First and foremost, I must state that this write-up is hatched out of my own little brain and is not intended to be truly scientific. It probably does not even qualify as a SWAG (scientific wild-assed guess).
That said, perhaps it will ring true through plain ordinary logic with a few facts mixed in. Please let me know where I have gone wrong on this. I have attempted to deliberately over-estimate the population to come up with what would be considered a less unpleasant number by all but the most misanthropic among us.
The first number I would like to introduce is the number 30 million. All other calculations will be based on this, so I would suggest it as your first point of attack if you are trying to disagree with my findings. This number was quoted by Jared Diamond in Collapse as a high but still conservative estimate for the number of humans on the North American continent prior to European invasion and conquest. (It’s not discovery of a new place when there are already people living there.)
The next concept I would like to consider is what the total population of a hypothetical Earth would be if the humans the world over at some point in history actually all had about the same level of technology as the native North Americans prior to contact with Europe. This was clearly never the case on this planet, I realize. People in different regions had very different levels of technology and civilization. However, on my hypothetical Earth, all people share the same level of technology as the Native North Americans and have populated all major land masses except Antarctica for obvious reasons.
For this calculation, I will essentially be taking the population of North America and its land mass and performing a simple extrapolation to the world. I will be using the land masses as quoted on wikipedia, which will be another good point for dispute if you’d like to dispute this logic. This means that I am assuming a worldwide population of around 3.16 people per square mile (from 30,000,000 people / 9,500,000 square miles).
Using the number 55,419,294 square miles, I only got 175 million or so people. I did not include the tiny islands where wikipedia claimed the list might not be complete anyway. In addition, certain tropical areas would support far more people than the arctic. North America has rather a lot of arctic in Canada. So, even though Eurasia also has a lot of arctic, let’s just increase this by quite a bit to about 300 million people. It’s a rounder figure and accounts for greater density of population in some areas. It should also quiet some of the attempts to say that my number is horribly low. (It also comes closer to what I came up with in my head once going continent by continent without really knowing their sizes and has one more advantage that will come up later.)
So, now the question becomes, was that original population in North America sustainable? Well, that depends on your definitions. The Anasazi appear to have caused quite a large desert, or at least enlarged one that may have been there before. Within a thousand years of the Native American discovery of the Americas, going by the still generally accepted time frame for the discovery of about 14,000 years ago, 83% of the large North American mammal species went extinct. Also in the time frame and with similar technology, 87% of the large South American mammals went extinct.
Some might argue that that is not a proof of lack of sustainability. However, given my misanthropic principles, I think that causing mass extinctions is not a sustainable thing to do. Even the huge bison herds that greeted Europeans here may have already been in slight decline. Though shooting the bison from train windows appears to have been a far faster way to kill them off than the natives were doing.
So, I would argue that the 30 million people in North America were already not living sustainably. If true, this puts the limit that of human population that the planet can sustain long term, i.e. thousands and tens of thousands of years and longer, at something under 300 million people. It means that above 300 million people we will not be sustainable with the level of technology used by Native North Americans prior to contact with Europeans.
Currently, we have 22 times that number on the planet.
This was the other advantage of the 300 million estimate. It divides evenly into our current population of 6.6 billion. Our lifestyle today takes a far greater toll on the planet than ever before and is still only increasing our per person impact on the planet.
Is this just disasturbation? Or, might I actually have a point here? (It’s not easy living inside my brain.)