The philosophy and obligations of statecraft in the era of climate change

By Dr Bertrand Ramcharan

Seventh Chancellor of the

University of Guyana

Previously Fellow of the LSE and Fellow of Harvard University

In a legal opinion rendered on 23 July, 2025, the International Court of Justice, the highest judicial authority in the world, recognized the perils of climate change in the following terms:

“The consequences of climate change are severe and far-reaching. They affect both natural ecosystems and human populations. Rising temperatures are causing the melting of ice sheets and glaciers, leading to sea level rise and threatening coastal communities with unprecedented flooding. Extreme weather events, such as hurricanes, droughts and heatwaves, are becoming more frequent and intense, devastating agriculture, displacing populations and exacerbating water shortages. Furthermore, the disruption of natural habitats is pushing certain species toward extinction and leading to irreversible loss of biodiversity. Human life and health are also at risk, with an increased incidence of heat-related illnesses and the spread of climate-related diseases. These consequences underscore the urgent and existential threat posed by climate change. In examining these consequences, the Court relies primarily on the reports of the Intergovernmental Panel on Climate Change (hereinafter the “IPCC”), which participants agree constitute the best available science on the causes, nature and consequences of climate change. It further observes that the adverse effects of climate change on the climate system have been acknowledged by the United Nations, including the United Nations Environment Programme, and its specialized agencies, such as the World Meteorological Organization, the World Health Organization and the International Maritime Organization”.

 The ICJ cited the conclusion of the IPCC with “very high confidence” that risks and projected adverse impacts and related loss and damage from climate change will escalate with every increment of global warming. These risks, projected adverse impacts, and related loss and damage are “higher for global warming of 1.5°C than at present, and even higher at 2°C”.

The ICJ was responding to a request of the UN General Assembly for a legal opinion, urged on by young people the world over, particularly in Asia and the Pacific. In requesting the advisory opinion, the UN General Assembly was mindful of the legal obligations of Governments under the Charter of the United Nations, the International Covenant on Civil and Political Rights, the Inter-national Covenant on Economic, Social and Cultural Rights, the United Nations Framework Convention on Climate Change, the Paris Agreement, the United Nations Convention on the Law of the Sea, the duty of due diligence, the rights recognized in the Universal Declaration of Human Rights, the principle of prevention of significant harm to the environment and the duty to protect and preserve the marine environment.

The General Assembly asked for the legal opinion of the court on the following questions:

(a) What are the obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic [man-made] emissions of greenhouse gases for States and for present and future generations? 

(b) What are the legal consequences under these obligations for States where they, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to: (i) States, including, in particular, small island developing States, which due to their geographical circumstances and level of development, are injured or specially affected by or are particularly vulnerable to the adverse effects of climate change? (ii) Peoples and individuals of the present and future generations affected by the adverse effects of climate change?’ 

In providing its legal opinion, the ICJ underlined that the Charter of the United Nations, “which is a pillar of contemporary international law”, requires States to act in accordance with certain principles – such as the principle of international cooperation – when addressing problems of common concern, such as climate change. The Charter, the Court emphasized, represents the core of the most directly relevant applicable law.

The Court, by unanimous votes, specified the following international legal obligations of States and their Governments in respect of climate change.

First, the climate change treaties set forth binding obligations for States parties to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions. These obligations include the following: States parties to the United Nations Framework Convention on Climate Change have an obligation to adopt measures with a view to contributing to the mitigation of greenhouse gas emissions and adapting to climate change; States parties to the United Nations Framework Convention on Climate Change have a duty to co-operate with each other in order to achieve the underlying objective of the Convention; States parties to the Kyoto Protocol must comply with applicable provisions of the Protocol; States parties to the Paris Agreement have an obligation to act with due diligence in taking measures in accordance with their common but differentiated responsibilities and respective capabilities capable of making an adequate contribution to achieving the temperature goal set out in the Agreement; States parties to the Paris Agreement have an obligation to prepare, communicate and maintain successive and progressive nationally -determined contributions which, inter alia, when taken together, are capable of achieving the temperature goal of limiting global warming to 1.5°C above pre-industrial levels; States parties to the Paris Agreement have an obligation to pursue measures which are capable of achieving the objectives set out in their successive nationally determined contributions; and States parties to the Paris Agreement have obligations of adaptation and co-operation, including through technology and financial transfers, which must be performed in good faith.

