Need a specific event that wrecks the surface, allows the race to survive in bunkers, and affords an aftermath suitable for them to rebuild
One rule: it cannot be caused by aliens or AI invading the planet. But it is okay if an alien race causes the destruction in any other way.
It's an Earth-like planet. I need the effects of the destructive event to be continuous there-after, i.e massive storms and natural disasters for years to come that threaten the small population that survived in bunkers.
I want the majority surface to get wrecked. I need all things that are required to rebuild a civilization to survive, i.e, an atmosphere, because I need characters to come up from the bunker and be able to live. I don't want them to be comfortable. Their lives are to be miserable. The planet should look like a hell-scape afterwards and they should desire finding a new home.
Hope you don't consider this a duplicate question because I feel my question is more nuanced than any others on this site.
Edit #1
This human race is quite advanced. They'd have technology to redirect asteroids, comets, etc. Unless an alien race were to guide some into the planet. The event also needs to be fast acting. So global warming is out of the question
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1 answer
Nearby Supernova.
Dr. Mark Reid, a senior astronomer at the Harvard-Smithsonian Center for Astrophysics stated:
"¦ were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects us from solar ultraviolet rays. It also could ionize nitrogen and oxygen in the atmosphere, leading to the formation of large amounts of smog-like nitrous oxide in the atmosphere.
Pretty unpleasant, no laughing matter - killing off huge swaths of animal and plant life some would recover in time but not without huge changes, the nitrous oxide would cause serious warming:
On a per-molecule basis, considered over a 100-year-period, nitrous oxide has 298 times the atmospheric heat-trapping ability of carbon dioxide (CO 2)
A hot Earth then, but what about the oceans:
....phytoplankton and reef communities would be particularly affected. Such an event would severely deplete the base of the ocean food chain.
It's clear that if you take away the base of a food chain then the whole thing falls flat.
Sure, deep ocean life feeding on bacteria at oceanic vents might be ok, but everything else would radically shift.
Given time, technology and resources to shift everything back and make new plantings and reseed the oceans with life - it could be done, but it would be harsh.
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