International Tribunal for the Law of the Sea Advisory Opinion on Climate Change 2024

Professor Mossop, could you tell us about the history of the Advisory Opinion?   

The current Advisory Opinion is one of three requests for advisory opinions about legal issues related to climate change that are being considered by international courts at the moment. This opinion was requested by the Commission of Small Island States on Climate Change and International Law (COSIS).  COSIS was created by a group of small island States in October 2021. In December 2022, COSIS wrote to International Tribunal for the Law of the Sea (ITLOS) asking for an advisory opinion on two questions. Essentially, the first question asked for an opinion on the obligations of State Parties to the United Nations Convention on the Law of the Sea (UNCLOS) to prevent, reduce and control pollution resulting from anthropogenic greenhouse gas emissions. The second question was a broader question about their obligations to protect and preserve the marine environment. A large number of States, including New Zealand, made submissions, and there was a two week hearing at ITLOS in Hamburg in September last year. Submissions were also made by NGOs.  On the jurisdiction point, the Tribunal found that it did have jurisdiction, although some States continue to argue against ITLOS having general jurisdiction to give advisory opinions not provided for in the Convention. 

Professor Foster, what is the problem the ITLOS Advisory Opinion is addressing? How do greenhouse gases affect the oceans?   

In a nutshell and citing the Intergovernmental Panel on Climate Change (IPPC), “climate change-related effects in the ocean include sea level rise, increasing ocean heat content and marine heat waves, ocean deoxygenation, and ocean acidification”.   

The Tribunal explains this really nicely, starting with the point that the ocean is “a fundamental climate regulator”. It “stores heat trapped in the atmosphere” and in this way it “masks and slows surface warming”, while at the same time it also “stores excess carbon dioxide”.   

As to ocean warming, “it is virtually certain that the global ocean has warmed unabated since 1970 and has taken up more than 90% of the excess heat in the climate system”. And a problem with ocean warming is that this not only “reduces the amount of oxygen it can hold, but also tends to stratify it” and “as a result, less oxygen is transported to depth, where it is needed to support ocean life”.   

As to sea level rise, this is reasonably self-explanatory, the ocean expands as it warms and as more ice melts into the sea. This causes intensity in storm surges and rainfall in tropical cyclones and of course the IPCC tells us, with medium confidence that “sea level rise poses an existential threat for some small islands and some low-lying coasts”.  

As to ocean acidification, this is caused by all the CO2 the ocean is taking up, which reacts with water and forms carbonic acid, putting coral reefs and polar ecosystems at risk as it “makes the water more corrosive for marine organisms that build their shells and structures out of mineral carbonates, such as corals, shellfish and plankton”. We are told that that “projected ocean acidification and oxygen loss will also affect deep ocean biodiversity and habitats that are linked to provisioning services in the deep ocean”. Further that “large-scale changes to foodweb structure are occurring in all oceans”.  

Changes due to past emissions are already locked in and irreversible for centuries to millennia… So you can see why the Tribunal was ready to characterise anthropic greenhouse gas emissions as “marine pollution”. The Tribunal reasoned through the definition of pollution in Article 1(1)(4) of UNCLOS and found anthropogenic emissions involved the “introduction” directly of “substances” into the ocean and indirectly of “energy”. The adverse effects being widely observed and reported in the science, anthropogenic greenhouse gas emissions were held to constitute pollution of the marine environment under UNCLOS.   

Well that’s the science, how about the law? Professor Mossop, can you tell us about ITLOS’ main legal findings on the first part of the question that COSIS put to the Tribunal?   

The first part of the question that COSIS put to the Tribunal asked “What are the specific obligations of State Parties to the United Nations Convention on the Law of the Sea (the “UNCLOS”), including under Part XII:  

(a) to prevent, reduce and control pollution of the marine environment in relation to the deleterious effects that result or are likely to result from climate change, including through ocean warming and sea level rise, and ocean acidification, which are caused by anthropogenic greenhouse gas emissions into the atmosphere?”  

