Some of my friends were born in 1925 when the population of the Earth was 2 billion people. Since that time it has grown to 7 billion and that’s 3½ times bigger. But, what if instead of having that huge population increase we had experienced a proportionate decrease? What if the human population had gone down by 3½ times to only 570 million during these friends lifetimes. Would people still be as happy and contented as they presently are or would they be feeling absolutely devastated by unrelenting disasters? Even the worst human tragedy of historical times, the Black Death, reduced population from 450 million to 350 which is only 22% of the people gone not 71%. What my friends experienced in their long lifetimes, and they are still going strong, was vastly more significant for humanity than the Black Death but in reverse. For all of the people who presently exist the other species of the world had to make adjustments and many simply died. That is their equivalent to the Black Death because we ate their food.
The human species from the long term perspective is in a very unusual population condition. Population explosions happen to other species occasionally when they have an abundance of food and for some reason an absence of predators but then they invariably have a population crash. Either there is a crash in food supplies or their predators reproduce and eat them. The explosion that the current human population grew up with we now believe is a normal world but trippiling a population in a single lifetime isn’t normal and a crash is inevitable. We have access to ancient but temporary energy sources like coal, oil, gas and uranium which give a huge but one time boost to our food supply which is also incredibly unusual but it won’t last forever.
When these various unique supports for the ongoing human population boom run their course and are exhausted the population must drop back to a smaller number. How can we know or even speculate what that new number will be? One way to estimate what that new number will be is to estimate the population back when people lived wholly by their own bodily effort. We can easily think back to Roman times when the world population at the year 1AD was about one hundred million people. They were living solely on sustainable energy sources created mostly through humanly mediated farming. It was dependent upon their own human muscular effort aided by some draft animals.
Unfortunately, because of the present permanent degradation of natural resources if those ancient people were forced to live that same life style here and now on our present planet the new complications would probably reduced them to half of what the population number was during their lifetime. The situation might be even worse than that because not only has the soil been striped of its nutrients much of it has been washed away into the sea. The best farmland soil in the world is now under salt water at the mouths of rivers. The situation might be a little better in some ways because modern technology has created new ways to get permanently available energy from the sun using photo-voltaics and from more sophisticated windmills. This electrical energy can be made to run a high tech societies toys but it can also be converted into food. The process is similar to the fossil energy of oil being pumped from wells which is being used to run tractors which ultimately gets a lot more food out of a plot of farmable ground. The day may come when wind and solar energy are used to charge batteries which power the tractors of the future. Or perhaps there could be power lines like trolley lines strung over fields to power the electric tractors. This is obviously doable at present but while we still have gasoline it isn’t economically practicable. It would be interesting if the people at Tesla automotive would build a farm tractor instead of just sports cars to demonstrate that it could be done.
I don’t like the idea of lowering the Earth’s human population to a sustainable number but if we don’t do it voluntarily using human intelligence and ingenuity, with some consideration for human feelings, nature will do it for us. Nature will supply the “responsibility” perhaps with a human war but in a way which will be very brutal. We could be much kinder than unfeeling and uncaring nature but it is doubtful that humans could muster the political courage to take responsibility.
I have no interest in making any particular group relatively larger or more powerful than any other my ambition with this is human population proposal is only that a substantial number of humans survive for a very long time and in what we would presently consider descent living conditions. I want to maximize human happiness.