Previous questions asked whether the human population would be reduced by 95% or more within 25 years of various catastrophes occurring before 2100, if such catastrophes occur. (The catastrophes in question were a global biological catastrophe, an artificial intelligence catastrophe, a nuclear catastrophe, a global climate disaster, and a global nanotechnology catastrophe.)
Such questions are especially important from a longtermist perspective and if they are diagnostic of the chance of extinction or some other existential catastrophe. Indeed, the questions were framed as partly intending to get at extinction risk. But how likely is extinction, given a 95% population loss?
(See also Will humans go extinct by 2100?, How long would humanity take to rebound from a global catastrophe?, and a soon-to-be-released question intended to get at the likelihood of unrecoverable collapse given a 95% population loss.)
Will extinction occur within 20 years of the human population falling below 400 million, if the population falls that much by 2100?
This question resolves positively if the human population falls to below 400 million by 2100 and, within 20 years of the population falling below that level, there are no longer any living humans. The extinction could occur at the exact same time as the initial population decline (if some event instantly causes extinction), gradually over the course of 20 years, or anywhere in between.
The question resolves negatively if the population falls to below 400 million by 2100 but extinction doesn't occur within 20 years. The question resolves ambiguously if the population never falls below 400 million before 2100.
For the purposes of this question, "humans" are creatures who at least one 2021 Metaculus user would judge are humans if they magically met them.
As stated on another question about extinction:
"N.B. Even though it is obviously the case that if human extinction occurs Metaculus points won't be very valuable anymore and that it will be practically impossible to check for true human extinction (zero humans left), I would like to ask people not to let this fact influence their prediction and to predict in good faith."