It is suggested that when the air temperature increases upward an efficient and economical method for modifying low temperatures near the ground is to force air downward through vertical stacks from the relatively warm air aloft. Theory is developed which shows that the necessary power per unit mass is mainly a function of the air velocity in the stack. The energy required by this method is compared with the energy required to heat the air originally near the ground, and it is shown that under a strong temperature inversion the power method requires considerably less energy than the heating method.