Earth rotates with a tilted axis. This tilted axis affects the amount of the solar energy received by the two hemispheres of the Earth when revolving around the Sun. This is also known as the circle of illumination. The part of the Earth that receives the maximum amount of solar energy is the equator as it always faces the Sun throughout the year. The tropics come at second position, because the zone receives less sunlight during the winters due to the tilt. The poles receive the least amount of sunlight as the rays pass tangentially through them. Hence the poles are icy.
If the tilt was absent, then the poles receive more direct sunlight and become warmer and the equator goes hot and barren due to the absence of slight variations in sunlight received due to the tilt.
The poles will make a significant gain of energy in absence of tilt.
