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Can humanity survive a population of over 10 billion people?

Illustration for article titled Can humanity survive a population of over 10 billion people?

By the end of this year, the human population is expected to reach seven billion people, just twelve years after we hit the six billion milestone. But how much more crowded is our planet going to get? Will we keep on expanding indefinitely, or are we approaching the upper limit? The current consensus is that we'll reach our maximum population by around 2050 and then start to slowly decline...but that might be based on two critically flawed assumptions.

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The United Nations estimates that the human population will reach nine billion people right around the year 2050. Considering how fast we went from six to seven billion people - and it also took only twelve years to get from five to six billion - it might seem strange that it could take nearly forty years to add another two billion. It's because the birth rate is actually negative in several post-industrial, generally affluent countries in southern and eastern Europe, and this trend is expected to spread outwards.

Indeed, that particular population trend is what scientists are counting on to bring the human population back down to a more sustainable figure. Once the 9 billion mark is reached, the population should max out at about 9.5 billion, and then start to decline as the countries with slowly shrinking populations are more numerous than those that are still growing. In this model, all remaining population growth is pretty much confined to Africa and South Asia.

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But what if that trend doesn't spread across the world? Then humanity might reach the eleven digits, as we could hit the 10,000,000,000 plateau by 2100. Could our planet sustain that many people over the long-term? Well, people have been predicting Earth's fatal overpopulation since the days of Thomas Malthus and our planet has scraped along all right so far, but that's hardly proof we can go on expanding indefinitely, particularly when one adds climate change into the equation.

There's another factor to consider. There's a sharp scientific divide over just how far we can push the human lifespan - some argue it's already pretty much tapped out, while others hold we could get the average life expectancy up to at least 100 by the end of the 21st century. We're hardly talking about immortality, but adding an extra twenty to thirty years of life to all the billions of people could create massive economic and sociological strains.

The current estimates are based on an eventually declining global birth rate and a relatively static life expectancy, both of which keep us beneath 10 billion. But what if both of those are wrong, and we both start living to a hundred and having lots of children? The high-end estimate says we could reach fourteen billion by the end of the century - double what we're looking at right now and almost certainly unsustainable without some massive technological and social leaps.

Now, obviously, a century is still plenty of time to find novel solutions that can sustain an unexpectedly large population. But the fact of the matter is that the best for we can do for the human quality of life and the environmental balance is to actively work to keep populations relatively low, as the Population Council's John Bongaarts explains:

"Almost all of the growth in world population will occur in poor countries, particularly in Africa and South Asia. But if we make much larger investments in family planning right now, the number of people could be closer to 8 billion. Such an investment would have a very beneficial impact on human welfare and any environmental issue we care about."

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For now, we can only guess what the future population will be and, in turn, what effect that will have on humanity and our planet. We may well be able to keep the human population to a manageable figure, but as for me...well, I think I'm going to start working on some Caves of Steel. You know, just to be on the safe side.

Via Population Council.

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DISCUSSION

This article makes two very common mistakes about global population and human longevity. First, it assumes that the number of people on the planet will continue to expand so long as conception and food supply continue unchecked. Second it makes the incorrect assumption that life span and population are somehow connected. Neither instance is true.

The critical factor in determining how many humans can be born is the length of the female viable reproductive period. As odd as it sounds, the female reproductive cycle has been extended about as far as we can expect it to go even if we allow for healthy human females living well into their 100's. If we max out a mother at an average of eight (average remember) children per lifetime then given any specific human life expectancy there is an upper limit to the number of humans who can be born. Remember that each child must wait an average of sixteen years before being able to give birth themselves and each birth has a minimum of nine months before the next conception can take place. The human birth mechanism has a built-in drag coefficient that is a powerful disincentive toward catastrophic overcrowding.

The second factor assumes that as life expectancy increases, age and viable human productivity remain the same. First and most importantly, the length of the productive human work life has not only been drastically extended (to at least 68 depending on who's numbers you trust) but this was done without appreciably extending the total human life expectancy AT ALL.

When you control for disease and nutrition, the human life expectancy has been just about 72 to 74 for nearly a thousand years. The term 'average human life span' is largely a mathematically derived estimation of how likely a non-biological event will terminate your life prematurely. In recent times (the past fifty years) the single major variable which has shifted the calculation of the human life span as been the likelihood of serving in the military and then the likelihood of dying in combat. As that number has decreased, the human life expectancy has increased. The next largest variable in the human life expectancy calculation (I believe - check me on this) is infant mortality. Controlling for those variables and you see that while man has nearly always lived to be about 72 we have in this past century made great strides toward keeping us all healthy and productive all the way up to our last decade.

In the instance where an increase in the human lifespan to 100 years would allow humans to keep producing right up to their 85th birthday might have a positive effect on personal wealth and overall output of food and resources depending on economical conditions. The point is that without the context of what a human can DO for 100 years, the life expectancy is utterly irrelevant. Keep in mind that it is exceedingly likely that the female reproductive potential will remain very nearly thirty years no matter what her productive life expectancy as a member of society. We could very easily find ourselves in a situation where we live longer and longer but have fewer and fewer children.

My point is this. We too often look at life expectancy and birth rate as THE variables in determining how many of us will occupy the planet and how rapidly we will expand our numbers. The fact is that the process of human reproduction is slow and to a great degree self limiting even controlling for all other societal and environmental factors. Unless overpopulation is something that our governments actively pursue, controlling the number births in any nation is not among that nation's most difficult social programs. So far, the second half of the Twentieth Century has shown that population is in fact self limiting so long as the citizens of a given nation are provided the means do so themselves. In as much as a third of Earth's population does not find itself in this happy circumstance, I submit there is still cause for concern. But I still chaff at the notion that population is a force that runs rampant over all barriers and across all surfaces unless radical means are employed to keep it in check (not BTW a notion found in the article above). Thus far, this idea is not supported by the circumstances in which we currently find ourselves.

I freely admit that my opinion is not shared by all scholars on the subject. But most have already pulled back from the 20 billion human hypotheses. And as one who has lived through two 'population bomb' scenarios already, I'm feeling more and more confident that the above scenario is more or less the truth.