This part of the question focuses on State obligations to prevent, reduce and control pollution of the marine environment in relation to the deleterious effects of climate change and ocean acidification caused by anthropogenic greenhouse gas emissions.  To answer this part of the question, the Tribunal focused on Article 194 of UNCLOS. Article 194(1) requires States to take measures, individually or jointly as appropriate, to prevent, reduce and control pollution of the marine environment from any source, using the best practicable means at their disposal and in accordance with their capabilities. Greenhouse gas emissions are considered pollution, and so mitigation measures come within this article.  

When States are considering what are necessary measures, the Tribunal said that they had to apply an objective standard based on science, international rules and standards such as the climate change conventions, and available means and capabilities.  Importantly, the Tribunal found that the obligation under Article 194(1) would not be satisfied simply by complying with obligations under the Paris Agreement. The obligation under Article 194(1) is independent of those obligations, and so it is possible that implementing Paris obligations is not sufficient on its own to satisfy the requirement. In addition, a failure to comply with the obligation would, in the Tribunal’s words, engage international responsibility.  

While the obligation does depend on the capability of the State concerned, a lack of means should not be used as an excuse to postpone necessary measures. It is clear that wealthier States are required to do more than poorer States. The obligation is one of conduct, or due diligence.  Because of the severe impacts of climate change and ocean acidification on the ocean, the Tribunal described the standard of due diligence as “stringent”.  Therefore, the Tribunal concluded that the obligation requires “States to take all necessary measures with a view to reducing and controlling existing marine pollution from such emissions and eventually preventing such pollution from occurring at all.'"The Tribunal clearly said that the obligation does not require the immediate cessation of marine pollution from GHG emissions. However the Tribunal also advised that under the law of the sea States must take action with a view to eventually preventing such pollution occurring at all.  

The Tribunal then considered Article 194(2), under which States must take all measures necessary to ensure that activities under their jurisdiction and control are conducted so as not to cause damage by pollution to other States and their environment, and that pollution from incidents or activities under their jurisdiction or control does not spread from areas where they exercise sovereign rights. Once again, the obligation is one of due diligence, although the Tribunal said that the standard was even higher than under Article 194(1) because of the nature of transboundary pollution.  The Tribunal found that a number of UNCLOS provisions require States to cooperate either directly or through international organisations to prevent, reduce and control pollution from greenhouse gases. This requires continuous, meaningful and good faith approaches. In relation to Articles 202 and 203, the Tribunal identified obligations that developed countries must assist especially vulnerable developing States to address marine pollution from greenhouse gas emissions. This could include capacity building, scientific expertise and technology transfer. In addition, States are required to give preferential treatment for such States for funding and services.  

Finally, the Tribunal reminded States of the requirement to conduct environmental impact assessments and monitor and report on the impact of activities under their jurisdiction and control. The Tribunal emphasised again the need to exercise the precautionary approach in assessing potential future harm. In relation to the threshold for an environmental impact assessment, the Tribunal essentially said that greenhouse gas emissions will always reach the threshold for substantial pollution or significant and harmful changes to the marine environment. This is because of the severity of the impacts of greenhouse gases on the environment. They gave a very strong steer that cumulative impacts should be considered in environmental impact assessments. Another interesting point was they acknowledged that land-based sources of greenhouse gases may require an environmental impact assessment under UNCLOS. 

Professor Foster, can you tell us about ITLOS’ main legal findings on the second part of the question that COSIS put to the Tribunal?    

The second part of the question that was put to the Tribunal asked “What are the specific obligations of State Parties to the United Nations Convention on the Law of the Sea (the “UNCLOS”), including under Part XII:  (b) to protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification?”  

