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troperville

While The End of the World as We Know It is very common in fiction, there are a wide variety of ways in which it can actually manifest; this can be measured on two sliding scales, depending on the size of the "world" in question, and to exactly what extent it "ends". This is derived in part from Bruce Sterling's analysis

of ways in which the Real Life world could theoretically end.

Scope

Regional: a part of a continent or landmass, be it a state, country, or sub-continent (eg. "Sub-Saharan Africa", "California", "The British Isles", "Central America", etc).
Continental: An entire continent or landmass ("Eurasia", "Oceania", "The Americas", etc).
Planetary: an entire planet, or the vast majority of one. (If the given setting does not involve space travel and/or other worlds, then the scale effectively stops here, or skips up to Multiversal if the other worlds are not elsewhere in space, but do exist.)
Stellar: a solar system.
Galactic: a galaxy.
Universal: the entire universe.
Multiversal: multiple universes (whichever flavor of Another Dimension you prefer)
Omniversal: all universes; reality itself.

Severity

Societal Disruption / Class 1: Civilization survives intact, but is forever altered. This may be due to the sheer amount of damage caused lowering the standard of living, or it may be a result of people being forced to adapt to the new threat(s) they face.
Societal Collapse / Class 2: Humanity backslides within the affected area, regressing to pre-industrial levels^note at best and pre-agricultural^note at worst. Civilization may recover on its own, but not for centuries at the least.
Species Extinction / Class 3: A dominant or major species is either wiped out completely or reduced to such a low population level that its recovery is virtually impossible barring intervention by an outside force.
Total Extinction / Class 4: Life itself ends. No living organism of any kind exists within the affected area.
Physical Annihilation / Class 5: The affected area physically ceases to exist, but stray remnants of it can still be found here and there; it's nuked into glass, sunk into the ocean, or blasted into asteroids.
Metaphysical Annihilation / Class 6: The affected area ceases to exist or have ever existed; this usually involves erasing it from time.

Not to be confused with the comedy survival guide by Rob Kutner

, which gives advice for surviving Class 0-2 events. Or the Discovery Channel series by the same name which explores various scenarios in which this could play out.

Related Tropes (ways this can be brought about):

See also: Sliding Scale of Villain Threat, Evil Only Has to Win Once and Why You Should Destroy The Planet Earth. If they actually show it, then you have an Apocalypse Wow.

Please don't identify by the numbers anymore - they are only there for older users of this site to compare the new scale to.

Class 0: Regional Catastrophe Now "Regional/Societal Disruption" or "Regional/Societal Collapse". Hardly apocalyptic at all.
Class 1: Human Die-Back Now "Planetary/Societal Disruption"
Class 2: Civilization Extinction Now "Planetary/Societal Collapse"
Class 3a: Engineered Human Extinction Now "Planetary/Species Extinction" (dominant species, engineered)
Class 3b: Natural Human Extinction Now "Planetary/Species Extinction" (dominant species, natural)
Class 4: Biosphere Extinction Now "Planetary/Species Extinction" (several species)
Class 5: Planetary Extinction Now "Planetary/Species Extinction" (all multicellular life)
Class 6: Planetary Desolation Now "Planetary/Total Extinction"
Class X: Planetary Annihilation Now "Planetary/Physical Annihilation"
Class X-2: Stellar Destruction Now "Stellar/Physical Annihilation"
Class X-3: Galactic Scale Destruction Now "Galactic/Physical Annihilation"
Class X-4: Universal Destruction Now "Universal/Physical Annihilation"
Class X-5: Multi-universal Destruction Now "Multiversal/Physical Annihilation"
Class Z: Total Destruction Of All Of Reality Now "Omniversal/Physical Annihilation" and "Omniversal/Metaphysical Annihilation."