17 July 2025 • 20 minute read
Countdown to the ICJ's landmark Climate Change Advisory Opinion: A recap of key arguments
Key takeaways
- On 23 July 2025, the International Court of Justice (ICJ or Court) will hand down its advisory opinion on the Obligations of States in respect of Climate Change. The UN General Assembly asked the Court to consider States' legal obligations to protect the environment from the adverse effects of climate change, and the legal consequences under international law for failing to do so.
- The ICJ received 91 written statements in the initial phase, the highest number ever in advisory proceedings before the ICJ. This was followed by 62 written comments on those statements, and 2 weeks of public hearings in The Hague in December 2024 with 96 States and 11 international organisations appearing for oral statements.
- States and international organisations’ submissions in the proceedings focused on States’ obligations under the climate change treaties (the UNFCCC, Kyoto Protocol, and Paris Agreement), the customary prohibition on significant transboundary harm and the precautionary principle, law of the sea, human rights, and the application of State responsibility.
- While the recent International Tribunal for the Law of the Sea and the Inter-American Court of Human Rights Advisory Opinions provide greater clarity regarding States’ climate change obligations in the context of law of the sea, and human rights, respectively, their conclusions do not provide a holistic assessment of States’ climate obligations. The breadth of the questions put to the ICJ is likely to provide greater clarity on States’ obligations under multiple areas of international law relating to climate change, including potential liability for breach of those obligations.
Introduction
On 12 April 2023, the United Nations (UN) General Assembly requested the International Court of Justice (ICJ or Court) provide an Advisory Opinion on the Obligations of States in respect of Climate Change (ICJ Advisory Opinion). Just over two years later, following the largest participation of States and international organisations in the ICJ’s history, the Court will hand down its opinion on 23 July 2025.
In Part One of this two-part series, we outline the background, historic participation, and the arguments States and international organisations advanced in the written and oral proceedings of the ICJ Advisory Opinion. In Part Two, we discuss the Court’s findings, the potential implications for governments and the private sector arising from the ICJ Advisory Opinion, and where to next.
Background to the ICJ Advisory Opinion
The ICJ Advisory Opinion represents a remarkable journey that extends far beyond the formal adoption of UN General Assembly Resolution 77/276 on 29 March 2023 (Resolution). The foundations of this initiative trace back to a 2019 grassroots movement led with determination and vision from Pacific Island youth, the Pacific Islands Students Fighting Climate Change (PISFCC), who are on the front-lines of the climate crisis. In March 2019, these students, determined to ensure that climate action occurred in their lifetime, wrote to all Pacific governments seeking support for their proposal for an advisory opinion from the ICJ. They received support from regional leaders and importantly, the Foreign Minister of Vanuatu.1
In 2019, Vanuatu tabled the PISFCC proposal at the Pacific Islands Forum (PIF) in the context of ‘recognising the need to formally secure the future of our people in the face of climate change and its impacts’.2 In August 2022, the PIF convened for its 51st Leaders Meeting. At that meeting, Vanuatu again tabled the PISFCC proposal to request the ICJ Advisory Opinion. PIF Leaders resoundingly commended Vanuatu on the initiative and endorsed the proposal leading to a historic campaign for support from all UN Member States.
The coalition responsible for the draft UN Resolution reflected unprecedented global cooperation. Vanuatu assembled and led a diverse core drafting group which included a mix of developed and developing States, including Angola, Antigua and Barbuda, Bangladesh, Costa Rica, Germany, Liechtenstein, Micronesia, Morocco, Mozambique, New Zealand, Portugal, Romania, Samoa, Sierra Leone, Singapore, Uganda, and Vietnam. The Resolution underwent three rounds of informal consultations and engagements with other States, with ultimately over 100 countries co-sponsoring the resolution. Co-sponsorship of the Resolution included States on every continent, representing every region and development level, from small island developing States to major economies.
What were the questions put to the Court and how did States engage?
On 12 April 2023, the UN General Assembly requested the ICJ to render an Advisory Opinion on two critical questions:
- 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?
- 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:
- 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?
