Lecture summary: The Energy Charter Treaty was concluded in 1994 on the assumption that fossil fuels could continue to be used for the foreseeable future. This article examines how ECT contracting parties can now withdraw from this treaty for climate change reasons without being subject to its 'sunset' clause, which protects existing investments for 20 years. It evaluates several strategies, including amendment and inter se agreements, and withdrawal on the basis of a fundamental change of circumstances (rebus sic stantibus). That fundamental change is not climate change itself, which was foreseen in 1994. It is the fact that, as recently stated by the IPCC, fossil fuels now need urgently to be abandoned, resulting in significant stranded assets. This was then unforeseen and radically transforms the extent of the ECT’s obligation to continue to protect existing fossil fuel investments for another 20 years. The article finally considers the implications of such a withdrawal for remaining contracting parties under Article 70 VCLT. Dr Tibisay Morgandi is a Lecturer (Assistant Professor) in International Energy and Natural Resources Law at Queen Mary University of London, School of Law. Professor Lorand Bartels is Professor of International Law, University of Cambridge.