While birth rates are lowering enough that the population based on current projections will start dropping in a few decades, UN projections also clearly indicate it will start increasing again soon enough, albeit at a slower rate.
To avoid that would take substantial further reductions in birth rates beyond that which is baked in based on current trends.
EDIT: Let me adjust this a bit. UNs World Population Prospects 2015 [1] says "Continued population growth until 2050 is almost inevitable, even if the decline of fertility accelerates." and their middle and top estimates shows continued growth until 2100, though rapidly shrinking growth. The low end estimate shows a reduction in the latter half of the century. Almost all of this growth is expected to be in developing countries, however.
So the people predicting a financial catastrophe in the next 20 years because of the demographic nightmare of the boomers leaving the workforce and not dying for 20 years, so we become a society with too few workers are wrong?
Awesome!
Seriously, which is it? Either capitalism is going to fail because there aren't enough workers, or it's going to fail because robots are taking all the jobs. Can't have both!
Because, of course, having both would be fine... no catastrophe, life continues as normal as it has in the face of every prediction of imminent disaster. We have less workers due to demographic changes, but that's cool because we need less workers. We sort out the political problem of how to stop all the money going to to <1% of the population, we're all good.
How does that help long-term? Let's say we, somehow, reduce the world's population to one billion. Great, so we only have one one seventh the workers to keep busy… but also only one seventh the market size. We're back to square one: Still the same unemployment rate, even if the total amount of unemployed is smaller.
To avoid that would take substantial further reductions in birth rates beyond that which is baked in based on current trends.
EDIT: Let me adjust this a bit. UNs World Population Prospects 2015 [1] says "Continued population growth until 2050 is almost inevitable, even if the decline of fertility accelerates." and their middle and top estimates shows continued growth until 2100, though rapidly shrinking growth. The low end estimate shows a reduction in the latter half of the century. Almost all of this growth is expected to be in developing countries, however.
[1] http://esa.un.org/unpd/wpp/Publications/Files/Key_Findings_W...