World Population is Stabilizing

You may be surprised to learn that the average human lifespan across the planet is now over 60 years.   When did that happen?  It has been happening all along, gradually increasing with each new increase in health care and food production.  And the average life expectancy increased dramatically as we radically reduced the number of deaths in early childhood.

But another surprising consequence of reducing childhood mortality is that people are having fewer children.  Makes sense when you think about it, but we do it without thinking about it.  At this time,  most of the world has families with about 2 to 3 children.

Please watch this great video: Hans Rosling: no more boring data.

The Myth of the Population Explosion

So the primary myth I would like to explode is that, because the world population is growing exponentially, it will soon explode if we do nothing to stop it.  I must admit I believed in this myth also until I learned the facts.   Where did this myth come from?  If you look at a plot over many thousands of years, averaging over hundreds of years, the exponential J-curve in the human population is apparent, as shown in the following graph:

But if you only do that, you would be missing what has been happening starting around 1960.   Look at the following chart which is a closeup of the period from 1750 up until 2010, and then projected to 2100.  You can see that the curve of the population graph changed direction around 1980.  Rather than going up faster and faster, the total world population is no longer accelerating, but it is now decelerating, slowing down.

While the growth rate has slowed, the population is still increasing, though at a slower rate than it would have been, and at our current rate, the population will peak at about 11 billion, in this projection. At least it is no longer exploding as it had been, and it is on a path toward stability.

By the way, many graphs labeled “world population growth” are really showing just total population, and you have to guess how it is growing by looking at the curve and how the curve is changing.  The chart above includes a growth rate curve, but below are a couple more charts that show more detail in the range 1950-2050.

Here is a graph that shows the change in the world population from year to year, rather than the total population.   You can see how the change has been declining from the high in 1990 of almost 90 million increase per year down to a projected 40 million in 2050, and it looks like it would not reach 0 for another 60 years.

The next graph shows the growth rate, which is the ratio of the change and the total population in each year.

Notice that in 1970, the growth rate was about 2% and the population increased by about 75 million people in that year, while in 2000, the growth rate was down to 1.25%, but the population again increased by 75 million.    The explanation is that it is a smaller percentage of a larger population that works out to about the same amount.  So you can see that even after the growth rate starts declining, the change in population lags behind by at least 30 years.

What is slowing the growth?

To understand why the population growth is slowing, we have to understand why it changes at all. The change in population is the same as the number of births minus the number of deaths in each year. While the number of deaths is related to health, and we all want to increase health as much as possible, the number of births is more complicated.

Hans Rosling argues in another excellent video What stops population growth? from Gapminder Foundation: “The only way to stop population growth is to have small families.”    That makes sense, but why are we having smaller families already?   And why are many poor people  still having larger families?

“One fact about the world is very clear, and that fact is that the world population is growing.”   “We have to plan for being at least 9 billion by 2050, but that is the point where the population of the world may level off.”

Students are thinking “Population growth destroys the environment, so poor children may as well die.”  Hans replies, “The problem with that thinking, with this thought, it’s not that it is not moral, it’s that it’s wrong.”

“So this worry you don’t have to have, that poor children should die.  It’s like this instead: so poor children must not die” because then eventually families can be smaller.

But why is the population still growing?

Why is the population still growing even while we are putting on the brakes?  Two reasons.    First, there is a typical pattern, called the Demographic Transition, which is caused by a lag between the reduction in the death rate and a later reduction in birth rate. This is shown in the following graph:

Even though the death rate (the blue line) starts to decline, we tend to keep our cultural
habits about how many babies we expect to have because of how many children tend to survive. It takes a while to change such habits before the birth rate (the green line) starts to decline to match the death rate.  As a result, during that delay, we typically see a “natural increase” in population.  Eventually, the increased competition for resources due to a higher population density will encourage smaller families.  We have seen this same transition pattern in many local populations around the world.

It is conceivable that we could reduce this lag more quickly by education, by making the connection more obvious between the declining death rate and the subsequent need to reduce the birth rate.

