Earth Population

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Earth Population and our Return to the Moon


The 21st century will be a century of problems and change. It has started with a rate of change at about five times that of the 20th century. There is every expectation that this rate will increase, not slack off.

Any program that is seen to be making a significant contribution to the solution of these major problems is likely to win support and funding. Any program that does not is likely to be terminated.

The question posed here is whether return to the Moon addresses any of the real problems of the American people. The answer arrived at is that in the long-term it does, but in the short-term it does not. The problem then is one of keeping the program viable for the long term.

World Population: A Family of Curves

The Population Bomb

The king of the problems of the 21st century is the human population of the Earth. All other problems such as global warming and energy change over are driven by stress caused by the growth of the human population.

The population of the Earth is currently about 6.6 billion people. It has been growing exponentially since the Industrial Revolution became firmly established in the early 1800’s. It cannot grow exponentially for very much longer.

The figure above shows four possible curves for the world’s population through the 21st century. Continued exponential growth is shown in red and labeled “Impossible”. Just try to imagine a world where there are 5.5 people for every person alive today. If we continue the exponential growth we have demonstrated since 1950, we would reach this level by the end of this century; the world’s resources will clearly not support this level of human population. This curve was first calculated in the 1960’s and has been called “The Population Bomb”.

The other three curves are members of a large family of curves that peak, fall some amount, and then stabilize for the long-term. These curves are generated by mathematical models featuring negative feedback in complex systems and suggest that it is possible for us, first, to control our population growth and then to achieve a sustainable level. In the hypothesized futures represented by these curves, the sooner we peak the less precipitous will be the fall and the higher the sustainable level of human population.

Any one of this family of curves is possible, though the outcomes represented by some would be much more attractive than others. The family is based upon a model of the Earth’s resources that considers some resources to be fixed, like oil, and some to be sustainable, like agricultural land.

In any future, the actions we take today will affect the curve that will actually occur. This curve is the driver for all the world’s problems. High population levels are stressing the environment and are using up energy reserves. The more severely we deplete the Earth’s resources, the lower the sustainable level will be. We must face this problem to address any of the other great problems of the 21st century.

Three Parameters

Figure 1 has three critical parameters: Peak Level, Peak Date, and Sustainable Level. All three are common in models of complex systems dominated by negative feedback and are interrelated. The later the peak date, the higher the peak level. The higher the peak level, the more stressed the resources needed by human beings and the lower the sustainable level of population.

Current United Nations world population estimates put the date of peak around 2050 and the peak level at about 9.2 billion people. This is almost three people for every two alive today. The UN does not even try to estimate the sustainable level.

The End to Growth

The real question is; what will stop the exponential growth of human population?

The most important, but rarely recognized, factor in interrupting this growth trend is the ability of nearly all mammals on Earth to limit their capability to reproduce to match the available resources. Only a few animals, like lemmings, have boom and bust cycles. A few others, like foxes and hares, exhibit predator/prey cycles. Virtually all other mammals adjust their reproduction so that they become a sustainable part of their environment.

Human beings are mammals, and we are at present doing what other mammals do. Reproductive rates are falling off in developed countries. Medical advances allow personal reproductive control. The age of new mothers is rising; women have more productive and fulfilling roles in society. Gays can achieve higher status in society. The UN numbers show that the exponential roll-off has already started.

This roll-off will undoubtedly be assisted by all four Horsemen of the Apocalypse: Pestilence, Famine, War, and Death. Pandemic diseases like AIDS and avian influenza are near certainties. The HIV virus alone dropped the UN peak estimate from 12 billion down to 9 billion. Starvation related to climate change crop failure is already present. Wars over resources like oil and water are likely to continue. Above all, the lead horseman, Death, will be omnipresent as we move from a peak around nine billion people to a sustainable level of population closer to four billion in less than 100 years.

World War I and the Spanish influenza pandemic at the start of the 20th century demonstrated both the reality of the Four Horsemen and their unanticipated limitations. Population growth recovered amazingly quickly after this major setback. The Horsemen must not and cannot be the major players in our move to sustainability. In fact, they are not even very good at playing this role.

Human genetic studies show that modern humans went go through a comparable population bottleneck about 64,000 years ago. Our numbers dropped from about ten million to around 10,000 individuals. The culprit was probably the eruption of a super volcano called Toba. What we are facing now is then a once-in-64,000-year event, one that is far rarer than anything that has ever happened in recorded history. This time we are playing the part of the volcano ourselves.

In truth, we do not know what human society will be like as we cross over the top of this curve, as we drop down the back side, or as we reach a sustainable value. One likely course is that we will keep our eyes on the prize. We will work steadfastly toward a final sustainable society through out the entire transition period. Whatever happens, to face the problem of population in the 21st century is to face reality. To ignore it is to live in a fantasy land.

