In a previous post, I considered some of the limits on the human population here on Earth. Now I'd like to discuss two things: the problems with trying to limit population growth, and how we can exceed the recognized limits.
At present, we expect the Earth's human population to stabilize at roughly 10 billion by 2040 or 2050. This estimate is based on a continuing reduction in the birth rate, which has been trending down, especially in the wealthier countries and in China which has legislated one child per family. The Earth can likely sustain that population, although with even more ecological impacts than at present. Several times that could likely be supported with severe impact on ecosystems. Note that population growth estimates wary wildly, and that low fertility rates in North America, Europe, Japan, and Australia may have dire consequences. See http://en.wikipedia.org/wiki/World_population.
There is a major problem with reducing the birth rate: not everyone will go along, and in the long term, those who are against population limits will have more children and will own the future. Those of us who choose to have fewer children than average are doomed to extinction. In the long term, our descendents will be those who are driven to reproduce. Hopefully, that will somehow include some significant proportion of intelligent people, as the alternative is a dumbing down of humanity. Do you know anyone who accidentally got pregnant?
Significantly, the recent human doubling time is short, currently about forty years. This is much higher than in the distant past, when much higher fertility rates were balanced by much higher death rates from disease and starvation.
A global conflict between wealthy, low population regions and poor, high population ones seems unavoidable. The have-nots will want to take from the haves. And they'll outnumber us.
There is hope: the intelligent and wealthy can choose to move into space where there are no short-term resource limitations on population growth. Some will. Those who remain on Earth may face ecological catastrophes, food wars, and other side effects of growing populations and dwindling resources.
In the long run, that is the only possible future of humanity. If we're stuck on Earth, we are doomed to die, or stagnate, at best. Perhaps something better will evolve and replace us. But we'll be dead.
In a convention speech back around 1980, Larry Niven said (and I'm paraphrasing here), "Humanity will reach the stars. It may not be the United States, or Europe, or any of today's leading nations. It may not be for hundreds of years. For if we don't move into space soon, our resources will become too limited for us to afford it. To deflect those resources would cause people to suffer, to die. But some day, some dictator will decide to spend a fraction of his resources not on some of his people, but rather on the future. Perhaps he will doom tens of millions of people to starvation, but he will fund a space program, and he will seed the planets and the stars with his descendents. And the far future won't give a damn about the millions of people his decisions killed; rather he will be remembered as the father of man in space, the greatest leader of all time."
What are the (relatively) cheap and readily found resources in space?
Asteroids and comets. A single 1-kilometer diameter comet contains enough resources to support a million wealthy people people for longer than we've tamed fire (this may require taming fusion, a higher form of fire).
How many comets are available? Some staggering statistics:
- There are perhaps 500-1000 easily reached near-Earth 1-kilometer-wide asteroids.
- There are an estimated 1,000,000 asteroids in the main belt at least 1km in diameter. Most of these are rich, carbonaceous chondrites, full of the stuff of life. Perhaps 5% are nickel-iron.
- There are an estimated 1,000,000 satellites 1km or larger in the Jovian Trojans (L4 and L5), 60 degrees ahead and behind Jupiter in its orbit around the sun, and their composition is closer to a comet, being mostly ices. Comets may have an ideal composition from a life support viewpoint.
- There are an estimated 10,000,000 cometoids in Neptune's Trojan orbits that are 1km or larger
- The Kuiper Belt (30-50 au from the sun) holds:
- an estimated 100,000 comets larger than 100km
- and 100,000,000 comets larger than 10km
- and likely billions more larger than 1km
- The Oort Cloud (out to about 100,000au, or half way to Proxima Centauri) holds:
- an estimated 1,000,000 comets larger than 100km
- It holds 1 billion comets larger than 10km
- and the Oort Cloud probably holds at least 1 trillion comets that are 1km or larger
Note that the Milky Way Galaxy holds perhaps a trillion times that many comets. All this without mining planets, or stars. Without destroying any ecosystems.
The Earth would make a very nice zoo, however. We should definitely save it. For old times sake.