The International Court of Justice (ICJ) or the World Court has delivered a groundbreaking Advisory Opinion, firmly establishing states’ legal obligations to protect the climate system. This landmark decision mandates limiting global warming to 1.5°C, marking a pivotal moment for international environmental law and climate justice.
The ICJ, often referred to as the World Court, rendered its Opinion after months of deliberation and extensive hearings. During these historic proceedings, the International Union for Conservation of Nature (IUCN) was among the states and international organizations presenting statements.
A particularly encouraging aspect of the Opinion is its explicit recognition of nature’s vital role and the imperative of a human rights-based approach to climate action. The IUCN, deeply involved in the proceedings, plans to integrate these crucial elements into its future work, including at the IUCN World Conservation Congress in October 2025 and the United Nations Climate Change Conference (COP30) in Belem, Brazil, in November.
Dr. Grethel Aguilar, IUCN Director General, welcomes the advisory opinion, emphasizing its strengthening of the global legal framework and reinforcement of the urgent need to limit warming. “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,” Dr. Aguilar states. She underscores that by undermining ecosystems, climate change threatens fundamental human rights. As the global authority on the state of nature, IUCN urges all states to bolster their commitments, recognizing nature protection as essential for climate justice.
IUCN’s participation is significant due to its unique composition of both state and non-state members, bridging governments and civil society. The organization leveraged its vast network of over 17,000 experts from 170 countries, particularly from its World Commission on Environmental Law (WCEL), to contribute substantial legal and scientific expertise.
Prof. Christina Voigt, WCEL Chair and Lead Counsel, spearheaded IUCN’s contributions. “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 asserts. She clarifies that this legal duty stems from the Paris Agreement, human rights law, the law of the sea, and the customary duty to prevent transboundary harm, aligning perfectly with IUCN’s arguments.
Prof. Sindico, Co-Chair of the WCEL Climate Change Law Specialist Group, who coordinated the WCEL team, expresses satisfaction that all key points presented by WCEL are reflected in the Court’s Opinion. He highlights the clear legal path outlined for states, grounded in various international legal frameworks, demanding a high level of due diligence.
This ICJ Advisory Opinion resonates with recent similar opinions from the Inter-American Court of Human Rights (July 2025) and the International Tribunal for the Law of the Sea (2024). IUCN, through WCEL, actively participated in all three proceedings, consistently demonstrating its leadership in international climate and environmental law.