Second, customary international law (which is a technical term for norms of  international law binding on all States) sets forth obligations for States to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions. These obligations include the following:

States have a duty to prevent significant harm to the environment by acting with due diligence and to use all means at their disposal to prevent activities carried out within their jurisdiction or control from causing significant harm to the climate system and other parts of the environment, in accordance with their common but differentiated responsibilities and respective capabilities;

States have a duty to co-operate with each other in good faith to prevent significant harm to the climate system and other parts of the environment, which requires sustained and continuous forms of co-operation by States when taking measures to prevent such harm;

Third, States parties to the Vienna Convention for the Protection of the Ozone Layer and to the Montreal Protocol on Substances that Deplete the Ozone Layer and its Kigali Amendment, the Convention on Biological Diversity and the United Nations Convention to Combat Desertification in Those Countries Experiencing Serious Drought and/or Desertification, Particularly in Africa, have obligations under these treaties to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions;

Fourth, States parties to the United Nations Convention on the Law of the Sea have an obligation to adopt measures to protect and preserve the marine environment, including from the adverse effects of climate change and to co-operate in good faith;

Fifth, States have obligations under international human rights law to respect and ensure the effective enjoyment of human rights by taking necessary measures to protect the climate system and other parts of the environment.

             Sixth, a breach by a State of any obligation identified above (a) constitutes an internationally wrongful act entailing the responsibility of that State. The responsible State is under a continuing duty to perform the obligation breached. The legal consequences resulting from the commission of an internationally wrongful act may include the obligations of:

cessation of the wrongful actions or omissions, if they are continuing;

providing assurances and guarantees of non-repetition of wrongful actions or omissions, if circumstances so require; and

full reparation to injured States in the form of restitution, compensation and satisfaction, provided that the general conditions of the law of State responsibility are met, including that a sufficiently direct and certain causal nexus can be shown between the wrongful act and injury.

In the course of handing down the legal opinions just summarized, the Court provided important clarifications on the content of contemporary international law in respect of climate change. On the duty of States to prevent significant harm to the environment, the Court recalled that in its Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, it had recognized that the duty to prevent significant harm to the environment applies to global environmental concerns. Therefore, this duty also applies with respect to the climate system and other parts of the environment. 

The duty to prevent significant harm to the environment, the Court underlined, is an obligation to act with due diligence. The determination of what is required by due diligence ultimately “calls for an assessment in concreto” of what is reasonable under the specific circumstances in which a State finds itself. This does could include the identification of a required standard of conduct at a general level, depending on the overall character of the risk to the part of the environment in question. This is particularly apposite with respect to climate change because the specific character of the risk of significant harm to the climate system is indisputably established. 

In these circumstances, the Court recognized that the standard of due diligence for preventing significant harm to the climate system is stringent. Moreover, due diligence entails not only the adoption of appropriate rules and measures, but also a certain level of vigilance in their enforcement and the exercise of administrative control. As concerns climate change, a heightened degree of vigilance and prevention is required.

 The Court concluded that the duty of States to prevent significant environmental harm applies in the context of climate change and that this duty forms part of the most directly relevant applicable law. The Court also considered that the duty to co-operate for the protection of the environment forms part of customary international law (binding international law) and can also serve as a guiding principle for the interpretation of other rules. It forms part of the most directly relevant applicable law. The duty to co-operate, the Court added, lies at the core of the Charter of the United Nations.

This obligation had been spelled out in the “Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations” of 24 October 1970. The Court has held previously that “the adoption by States of this text affords an indication of their opinio juris as to customary international law”. That observation also applies to the duty to co-operate in so far as it finds expression in many binding and non-binding instruments relating specifically to the environment. In view of the related practice of States, the Court considers that the duty of States to co-operate for the protection of the environment is a rule whose customary character has been established. This duty to co-operate is intrinsically linked to the duty to prevent significant harm to the environment, because uncoordinated individual efforts by States may not lead to a meaningful result.

In the Court’s view, intergenerational equity, as an expression of the idea that present generations are trustees of humanity tasked with preserving dignified living conditions and transmitting them to future generations, is a manifestation of equity in the general sense and thus shares its legal significance as a guide for the interpretation of applicable rules.

The Court expressed the view that a clean, healthy and sustainable environment is a precondition for the enjoyment of many human rights, such as the right to life, the right to health and the right to an adequate standard of living, including access to water, food and housing. The right to a clean, healthy and sustainable environment results from the interdependence between human rights and the protection of the environment. Consequently, in so far as States parties to human rights treaties are required to guarantee the effective enjoyment of such rights, it is difficult to see how these obligations could be fulfilled without at the same time ensuring the protection of the right to a clean, healthy and sustainable environment as a human right. The Court thus concluded that, under international law, the human right to a clean, healthy and sustainable environment is essential for the enjoyment of other human rights.

How will every Government organize itself so as to discharge these international legal obligations in respect of climate change? Of particular importance, how will every Government discharge “the duty to prevent significant harm to the environment” ? As the ICJ put it, “The duty to prevent significant harm to the environment is an obligation to act with due diligence.”

Every government must be able to show that it has in place a national preventive and protection system that it is implementing “with due diligence.” It must also have in place a system to safeguard intergenerational equity.