Effect of Sun angle on climate

The amount of heat energy a location on Earth receives depends directly on the angle of the Sun, since the solar zenith angle, the angle at which sunlight strikes Earth's surface, varies by location, time of day and season. This variation arises from Earth's orbit around the Sun and its rotation on a tilted axis, and the axial tilt is the fundamental reason seasons exist, producing warmer summers and colder winters. Changes in day length across the year also contribute to seasonal temperature differences, though this effect is considered secondary to the sun angle mechanism itself.