The Real Population Problem

[An expanded treatment of some of this material appears in Chapter 3 of the Energy and Human Ambitions on a Finite Planet (free) textbook.]

Sometimes considered a taboo subject, the issue of population runs as an undercurrent in virtually all discussions of modern challenges. Naturally, resource use, environmental pressures, climate change, food and water supply, and the health of the world’s fish and wildlife populations would all be non-issues if Earth enjoyed a human population of 100 million or less.

The subject is taboo for a few reasons. The suggestion that a smaller number would be nice begs the question of who we should eliminate, and who gets to decide such things. Also, the vast majority of people bring children into the world, and perhaps feel a personal sting when it is implied that such actions are part of the problem. I myself come from a long line of breeders, and perhaps you do too.

Recently, participating in a panel discussion in front of a room full of physics educators, I made the simple statement that “surplus energy grows babies.” This is motivated by my recognition that population growth bent upwards when widespread use of coal ushered in the Industrial Revolution and bent again when fossil fuels entered global agriculture in a big way during the Green Revolution. These are really just facets of the broader Fossil Fuel Revolution. I was challenged by a member of the audience with the glaringly obvious statement that population growth rates subside in energy-rich nations—the so-called demographic transition. How do these sentiments square against one another?

So in the spirit of looking at the numbers, let’s explore in particular various connections between population and energy. In the process I will expose the United States, rather than Africa, for instance, as the real problem when it comes to population growth.

A Brief Look at Population History

For many thousands of years following the end of the last Ice Age, human population rose steadily and slowly, at a rate of about 0.032% per year—translating into a leisurely doubling time of some 2000 years. About 3000 years ago, spreading agricultural practices led to a modest boost in growth rates. But the wild ride did not start in earnest until modern times.


Lograithmic plot of historical world population, with two-segment exponential fit.  Data from Wikipedia.

Even on a logarithmic plot—on which exponentials are tamed into straight lines—our population trend resembles the infamous “hockey stick” curve seen in so many domains (atmospheric CO2, global surface temperature, and practically any measure associated with human activity). A logarithmic hockey stick is truly scary. Because human impacts on the planet scale with population, it is not terribly surprising that a hockey-stick population curve should translate into hockey sticks everywhere. It is in this sense that population underlies nearly every issue and challenge of our times.

But what can we understand about population? What governs its rate? What accounts for the discontinuity in slope? Why did we leap into 1% growth and a 70 year doubling time in recent centuries?

One hint comes from a closer look at the recent history. Plotting global population in the last thousand years (below), we see a few breaks in the slope. For most of this period, we saw a modest 0.12% growth rate, amounting to a 600 year doubling time. Around 1700, the rate stepped up to 0.41%, doubling every 170 years. The next break happens around 1870, jumping to 0.82% and 85 years to double. Then around 1950, we see another factor-of-two rate jump to 1.7% and an impressively short 40 year doubling time.

Logarithmic plot of recent world population trend, broken into four exponential segments.

Logarithmic plot of recent world population trend, broken into four exponential segments.

We can perhaps attribute the 1700 jump to the Renaissance and scientific progress. We learned to wash our hands after wrestling with our pigs, and that diseases were not caused by bad vapors conjured by impure thoughts. The jump around 1870 corresponds to the Industrial Revolution, in which coal transformed the production of steel (providing agricultural tools), rail transport of commodities, and began to mechanize agriculture in a limited way. 1950 marks the Green Revolution: full-scale petrolification of agriculture, accompanied by massive fertilizer campaigns using natural gas as the chemical feedstock.

This leads to a rather simple thesis: the surplus energy presented to us by fossil fuels allowed us to feed people more easily the world over. The bounty of fossil-fuel-turned-food encouraged an explosion in birth rates, as happens for virtually all organisms given similar circumstances. It’s so blindingly obvious that I am embarrassed to have belabored the point as long as I have.

Does Energy Grow Babies?

Surplus energy grows babies. That was my statement to the audience, based on the dots I connected above. So what about the astute comment that countries with the largest excesses display the weakest—and even negative—population growth rates? This statement also rings true, so how can we hold both thoughts in the head?

Before digging into data, I’ll share my intuitive response. Developing countries are recipients of food, medicine, and manufactured goods from the industrial nations of the world. Surplus energy “here” can grow babies “there.” Such redistribution seems plausible, in any case.  But why energy rich nations slow down was less obvious to me, aside from increased education and greater autonomy of women.

Dump Truck of Data

Clear some space, because I’m about to back up a truck full of data and dump it on your lap. Mostly, it comes from the International Energy Agency’s Key World Energy Statistics, 2012. Ten pages in this publication contain tabular data on the world’s energy appetite, along with population, GDP, and CO2 emissions. A little cut-and-paste, editor magic, and Python parsing can turn this into a truckload of graphs. I added data on population growth rates, mostly from the CIA statistics. Spooky, yes, but these were the most up-to-date numbers on the Wikipedia page.

The IEA table includes 139 countries, but also aggregates several key groupings of countries in the world. Besides giving figures for the whole world, the seven groupings include:

  • OECD (the Organization for Economic Cooperation and Development) includes the countries: Australia, Austria, Belgium, Canada, Chile, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Israel, Italy, Japan, Korea, Luxembourg, Mexico, the Netherlands, New Zealand, Norway, Poland, Portugal,the Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey, the United Kingdom and the United States.
  • The Middle East includes: Bahrain, Islamic Republic of Iran, Iraq, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, Syrian Arab Republic, United Arab Emirates and Yemen.
  • Non-OECD Europe and Eurasia includes: Albania, Armenia, Azerbaijan, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Cyprus, Georgia, Gibraltar, Kazakhstan, Kosovo, Kyrgyzstan, Latvia, Lithuania, the Former Yugoslav Republic of Macedonia, Malta, Republic of Moldova, Montenegro, Romania, Russian Federation, Serbia, Tajikistan, Turkmenistan, Ukraine and Uzbekistan.
  • China includes mainland China and Hong Kong.
  • Asia includes: Bangladesh, Brunei Darussalam, Cambodia, Chinese Taipei, India, Indonesia, Democratic People’s Republic of Korea, Malaysia, Mongolia, Myanmar, Nepal, Pakistan, Philippines, Singapore, Sri Lanka, Thailand, Vietnam and Other Asia.
  • Non-OECD Americas captures: Argentina, Bolivia, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, Jamaica, Netherlands Antilles, Nicaragua, Panama, Paraguay, Peru, Trinidad and Tobago, Uruguay, Venezuela and Other Non-OECD Americas.
  • Africa membership is self-evident.

Graph legends, in order to remain compact, leave off some of the qualifiers in the above list. Also, peripheral dots for individual countries are labeled in the graphs by an automated process. I did not make special effort to clean up unfortunate collisions between labels. I should also preface with a statement that the whole set of graphs to follow are not necessarily central to my main point. But I imagine they will be as interesting to many of you as they were to me, so why not make it an extravaganza?

Let’s start with a look at a familiar plot of energy as a function of income (click to expand).

Rate of energy usage as a function of income for the world's countries.  Data from the IEA 2012 report.

Rate of energy usage as a function of income for the world’s countries. Data from the IEA 2012 report.

I am using the purchasing power parity (PPP) flavor of GDP (gross domestic product), intended to put everyone on the same footing for meaningful income comparisons. I have converted the yearly per-capita energy into a power (Watts)—because that’s my favorite unit, and it gets away from “tons of oil equivalent,” as the original data are expressed. The trend is not at all surprising here: inhabitants of wealthy countries enjoy a greater rate of energy use, on average. Outliers are always interesting and instructive. The U.S. (always represented by a red dot on these plots) pushes well out from the pack in both dimensions, but not in an extreme way—ranking twelfth in total power per person and eighth in wealth. Some may recall from earlier posts the rule-of-thumb that Americans each run about 10 kW of power, equivalent to roughly 100 metabolic human (slave) equivalents.

Rate of delivered electricity as a function of income for the countries of the world.

Rate of delivered electricity as a function of income for the countries of the world.

Since it’s in the table, let’s look at what happens if we restrict our attention to energy in the form of electricity. Iceland was so outrageously high (about double the runner-up Norway) that I had to rescale the plot and indicate Iceland’s stratospheric datapoint. The U.S. ranks ninth in per-capita electricity usage. Note that the statistic is for delivered electrical power. The primary energy required to generate and deliver the electricity might run up to three times higher than the delivered rate, owing to typical 30–40% conversion efficiencies in power plants. For the U.S., electricity accounts for about 40% of primary energy, not 15% as a direct comparison of the previous two graphs might imply.

Before we circle back to population statistics, let’s take a look at how CO2 emissions stack up among the nations of the world.

Per capita CO2 production as a function of energy usage rate for the countries of the world.

Per capita CO2 production as a function of energy usage rate for the countries of the world.

Most fundamental is the carbon intensity of energy production. Basic chemistry suggests that each gram of fossil fuel creates three grams of CO2 and delivers about 10 kcal, or 41840 J of energy. Running 10000 W for a year (3.155×107 seconds) should therefore require 7.5 tons of fossil fuel, generating about 22 t of CO2. The graph above shows the typical U.S. citizen coming in at about 17.5 t of CO2 per year. This is short of our crude estimate because nuclear, hydroelectric, biomass, and other renewables account for almost 20% of the total energy, incurring effectively no carbon penalty (also, the U.S. comes in a little shy of 10 kW). Countries below the principal trend line have lower carbon intensities than the U.S. (1.82 t/yr per 1 kW of energy rate). Iceland is notable, getting abundant electrical power from geothermal sources.

CO2 production as a function of income for the countries of the world.

CO2 production as a function of income for the countries of the world.

Now we pull income back into the mix to see how CO2 emission correlates to wealth. European OECD countries tend to appear on the “good” side of the correlation, while the Middle East tends to perform poorly by this measure.

Population Preview

Looking at the above graphs, we can learn something important about adding people to the planet. Adding a person in Africa has very little impact on energy use and (therefore) CO2 emissions compared to adding a person to the U.S., by a factor of 20. Picture an American baby 20 times bigger than an African baby. A Quatari towers 45 times higher than a typical African citizen when it comes to CO2. If one is inclined to think about where to limit population growth, the countries high on these graphs have their necks sticking out. Just sayin’.

Population Growth Correlations

So far, we’ve only looked at metrics present in the IEA Key World Energy Statistics publication. Now let’s add population growth rate and see how things stack up.

Growth rates as a function of income.

Population growth rates as a function of income.

First is the growth rate against average income. We have a clear correlation at the left edge: poorer countries have high growth rates, but rapidly dive to lower—and even negative—rates by about the time average earnings reach a quarter of those in the U.S. Then a funny thing happens: the cluster turns up again! This narrative-busting truth made me sit up straight, I’ll tell you. I fully expected a more-or-less smooth and gradual transition: rich means fewer offspring, according to the demographic transition idea. Granted, immigration plays a role here. It certainly is responsible for growth in the U.S. population. But it would be hard to convince me that the wholly lopsided statistics at higher incomes are all about immigration. Where are the rich nations with negative growth? After Germany, the negative growth countries are not to be found. Note that peeking out from behind the legend is Quatar, standing in open defiance of the “wealth reduces growth” mantra—boasting superlatives in both growth and income simultaneously.

Maybe this shouldn’t be too surprising from the perspective that economic powerhouses are dependent on growth, and a flagging population is a recipe for recession. A key ingredient for guaranteeing a bigger future is more working young people: in addition to providing labor, the growing youth enables pension systems and health insurance to function. Indeed, Germany is trying to battle its population decline, which imperils economic competitiveness. When I saw this article in the NYT, I lamented that the policy of protecting economic growth enslaves us to produce more children. I would rather humankind be the master of the economy, rather than the other way around. A quote from the article:

There is perhaps nowhere better than the German countryside to see the dawning impact of Europe’s plunge in fertility rates over the decades, a problem that has frightening implications for the economy and the psyche of the Continent.

How about the energy correlation, which I find more intrinsically interesting?

Population growth rates as a function of the rate of primary energy use.

Population growth rates as a function of the rate of primary energy use.

Naturally, the existing correlation between energy and income sets us up to see a similar pattern emerge. And indeed we again see the fertility trough appear at modest energy rates. Aside from Trinidad and Tobago, no country with an energy usage rate higher than 7 kW cares to join the negative-growth club. If anything, I find this graph more compelling than the previous one: the U-shaped sweep is more apparent. Again, it is difficult to argue that increased availability of energy dials down the baby spigot.