- Peoples and individuals of the present and future generations affected by the adverse effects of climate change?
The level of engagement with the ICJ Advisory Opinion was unprecedented. The ICJ received 91 written statements in the initial phase, the highest number ever in advisory proceedings before the ICJ. This was followed by 62 written comments on those statements, and 96 States and 11 international organisations appearing to present oral statements before the Court during 2 weeks of public hearings in The Hague in December 2024. At the conclusion of the oral hearings, 65 States and international organisations provided written replies to questions from the judges.
The written statements included submissions from 11 Least Developed Countries (LDCs), 22 Small Island Developing States (SIDS), and 4 States that are both LDCs and SIDS.
What were the arguments States and international organisations made?
There were five focus areas of substantive law in most submissions:
1. Climate change conventions
Key issues:
- Are the UNFCCC, Kyoto Protocol, and the Paris Agreement (Climate Change Regime) the only international law instruments that regulate action on climate change (lex specialis)?
- Do all States have the same legal obligations to combat climate change (the principle of common but differentiated responsibilities (CBDR-RC))?
- Which obligations are characterised as obligations of conduct rather than result?
- What does the temperature goal at Article 2 of the Paris Agreement require of States?
- What is the due diligence standard for obligations of conduct?
- What are developed States’ obligations relating to providing climate finance, capacity building, and technology transfer to developing States?
States were divided on whether the Climate Change Regime constitutes lex specialis, excluding other aspects of international law. Generally, high-emitting States argued the Climate Change Regime is the controlling legal framework, while climate vulnerable States supported a harmonious interpretation with the broader corpus of international law (eg law of the sea, human rights, biodiversity). The latter group stressed that the Paris Agreement could not be intended to exclude preexisting environmental protection obligations and therefore should be read in a way that promotes systemic integration of States’ obligations across different areas of international law.3
Most States agreed that the principle of CBDR-RC was relevant to States’ climate change obligations, though they disagreed on its application. For example, some States argued that CBDR-RC does not imply any categorical differentiation between or among groups of States to an international agreement.4
However, other States considered that while all States must implement measures to combat global warming, CBDR-RC acknowledges that developed States have greater responsibility to do so in light of the means available to them. This also reflects the economic and development benefits derived from developed States’ historical emissions contribution, in turn, also obliging developed States to assist developing States to meet their obligations to combat climate change.5
States made divergent submissions about the status of obligations States may have under Article 4 of the Paris Agreement (the obligation to reduce emissions and submit an NDC), with some States arguing that Article 4 imparts purely procedural obligations, with no requirement for States to realise or achieve the targets in the NDCs.6
On the other hand, other States considered that improperly low NDCs would lead to a violation of the obligations under the Paris Agreement.7 Some went even further and argued that NDCs must be implemented in good faith and in accordance with the duty of care, available under the standard of due diligence.8
Yet, in contrast, other States noted that the Climate Change Regime does not set forth any standards, rules, or other legal requirements for apportioning respective shares of the remaining global carbon budget among States.9 Most States were of the view that the obligation to pursue domestic mitigation measures with the aim to achieve NDC commitments, constitutes an obligation of conduct, subject to due diligence standards.10
Many States made submissions that the temperature goal in Article 2(1)(a) of the Paris Agreement (keeping global warming well below 2°C, and ideally limiting it to 1.5°C) constitutes a collective standard and accepted benchmark for the proper interpretation and application of the Climate Change Regime.11
Others argued that the Court could not interpret the treaties in a way which may go beyond the negotiations of States – in that States did not intend for the temperature goal to impose legally binding obligations.12
Further, some argued that the 1.5°C target is a range, up to 2°C, as opposed to a ‘hard target’. Generally, States who saw the temperature goal as imparting an obligation also submitted that the temperature goal was subject to a ‘stringent’ due diligence obligation, in that States who do not take all measures to comply with the temperature goal would be in non-compliance with due diligence obligations.13
Many States contested the due diligence obligation (the obligation to take all necessary measures to reduce emissions) in various forms. For example, some argued that the due diligence obligation arises in the context of the Climate Change Regime in defining the standard of conduct for mitigation and adaptation obligations. Some States explicitly noted that compliance with the Climate Change Regime, would not, itself, satisfy due diligence obligations.14
