Recent court decisions have further developed the principle of systemic coherence in international law, and the interplay of treaty, custom and principles. In ICJ AO Climate Change lex specialis and lex posterior are not used, as some emitting states argued, to read down international law obligations by dealing with each one of the sources separately to create conflicts that are resolved under a lex superior principle, but instead to apply the sources in parallel to clarify the duties of states in the system of international law, taking account of interlocking legal orders and rules.

Together with the CJEU rule of law case law and most recent climate opinions in the ECtHR and the ITLOS, this strengthens the systemic coherence, with consequences also for domestic law and national courts. The outcome of the interplay of sources and legal orders, is a more complete and thicker law.

The challenges to courts and legal scholarship are pressing, and they are required to use the methods of interpretation, as exemplified by Article 31(1) VCLT (good faith, text, context, object and purpose), and move freely over many traditional barriers that divide these fields of law, in order to clarify the law and underlying principles that they are applying. The principle of systemic coherence, as exemplified by Article 31(3) VCLT, requires that the obligations are applied in a system of law which makes them effective, and require of that system that it does not render legal obligations ineffective or incomplete in a way that dematerialises law and makes them discretionary and compliance voluntary without remedies for states or individuals.

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Prof. Mads Andenas

Professor Mads Andenas, is a prominent Norwegian legal scholar known for his expertise in international and comparative law, as well as European and domestic private and regulatory law. He is a Professor of Law at the University of Oslo since 2008, Prof. Andenas has held various distinguished roles within the legal and academic communities worldwide.
Prof. Andenas was a member of the United Nations Working Group on Arbitrary Detention (UN WGAD) from 2009 to 2015, where he served as Chair-Rapporteur from 2013 to 2015. In this capacity, he contributed to significant UN deliberations, including the formulation of guidelines on arbitrary detention. His contributions to legal scholarship earned him the title of Honorary Queen’s Counsel (QC) in 2019, later changed to King’s Counsel (KC) following the accession of King Charles III.
His academic journey extends across multiple continents, with degrees from the University of Oslo, Cambridge, and Oxford, and notable appointments at institutions such as King’s College London, where he served as Director of the Centre of European Law, and the British Institute of International and Comparative Law. Andenas has held visiting professorships and fellowships at esteemed institutions, including the University of Oxford, Sciences Po, Paris, and the European University Institute in Florence.
Beyond academia, Prof. Andenas practises law as a barrister in England and Wales and an Advokat in Norway. He has represented clients before the European Court of Human Rights and other international tribunals. He has intervened in landmark cases, including the Belhaj v Straw case in the UK, addressing state immunity and human rights.
Professor Andenas’s work is recognised globally, and he holds honorary fellowships and memberships in prestigious legal and academic organisations, including the Légion d’honneur and the Ordine al Merito della Repubblica Italiana. He continues to impact the field of international law through his editorial work, membership on advisory boards, and contributions to legal reforms.

General Principles in the International Legal System after the ILC Draft Conclusions and the ICJ Climate Opinion

Prof. Mads Andenas

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