Human-induced intensification of sea surface temperature regime shifts threatens global Large Marine Ecosystems.

Global oceans have warmed markedly and will continue to do so. Superimposed on this trend are abrupt, persistent decadal regime shifts between warm and cold phases that alter ocean-atmosphere dynamics and reshape ecosystem composition and function. Despite recognition of the increasing risk of irreversible climate tipping points, the past and future evolution of these decadal warm-cold shifts remains unclear. Here, combining observations and simulations, we show a widespread 130-140% increase in the frequency and amplitude of sea surface temperature regime shifts across global Large Marine Ecosystems over the past 150 years, with asymmetries stronger in the Northern Hemisphere. Climate models attribute these trends to anthropogenic warming, which suppresses cold-regime transitions and reinforces warm regimes. Without mitigation, these shifts are projected to rise 130-180% by the late-21st century relative to recent levels, whereas only the lowest-emission scenario could constrain their intensification-except in the Arctic oceans. Further analyses reveal close links between intensified temperature regime shifts and abrupt ecological and fishery changes, showing 21-46% synchrony that is rising, potentially amplifying decadal ecosystem instability and socio economic challenges. From a marine perspective, these findings underscore the urgency of achieving the Paris Agreement's target and the Arctic's marked vulnerability.