Talking about population numbers, what should we consider to be a long term sustainable population figure? Eight billion or more? Less than that? Or is perpetual growth a possibility?
At out current tech level it's about 12 billion, and it will only continue.to go up from there.
I see a bit of a problem. Mainly food production shortfalls. Food production can only be ramped up by a finite amount and I bet we're close to the limit. I know, we could quit putting corn in gas tanks but what else? The other problem I see is energy. Not to mention all the sewage. Can you imagine the surface water in China and India? I would think Asia in particular is ripe for a population adjustment if a deadly pathogen gets loose as compared to the candy ass Covid19.
Keep in mind, there's two sides to this equation. And extra 4 billion people is a lot of additional labor, and our rate of innovation's great than you imagine.
In 1900 it took 50% of Americans to feed the U.S. Today 2% of Americans feed our country 2 and a half times over, and as you point out, that doesn't include all the corn we put in our gas tanks. We can make the food. The biggest problems are in distribution, and corrupt governments steeling so much money from their people they can't afford food from the highly productive regions.
In 1865 Stanley Jevons published
"The Coal Question; An Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of Our Coal Mines" In it, Jevons predict all the coal in the entire earth would be exhausted by 1965. Well.....he was wrong. We have hundreds, if not thousands of years worth of know coal reserves. Additionally, there's this trick of economics that prevents scare resources from becoming exhausted. It's called the price mechanism. As resources become scare, price goes up, and people either find substitute products, or new more innovative way to produce them more cheaply. An example of this is the fracking revolution in oil production and the hundreds of other revolution of the last century.
Heck if everyone, starting with Russia and China would just stay on their square and cooperate a little bit, we could do 20 billion without much sweat.
