Interpreting the ICJ Advisory Opinion on Climate Change Obligation for International Civil Aviation through the Lens of Sustainable Aviation Fuel under CORSIA

Abstract

This article argues that the International Court of Justice’s (ICJs) Advisory Opinion of 23 July 2025 on the ‘Obligations of States in respect of Climate Change’ (the Advisory Opinion) resets the legal coordinates for sectoral international regimes, including international civil aviation. By (1) identifying the ‘most directly relevant applicable law’ across multiple branches of international law, (2) rejecting any blanket lex specialis claim that would relegate general obligations behind sectorspecific arrangements, and (3) insisting on a stringent, science-informed due diligence standard coupled with duties of cooperation, the Court closes the doctrinal escape hatches that have historically insulated offset-heavy approaches such as Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). The Opinion expressly acknowledges the role of organizations like International Civil Aviation Organization (ICAO) and directs states to have ‘due regard’ to obligations assumed within the specialized international regimes but clarifies that treaty performance under a specialized scheme such as CORSIA neither displaces nor fully satisfies other international obligations such as independent customary and human-rights-based duties to prevent significant environmental harm. Read together with ICAO Assembly resolutions and Annex 16, vol. IV (CORSIA), the Opinion implies a legal floor that favours real-economy mitigation, notably through Sustainable Aviation Fuel (SAF) with robust lifecycle accounting, over credit purchases as primary compliance. The article contends that, in the aftermath of the delivery of the Opinion, states cannot rely on CORSIA participation alone to meet their international obligations; rather, they must progressively tighten aviation measures in line with the temperature goal as agreed upon in the Paris Agreement of 2015, and the Court’s prevention/precaution benchmarks. The article outlines specific legal avenues, such as amending Annex 16, implementing Assembly resolutions in accordance with Article 44 of the Convention on International Civil Aviation (Chicago Convention) (1944), or negotiating a supplementary instrument, to establish SAF mandates, monitoring, reporting and verification (MRV) protocols, and equity mechanisms. In conclusion, while CORSIA is still relevant in jurisprudence and regulation, it is no longer a legal ‘safe harbour’ or an exclusive remedy for climate change in aviation.