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. Another question asks how likely extinction is within 20 years of such a population decline. This question is intended as an imperfect proxy for the chance of another type of existential catastrophe: Unrecoverable collapse.

(See also How long would humanity take to rebound from a global catastrophe?.)

Will human population size recover to 5b by 3000CE if, by 2100, the population falls below 400m without extinction occurring within 20 years?

This question resolves positively if the human population falls to below 400 million sometime before 2100, extinction doesn't occur within 20 years of that population decline, and the population recovers to >5 billion people sometime by the year 3000 (whether or not it remains >5 billion in the year 3000). The question resolves negatively if the population falls to below 400 million by 2100, extinction doesn't occur within 20 years, and the population remains below 5 billion from then till the year 3000 (whether this involves extinction or not, and regardless of what happens after 3000). The question resolves ambiguously if the population never falls below 400 million before 2100 or if extinction occurs within 20 years of such a population fall.

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 such extreme events:

"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."