Both Elon Musk and Jeff Bezos say that the human population needs to be greatly increased. Their argument summarized is that "If we had a trillion people we would have a thousand Mozarts at any one time."
Apart from the implied assumption that a decent quality of life could be maintained in a world with one hundred times as many people as exist on Earth today, the claim is startling in its assumption that such a massive increase in population density is even feasible. But remarkably, as I show here, it probably is.
The Earth's surface area is five hundred million square kilometers. Of that, dry land accounts for only one third, or one hundred and sixty-six million square kilometers. Of that total land area, only about two-thirds, or about 11 billion hectares, might ever be considered habitable.
An increase in global population from the current seven billion persons to one trillion would mean a reduction in habitable land per person from 17,000 square meters to just 110 square meters, or less than half the size of a tennis court. A bit crowded that at about twice the density of present-day Greater London, although still three times as spacious as Manhattan Island.
Which raises the question, where would food be grown. Well, consider Manhattan, all residents could be accomodated in a total of 444 100-storey tower apartments with an average of 36 residents per floor. Occupying just 5% of Manhattan's total area, these buildings would leave nearly all of the Island free for agriculture and recreation.
Alternatively, the entire population of Manhattan might be accomodated in a total of just 16 one-mile-high buildings such as proposed by Frank Lloyd Wright.
So one trillion people could be accommodated on around one-third of the world's habitable land leaving the remaining two-thirds unoccupied.
But this may not be the optimal arrangement. Why live on the land at all? The oceans cover twice as much of the Earth's surface as the land. So why not create floating structures, fully engineered human habitats, where transportation, resource-use efficiency, and food production can be optimized? That would leave the World's continents free for recreation.
The oceans could be colonized by the creation of a network of "floats" arranged around "lagoons" in the shelter of which all kinds of much less massive floating structures could be safely harbored. Thus, for example, a network of hexagonal lagoons surrounded by floats 10 km long and one km wide. If each float were occupied at the density of present-day Manhattan Island, each floating cell would accomodate 1.1 million people, or about 3,666 people per square kilometer of ocean surface. At that density, one trillion people would occupy about 273 million square kilometers or about 80% of the entire ocean surface area.
Much of the ocean is not well suited to human occupation, because of low temperatures, stormy weather, etc. It would be necessary, therefore, to raise the population density to around 7,500 per square km, which is comparable to the density of today's Greater London. This could be achieved by covering around 5% of the area of each lagoon with houseboats. The rest of the lagoon would be available for floating factories, farms, and solar panels.
Energy
Current global energy consumption is around 2.5 kW per person. At that rate the Trillion Person World (TPW) would require 2,300 TW of power, or about 154 times as much as currently produced worldwide. Oil reserves are about to run out. Gas and coal reserves, though much greater than those of oil, would not last until the transition to a TPW. Nuclear fusion might provide energy for a TPW, but solar power will be adequate.
The Earth's receives a year-round-average of around 0.25 KW of solar radiation per square meter. The total solar energy imput to earth is, therefore, 1.25 ✕ 108 TW, or just over eight thousand times current energy consumption and 50 times the anticipated requirement of the TPW. Thus, assuming advanced solar cells with an energy conversion efficiency of 50%, the entire energy requirement of the TPW could be met with solar cells covering about 2% of the Earth's surface.
Food
Human food requirements vary with body weight, age, and activity. For an entire population, I will assume an average consumption of 2400 Calories oer day, which is equal to 2.79KWh per day, or as a rate, 0.116KW.
All human food is, directly or indirectly, of plant origin and therefore its energy content derives from the conversion of solar radiation. Plants vary in the efficiency with which they convert solar radiation into the chemical energy of biomass. The highest conversion efficiency under ideal conditions is around 7%, although for field-grown plants year-round efficiencies are lower: probably around 2%. However, only about half of crop biomass comprises edible matter. Therefore, humans derive energy fromn sunlight falling on cultivated crops with an overall efficiency of about 1%.
To derive 0.116 KW of energy from sunlight by way of a vegetarian diet, each human thus requires a year-round mean solar energy flux of about 11 KW, which equals the sunlight falling on approximately 40 square meters of the Earth's surface in the temperate and tropical zones.
Today, arable crop lands comprise around 11% of earth's land area, or just under 16 million square kilometers. That is only 39% of the area needed to feed one trillion people with a vegetarian diet. However, the land area devoted to arable crops is a function of demand. If food demand increases, so also will the area of land developed for crop production. Urban expansion at the expense of crop land may be reversed. Lower grades of land will be converted to arable production. Mountain sides may be terraced, deserts irrigated, swamps drained, forests cleared. A 150% increase in the proportion of the Earth's land area devoted to crop production, from 10% to 25% of total area, is thus quite feasible given sufficient time and capital.
Theoretically, therefore, a population of one trillion could be fed, barely, by extension of conventional field crop production. However, food production need not be limited to the land, and if most of the population is located on the ocean, food production will likely also take place there.
Populations living on floats surrounding a network of oceanic lagoons, would grow food crops within the shelter of the lagoons on low-cost floating structures. Most crops would likely be protected by greenhouses, which by optimizing climatic conditions, achieve the most efficient use of solar radiation. With only modest advances in crop plant genetics, and crop management techniques, one could expect light utiliztion efficiency of three to four percent, meaning that a minimal diet for one trillion people could be produced with a growing space of about 11 million square kilometers. That is about 8% of the ocean surface covered by the proposed network of lagoons, or an average of about 2,000 hectares (4,500 acres) per lagoon.
An implication of the foregoing calculations is that global food production could be increased to support a population of two, four, or even eight trillion. Beyond that point food production would be limited by the solar radiation interecepted by the Earth: a limit that could be exceeded only by the adoption of a radical new energy source for food production.
Water
For a population living near the ocean, water supply is not a significant problem as sea water desalination by reverse osmosis is cheap, around $0.60 per cubic meter, or six one hundredths of a cent per liter. This is much less than the cost of desalinated water on land because it avoids the energy cost of pumping desalinated water up hill, which over a significant elevation greatly exceeds the cost of desalination.
In a totally engineered floating habitat, the cost of fresh water should be well below that of desalinated sea water, as sanitary, industrial and agricultural sources of waste water, plus rainwater would would flow into separate sewer systems each to be purified in the most efficient way, with the recoverty of useful constituents, including metal ions, and plant nutrients.
Other Resources
The main resources required in the construction of a floating habitat are abundant: these include limestone from which to manufacture cement, and sand from which the concrete floats would be built. Use of aerated concrete would reduce the quantity of concrete used and make all floating structures unsinkable, even if flooded.
The demand for other resources, in particular metals and feedstocks for plastics and organic chemicals would be enormous compared with the present day. However, structures and processes would be designed to minimize the requirement for limiting resources. Plastics made from plant matter such as cellulose and starch would likely be used widely, as would abundant metals such as aluminum and iron, the third and fourth most abundant elements in the Earth's crust.
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