English: This graph shows a very simple approximation of relative solar-noon heating on Earth as a function of season and latitude, as resulting from the geometry of the sun elevation angle.

Approximations include a perfectly steady, circular orbit, a perfectly spherical Earth with perfectly steady rotation, complete neglect of any atmospheric effects, and complete neglect of albedo or radiative-cooling (greenhouse) effects. The utility of this model also depends on the correlation between daily total heating and daily peak insolation, which isn't perfect. The model does illustrate the highest order effects of sun angle vs latitude: poles are only heated due to axial tilt; zero tilt gives zero polar heating, maximum tilt gives maximum polar heating. Note also how seasonality -- max-vs-min heating -- is much lower at the equator than the poles. Lower polar heating promotes permanent icing. From ~2.5 mya to ~1.0 mya, glacial cycles matched the ~41 kyr axial tilt cycle, however in the last million years, glacial cycles instead have ~100 kyr periods, indicating that the axial tilt cycle is no longer the primary driver of glacial cycles. Polar icing is thought to be quite sensitive to polar insolation, as albedo and carbon sequestration effects can significantly amplify relatively small changes in heating.

For comparison to present axial tilt, the polar line also includes the max tilt and min tilt expected over the next million years.