Analysis of variations in the monthly-average air temperature of the Northern Hemisphere in the nodes of a regular grid (5° of latitude by 10° of longitude) for the period from 1891 to 1986 (based on data from the All-Union Meteorological Information Institute's data base (VNIIGMIMTsD)) revealed a strong inverse correlation between deviations of the average temperatures and anomalies of their lateral temperature distribution during the cold half of the year in nontropical latitudes of the Northern Hemisphere (85° to 25° N). This analysis of the relationship between the atmospheric temperature and its lateral variation reveals that advection and outgoing radiation-induced fluctuations in the average temperature represent the main components of its year-to-year climatic variation during the cold half of the year, and contribute a significant part of the variation for the year as a whole. These fluctuations provide a key to understanding the mechanism governing the natural year-to-year variation of temperature in the atmosphere produced by free and forced fluctuations of the atmospheric and oceanic circulations. Our data suggest that a more critical approach to interpretations that find a human influence in the time series of air temperatures is in order.