The North Atlantic Oscillation (NAO)—a key atmospheric pressure system influencing winter weather across Europe and North America—is projected to intensify dramatically by the end of the century unless greenhouse gas (GHG) emissions are significantly reduced [2,3]. In a new study, Smith et al. [4] reveal that current climate models may be underestimating the risk of unprecedented multi-decadal NAO changes due to systematic errors in representing atmospheric processes, particularly the distribution of water vapor.