And finally comes a plot that I found to be rather striking. The IEA statistics include measures of total energy production, consumption, and net imports/exports. So I looked at growth rate as a function of the fraction of a nation’s energy consumption that it produces.

Population growth rates as a function of fractional energy produced by the country or region. Energy exporters are to the right of the vertical line.

Population growth rates as a function of fractional energy produced by the country or region. Energy exporters are to the right of the vertical line.

I had to put the horizontal axis on a logarithmic scale to spread the points out reasonably. Many countries are cut off on the left-hand side (less than one-tenth of their energy consumption is domestically produced), but all net energy exporters are represented. We see that countries with surplus energy (the exporters) tend to be growers of population as well. To the left of the parity line (100 = 1 means balanced production and consumption), countries are far more likely to have lower or negative growth rates. Looking at the aggregate data points (colored shapes) perhaps reveals the correlation more strongly. Surplus energy tends to lead to surplus people, in our real world.

Collecting Thoughts

This is a complex topic. To do a thorough job I would have to disentangle immigration from domestic birthrates. But certainly the graphs above cast doubt on the intuitive story that nations rich in energy or money trend toward lower growth rates.

Why the U-shape tendency? The rapid downward slope is very likely due to improvements in education as nations have greater access to resources. Particularly important is the education of young women. Want to cut back on out-of-control pregnancy rates? Give the girls books. It’s much more than just educating women about birth control and reproduction, etc. Education empowers women to take jobs and make free choices. Lacking this, imported food financed by governments of industrial nations and by charities allows surplus to cross borders and provide the feedstock for new babies.

It makes me question the global benefit of increasing population by providing food assistance. I once contributed to such funds, but now find myself confused: what’s the plan, here? I get the humanitarian urge to support starving populations—really. This universal sympathy is part of human nature, but may become one of the forces that binds us to the railroad tracks leading to overpopulation and eventual collapse. That’s my concern. By supporting starving populations now, are we only doubling down so that the number of ultimate sufferers is larger? Is the bad news inevitable? Until I have a clearer picture, I’m somewhat paralyzed in my intrinsic desire to offer support.

In any case, it is easy enough to find reasons why the growth rate should plummet as energy/wealth break free from the bottom of the barrel. But why the reversal? One way to answer is to ask: why did the U.S. experience a baby boom after World War II? Significantly, the U.S. dominated oil production in this period: we were to the world then what the Middle East is now. Times were swell. We were full of hope and optimism, and believed we could do anything. That’s good baby-making weather, folks. We make decisions about what we can afford to support based on current conditions and some sense of the brightness of the future. Energy surplus, combined with a primal instinct for passing our genes and raising families, sets us up on a predictable path.

Where is the Real Population Problem?

We in the Western World tend to point the finger at developing countries as being the major culprit for population growth. And it is true that the fractional growth rates in such places is alarming, with doubling times of a few decades. We are justified in wondering how this population will be fed.

But we also saw that in terms of resource consumption, adding a Quatari is about 45 times worse than adding an average African. Adding a U.S. citizen is about 20 times worse. Yet what does it really matter how extravagant the life of an average Quatari, Kuwaiti, Trinidad & Tobagan, or Luxembourgian is? These are small countries. Shouldn’t our concern land on places like India or China? Couple large populations with aggressive development, and these countries stand to change the global calculus rather dramatically.

Given data on the population and growth rate, we easily compute the number of people added per year in each country. Now let’s assume that the added people share the average conditions of the nation as a whole. So we can multiply the number of people added by the national per-capita energy use to get a total amount of energy demand added to the planet because of population growth. Off to the graphs…

Annual absolute energy demand added as a result of population growth, as a function of the number of people added per year.

Annual absolute energy demand added as a result of population growth, as a function of the number of people added per year.

India adds about 15 million people per year (wow). China adds a little over 6 million. Nigeria is next, at about 4 million. Then we have the U.S., adding 3 million per year. But of those, the U.S. is the hungriest in energy terms. The graph shows how many petajoules (PJ) of demand are added each year per country due to population growth (other factors can also contribute to energy growth or decline; here we isolate the population portion). For reference, the entire world’s annual appetite is 530,000 PJ. What we see is that population growth in the U.S. is adding energy demand faster than any nation on Earth. China and India are also important (and in absolute terms they are certainly more important energy growers, due to a rapidly changing standard of living). But the answer to the question: who’s population growth is having the largest effect on global energy demand?—it’s the U.S.

One could easily argue that over the lifetimes of the newly added, ultimate energy additions due to China’s present population growth will outstrip those from America because of the changing standard of living. Firstly, it is not crystal clear how long the Chinese juggernaut will last against the unknown challenges of the future. But perhaps more important is that jostling for top position could obscure the glaring outcome evident in the graph. It’s the U.S., China, and India where population growth is driving global increase in resource demand—to the extent that energy is a proxy for generic resources. The rest of the world is of secondary importance on this score. Where is population growth putting the biggest squeeze on resources?  It’s these three countries, with the U.S. presently well ahead of the others. Meanwhile, the Ukraine is doing the best job of removing demand from the world.

Annual electrical power capacity added as a result of population growth, as a function of the number of people added per year.

Annual electrical power capacity added as a result of population growth, as a function of the number of people added per year.

The electricity story is similar. Population growth in the U.S. is driving the addition of about 4 GW of annual electrical generation capacity. Again, China and India are on the map, with the rest of the world crowded into the lower-left corner.

Annual absolute CO2 added as a result of population growth, as a function of the number of people added per year.

Annual absolute CO2 added as a result of population growth, as a function of the number of people added per year.

Something moderately interesting happens when we cast the plot in terms of CO2. Because India and China use “dirtier” energy sources, in terms of CO2, the gap between the U.S. and China/India is reduced. The U.S. still stays on top, but less overwhelmingly so. Some Middle-Eastern countries are straining to break away from the pack as well—but not in a good way.

Child Free by Choice

The list of reasons for why my wife and I decided not to have kids is long (not to say that we did not also see benefits). This post gets at one of the facets. Adding a child in the U.S. has a disproportionately large impact on global resources, whose finite nature is becoming increasingly apparent. At some level, ours is an attempt to arrest the innate human drive to reproduce (which I do share), because this results in adding more people to the planet—perhaps not the wisest course at present. Parents readily portray our choice as selfish—probably because we have more freedom in how we spend our time. But selfish arguments are destined to fail: virtually all choices humans make involve self-consideration, and therefore have a selfish component. Flipping the argument around, by not having kids, we deprive ourselves of: the undeniable joys of parenthood (mixed with occasional exasperation); potential caretakers as we age and lose facilities; and a genetic link to the future. In part, I forfeit these advantages because I have trouble justifying why my personal needs should come at an outsized cost to a unprecedentedly challenged civilization. In this way, I can just as easily cast the decision to have kids as the selfish choice. Not popular with the breeding sort: people don’t appreciate being labeled as selfish. I expect a few howls.

Oil-Clouded Crystal Ball

I try to be careful not to convey certainty about the future—which I note is not a behavior i often witness from optimists. Rather, I try to point out distinct possibilities that we collectively tend to ignore or deny. Only via increased awareness to neglected issues can I ever hope to be proven wrong in my concern. That would be a lovely outcome, and in fact is the whole point for me.

We are in the midst of an unplanned experiment of unprecedented scale. We have 7 billion people on the planet, growing at almost three new (net) people per second. It’s an uncontrolled mad dash into the future. One could imagine metaphorical scenarios of crashing into a brick wall or running off a cliff, exhausting ourselves and stopping to catch our breath, or leaping into space to leave the planet. I certainly have my guesses, but I can’t spell out an unwritten future.

I dredge back up the single-most important graphic that informs my world-view. We know that fossil fuels have far-and-away dominated the scale of our energy use, and that these are finite resources. We can therefore make the following plot with some confidence. I am especially confident about the big question mark in the future.

On the long view, the fossil fuel age is a blip, with a down side mirroring the (more fun) up side.

On the long view, the fossil fuel age is a blip, with a down side mirroring the (more fun) up side.

To the extent that surplus energy is responsible for the population boom, does the symmetry of the fossil fuel curve carry predictive power for population as well? These curves have been historically tied together. The burden of proof is on the optimists who presume that we can break the dependence. In a prior post, I emphasized the difficulties associated with breaking from this curve. Another post tabulates the relative superiority of fossil fuels over present-day alternatives, amplifying the challenge. It is not physically impossible, but supporting billions of people on this planet for the long haul is not something we are proving adept at doing. When the historical record is riddled with examples of civilizations peaking, overreaching, and collapsing, it becomes rather difficult to subscribe to the notion that this time is different, when faced with so many monumental and simultaneous challenges.

Population, as a reflection of human nature, may well be the mother of all challenges. Tightly bound to resource demands, the problem isn’t going to go away by ignoring our own personal roles and instead focusing attention on poor nations half-a-world away. Economic growth incentivizes population growth, which plays right into our biological desires. It would be refreshing to no longer be enslaved as victims to either of these forces. Otherwise we don’t really get to write our own future. And nature doesn’t care if we don’t understand.

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127 thoughts on “The Real Population Problem

  1. What about having just one child? That still brings medium and long-term population reduction, while allowing you to enjoy parenthood. For example, me and my girlfriend are both lone children, if we also have only one child, in the span of a two generations we would have one person in the stead of four, a pretty dramatic reduction rate.

    • No doubt this is an improvement, and drives reduction, which is great. Consider, though, that this one child, if born in a high-energy-consumption country, will be a monster consumer added to the planet. There are no great solutions here—such is the mess we’re in.

      It is also worth adding that China supported a one-child policy for many years. This action did not produce dramatic results (like halving population), while being extremely unpopular and causing untold number of atrocities. It’s a very nice personal choice, for the few willing to do so.

      • What, this isn’t dramatic enough for you?

        The full effects of the policy haven’t been felt yet because the people who were children when it was instituted have seen a dramatic increase in life-expectancy. In the next couple years the true effects will be seen, a crest like what’s predicted is absolutely unprecedented and may well have a very positive effect on the outcome of all these crises.

        • Fair enough: demographic inertia is a powerful force left out of my “right now” plots. More often than not, it works the other direction: lowering fertility to replacement rates still sees population grow for decades to come. Autocracies can bend the normal rules.

          • How is that “the other direction”? Birth rates are below replacement in most of the rich and much of the poor world. In only a few countries has that translated to declining populations yet.

            China’s only unusual in having had such a coercive policy, and I’ve seen people question whether that even had much effect. Its TFR is low but it’s like #154 out of 200 or so; dozens of countries have lower TFR without one-child policies, whether rich ones like Switzerland or poor ones like Bulgaria.


  2. Tom,
    I think sometimes that one reason some narratives we take for granted as being “truth” don’t actually seem to line up with reality is that they are based on widely disseminated, out of date information that was generally accepted as “truth” at some point in the past.
    At some point, it was standard school curriculum to teach that birth rates decrease with affluence – that may have been true to a point, but the world is obviously a rapidly changing place.

    Of all those people that learned x, y or z in school, how many continued to update their “picture” after they left school by keeping up with all the latest developments in fields related to x, y or z?

    • I also meant to say:
      Keep up the good work with the “narrative busting”.

    • No, it’s still true that birth rates decline with affluence among nations. Tom didn’t give any graphs of birth rate, he gave graphs of population growth. There’s a demographic intertia effect. Outside of the Arab-oil states, most of those rich countries are on track for population decline, they’re just not there yet.

      As for the bottom of the U, where countries are shrinking, that’s in large part because people are actively emigrating away from bad economies. Particularly for Eastern Europe; don’t know about Jordan, which seems to be bad data: Google “Jordan population growth” gives 2.2%, not -1%. The bottom of the U might snarked as “just (energy?) rich enough to leave for somewhere richer.”

      Other notes: the climate importance of hydro, geo, and nuclear power is pretty obvious. Only one of those is expandable.
      Perhaps also important: the importance of local climate. Hong Kong is rich while low in energy use, but it’s also subtropical if not tropical in climate; they certainly don’t need any heating fuel the way Nordic countries, Canada, or the northeast US do! And relatively even day lenghts, vs. long winter nights, so cutting down on artificial light for what that’s worth. Though Hong Kong’s also very dense with good public transit. Cold sprawling countries are going to burn a lot.

      (Glaeser argued that the best thing the US could do for the climate would be to move into super-Manhattans along the California coast. Shame about the redwoods, but energy use for transportation and climate control would drop precipitously, compared to car and A/C sprawl in Texas.)

      • Damien RS,
        Ah, fair enough – my mistake.
        That’s what I get for posting in a hurry.

