From NASA's Solar and Heliospheric Observatory's "Not So Frequently Asked Questions" section:
Many active regions produce giant outflows of material that are called Coronal Mass Ejections. These ejections drag with them some of the more intense magnetic fields that are found in the active regions. The magnetic fields act as a shield for high-energy particles coming from various sources in our galaxy (outside the solar system). These "cosmic rays" (CRs) cause ionization of molecules in the atmosphere, and thereby can cause clouds to form (because the ionized molecules or dust particle can act as "seeds" for drop formation).
If clouds are formed very high in the atmosphere, the net result is a heating of the Earth - it acts as a "blanket" that keeps warmth in.
If clouds are formed lower down in the atmosphere, they reflect sunlight better than they keep heat inside, so the net result is cooling. Which processes are dominant is still a matter of research.
Most clouds exist below where jets fly and have a powerful cooling effect during the day, blanketing effect at night. We can't control the Sun but we can influence Earth's natural iris cost effectively. Global warmongers hate this subject and always say we know little about clouds.