Differential heating is the term used to explain the ways sunlight heats the Earth's zones differently depending on tilt, revolution around the sun and daily rotation. This process results in what human beings perceive as seasons and other climatic shifts.
The Earth's equator undergoes a net energy gain from sunlight over the course of the year, its place ensuring constant sunlight and exposure to energy. The rest of the world experiences a shift from gain to loss on a seasonal basis during the changing tilt of the Earth's axis and on a daily basis during the Earth's rotation.
The Earth depends on the sun for the energy that makes the processes of life possible. Without sunlight, there would be no plant growth and no breathable atmosphere. The heating differential is the metric by which this life-giving energy's contributions to an area are measured for purposes of assessing information like ideal growing seasons and solar radiation exposure.
Just as the equator is always bathed in energy, the poles are largely isolated, cold and barren. Locked beneath ice, they seldom experience any positive gain in energy because the sun's light shines on them much less than it does on other parts of the world.