        Although I stand by the larger point that I was trying to make, ie, that many of the narratives that are generally accepted as being “truth” (and that may have even at one point been true) can often be demonstrably false, yet they persist regardless.

  3. Population growth rate is a useful, but problematic value to look at to evaluate the ‘surplus energy grows babies’ thesis. A big part of population growth rates in these areas will be due to extensions in life expectancy (as well as immigration, as mentioned). How do the correlations between energy usage and total fertility rate look? ( Replacement rate (zero world population growth presuming stable life expectancy) is going to be some value a bit above 2 (demographers use a short-hand of 2.1, although one can quibble with it).

  4. “The bounty of fossil-fuel-turned-food encouraged an explosion in birth rates ..” Any proof for this claim? My understanding is that birth rates were always high, but industrialization enabled reduced mortality and therefore higher population levels. You seem to suggest that people decided to have more babies instead. Overall I have a feeling that this was one of your less well thought out posts. As mortality is reduced population increases, but people have adapted to this by reducing the number of babies they have. . This has been especialIy clear in places where environment has made such decisions possible/attractive (cities, economic growth, education, role of women, green revolution etc.) We have a one-off population increase going on with population settling to around 9 billion. In many wealthy nations population will decline. I warmly recommend Fred Pearce’s “The Coming Population Crash: and Our Planet’s Surprising Future”.

    • A fair point. How much control people have over the number of children they end up with varies a lot from person to person, I suspect. Some families do make decisions, and some of those will be tied to resource availability, I expect. Food availability is also important to survival, whether or not decisions are involved. And there is no doubt that fossil fuels extended our ability to grow food dramatically, supporting larger populations. I could be wrong, but the correlation is remarkable, and there is a clear line of causation involving food.

      • A wonderful source of statistics and visualization off all sorts of things including some of the data here is

        • As a demonstration:

          On the x-axis we have per capita energy use on the y-axis the fertiliy level. Color indicates life expectancy and the size infant mortality. Good societies are redish small balls. As you can see, as time goes by fertility rates drop while per capita energy consumption tends to increase. While this is going on life expectancy increases and infant mortality declines.

          (If the short link doesn’t work here is the long one$majorMode=chart$is;shi=t;ly=2003;lb=f;il=t;fs=11;al=30;stl=t;st=t;nsl=t;se=t$wst;tts=C$ts;sp=5.59290322580644;ti=2010$zpv;v=1$inc_x;mmid=XCOORDS;iid=0AkBd6lyS3EmpdHRmYjJWLVF0SjlQY1N5Vm9yU0xxaGc;by=ind$inc_y;mmid=YCOORDS;iid=phAwcNAVuyj0TAlJeCEzcGQ;by=ind$inc_s;uniValue=8.21;iid=0ArfEDsV3bBwCcGhBd2NOQVZ1eWowNVpSNjl1c3lRSWc;by=ind$inc_c;uniValue=255;gid=CATID0;iid=phAwcNAVuyj2tPLxKvvnNPA;by=ind$map_x;scale=lin;dataMin=-1.3096;dataMax=8.4$map_y;scale=lin;dataMin=1.009;dataMax=7.55$map_s;sma=49;smi=2.65$map_c;scale=lin$cd;bd=0$inds=)

          • Thanks for finding this—looks like a useful interactive tool. Definitely flatter at high energy use. But a slight U-shaped tendency remains (low point still about 1/4 of the way along the energy scale). The net effect of decreasing infant mortality and longer life expectancy obviously also contributes to population growth, and these advances would seem to be correlated to energy availability as well. Add immigration and the net effect is still that energy rich countries expand their population and put ever greater strains on resource use. Maybe a more generic statement is that surplus energy tends to grow population (by several mechanisms), which acts to accelerate the consumption of energy.

          • This is a fairer representation of the demographic transition, although the scale on the TFR axis doesn’t seem to appear correctly for me. Hovering over values displays values reasonably close to what other sources I have seen say they are.

            The results as I am seeing them is that the only states which are above the replacement fertility line are petro-states with relatively low socioeconomic freedom (complicating factors already recognized by demographers). The remaining curve flattens out quite nicely into a TFR of ~1.6. This really does seem to blow the thesis out of the water.

            China is well below replacement, but it has an aging population. India has a shrinking TFR, but if increased energy consumption is required to get them into negative territory, average energy use is going to have to double or triple. We also see by the difference in TFR and Pop. Growth how reducing new population isn’t going to work in the medium term to reduce total populations much.

            It does tell us what demographers have been saying for a while, improve living conditions to some minimum threshold and make family planning services available and people will have fewer babies. If we are going to get through this without drastic human die-offs, we have to focus on dragging more people into the base of that L, meaning making the elements of happiness available for less energy.

        • From the gapminder graph it seems there is an energy per capita transition as well as a demographic transition, and it goes the wrong way.

          Compare China and South Korea. SK without any coercion has a lower birth rate, but note that as SK gets around 1.7 children/woman, the birth rate declines very slowly thereafter, but the energy use rises steeply from 1.6 to 5.2 units per capita.

          And China is going the same way. Energy per capita rising steeply as birth rate hits 1.7 children per woman and declines thereafter very slowly.

          I think it’s consumeritis. “Have fewer kids, buy more stuff.” And it’s not good.

  5. Before I forget, I will be extremely busy over the next little while, and often away from a computer for extended periods. Comments may go unapproved for a long time. I may get a substitute moderator to keep things flowing, but may not be able to give the comments any personal consideration. Sorry…

  6. Wow. As usual, really interesting post!
    Thanks for the friendly warning about all the data!
    Going to take some time to chew over what you present here, but its good stuff!

    Bottom line, I found it interesting your link to energy. I have always heard that money is not the end of the line, its all about energy. Our money moves around via computers, with no energy, there is no money flow.
    Your ‘twist’ on energy ‘here’ is growth over ‘there’ is fascinating.

  7. “…surplus energy tends to grow population (by several mechanisms)” I disagree. I think the issue is that fertility rate responds more sluggishly to technological changes than mortality rate and life expectancy. This means that people start with high fertility levels. Then with improved hygiene, food supply etc. mortality is reduced and life expectancy increases. The result is that population increases UNTIL the more slow fertility rate is adjusted to the lower level. I think this is what you see in the data (for example when you play with gapminder) Some arab countries have the combination of high fertility and high energy consumption, but they are outliers. Most of humanity is behaving differently. So we are not talking about permanent population increases made possible by energy consumption, but transient effect due to changes in society. This transient can be made shorter with sensible policies. This is I think also the main message from population experts (although they seem to disagree slightly on the final population size. 9-10 billion seems to be the right ballpark AFAIK.)

    The guy behind (prof. Hans Rosling) has also very nice presentations in TED about these issues. Energy consumption can (and usually does) increase even as the fertility rates drop. Also increasing mortality is a very bad way of reducing population. Here is what happened in Ruanda. It took just few years to increase the population above the levels before the genocide!ctype=l&strail=false&bcs=d&nselm=h&met_y=sp_pop_totl&scale_y=lin&ind_y=false&rdim=region&idim=country:RWA&ifdim=region&hl=en_US&dl=en&ind=false

  8. A few things that have to be pointed out:

    1. It is correct that people rich countries have a much larger impact on the environment than people in poor countries. It is not correct to assume (I am not saying you do, but it has to be clearly pointed out) that this means there is no problem in poor countries. We usually evaluate impact in global terms such as CO2 emissions, but this is by no means the only way to wreck the environment – it can be very successfully wrecked locally by very poor people who hunt for bushmeat, use unsustainable subsistence farming practices and cut down their forests for firewood. See what happened in Haiti for one of the best examples. Most of the developing world is already or is soon going to be drastically overpopulated at present.

    2. The reason for the demographic transition is not education. The hardwired evolutionary mandate is to increase inclusive fitness, not to increase the number of offspring you have. Those are not necessarily the same things and they certainly are not the same in humans. Keep in mind that humans are perhaps the only species that has grandparents contributing to raising the offspring. We (or at least most of us) tend to look farther into the future than the number of kids we have when it comes to inclusive fitness maximization and factor in such things as maximizing the quality of the offspring and its own chances of reproducing.

    In a modern western society this translates into having to train your kinds well in the complex behavioral codes of such a society, ensure they get a good education and a well-paying job, etc. All of this is necessary because you want your kids to have the best chances of securing quality mates and reproducing themselves. But all of this takes enormous effort and resources in such a complex society, and combined with the fact that both parents have to go to work and earn the money to pay for all of that, it is easy to see why people can barely afford to have 2 kids, often even less than that. With the key word being “afford” – as paradoxically as it sounds, people in rich countries cannot afford to have as many children as people in a poor country can, because the cost of raising them does not scale linearly with GDP. In some cases it is indeed because people got educated and enlightened enough not to want more kids, but those are the minority. This is the explanation for the “demographic transition”. Also, very importantly, it applies to the middle class, not to the superrich, to the people that are so poor that they don’t care about such things as college education, to the people that are not very rich or very poor but who who highly desire fertility and don’t factor those things in their inclusive fitness maximization “calculation” either, usually for religious reasons. The Saudi royal family has ballooned to more than 10,000 members over the last 70-80 years and they did have all the money they needed and in later years the education too. But precisely because money is not a problem for them, and because of their religion, it has come to this.

    • “The hardwired evolutionary mandate is to increase inclusive fitness”

      The only really hardwired mandates are “enjoy having sex” and “enjoy taking care of the children that result”. The rest is subject to human reason.

      • I’m not a neuroscientist, a psychologist or an anthropologist, but I would bet that the really hardwired one is “enjoy sex”. Childcare practices change too much across and within cultures, from extensive life-altering personal involvement through complete abandonment and/or delegation to other adults. There is, for sure, the “cuteness” empathic factor, but that’s not like a genetically hardwired enjoyment in childcare.

  9. Those U-shaped curves of population growth are unexpected and astounding.

    I wonder if they hold up in the past; was ~2,000 W/capita at the bottom of U in 1950 too? Is 2,000 W/capita some kind of universal aspect of human nature?

    • I could be wrong, but I suspect not a few people had access to 2kW/capita in 1950.

    • A lot of the visually U-shaped impact in the population growth vs. income curve comes from extremely small, rich, nations with high growth and income. These are not very important. I am quite curious about the nations “in the trough— would like to see which they are”. The labeled ones, like Bulgaria and Moldova, seem to be small to medium-sized eastern European nations.

  10. I find that figure 530,000EJ total annual consumption is little bit off; are you sure about it? Exa = 10^18, 530,000EJ = 5.3*10^23J, divide that by 7 billion people, and number of seconds in a year (31536000 seconds), and you get average power needs of a human as 2.4 megawatts! Even if all of the 7 billion had the power consumption of 10kilowatts of average american, then, the total energy consumed in a year would be only 2208 EJ, not 530 000 EJ!!

    Human diet: 10MJ per day -> 115 watts. Thou, food energy is obtained by consuming ten times more oil than joules produced as food, so, more like 1.15 kilowatts. Litre, or kilogram of fat / oil / gasoline has 40MJ of energy, but as conversion is so inefficient, you need 2.5 kilos of oil for your daily diet.

    Recently I got into calculating these energy issues too, particularly about having a 10 000 km flight, and I found out, that it’s in the same order of magnitude as if driving that lenght by jet plane, car or even biking! Cause human calories are kinda costly, if the food consumed is produced by modern method. That flight consumes about 1000 kilograms of fuel, would take you about 400 days of biking, yet, you consume about 2.5 kilograms of fuel yourself, too.

  11. I think surplus energy grows babies till the saturation point caused by economic limitations such as cost of education,housing,…etc.

  12. Tom, surely you understand your personal decision to not have children will have no effect on the trajectory of population growth. So, it merits neither criticism or praise. As K strategists, you also know that it’s pretty clear humans do indeed take the signals from resource constraints, which is why fertility rates are already guiding downwards. Fertility rates in both the OECD and the Non-OECD are already guiding downwards, and, will show up decades from now with enormous impact.

    We were all entranced with the presentations over the past decade of Wolf-Sheep-Grass systems, and doubling times in yeast cultures. Alas, while humans no doubt will continue to overshoot limits in local domains, more broadly we have already responded. This is why your citations of absolute numbers, such as India’s annual addition of 15 million people, sound impressive to the layman. But, it’s not really about India, per se. BTW, just on this point, I have no doubt a few regions will overshoot hard and may experience very nasty social/conflict outcomes. (Nigeria comes to mind.)



