The Place of Customary Norms in Climate Law: A Reply to Zahar

In his essay on the thesis of my book, Alexander Zahar objects to my characterization of customary international law as one of the sources of the international law on climate change and, in particular, to my conclusion about the relevance of the no-harm principle. I disagree. In the first part of his essay, Zahar’s analysis of the no-harm principle is limited to arguments by analogy, but a valid international legal argument can be based on deduction from axiomatic premises of the international legal order. In the second part of his essay, Zahar claims that the UNFCCC regime excludes the application of the no-harm principle when, in reality, the UNFCCC regime really seeks to facilitate the implementation of general international law.