A critical appraisal of the BBNJ agreement not to recognise the high seas decline as a common concern of humankind

The global ocean, the largest single ecosystem in the world, is in continuous decline due to increasing human pressures. New challenges, such as ocean warming and deoxygenation, ocean acidification, plastic pollution, and unsustainable use of marine resources, have no borders and boundaries. However, the recently adopted 2023 BBNJ Agreement does not recognise the high seas decline as a common concern of humankind - a legal notion/concept and treaty-based principle for internationally shared problems such as biodiversity loss and climate change. This article attempts to define the common concern of humankind by examining its legal basis, enshrinement and effect, as it still lacks a generally accepted legal definition. This article aims to propose why the high seas decline should be recognised as a common concern of humankind and to explore the underlying legal and regulatory implications of this notion for the conservation of the high seas. It is suggested that the common concern of humankind, which highlights the shared obligations and responsibilities with respect to common problems facing humankind, has both theoretical and operational significance in promoting international cooperation to address current and future ocean governance challenges.