Climate Change and the Evolving Obligations of States under International Law

Abstract

Climate change is now a clear issue of international law, not only a matter of treaties and diplomatic negotiations. This paper looks at how treaty rules, customary international law, human-rights law and the law of the sea shape the duties of States, and how those duties appear in domestic law in the United Kingdom, Australia, India and Pakistan. The study uses the UNFCCC, the Paris Agreement, UNCLOS, the law of State responsibility, and the 2024 ITLOS and 2025 ICJ advisory opinions. It then compares important legislation and cases from the four countries. The main finding is that international law now gives States clearer standards of conduct, especially in relation to due diligence, prevention of serious environmental harm, cooperation, mitigation planning and adaptation. At the same time, many practical questions are still left to national institutions, including causation, standing, implementation and remedies. The four countries do not follow the same model. The United Kingdom mainly works through statutory carbon budgets and judicial review. Australia has statutory climate targets, but its federal courts have rejected a new federal climate duty of care in Sharma, while the Pabai appeal was still pending in September 2026. India has recognised constitutional protection against the harmful effects of climate change, and Pakistan combines constitutional environmental rights with continuing judicial supervision. The main comparative point of this paper is therefore how international climate standards are received through different domestic legal routes. The paper argues that after the ICJ advisory opinion, the important question is less whether climate change is legally relevant and more how States are expected to meet the standards of diligence that international law now recognises.