The ICJ’s advisory opinion on climate change and implications for COP30

On 23 July 2025, the International Court of Justice (ICJ) delivered its advisory opinion on climate change. Described by many as ‘historic’, both the proceedings and the opinion represent firsts in the court’s history, with the largest number of participants of any advisory opinion proceeding and the first Court’s first unanimous advisory opinion ever.

This article examines elements of the opinion that are likely to significantly influence the COP30 climate negotiations, set for November in Brazil, and other negotiations under the United Nations Convention on Climate Change (UNFCCC) and the Paris Agreement. For a full analysis of the question before the ICJ and the parties’ arguments, please read our full, two-part analysis here.

 

Understanding the Overlap between the ICJ and the Paris Agreement

Although many parties to the Paris Agreement participated in the advisory proceedings before the ICJ, and the advisory opinion is relevant to all UN member States, the ICJ process and processes related to implementing the Paris Agreement (i.e., the Conference of the Parties (COP) and the Conference of the Parties serving as the Meeting of the Parties to the Paris Agreement (CMA) are not formally linked. Rather, each operates independently and for distinct purposes. But what happens in one is nevertheless relevant to the other. In particular, the ICJ, as it has in its recent advisory opinion, can make decisions that impact the interpretation of the UNFCCC, Kyoto Protocol and Paris Agreement, subsequently influencing Parties’ approaches to negotiations and the decisions made at the COP.

ICJ advisory proceedings

This case began when the UN General Assembly, as the UN’s universal representative body, requested an advisory opinion of the ICJ, as the principal judicial body of the UN, on States’ obligations regarding climate change and the legal consequences of failing to uphold such obligations. In responding to the questions, the ICJ could consider all sources of public international law, including treaty law, customary international law, principles of international law and international human rights law. In rendering its opinion, the ICJ analysed States’ obligations under treaties concerning climate change, namely the UNFCCC and the Paris Agreement, and their relationship to other sources of international law.

Crucially, advisory opinions delivered by the ICJ are not legally binding on States, meaning States do not have to comply with the ICJ’s findings. That is not to say that an advisory opinion lacks normative power or legal sway. In fact, the role of advisory opinions is to clarify legal issues so that States can proceed accordingly. And as our previous analysis suggests, the unanimity and scope of this opinion will likely strengthen its influence. 

The COP and CMA

Negotiations by the COP (the decision-making body of the UNFCCC) and CMA (the decision-making body of the Paris Agreement) address only those matters within the scope of those agreements. Parties convene in these bodies to negotiate the implementation of these treaties. These are party-led processes without independent authority to compel parties to act or punish them for failing to uphold their obligations. Decisions of the COP may in some cases create legally binding obligations on States and, even when they do not, they still have normative power and precedential effect. 

The links

Despite these distinctions,  these processes are entangled. First, they involve many of the same the States. 195 States are parties to the Paris Agreement, all of which are members of the UN. Of these, 96 actively participated in the proceedings before the ICJ¹. Second, the substance of these processes overlaps significantly. Third, the ICJ’s findings and their ramifications on international law more broadly are likely to influence negotiations under the UNFCCC and the Paris Agreement and how parties interpret their obligations under the treaties.

 

In focus: the potential impact on COP30 and future negotiations

A significant portion of the advisory opinion is dedicated to analysis of States’ obligations under the UNFCCC and the Paris Agreement. Notably, the ICJ is the first international court to interpret States’ obligations under the Paris Agreement. Further, the ICJ confirmed that States’ obligations under the Paris Agreement are subject to the international rules of state responsibility, and breaches of those obligations could lead to legal consequences including cessation, non-repetition and, in the event of demonstrable harm caused, reparations. Here, we identify three specific elements of the opinion likely to have the most significant impact on negotiations: (i) the ICJ’s findings on the normative power of COP and CMA decisions; (ii) whether the status of countries as developed or developing is static; and (iii) the duty to cooperate to achieve the Paris Agreement’s temperature goal².

1. Normative power of COP decisions confirmed

The ICJ confirmed that the primary temperature goal of the Paris Agreement is to "limit the temperature increase to 1.5°C" above pre-industrial levels, rather than the less ambitious alternative of "well below 2°C"³.  The Court based this finding on two decisions of the CMA. The first of these, taken by the third CMA at COP26, stated that parties "[r]ecognize[d] 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 efforts to limit the temperature increase to 1.5°C"⁴. The second decision relied upon by the ICJ was taken by the fifth CMA at COP28 and encouraged all parties to submit "ambitious, economy-wide emission reduction targets, covering all greenhouse gases, sectors and categories and aligned with limiting global warming to 1.5°C, as informed by the latest science, in the light of different national circumstances"⁵.

The ICJ’s findings confirm that decisions reached by the CMA and at the COP can create legally binding obligations and inform the content of existing legal obligations. This is not entirely unexpected. Commentators have long recognised that COP decisions could create legal obligations⁶. The focus, however, had previously been on decisions mandated by a treaty provision, such as Article 4(8) of the Paris Agreement, which states that parties shall provide information in accordance with "decision 1/CP.21 and any relevant decisions of the Conference of the Parties”.

From now on, parties will likely consider the legal consequences of COP and CMA decisions even without a mandatory treaty provision. This could have a chilling effect on negotiations and complicate consensus on key future decisions, especially with respect to historically sensitive topics⁷. In some circumstances, States may seek to expressly disclaim any intention to create new or different legal obligations.

