The 2025 Record Low in Arctic Sea Ice Extent: Dual Forcing from La Niña and Southern Indian Ocean Warm Anomaly

Abstract

In February-March 2025, the Arctic experienced record-low sea ice extent, despite a decadal slowdown in ice loss [1,2]. Although a weak La Niña was present, its influence alone is insufficient to explain this extreme event. Here, we demonstrate that this record low on an interannual scale was driven by the synergistic effects of La Niña and concurrent South Indian Ocean warm anomaly (SIOW). La Niña perturbed the Walker circulation, while SIOW altered the Hadley Cell. Their combined forcing over the tropical Indian Ocean generated intense anomalous downward motion and upper-level convergence, exciting a northeast-propagating Rossby wave. This wave train produced a significant anticyclonic anomaly over the Okhotsk Sea, which enhanced air temperature and accelerated sea ice melt. Our findings reveal an inter-basin atmospheric bridge, initiated by La Niña and SIOW, establishing the essential role of synergistic Indo-Pacific forcing in driving extreme Arctic sea ice loss, superimposed on a long‑term decline.