Population growth has slowed fairly dramatically and for most of the 90's the concern was underpopulation, based on the finding that as economies develop fertility drops.
It's called the fertility transition (1), and the current below replacement fertility in countries like Spain and a few others were seen as the future. For a while the US was thought to be exempt from this trend, but recent headlines suggest otherwise (2).
for most of the 90's the concern was underpopulation
Among a rather select set of those interested in the subject.
Yes, a great deal of fairly short-term (on a civilization/species perspective) issues arise when your birthrate suddenly falls, especially if it had previously been rising markedly. But concerns over the Earth's carrying capacity and how many humans can be supported, sustainably, and at what level of per-capita resource consumption (and hence, at what standard of living) are, without exaggeration, the single biggest challenge of the next 50-100 years.
And all three factors come into play: population, per-capita resource consumption (PCRC), and sustainability.
You can get a large sustainable population at a low level of PCRC. Do you really want a world of 10 billion living in the conditions of Kolkotta, Bombay, Manilla, or a Brazilian favela?
You can get a large population and high PCRC ... but low sustainability. Do you really want modern technological civilization to run into a brick wall / off a cliff in 20, 40, 80 years? A fair number of people reading this can expect to be alive then.
You can get a sustainable but smaller population at a higher PCRC. At which point the questions become, what's the minimal level of consumption you want to support, how many people can it support, and how do you get from n(0) to n(t) where t is the end of the transition period. History shows that periods of depopulation tend not to be particularly tranquil.
For the HN twist: thinking about these sorts of problems seems rather more pertinent then trying to craft the next Uber for windsurfing or video ad pre-roll monetization scheme for Mexican K-Pop tweens.
But the problem's hardly easy. A bit posted a few weeks back on how Kleiner-Perkins has stumbled in trying to pursue a green strategy struck me as immensely sobering. A business whose business is making money hand over fist over commercializing new ideas losing money hand over fist failing to commercialize on new ideas suggests that cracking this nut is going to be really, really fucking hard.
John Doerr investing $200 million in green energy while simultaneously lobbying for California to cap carbon emissions? No conflict of interest there...
Both are worrying. Overpopulation obviously has problems with dividing up natural resources among more and more people and/or trying to find jobs for them all.
But too low birth rates mean there won't be enough kids to replace the current workers, and we will have fewer people supporting a larger population of retired people (though this might be possible with technology and of course, immigration.
It's called the fertility transition (1), and the current below replacement fertility in countries like Spain and a few others were seen as the future. For a while the US was thought to be exempt from this trend, but recent headlines suggest otherwise (2).
(1) http://en.wikipedia.org/wiki/Demographic_transition
(2) http://money.cnn.com/2013/09/06/news/economy/birth-rate-low/