States largely agreed that the applicable due diligence standard was ‘stringent’, citing the International Tribunal for the Law of the Sea (ITLOS) Advisory Opinion on climate change. Many States submitted that States have obligations to exercise due diligence in satisfying their obligations under the UNFCCC and the Paris Agreement, as well as other relevant sources of law. Some States noted that the due diligence obligation to meet the Paris Agreement temperature goal arises under human rights law as well as the Climate Change Regime15 and others noted that it was only through cooperation that States could achieve the 1.5°C standard and address the harm caused by climate change.16 Others submitted that the temperature goal informs States’ obligations to protect the climate system, that originate in the Climate Change Regime and customary international law.17
Article 9 of the Paris Agreement obliges developed State Parties to provide financial support to developing State parties for mitigation and adaptation activities, amongst other things, including the mobilisation of climate finance. States made submissions on the binding nature of Article 9, and that climate finance under Article 2(1)(c) (making financing flows consistent with a pathway to low emissions development) is not a substitute for Article 9.18 Some States stressed that the obligations under Articles 8 and 9 of the Paris Agreement are based on cooperation and do not involve any liability for the climate crisis or compensation for impacts.19
Consistent with CBDR-RC, a large majority of States (including both developed and developing States) argued that the Climate Change Regime obliges developed States to provide financial, technical, and capacity building resources to developing States.20 While States did not dispute the obligation, some submissions drew attention to the difficulties with climate finance, noting that climate finance flows are pitifully slow, vague, fragmented, not-precise, and require excessive specialised capacity to access, creating an injustice to the most vulnerable, without meaningful remedial measures.21 In the eyes of some, the current climate finance systems are inadequate, effectively inaccessible for most in need, or impose additional debt burdens on States for addressing a crisis they did not create.22 Some noted that the obligation to provide financial support should be interpreted to prescribe practical assistance that addresses developing States’ specific needs, which could include providing debt relief, debt-climate swaps, and financial grants for adaptation and mitigation efforts.23 Others also noted that developed States needed to do better to fulfil their financial obligations under the Climate Change Regime.24
2. Prohibition on significant transboundary harm and the precautionary principle
Key issues:
Do the customary rules on the prohibition of significant transboundary harm (‘no harm rule’) and the precautionary principle apply in the context of climate change, and how?
Introduction
Similar to the discussion regarding the status of the Climate Change Regime, and whether that is lex specialis, the proceedings canvassed the disagreement between States with respect to how extensively customary international law applies to the Climate Change Regime and the scope of its obligations. As a starting point, many States considered that customary international law on significant transboundary harm applies to greenhouse gas emissions, arguing it complements the Climate Change Regime.25
Some States were explicit that the prohibition on transboundary harm (the principle that obliges States to prevent environmental damage that may result from activities within their territory or jurisdiction from affecting other States) applies under customary international law to greenhouse gas emissions.26
However, other States considered that there was insufficient State practice and opinio juris to show that the prohibition had achieved the status of customary international law,27 or contended that it did not apply to climate change or was impractical in its application28 because harm to the climate system results from the diffused collective action (or inaction) of States over time.29
Other States considered that while the primary source of climate change laws is the Climate Change Regime, this regime does not exclude or replace other rules including customary international law, and asked the court to interpret the obligations harmoniously.30
Several States also argued the precautionary principle (a principle that dictates that even in the absence of full scientific certainty, States should take preventative measures to prevent serious or irreversible damage to the environment) is central to States’ general obligations under customary international law to protect the environment in the context of climate change.31
In contrast, other States considered that the precautionary principle had yet to be definitively recognised as a binding principle of customary international law.32 Even of those States who did not recognise the binding nature of the precautionary principle, some still recognised that taking precautionary measures might, under certain circumstances, form an integral part of the general due diligence expected of States pursuant to the obligation to prevent transboundary harm.33
3. Law of the sea
Key issues:
- Are anthropogenic greenhouse gas emissions ‘marine pollution’ for the purposes of States’ obligations to protect the marine environment under the United Nations Convention on the Law of the Sea (UNCLOS)?
