A Landmark Case at the ICJ

Last month, the International Court of Justice issued a landmark “advisory opinion” stating that nations can be held legally accountable for their emissions. Our editor Adrienne Buller met with Harj Narulla, a barrister on the team representing Solomon Islands before the ICJ, to discuss what the ruling means in the global fight for climate justice. This interview took place remotely on 5th August, 2025, and has been lightly edited for length and clarity.

ADRIENNE BULLER: Could you walk us through what the ruling implies? It’s an “advisory opinion”, and I imagine many people will be wondering what that means in terms of its effects.

HARJ NARULLA: Maybe I'll just start with explaining what advisory opinions are and how they're different to the cases most people are familiar with. Advisory proceedings are different to contentious cases, where you have two different parties coming together to resolve a specific dispute. Instead, they’re a way for international courts to answer questions put to them. The International Court of Justice (ICJ) has a particular procedure for how they receive questions, which come from the UN General Assembly, which itself has to pass a resolution and make a request to the court.

In this case, there was a unanimous decision by the UN General Assembly to request the opinion on what countries have to do under international law to address climate change, and that gave the court a big mandate.

Advisory proceedings do not issue a binding decision, forcing any country to do anything specific. It's not like issuing a court order or an injunction. But they do give a very authoritative position on what the state of the law is in response to those questions, and they have a very significant influence, both for future international cases but also for cases at the domestic and regional level as well. And because the ICJ is the World Court—it's the principal judicial organ of the UN—the scope is global. This is also the largest case that the ICJ has ever heard: nearly 100 countries participated in the proceedings, and another 12 intergovernmental organizations made submissions. This was almost double the next largest proceedings in the court’s history.

So the stage was set by this unanimous request from the General Assembly, and there were two quite broad questions. The first question was: what do states have to do under international law to address climate change? What are their obligations? And the second question was: what happens if they breach those obligations? This gave the court the opportunity to make a really bold finding. It's not necessarily known to be the most adventurous court, but they surprised quite a few of us and made this incredibly progressive, landmark finding.

There are three highlight features, I think, to take from this case. The first is that it locks in a 1.5-degree temperature target as a legal standard. That was something that had emerged in the last few COPs [Conference of the Parties, annual climate meetings], where developing states were pushing for 1.5 degrees to be the legal standard. Locking this in was obviously crucial to small island developing states, and states that are very, very vulnerable to climate change.

The second ruling was that if states breach their obligations under international law, they are liable to pay reparations in the form of compensation, as well as to provide restitution. And that can look like restoring ecosystems, rebuilding infrastructure or providing other forms of support to states that have suffered from climate damage.

The third point is what this all means for COP negotiations. Developing countries have had to go to the COPs and essentially make a moral argument for why their demands should be taken seriously, why the developed world should be paying for things like climate finance and assisting them with technology transfer. Now they've got a legal tool to really strengthen their arguments. And they can credibly say to developed states: if you don't provide us with the things that we need in the COP process, we can go to court and pursue it there.

AB: You mentioned the United States. How would this apply to different countries around the world, given that certain elements of the ruling, like the 1.5 degree target, for instance, are based out of, I'm assuming, processes like the Paris Agreement. How would it then be applied to countries that are no longer parties to the Agreement?

HN: Interestingly, this was one of the things the court went out of its way to address. And maybe it's useful getting into some of the legal weeds here to unpick how it was that they kept the US on the hook.

As we know, the US has withdrawn from the Paris Agreement. One of the key questions in this case was therefore what happens when states are not parties to not signatories to the Paris Agreement or the Kyoto Protocol or the UNFCCC [United Nations Framework Convention on Climate Change]. Are there other international treaties, other sources of law—whether that's human rights law or the law of the sea, or what's called general and customary international law—that will still apply to those states to mean that they still need to address climate change? And the court's answer to that question was: yes. They rejected the argument made by the US, Brazil, China, Saudi Arabia, and a lot of large emitting states that basically said that if a state has signed up to the UN, if they've signed up to the Paris Agreement, then that is the sum total of what they have to do under international law to address climate change. The court said no: we need to look at the whole bucket of options and think about what each of them mean for a state's obligations when it comes to climate change.

“There were other attempts to try and criticize climate science, to try and say that it's too difficult to show that particular events are a consequence of climate change, and therefore to construct legal causation or attribution is too difficult. The court rejected all of those arguments.”

So what that all means is that even having pulled out of the Paris Agreement—and the court went out of its way to make this point—customary law and other relevant sources of law will still apply to countries that have withdrawn. It didn't name the US specifically, but I think all of us noticed that they were very clearly targeting the US and other countries that might follow suit.

