volcanic activity and weather seem to be linked to solar activity and weather. The weakening magnetic field makes us more vulnerable to space weather. Once the flip happens our planet won't have a magnetic field for a while, that's when the fun starts. Every small solar flare will cause massive disruptions - powerlines on fire, stuff like that.
The magnetic field might also influence or even be the sole cause of our planet's rotation. That might also change with the reversal.
We are well into a pole reversal already. The magnetic field is weakening quite fast at the moment. We might be less than a decade away from the reversal.