One of the important decisions I need to make is Earth’s population growth. In the past, many science fiction authors have assumed that it would grow quite large, sometimes to the point that people would be stacked four high to every square meter (you will recall Heinlein’s description of India in The Moon is a Harsh Mistress). Even though some of this is probably hyperbole, the description of Earth as a nightmare of crowds is all over the genre.
Of course, while current population estimates are much less dramatic, they still predict 9+ billion people. And if all of those people want to have a standard of living comparable to what we enjoy in Europe or North America, then we’re going to run into severe resource issues. Oil is the most popular example of something that can run out, and this would not only affect the economy because of increased fuel prices. Fertilizer is oil-based as well, and if food production doesn’t keep up with population growth, then a whole lot of those nine billion people are going to go hungry. And food being a basic need, that would trigger conflicts than not being able to drive one’s kids to school in a SUV surely wouldn’t.
Food and fertilizer, however, I am not quite so worried about. Anything that is organic basically just requires carbon, energy, and a bunch of other elements. Throw them together, mix them around, and you can create pretty much anything you want. It’s all a question of technical expertise and cost effectiveness. But that wealth that those nine billion people crave requires metals. Just take copper – we need it for pretty much everything that keeps our society going. What do we do when copper runs out?
The answer is, of course, that we will mine more. Humans are an inventive lot and when we are faced with a serious problem, then we solve it. It may be a painful process, but I am convinced that we will come out on top. There’s a lot of untapped copper – mostly in the depths of the oceans. Extracting it is expensive, but possible, and at some point when copper becomes scarce and expensive enough, companies will begin to mine it. Alternatively, there is an entire solar system out there that we can use for resources. Again, this simply requires improvements in technology and practice and a slightly more “favorable” economic climate.
So, for my Future History, I do not predict any breakdown of civilization based on resource shortages. I also don’t believe in a large-scale nuclear exchange (regional, that is a different matter). For population, I’ll follow something along the lines of the UN “medium” prediction:
The green line is, until 2300 AD, the UN “Medium” projection (after 2300, I extrapolated unscientifically). The blue line is my version, which of course I may change if the simulation of Earth’s history shows up anything unexpected.
For this baseline, my reasoning is that towards the end of the 21st Century, we will feel the effect of peak oil and other resource shortages coupled with the effects of global warming. Food will be expensive and there might even be some regional famines, and things we take for granted – for example, personal transportation, i.e. cars – will become unaffordable (or remain so) for a majority of the world’s population. It will be a while before technological fixes kick in. AIDS and antibiotic-immune diseases are also going to take a minor toll (minor when compared with the total world population).
Many countries will follow China’s “One Child” policy, except they are going to use economic incentives instead of penalties. If for example, instead of raising five kids and barely feeding them, a family could raise one kid and send it off to college so that he can have a much higher income than those five kids without the education will have combined, and if this means the difference between going hungry and being fed for the entire family, then people are going to catch on pretty quickly. And college-educated women tend to have much fewer children, and have them much later, than less educated women.
A decline by 2 billion in 100 years may be a bit drastic, but the basic premise, I feel, is sound.
Wold population will slowly recover as technology catches up and new resources become available again, but it will never peak again at previous levels. After a minor peak in the 25th Century, it will slowly fall into sustainable levels just under 8 billion.
Note that I do not think interstellar emigration will make any difference whatsoever during this time period. In a Space Opera type setting, where massive transportation capacity is available, it might; but at these “reasonable realistic” levels the birth rate is always going to outpace the capability to ship people off to other planets.