AB: There's a couple of points there I want to pick up on. The first is what kind of evidence was brought. Obviously there's quite a strong scientific basis behind the ruling. But I'd be interested to hear what kind of arguments were made against their eventual conclusion.

HN: Because the nature of these proceedings is advisory, it wasn't that countries were coming in arguing that a particular cyclone had caused them damage or sea level rise had meant that they had lost land and therefore asking for a court to remedy that. This was a conversation and a case about legal principles rather than facts.

So the defensive arguments made by developed states or high emitting states were generally along the lines of what I just mentioned. They argued that the full scope of obligations when it comes to climate change is just confined to those three climate treaties: the UNFCCC, the Kyoto Protocol and the Paris Agreement. That was known as the “lex specialis” argument—there’s a bit of Latin for you—which is the idea that there is a specialized legal regime, meaning you don't need to look at other sources of law when thinking about what a country has to do to address a given issue. The court rejected that.

And really, that had a ripple effect through the rest of the logic of the case. Think back to those two questions. The first question is: what are the obligations of states? What do they have to do? If you're saying our obligations are only these three treaties, then that second question—of what the consequences are when you breach your obligations—the color and the shape of that question changes quite a lot.

There were other attempts to try and criticize climate science, to try and say that it's too difficult to show that particular events are a consequence of climate change, and therefore to construct legal causation or attribution is too difficult. The court rejected those arguments. They said that attribution science and the IPCC have sufficient credibility to be used as a basis for bringing cases in the future.

AB: That’s really interesting, and I'll flag to anyone reading that we have an interview with Dr. Friederike Otto, a leading attribution scientist, in one of the earliest episodes of the BREAK—DOWN, which explains both how that science works and how it could be applied in these sorts of cases. So for anyone interested, check it out.

On the point about attribution—this falls outside the scope of this advisory opinion, but I want to think through where this goes next in a practical sense. Specifically, what is the yardstick against which states will be evaluated to say: yes, you are meeting, or you are failing to meet, your obligations? Because one version of that might be the NDCs: the nationally determined contributions that countries submit under the Paris Agreement outlining their targets and so on. Many of those are not on track for a 1.5 degree target, and until now it’s been something of a “grade your own homework” approach.

Or, you might plausibly be able to say, as a major emitting country: fine, we'll make these emissions cuts, but we’ll start ten years from now or 15 years from now, and you need to give us room in the near term.

So how, in practical terms, will they be evaluated?

HN: Interestingly, the court addressed quite a few of the points you just mentioned there, specifically around NDCs, and they established what's called a due diligence standard, which is essentially an obligation that states must not only implement the “primary obligation”, but do it to a sufficiently high standard. In this case what they’ve said is that you can't just come up with any old NDC; it has to be based on your highest possible ambition, and that must be determined by reference to the best available science, and by taking all countries’ NDCs together. So your NDC has to be compatible with a 1.5 degree temperature limit. And even though the court didn't step as far as saying “this particular methodology must be used by states”—for example, a fair share methodology which appropriately proportions responsibility based on historical responsibility and economic capacity—even though the court didn't say that, I think there's a lot of scope to argue that if you put all those elements together, you need to have the highest possible ambition based on the best available science and 1.5 degree compatibility.

The court stepped quite deeply into a lot of these questions, which have been difficult for the climate movement to get politicians to respond to. And it's those types of issues now that I think will form the basis of the next wave of climate litigation. It'll be NGOs, affected communities, young people, older people bringing cases against their governments when they come up with inadequate NDCs. So the ICJ has really, I think, empowered the climate litigation movement to be much more muscular.

AB: Interesting—so do you think it will be more likely, off the back of this, to see a group suing its own government rather than, say, a small island state looking at a country like the US or Saudi Arabia and pursuing them for reparations?

HN: Yes. Well, I think it's all of the above. There have been thousands of cases since 2015 when the Paris Agreement was passed and when this field really took off, mostly at the domestic level. You could see a public law challenge against a government brought by people on the basis of human rights, for example. But the ruling might also be cited in cases against corporations, so against fossil fuel companies, say, for not having sufficient emissions reduction plans, or against the directors of those companies for not discharging their director's duties to decarbonize or have plans around the transition. But it will also set up a new generation of interstate cases that will be litigated at the ICJ.

