Eccentricity changes the total energy received by the earth system from the sun, but all three have most effect on seasonality. Because of the difference between land and water in the northern and southern hemispheres, differences in seasonality leads to differences in the storage of energy. Astronomical theory matches the timing of climate changes, but does not explain the total amount. Ice and snow create a positive feedback.
Clouds are a question.
CO2 in the ocean and atmosphere can create a positive feedback Carbon also goes into the biosphere and then to the lithosphere.