Drivers of consensus-based decision-making in international environmental regimes: lessons from the Southern Ocean

1. The global environmental crisis (characterized by declines in biodiversity, transboundary pollution, habitat degradation, and climate change) has inspired international environmental regimes, such as the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), to establish large‐scale networks of marine protected areas (MPAs) in areas beyond national jurisdiction. 2. The Southern Ocean surrounding Antarctica comprises roughly 10% of the global ocean and plays a crucial role in regulating global climate and marine ecosystems. Although the Antarctic marine environment currently remains one of the most intact on Earth, it is threatened by fishery expansion and a rapidly changing climate. In response, CCAMLR has been developing a representative network of MPAs to sustain ecosystem structure and function, protect areas vulnerable to human activities, and conserve biodiversity. 3. Whereas significant research has focused on the role of formal mechanisms and state power in international environmental regimes, very little is known about the role of non‐state actors and informal approaches, particularly in the negotiation of agreements to establish large‐scale networks of MPAs. 4. Case analysis of the 2016 Ross Sea Region MPA agreement reveals that CCAMLR is undergoing a significant period of learning and institutional evolution, as actors seek novel ways to negotiate a network of Southern Ocean MPAs. Key drivers of consensus include external political dynamics, internal leadership and group dynamics, and shared concern for the future of CCAMLR and Antarctic MPAs. 5. Actors also rely on informal principles of negotiation (such as increasing transparency, developing trust, and engaging in dialogue) to fill institutional gaps in both CCAMLR's formal structure and the current process for developing and negotiating MPAs. 6. As environmental threats grow in complexity and scale, non‐state actors and informal negotiations will become increasingly critical to support the ongoing success of formal international institutions dedicated to protecting the ecological integrity and function of the global environment