There are a few questions that you need to work through before you can think about what a case would look like at the ICJ that's, for example, brought, for example, by a developing country against a developed state. The first is: who can you bring it against? This judgment made it very clear that developed states have the greatest responsibility, but interestingly, they complicated the distinction between developed and developing states. This is an ongoing discussion in the COP process: high emitting states that have rapidly developed in the last 30 years, like China, Brazil, India. They classify themselves as and claim to be developing states under the terms of the Paris Agreement. This all stems from the principle of “common but differentiated responsibilities”, and the court looked at this principle and they expressed a view in line with the submissions that I made to the court—which is that you need to look at the wording of the Paris Agreement, which says that the common but differentiated responsibilities need to be interpreted in light of different national circumstances. And what that means is that if a country rapidly develops and increases its economic capacity, then they have a greater responsibility to address climate change if they massively increase their emissions.

“So I think that's a really big deal, and it will be a big part of any future litigation against developed countries.”

That's also relevant in terms of assessing their obligations. So equally, if a country’s economy collapses, they might reasonably have less money to spend on addressing climate change and so on, their responsibilities are reduced. What this allows, essentially, is a framework in which China, Brazil, India, other rapidly developing states can graduate to the status of a developed country under the terms of the Paris Agreement, and therefore attract the more stringent and onerous obligations that sets out. They might have to provide things like climate finance, technology transfer, or capacity building, which the Paris Agreement says developed states owe to developing states. So that is all very interesting, because in the next 5 or 10 years we could see cases against some of those kind of “middle” states, rather than just the usual suspects like Western Europe or North America.

AB: You mentioned this now involves not just state-to-state or within-state interactions, but also corporations themselves, which feels quite new. Is that right?

HN: One of the most important parts of this judgment was that the court went out of its way to not only focus on the fossil fuel industry, but to focus on the fact that countries have obligations to regulate the activities of corporations within their jurisdiction. What that means is that if you have a fossil fuel company headquartered in the UK, for example, or the US, then it's the UK's responsibility or the US’s responsibility to curb their emissions everywhere. That’s a huge shift, because it means that you now have a legal basis to go to the UK government, either through litigation or just to lobby them, and say: it’s your problem, what Shell and what BP are doing; what are you going to do about it? And if you don't do something about it, then you could be taken to court here [domestically] or at the ICJ.

That’s a really big shift. It essentially pits governments against the fossil fuel industry, rather than their current relationship, which is one in which the fossil fuel industry has very much captured a lot of these governments.

AB: Correct me if this is wrong, but I was interested to see that this opinion formally applies both in terms of fossil fuel combustion—the actual emissions from burning fossil fuels—but also in terms of production. Canada, where I am from and where I am now, is a great example of why this matters: when you look at our territorial emissions, we’re much smaller in aggregate than say a US or a China. However, not only are we among the worst per capita emitters, but the scale of what we contribute through the production of fossil fuels that we export is vast. So is it correct that production can now be formally taken into account?

HN: This was, I think, one of the most remarkable aspects of this decision, which is the court directly calling out the fossil fuel industry—which they didn't need to do—and naming specifically that states can be in breach of their international obligations if they don't address fossil fuel production, consumption, licensing and subsidies. They didn't need to talk about these issues, but they chose to. And that, I think, really signals the legal death knell for the fossil fuel industry, because suddenly developed states know that they have clear obligations to address all those different fossil fuel related activities.

And it's not good enough to say that we are a major fossil fuel exporter, as Canada is and as Australia is, and that it's someone else's emissions, someone else's problem when they burn it. The ICJ has said it matters that you are producing fossil fuels, and it's part of your obligations to address climate change to tackle that particular problem. So I think that's a really big deal, and it will be a big part of any future litigation against developed countries.

AB: It certainly feels incredibly radical as someone who has spent a long time just watching companies publish their emissions targets for, say, office electricity use rather than the fossil fuels they produce.

Now, this may seem obvious to you, but I think it's maybe not obvious to many of us outside of the legal profession: what does this actually look like in terms of being held responsible? Say, hypothetically, a group has successfully sued a government, the case has been ruled in favour of the people bringing it. If you are the government of Canada, and you’ve been found to have failed to meet your obligations, does that mean you're paying compensation? Or, is it that you suddenly have to, say, submit new targets within a certain time frame?

HN: This is what the second question was all about. There’s a relevant legal framework called the Responsibility of States for Internationally Wrongful Acts. It's the technical term for breaching your obligations, and the court said that that body of law applies here. What that means in practice is reparations, which is an umbrella term to refer to a menu of different remedies—those can be requested by states.

