Question

What effect does the axial tilt have on solar radiation on Earth?

Answer 1

It enhances or reduces the effective amount of solar radiation received at a particular geographical location.

Explanation:

If you think about solar radiation arriving at earth in essentially parallel streams (due to the distance of the earth from the sun), then the curvature of the earth can be seen to be the dominant factor in the concentration – or radiation per unit area – the received radiation.

The axial tilt of the earth is a simply a factor in which parts of the earth present a particular curvature towards the incoming parallel radiation. It is responsible for the generation of seasons. See also:
http://www.universetoday.com/47176/earths-axis/