Climate change before international courts – Explaining advisory opinions and why they matter 

The unprecedented challenge of climate change is provoking complex questions about the obligations states owe to each other – and to their own citizens – under international law. While domestic courts have increasingly scrutinised climate change issues over the last few decades, international judicial bodies are now putting these issues under the microscope too. Among other things, this is happening through a series of advisory opinions which seek to clarify the scope of state obligations in respect of climate change under international law.

The International Tribunal for the Law of the Sea (ITLOS) has been the first international law body to weigh in on these issues. In May 2024, it issued an advisory opinion on states’ obligations under the United Nations Convention on the Law of the Sea (UNCLOS) to preserve and protect oceans from the adverse effects of climate change caused by anthropogenic greenhouse gas (GHG) emissions.

Two other international courts, the Inter-American Court of Human Rights (IACtHR) and the International Court of Justice (ICJ), are expected to issue advisory opinions on climate change issues under international law within the next 18 months.

These three advisory opinions (together, the Opinions) are expected to accelerate the crystallisation of international law on climate change and bring greater clarity to issues of climate change adaptation and mitigation on a global level.

What are advisory opinions under international law?

Advisory opinions are statements or interpretations of law provided by a court or tribunal in response to legal questions submitted by authorised states, agencies, international organisations or other bodies, such as the UN Security Council and the UN General Assembly (UNGA).

Advisory proceedings are typically initiated by an authorised state or body filing a request for an opinion on a particular legal question. Submissions and commentaries are then filed by states and, in some cases, by intergovernmental and non-governmental organisations. Oral hearings will usually be held.

Origins and scope of the Opinions

The United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement have been the most significant international law instruments addressing climate change to date. However, these instruments do not address in detail issues of liability or compensation as between states, with these subjects being a major focus of many inter-state negotiations in recent years.

As we head towards COP29, high on the agenda is the Loss and Damage Fund by which states may contribute towards the adaptation efforts of more climate-vulnerable regions. This makes questions about precisely what international law requires of states in these circumstances a critically important one. In this context, three major international law bodies have been asked to help clarify further the extent of the international law obligations on states.

In December 2022, the Commission of Small Island States on Climate Change and International Law (COSIS), a coalition currently composed of eight island states that are vulnerable to rising sea levels, requested that ITLOS provide its opinion on state parties’ obligations under UNCLOS with respect to climate change, in particular their obligations to:

• Prevent, reduce, and control pollution of the marine environment that results from climate change caused by the release of anthropogenic GHG emissions into the atmosphere.
• Protect and preserve the marine environment from the adverse effects of climate change.

In January 2023, Chile and Colombia requested the IACtHR to opine on state parties’ obligations under the American Convention on Human Rights in connection with climate change. They have sought clarity on the relationship between the threat of climate change and states' duties to protect various human rights, including the rights to life and survival, the rights of children and future generations, and the rights of indigenous communities.

In April 2023, Vanuatu, a member of the COSIS, led efforts resulting in a UNGA resolution requesting the ICJ advise on states' obligations in relation to climate change under international law, including under the Charter of the United Nations, the UNFCCC and the Paris Agreement, including:

• State parties’ obligations to protect the climate and environment from anthropogenic GHG emissions for present and future generations.
• The legal consequences for states that have caused significant harm to the climate and environment, to states who are vulnerable to the adverse effects of climate change, and to peoples of the present and future generations adversely affected by climate change.

Against this background, the Opinions are expected to:

• Significantly influence international law norms and contribute to the harmonisation of state obligations and behaviours with respect to climate change.
• Provide an underlying legal framework for future claims, decisions and policies related to climate change.
• Assist in providing clear legal benchmarks – a previous barrier to progress in international cooperation - concerning states' obligations to address climate change. This could provide much greater impetus for political change and other international law developments.
• Inform future discussions of state-to-state equity. There may be attempts, for instance, to use them as the legal basis for claims by small-island states, who are disproportionately impacted by climate change, to seek compensation from larger and more developed states. In this regard, the ICJ has been asked to opine specifically on the liability of states that have caused significant harm to the environments of “specially affected” or “vulnerable” states. Similarly, ITLOS expressly noted in its advisory opinion states' obligations to assist other developing states. Such findings may feed into discussions around the Loss and Damage Fund established at COP28 in connection with the Paris Agreement, or for negotiating a range of other treaties and instruments, such as in trade negotiations under the auspices of the World Trade Organization. It is expected that future COPs, including COP29, will build on the conclusions of these Opinions in taking these issues further.

Impacts for corporate actors

While the outcome of the ICJ and IACtHR opinions remains to be seen, they are widely expected to develop in the same general direction as the ITLOS opinion in finding that states have a responsibility under international law to take certain actions to mitigate climate change and its effects.

While the Opinions primarily consider the obligations of states under international law, there will be indirect implications for both the public and private sectors. These Opinions (individually and collectively) are likely to create further pressure on states to ensure their domestic regulations and actions on climate change are in line with their obligations under international law. States may therefore bolster domestic measures in relation to climate change, including compelling or incentivising companies to reduce GHG emissions and potentially seeking financial contributions (including through taxes, tariffs and levies) which states can use to discharge their own obligations. Any such legislative measures are likely to create both challenges and opportunities for businesses. For instance, states may introduce:

• GHG emissions limits or financial contributions.
• Bans or limits on the development of new fossil fuel projects or other GHG-intensive business activities. In particular, the IACtHR is expected to specifically consider the extent to which fossil fuel and agricultural industries drive climate change, and states' human rights obligations to protect their citizens from the activities of these sectors through appropriate regulation.
• Economic incentives to create or shift demand to sustainable solutions.
• Stronger due diligence and environmental impact assessment requirements.

The Opinions will also likely affect how other international and national courts and tribunals address issues relating to climate change. For instance, claimants may rely on the Opinions to bring domestic or international claims against high-emitting states for failure to take steps to curb emissions. There has already been an emphasis in domestic litigation on states' obligations under the Paris Agreement (which were referred to extensively in the Urgenda case before Dutch courts in which the Netherlands was found to have a duty of care under Articles 2 and 8 of the European Convention on Human Rights (ECHR) to reduce GHGs – see here) and the UNFCCC. Further momentum has been created by international decisions such as the recent European Court of Human Rights ruling that found Switzerland in breach of the ECHR for failing to take sufficient action on climate change.

It is arguably inevitable that states being held to account in respect of their international law obligations will translate into both more stringent regulation on, and rulings against, corporate actors on climate issues.

The ICJ and IACtHR opinions are expected to address the obligations of states to protect against adverse impacts on human rights connected with climate change and will therefore be relevant for business enterprises carrying out human rights due diligence.

1. As an example, the UNGA resolution seeking the ICJ opinion came about through extensive multilateral support as it was drafted by 18 states, co-sponsored by 105 states, and with 130 states voting in its favour.