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The one billion people in the year 1800 did have one advantage over us; they were living in an ecologically sustainable balance with nature. Their communities could have continued living the way they were for thousands of years without destroying the world’s natural habitat. But the current 6.7 billion people are currently destroying the environment by their shear numbers, and by the way they are consuming natures single-use resources. It is clear that humanity can not live at the current population levels with our current life styles forever without destroying the sources of those life giving materials.

So how long will the world supply us with its bounty to keep us living on the way we do? That is beyond any exact prediction, but it is impossible that it would sustain us for another 200 years. It is unlikely that it would maintain us for even 50 years, and maybe not even 10 years—without something dreadful happening, a tipping point or a war.

Perhaps we should pose the question – How many people can the Earth sustain permanently at the current middle class level for typical Europeans? They currently live long and pleasant lives, with a more modest carbon-footprint than Americans. But even their lifestyle is probably unsustainable if everyone on Earth were living at that consumption level. With modern communication and transportation there is a pulling of people in different locations toward a similar standard of living. Everyone wants a pleasant good life after all, and over a period of time there would be a moving about of people, and a balancing of consumption. So, it is reasonable to take the total human carbon-footprint of the year 1800 when things were in balance and dividing it by the carbon-footprint of the current European. Thus we can estimate the total sustainable carrying capacity of Earth’s of people living at our new more energy consumptive life style.

From the UN Human development reports we find that the current average carbon footprint of France is 6.0 tonnes per capita per year. This is a bit lower than European average, but I have personally observed that life in France is quite pleasant. North Americans are using far more energy at 20 t CO2 per capita. The world CO2 emissions 4.5 t CO2 per capita, but that averages out everyone, the mass users and minimal users. The total world CO2 emissions is 29.0 Giga tons. Agricultural countries like Ethiopia and Bangladesh are 0.1 tCO2 per person which is about 1/200th of a North American’s. Since my target year for comparison is 1800 before the industrial revolution began we may consider this 0.1 t CO2 as a proxy for those people who were then living in balance with nature. This is using modern farmer-herders as the comparison to the farmer-herders of the year 1800. So, we take those billion people living in 1800 times their estimate of 0.1 t CO2 per capita which calculates out to be 100 million tons of CO2. That appears to be the quantity of CO2 that the Earth can recycle and permanently sustain in an ecological balance. Fifty years later, after the year 1850, the earth can’t keep up with recycling the CO2 and it begins to accumulate in the atmosphere and ocean.

Now the painful part—how many modern people can be sustained in CO2 balance on a modern Frenchman’s life style? Earth’s sustainable 100 million tons of CO2 divided by 6 tons CO2 per person (the French average) gives only 16+  million people on tomorrow’s Earth living at the level of a modern Frenchmen. And remember the French are among the least consumptive of the modern high tech societies. But there could only be 5 million Americans. That is the population of the state of Colorado. That sounds bad, but then the anthropologists tell us that 70 thousand years ago human population was only one one-thousandth of that small number, at a mere 5,000 people.

When I started this calculation it seemed reasonable there would have to be some decrease in population and some pullback in consumption but I had no idea it would be this drastic. I hope I am wrong! Probably the farmers back in 1800 were putting out a lot more pollution than modern day Bangladesh farmers. Would some one with more access to good data and more mathematical skills than I possess please correct this terrible conclusion?! I just checked current the US Census bureau’s world population clock at 6.786 Billion people. If the above calculations are correct, and I hope they are not, then 6.770 of the 6.786 are excess population which the Earth can not sustain. The sad conclusion is that 399 our of every 400 people are going go. Sooner of later Mother Nature is going to say “You will reduce your numbers!” and she speaks with authority. I am only speculating.

This was posted on February—14 Happy Valentines Day !

2009/01/29 See also: What will be the Earth’s maximum population? lists 300 years of prominent speculations of that number.