How solar variation cause mayor climate variation?

Since the Sun has been proven to be constantly changing, it is not unreasonable to assume that the long-term climate changes, such as the ice ages, are effects of major, long-term solar activity variances. If the power flowing into the Sun is fluctuating, its  associated  'space weather' pattern is also fluctuating. The Sun creates its own 'weather' as it were, determined by the intensity of the solar winds that flow out from it, resulting from the energetic, electric reaction that lights up the Sun.

The space weather is contained within the solar-created environment called the heliosphere. As the solar winds flows away from the Sun, they are electromagnetically accelerated  to  speeds greater than a million kilometers per hour. Near the interstellar medium  app. ten billion kilometers distant, the solar winds slow down. The zone where this happens is called the " termination shock." 

solar map

The point where the interstellar medium and solar wind pressures come into balance, whereby the solar winds are stopped, is termed the "heliopause."  The final zone, further away, where the interstellar medium, moving in the opposite direction, begins to slow and collide with the heliosphere, is termed the "bow shock." 

This three-layer zone, far past the orbit of Pluto, is critical for our climate on earth, because it is here where the interstellar cosmic background radiation, consisting of immensely energetic protons, electrons, and ions (the cosmic rays) becomes attenuated. The density of the termination shock, the heliopause, and the bow shock determines the density of the cosmic-ray flux that penetrates this barrier. When the solar power activity is high, the barrier is more dense, and correspondingly fewer cosmic rays get past the barrier. Inversely, when the solar power activity is low, the solar wind pressure is lower, the barrier is weaker, and penetrating cosmic-ray flux is stronger. 

Studies have revealed patterns of cyclical variations in cosmic-ray flux that peak in synchronism with the deep glaciation periods of 450, 300, and 150 million years ago, and also with the modern glaciation period.