Discussion about climate disruption and mass extinction rarely mention human population as a significant factor in exacerbating those problems.  In the last ~100 years, the human population has increased dramatically as shown in Figures 1 and 2.  The global human population, as of 2019, was 7.7 billion and climbing.  At this point, experts are estimating a global human population of ~10 billion by 2050.

Figure 1

Figure 2

Not only has the human population increased dramatically over the last 100 years but the average level of human resource consumption and pollution generation has increased dramatically over that time, particularly over the last 30 years due largely to the increased affluence of people in developing countries like China and India.

Human population and the level of resource consumption have a dramatic effect upon both mass extinction and climate disruption.  A larger human population means that more land area has to be devoted to activities such as agriculture and that land must be used more intensively.  That leaves less habitat for wild animals so their populations decrease (See Figure 3).  With a larger human population, water related resources are used more intensively leading to population declines of species in that water environment.

Figure 3

A larger and more affluent human population leads to a higher level of greenhouse gas emissions and higher level of climate disruption.  At this point, no level of technology can make the impact of population and affluence compatible with what is needed to prevent serious climate disruption consequences.

In 1970, the gloal human population was 3.7 billion people while the U.S. population was 203 million. At that time, I thought the global and U.S. populations were above sustainable levels.  The situation has only grown substantially worse.  Those figures are now (2019)  7.7 billion for the global population and 327 million for the U.S. population.

Figure 4 shows the relative impact of various efforts to reduce one’s carbon footprint.  The carbon footprint is a function of both population and affluence.

The top ways to reduce your carbon footprint

Figure 4

*Credits: (Graphic) J. You/Science; (Data) Seth Wynes and Kimberly A Nicholas, Environmental Research Letters (2017)

The human population was able to grow rapidly over the last ~100 years due to five main reasons:

1). The discovery of nitrogen fixation in the early 1900s, which led to synthetic fertilizer

2). The discovery of methods to prevent infectious diseases, which lowered death rates, particularly in children

3). The intensive use of fossil fuels

4). The development of high yielding grain seeds

5). The use of fossil water in agriculture to improve yields

We have now essentially run the course on what those five developments can produce.  We’re rapidly depleting fossil fuels and fossil water.  We’re also rapidly building up atmospheric greenhouse gases which will negatively affect agriculture.

If humans don’t desire to control human population, nature will find a way to adjust the human population to fit the available resources.