This part of the question mainly involved Article 192 of the Convention, which provides that “States have the obligation to protect and preserve the marine environment”. The Tribunal said this included an obligation to maintain ecosystem health and the natural balance of the marine environment and may also include obligations to restore marine habitats and ecosystems where the process of reversing degraded ecosystems is necessary in order to regain ecological balance. States’ obligations under the Convention of Biological Diversity were relevant here too.   

Article 192 was also a due diligence obligation and, given the severity and irreversibility of the impacts of climate change and ocean acidification on the marine environment as described by the IPCC, the due diligence standard was again stringent.  

The Tribunal drew special attention to coastal “blue carbon” ecosystems, such as mangroves, tidal marshes, and seagrass meadows, which are important carbon dioxide absorbing sinks. As well as being protected for their own sake, looking after these ecological features will help mitigate atmospheric anthropogenic greenhouse gas concentration by enhancing carbon sequestration as envisaged in the Paris Agreement.    

Article 192 also embraced obligations under Article 194(5) in respect of rare or fragile ecosystems and the habitat of depleted, threatened or endangered species including in ice-covered areas, and the Tribunal referred out to the Convention on International Trade in Endangered Species here as a source of guidance for States to identify endangered species. States did not have absolute discretion regarding Article 194(5) measures. States had to take objectively reasonable approaches on the basis of the best available science.  

ITLOS’ response to the second part of the question also addressed matters relating to how the impacts of climate change and ocean acidification will mean that fish stocks move location, with shifts in fish distribution and decreases in fisheries that can affect livelihoods and food security. Article 61 contains obligations to ensure through proper conservation and management that the living resources in the Exclusive Economic Zone are not endangered by overexploitation. Similar obligations under Articles 117 and 119 require measures for the conservation of the living resources of the high seas with specific obligations also in respect of high migratory fish stocks and stocks that straddle States’ maritime zones found in Articles 63 and 64. Here the precautionary approach and an ecosystem approach were required.  

The Tribunal discussed the application of Article 196, observing that the introduction of alien species to new parts of the ocean as a result of climate change and ocean acidification “may cause significant and harmful changes” to the marine environment. According to the IPCC: “non-indigenous marine species are major agents of ocean and coastal biodiversity change, and climate and non-climate drivers interact to support their movement and success … . At times, non-indigenous species act invasively and outcompete indigenous species, causing regional biodiversity shifts and altering ecosystem function…”. The Convention requires States to take appropriate and precautionary adaptive measures. Finally the Tribunal endorsed the use of area-based management tools to try and help combat the effects of climate change, such as marine reserves, and no-take seasons, as provided for also in the new Agreement on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction, known as the “BBNJ” or “High Seas Treaty”. 

Professor Foster, what do you see as the most significant feature of the Advisory Opinion?   

I was really struck by the alignment of climate change science, law and politics reflected early on in the Advisory Opinion. That is to say, the Tribunal called on the authority of the Paris Agreement and the IPCC, as well as the resolutions of the Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC) and the UN General Assembly. They were all in harness together. This was very powerful as a starting point for the Tribunal’s analysis under UNCLOS.  

 As to the law, we know that the Paris Agreement temperature goal is “Holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change”.   

On the science, the Tribunal noted that in the 2018 Report, the IPCC concludes that there is a high risk of a much worse outcome if temperature increases exceed 1.5°C above pre-industrial levels and points out significant differences in impacts when global temperature increases are maintained within 1.5°C as compared to 2°C. It states with high confidence that limiting global warming to 1.5°C “is projected to reduce risks to marine biodiversity, fisheries, and ecosystems, and their functions and services to humans.” The IPCC also stated unambiguously with high confidence in its 2023 Synthesis Report that “deep, rapid, and sustained GHG emissions reductions, reaching net zero CO2 emissions and including strong emissions reductions of other greenhouse gases, in particular CH4,” are necessary to limit warming to 1.5°C … or less than 2°C … by the end of century.   