Working assumptions about human population

As a working assumption for this analysis we can take the UN figures for Peak Date of 2050, and Peak Level of 9.2 billion people. The Sustainable Level is completely dependent on our current actions and is here assumed to be somewhere between two and six billion people.

What we need to understand is that we are entering a completely different world from anything that has happened in all of recorded history. We are on new ground here, and it is bound to be profoundly upsetting to the great majority of people.

No Cities in the Sky

One dream from SciFi is to move a large segment of the human population off the planet. This dream is simply not to be. For the near future, the cost of launching mass into low Earth orbit (LEO) is still too high and our experiences in building large facilities in space, like the International Space Station, show the project cost is also way too high.

Small outposts may be built, yes, but large population transfers, no: not in Earth orbit, not on the Moon, and not on Mars. The physics and economics simply do not work. Maybe some time after 2100 such cities will be built but not before that and by the time they are built society will be so different that we can hardly imagine the choices that will be open.

Also all that is necessary at any time to establish an off-world human population is a few hundred women and a frozen sperm bank. No significant fraction of Earth’s population will ever physically move off his planet. No relief from population pressure is to be found in space.

The work ahead for NASA

The Earth has seen many die backs, large and small. People understand this situation intuitively: if the Earth has a population limited by sustainable resources, then the only way to expand our horizons is to move off-planet. This has been our dream since NASA’s conception. Retaining this vision is critical to all our mental heaths in the transition to a sustainable planet.

In contrast, NASA’s work in Earth science directly addresses a large number of Earth’s problems in the 21st century. Monitoring to address global climate change is predominately a robotic remote severance activity from LEO. Alternate energy systems, such as wind and solar, require a very large amount data on local weather at every one of their distributed locations. Growing biofuels is basically farming on marginal land in a changing climate which also requires large amounts of data. All forms of alternate energy require high quality space data.

As our population moves toward stability, the American people will be very upset. One of the few sources of succor is the idea of human beings moving out into the universe. We can turn that dream into reality. This long-term need plays powerfully into NASA’s current plan for a return to the Moon and on to Mars.

Alternate Energy from Space

There are also two hard space power possibilities that directly address real 21st century problems: solar power satellites, and helium‑3 from the Moon.

Solar Power Satellites

Solar power satellites are large structures built in space that collect solar power and beam it back to Earth by microwave. They need to be in Geocentric Orbit (Geo) to provide uninterruptible power. The idea is attractive and is supported by a major new Department of Defense (DOD) study.

Unfortunately, solar power satellites are a very long shot. First, they require low-cost launch of mass to Low Earth Orbit (LEO), which has not been achieved and is not expected to be developed any time soon. Second, they require large constructions in space, which our experience with the International Space Station (ISS) demonstrated is difficult and very expensive. Third, there are environmental concerns about the microwave links.

Helium-3 from the Moon

The near-term progress of nuclear power generation is expected to produce another generation of fission reactors and then the move to fusion reactors. These would fuse two low-mass atoms instead of breaking apart one high-mass atom.

There is an abundance of deuterium, or hydrogen-2, in the ocean that could be used for fusion fuel. Its problem is that its reaction gives off large quantities of hard radiation. There is, however, a way out. The lunar regolith contains attractive qualities of helium‑3 which, in theory, will fuse producing power accompanied by several orders of magnitude less radiation.

The plan for helium-3 from the Moon has two long shots stacked one on top of the other. First, fusion reactors must be developed to the point of being commercially workable. This is technically very difficult and progress has been slow, despite major efforts in several countries. Second, it must be demonstrated that large commercial operations on the Moon are possible. Thousands of tons of regolith have to be processed to produce commercial amounts of helium-3.

Even with these problems, helium-3 from the Moon is the strongest commercial possibility that can be expected to come from NASA's current plan to return to the Moon.

Our Return to the Moon is at risk

NASA’s current plan to return to the Moon is in serious danger of meeting the same fate as our 1989 attempt. It simply does not address the short-term problems of the 21st century while programs that do, like Earth science, are likely to receive more of the limited available funding.

In the long-term, returning to the Moon does meet our needs for vision and possibly for energy. Losing it now will cost us our uninterrupted experience of manned space exploration. If that happened, then when we do need manned space technology again we would have to reinvent the entire technology from the ground up.

Action is needed now to save this mission.

See Also


[1]United Nations World Population Estimates


D. H. Meadows, Jorgen Randers, Dennis L. Meadows, Limits to Growth (Earthscan, 2004 edition)