Post-2000 faster ENSO phase transitions amplify autumn sea ice loss in the Laptev–East Siberian Sea

Sea ice variability in the Laptev and East Siberian Seas (LESS) notably affects Arctic climate and maritime safety. While El Niño-Southern Oscillation (ENSO) winter sea surface temperature anomalies influence global climate, their effect on subsequent autumn LESS ice remains unclear. This study reveals a post-2000 intensification of winter ENSO's impact on subsequent autumn LESS ice, driven by accelerated ENSO phase transitions compared to the pre-2000 era. Rapid phase transitions of El Niño after 2000 generate persistent cold anomalies in the tropical central-eastern Pacific during the subsequent autumn, strengthening and displacing the Western North Pacific anticyclone (WNPAC) northward. This WNPAC triggers Rossby waves establishing an Arctic anticyclone, warming, and moistening the LESS atmosphere, thereby driving substantial ice loss. In contrast, pre-2000 slower El Niño decay exhibited weaker tropical-Arctic connectivity. These results identify ENSO phase transitions rate as a critical regulator of Arctic sea ice variability, with important implications for seasonal forecasting.