    • Who knows?
      This articles may lead 10 viewers to decide to have less children, which in turn might lead 100 of their friends to change their view on parenting.
      100 US babies are the energy equivalent of 2000 African babies 😀

    • Humans do take signals from resource constraints, but not even remotely close to what is necessary. Humans, including yourself, have completely overlooked the humongous build up of potential premature death. That potential is evident in the fact that we must consume resources faster than they renew in order to keep our numbers alive. We have no clue how to keep 7 billion humans alive at one time without burning oil, and oil is a non-renewable resources. In simple terms we have bred our numbers up so high that we are eating stores of food (oil, coal, etc) and not even remotely coming close to feeding ourselves off the land. This fact makes a mockery of the notion that humans take signals from resource constraints.

      A fertility rate trend is utterly useless. Take it to extreme and you’ll see. If 10000 people and their descendants average more than 2 children, while all other 7 billion humans have NO children from now on, all demographers will say that the fertility rate is zero. Yet, humans are still attempting to grow their numbers to infinity at an exponential rate. The ridiculous notion is 7 billion having zero children not the 10000 people averaging more than 2. Yet even that that extreme cannot prevent overpopulation.

      The doubling time for yeast example was never presented or understood correctly. It does not tell us that our environment will become full soon, it tells us that it has always been full. It is simply idiotic to think that for as long as humans have been on Earth we have not reached the limit. The example should have shown how yeast were overflowing the beaker, and that represents child mortality. The example should also have shown the beaker being extended higher and higher (improving our ability to extract sustenance from the environment, e.g. farming over hunt/gathering, and fixing nitrogen to make fertilizer), but not quite fast enough to prevent the yeast from overflowing (premature death) in order to properly represent what is going on with humans on Earth.

  13. > “Economic growth incentivizes population growth”

    Completely wrong. Poverty is the primary driver of population growth. That’s why we see *negative* population growth in wealthy countries like Germany.

    Give this fundamental error, the rest of the article falls to pieces.

    • But fears about economic recession/decline are prompting Germany to goose up their fertility. This is what I mean by incentivizing. There are actual incentives/programs to grow more babies based on a desire to maintain economic growth.

    • “Economic growth incentivizes population growth”

      It’s not clear what “incentivizes” is supposed to mean here. Maybe what you mean to say is that population growth promotes economic growth. That is often, though not always true, simply because more people create more demand for goods. Of course, any sane discussion of economic growth would distinguish between bulk growth and per-capita growth, and any sane economist would acknowledge that the relevant measure for material well-being is per capita growth. But alas, sane economists are hard to find (there are some:

      “But fears about economic recession/decline are prompting Germany to goose up their fertility.”

      There is occasionally talk about “demographic decline” in Germany, and discussions about “family-friendly” policies to encourage child-bearing. Many such policies exist btw, without the effect of boosting birth rates. But these discussions are taken far less seriously in Germany than they are by the New York Times and other American observers, where there is a virtual propaganda campaign in favor of population growth, to the point where some have even discovered an “under-population crisis” in China. I’m not making this up. See slides 39-52 at As I show in detail with the example of Japan, the whole “demographic crisis” argument is unfounded. The share of economically active Japanese (i. e. ages 15-65) is currently higher than it was in 1950. Even if that share declines in the coming decades, there is no reason to expect a labor shortage. Instead, full employment and a slightly longer work life can amply compensate for the change in the population structure. What this issue really shows is the importance of culture. Murphy is looking for correlations between demographics and physical parameters. While such correlations exist, they can and will never provide the whole picture.

      • Economists fail the most basic accounting principle. Economists do not treat the destruction of fossil fuels the same as an accountant treats a bank account. It makes absolutely no sense to state that the corporation is doing OK while the bank account is plummeting to pay the employees.

        We must destroy fossil fuels in order to keep 7 billion alive.

        • So you have money in the bank that you propose not to spend because then you would have less money in the bank? How about you spend the money in the bank and work toward an alternate source of income (solar or nuclear), which is more or less what we are doing.

          • Money in the bank is principal or capital. Sustainable use of that money means living on interest. Spending of principal is non-sustainable and leads to bankruptcy. Burning fossil fuels is spending natural capital, as opposed to making plastics which is converting natural capital to a more usable (and re-usable) form, which we can see as investment.

            It’s a bit more complex: burning coal to make steel and bricks and glass is also conversion. But burning gas to make fertilizer when we don’t capture runoff, and burning oil so we can zip around faster and have larger homes (which also take more fuel to heat and cool and light) rather than getting around by streetcar, is living on principal.

            It’s the difference between spending your inheritance on a college education and spending it on a trip to Cancun. Most fossil fuel use has been spent on Cancun, zipping around in cars and feeding (and powering) an dubiously large population in light of long term energy flows.

  14. A physicist or engineer gets an idea that seems to explain much of the world. He barges into some other field, and with some graphs or math tells the field experts how his idea sheds unprecedented light on their subject. Sometimes this actually works; I’ve heard of physicists bringing insight to geology or molecular biology. Sometimes it’s just an act of crankitude, in ignorance of the actual key ideas and complexity of the subject.

    I’m not calling you a crank, but I think crankitude is within horizon range with this post. “Hey demographers! Energy explains population growth!” But there’s total fertility rate and replacement rate vs. the simple “population growth right now” numbers; there’s the multi-stage model of demographic transitions, where the early boom stages are driven not by energy but by childhood vaccines, antibiotics, and clean water; there’s migration and population change, as I mentioned, and the cultural nexus of eastern European modest-energy states; there’s most of the oil states having distinctive cultural factors other than energy, apart from Norway, which hey doesn’t look like them (though possibly low effort oil wealth has allowed the survival of such cultures.)

    The graphs *are* interesting (but maybe based on flawed data, below), per capita energy use clearly is a major part of environmental impact, and we have used fossil energy to boost populations, from South American guano deposits in the 19th century to fossil fuel made (with stranded natural gas more than oil, I think) fertilizers. But “more energy, more people” is I think far too simplistic.

    It’s not just Jordan, BTW; the population growth numbers for Luxembourg and Kuwait are also different to a Google search, though off by one point instead of 3. Google credits the World Bank. I don’t know why it and the CIA would differ so much, but -1% for Jordan frankly is far less plausible than 2%. You might try making your graphs with a different data set and see if the curves are robust under such a change.

    • And what if the foundations of a field are not solid?

      Economics is the classic example – complete disregard of the laws of physics reigns there even though the economy is something very much physical. Do you think physicists (and other physical scientists) have nothing to say to economists?

      Demographers also have a blind spot and it is evolutionary and behavioral biology because if there are subjects that have something to say on how organisms make reproductive decisions, it is those. Yet, I never see them mentioned by demographers, instead it’s the same mantra of the “demographic transition”, “economic growth leads to lower fertility”, etc.

      Well, maybe it does in some cases, but that does not mean it always does or that the relationship is what you think it is. It is not a bad idea to hear what others, who have not been living in your bubble, have to say on the subject.

    • I hear you. I’m definitely not up to snuff as a demographer. I’m not trying to put them out of business or claiming I have some amazing insight that has slipped their attention. I got data and plotted it, and was surprised by what I saw. Worth sharing. The context is clear enough: I am not isolating fertility, but looking at the end result of many factors influencing population growth. Energy rich countries tend to grow their populations. This has big implications for future energy demand. I care about that.

      Also, it was energy-enabled revolutions that stymied Malthus in his predictions of running out of food. So whatever criticisms this post deserves, I am still sold on the notion that surplus energy played a huge role in agriculture and therefore food production, and therefore population. It wasn’t the only way that fossil fuels aided the population boom. But the fact remains that we don’t have a prior experiment to tell us how population responds to the tail end of the finite resource that has given us so much.

      • “I am still sold on the notion that surplus energy played a huge role in agriculture and therefore food production, and therefore population.”

        This is just so obvious I can’t imagine how anyone would take issue with it. We haven’t been able to escape the limits imposed by ecological production of complex carbon molecules (which provide 97% of the energy we use today), so therefore we are still subject to the same rules governing die-offs that hares or deer on an island are, or what have you.

        The simple fact remains that without our external energy sources from fossil fuels (or some other replacement, which we do not currently have nor will likely develop in time), there is no way the world would be able to support 7 billion people, end of story.

        Of course it gets a bit more complicated in determining how exactly those issues interact, of increasing energy use –> leading to increasing population growth as mortality rates drop –> and then subsequent decreasing population growth rates as fertility rates drop (or sometimes don’t) due to a variety of issues that have been brought up well in the comments here.

        The big question in my mind is what will happen to population growth rates when we start going down the back side of fossil fuel curve and people are thrown back into poverty, and social order falls apart, along with education and medicine etc. Will all those previous gains in reducing fertility rates drop?

        • When we start seriously sliding down the back side of the Hubbert curve, what will happen in the most likely scenario is the following:

          1. In advanced industrialized countries, you will see an initial decrease in fertility. This has in fact been observed in real life after the collapse of the Soviet Union and it also likely happened during the collapse of the Roman Empire (though obviously good data is hard to obtain in that case) So it’s reasonable to think that when the analogous processes play out in the West, the consequences will be similar.

          2. This, however, will be the case only until society has collapsed to a sufficiently low third-world level. Then two things will happen. First, the majority of people will become subsistence farmers again, child labor will become a normal thing again, and children will be again valuable as a resource and not burden. Second, as whatever small gains have been made in moving us towards a more rational society are lost with the falling apart of educational and scientific infrastructure, religion will regain its complete dominance over people’s thinking. This will be in who knows what twisted insane forms, but more likely than not it will be strongly pronatalist as that’s the the attitude of its most aggressive forms today, which are most likely to survive and become dominant in the future. In the end, it will be back to a present-day Sub-Saharan Africa situation everywhere in terms of fertility. I obviously cannot give you a timeline though.

          3. In the present-day Third World, it will be just a continuation of BAU

          Note that the above concerns fertility expressed in expected number of children per woman that reaches reproductive age. In the same time this is happening, population will likely be decreasing because mortality will go through the roof due to the inevitable consequences of our ecological overshoot plus the occasional (possibly waged with WMDs) war here and there.

    • Demography is most definitely a field that needs to be barged into.

      One clue is their own pathetic lack of definitions and understanding of existing definitions. The definition for “overpopulation” that is shown on Wikipedia illustrates the inability to comprehend the meaning. The definition states that it is the situation where the organism’s numbers EXCEED the carrying capacity. That can only happen if the organism is consuming resources faster than they renew. Humans are blatantly doing this. The rest of the article shows countless demographers failing to comprehend a simple definition.

      They have no definition for the situation where the species is at the limit of what can be provided for (notice I say “provided for” in contrast to “sustained” because provided for allows the use of resources faster than they renew). It is impossible to exceed what can be provided for by definition. What must happen if adults average too many babies? Children must die. The only way the environment can prevent the population from growing faster than the environment can provide for them is by killing children.

      Demographers have no definition for this. They never ask the question as to whether humans are in this situation. They assume we are not at the limit. We are at the limit. We have always been at the limit. We have always been causing the death of children when we create a baby. We have always been attempting to drive our numbers higher at a rate that exceeds what we have managed to provide for.

      Demographers are utterly clueless to these fundamental concepts.

      • “The definition for “overpopulation” that is shown on Wikipedia illustrates the inability to comprehend the meaning.”

        “Overpopulation” is not a well-defined scientific concept. Better not to use it. It’s counterproductive at best. Remember the damage done do sane debate by Paul Ehrlich’s “Population Bomb”.

  15. Great work Tom,
    If you plot fertility rate instead of population growth rates, many of the distorting issues surrounding immigration would be resolved. For instance, Singapore has a fertility rate of 1.4 children per woman, but its government sponsored immigration lifts population growth rate to 2% on your graph. Australia’s population is growing at 1.8% pa, but 60% of that is via immigration where fertility rate is 1.9.
    So energy sucks in population from around the world.

    • If I’m not mistaken that was the whole point: effective population growth is higher, whether it comes from fertility or migration isn’t important.

      • Except it is important, because fertility is making new people, while immigration is a person moving from somewhere else — energy use goes up here, goes down over there. Migration from a low to high energy country might mean more energy use overall, but not as much as from simply adding a new person. And Earth as a whole has no immigrants, so if wealth leads to low national fertility, global wealth leads to global low fertility.

  16. I can’t help but feel like Prof. Murphy is carefully dodging the elephant in the room on this one: religion. Most of the countries that have high population growth and high per capita income are strongly religious, in particular the the middle east and (in some groups) the US. The countries that are rich and have low or negative growth are, for the most part, the countries with the lowest levels of organized religion.

        • Hans Rosling is a fine example of the conventional wisdom of demographers. His presentation is totally based upon projections of the past to the future. That’s all that demographers do.

