An international obligation for States to protect the global climate system – an observation

The hearings before the International Court of Justice on the responsibility of States in light of climate change have been underway since December 2^nd 2024. A number of general observations can already be made in light of the submissions made by States, recent case law and the development of international law in relation to climate change. 

Case Law and international developments

In June 2022, the United Nations General Assembly recognized a ‘clean, healthy and sustainable environment’ as a human right. In April 2024, the European Court for Human Rights gave an ‘evolutive interpretation’ of the positive obligations of States with regard to human rights and climate change in the KlimaSeniorinnen-case. In May 2024, the International Tribunal for the Law of the Sea (ITLOS) acknowledged in its Advisory Opinion the ‘high risks of serious and irreversible harm to the marine environment’ from CO2-emissions. The need for an international opinion on the international obligations for States in light of climate change was laid down in two requests: the Request for an Advisory Opinion on the Climate Emergency and Human Rights, submitted to the Inter-American Court of Human Rights, and the Request for an Advisory Opinion on the Obligations of States in Respect of Climate Change submitted to the International Court of Justice. 

This blog will address the latter request, by focusing on the following discussion points and observations from recent international developments: 1) the role of accountability and liability in international law, 2) the climate change due diligence of States in international law, and 3) the role of the Paris Agreement in determining State (and corporate) responsibility.

1) The role of accountability and liability in international law 

The international law of accountability is customary international law, enshrined in the Articles for Internationally Wrongful Acts (ARSIWA). An internationally wrongful act gives rise to State responsibility, and State responsibility gives rise to an obligation to make reparation for the damage reasonably resulting therefrom (Art. 1 and Art. 30 ARSIWA). The form and manner of reparation will depend on the nature of the violation and the nature and gravity of the right violated, ranging from an apology to payment of non-pecuniary damages. It is not necessary to prove a causal link between the act and the damage, but it is sufficient to show that the damage was reasonably caused by the violation. This ‘simplified’ burden of proof for the victim and duty of reparation for the perpetrator is explained by the addressee of this liability: the State. In international law, the State is the most powerful actor whose actions can have significant consequences for anyone under its authority. Noblesse oblige. Both the recovery of damages and the proof of a causal link between the wrongful acts of the State and the damage suffered would place an undue burden on the injured parties.

This does not mean that the duty of reparation is unlimited. In addition to a number of justifications, there is also a limit to this duty of reparation in international law. It applies only to an internationally wrongful acts attributable to (actors acting on behalf of) the State (Art. 3 ARSIWA). Internationally wrongful acts are, for example, the violation of internationally binding law (ius cogens) or of agreements from international treaties to which the state has (voluntarily) committed itself. The role for the International Court of Justice in this proceeding is to determine 1) what are the international obligations of States to protect the climate and environment for present and future generations, and 2) what are the legal consequences when States – contrary to this international obligations – have caused significant harm? 

2) The climate change due diligence of States in international law

In the international context, environmental law has been on the agenda since the founding of the United Nations (UN), back then in the context of the right of disposal of natural resources. As environmental issues and climate change were felt more urgently, the call for responsibility grew larger.  In its Nuclear Weapons Advisory Opinion (1996), the International Court of Justice (ICJ) recalled Principle 2 of the Rio Declaration, expressing States have a duty ‘to ensure that activities within their jurisdiction and control respect the environment of other States or of areas beyond national control [which] is now part of the corpus of international law relating to the environment’ (para 27) and that ‘the environment is not an abstraction but represents the living space, the quality of life and the very health of human beings, including generations unborn’ (para 29). By stating the principle of prevention of environmental harm, it became clear that the protection of the environment was not governed by rules of general international law. 

A year later, in the Gabčikovo-Nagymaros-case, the ICJ recognized ‘sustainable development’ as an international legal term and pointed at the relevance of continually assessing a State’s environmental considerations, although it did not shed light on the contents of environmental law:  

‘Throughout the ages, mankind has, for economic and other reasons, constantly interfered with nature. In the past, this was often done without considerations of the effects upon the environment. Owing to new scientific insights and to a growing awareness of the risks for mankind – for present and future generations – (…) new norms and standards have been developed, set forth in a great number of instruments during the last two decades. Such new norms have to be taken into consideration, and such new standards given proper weight, not only when States contemplate new activities, but also when continuing with activities begun in the past. This need to reconcile economic development with protection of the environment is aptly expressed in the concept of sustainable development.’ (para 78)

The principle of prevention, as a customary rule, has its origins in the due diligence that is required of a State in its territory. In its 2024 Advisory Opinion, the International Tribunal for the Law of the Sea (ITLOS) recently recognized a ‘stringent’ due diligence for States to take all necessary measures to prevent, reduce and control marine pollution from anthropogenic GHG emissions ‘given the high risks of serious and irreversible harm to the marine environment from climate change impacts’ (para 243). States have a specific obligation to ensure that emissions ‘under their jurisdiction or control do not cause damage to other States and their environment’ and pollution from such emissions ‘does not spread beyond the areas where they exercise sovereign rights’ (para 258). Through the decades, the responsibility of States for climate and environment grows from ‘respect your neighbor’s interests’ to a specific obligation to prevent extraterritorial damage. 

3) The role of the Paris Agreement in determining State (and corporate) commitments

International law is characterized by ‘systemic integration’ (para 37), which could be explained by international lawyers’ continuous quest for unity, uniformity and coherence. Because of this systemic integration, treaties are not interpreted in a vacuum, but are considered as part of the larger legal system (art. 31-33 Vienna Convention on the Law of Treaties (VCLT)). This gives international environmental law the opportunity to take into account national and international developments and to involve them into the legal system, thereby evolving the system as a whole. International environmental law has also integrated matters of sustainable development, of economic development, environmental law and climate change. These developments in turn catalyze new and needed actions: by states, by international organizations, by the private sector, by NGOs, and by individuals. In developing the law, international tribunals can and do play a useful role and contribute to a change of consciousness.

The UNCLOS is binding States since 1982 and establishes international environmental concepts that resonate in later environmental treaties. And thus, the interpretation of ITLOS is of relevance to the development of international environmental law. More importantly, previous treaties cannot be set aside by later agreements between States (VCLT). Although the issues of responsibility and liability did not fall within the scope of the request for the Advisory Opinion, ITLOS stated that ‘simply complying with the obligations and commitments under the Paris Agreement’ would not satisfy the obligations of States under international treaties (such as UNCLOS). A similar conclusion was reached by the Dutch Court of Appeal in Milieudefensie v Shell (para 7.27):

‘[C]ompanies like Shell, which contribute significantly to the climate problem and have it within their power to contribute to combating it, have an obligation to limit CO2 emissions in order to counter dangerous climate change, even if this obligation is not explicitly laid down in (public law) regulations of the countries in which the company operates. Companies like Shell thus have their own responsibility in achieving the targets of the Paris Agreement.’

The goals under the Paris Agreement may be a target for States to move towards when it comes to reducing CO2 emissions, but this commitment may go further when looking at 1) their past emissions and 2) commitments from older treaties such as UNCLOS.

Anticipation

According to ITLOS, failure to comply with its international obligation(s) could engage international responsibility for the State (para 223). An answer to this question will be given by the ICJ in – presumably – 2025.