There are two things that cause the change in seasons. 1. The earth’s orbit. 2. The tilt of the earth’s axis.

The Earth’s axis is the cause of our seasons. It is not vertical, but slanted at a 23.5 degree angle. If it were not slanted, we would not have seasons.

If the axis was at 90 degrees the northern hemisphere would have some very cold weather for a 6 month long winter. The southern hemisphere would have a very hot 6 month long summer.

If the axis was straight, we would always have forever sun with no change in seasons or temperature!