          Imagine if it was 500 years ago and I published a projection into the future of the number of islands discovered by Europeans during the past several years. My projection would suggest that the discoverers could find new islands every year. We know this is ridiculous because we know there are only so many islands on Earth to be discovered. Demographers do this by projecting population sizes into the future, as if it is just a matter of human will power to provide for as many humans as we pack onto the Earth.

          Hans totally abuses the projection technique when he projects lower fertility rates into the future. There is no mass or momentum to fertility rates. Demographers have found no mechanisms, only correlations. The mechanisms that they propose to explain the drop in fertility in relation to wealth is utterly ridiculous. We know the mechanism that is certainly present. Too many people causes poverty. Too high a fertility rate causes poverty. To flip this around and say that the poor countries must become rich in order to stop making babies so frequently horrible science. It is nothing more than a systematic abuse of correlations, and projections.

    • Religion is one the two elephants in the room. The other is the need for a quick and organized by states worldwide population reduction if we to avoid it being forced on us by nature.

      Both are too inconvenient to touch, which is why the discussion on the topic is what it is today.

      Why is it that economists are so in love with perpetual economic growth? Part of it is simple indoctrination into the religion, but the root cause is that t is an extremely good message to send politically so that’s what they do.

      The reason why we have the “demographic transition” theory is the same – it is a politically correct, feel-good message to send, especially in its simplest from – raise GDP and fertility will drop. Of course, there is a slight problem and it is that it is directly contradicted by data once one looks at the oil kingdoms and the US. The economists just ignore that, but the more thoughtful social scientists reframe the argument into “education and empowerment of women will bring down fertility”. Well it does. However:

      1) It is not for the reasons they think it does. It is not that people all of a sudden want smaller offspring because they got educated, it is because once you start living in a world in which education matters the investment in resources you have to make into maintaining your social status in it puts a limit on how many kids you can have. Unless you’re a celebrity and/or a billionaire, in which case you can afford nannies, private tutors, etc. and you can have all the kids you want (and, indeed, if you’ve noticed, most such people do not stop at two),

      2) More significantly, education and empowerment of women will bring down fertility globally down to sub-replacement level on a time scale of many decades to a century. Well, we neither have that kind of time, not do we have the resources to support the economic growth in the Third World that is supposed to bring that change.

      But, again, nobody has any desire to hear that, so we’re back to “improve the economy, educate people, bury our heads in the sand”

      • If the cost of education is the limiter, then the US, with common private schools and increasingly expensive college, should have a lower birth rate than Europe where education through college is cheap or often free. European countries also subsidize families in many other ways: extended parental leave, cheap day care, free health care, further lowering the cost of having kids.

        This is not the case; US has higher birth rates.

        “education and empowerment of women will bring down fertility globally down to sub-replacement level on a time scale of many decades to a century”

        Rates are dropping as we speak. World fertility rate is 2.55. The replacement rate is actually the inverse of how many children don’t make it to having kids of their own, so 2.1 or less for the First World, but higher for less healthy countries.

        “quick and organized by states worldwide population reduction”

        Meaning what? Mass forced sterilization? Death camps?

        • 1. You display the same kind of simplistic thinking that leads to declarations such as “fertility will drop as GDP rises”. I never said the cost of education is the only factor, that’s a strawman. I said that the drop in fertility with increased economic development is the result of people having to invest resources they would have otherwise invested into raising offspring into achieving/maintaining social status for themselves and for their kids. There are opposing factors though, one of which is social norms and traditions that prize high fertility. In the US the latter are much stronger than they are, and that’s not true for the whole of the US, but for certain parts of it and certain ethnic groups in it. Massachusetts is a lot closer to Europe than the average for the US towards which the fertility of Mormons, Quiverfulls and other fundamentalists, Latinos, etc. is counted.

          2. The more important observations is that tates have not been dropping as fast as predicted. That’s why the UN had to push its projections for the end of the century up. The simple mathematical reality of exponential is that a global fertility of 2.55 is nothing to be happy about, it’s a disaster. Withdraw fossil fuels and watch how we feed 7 billion people – we can’t. Now what about the 10.5 billion projected under the optimistic scenario? Which itself is based on the assumption that the Third World will develop economically, which itself is an absurd assumption because the resources for that are simply not available. Even if the resources were available, that would result in an even bigger global environmental catastrophe – more degrees of warming, more extinctions, more ecosystems collapsing, etc. I have never been able to understand how anyone can think that there is nothing to worry about because we will supposedly reach 10 billion and then growth will level off. Just look at what the effects of 7 billion people are – how is 10 billion going to be anything but much worse (the environmental damage each additional person does not scale linearly with population size).

          3. Of the people alive today, at most a few tens of millions will be alive in 2100. There is no need for death camps – all that has to happen is for most people to go childless. If that doesn’t happen, I am willing to bet there will be a lot of death camps in the future, but not ones set up with the explicit intention of population control. Of course, most people will strongly object, which means that forced sterilizations, abortions and infanticide will have to be implemented, combined with a mass educational campaign so that the next generations grow up fully aware of these issues and why population needs to be kept in check. But that’s much better than the alternative.

          It’s not going to happen though, so there’s no need for you to worry about it.

      • “not do we have the resources to support the economic growth in the Third World that is supposed to bring that change.”

        Do you have numbers behind that? I am quite dubious about that assertion. Said growth doesn’t have to be as intensively fossil-fuel based as it has been in the currently developed countries. And if we are discussing multi-state efforts to accomplish highly controversial goals with world welfare in mind, a world-wide push for more sustainable forms of economic development (and less resource-intensive economic activity across the board) would seem to be on the table too.

        • “Do you have numbers behind that?”

          I was curious about those numbers too so I did the calculations. I’m pretty proud of how my fairly simple calculation of the proportion of global Net Primary Production appropriated by humanity came to 10% of the total for the world, which is very close to official estimates that peg it at 12%. Whether that’s by fluke or good math, I’m not sure…

          The problem is, our agriculture doesn’t “produce” more food; we merely destroy natural ecosystems and replace with our own domesticated ones, totally subsidized with unsustainable fossil fuel and irrigation inputs, and with no replacements on the horizon.

          Arguably, the total NPP of the planet has not gone up at all; many say it’s even gone down a bit, even with all the agricultural gains we’ve enjoyed via the Green Revolution over the half last century.

          The results of the calculations are pretty sobering, actually downright depressing. It might be theoretically possible for everyone to put solar panels on their roofs and drive EV’s around, and transition to a manufacturing sector using electricity rather than natural gas and coal, but the completely transformative changes that would be required for this are well beyond the time frame (and fossil fuels to manufacture it all) that we have left. It’s not about bringing the third world up to western standards; it’s about preventing the first world from sliding down to third world standards.

      • Without watching the video, I’ll note that the populations may not be as religious as their recent reputations, or as their government. There’s often a strong secular backlash to clerical domination, cf. Quebec.

  17. Your proposal to not have children or at least consider it as an intelligent response seems only rational given your view of the future.

    On the other hand, it could also considered a kind of suicide because one is afraid of dead.

    When my parents decided to have children around 1979 they were terrible concerned with dying forests (Germany), atomic war (cold war), energy and economic uncertainty (aftermath of the oil shock) etc. and yet despite frequent crisis and much complaining about the increasingly pessimistic outlook I must say that I have had a terrific life (so far). My hope is that the same will be true for my unborn daughter. And if everything collapses there might be hope because I also do not believe that a life can be very enjoyable without most of our modern luxuries.

  18. You ask “by supporting starving populations now, are we only doubling down so that the number of ultimate sufferers is larger?”

    Well, Ethiopia had their infamous famine in 1983-5, the one that prompted “Band Aid” and a massive international response. The population of Ethiopia in 1983 was around 33.5 million, of which about 1 million died (if you accept a disputed UN estimate).

    The population in 2013? An estimated 86.6 million, to which you can another 6 million in Eritrea (which split from Ethiopia in 1991). So that’s not far short of a tripling in population since the famine and the aid.

    • This is typical bad reasoning. If the population was able to triple, then we can conclude it can triple again. If the population had famine with 33 million and just normal starvation with 86 million, then clearly we need to add more people!

      Clearly this is nonsense logic, but the only difference between this bad logic and the logic that demographers are doing is how sophisticated their correlations and projections are.

  19. It seems to me that the nature of, well, nature, is that it chases energy. Virtually all life will expand to consume all the accessable energy available to it. From algae to weeds to bacteria to rabbits to foxes to reindeer. Provide a species with more accessable energy, you get more of the species. For virtually all other species, energy is only accessable in whatever form nutrients are provided for that species. Generally, we call this food. Clever man, however, differentiates himself not in his inate nature, but in his clever ability to have made previously inaccessable energy accessable for consumption. We domesticated plants, then animals, and relied on forced slavery and indentured servitude to provide make more energy accessable. But these “tools” are limited in their ability to unlock additional excess energy to harness and consume. But Clever Man wasn’t done. He then figured out how to convert fossil fuels to energy and the energy genie was out of the bottle. With all that additional energy now accessable, we did what species do… we grew to consume it. We used it to create more and more food, more and more economic wealth. More food to consume leads to more of a species. And here we are.

    There’s a real question about feeding the population. But the question isn’t whether we have enough food to do so. It’s whether we do so by sharing what we have or by trying to always grow more. Food production continues growing not primarily because we don’t have the food, but because of the inequality of distribution and the economics of agriculture. There is enough food produced globally to provide every human a very healthy (2Kcal+) daily diet, but the food is not made available equitably. It is rationed, primarily by price. Politics, economics, and human nature prevent us from sharing what we have in a truly equitable manner. Absent this option, we are faced with images of starving children. Clearly, we must act, so we are led down the path of trying to always produce more. More food to consume leads to more of a species. What puts this option on the table, for now, is accessable energy. Look at Tom’s last figure. At some point, this option will be off the table. At that point, the amount of available food will no longer be able to grow and will, in all probability, begin to decline to levels much lower than today (some of this depends on whether humans can really be “wise” and not just clever; for instance, can we widely convert from mass-agro-business to well-understood, intelligent and sustainable permaculture techniques, or do we just keep whipping the horse until it drops). What will we do then? What will be the effect on population? Practically speaking, the effect of less accessable energy on human population is likely to be precisely the same as it is on every other species.

    Why is it that humans presume that we are inately different from all other life forms? Why is that we assume that natural laws and limits that are entirely consistent across all other life on this rock don’t apply to us? Why do we make these assumptions in the face of graphs like the ones in this post? As a species we may be much more like yeast than we want to believe…. that is, yeast with money, guns and lawyers.

    In reality, I don’t think we have resource problems, or a climate problem, or an ocean problem, or a fresh water problem, or a soil problem, or a biodiversity problem. What we have is a human behavior problem. All of the others are the result of this one. Unfortunately, the large scale behavior of humans appears, based on observation and the historical record, to be much less conscious and intentional than unconscious and instinctive.

    Look at Tom’s last figure. Then look up what happens to populations in closed environments. The question is, can humans (as a species) change their nature and, if you think they can, will they? Or are we, actually, just well-read yeast after all.

    • All of what you say seems correct. However, nothing stops us from educating everyone that when you have more than 2 children, you are attempting to grow the next generation and that is a deadly thing to attempt on a finite planet.

      In other words, there is nothing that stops us from learning and committing our self and our selves to limiting the number of births we create such that our numbers drop.

      We must average less than 2 children until we are no longer consuming resources, that we depend upon to keep our numbers alive, faster than they renew.

      • No doubt John, that is the challenge. And you are absolutely correct that the logic of reality requires that we try to make sure that education happens.

        My question is whether that is actually possible. Clearly, we can tell people what reality is. But, can we make them care? Even more, can we make them act? In some ways, this seems to me a classic horse-to-water problem.

        The difference is that it is in the horse’s nature to eventually drink, but I’m not sure that it’s in human nature to have fewer children.

      • “However, nothing stops us from educating everyone that when you have more than 2 children, you are attempting to grow the next generation and that is a deadly thing to attempt on a finite planet.”

        I have to admit that I have become quite a bit more cynical over the last few years after having learned about how the financial and economic systems work. Our leaders have no interest whatsoever in informing everyone of the perils of having more than 2 children. This probably has three contributing factors.

        Firstly, most of our leaders are delusional power-mongers who probably place their faith in the ability of Treknology to save us. “Wow, look at this iPhone! Look how much better they get every year! Surely technology will be able to solve our energy and food problems!” And this is a difficult argument to refute in only a few sentences, especially given all the advances made via the Green Revolution. It takes more than a few short sentences to explain where the gains actually came from, why they are now diminishing, why they cannot be expected to continue, and why things will soon reverse. This unfortunately seems to be beyond the attention span of our leaders towards understanding these issues. Even then, when presented with the facts, they may still disagree on ideological grounds because most leaders aren’t rational people. They surround themselves with the advisors they want to hear.

