Milankovitch Cycles

In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession of the Earth’s orbit resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced climatic patterns on Earth. However, the Earth’s eccentricity is always so small that the variation in solar irradiation is a minor factor in seasonal climate variation, compared to axial tilt and even compared to the relative ease of heating the larger land masses of the northern hemisphere. This means that solar radiation due to (1) axial tilt inclining the southern hemisphere toward the Sun and (2) the Earth’s proximity to the Sun, both reach maximum during the summer and both reach minimum during the winter.

Source: en.wikipedia.org