CISDL Voices on the ITLOS, IACtHR, ICJ and (future) AfCHPR Advisory Opinions on Climate Change: Sustainable Development Dimensions of International Tribunals’ Advice on State Responsibility for Climate Change

On July 23, 2025, the International Court of Justice (ICJ) issued its Advisory Opinion on the Obligations of States in Respect of Climate Change, following a request by the United Nations General Assembly. In its AO, the ICJ affirms that States have binding obligations under international law to prevent significant harm to the world’s climate system for present and future generations. The ICJ advises that State climate obligations are owed erga omnes and erga omnes partes at paras 444 – 445, noting that States are required to implement the necessary domestic measures to achieve their progressively more ambitious Nationally Determined Contributions under the Paris Agreement. If such measures are not taken, the ICJ found, an internationally wrongful act will result in State responsibility. cessation of harm to the climate system, opening the door for climate vulnerable States and low-income States to bring contentious proceedings for relief. In this regard, due diligence also features heavily in the opinion with the ICJ opining at para 427 that  “failure of a State to take appropriate action to protect the climate system from [greenhouse gas] emissions – including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences or the provision of fossil fuel subsidies – may constitute an internationally wrongful act which is attributable to that State.” 

Key principles from the 2002 ILA New Delhi Declaration on Principles of International Law relating to Sustainable Development were central to the Court’s reasoning. The ICJ confirms that as per treaty law, but also human rights law, and customary law which imposes a duty to prevent significant harm to the environment and a duty to cooperate for a stable climate system, principles such as intergenerational equity, common but differentiated responsibilities, precaution and sustainable development which requires States to reconcile or integrate environment into socio-economic development decision-making will guide the interpretation of State obligations. In particular, the ‘sustainable development principle’ of integration features heavily in the ICJ’s AO. The ICJ conducts analysis of this principle especially at paras 146-147:

“146. The Court must also determine whether certain other principles are part of the applicable
law for the purposes of the present Advisory Opinion. Participants variously considered that the
Court should address the principles of sustainable development, common but differentiated
responsibilities and respective capabilities, equity, intergenerational equity, the precautionary
approach or principle, and the “polluter pays” principle. Most of these principles are referred to in
the UNFCCC as guiding the interpretation and implementation of the Convention and related
instruments (preamble and Article 3).
(a) Sustainable development
147. The principle of sustainable development concerns the “need to reconcile economic
development with protection of the environment” (Gabčíkovo-Nagymaros Project
(Hungary/Slovakia), Judgment, I.C.J. Reports 1997, p. 78, para. 140). The climate change treaties
describe sustainable development as a “principle” by which “the Parties shall be guided” in their
actions to achieve the objective of the Convention and to implement its provisions (UNFCCC,
Article 3, paragraph 4; Kyoto Protocol, Article 2, paragraph 1; and Paris Agreement, Article 2,
paragraph 1). This principle has also been developed independently of treaties. For example, it plays
a prominent role in the Rio Declaration (Principles 1, 4, 5, 7, 8, 9, 12, 20, 21, 22, 24 and 27) and is
the focus of the Sustainable Development Goals which were adopted by the General Assembly in
2015 (General Assembly resolution 70/1 of 25 September 2015). Given its continuous and
uncontested universal recognition, the Court considers that the principle of sustainable development
guides the interpretation of certain treaties and the determination of rules of customary international
law, including the duty to prevent significant harm to the environment and the duty to co-operate for
the protection of the environment.”

In affirming at paras 162-171 that lex specialis did not apply to climate change treaties, and in recognising the relevance of human rights law at para 373, the ICJ reinforced the importance of an integrated international treaty framework in addressing climate change.  This is further reflected in the ICJ’s particular attention to climate vulnerable groups such as children, women and indigenous people were given special attention (para 382).