        Secondly, even if they did understand its perils, our leaders have zero incentive to halt population growth. When growth stops, we get unemployment and financial disasters. Politicians want us to remain more-or-less satisfied and placated, and it is political suicide for any politician to enact policies that would hurt people today for the sake of a better tomorrow.

        Thirdly, our economies are set up so that the elites in charge can perpetually steal from the masses. This requires overall economic growth, to prevent the middle class from becoming lower class. This theft is effected through the design of the debt based monetary system which enslaves everyone and forces them to go to work to feed the empire. More recently, over the last few decades, the derivatives ponzi scheme has made this theft of the middle class’ wealth even more lucrative and brazen.

        In a way, our economies can be understood to be no different fundamentally than any animal population. Every animal in a population strives to maximize the amount of energy (complex carbon molecules) it can acquire and burn, or provide to its offspring. People in our economies act exactly the same. The lower and middle class aims to get ahold of enough carbon molecules to eat, or raise a family and then die. The upper class strives to steal as much carbon from the lower and middle classes as possible, as well as gaining ownership of the productive assets that provide that wealth. In this system, everyone is trained to act this way, and you can’t really function normally unless you do. To think that we can voluntarily stop, I think may be asking way too much of our species. We’d have to undo millions of years of genetic hard wiring.

        Growth is baked into our economies to their very core, and growth will not stop until it is forced to stop after things collapse because we’ve used up the resources to support growth.

        • Sorry, but you are confusing the desire for economic growth and per captia growth with averaging too many children. The two are different. While every individual and countries and corporations all have a desire to increase their market share, profits, wealth etc, they have provided no significant influence on the number of children we average. There are no coke commercials that hint or suggest that we should average more babies to increase the consumers for coke. It is true that many people in government are confused and think that we need to make more babies to fix social security, and many think that the economy will do better if we do not average less than 2 children, these views are totally driven by ignorance.

          The scientists that have provided the concepts that the economy suffers when we average less than 2 children are oblivious to the fact that we have always been at the limit, where births kill children. They have never factored that into their studies. They never factor in the fact that we cannot keep 7 billion alive without consuming non-renewables. Instead of recognizing that we are destroying a huge energy store, which is equivalent to draining a bank account, economists treat burning oil as a positive economic activity.

          In short, the education must start with the scientists that we are taking our information from. We must not draw conclusions about whether this is possible to change or not. We must act.

          • Here in Canada, the government provides significant financial incentives to lessen the burden of parenthood, in effect encouraging people to have more children, because I believe, although I’m not sure of this, that our replacement rate is less than one.

            But that is countered by the fact that pretty much every country that has an otherwise declining population due to low birth rates makes up for that by immigration (in the Western world, I’m not too sure about Eastern Europe). Canada and the USA both have very significant immigration programs. This is how we effect economic growth, because without population growth, you can’t have economic growth (at least, in a modern industrialized country that has no opportunities left for productivity improvements).

            The one exception to this is Japan, which has a xenophobic attitude towards immigration; there basically isn’t any. Their population is declining. And they also have the highest official debt-to-GDP ratio in the world, upwards of 300% and growing. Their economy is crashing and will burn. Economists actually call the previous decades of slow and negative economic growth in Japan the “Lost Decade”, believe it or not.

          • Sorry Mark, but very little of that is accurate.
            “replacement rate is less than 1” is at best not any standard terminology. Canada’s fertility rate is about 1.6, which yes is well below replacement rate and not much higher than China’s.

            Modern industrialized countries in fact have rising productivity, and rising GDP per capita; progress may have slowed but it is by no means done. Both new technology and accumulating more capital per labor increase productivity; adding people is not needed for economic growth.

            Japan’s lost decade is famous, but their economy isn’t crashing and burning, it’s limping along. May even pick up now that Abe is trying out looser monetary policy. At any rate, they’ve managed positive GDP growth over the last two decades despite the declining population, hardly a crash… in fact, looking around, the existence of a real Lost Decade is disputed, as it’s not evident in standard of living, GDP, or GDP per capita terms, just a somewhat higher unemployment rate and loss of the 1980s excess.

  20. Tom,
    You correctly point out that adding Americans results in much greater added energy use than population increases in other countries, and advocate fewer Americans as an answer. Of course, you use increases in population as your metric rather than a comparison of native birthrates, which means that the US (with the highest immigration rate in the world) shows more growth in your data. The US takes in about 1.4 million immigrants annually. It has a native birthrate of about 4 million per year and there are 2.5 million deaths, so the net annual population increase from US natives is 1.5 million. Immigration therefore accounts for about half of our high growth rate in both population and energy use.

    All those immigrants end up using as much energy per capita as the native born. China and India are 2nd and 3rd in rank for supplying immigrants to America, so these countries are essentially outsourcing the energy use of these people to the US. Before castigating (or castrating) ourselves, shouldn’t we credit those countries with the energy their former citizens now use? Using your data, one could argue that preventing all immigration to the US would save just as much energy as curtailing our own reproduction.

    Fortunately, reproduction and immigration are both energy dependent. The US has the highest immigration rate in the world partly because it has attractively large per capita energy flows. Given that the future of inexpensive energy is limited, reproduction, immigration and per capita energy use are likely to decline naturally over time without a need for social engineering. I believe (and suspect that you agree) that Americans should strive to produce only those children they can afford, limit energy use as much as they can, and continue welcoming immigrants. As energy availability declines, population and energy inequities will also eventually decline.

  21. “surplus energy grows babies.” is too ambiguous. Do you mean it enables the creation of babies, or that it allows babies to grow? If you are saying that it allows babies to grow into adults, you are correct. I suspect you mean that surplus energy grows a larger population.

    This article and all population experts are dreadful at differentiating between creating babies and population growth. The two are not the same. We humans have always attempted to grow our population exponentially. That attempted growth can only be stopped by the death of children. If we are unable to expand our environment, and we average say 3 babies, then 1/3 children will die. If we average 4 babies, then 1/2 of all children must will die. If we can expand the environment, by burning fossil fuels in larger and larger amounts for example, the population can grow, which means the child mortality will be lower for a given average number of births.

    Has it ever dropped to the point where we can say that births are not killing children? No, it has not. Because we have always suffered significant numbers of competent individuals dying of starvation.

    The problem is not a growing population. The problem is that we are attempting to grow the population. That attempt happens when we have more than 2 babies. When you create 3 babies, you are attempting to grow the next generation by 50%. This is a murderous act on a finite planet. This tells you your moral responsibilities when it comes to making babies.

    I agree that a birth in the USA is much more deadly than a birth elsewhere. That birth will consume more resources than a birth elsewhere, thus contributing more to the evil tradeoff of one new life for a portion of an existing one. Births anywhere in the world contribute to the death of a child.

    • Actually, in the last century or so, it indeed has become the case that births are not killing children. The future is not quite evenly distributed, but famines in the 20th century, especially latter 20th century, have tended to be due to mismanagement or wars rather than intrinsic global shortages.

      Birth rates themselves are plummeting worldwide. In the last few years we’ve had Peak Children; all we need to do is stay the course and we’ll have Peak Population when those children hit adulthood, in a few decades. With a bit of care, nobody needs to starve ever again.

      • “Actually, in the last century or so, it indeed has become the case that births are not killing children.” This is false. You cannot use “intrinsic global shortages” and the quantity of famines as any proof one way or the other.

        First, famine is not a requirement for being at the limit. Famine is a large amount of starvation. Second, we have significant starvation deaths every year. These starvation deaths are generally grouped together and consist of humans that are not incompetent. These starvation deaths prove that we are totally capable of having the record high average standard of living and record high adult life expectancy and STILL be suffering deaths caused by too many births. As a thought experiment, take all the people that died of starvation last year and put them on Earth without any other humans. Would they all die? I am sure they would have a horrid death rate, but it would not be 100%. They would muscle other animals away from the food they need. They were not capable of muscling other humans away from the food they needed.

        There will always be a proximate cause of death. Of course people die due to mismanagement. Of course people die in wars. The existence of these proximate causes of death do nothing to prove that we are not pumping babies into the world faster than we can provide for them.

  22. Restricting one’s family size to one child and two at the most, is the optimum policy. This would not only stabilize but also slowly but surly decline population in a socially and economically manageable way.
    Apart from all the economic reasons analyzed in the article, there are the cultural, religious and social reasons why people want large families. There is plenty of anecdotal evidence in this respect, but the one that annoys me is the South African president. He has 6 wives and countless children, all living in luxury at taxpayers’ expense. He sees it as his cultural heritage to afford those wives and children.
    He is culturally very selective in that his economic lifestyle is based on western values and he heads a country with a constitution based on western values.
    Breaking this cultural nexus is just as important as the economic one.

    • In 2013, the optimum cannot be limiting family size to 1 or 2. That ship sailed 50 years ago. Now it would have to be an average of 0.1-0.2 children to make a difference, i.e most people going childless. We know what the chances are of this happening

  23. The per capita approach basically gives China and India a free pass (and they will continue to milk this), but is it deserved? Both countries have millions of people who consume and emit next to nothing, and a small population of the worst emitters on earth. I’m not sure your analysis does this justice.

    Say China eliminates the one-child policy and instead adopts a 10-child policy. The population curve exceeds the energy consumption curve, and, according to your per-capita analysis, they will soon be the lowest emitters and consumers in history (lower than the Aztecs!). Progress!

    Consider modelling on a per-square-km basis. After all aren’t we really stuck with a finite amount of earth, rather than a variable amount of people?

    • Of course prices change the actions of people. We have no clue how to feed 7 billion people without burning oil, and we know oil will become scarce. This tells us that given what we know today, we are acting in a manner that will cause premature death. The action that is murderous is making too many babies.

      Of course the absolute cost of oil will rise as it becomes scarce. Of course this will change our actions. No economic study can possibly prove or predict we will or will not have premature death as a consequence. Economics is fundamentally the wrong scientific technique for this job. It measure relative wealth. It does not measure premature death. This topic is about absolute wealth and premature death.

      There is no excuse to assume we will be able to find a substitute and keep our numbers alive as this energy source becomes scarce.

      • “We have no clue how to keep 7 billion humans alive at one time without burning oil”

        Sure we do. There’s no specific dependence on oil. There’s dependence on energy inputs, but that’s very different. We need artificial fertilizer and fuel for machinery, both of which can be synthesized in general. Nuclear power or solar power[1] will do fine, though at higher cost.

        Sidenote: most ammonia fertilizer is made with natural gas, which provides both energy and abundant hydrogen atoms, not oil. Not that this changes the real point about fossil fuel dependence, but it counters some of the oil fetishism that’s out there.

        [1] Storage is less of a problem for industrial purposes; if storage is expensive it can be cheaper to build twice as much of power unit and factories to run during the day and idle at night, vs. homes or businesses needing nighttime A/C, fridges, and lighting.

  24. I am stumbling on something that seems to throw these results off. And that is that China’s CO2 emissions are now much more than America’s and soon will be in fact double America’s. Currently increasing at 10% per year. The absolute magnitude of this problem seems to undermine your analysis that American population increase is more of an energy problem than Chinese population increase.
    What is going on here? There are many more Chinese babies, associated with increased CO2 emissions, relative to America. So apparently each Chinese baby is ‘less of a problem’ than each American baby. But that analysis breaks down because the magnitude of the impact of CO2 emissions from China. It doesn’t matter that each Chinese baby is less of an energy sink when there are so many more Chinese babies. Also Chinese emissions are soaring and American emissions are declining. So the trajectory is in fact that we will all be destroyed by Chinese carbon emissions – that contradicts your analysis.

    • Chinese emissions are effectively the western world’s emissions, as they have taken over most of the world’s manufacturing. The average Chinese person doesn’t consume that stuff; it gets sent overseas.

      This was a monumental shift away from the USA over a period of a few decades, effected by currency manipulation on both sides of the Pacific, to prop up the dollar and devalue the Renminbi. It’s actually a very important and interesting situation in the world of economics because it’s not at all sustainable and we will soon see the US trade deficit end, and the loss of its global reserve currency status. The world will soon be a very different place.

  25. I’m sorry, but I think you’ve got this completely wrong.

    Don’t get me wrong; I can see why the idea has it’s attraction, and I can see the correlation between energy and population (as a computer engineer – I can see its elegance, and once I would have agreed with you), but I don’t think that it is causation in this case.

