(Clicking any of the underlined text in blue will take you to a reference on it.)
Let’s take a road trip and observe world population levels from the invention of agriculture about 12,000 years ago to Earth as an imagined “Biosphere 3″ in the year 2224.
There were about one million homo sapiens in the whole world at the dawn of agriculture 12,000 years ago. All were hunter-gatherers dependent for their livelihoods on whatever the land offered them in their time and place. Human intelligence had made a few dents in natural systems, such as by using fire to clear forests so it was easier to hunt and by using social organization and stone weapons to drive a few large, slow-moving species like the mammoths into extinction, but “Biosphere 1″ was largely unmarked by its million human occupants.
Agriculture changed all that as people started planting crops, domesticating animals, creating villages and cities and using more and more of the Earth’s produce for themselves. By 1800, early in the Industrial Revolution, world population had increased to about one billion and had reshaped landscapes on much of the planet. Technology and bending natural systems to civilization’s needs has continued to grow since then at accelerating speeds, and there are now about seven billion people on Earth.
Wikipedia has useful definitions of “Sustainability,” “Overpopulation,” “Ecosystems Services,” “Carrying Capacity,” and “Ecological Footprint,” and the bottom line is that the total impact of our seven billion is well beyond the existing “carrying capacity” of the Earth. We are eating the “seed corn,” consuming more than is sustainable under our present technology. But let us imagine a distant future in which Earth’s carrying capacity has increased exponentially: human imagination, diligence and advanced technology have covered the Earth totally in a two-mile-high, metal-shelled building over the entire planet, oceans and all. The atmosphere has been sucked within that shell, and the shell admits the sun’s energy as necessary to provide for human needs. Problems like Earth’s moving tectonic plates with their volcanos and earthquakes have been solved, and the people living in their two-mile-high, spherical apartment building number in the trillions rather than our present billions. All Earth’s life forms are harnessed to provide for human needs; it is truly a “spaceship Earth.”
Even with wonderful technological innovations beyond our dreams, such a spaceship Earth is probably impossible so long as humans are flesh and blood. Each of our bodies contain some 100 trillion bacteria of hundreds of types, many of which are essential to human life. About 99% of the genetic information within your body is contained in the many different types of microbes that inhabit you. In addition to having lots of different flavors, microorganisms reproduce very quickly and are capable of almost infinite mutations; some kill people, as we know from countless plagues humanity has experienced in the past and current worries about bird flu, antibiototic-resistant bacteria and exotic diseases like ebola. It’s inconceivable to me that technology will tame all those little creatures, make them serve human needs only, and prevent them from rebelling against a world packed with juicy, bossy humans.
The judgment that “spaceship earth” couldn’t work is strengthened by experiences with small man-made environments in space travel and most ambitiously in the “Biosphere 2” program. In 1991, eight people were sealed within the three-acre, air-tight Biosphere 2 building in Arizona for what was supposed to be three years of living independently of Earth’s natural systems. Duplicating Biosphere 1′s life support systems ran into unexpected problems, like the oxygen in the building dropping by 50% to dangerous levels. One of the outside support team figured out that exposed concrete within Biosphere 2 reacted with carbon dioxide to form calcium carbonate, which took free, breathable oxygen out of Biosphere 2′s air, a problem no one had anticipated. Overall, self-sufficiency using man-made ecosystems was challenging, and the eight “biospherians” left early – thin, pale and very glad to be outside. The real Earth’s “ecosystem services” were too numerous and too subtle to replace.
So let’s take our journey out 212 years, the same distance we now stand from 1800 and the early Industrial Revolution. The effects of humanity’s drawing down Earth’s accumulated reserves, abusing natural systems, carelessly forcing climate and other changes, will hopefully be past, and 2224′s generations will have conformed their consumption habits to what Earth will sustainably support. Their use of advanced technology will harmonize with natural systems in recognition that Earth does not have any “extra parts” that can be degraded or destroyed with impunity. How many people will live on our dream “Biosphere 3″ in 2224? My best guess puts human population nearer 1800′s one billion than to our own seven billion. I have no prediction as to how humanity will cut its numbers by more than half within the next 200 years, but I a much-reduced human population will be essential to a healthy Biosphere 3.
Many ethnic groups of European descent have already reduced their birth rates below the 2.1 children per woman, zero-population-growth rate through contraceptives and other measures, but very high fertility in countries such as Nigeria has continued to push world population up. Wikipedia’s “World Population” article has a good summary of current trends, with brief discussion of opinions that world population will fall to two billion by 2050 because of resource scarcities. Let’s work for a softer landing, for a sustainable world population reached through group and individual decisions coming from enlightened self interest, not through systems’ collapse.