Ultimately all life is based on the food supply available to a living species, and that includes humans. Thomas Malthus developed that idea back in 1801, and he expected that most individuals of the human species would be living in a state of subsistence. “The power of population is indefinitely greater than the power in the earth to produce subsistence for man.” He didn’t recognize that the recent invention of the steam engine would change that state of affairs and many more methods of generating energy out of fossil fuels would be invented. Our current civilization is based on the production and consumption of fossil fuels and a world that can absorb their combustion products. Both the supply of fossil fuels and air and water to store the combustion products are huge compared to an individual human, but we now have 7.7 billion people, and all of them wish to live as well as possible. Even at current projections, the supply of these one-time-use resources won’t last for the lifetime of children alive today.
Humans are creative, and many of them are aware of these problems and will probably dedicate their lives to finding ways of combating this population-versus-resources problem. Already there are huge wind farms, and solar panel farms too, that are not fossil-fuel dependent once made, and they will no doubt grow in size and efficiency. These will supply energy for many of the needs now filled by fossil fuels, and if there is great effort to make those limitless energy systems ubiquitous, civilization could potentially last as long as the sun shines, which might be a million times longer than our current society’s life expectancy. That’s not likely with the swarm of other problems that will inevitably arise, but it is potentially possible.
And yet, Malthus and his theory of population expanding to the limits of the food supply will eventually be right because the population of well-fed people can expand to an infinite size! But the world is fixed in size, and its resources are fixed also, and so there is a limit to how many people it can supply with necessities, such as food, water, and shelter. What’s the solution?
There are two solutions to infinite population growth: either humans voluntarily as a whole species limit their population to the carrying capacity of the world, or natural processes will do it for them. If humans can consistently limit their population to half the ultimate carrying capacity of their world, everyone can live well. If humans can not do that, nature will slaughter them in a myriad of unpleasant ways, and if all else fails they will be starved back to compliance within the limits of what’s available.
When nature is overstressed and cannot produce enough resources, food being the critical one, it creates political problems which often result in war. The problem with war as the solution is that we already possess weapons of annihilation! Not weapons of mass destruction, but weapons of annihilation. Once those weapons are used, it will be difficult to bring a war to a reasonable end, and most of the people of Earth will be killed. Sorry, but the inventions to solve these problems are social inventions.
Because humans are scattered far and wide and some have stockpiles of food, a few may survive long enough for the planet to recover, and we can repeat the cycle. Or not.