    The best way to understand population growth isn’t at this big macro level, it’s on a micro level, and can be summed up by a single question. (hold off on energy for the time being)

    “What are the costs and benefits to me of child ‘n’ ” where the magic number of ‘n’ is 3.

    If you do this exercise, first from the mindset of a rich person in a ‘western’ country, then a poor person in a poor country, you’ll very quickly see why population drops for richer countries.

    In a rich country, children are horribly expensive. You need a larger house, long years of education, and there’s a huge opportunity cost to the parents in terms of time and resources.

    Critically, the higher educated the woman (traditionally the person who has to raise the child), the greater the opportunity cost of taking time off to raise the child (still the norm in most countries)

    In return, in rich countries, especially those with a level of social security, children aren’t expected to give back financially to parents.

    Yes there is a biological imperative to breed, but the first child and possibly second tends to satisfy that.

    In the west, in short, children are expensive hobbies.

    In developing, especially agricultural, countries however those costs and benefits are different. There is no social security, so children are a parent’s retirement investment, and workers from a young age. Women have little education, so there is little opportunity cost for child rearing, moreover high infant mortality means that more children must be raised to have a hope of children surviving to adulthood.

    Think I’m wrong? Look for the correlation between infant mortality and population growth. Population growth drops *after* infant mortality drops. As people get used to the idea of their children surviving to adulthood, they have less.

    And the correlation between energy and population? Let me put another hypothesis to you. More people use more energy. i.e. the population causes the energy increase, not the other way around, as more people find and exploit energy sources.

    The good thing about thinking about the problem this way is that population becomes a very solvable problem, with no draconian measures needed.
    1) Good healthcare – prevent infant mortality, so that people don’t need more babies
    2) Some sort of social welfare, so people don’t need kids to look after them in their old age. (notice how the REALLY low birthrates are in socialist countries?)
    3) Education, especially of girls. This makes kids more expensive to raise, so people have less.
    4) Birth control, so people have a choice.

    Population, I’d argue, is a ‘previously solved problem’ – basically western (perhaps more european) culture.

    And so the problem of how to solve the greenhouse issues becomes a technological one. How do we provide a western style lifestyle with zero emissions and no fossil fuels? This I’d argue (and reading your blog, I know you agree) isn’t an unsolvable issue either.

    • I generally agree with how you describe people’s decision making on the micro level.

      But I don’t agree with your prescriptions – those ignore the rate problem. The problem isn’t “How do we lower the global population?”, the problem is “How do we get back within the carrying capacity of the planet in time to prevent the collapse of civilization?”. That’s a very different problem to solve.

      • If people can have a western lifestyle (comfortable, high cost, high energy use) without fossil fuels, why would civilisation collapse?

        There *are* other energy sources available, and huge efficiencies yet to be gained. We just don’t use them much yet. Those will become more viable as fossil fuels dwindle and become more expensive.

        Like I said (and you said), the problem isn’t the population. It’s how we have the western lifestyle without the environmental cost.

        • Yeah, France shows you can get 80% of your electricity from nuclear power at a large scale. That’s not all the energy we need, but home insulation, heat pumps, and electrified transit make up much of the difference without having to get weird.

          If more expensive energy halved US GDP/capita, that would still put us in the First World, if the lower end. Portugal, Spain, Greece. Though per an earlier point I made, I grant those don’t have to spend much energy on climate control.

        • There is no way for 7 billion people to have a Western lifestyle on alternative energy sources.

          It’s highly unlikely even the 1 billion who currently do could maintain it on those.

          Also, something I did not say in the post above (but said one other post here) is that 7 billion would be too much even if they lived a subsistence-farming lifestyle. We tend to focus on CO2 emissions and other global metrics, but an overpopulated village in the Third World can very successfully wreck its local environment just by collecting firewood, poor farming practices and hunting for bushmeat. A lot of such villages exist in the Third World at present, and all of the Third Wold that has not yet reached that point is heading in that direction because one thing that is true about the demographic transition theory is that poor uneducated people do not stop at two.

          You need the whole world to be at a level of education and environmental awareness that will allow it to consciously and voluntarily limit its fertility so that we never exceed the carrying capacity of the planet again. But you can only achieve that if each and every human being lives a lifestyle that allows that slow and laborious process of education to take place. That takes some minimal level of resource use, not on the level of the US, but certainly not as low as in Chad either. Which in turn puts a hard limit on how many people there can be in the world as a whole, and it’s nowhere near 7 billion, it’s likely in the hundreds of millions or less

          • “There is no way for 7 billion people to have a Western lifestyle on alternative energy sources.”

            Technically, I disagree with you but practically I agree, given human nature. It is theoretically possible that we could have a nice electric transportation infrastructure and recycle all our old materials to build this out, along with other technology. It could all be powered by solar panels on everyone’s roof (virtually limitless potential), and everyone could have some battery banks to tide them over during bad weather (I know Tom’s Nation-sized battery post calls the possibility of that much battery power into doubt, but I think technically it could be done if we all recycled and moved in that direction of treading lightly and wearing sweaters when needed.) We could live low-carbon lifestyles and for those applications specifically needing carbon chemistry feedstock, we could use some biofuels for that.

            We’d all take care of our local ecosystems and only buy environmentally friendly food that doesn’t require unsustainable fertilizers and farming techniques.

            This would be different than the way the “first world” is organized today, but it could still be a very comfortable way of living.

            Will that happen, given the mentality of the public dialogue on these topics, and the direction our leaders seem to be taking us? IMHO, not a chance.

          • [edited for family-friendly language–ironically]

            “There is no way for 7 billion people to have a western lifestyle on alternative energy sources”

            To play devil’s advocate, why […] not? Do you have any real physical reason why say 9 billion (let’s up the ante) people can’t have nice lifestyles with big ass csp plants in the deserts and wind and nuclear power and hydro etc? And even if there is some physical reason that that is impossible, is that even a big deal? It’s not like we eat electricity.

            I’m not talking tomorrow obviously, but transitioning over 50-100 years. I don’t see why not.

            As for voluntarily and conciously limiting fertility, no one needs to do that. You need to read my first post again. Healthcare, education, social welfare, birth control, and fertility drops. The country doesn’t even need to be rich. Look at say Bangladesh or Greece (remember when Greeks had big families? No longer. )

          • There something called Liebig’s law of the minimum, which states that growth is limited by the scarcest limiting factor.

            Ultimately, energy is that factor because if we had unlimited energy, we would not be facing any other material limitations (though we would then simply cook the planet, as explained in one of the very first posts on this blog).

            But more directly it can be many others. Agriculture at present feeds 7 billion by an extensive use of petroleum and natural gas-derived fertilizers and pesticides. Without those, yields will plummet. But even more crucially, it is also dependent on phosphorus fertilizers, and phosphorus is also a finite resource, that is mined and will peak and be exhausted at some point. Reduce the maximum possible yields even further once you account for that. Then there is the even more long-term factor of soil degradation, which is the direct and inevitable result of agriculture itself, unless it is practiced with extreme care to limit that (and that is almost invariably not the case) or you happen to live around some volcanoes or a river that floods to replenish it.

            In the same time arable land is also a very limited resource and it is an extremely bad idea to convert whatever wild areas are left into feeding lots for humans, for obvious reasons.

            Put all these considerations together and tell me how exactly we are going to feed 7 billion people, let alone the projected 10-11, or the more likely without a dieoff event between then and now 12-15 billion?

          • Phosphorus can be recycled.

            And increasingly the limiting factor on population growth is women’s desire to have children. Something we should welcome, not deny.

            Some people are as attached to unavoidable doom as others are attached to endless growth.

          • Sure, once it’s flushed into the ocean, it is recycled. On a time scale of hundreds of thousands and millions of years…

            Also, it is not substitutable at all.

    • Ben said:
      “I can see the correlation between energy and population … but I don’t think that it is causation in this case.”

      You make some good points on the micro level about why fertility rates drop as societies become “developed”, but you may be brushing off the correlation with energy too easily. I think you need to take a step back and look at the macro level and ask why it is that “non-western”, undeveloped countries provide(d) the social and financial incentives to have lots of kids while developed ones present the opposite incentives.

      Could it be that the “developed” countries of the west incentivize low birth rates because they are also resource hogs? In order to extract and use lots of energy and manufacture all the gizmos to do this and supposedly improve our lives requires lots of technical jobs.

      Could it be that in undeveloped nations (with the Middle East theocracies excepted) with historically higher birth rates, the majority of the energy people use (and expenses people have) comes directly from the land, in the form of food and biofuels? That’s manual labour, and well suited to children. As countries “develop”, a greater proportion of the energy use comes from non-biofuel, non-food based sources — which basically just means fossil fuels (i.e. biofuels from 100 million years ago). And a society built around that kind of more technical energy does not suit itself very well to child labour? In this case, children are a drain of energy, because the parents have to go out and work for money (which is fundamentally just a claim on energy) to support the kids. In non-mechanized agricultural societies, kids can soon become a net supplier of energy to the family, because they’re out there harvesting ecological productivity directly.

      “the population causes the energy increase, not the other way around, as more people find and exploit energy sources.”

      I don’t think it’s about one-causes-the-other, it’s a process that is mutual. And it is more than a greater population using more energy — it’s a greater population (attempting to) use vastly increasing amounts of per capita energy as well. It’s multiplicative.

      • Given that population growth even in the third world happens in cities for a large part, I don’t think that’s the case. At most indirectly, as societies that used to be agricultural had their value system influenced by that economic undergirding.

    • People say population growth in a single country boils down to having children. But that’s because they explicitly (they say it themselves) do not count immigration as population growth, even though it’s making the population grow. When you do count immigration, western countries populations haven’t stopped growing at all, which means they haven’t broken the link between energy use and population growth.

      If you switch from a national to a global scale, then it stops being true that population growth through having children is a previously solved problem, because it clearly isn’t, in that arena. The whole argument is like a magician’s pea-counting trick, who carefully moves the peas around so you can’t see that some of them aren’t being counted at any point.

  26. “Maybe this shouldn’t be too surprising from the perspective that economic powerhouses are dependent on growth, and a flagging population is a recipe for recession.”

    Some of that is because of the way we define recessions. Consider two economies. In the first, population is declining but productivity and per-capita consumption are increasing. GDP in this economy nets out as slowly shrinking. In the second, population is growing, but productivity is declining slowly and per-capita consumption with it. GDP in this economy nets out as slowly growing. By the rough rule of thumb that two consecutive quarters of shrinking GDP makes a recession (the NBER’s decision includes more variables, but the two-shrinking-quarters rule is a good approximation), the first economy is in a permanent state of recession even though the population is becoming steadily richer. The second economy is not in recession, even though the population is becoming steadily poorer.

    Economics as a social science has developed during a period of history when all of the numbers — population, productivity, consumption — ran in the same direction. The definitions and measurements that emerged are ill-suited to a period when that’s no longer true. Consider how much different public policy might be if the measure of “success” were not growing GDP, but growing median income.

  27. Tom,
    This is a great blog and now that it is on my radar I will be visiting regularly. I am not a physicist and appreciate the way you have used the numbers to make valid points. As a health provider working in both developed and developing countries I would like to weigh in on some potential social deterministic impacts here.

    Low income developing countries, like many Sub Saharan African nations, have high birth rates in order to off set high child mortality rates. If one in five African children die before age 15 and these children are a family’s labor force then a surplus is needed. As a country moves from a low income status to a middle income economic status the delivery of health improves, child mortality decreases and the need to have a surplus of children to replace those lost to childhood illnesses and accidents decreases.

    Is it possible the lower end of the U logarithmic curve’s energy use is due in part to the use of alternative energy sources in some countries that we just don’t seem to be able to achieve here in the US?

    The upswing to the curve, as you said, may very well reflect immigration patterns and improved health delivery (although I question that in the US) but could it also reflect an increase in poverty and disenfranchised populations in the US?

    One final note: I feel much like you do about feeding the world. While our intentions may be good it has potential negative consequences and must be well thought out. We have succeeded in delivering to developing countries the same bad nutritional choices of food that have resulted in our own epidemiological transition from infectious diseases to chronic ones like cancer, diabetes, obesity and lung disease. The globalization of food and energy has resulted in a striking surge in chronic diseases in developing countries that is beginning to mimic patterns seen in OECD nations including the US.

  28. It seems much of your argument about not having a baby relies on the set of charts in “Where is the Real Population Problem?”. However, these charts simply show that the US is highly developed and a large country. What happens when you compare to the EU as a whole? Would your decision, or argument, change if you lived in one of those countries or Canada?

