IUCN welcomes International Court of Justice's historic climate change Advisory Opinion

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Press release 23 Jul, 2025

Today, the International Court of Justice (ICJ) delivered its Advisory Opinion on the obligations of States to protect the climate system.

The ICJ have given its opinion on the climate accountability in a landmark legal case brought by Vanuatu

IUCN Director General Dr Grethel Aguilar addressing the ICJ last year

Photo: ICJ

WCEL Chair Prof Christina Voigt and Dr Aguilar at the ICJ last year">

WCEL Chair Prof Christina Voigt and Dr Aguilar at the ICJ last year

The Court found that States have a legal obligation to limit global warming to 1.5°C, marking a landmark moment in international environmental law and climate justice.

The ICJ, also known as the World Court, gave its Opinion following months of deliberations, and the public hearing of statements from States and International Organisations, including the International Union for Conservation of Nature (IUCN) at the historic proceedings.

Particularly encouraging is the Opinion’s recognition of nature and the need for a human rights-based approach to limiting climate change. IUCN will carry these essential elements forward — including into our work at the IUCN World Conservation Congress in October 2025 and the United Nations Climate Change Conference (COP30) in Belem, Brazil, in November.

“IUCN welcomes this important advisory opinion, which strengthens the global legal framework and reinforces the urgent imperative to limit warming to 1.5 °C. IUCN has been actively engaged at every stage of these historical proceedings and congratulates the ICJ on this key decision that will shape the future of our planet,” Dr Grethel Aguilar, IUCN Director General, said.

“Climate change is not only a crisis of rising temperatures; it is a crisis for both humanity and nature with profound implications for human rights. By undermining ecosystems, climate change weakens the life-support systems upon which people’s rights to life, health, food, water, and culture depend. As the global authority on the state of nature, IUCN urges all States to strengthen their commitments — recognising that protecting nature is not just part of the solution, it is essential to delivering climate justice and safeguarding our collective future."

IUCN’s participation in the case is notable because, as a Union, it represents both State and non-State members, underscoring its unique position as a bridge between governments and civil society.

It also draws upon the extensive legal and scientific knowledge from its more than 17,000 experts in 170 countries, especially those of the IUCN World Commission on Environmental Law (WCEL), adding significant weight to its arguments to the Court.

IUCN’s contributions were coordinated by the WCEL and the process was led by Lead Counsel, and WCEL Chair, Prof Christina Voigt, who collaborated with a broad team of legal counsel and attended the formal reading of the Opinion in person at the Peace Palace in The Hague.

“The highest judicial body of the UN has spoken — and it has spoken clearly: every State has an obligation under international law to act with a stringent level of due diligence to prevent global warming from exceeding the 1.5°C threshold,” Prof Voigt said.

“This 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, which fully aligns with IUCN’s arguments, 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."

Prof Sindico, Co-Chair of the WCEL Climate Change Law Specialist Group, who coordinated the WCEL team, said: “Today marks the end of a long journey. WCEL has worked tirelessly for more than two years on these historic proceedings. We were present at every step.

“We are pleased to see that all our key points are reflected in the Court’s Opinion. We welcome the Court’s articulation of a clear legal path for States — one grounded in the Paris Agreement, other international treaties, and customary international law.

“This path demands a high level of due diligence and close attention to the Paris temperature goal. WCEL will now turn its focus to the potential impact of these three Advisory Opinions on climate multilateralism and nature protection.”

The ICJ’s Advisory Opinion aligns closely with recent opinions from other international courts: the July 2025 Advisory Opinion of the Inter-American Court of Human Rights and the 2024 Advisory Opinion of the International Tribunal for the Law of the Sea. IUCN, through WCEL, participated in all three proceedings, demonstrating its ongoing leadership in international climate and environmental law.

IUCN contributed at all stages of the proceedings. All IUCN submissions are publicly available and include:

•    IUCN´s written submission
•    IUCN´s comments on submissions by other parties
•    The IUCN oral statement, delivered jointly by Dr Aguilar, Prof Voigt, and Prof Sindico. (text and video)
•    Written responses to questions posed by the judges