What phenomenon is most often implicated in causing the most noticeable biological effects on Earth?

Answer

The resulting geomagnetic storm

While the flare initiates the process, it is the subsequent collision of the CME plasma cloud with the magnetic field that creates a geomagnetic storm, and this resulting magnetic turmoil is what is often implicated in biological effects.

What phenomenon is most often implicated in causing the most noticeable biological effects on Earth?
sunhumanSleepradiationsolar flare