4 ms·

Actually my reading is that the uncertainty here is driven entirely mostly the uncertainty in the fertility rate. People living longer has a relatively linear e

Actually my reading is that the uncertainty here is driven entirely mostly the uncertainty in the fertility rate. People living longer has a relatively linear effect on population, fertility is much stronger. By eyeball this uncertainty projection for fertility seems extremely high, given the relatively smooth and predictable decline we've seen in the past [1]: https://population.un.org/wpp/Graphs/Probabilistic/FERT/TOT/900 https://population.un.org/wpp/Graphs/Probabilistic/FERT/TOT/... I spend a bit of time looking for the publications underlying this model right now, but couldn't find any. But accepting the error bars doesn't change the story. Which is that this isn't that much of a prediction. The main driver behind the population dynamics of the next century is the decline in fertility that has already happened. It's not a highly uncertain prediction that can turn out to be vastly different based on minor changes in the initial conditions. But if we underestimate the decline of fertility in Africa (where it is changing the most at the moment [2]) over the next decade or two it could easily end up being off by 10% or more. It's all fairly predictable. [1] For example the 95th percentile prediction sees a sudden bump in Asia, taking it up to fertility levels not seen since the early 2000s by the mid 2020s, despite a perfectly smooth decline since: https://population.un.org/wpp/Graphs/Probabilistic/FERT/TOT/935 https://population.un.org/wpp/Graphs/Probabilistic/FERT/TOT/... [2] https://population.un.org/wpp/Graphs/Probabilistic/FERT/TOT/903 https://population.un.org/wpp/Graphs/Probabilistic/FERT/TOT/...

Retric 7y ago
On it’s own WWII killed off around 3% of the world population. The plague may have reduced the world population from an estimated 450 million to 350–375 million in the 14th century. Long term estimates need to consider such black swans as a real possibility. Relative amounts of war and disease in Africa over the next 20 years will have a real impact.
- Spooky23 7y ago
  Remember as the power dynamics shift, the action will too. In 30 years what’s left of Pax Americana will be done. Much of existing US Naval and Air power will have attritted away. Asia/Africa will be the battleground. As those countries get more powerful and develop nuclear, the consequences of conflict get nastier. Things like restricting water supply bring back old style 20th century slaughter.

Retric 7y ago

On it’s own WWII killed off around 3% of the world population. The plague may have reduced the world population from an estimated 450 million to 350–375 million in the 14th century. Long term estimates need to consider such black swans as a real possibility. Relative amounts of war and disease in Africa over the next 20 years will have a real impact.

Spooky23 7y ago
Remember as the power dynamics shift, the action will too. In 30 years what’s left of Pax Americana will be done. Much of existing US Naval and Air power will have attritted away. Asia/Africa will be the battleground. As those countries get more powerful and develop nuclear, the consequences of conflict get nastier. Things like restricting water supply bring back old style 20th century slaughter.