The Super Novas correlate well with cosmic ray density. The laboratory experiments (and observations of a coronal mass ejection) prove cosmic rays create conditions for production of sulfur compounds that serve as particles around which water droplets/ice can form to create clouds.
It's simpler than I thought it would be ~ not at all Rube Goldburgish ~ just happens all the time.
It's a universal machine, so anywhere in our galaxy, or any galaxy, where there are clouds of gas that can be crunched into potential super novas, the life on the worlds in the vicinity (which is an enormous vicinity BTW0) will be subjected repeatedly to biologically destructive levels of cosmic rays ~ which act through the climate (atmospherics) to do bad stuff to critters.
The theory is it's galactic cosmic rays emitted by distant super novas. The galactic cosmic rays help promote cloud formation and COOLING on Earth. The sun's magnetic field acts to repel GCRs, more or less depending on the current level of solar activity. More sunspots = less low-lying, thick cumulus, cooling-effect clouds = warmer temps