The abrupt decline in sea ice in the Barents-Kara (BK) Sea because of global warming has been argued to influence not only higher latitudes but also the tropics. Using EC-Earth model simulations, we demonstrated that the El Nino-Southern Oscillation (ENSO) period becomes longer when BK sea ice substantially decreases. As BK sea ice was forcibly reduced through nudging experiments, the mean Walker circulation shifted to the west, and the zonal sea surface temperature contrast in the tropical Pacific was enhanced. Consequently, the western Pacific mean thermocline became deeper, which reduced the sensitivity of oceanic wave response to wind forcing. Therefore, the oceanic Kelvin waves reflected by ENSO-induced surface winds, a primary delayed negative feedback factor, were significantly weakened. Thus, ENSO phases could be sustained for longer.