I feel like GW causes us to get stuck in more extreme patterns for longer durations of time....no research, just my anecdotal ob....this can sometimes lead to some extreme cold of duration, like '13-'14 and '14-15'. But more often than not, it means warmth, obviously....so maybe in that sense, the strong of warm NE winters relative to the rest of the nation IS due to GW to some degree, but that isn't permanent.