Capture on the High Seas: Climate Change and Implications for NeutralShipping and International Security

The briefing note argues that climate change is not only transforming the Arctic environment but also widening a poorly governed security space at sea, with significant implications for international stability. As ice recedes, newly accessible international waters are drawing commercial shipping, shadow fleets, and state activity into a region where legal disputes, diplomatic confrontation, and environmental harm are increasingly likely. The central concern is that international maritime law, including UNCLOS, remains insufficiently clear on the circumstances under which civilian merchant vessels may be boarded, diverted, detained, or seized on the high seas — particularly in the ambiguous space between peace and war that now characterises much state conduct at sea.

Drawing on recent incidents involving merchant shipping, notably the contested capture of the Russian-flagged Marinera in January 2026, alongside historical parallels with the Royal Navy's contraband control operations during the early years of the Second World War, the briefing note demonstrates that uncertainty over maritime authority, responsibility for navigation during diversion, and the lawful basis for interception can rapidly escalate tensions, strain neutral shipping, and reshape wider military strategy. It contends that these unresolved legal grey zones are particularly hazardous in the Arctic, where climate-driven access is opening routes without established precedent and where geopolitical competition, environmental vulnerability, and limited enforcement capacity intersect. The briefing note further observes that civilian shipping insurance has, in some respects, advanced further than political or military frameworks in defining "war-like conditions," offering a conceptual starting point for legal clarification.

The briefing note concludes that the security, legal, and environmental dimensions of a changing Arctic cannot be addressed in isolation. It calls on states to clarify international rules on visit, search, diversion, and capture at sea and to pursue Arctic collaboration as a deliberate conflict-prevention strategy - treating climate change as an immediate national security threat.

See full report here.