Politically, the Tribunal referred to the 2022 Sharm el-Sheikh Implementation Plan, adopted by the Conference of the Parties to the UNFCCC (who number 198 countries), which reiterated “that the impacts of climate change will be much lower at the temperature increase of 1.5°C compared with 2°C and resolve[d] to pursue further efforts to limit the temperature increase to 1.5 °C”.  

By triangulating the climate change science, law and politics, the Tribunal created a stable and persuasive base on which to give its response to the questions from COSIS.   

Of course in the meantime at the 2023 Dubai Conference of the Parties governments further expressed their agreement that to keep the 1.5°C goal within reach there is a need for the second round of Nationally Determined Contributions under the Paris Agreement to be more ambitious, economy-wide, and cover all GHGs and sectors, in line with the Paris Agreement and subject to national circumstances, as well as for enhanced finance and support, all in the context of just transitions; and that peaking of global GHG emissions as soon as possible, and accelerating action towards achieving net zero by mid-century or before, in line with national circumstances and capabilities and development priorities, is essential to keeping the 1.5°C goal within reach.  

The other thing I was struck by was how the Tribunal highlighted comments by the IPCC that because climate change is a collective action problem a collective response is required. And the Tribunal went on to parse a good many UNCLOS provisions calling for international cooperation on climate change through the development of international rules and standards and their domestic implementation, describing the ongoing evolution of a “common regulatory framework” at the international level, grounded in science.  Importantly, though, the Advisory Opinion also emphasises States’ individual obligations to control GHG emissions. 

And Professor Mossop, what do you see as the most significant feature of the Advisory Opinion?  

What struck me is the strong connection between this Opinion from a law of the sea tribunal and international environmental law. At an early stage in the Opinion, the Tribunal carefully set out the provisions in UNCLOS that allow tribunals to draw on external rules of international law that are consistent with UNCLOS. In doing so, it clearly envisaged that this Opinion sits in the broader framework of international environmental law. The Opinion is replete with references to climate change conventions and other international environmental law conventions such as the Convention on Biological Diversity and Convention on International Trade in Endangered Species. It draws very heavily on customary international law norms that have developed in international environmental law, including obligations to conduct environmental impact assessments and prevent transboundary harm.  

The Tribunal resisted any implication that the climate change conventions override or supersede environmental obligations in UNCLOS. It rejected an argument that the Paris Agreement supersedes UNCLOS and found that Paris was not lex specialis in that obligations under both treaties were consistent. Instead, the vision the Tribunal provided was of sets of obligations that sit alongside one another. This is why the Tribunal explicitly mentioned that complying with Paris Agreement obligations would not necessarily mean that the UNCLOS obligations were satisfied.  

The Tribunal went beyond what previous advisory opinions have done in terms of how they phrase certain obligations. For example, while other decisions have referred to the standard of due diligence as variable depending on the level of risk, the Tribunal clearly stated that States had to exercise a “stringent” degree of due diligence in relation to greenhouse gases.  This goes back to Caroline’s point about the connection between the science here and the law. I also think the way they referred to precaution was interesting, but I’ll come back to that.   

Caroline, would you like to add to what Joanna has said here?    

I might say a word about customary international law here.  The Tribunal’s Advisory Opinion was grounded in treaty law (after all its jurisdiction derives from UNCLOS) but there were a few places where customary international law got a “look in”.   

First, the Tribunal was clear that the UNCLOS Article 206 environmental impact assessment (EIA) obligation was also customary international law. This obliged parties to carry out environmental impact assessments (EIAs) in respect of planned activities that may cause harm to the environment of other States through greenhouse gas emissions that may pollute and harm the marine environment. This means that non-parties to UNCLOS will be obliged to carry out EIAS.  Planned activities include greenhouse gas emitting activities on land. This is a significant finding. Second, the Advisory Opinion referred to the “well-established principle of harm prevention” which many authorities regard as customary international law in light of the International Court of Justice’s Nuclear Weapons Advisory Opinion (see for instance the COSIS written submission). The Tribunal also relied on the notion of a “duty of vigilance and prevention” as referred to by the International Court of Justice in the Gabčíkovo-Nagymaros Project (Hungary/Slovakia) case. Third, the Tribunal noted that submissions had argued there was a customary international law duty to cooperate under general international law, although ITLOS grounded its own remarks on cooperation in the many relevant UNCLOS provisions. Finally, the Tribunal did not declare the precautionary principle to be customary international law, but did develop further our understandings of its importance, precaution being “all the more necessary given the serious and irreversible damage” that may be caused to the marine environment by greenhouse gases.    

