Mana Storm Growing
The Mana Storm is a collection of magic that has been building since the magic returned to the world. No one is quite sure what is causing it an any who enter never return.
The Mana Storm opens up into an extra-dimensional space that hold all those who have disappeared to fuel the Portal Network. The fear is that if left unchecked the Mana Storm will eventually overtake the planet.
This takes inspiration from the current Climate Change crisis. While it could be natural, man-made, or a combo the fact that the climate is changing is a fact. Ice caps are melting, even if they melted before as part of a natural event, it is still happening. This is a representation of that. Magic will overtake all like and likely kill it off if something isn’t done to stop it.