- Are States’ maritime entitlements fixed despite the impact of rising sea levels as a result of climate change?
- For States at risk of total submersion resulting from climate change induced sea-level rise, does international law provide for continued recognition of statehood?
Introduction
A significant number of States made submissions on the interaction between climate change and the law of the sea. The ICJ Advisory Opinion coincided with ITLOS being asked to render an advisory opinion on States’ obligations to protect and preserve the marine environment from the impacts of anthropogenic greenhouse gas emissions. The written and oral proceedings took place simultaneously with the ICJ’s written proceedings, and on 21 May 2024 ITLOS issued its opinion. ITLOS concluded that anthropogenic greenhouse gas emissions amount to pollution of the marine environment for the purposes of UNCLOS, and therefore States have a ‘stringent’ duty of due diligence under which they have to put in place legislation, administrative procedures, and enforcement mechanisms to regulate activities emitting greenhouse gases, including from the private sector, to protect the marine environment. Our two-part series on the Key Insights from the ITLOS Climate Change Advisory Opinion and the Potential implications for governments and the private sector arising from the ITLOS Climate Change Advisory Opinion discusses the ITLOS Advisory Opinion findings in detail.
With ITLOS releasing its Advisory Opinion shortly before the close of the ICJ’s written comments round, many States supported ITLOS’ findings, arguing that anthropogenic greenhouse gas emissions constitute pollution of the marine environment.34 Similarly, as was argued in the ITLOS Advisory Opinion, some high-emitting States considered that the absence of terms like climate change, ocean acidification or greenhouse gases in UNCLOS indicated a lack of mandate to regulate these issues.35
However, the questions asked of the ICJ were significantly broader than the questions asked of ITLOS. As such, while many States reiterated their ITLOS submissions regarding States’ obligations to protect and preserve the marine environment, many also made submissions concerning the wider adverse effects of climate change-induced sea-level rise and the potential implications under UNCLOS and the law of the sea (an issue that went beyond what was asked of ITLOS).
For example, many SIDS emphasised that maritime entitlements are fixed and are not subject to reduction in the event of sea level rise.36 For those States at risk of total submersion resulting from climate change-induced sea-level rise, some States argued that international law does not presently contemplate the extinguishing of statehood, and that in circumstances of the complete loss of a State’s territory and displacement of its population, the presumption of continuity of statehood should still to apply.37
4. Human rights & future generations
Key issues:
- Are States obligated to take action on climate change in order to fulfil their human rights obligations?
- How does the right to sustainable development interact with the Climate Change Regime and human rights obligations?
- Do human rights extend to future generations?
- What rights are owed to people displaced due to climate change?
Many States argued climate change threatens fundamental human rights including life, health, food, water, a clean and healthy environment, and self-determination, with some claiming extraterritorial application of human rights obligations due to significant transboundary harm. Some developed States generally contested direct linkages between climate obligations and human rights law, with some noting that there are no specific obligations for States under existing human rights treaties to ensure the protection of the climate system.
While many States agreed that the right to sustainable development is embedded as a principle within the Paris Agreement, they diverged on its implications for climate obligations, particularly in relation to developing and emerging economies.39
Some States contended that this right must be balanced against decarbonisation commitments,40 maintaining that developing and emerging economies should retain broad policy space to maintain or increase GHG emissions in pursuit of poverty alleviation and long-term economic growth, in line with the principle of CBDR-RC.41
Others, including certain developing States, rejected the notion that sustainable development justifies ongoing emissions, emphasising instead that climate change is the greatest threat to economic development.42 These States argued that the Paris Agreement adequately safeguards the right to sustainable development through obligations placed on developed States to provide financial support, technical assistance, and technology transfer to developing States.42 As such, developing and emerging economy States must pursue sustainable development whilst simultaneously reducing their emissions output.