Joanna, would you like to add to what Caroline has said here?    

Caroline has mentioned that the Tribunal did not make a clear statement about whether precaution is a customary international law principle yet. However, it is very clear that they consider the precautionary approach a binding part of how UNCLOS environmental provisions are to be interpreted and applied. They said that the Paris Agreement was applicable in determining necessary measures under Article 194. Precaution was also raised in relation to consideration of environmental impact assessments and the provisions on fisheries management. The conclusion that a State’s discretion might be limited by the Paris Agreement is a fairly significant move forward in terms of application of the principle.  

Caroline, what part did the concept of due diligence play in the Advisory Opinion?  

Due diligence played a central part in the Advisory Opinion. Many of you may know due diligence is the standard commonly articulated as applying to preventive obligations in international law, notably where States have to control the activities of private actors. The civil law has had an influence here and in the last 15 years or so relevant international legal obligations have been described as “obligations of conduct” as opposed to “obligations of result”. It is these obligations of conduct that are described as due diligence obligations. They don’t require a particular result or outcome to be achieved – what they oblige is efforts toward that outcome, including the taking of all necessary measures toward the specified end. But importantly the Tribunal said that “In many instances, an obligation of due diligence can be highly demanding” and such obligations do not necessarily require a lesser degree of effort. At the same time the Tribunal was clear that the content of an obligation of due diligence is not a matter of a State’s discretion and is to be determined objectively, taking into account relevant factors.   

The Advisory Opinion was replete with qualifications of certain obligations under UNCLOS as obligations of conduct that require States to exercise due diligence. Particularly under Articles 194 and 192. As a starting point, under Art 194(1) due diligence required “a national system, including legislation, administrative procedures and an enforcement mechanism necessary to regulate the activities in question, and to exercise adequate vigilance to make such a system function efficiently, with a view to achieving the intended objective”. In general, the due diligence standard will vary according to the circumstances, including the scientific and technological information, relevant international rules and standards, and the risk of harm and the urgency involved, and may change over time, as these factors evolve and looking at the best available science. As we have alluded to already, presently there is “broad agreement within the scientific community that if global temperature increases exceed 1.5°C, severe consequences for the marine environment would ensue”, therefore the due diligence standard is “stringent” (under Articles 194(1) and 192, and even more so for Article 194(2)). The due diligence standard is linked to the precautionary approach: and so even if scientific evidence as to the probability and severity of harm to the marine environment of such activities were insufficient States would have to consider and account for the risks involved in activities under their jurisdiction or control. Due diligence also varies according to a State’s capabilities and available resources.   

Joanna, this sounds important for developing countries, what more did the Advisory Opinion have to say about the position of developing countries?   

I’ll make three key points. First, the Tribunal found that although the principle of common but differentiated responsibilities and respective capabilities (CBDR) is not expressly mentioned in UNCLOS, elements of the principle are found in UNCLOS. Articles 202 and 203 provide explicit obligations that developed countries must assist especially vulnerable developing States to address marine pollution from greenhouse gas emissions. This could include capacity building, scientific expertise and technology transfer. In addition, States are required to give preferential treatment for funding and services. The Tribunal mentioned that focusing on vulnerable developing States might help to address an inequitable situation.  

