Population Growth as the Principle Resource Driver

Well yeah of course, but it's not as simple as this because the coupling of resource usage to population growth is highly nonlinear. It is precisely for these reasons that future growth scenarios are so hard to accurately predict.

This can easily be seen my comparing resource rate usage over the period 1950-2000:

1950 2000 1950-2000
50-year change
Human population (billions) 2.52 6.06 247%
Registered vehicles (millions) 70 723 1030%
Oil Consumption (million barrels per year) 3,800 27,635 727%
Natural gas consumption (trillion ft3 per year) 6.5 94.5 1454%
Coal consumption (million metric tons per year) 1,400 5,100 364%
Electricity generation capacity (million kilowatts) 154 3,240 2104%
Corn (maize) production (million metric tons per year) 131 594 453%
Wood pulp production (million metric tons per year) 12 171 1425%
Iron production (million metric tons per year) 134 580 433%

The biggest thing to note here is that electricity usage scaled as (population growth)3.5

If this trend continues, this means that a population growth of 20% would carry with it a factor of 2 increase in total electricity usage. This is what is meant by a nonlinear scaling.

Clearly, sustainability cannot be reached in any scenario where resource usage scales as (population growth)n where n > 1.

But it is precisely global economic development that drives these nonlinear scalings.

Population growth is determined entirely by average fertility rates:

Here is the situation for the US. Note that the rate has increased since the mid 80's primarily due to a significant increase in teenage pregnancy.

The current situation for the entire world:

In addition, world average life expectancy (not properly factored into any population models) is continuing to grow.

The linear trend that the data indicate (starting around 1975) is that life expectancy is increasing at the rate of 7 years every 30 years. Hence, people born in the year 2038 will have a life expectancy of, on average, 7 years higher than now.

However, advances in medicine could make this much worse: