Interesting. Time to take a closer look at the timeline going further back, then.
To be edited...
As promised:
2072:
Nothing really strikes me as potentially related; lots of politics, space age nanotech and space elevator, Az-Am war breaks out
2071:
Again, nothing really strikes me as potentially related; politics as usual, the tempo crisis (seems like a stretch that tempo would be "the" cause, but could it be contributing?)
2070:
Same as before; the Emergence, new AIs appearing, Seattle election (booo, Brackhaven!)
2069:
Major earthquakes mess up California; could be related to increased magic, perhaps? Another byproduct, same as HMHVV power increasing?
2068:
ESUS arcology meltdown in the SOX; more toxic energy/mana in the world?
I don't really recognize anything that could be related until 2064:
As part of their Operation Jormungand (and/or Firnbul) Winternight managed to seize control of and use several mana nexi around the world for ritual magic. They also set off a nuclear physics lab, as well as 6 conventional nuclear weapons, fifteen EMP bobms, and one of their members commit "magical suicide.
New Revolution stirs up a lot of bad juju across the UCAS.
Ibn Eisa turns out to be a Master Shedim; who knows what kind of horrors he and his kind have set in motion.
To my mind, Winternight's orchestrations, along with the Shedim menace, stand out as the most significant "taints" on mana, at least on a massive, maybe even global, scale.