Source: N.D. Marsh and H. Svensmark, 2000. "Low Cloud Properties Influenced by Cosmic Rays," Physical Review Letters, Vol. 85, pp. 5004-5007
Cosmic radiation comes to the Earth from the depths of the Universe, ionizing atoms and molecules in the troposphere, and thus enabling cloud formation. When the Sun's activity is stronger, the solar magnetic field drives a part of cosmic radiation away from the Earth, fewer clouds are formed in the troposphere, and the Earth becomes warmer.
The figure shows an astonishing coincidence between the changes in the cloud cap in the troposphere and the changes in cosmic radiation intensity in the period 1984-1994.