Ad I am sure Diners are aware although typical J6P is not, projections of this sort made by UN statisticians and demographers are loaded with assumptions that BAU will continue over the next 25 & 75 years.  They assume current rates of decline will continue along in a smooth curve that can be modeled as a mathematical function.  they don't account for "black swan" events like Global Thermonuclear War, global famine or a global pandemic that actually kills a significant number of the people it infects, unlike COVID or flu pandemics with relatively low mortality rates.

They also assume that we'll continue to supply enough energy to the population to maintain these rates through the entire timespan, which is unlikely.  All of which makes any projection that goes more than 10 years ahead is practically worthless.  Maybe the 2050 projections will be in the ballpark without a black swan landing in the next 25 years, but the likelihood we make it to 2100 under 2024 BAU conditions is vanishingly small.

Still, the charts are nice to look at as a "best case" scenario.

https://www.dailymail.co.uk/health/article-13309391/Mesmerising-charts-worlds-populated-countries-time-Britain-slipped-rankings-20.html

Mesmerising charts show world's most and least populated countries over time - and how Britain has slipped down the rankings and out of the top 20

RE