The ICJ’s Advisory Opinion on Obligations of States in Respect of Climate Change: An Earth System Law Case Commentary

In July 2025, the ICJ delivered its eagerly awaited advisory opinion on the Obligations of States in Respect of Climate Change, following an increasing amount of judgments at national (e.g., Urgenda in the Netherlands or Neubauer in Germany) or regional (the ECrtHR’s Klimaseniorinnen case, the IACrtHR’s advisory opinion AO-32/25) levels, or with regards to a specific ambit (ITLOS’s advisory opinion N° 31). The ICJ’s opinion finally establishes in a systematic and somewhat didactic manner States’ obligation to fight climate change in regards of, inter alia, international treaties, customary international law, and international human rights legislation; as well as the “legal consequences arising from states’ acts and omissions that cause significant harm to the climate system and other parts of the environment”. Precisely, by linking the climate and “other parts of the environment”, the opinion reflects the planetary thinking inherent to Earth system law. On the other hand, the Court only considers scientific insights arising from the IPCC, in view of the latter’s political “approval”. This hints at an important issue with regards to the legal response to the various ecological pressures (as conceptualised, e.g., in the Planetary boundaries framework), i.e. that, safe for biodiversity erosion with IPBES, most other environmental issues do not benefit from a dedicated global, ideally UN, institution whose conclusions, due to their political recognition, can become the basis for legal obligations and the assessment of the respect of the latter. The intervention is a presentation of a case commentary of the ICJ’s opinion focusing, in particular, on those two dimensions.