2. Developed and developing country statuses can change

The Court also analysed Article 2 of the Paris Agreement, which states that the agreement will be "implemented to reflect equity and the principle of common but differentiated responsibilities and respective capabilities, in the light of different national circumstances”. Specifically, the Court concluded that the phrase “different national circumstances” does not change the principle of common but differentiated responsibilities and respective capabilities, but instead that it "adds nuance to the principle by recognizing that the status of States as developed or developing is not static"⁸.

The UNFCCC divides parties into Annex I countries—generally considered “developed countries” under the treaty—and non-Annex I countries—usually deemed “developing countries”. Tensions between these two groups has been building over many years, particularly in relation to high-income and high-emitting non-Annex I – or developing - countries. These tensions were especially evident in the negotiations at COP29 concerning the "new collective quantified goal on climate finance”. The final decision referred to "developed country Parties taking the lead” and encouraging them “to make contributions”⁹, but crucially it did not restate developed countries’ obligation under article 9(1) of the Paris Agreement to provide financial resources to assist developing countries’ mitigation and adaption efforts. Naturally, these textual choices were intensely negotiated, with several developing, non-Annex I countries expressing displeasure at the absence of a reference to Article 9(1)¹⁰.

With the Court’s confirmation that a country’s status as developing or developed is not static, negotiations concerning different obligations between developed and developing countries (such as finance, technical assistance and capacity building) will likely face tougher challenges. Annex I countries may seek increasingly to include wording that reflects the need for collective efforts, moving away from the differentiated obligations in the Paris Agreement.

Additionally, the Court’s comments on country status may cause difficulties within negotiating blocs and existing alliances. Large blocs comprising high and low-emitting non-Annex I countries, like the G77 + China, may find consensus difficult to achieve on negotiating positions  concerning the obligations of developed versus developing countries. This may move low-emitting and climate vulnerable countries that straddle multiple negotiating blocs towards alliances that greater reflect their needs and national circumstances, or even consider unlikely alliances with a view to widening the pool of developed countries.

3. The duty to cooperate in current and future negotiations

Finally, the Court’s analysis of the customary international law duty to cooperate states that “while States are not required to conclude treaties, they are required to make good faith efforts to arrive at appropriate forms of collective action”¹¹. The court explained that the duty to cooperate has a special importance in the context of the Paris Agreement temperature goal¹², which requires States to cooperate to achieve emissions reduction targets and agree to a methodology “for determining contributions of individual States” toward fulfilling the temperature goal.

The duty to cooperate is not new. But the court’s spotlight on its special importance to the temperature goal could feature prominently in negotiating positions, not least because repeated obstruction at negotiations may indicate a breach of the customary legal obligation of international law to cooperate. Further, if parties find themselves unable to cooperate to meet the temperature goal, States may have a collective obligation to conclude a new or different treaty under the UNFCCC, as a framework convention, to achieve it.

 

Looking ahead

Although purely advisory, the ICJ’s opinion may have somewhat sharpened the Paris Agreement’s teeth. In doing , it shines a probing light on States’ behaviour at home and on the international stage, including in multilateral climate negotiations. At COP30 later this year, the buzz surrounding the opinion will continue to grow, with parties feeling out how it will filter into the negotiating rooms. However, it may be several years before the full impact of the opinion on negotiations is clear.

What is certain is that, for the first time in the more than 10 years since the Paris Agreement took legal effect, parties now have less room for disagreement as to the obligations and the legal consequences that could follow from breaching them. Whether this newfound clarity will lead to more productive and proactive outcomes or more entrenched and intractable negotiating positions remains to be seen.

 

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¹The 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 two weeks of public hearings in The Hague in December 2024, with 96 States and 11 international organisations appearing for oral statements.
²For an in depth analysis of the court’s findings on States’ obligations under the Paris Agreement, please see our full analysis on the decision: ICJ Climate Change Advisory Opinion: Key findings and impacts explained | DLA Piper
³Article 2(1)(a) Paris Agreement
⁴UNFCCC, Decision 1/CMA.3, Glasgow Climate Pact, 13 November 2021, UN doc. FCCC/PA/CMA/2021/10/Add.1, p. 4, para. 21.
⁵UNFCCC, Decision 1/CMA.5, Outcome of the first global stocktake, 13 December 2023, UN doc. FCCC/PA/CMA/2023/16/Add.1, p. 7, para. 39.
⁶See for example: Legal Response International, ‘Treaties, COP decisions and unilateral declarations’, Legal Assistance Paper (February 2010), https://legalresponse.org/legaladvice/treaties-cop-decisions-and-unilateral-declarations<https:>
⁷Christina Voigt, The ICJ and the UN Climate Regime: Clarifying Mitigation Obligations Under the Paris Agreement, Völkerrechtsblog, 04.08.2025.
⁸[226]
⁹UNFCCC, Decision 1/CMA.6, New collective quantified goal on climate finance, FCCC/PA/CMA/2024/17/Add.1, [8]
¹⁰See for example the comments of India and Bolivia (on behalf of the Like-Minded Developing Countries) during the closing plenary of COP29.
¹¹Obligations of States in respect of Climate Change (Advisory Opinion) (International Court of Justice, General List No 187, 23 July 2025) [304] (ICJ Climate Change Advisory Opinion)
¹²ICJ Climate Change Advisory Opinion [305]</https:>