Reparations are sort of classically broken down into: firstly, “restitution”, which is restoring the situation to what it was prior to the harm. Secondly, “compensation”, which is monetary compensation. And thirdly, “satisfaction”, which is things like symbolic apologies and other acts of recognition. And they're generally viewed as a hierarchy.

So first you try to, for example, restore an ecosystem. But if you're not able to fully do that—you can't, you know, fully clean up the oil spill—then you pay compensation for the harm that can't be remediated by the restitution. Then potentially satisfaction can come in as well, maybe a formal apology. The idea is that you can sort of mix and match from these different types of remedies, and in that way pursue different climate-related policy goals. It was really important that the court said that claimant states can pursue—and this is the phrase they used—the “full panoply” of the law of state responsibility. So: restitution, compensation, satisfaction, but also some rules around what's called cessation and guarantees of non-repetition, which is essentially the idea that you cease the wrongful act which is harmful (in this case to the environment) and then you provide guarantees that you're not going to do the same thing again. That could be, again, a category to argue for banning new oil and gas projects, for example.

I think the billion or maybe trillion-dollar question is whether a lot of states will be looking for compensation, and that's certainly possible in the wake of this judgment. The court didn't say a lot about what that looks like. But they did open the door to those sorts of cases.

AB: I want to step back a bit to the story of this case itself. This was initially brought forward by a group of students. Could you tell us about their story and how you came to be involved?

HN: There was a group of students in a course on international law and learning about advisory opinions, learning about the ICJ. And they essentially came up with the idea of bringing this case to the ICJ.

There had been an attempt to do this in 2013, by Palau, which had failed. It had been kind of rapidly shut down by developed countries, but I don't think the students were necessarily aware of that when they came up with this idea. It was sort of a parallel process, and they organized very quickly and very effectively. They created an organization, the Pacific Island Students for Climate Action, and they just started lobbying, firstly local politicians, but then they managed to get the government of Vanuatu onside. And to their immense credit they saw the importance and significance of it and took it to the Pacific Islands Forum and started essentially bringing together first a coalition of Pacific states, and then a much larger coalition of sponsoring states that guided it through the diplomatic process. And it's been, I think, one of the most remarkable and inspiring aspects of this process to see the leadership from those Pacific students.

One of the students, the president [of the organization] is from Solomon Islands, and she spoke on the first day of the proceedings. A lot of them have continued to be centrally involved not only in the campaigning and the visibility around the case, but actually in the legal work as well, which I think is a remarkable achievement, to have youth centered in a really complex and high stakes legal process.

AB: I want to ask a question not about this case in particular, but one that I think is always interesting, which is: how do you see the role of the courts and of litigation in the fight against climate change? Because it feels right now to be where many of the wins, as few as they are, are coming from. And yet, a lot of people might say that the fact that we're navigating this route means in some ways that we've failed on the legislative side. I'm interested in how you understand your role in this fight.

HN: I think the first thing to say is that the law is not a silver bullet, and I don't view it as something that can provide all the answers by itself. I think the appropriate way to think about strategic litigation is as part of a broader campaign, and pretty much every case does have a campaigning element to it, a communications element to it, where you are trying to shine a light on the conduct of, say, a bank for funding fossil fuels or a company for breaching human rights.

I think about law as complementary to other forms of campaigning and public pressure. One of the nice things about law, and you just touched on it, is that it's not reliant on the political process. If you have a party in government that is not doing anything about climate change or is not moving fast enough, one of the nice things about the courts is that you don't have to rely on the politicians in power, and you can ask for the government to comply with its legal obligations. Now, this is only really available in countries where you have a strong rule of law, a functioning democracy. And that is a big caveat. But I think that's why it’s grown in attractiveness to people who are looking to move quickly on climate change, because you're not waiting on a political cycle.

But the reality of litigation is that it takes forever. It's really expensive. And you often lose. So I think that we shouldn't confuse the impacts and the success of climate litigation. Impact doesn't just come from winning in court. And there are, I think, plenty of examples of where just filing a case can either catalyze a change in behavior or is a win in and of itself, either because it draws attention to a bad actor and they shift what they're doing, or because it can crystallize litigation risk, which, particularly for corporations that are worried about managing different types of risks, can change their behavior in response.

So I think litigation is about more than just the mechanics of going to court and arguing the case and getting the judgment. It's both the threat of litigation—what the filing achieves outside of the courtroom— and how it's communicated and utilized by advocates.

AB: There are a few more “in the weeds” points to the ruling that I think our readers will be really interested in, and they relate to how much the world is changing in the context of the climate crisis. This applies to the boundaries of what it means to be a state and what it means to belong to a particular state as coastlines erode or regions become uninhabitable, with millions of people due to be displaced by the climate crisis. And on several of these points, this ruling took a position. Could you walk us through some of these finer points and why you think they matter so much?

