Some Observations on the ‘Ambulatory’ Nature of the Normal Baseline

Abstract

Abstract From the start of the discussion about the implications of sea level rise for the entitlements of coastal States to maritime jurisdictional zones, the question of the interpretation of Art. 5 unclos (and the corresponding rule of customary international law) on the ‘normal’ baseline of the territorial sea became an essential element of the debate. The then generally accepted interpretation of Art. 5 assumed that this normal baseline, viz., the low-water line along the coast, when physically moving as a result of sea level rise, would have the effect of also moving the outer limits of the maritime zones. This interpretation became known as the ‘ambulatory’ baseline, and was inter alia adopted by the ila Committee on Baselines in the Law of the Sea and the ila Committee on Sea Level Rise and International law. However, this interpretation has recently been challenged by a few authors, as well as, more importantly, by some States. This contribution briefly examines State practice, and concludes that the normal baseline of the territorial sea is indeed ‘ambulatory’ under the current law as reflected in Art. 5 unclos. However, a significant change in the interpretation (and application) of this provision is developing in State practice, to the effect that coastal States affected by sea level rise should be allowed to maintain their current normal baselines, as determined in accordance with the provisions of unclos, notwithstanding future changes to the low-water line. If this changed interpretation is not also reflected in a change of the text of Art. 5 (which would involve an amendment of unclos under its articles 312 or 313), we may be witnessing an example of tacit amendment (modification) of a treaty provision by subsequent practice. At the same time the relevant rule of customary international law would then be changed as well.