Climatic hazards originate with the processes that move air across the Earth's surface due to differential heating and cooling. Surprisingly, examination of these processes has focused upon heating at the tropics and downplayed the role of cold air masses moving out of polar regions due to deficits in the radiation balance in these latter regions. Fluctuations – in the intensity of pulses of cold air moving out of polar regions or of heating at the equator – and the location of the interaction between these cold and warm air masses, are crucial factors in determining the magnitude, frequency, and location of mid-latitude storm systems. While most of these factors are dictated by internal factors in the Earth–atmosphere system, modulation by 11-year geomagnetic cycles linked to solar activity and by the 18.6 year MN lunar tide also occurs. This chapter examines these processes and mechanisms. The responses in terms of centers of storm activity will be examined in the following chapter.