To arrive at this number, I assumed that 20 percent of the people consume 80% of the resources and 80% of the population consume the remaining 20%.

I was very optimistic and I assumed that population stopped growing, and that per capita consumption was capped at the average of the rich group.

I assumed that current human footprint was at the current global carrying capacity.

And I assumed that humankind discovered enough new oil deposits to carry us forward at present consumption levels and we learned to safely sequester CO2 that we burned.

Then I calculated, how many times over that carrying capacity will the human community be if the "have not" group rises to the per capita cap of the "haves?"

You can look this up in Time Blind-1 Chapter 6 or your can figure it out. It is a 6th grade math exercise. The answer is 4 times. Which means implementing social justice all by itself requires either 4 earths or one quarter of the present population or 1.6 billion.

Now lets take something like soil. We are using it up, washing it away, mining the minerals out of it, with agriculture at 16 times the rate they are being put back in.

If we want to be sustainable we have to live on the output of 1/16 of the land that is now under cultivation. Which means we have to have a population of 1/16. (That's 400 million not 100 million.)

Well now when you consider soil quality maintaining agriculture and social justice at the same time 1/4 of 1/16th is _________. (do the math)

That is 1/64th of the present population or 100 million. QED

Of course now that you are at 100 million people and you have social justice and you have soil sustainability, are you home free from consuming more than the carrying capacity?

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------some additional considerations to help see the actual populations the earth can support -----------

Continued improvement of well being

Now with everyone trying to improve their life style at the rate of 2.5% a year that means double their consumption every 25 years, which means doubling their wellbeing 8 times in a life time.

This means that we have to have 1 child per family RPD for as long as people want 2.5% improvement in wellbeing each year.

Other ways we will have total human footprint exceeding carrying capacity ==> a busted environment.

Exhaustible resources

The above RPD did reduce the rate of consumption of exhaustible resources. RPD did this by getting rid of 100% of the population that was consuming 20% of the fossil fuels. And getting rid of 93% of the population that was consuming 80% of these fossil fuels. This might lead one to believe that we would have 20% plus 93% of 80% or a 93% reduction in annual fossil energy consumption.

We are still consuming oil for transport at 7% of the current rate.

However if our electric power generation requirement is also 7% of current levels then no fossil fuel will be required because currently nuclear and hydro electric power produce 7.5% of our needs. Of course this is without electric cars.

With 98% of the population gone, there are lots of options with other renewable sources.

On the other hand the lower cost energy might encourage faster increases energy consumption that the present 2.5%. People might fly lear jets as their mode of transport. The 70 million drivers might all want to drive Super Hummers.

The common person and calculations

I wrote this argument in 1974. I have said it thousands of times. I have never been able to get listeners to do the math on paper or in their heads. Even getting them to calculate the "four times" part is hard. Getting them to calculate the 1/16 part is very hard. Finally getting them to compute a product of two fractions is nearly impossible for most college grads, who don't remember what they should have learned in 6th grade. Please remember that most people think they got a good education and they think they can muddle their way into the future without adding and subtracting.

The URL for this argument is (click here)