A landmark advisory opinion from the International Court of Justice clarifies that states have a duty under international law to prevent climate harm – with serious implications for Australia’s fossil fuel approvals and future litigation.

From time to time major judicial decisions pass relatively unnoticed until a major event focuses attention. In the current debate over the government’s proposed reforms to Australia’s environment legislation, it is remarkable that little or no attention is being given to the implications of a momentous 23 July 2025 advisory opinion by the International Court of Justice (ICJ) : Obligations of States in respect of Climate Change.

In brief, the Court held international law requires states to prevent harm to the environment. The advisory opinion spells out in some detail what that requirement means and goes on to explain that failure to comply can trigger legal responsibility.

The advisory opinion may open the door for states damaged by climate change, such as Pacific island nations, to bring legal proceedings against high emitters, including Australia. The advisory opinion may also provide ammunition for those seeking to challenge, in Australia’s domestic courts, approvals of coal and gas exploration licences.

The ICJ is the principal judicial organ of the United Nations, established by the UN Charter and consists of 15 judges elected by the General Assembly for nine-year terms. 

The UN Charter provides that the General Assembly or the Security Council may request the Court to give an advisory opinion on any legal question. Courts including the ICJ normally hear disputes between parties. An advisory opinion is different. It is not a resolution of a dispute between parties.  So no parties are directly bound. But it is an authoritative statement of the law and is likely to be the source of legal principle in future international litigation in the Court. Whether in domestic litigation Australian domestic courts will give weight to an ICJ advisory opinion remains to be seen.

The questions put to the Court by the General Assembly (resolution 77/275 adopted by consensus) were:

(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 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?

The questions put to the ICJ attracted enormous international interest and a very large number of states made written submissions to the Court. Many of those submissions were lengthy and detailed. The Tuvalu submission was 397 pages, Tonga submitted 99 pages and Australia 88 pages.

Issues raised by Pacific island states in their submissions focused on the special relationship of indigenous peoples with the natural environment, vulnerability to the adverse effects of climate change, loss of traditional harvesting sites, loss of tangible indigenous cultural heritage and forced migration.

High emitting states (including Australia) specifically addressed the sources of international law relating to climate change. They submitted to the Court that the climate treaties (the United Nations Framework Convention on Climate Change and the Paris Agreement) are the only applicable sources of law relating to climate change. One must go to the specific obligations in those treaties: there are no applicable underlying general principles of customary international law (a view ultimately rejected by the Court).

The Court in its very lengthy advisory opinion gave extensive consideration to scientific evidence, concluding that it is scientifically established that the climate system has undergone widespread and rapid changes. The Court said it will rely primarily on the IPCC reports, which participants agree constitute the best available science.

The Court identified a very large number of applicable treaties.

Turning to customary international law, the Court found states have a duty under customary international law to prevent significant harm to the environment:

‘[a] State is . . .obliged to use all the means at its disposal in order to avoid activities which take place in its territory, or in any area under its jurisdiction, causing significant damage to the environment of another State.’

This duty applies with respect to the climate system and other parts of the environment.

The underlying principle – the duty to prevent damage to the environment – is an uncontroversial principle of long standing. What is significant is the ICJ’s clear finding that this duty applies to the climate system. The implications are enormous.

The Court went on to say it considers that the argument that the climate change treaties constitute the only relevant applicable law cannot be upheld and finds that the principle of lex specialis does not lead to a general exclusion by the climate change treaties of other rules of international law.

The Court went on to spell out what the obligations meant: that states must fulfil their duty to prevent significant harm to the environment by acting with due diligence.

The conduct required by due diligence has several elements. These include states taking, to the best of their ability, appropriate and, if necessary, precautionary measures, which take account of scientific and technological information, as well as relevant rules and international standards, and which vary depending on each state’s respective capabilities.

The standard of due diligence for preventing significant harm to the climate system is stringent. Due diligence requires a state to use all the means at its disposal. Rules and measures must regulate the conduct of public and private operators within the states’ jurisdiction or control and be accompanied by effective enforcement and monitoring mechanisms to ensure their implementation.

Failure of a state to take appropriate action to protect the climate system from green house gas emissions — including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences or the provision of fossil fuel subsidies — may constitute an internationally wrongful act which is attributable to that state.

Attribution involves attaching to a state its own actions or omissions that constitute a failure to exercise regulatory due diligence.

Pausing here, it is important to note that states must regulate both public and private operators and that granting of fossil fuel exploration licences may constitute an internationally wrongful act. These findings are directly relevant to Australia. 

In relation to responsibility and liability for wrongdoing, the Court specifically addressed the fact that multiple states have contributed to climate change and this may increase the difficulty in determining whether and to what extent an individual state’s breach of an obligation has caused significant harm to the climate system. The Court answered that issue in general terms: the rules on state responsibility under customary international law are capable of addressing a situation where there exists a plurality of injured or responsible states. 

The Court considers that each injured state may separately invoke the responsibility of every state which has committed an internationally wrongful act resulting in damage to the climate system and other parts of the environment. And where several states are responsible for the same internationally wrongful act, the responsibility of each state maybe invoked in relation to that act. Factual questions arising in the context of attribution and apportionment of responsibility are to be resolved on a case-by-case basis. 

So if a Pacific state sought to bring proceedings against Australia, it would not be open to Australia to avoid responsibility on the basis that other states were also emitters. Having said that, it is clear that both attribution and apportionment of liability are likely to be complex hurdles facing any applicant for redress. Implementation of this approach may prove fascinating.

The Court’s advisory opinion is just that – an advisory opinion. As such it does not directly create enforceable obligations on member states.

Have we understood the implications for Australia? Have we understood that approval of a new coal mine or approval of new gas projects may expose Australia to litigation in the International Court of Justice brought, for example by Pacific island states?

Have we understood that Australians may seek to rely on the legal principles articulated by the International Court of Justice in domestic challenges to approvals of new coal mines or new gas projects, such as the Australian Conservation Foundation’s challenge to the extension of Woodside’s North West Shelf gas project?