When Science Meets Law: Climate Law and International Environmental Adjudication After the ICJ and ITLOS Advisory Opinions

Abstract This article examines how the International Court of Justice and the International Tribunal for the Law of the Sea integrated science into their recent advisory opinions on climate change, arguing that these decisions mark a significant shift in the role of scientific evidence in international environmental adjudication. Drawing on the central role of the Intergovernmental Panel on Climate Change and expert evidence, it shows how the courts treated the ‘best available science’ not merely as background fact, but as an authoritative basis for interpreting and specifying states’ legal obligations. The advisory opinions embed scientific consensus within core doctrines of international environmental law, including due diligence and precaution and recalibrate the treatment of probabilistic and cumulative harm. They also reshape future litigation by establishing a science-informed framework for causation, attribution, and reparation in complex, multi-actor disputes, shifting the focus to the presentation and evaluation of scientific evidence.