States fundamentally disagreed on whether legal obligations are owed to future generations. The principle of intergenerational equity means that each generation is entitled to inherit a planet at least as good as previous generations, meaning that the climate system cannot be used as a ‘dumping ground’ for any one State.44
Some States contended that human rights treaties of global application are limited to individuals that already exist, and so these treaties do not refer to the human rights of indeterminate, unidentifiable future generations.45 As a result, according to some States, international law does not specify any legal consequences with respect to future generations, for States who, through their internationally wrongful acts, fail to protect the climate system.46 However, other States considered that the Climate Change Regime endorses the principles of intra-generational and inter-generational equity.47
Finally, some argued that international law should respond to ensure equity across present and future generations, to safeguard the interests of future generations.48
Several States addressed obligations regarding climate-induced displacement, with some observing that climate change displacement affects the realisation of basic human rights.49 Moreover, some States considered that States whose wrongful conduct made a significant contribution to climate change are under an obligation to provide restitution for climate displaced people.50
Some States argued that there was an obligation to cooperate in respect of displaced persons beyond territorial jurisdiction.51 As some observed, no State can handle migration alone, but rather States have duties to facilitate cross-border movement and/or offer possibilities to accommodate displaced persons in the short- or long-term.52 Moreover, another State considered that international law needed to evolve its understanding of a refugee, which accounts for situations the drafters of the Refugee Convention may not have foreseen.53 Noting these difficulties, others argued that climate refugees should be afforded protection.54
Nevertheless, others argued that the grounds for refugee status under the 1951 Refugee Convention and its 1967 Protocol do not recognise climate change grounds for refugee status.55 These States, suggested, however, that without an applicable regime for climate-displaced persons, human rights law may provide the relevant framework.56 Many States made submissions that States have obligations to provide technical and financial assistance to those affected by climate displacement, and that there is generally an obligation to cooperate to protect persons displaced by climate change impacts.57
5. State responsibility
Key issues:
- Does the law on State responsibility apply to States’ climate change obligations?
- How can responsibility for anthropogenic climate change be attributed to a State or group of States under international law?
- When did States become liable for their actions which contributed to climate change?
- Are high-emitting States obliged to cease actions which may contribute to climate change, or provide some form of restitution or compensation to climate vulnerable States?
- Do States have legal obligations to provide assistance with respect to climate change related-loss or damage?
Introduction
Part B of the General Assembly’s question concerned the legal consequences for States that had breached their obligations to protect the climate system. States expressed differing views on the application of the Articles on State Responsibility for Internationally Wrongful Acts.
Climate vulnerable States argued for individual State responsibility based on historical and current emissions, noting that a State is separately responsible for conduct attributed to it and other States’ responsibility does not diminish or reduce this.58
In contrast, many high-emitting States raised difficulties in establishing a causal link between a State’s emissions and their consequences and temporal concerns about historical emissions, noting that the law of State responsibility cannot adequately address consequences for harm to the climate system because the emission of greenhouse gas in and of itself is not an internationally wrongful act and complex causation issues would emerge.59
Some States argued that responsibility arose for damage to the climate system when States became aware of climate risks, though States presented different timelines from when such knowledge became available. While some argued awareness began in the 1960s based on scientific evidence,60 others claimed that general awareness arose years later, for example with the 1990 Intergovernmental Panel on Climate Change report.61 States proposed various solutions to State responsibility including, for example:
- cessation by denying project approvals for new fossil fuel emitting projects;
- restitution through continued recognition of States’ maritime entitlements and sovereignty in situations where the adverse impacts of climate change-induced sea-level rise affect certain States; and
- compensation, for loss and damage, or in the form of financial support or debt forgiveness62 for climate vulnerable States bearing significant adaptation costs. Additionally, some States considered that obligations to ensure sufficient finances for loss and damage should become mandatory rather than voluntary.63
Nevertheless, some States were of the view that the Climate Change Regime, and in particular, Article 8 of the Paris Agreement, did not involve nor provide any basis for any liability or compensation.64 Some States further contended that the Climate Change Regime does not create any liability or obligation to provide assistance in respect of climate change-related loss or damage.65 Some States, however, submitted that the agreement at COP was that Article 8 of the Paris Agreement did not involve or provide a basis for any liability or compensation, but that this understanding does not extend to the obligations of a State under other provisions of the Paris Agreement, other obligations, or customary international law.66
Where to now?