HN: There are three points here, relating to statehood, maritime boundaries and what happens when people are displaced.

On the question of statehood, one of the key questions raised was in relation to what happens when a country is completely inundated due to sea level rise. So Tuvalu, the Maldives and the Marshall Islands are projected to lose all of their territory sometime this century or next century. What happens to those territories? Those countries continue to persist, but where do the people go? What is their legal status?

“The developing world now has essentially a credible alternative where they can say: if you don't provide us with what we want, we can go to the ICJ to try and pursue a legal remedy.”

There's been a parallel process by something called the International Law Commission, which has been looking at this question for seven years, and they issued a decision in June 2025, very helpfully, just before this opinion. They said that even where you have complete inundation—a country disappears—that it will still be considered a state, so that you can have essentially a kind of a “state in exile”. That’s a huge finding for those states in particular that are existentially threatened by climate change. It gives clarity, again, for the states that are neighbours. Where are those people going to go? It's going to be to countries like Australia, for example, who have signed a treaty with Tuvalu, the Falepili Union, which essentially created a visa pathway for that population to over time move to Australia. So it provides real certainty and structure as to how we navigate that aspect of the climate crisis.

A related question is maritime boundaries. So, even if your country is not going to disappear entirely, a lot of states are going to lose significant portions of their coastline due to sea level rise. That raises a question of what your territorial sea is. Under The Law of the Sea [formally referred to as the United Nations Convention on the Law of the Sea], countries have a certain zone around their territories which is their exclusive economic zone. But what happens when sea level rise means that your coast shifts inwards? Do you have the same territorial sea that you previously had, or does that change as sea level rise changes? Helpfully, again, the court addressed this issue, and said that as long as you have established your maritime boundaries, they will remain fixed. This again provides certainty, and helps prevent disputes like “Can I drill potentially or fish in your waters?” This is an important source of economic security for small island nations or “big ocean” nations, as they often refer to themselves.

The last, which relates to all of this, is what happens when you have people displaced across borders due to climate change? The vast majority of the displacement that will occur this century—and there’s due to be hundreds of millions of people potentially displaced due to climate change—most of it will happen within borders. They'll be internally displaced people. But the court looked at a separate question, which is: what happens when you are displaced to another country? Normally people think about that through the framework of the Refugee Convention—are you a refugee? This was an issue where I made a submission on behalf of the Solomon Islands, because it's a huge issue there. They've already lost five islands, and already 6% of the population has been displaced due to climate change. So we really focused on this issue, and we were the only state to make submissions on this point. We said that the principle, the human rights principle called non-refoulement, should apply so that when someone is displaced from, say, the Solomon Islands to Australia, they can't be sent back if there's a threat to their right to life. That’s relevant for so many different people who will be fleeing countries where they don't have a safe home to go back to.

In the case of states that may disappear entirely, there's simply nowhere for them to go. So that ruling of the court offered legal protection for, I think, millions of people in the future and is very, very significant, even if it isn't one of the headline findings.

AB: Final question—and I won't ask you what you personally are going to do, because I'm sure you're not really at liberty to discuss it—but I'd be interested to know how you see the near-term strategic priorities that stem from this. What are the things that people might be able to do to respond to this ruling?

HN: For the community of climate litigators, they're already thinking about or already working on the cases that will draw on this decision. As I said, it will affect domestic litigation, international and regional litigation. But one of the most pressing things in the next few months is around the new NDCs and the upcoming COP. All of the NDCs were due at the end of last year but were extended, so that a lot of large countries have not actually communicated their new NDCs. This, I think, was a source of dismay for a lot of us in the climate movement.

But now, we have the ICJ putting a lot of pressure on those countries, or at least it should, to increase the ambition of those NDCs. Because, as I explained before, if it's not high enough, they could be in breach of their international obligations. There’s pressure that needs to be placed by campaigners and climate advocates on governments to make sure not only that these NDCs are sufficiently ambitious, but we can now say legally compliant—that they are lawful in accordance with the ICJ’s decision.

For this forthcoming COP, the stakes have changed fundamentally. The developing world now has essentially a credible alternative where they can say: if you don't provide us with what we want, we can go to the ICJ to try and pursue a legal remedy. So there’s also work to be done around building the capacity and knowledge of developing states to make those arguments strongly in the COP process, and to make sure that we're holding developed countries’ feet to the fire when it comes to holding up their side of the bargain.