Imagine that the Earth's orbit were to become perfectly circular around the Sun so that the distance between the Earth and Sun was always the same. How would this affect the seasons we experience on Earth?

If the Earth's orbit were a perfect circle, we would not have seasons.

Explanation:

A perfectly circular orbit would mean that the earth is always the same distance from the sun. However, the primary cause of our seasons is the tilt of the earth's spin axis with respect to its orbital plane.