The Northern Annular Mode (NAM) is the dominant pattern of atmospheric circulation variability in the wintertime Northern Hemisphere extratropics. This study utilizes a large ensemble atmospheric simulation dataset to examine the seasonality of the NAM variability and its modulations under global warming. We show an enhancement of the Aleutian Low anomaly associated with the NAM in a warmer climate. This enhancement is related to the emergence of the Aleutian-Icelandic Low seesaw (AIS) from early winter, which is in contrast prominent only in late winter in the historical climate. The large ensemble reveals a significant increase in the fraction of the NAM variance explained by sea surface temperature and sea ice variability, suggesting a higher potential predictability. In particular, the eastward extension of the El Niño-Southern Oscillation (ENSO) teleconnection under global warming contributes to the AIS formation even in early winter and a higher NAM-ENSO correlation.