But even if we somehow make a rapid transition to only having two children per family (which would mean zero growth, after stabilization) there is a second reason the population will continue to increase after a decrease in childhood death rate.  The reason is that there will be a bubble of a larger number of surviving children who will grow up and have children themselves.  This lag takes a whole generation or more to stabilize.  These two reasons are connected, however, because if the lag in the birth rate decline can be shortened, there will not be as much of an increase in surviving children to create this later bubble.

Jane Goodall has the right message here about how a little family planning can go a long way toward improving the lives of those in the developing world:

Another way in which the death rate is decreased is by lengthening lives.  Again, the resulting increase in population density should indirectly affect the number of children that people will tend to have.

Human Populations Stabilize Naturally

But lets look again more closely at the plot of historical population growth above.  Also look at the following two plots (from Population Ecology).   Notice that for several thousand years starting around 10,000 years ago (8000 BC), we had a relatively stable population of about 100-200 million.  These are necessarily rough estimates, of course, but close enough for our purposes here.

Why is there a long plateau for about 9000 years, and what happened each time the population started growing, before that time and after?

First, take note of the fact that we have reached stable population levels in the past.    We didn’t dramatically overshoot the carrying capacity of our environment given the level of technology we had at the time, certainly not anything like 10 times the carrying capacity that some people imagine.  As we approach the maximum carrying capacity, growth generally slows with the increased strain on the available resources.  ALL life tends to do this, not just human beings.  Life grows to fill any available niche, and we are no exception.   But life does not typically overshoot carrying capacity by a large amount because that would usually be followed by a catastrophic decline and ecological chaos, thus risking extinction, and an extinct species doesn’t survive to repeat the experiment.  One way life tends to moderate the extremes is by developing rich complex ecosystems with many species that balance each other out.

Second, if you look at when these population increases occurred in the past, and remember a little history, you’ll note that it was technology advances that preceded and allowed the population to increase because it was easier to support more people.   The agricultural revolution allowed people to harness the power of animals to help us grow more food and to build stable small communities.  The industrial revolution allowed us to use machines, powered by fossil fuels, to do much more, and support much larger and denser communities.

So it is very important to realize that it is an illusion to imagine that the world population has increased exponentially regardless of what our technology and the environment could support.   The advances in technology have allowed the population to increase, and while the population did increase at exponential rates, ignoring the intervening plateaus, this is because our technology has been advancing exponentially as well, thus allowing the population to increase.

Exponential Technology Growth Allowed Population Growth

Now we are on the cusp of a new revolution, the information revolution, where our exponentially increasing knowledge of how to manipulate the world is allowing us to exploit our resources even more effectively.  It may be that the information revolution will allow our population to continue growing to a much higher level, but it won’t happen just because we are growing exponentially, and many other changes must occur as well to continue to support a larger population.

Ray Kurzweil on how technology will transform us makes it clear that our information technology is racing ahead at an exponential rate.

If we are wise enough, we will learn that we must find ways to live sustainably, using clean renewable resources rather than dirty non-renewable resources that would quickly challenge our ability to survive.  Indeed, the impact of humans is now global, as never before, and what we do makes a huge difference to all life on Earth.

The video “Alex Steffen sees a sustainable future” (from Worldchanging.com) argues that reducing humanity’s ecological footprint is incredibly vital now, as the western consumer lifestyle spreads to less developed parts of the world.

The increasing costs of non-renewable resources, together with an increasing intolerance to the toxic side-effects of pollution will most likely force this realization of sustainability upon us eventually.    But if we hide the true costs of resources, and push the pollution problems off on someone less fortunate than ourselves, this short-term gain will only create a longer-term worse problem, and we don’t have much time.  If we continue on in the same direction we are now headed, we could find ourselves in a simultaneous global collapse of our socioeconomic system and the ecosystem.  The question is whether we will realize what we are doing and what we need to do,  and whether we take action before it is too late.

We need to accept that, while populations will stabilize on their own, we probably should not rely on doing nothing but waiting because we will likely experience a larger overshooting of the carrying capacity that could be avoided if we make conscious efforts to encourage restraint.   We also cannot afford to do nothing at this time because of the global effects that humans are having on the world.  We may trigger massive species extinctions and ecosystem collapse – we are well on our way to doing that already.