Second, the Tribunal also noted that many of the provisions in Part XII are qualified by words such as in Article 194(1) that States must take measures “using the best practicable means at their disposal and in accordance with their capabilities”. Therefore, the scope and content of necessary measures may vary in accordance with the means available to States. This did not mean that States could use this to “unduly postpone or even be exempt from” the need to take action.  Instead, it means that States with greater means and capabilities “must do more to reduce such emissions than States with less means and capabilities.”  

Third, although CBDR is a concept we are very used to in international environmental law, it is worth considering for a moment what this practically means in a law of the sea context. Certain measures will need to be implemented by flag States. Many of the world’s largest flags are developing countries. Shipping companies based in developed countries will often flag their vessels with open registries to reduce costs. If developing countries can take lesser action due to reduced capabilities, we might need to think about what this means for the measures ships are subject to.   

Caroline, what are some of the implications of the Advisory Opinion for New Zealand? 

This Advisory Opinion tells us that UNCLOS requires control of land-based and atmospheric pollution. The implication is that the world needs to get off carbon, we need to convert our economies to renewables and hydrogen.   

Domestically, UNCLOS is a treaty and relevant New Zealand statutes are to be interpreted in the light of it where appropriate. UNCLOS may also be an important consideration for members of the Government when exercising statutory powers or executive discretions. What the Tribunal has said about the UNCLOS may potentially also be relevant in the development of the common law, and of course so far as the Advisory Opinion touches on customary international law it is helpful to remember that customary international law is a source of the common law. We may hear more on relevant customary international law from the International Court of Justice in its forthcoming Advisory Opinion on Climate Change.   

Also among other matters the ITLOS Advisory Opinion’s rulings and remarks on environmental impact assessments may be important, and perhaps some of its content on ecosystem preservation and restoration including coastal mangrove ecosystems, and on rare and fragile ocean ecosystems.  

As to foreign policy, as the Tribunal notes the IPCC observes that “1.5°C implies very ambitious, internationally cooperative policy environments that transform both supply and demand (high confidence)”.  So the foreign policy implications are wide-ranging. Inter alia there is important scope for New Zealand to help ensure States pursue negotiations developing multilateral international trade rules essential to advancing the climate and environmental agenda.  

Finally I’d emphasise that the Advisory Opinion also highlights States’ individual obligations to control GHG emissions, and that as Joanna mentioned States cannot just rely on the fact they are a party to the Paris Agreement to satisfy their obligations under Article 194 regarding pollution of the oceans through GHG emissions. UNCLOS obligations are separate obligations to those in the Paris Agreement.  

Joanna, what do you see as some of the implications of the Advisory Opinion for New Zealand?  

I would like to return to the findings on fisheries management. The Tribunal found that a State’s management of fisheries in Exclusive Economic Zones must include consideration of the impact of climate change and ocean acidification on marine ecosystems. They said that this requires use of the precautionary approach and an ecosystem approach. New Zealand’s fisheries legislation does require a precautionary approach, but there might be some fruitful thinking about whether NZ fully complies with this. In addition, there might be a question as to how well New Zealand’s fisheries management incorporates and accounts for climate change.  

It also has implications for fisheries management organisations internationally, as similar obligations apply on the high seas. The Pacific regional fisheries management organisations seem to be a few steps ahead of many regional fisheries management organisations in that, at least in the Western and Central Pacific Fisheries Commission, they are very conscious of the changing distribution of tuna species. However, numerous articles have found that regional fisheries management organisations in general have been very slow at incorporating climate change into management decisions, let alone applying precaution and ecosystem approaches. The Tribunal also emphasised that the implications for vulnerable communities and specially affected States should be considered. NZ should be taking a good look at its approaches in regional fisheries management organisations to promote these findings.  

Professor Caroline Foster assisted the International Union for the Conservation of Nature (IUCN) with its submission to the ITLOS in respect of this case.  Professor Joanna Mossop is on the list of Arbitrators and Conciliators under Annexes V and VII of the UN Convention on the Law of the Sea.