In Judge Xue’s extraordinary Separate Opinion, sustainable development is further emphasised. Indeed, as she argues at para 19, “States need to shift their reliance on fossil fuels, reconsider their approach to industrialisation, change their unsustainable agricultural practices and readjust their consumption patterns. The impact of such shifts and changes is profound and far-reaching across all sectors of the economy and social development.” As she further explains at para 20, “The relationship between the right to development and the right to environmental protection is not a new issue that only arises in the context of climate change. Both rights inherently bear on some fundamental human rights, such as the right to life, the right to development and the right to health… The interdependence between the vulnerability of human populations and that of ecosystems, underscored by the IPCC, in a way exacerbates the conflicting interests between development and environment in the context of climate change, as human rights protection hinges on both dimensions. Therefore, to promote human rights, socio-economic development must be pursued on a sustainable basis without causing significant damage to the environment.” She argues that “States parties, in taking mitigation measures, should be guided by the principle of sustainable development to change current unsustainable patterns of production and consumption so as to move over time towards sustainable development.” Further, as she notes at paras 29-33, “Paragraph 4 of Article 3 further specifies the principle of sustainable development. It states that “[t]he Parties have a right to, and should, promote sustainable development…. This provision reaffirms the right to development. This right, definitely, is not absolute. It must be exercised on a sustainable basis. Accordingly, climate policies and measures must be integrated with national development agendas. In this regard, two conditions are required.

First, climate policies and measures must be appropriate for the specific national conditions of each State and, second, sustainable economic development will strengthen the capabilities of a State to adopt measures to address climate change. At the world level, the ultimate goal for the global action against climate change is to promote through international co-operation a supportive and open international economic system that would lead to sustainable economic growth and development in all States, in particular developing countries (Article 3, paragraph 5, of the UNFCCC).” As she also explains, “Article 4, paragraph 1 (c), provides that States parties shall promote and co-operate to develop technologies, practices and processes that control, reduce and prevent GHG emissions in the sectors of energy, transport, industry, agriculture, forestry and waste management. Apparently, the key element of the provision is… what States parties are required to do under this provision, certainly with the aim of achieving a result. The thrust of the obligation is the duty to promote and co-operate in technology development across various sectors that will produce a synergised result: GHG emission reductions in economic development. To promote sustainable development thus becomes a concrete obligation for States parties.” And as she underlines in addition, in the UNFCCC Para 1(d) requires States parties to promote sustainable management in the conservation and enhancement of sinks and reservoirs of GHG emissions. To her, “this is the other side of mitigation… Apart from creating sinks and reservoirs for the purpose of protection of the climate system, conservation and enhancement of biomass, forests and oceans have long-term effects on the sustainability of economic and social development.” As she also highlights at para 35 of her Separate Opinion, State obligations under the climate treaties also emphasise “international co-operation and integrated planning for adaptation. To build up agricultural resilience by developing drought-resistant crops or improving irrigation systems, for example, requires integrated planning and long-term environmental strategy. Evidently, the duty of due diligence should be applied in the context of sustainable development.”

Climate treaties do require States parties to “[t]ake climate change considerations into account, to the extent feasible, in their relevant social, economic and environmental policies and actions, and employ appropriate methods, for example impact assessments, formulated and determined nationally, with a view to minimising adverse effects on the economy, on public health and on the quality of the environment, of projects or measures undertaken by them to mitigate or adapt to climate change,” and this provision, she highlights at para 36, “fully reflects the three dimensions underlining the principle of sustainable development, namely economic considerations, social considerations and environmental considerations.” As she observes at para 37, “At the turn of the twenty-first century, a series of United Nations initiatives were launched to address global development challenges, which exerted great impact on the transformation of the development patterns and enriched the substantive elements of the principle of sustainable development” and citing CISDL Senior Fellow Prof Nico Schrijver, she highlights that “[f]or sustainable development, States acknowledge that efforts should be made to promote “the integration of the three components of sustainable development — economic development, social development and environmental protection — as interdependent and mutually reinforcing pillars. Poverty eradication, changing unsustainable patterns of production and consumption and protecting and managing the natural resource base of economic and social development are overarching objectives of and essential requirements for sustainable development.”

Based on this understanding, in recognition of the UN Sustainable Development Goals (SDGs) and also the Paris Agreement, in her Separate Opinion she argues, “as a matter of principle, mitigation and adaptation measures must take various economic, social and environmental interests into account so such measures will be integrated into sustainable development and enhance the efforts of poverty eradication.”

