In simple terms of physical space, there is room for hundreds of billions of people to have generous housing - 400 square feet of indoor living space (e.g., 1600 square feet for a family of four), with running water, electricity, HVAC, telephone, radio, internet, and television. There is no shortage of space.
But living space is merely one variable. What about clean water, clean air, food, and energy?
Warren Weaver earned his Ph.D. at the University of Wisconsin, and taught at Caltech (The California Institute of Technology) before working at the Sloan-Kettering institute. He analyzed food production in terms of energy: sunlight is energy which plants store by means of photosynthesis.
The effectiveness of agriculture can be measured by the efficiency with which sunlight’s energy is converted into, and stored as, chemical energy in plants.
Calculating what the carrying capacity of America might be, Weaver, in the words of author Charles Mann, suggested
that in terms of energy, the theoretical carrying capacity of the United States was about 80 billion people.
Weaver was one of the first to apply advanced mathematics, physics, and chemistry to the question of Earth’s carrying capacity. Charles Mann continues:
Think in these terms was clarifying, Weaver thought. It showed that viewing the human dilemma in terms of an ecological carrying capacity was a mistake. The planet’s actual, physical carrying capacity was so large - scores of billions of people - as to be irrelevant. The true problem was not that humankind risked surpassing natural limits, but that our species didn’t know how to tap more than a fraction of the energy provided by nature.
Weaver calculated that even modest progress in agricultural productivity would yield enormous advancements. Baseline farming practices convert energy at a microscopic efficiency of 0.00025%, but
if we had a more efficient way of turning solar energy into food - and let us now say to be more reasonable, a way that had efficiency of only 1 percent - then an area the size of 1/100 the state of Texas would produce food enough to give 3,000 calories per day to a world population 50 or 60 times the present one.
As generous as Weaver’s estimates are, the planet’s carrying capacity is, in fact, many times greater than he suspected. To his numbers can be added, e.g., the farming of the seas (kelp), which would feed billions more.
Turning from food to water, it is clear that the planet Earth contains immeasurably more water than any conceivable human population might need. The trick is, however, to provide water which is both clean and desalinated.
The majority of the planet’s water is saltwater, and the majority of the needed freshwater is not for drinking, but rather for agriculture.
Water use can be analyzed from a variety of perspectives: sea farming doesn’t require desalinated water; industrial large-scale desalination processes have been refined to point at which they can provide huge amounts of water.
It is quite reasonable to estimate that we can provide sufficient energy while retaining or even improving air quality. In the United States, for example, air quality was at its worst in the late 1960s and early 1970s, and it has been getting better ever since. During this same time, the U.S. has increased its energy production and energy consumption.
Clean air and plentiful energy are not mutually exclusive.
Reports generated by the Food and Agriculture Organization of the United Nations confirm that, relative to the planet’s population, the world has a food surplus.
Starvation and malnutrition, wherever they occur, are the results of mismanagement, corruption, and bad distribution practices.
So what is the Earth’s carrying capacity? A definitive answer eludes researchers, but a generally acceptable number would be significantly greater than 100 billion.
