Earth axis is tilted to one side .which phenomenon would cease to exist in the absence of this axial tilt?

The earth's tilt of 23.5 degrees to it's axis as it revolves around the sun causes seasons; summer, spring, winter and autumn. This is due to the orientation of the earth with respect to the sun that cause variations in how to sun rays 'strike' the earth. Consequently, there are variations in temperatures across the earth, over its complete revolution, causing seasons.