For comment, see:

• Prof Christina Voigt, CISDL Senior Fellow in her blog Clarifying Mitigation Obligations Under the Paris Agreement observed that “In the, so far, 10 years of its existence, the Paris Agreement has often been dismissively characterised as “soft”, “weak” or “voluntary”. The Court set an end to such misleading characterisation.
• Prof Payam Akhavan, in an interview with the Business Standard opines,“The advisory opinion is probably the most consequential in the history of the court because it clarifies international law obligations to avoid catastrophic harm that would imperil the survival of humankind,”
• Dr Margaretha Wewerinke-Singh, CISDL Fellow, in a blog for the European Journal of International Law entitled “ The Great Reset: The ICJ Reframes the Conduct Responsible for Climate Change Through the Prism of Internationally Wrongful Acts opines, “it sets a new legal baseline under which the conduct responsible for climate change is not assumed to be lawful but reframed through the prism of internationally wrongful acts, with the full panoply of ensuing legal consequences. It is, effectively, a new baseline where such conduct is deemed in principle unlawful, unless a display of consistently stringent due diligence can be shown.”  
• Adv Tejas Rao CISDL Senior Manager, Prof Marie-Claire Cordonier Segger CISDL Senior Director and Governor, and Prof Markus Gehring CISDL Lead Counsel observed in their blog that the ICJ’s Advisory Opinion can “reshape global climate governance” by affirming States’ legal duties to protect the rights of current and future generations from climate harm under international law.
• Adv Zunaida Moosa Wadiwala, CISDL Associate Fellow, noted in a recent article that the ICJ Advisory Opinion could strengthen global climate governance by clarifying States’ legal duties to mitigate harm and support vulnerable nations, arguing that the AO highlights how climate change threatens not only human rights, such as the right to life and health, but also the development prospects of least-emitting countries, reinforcing calls for equitable climate action and just transitions. In another article, Adv Zunaida explains that the ICJ’s AO affirms States binding obligations under international law to prevent and address climate change, framing failure to act as a potentially internationally wrongful act. She explains that the AO reinforces global climate accountability, empowers vulnerable nations to seek reparations, and warns that continued fossil fuel expansion may violate international law. This article is also available in French. In a blog on a South African perspective, Adv Zunaida unpacks South Africa’s submissions and positions, emphasising equity and CBDR-RC, integrating UNFCCC, Kyoto and Paris and elevating adaptation, warning against legal fragmentation and drawing out regional implications for finance, just transition and future litigation. Finally, in conversation on a morning radio interview, Adv Zunaida outlines why the ICJ AO matters for South Africa and the region; in that it clarifies binding duties to address human-driven climate change and could catalyse stronger accountability and governance across Africa.
• Prof Christina Voigt, CISDL Senior Fellow, in a joint statement issued by the IUCN opined that a “legal duty stems not only from the Paris Agreement, but also from human rights law, the law of the sea, and the customary duty to prevent transboundary harm. The ICJ’s clarification… is crucial for the coherence of international law, which now offers a full canvas of parallel obligations — all pointing in the same direction: to protect the climate system on the basis of stringent due diligence.”
• Dr Ashfaq Khalfan, CISDL Board of Governors Chair, provided initial reactions by describing the opinion as “ A shot in the arm for climate litigation.” He provided analysis to Climate Home News in two articles about the implications for litigation on the adequacy of international climate finance and on the implications for litigation relating to the United States. 
• Prof Markus Gehring, CISDL Lead Counsel and Adv Zunaida Moosa Wadiwala, CISDL Associate Fellow, participated in a joint radio interview, offering expert perspectives on the ICJ’s advisory opinion on climate change. Prof Gehring examined the opinion’s potential to influence the evolution of international law, highlighting its intersections with sustainable development and trade law, and the ways it could establish new legal obligations that enhance accountability across both developed and developing nations. Adv Zunaida focused on the implications for South Africa and the Global South, discussing the legal challenges faced by States in meeting climate commitments, the role of climate litigation in advancing policy and how the opinion could strengthen climate governance and justice while empowering civil society. Together, their analysis underscored the opinion’s significance as a catalyst for legal and policy transformation at both national and transnational levels.