snarfed
commented
5 years ago it seems to be true as far as anyone can tell, and kind of a landslide at that. i wrote a tiny bit about it here.
UN projections vary, but the realistic ones seem to be that it peaks around 11B in 2100 (source):
this is driven by the drastic drop in fertility we've seen over the last few generations (more). the developed world is pretty much all at or below the replacement rate of ~2.3. only africa and south asia (ie the "global south") are meaningfully above, and they're falling like rocks.
lifespan is increasing globally, which offsets this, but nowhere near enough to keep population growing.
as to why this has happened, there isn't yet a strong consensus, but most people believe it's a combination of improved empowerment and education for women, higher income, better health care (which means families need fewer children to "beat the odds" of surviving), and access to birth control. fertility rates by country and region seem to correlate pretty directly (inversely) with development.
one obvious important point here is that this is counterintuitive. most people still think overpopulation is a big problem now, and will be worse in the future, and are surprised to hear that growth is slowing down and will peak.
personally though, i think the even bigger story is the global "graying," ie the combination of dropping fertility and increasing lifespan means that the world's population will gradually get older and older, which means there will be fewer younger people contributing to the economy and more old people depending on it. this problem has already developed pretty far in a number of countries; japan, italy, and scandinavia are common examples, among others. they've been working hard to figure out how to care for more old people with less human help and cost, how to incentivize people to have more kids, and how to attract more young immigrants.
more importantly, this overall "drag" on the world economy sadly has a direct negative effect on fighting climate change. if it drags down economic growth, and also requires more investment in health care, elder care, etc, that means resources for investment in clean energy, transforming infrastructure, alternative transportation, etc will be harder to come by. that's a problem, and we don't really have an answer yet.
This is a bit of an ill-formed question I've had for a long time. It seems like in all other life forms, populations will grow until resources are exhausted, and then usually crash. Human population doesn't seem to be behaving this way. Is that true, and if so why?