity, acknowledging the duty of States to preserve a healthy environment not only for current populations but for future generations.
III. Due Diligence and the Standard of Conduct
The Court confirmed that greenhouse gas emissions are ‘unequivocally caused by human activities’ , but it stopped short of defining specific mitigation targets, while still outlining the standard of conduct expected from States.
According to the opinion, States must adopt and implement effective measures based on the best available scientific evidence, including reports from the Intergovernmental Panel on Climate Change (deemed the ‘most authoritative source of scientific knowledge’ on the subject), in accordance with their respective capabilities
In addition to mitigation, the Court highlighted the importance of adaptation and financial support for developing countries. Developed States, given their historic responsibilities and greater capacities, have heightened obligations under the principle of common but differentiated responsibilities.
IV. Legal Consequences for Harmful Conduct
The ICJ addressed the consequences for States that fail to fulfill their climate obligations. Without identifying specific perpetrators, the Court held that such failures may entail the duty to cease harmful conduct, make assurances of non-repetition, and provide reparations when damage has occurred. These conclusions echo principles of State responsibility for international wrongful acts under international law and signal potential pathways for future claims. The opinion also addressed the extraterritorial dimension of climate harm, noting that States may bear responsibility for greenhouse gas emissions that affect communities beyond their borders.
V. Implications for Global Climate Governance
While the ICJ’s advisory opinion does not create new binding obligations, it significantly shapes the normative landscape of climate governance. It affirms the centrality of international law in addressing the climate crisis and provides a legal compass for the international community, it will likely influence upcoming negotiations at COP30 in Brazil, and it may also guide future cases before domestic courts and regional tribunals, providing a universal standard against which State conduct can be measured. Its emphasis on cooperation, equity, and scientific evidence reinforces multilateralism at a time of geopolitical fragmentation.
In the coming years, its most powerful legacy may lie not in judicial enforcement, but in its role as a moral and legal compass for climate justice. As the planet heats and the window for action narrows, the ICJ has spoken with clarity, placing international law in the service of planetary survival: climate action is no longer a choice, but a legal obligation and the world must rise to meet it.