If a hot and a cold body are allowed to interact by exchaning thermal radiation, the hotter body will transfer its heat to the colder body until radiative equilibrium is achieved. If both bodies have the same radiation characteristics, they will eventually both have the same temperature.
Radiative cooling drives the large-scale circulation of the Earth's atmosphere, as the sun heats the Earth more in the Tropics. Earth loses heat by radiation to outer space at both equator and the poles (in fact, more at the equator, because its hotter there). However, there is still a heat imbalance, and so between equator and pole atmosphere and ocean transport sensible heat and latent heat polewards, partially via eddies, known as cyclones in the atmosphere. The process is dependant on an external heat source, the sun, and will continue as long as this source is maintained.
