The tilt of the Earth's axis causes the difference in temperature between the Equator and Earth's polar regions. While the Equator receives direct light from the sun at all times of the year, the tilted axis prevents the poles from receiving such prolonged exposure. The tilt causes various other effects, such as the extreme length of day and night at polar locations.
The Tilted Earth
The Earth is tilted 23.5 degrees away from the sun, and remains in this position throughout the year. The northern hemisphere tilts toward the sun half of the year, while the southern hemisphere tilts away, and vice versa. Consequently, polar areas spend half of the year pointed away from the sun.
The tilt of the Earth means that when sunlight does reach the poles, it is diffused, or broken up, by the planet's atmosphere. This reduces the heating effect of sunlight. A similar but less drastic effect causes cold winters in the temperate areas between the poles and the Equator. Polar ice reflects sunlight, further reducing the heat of the sun on the poles.
Equatorial areas receive direct sunlight no matter what the Earth's position is relative to the sun. Consequently, the length of the day at the Equator is almost exactly 12 hours, all year long. Since there is little diffusion of sunlight at the Equator, most equatorial regions effectively experience summer throughout the year.