On 21 May 2024, ITLOS handed down its Advisory Opinion on States’ obligations to protect and preserve the marine environment from the adverse effects of greenhouse gas emissions, and
On 3 July 2025, the Inter-American Court of Human Rights (IACtHR) handed down its advisory Opinion on human rights and the climate emergency which clarified the scope of the Inter-American States’ obligations to respond to the climate emergency within the framework of international human rights law.
In short, the IACtHR Advisory Opinion stated that:
- the obligation not to create irreversible climate and environmental damage has a jus cogens character;67
- the right to a healthy environment and the distinct right to a healthy climate, require States to undertake specific obligations including mitigating greenhouse gas emissions, protecting nature and pursuing sustainable development;68
- States must impose specific obligations on companies;69 and
- States must establish targets based on limiting global temperature increases to 1.5°C, calculated using the best available science and carbon budgeting.70
The ICJ Advisory Opinion succeeds these two climate-orientated Advisory Opinions. While the ITLOS and IACtHR Advisory Opinions provide insight on States’ obligations regarding climate change in the context of law of the sea and human rights, respectively, their conclusions do not provide a holistic assessment of States’ climate obligations, and subsequent responsibility, under international law. The breadth of the questions asked of the ICJ, including the scope of areas of international law to be considered such as the Climate Change Regime, law of the sea, human rights, biodiversity, and State responsibility, is therefore likely to provide greater clarity on States’ obligations relating to climate change, including liability for breach of those obligations.
Stay tuned for the release of the ICJ Advisory Opinion on 23 July 2025 and Part Two of this series where we discuss the Court’s findings, the potential implications for governments and the private sector arising from the ICJ Advisory Opinion, and where to next.
DLA Piper’s involvement in the ICJ Climate Change Advisory Opinion
DLA Piper was proud to appear before the ICJ in its Advisory Opinion, the most significant legal proceeding in relation to climate change, supporting the Democratic Republic of Timor-Leste, the Kingdom of Tonga, Solomon Islands, and the Republic of Zambia. Our advocacy in the ITLOS and ICJ Advisory Opinions resulted in DLA Piper being shortlisted for the Innovation in Responsible Business Award at the FT Innovative Lawyers Asia Pacific 2024 Awards.
The international DLA Piper team at the ICJ comprised partners Stephen Webb (Brisbane), Gitanjali Bajaj (Sydney), Claire Donse (London), Cate Martin (Sydney), senior associates Claire Robertson (Singapore), Milly Thomas (London) and solicitors Riley Arthur (Brisbane), Benjamin Crowley (Melbourne) and Paivi Adeniyi (Brisbane). Eran Sthoeger Esq. acted as Counsel for Timor-Leste, Harj Narulla as Counsel for Solomon Islands, and Professor Christian Tams and Olivia Flasch as Counsel for Zambia. The DLA Piper team was also supported by John Ridgway, Dirk Heinz, Damian Kelly, and other members of the Pacific Legal Network in relation to Solomon Islands.
The ICJ proceedings follow the recent climate change advisory opinion before ITLOS on States’ obligations to protect the marine environment from the impacts of climate changes. DLA Piper also supported Timor-Leste in those proceedings (read more here).
DLA Piper has a depth of experience in high profile public international law matters of historical significance. DLA Piper is a leader in understanding and advising on legal liability and the legal risks associated with the impacts of climate change. We advise governments and the private sector on climate change related matters, including being the provider of legal services for COP26 - United Nations Framework Convention on Climate Change Conference of the Parties. On commercial projects, the firm has been ranked No. 1 for turnover of closed renewable projects and M&A deals closed for several years. If you would like further information about the Advisory Opinions proceedings before the international courts, please contact the team below.
