The eruption of a supervolcano eg Yellowstone or Toba would wipe out almost ALL urban humans. Blackening of the skies would lead to widespread crop failure. As roads would be clogged with ash, food would simply not get into cities.No way would this feed the billions that inhabit the world currently. What would be the biggest source of food left ? ................fellow humans
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All the more reason to head for the hills and dark skies, although astronomy would have to be put on hold for a while
Better still
beam me up Scotty, and wait it out with the aliens out where the skies are always clear.