To Infinity, And Beyond

But here is the good news.  While we are trying to merely survive, we will have to solve the problem of obtaining clean renewable energy, enough to reduce the ecological footprint of each person to zero, and once we do that, there is a huge amount of energy available to us, more than enough to clean up all the mess we have been creating.  And furthermore, the large population we currently have will no longer be a problem at all.  Most likely the population will start growing again, because it can, until we reach a higher level that approaches a much larger carrying capacity.   We will also very likely have enough energy to move out into space, no longer being dependent on the Earth.

So are we having too many children?  Ben Wattenberg says “that’s baloney”.

Notes

• • If you have a problem with any of this presentation, please let me know why.  Post a comment or email me.  If you read this carefully, you will see that I am not an overpopulation denier, nor am I an overpopulation alarmist.

References to this page (many from me)

• Matthew Walker  Claudia, it seems population is levelling out all by itself (or possibly with the help of improving adult and infant health and the availability of birth control).. (http://www.facebook.com/ScientificAmerican/posts/303839446319693)
• “7 Billion” (http://climatecrocks.com/2011/01/05/7-billion/)
• “Population and Sustainability: Can We Avoid Limiting the Number of People?” (http://es.wiser.org/article/3c8be4679863a2f0279c4e1d7b44f5c0)
• “The problem with the WWF study is it extrapolated based on current population growth rates. It fails to understand that modernized societies enter negative population growth stages. The only reason the US has a high population growth rate is because of immigration. If you look at the rate that less industrialized countries are becoming more industrialized, and adjust for that, human population will most likely stabilize at around 9 billion in 2050. (http://archive.installgentoo.net/sci/thread/1906386)
• “GLOBAL POPULATION SPEAK OUT” (http://en.wiser.org/forum/view/f88781b7f54911c57e5d69111538d784)
• “Visualizing World Population” (http://www.urgentevoke.com/profiles/blogs/visualizing-world-population)
• “Population Overload” (http://www.realitysandwich.com/population_overload) “Note that I am *not* saying that we don’t have to be concerned about population issues.  We do! But the issues are much more complex and interesting than the over-simplified extremes on both sides, so if you want to effectively address the concerns, it doesn’t help your case to be making incorrect arguments that are easily defeated.”
• “Population is no longer growing exponentially” in Population Matters “…it doesn’t help our case to be focusing on the wrong problems, on things like the population, which is not going to decrease significantly unless we are planning on genocide, and which is really only a problem because of our mismanagement of resources and enormous social-economic inequity.”  Also posted on my facebook stream, with the comment “Current American and European lifestyles suck, as I am sure you agree. So why base your argument on that? 2 billion more people living like we do would be a problem, but fortunately, those new people are being raised much closer to the land, and they are developing with renewable resources much more than we are. No sense denying that we are the problem, not them.”

Pages making similar arguments

• “World of 7 Billion: Part 1, Population Prospects” (http://knowledge.allianz.com/demographics/population_growth/?1621/UN-expert-interview-world-of-seven-billion-part-one-population-prospects)
• “World Is Less Crowded Than Expected, the U.N. Reports“, November 17, 1996|By New York Times News Service. (http://www.nytimes.com/1996/11/17/world/world-is-less-crowded-than-expected-the-un-reports.html)  ”The world’s population is stabilizing sooner than we thought,” said Joseph Chamie, director of the United Nations Population Division, which collects and analyzes population data. ”We had some glimmer that this was occurring several years ago, but we weren’t sure if it was simply a blip. Now we actually have concrete results showing this is a global trend.”
• “The Climax of Humanity” (http://www.scientificamerican.com/article.cfm?id=the-climax-of-humanity&sc=I100322) “After several centuries of faster-than-exponential growth, the world’s population is stabilizing. Judging from current trends, it will plateau at around nine billion people toward the middle of this century. … As humanity grows in size and wealth, however, it increasingly presses against the limits of the planet. Already we pump out carbon dioxide three times as fast as the oceans and land can absorb it; midcentury is when climatologists think global warming will really begin to bite.”
• “Distilled Demographics: Population Projections” (http://www.prb.org/Journalists/Webcasts/2011/distilled-demographics-population-projections.aspx) – video about how projections are made for the likely population in 2050.