Remarkable International Court of Justice advisory opinion gives legal muscle to climate accountability

Daily Maverick

28-07-2025

The advisory opinion from the International Court of Justice is a legal milestone. Conceived by law students from small islands, it gathered wider support and makes a very strong legal case for climate accountability.
The International Court of Justice (ICJ) has issued a remarkable advisory opinion on the obligations of states in respect of climate change. The world's highest court left no doubt that the duty of states to protect the climate are binding under UN climate treaties, and international law more broadly.
Among the most striking elements are that major emitters can be held liable for climate reparations; that the 1.5°C goal under the Paris Agreement is legally binding; and that the statehood of small islands, which with sea-level rise might literally go under water, is protected.
The 140-page advisory opinion itself is non-binding, but points to what is binding under climate treaties and broader law, internationally and locally.
Responsibility and accountability for climate change are complex, but not so complex as to exclude suing a state for a wrongful act or breach of obligation. Harm can be attributed to such a breach, and the responsible state is under a duty to compensate.
But how this plays out depends on whether the country has committed an internationally wrongful act, and on the facts of each case. My take is that the basis for litigation is stronger now. That said, how a specific court — say, in South Africa — would move from a breach of obligation to a compensatory award involves many steps.
Major emitters across the world should take note. Eskom's bizarre move to 'decouple' the decommissioning of coal from its just energy transition plan will not measure up to stringent due diligence. And Sasol may well have to defend its massive greenhouse gas emissions and the cutting of funding for its own emission reduction roadmap in court.
Advances in attribution science
The ICJ finds that responsibility for 'internationally wrongful acts' can be established in principle, with apportionment depending on the facts of each case. The advisory opinion builds on advances in attribution science. The court distinguishes scientific attribution from legal attribution: science evaluates relative contributions and quantifies confidence levels. Courts attach responsibility to a state for its actions or omissions.
The wrongful acts are not the emission of greenhouse gases per se, but the breach of climate and customary obligations. Importantly, the ICJ sees greenhouse gases emissions in other countries as relevant. So when vulnerable people sue a government for failing to act on climate, the emissions of other countries can be used in determining responsibility.
For reparations to be awarded, a causal link must be established, says the advisory opinion. This is complex but possible. The ICJ acknowledges that causation in climate cases is more indirect than for local pollution, but not impossible. Attribution science will be crucial in specific cases, 'in concreto', as the ICJ seems fond of saying.
Forms of reparation include restitution, compensation, and satisfaction. Expect more claims following this ICJ advisory opinion.
Nationally determined contributions are how countries commit to actions under the 2015 Paris Agreement, and this year countries are preparing their second nationally determined contributions. The ICJ argues that while content is nationally determined, there are limits to discretion on how little countries can do.
That seems good; some have taken national autonomy to extremes. The advisory opinion makes strong points that nationally determined contributions must show 'progression' and the 'highest possible ambition'. The court says that nationally determined contributions, taken together, must be capable of realising its objectives. By this, the advisory opinion means keeping the 1.5°C target alive, quite correctly.
But climate is a problem of overusing a global commons, the atmosphere. That means only collective action, by all, can limit global warming levels. How individual countries connect to the collective effort depends on time, space (what others do), and therefore equity.
However, the ICJ does not apply equity operationally to nationally determined contributions, which not only would have strengthened the opinion, but is also consistent with Paris Agreement provisions.
Puzzling lapse
This lapse is puzzling, as the advisory opinion generally strongly affirms the principle of equity, and common but differentiated responsibilities and respective capabilities. The advisory opinion clarifies that, adding 'in the light of different national circumstances' makes common but differentiated responsibilities and respective capabilities dynamic. The core principle applies, and how it is applied changes as countries' circumstances evolve.
With the ICJ's strong legal basis for applying common but differentiated responsibilities and respective capabilities, it will be important to apply equity and common but differentiated responsibilities and respective capabilities in practice.
The advisory opinion strongly emphasises the obligations of all states to mitigation. The ICJ is clear on fossil fuels, citing scientific consensus as assessed by the Intergovernmental Panel on Climate Change that they are the main source of greenhouse gas emissions.
The advisory opinion addresses both production and consumption. The decision from the global stocktake on transitioning away from fossil fuels is now a key component of states' mitigation obligations. States must implement domestic mitigation measures to achieve their nationally determined contributions.
Failure to act — whether by granting exploration licences or providing subsidies — can constitute an internationally wrongful act, according to the advisory opinion. Countries also have an obligation to regulate private actors as a matter of due diligence.
Again, this provides a strong legal basis for court cases against fossil fuel producers and consumers – and the latter includes all of us.
The ICJ rejects the idea that climate treaties are a 'lex specialis' that excludes other rules. It finds no 'actual inconsistency' or 'discernible intention' to displace customary international law.
This means even the US, despite President Donald Trump's withdrawal from the Paris Agreement, is not off the hook. Obligations apply to all states, whether or not they are parties to climate treaties. The legal term is erga omnes, here meaning every country owes it to the global community to protect the climate.
If a non-party state does not cooperate, it bears the full burden of demonstrating that its policies conform to customary obligations.
On adaptation, the advisory opinion outlines obligations under the United Nations Framework Convention on Climate Change and the Paris Agreement. However, it is less specific on what stringent due diligence would mean in practice, other than for mitigation.
The advisory opinion does, however, extend the basis for action on loss and damage. The ICJ notes that Paris Article 8 on loss and damage will not lead to liability or compensation. However, the Agreement is not a 'lex specialis', and so while there is considerable contention about states being liable for compensation from climate change impacts, the advisory opinion opens the door for using customary international law in climate litigation.
Due diligence
The advisory opinion strongly promotes a stringent standard of due diligence for preventing significant harm to the climate system. This heightened vigilance is required because of the seriousness and universal character of the climate threat.
The standard varies depending on a state's capabilities, available scientific knowledge, risk of harm, and urgency. It requires an 'assessment in concreto '. The advisory opinion is not legally binding nor does it determine specifics.
In South Africa, our 2024 Climate Change Act has as one of its objects to 'give effect to the Republic's international commitments and obligations in relation to climate change'. We have already chosen to take obligations seriously in our own law.
On finance, the ICJ is quite brief but potentially very impactful. The advisory opinion is clear that finance obligations under Paris Article 9 must be implemented in the context of achieving the objectives in Article 2 — those include the temperature goal and financial flows.
I read that as supporting the notion that if we want climate mitigation consistent with the 1.5°C target, we need finance commensurate with 1.5°C. The court said actual levels can be evaluated against the capacity of developed countries and the needs of developing countries.
That finding will no doubt be debated in climate negotiations, as will the advisory opinion as a whole. Hopefully, countries will be more willing to agree in negotiations, knowing that if they do not, they may be sued.
In sum, the advisory opinion is a legal milestone. Conceived by law students from small islands, it gathered wider support. The ICJ makes a very strong legal case for climate accountability.
The world's highest court found that the 1.5°C goal is legally binding – the implications for action on mitigation, adaptation, loss and damage and support are very far reaching. Every country owes it to the global community to protect the climate.
And private entities can expect stronger regulation of emissions. The basis for litigation is stronger now, including claims for reparations and failure to phase out fossil fuel.
Courts across the world will be guided by the advisory opinion and must apply stringent standards of due diligence. As they do so, equity and ambition, informed by the best available science, should remain fundamental bases. DM
Harald Winkler works as a professor at the University of Cape Town's School of Economics. He writes in his personal capacity.