  29. I’ve long puzzled over the so-called “demographic transition.” Supposedly, affluence causes a reduction in birth rates.

    I think this is true if you narrowly define “affluence” as “access to energy.”

    Throughout the ages, we’ve bred our slave labour force and retirement support. But with cheap energy, we can “buy” labour and retirement.

    It will be interesting to see what happens in the upcoming phase reversal.

  30. Tom, your decision not to have a child is depriving the world of exactly what we need – people with reason, education, vision, and motivation to look beyond the headlines and into the facts. I believe someone said “We are first-derivative machines…we would do better with second-derivative sensitivity.” Oh, wait, that was you. Sure you wouldn’t mind just one second-derivative? 😉

    • Exactly. If people who have the inclination and the knowledge to live within their limits don’t pass on this attitude to their offspring, the next generation will descend from breeders only. Self-sacrifice is not always a good idea, even if it feels noble.

  31. For a more optimistic view, watch some Hans Rosling of Gapminder…[1]

    The future is not assured, but there’s a very plausible path that we can take through the 21st century with good outcomes all around. We may need to work for it, but there is good hope.


  32. [shortened by moderator]

    I want to recommand a book. “Too smart for our own good” from Craig Dilworth, edited by Cambridge university presss. A great book that shows with score of historical details the vicious circle that links demography and technical innovation and that leads to irreversible ecosystem degrading and possibly to our future extinction.

    (note: technique, when generalizad in its use, is a mean to break an equilibrium in ecology to exploit an environement unsustainably, ie to get more than the equilibrium productivity can assure)

    This book does not solve your issue but shows how profund is this link and the present technological surge should not be an exception: it is necessarily not “free” but pushed by the needs of a growing population in a degraded environnement and it must give room, as it always create a surplus if successfull, for further population growth. As the author shows, the vicious circle is now even cycling faster and faster.

  33. Tom: This is provocative. Thanks for your blog.

    I often reference Murtaugh and Schlax’s 2009 paper “Reproduction and the carbon legacies of individuals” ( in my classes.

    You might like Figure 7, which “presents average carbon legacies for the 11 most populous countries in the world, with ranges corresponding to the different
    emission scenarios. Each legacy is the sum of the lifetime emissions of the ancestral female subject to the 2005 fertility rate, plus the weighted emissions of her descendants, assuming all future reproduction follows the medium-variant projection of fertility for her home country. The range of values is enormous: under the constant-emission scenario, the legacy of a United States female
    (18,500 t) is two orders of magnitude greater that of a female from
    Bangladesh (136 t).”

    This then sets up the nice Table 3, a comparison of “lifetime emissions of CO2 saved by different actions” including greater fuel efficiency, less driving, window upgrades, lightbulb upgrades, over-the-top recycling, and… reducing your number of children by one.

    This will not surprise you: the savings of the last action are nearly two orders of magnitude (~9,400 metric tons) greater than some of the others!

    • ” assuming all future reproduction follows the medium-variant projection of fertility for her home country -”

      But this is in average wrong. Bengali do emigrate and so do niger, mali, somali people, given the disatrous situation their land faces.
      This completely changes the result. See my post above.

      Look at USA. White people are about to become a minority. If we would cling to your way of accounting, we would be completely unable to explain at least half of USA present emission.
      Some years ago they would have shown a graph with a mexican woman and the low emission of her theoritical offspring.
      Today, there are mexican that drives SUV in the US. Besides even in Mexico, use of energy have changed also.

  34. My brother-in-law happens to be associated with the Max Planck Institute for Demographic Research and I so I figured I’d run this blog post by him. The topic isn’t within his specialty (“evolutionary demography,” i.e., what evolutionary processes promote various demographic patterns in various species), but anywho… here’s what he wrote back to me:

    I just happen to know people who have been working on this question for some years, and the short answer is, “it’s complicated.” It is certainly not true that when the US had energy consumption as low as Bulgaria’s we had intrinsic population growth rate as low as theirs, nor that if our per capita energy consumption was to rise as high as one of the gulf oil states that our fertility would increase to their level. In other words, one has to look at the pattern of change within each country over time, rather than across countries at a single time. And when one does that, the pattern for the last 150 years is pretty clearly a decline in fertility (as well as mortality) leading to an overall decline in intrinsic growth rate with increasing energy consumption, but only up to a certain point. Beyond that point, the effects are small enough that depending on how you set up your regression analysis, you can find that there is a small effect for continued decline in growth, or a very slight rebound (increasing growth with greater wealth). Before the last 150 years things are even more complicated, as we basically have no reliable data, but clearly for a long time technological advancement led to lower mortality and improving nutrition.

  35. I seem to get a different take away than most from Tom’s graphs. The U-shaped ones, especially. By all means, let the poorer countries who are consuming less move to the right and decrease their population growth. But more significantly, we need to get people in the richer countries to consume less. If Tom’s graph is right, this will bring their population growth down, but even if it doesn’t, it would make a really significant reduction in use of energy and other resources. And that in itself would solve a great many of the world’s problems.
    Of course, you will say how can this be done — the rich countries won;t stop consuming. But I didn’t say the rich countries, I said the people in the rich countries. That’s us. And reducing consumption is certainly something we can choose to do. If people in the US are using 20 times as much energy as those in Africa, every American who cuts his consumption in half has the same effect as 10 Africans dying.
    For me, this is the real elephant in the room. Rather than discussing actually doing “voluntary simplicity” or “deliberate descent”, which are actually possible, we’d rather consider the most extreme schemes for limiting population.

    • But as I said, I don’t think the U-shaped graphs are right, in any meaningful sense. Jordan’s data point seems likely to be outright *wrong*. And for the other labeled countries at the bottom of the U, they’re having ‘declining population’ through substantial emigration. It’s not that moderate energy use means crashing population, it’s that several countries with moderate energy use are Eastern European with crappy economies and easy access to better life in the EU.

      Or hey, Russia. Russia was having negative population growth after the USSR fell, and is probably too big for emigration to be the answer. Instead: alcoholism, unemployment (and lack of purpose), and maybe a hollowed out health care system. Not exactly a recipe to imitate.

      There’s no real reason to think “using less energy will lead to less population growth” except maybe in a dystopian sense where we can’t use fridges any more and get food poisoning more.

  36. All of this talk is quite interesting. However, if you don’t think the benign demographic transition will prevent collapse, then the discussion regarding future fertility rates is pretty darn useless. Why?

    If preventing collapse requires a human population of only 4 billion, then a three billion reduction. Right now, humans increase at about 200,000 per day. A reduction of 200,000 per day (quite severe) would take about 15,000 days or 41 years.

    • 1. That 200,000 a day increase is the result of something like 400,000 births minus 200,000 deaths. Remove 380,000 of the births, and you will get the roughly 200,000 decrease without any real pain being inflicted to anyone apart from people making a fuss about going childless and never retiring (but those are completely insignificant issues given what is at stake)

      2. Population dynamics is not really a linear process – in the above scenario the decrease in population will accelerate with time as the population ages and the natural death rate increases.

  37. Looking at the chart of income versus CO2 production, the countries with high income but low emissions ( bottom left of the chart ) – France, Sweden, Switzerland and Hong Kong – all get about half of more of their electricity from nuclear power. Hopefully some of the higher emitting countries with ambitious nuclear build plans – Finland and Korea especially – will migrate down to join them within the next twenty years. Followed by everyone else.

    • What you say isn’t really true, though vaguely true in spirit. France, yes. Sweden and Switzerland each get over half their electricity from *hydro*; nuclear makes up the rest, about 40%. Hong Kong gets over 3/4 of its electricity from coal or natural gas, the rest is nuclear — a percentage comparable to that of the US, which is actually slightly cleaner percentage wise. Hong Kong may simply use less power; probably more importantly, Hong Kong is dense with good transit so will see much less driving, and it’s a hot country with I suspect not much industry, so there’ll be much less fuel burned for heating. So it can emit less carbon per GDP without having cleaner electricity, because electricity isn’t all that matters.

      • Electricity is a good start, and should be the easiest sector to decarbonize. I stand corrected on Hong Kong, but hopefully not for long- they should have 1600MW from their first French-designed EPR by the end of this year, and the same again from their second a year later.

  38. I have a few quarrels with this post, as do other commenters, to wit:
    – The thesis depends too much on tiny rich countries like Qatar, Singapore or Luxembourg, which should be expected to be outliers.
    – Using population growth rather than fertility is misleading if your thesis is that “energy makes babies”. When fertility is plotted against affluence and small outliers are excluded, the negative correlation is very consistent (

    Population growth includes immigration, which is especially high in some of the tiny rich countries mentioned above, and it also reflects population inertia (or population momentum) rather than the rate of baby-making. Population inertia is so little known and understood in lay circles that it deserves some explanation. In the long run, a population will decline if its total fertility rate (the number of children per woman, TFR) is below replacement (about 2.1). But in the medium term, its demographic trajectory is dependent not just on fertility but also on the age structure of the population, i. e. the share of the (female) population that is iof reproductive age. Global fertility is currently well above TFR (2.5) but it has been cut in half since its peak around 1960 (look it up on google public data) and is declining further. However, because of past growth, population inertia saddles us with a growth bulge that will boost birth rates for several decades more until stabilization and then decline will occur globally.

    Ultimately, the “bulge” will move up the population diagram and for a while increase the share of old people, whose care will require more of society’s resources (the famous “greying” of the population). Due to this age structure, the death rate increases, the birth rate decreases and population decreases substantially. There is now, especially in affluent countries and especially in the US, an increasingly vocal campaign in favor of higher fertility in order to avoid the “demographic crisis” thought to be associated with greying. It is based on flawed demographics and flawed economics. It is important to understand that given current demographics, greying is an indispensable phase in the demographic transition. There are only two ways to avoid greying: continue population growth indefinitely – which isn’t possible – or decrease life expectancy, which is possible but not desirable.

    In discussions about demographics, one often encounters the argument that individual countries should aim at population replacement or even some growth – just not too much. But if all countries were to follow that policy, we’d never reach stabilization! Global demographics is the average of hundreds of individual populations. For the average growth to come down to zero, some must be below zero to compensate for those above zero. Even worse, if each country tried to limit its share of older people under a certain threshold to reduce the burden on retirement and health care systems, no population would ever reach stabilization. Again, no stabilization without greying!

    Now we must confront the core economic argument, which sadly pretty much every wannabe expert has bought into (and which Tom has echoed in his remarks about Germany): does greying inevitably lead to economic crisis, bankrupted retirement systems, and labor shortage? The argument is that a shrinking working age population must provide for an increasing retiree population. What is always ignored, amazingly, is that children also need to be provided for. In the very instructive case of Japan, in 1950, 35% of the population were children and 5% above 65. Now, about 13% are children and 22% above 65. The share of the working age population has actually increased! At the same time, the labor force participation rate has also increased, women have entered the work force, and productivity has gone through the roof anyway. Economically, there is no question that even a slowly shrinking labor force can provide adequate living standards for a slowly greying population. That is not to say that demographic change doesn’t pose problems – change always poses problems. But they are more likely to be social and political than economic. Politically, the challenge is that while most children are being cared for by their parents (with a big dose of public subsidies, to be sure), in a developed society, retirees have to be cared for by society at large via collective mechanisms such as retirement insurance, aka the intergenerational contract. These mechanisms are under attack not because they are economically unsustainable – the Bismarckian retirement system has survived longer than most existing banks or insurance companies or private corporations – but for ideological reasons and due to the profit motives of the financial industry.

    And here we arrive at another indispensable fact about our demographic future: without a functioning intergenerational contract, there is little hope of completing a benign demographic transition. Because without a retirement system a la Social Security, having many children is the only realistic insurance against spending one’s old age in misery.

    Please check out, especially from slide 39. You’ll be astonished at how irresponsibly the mainstream media and “experts” are beating the drum for more population growth.

    • ” immigration, which is especially high in some of the tiny rich countries mentioned above”

      Doh! I kept beating the drum about people leaving the poorer countries of Eastern Europe, I passed over the more obvious “rich countries attract immigrants” point.

    • “Global fertility is currently well above TFR (2.5)” should read: “Global fertility is currently 2.5, well above replacement.”

      • Not that above:
        2.1 isn’t a hard figure, it’s an industrialized countries approximation, based on our low mortality rates before the end of childbearing years. The world average is 2.33. I don’t know if that average is calculated the same way as the TFR 2.5 average, but if so they’re not too far apart. Both mortality and birth rates should drop; if you can find or make graphs of their trends, kudos.

        • Go to Google Public Data,, and do a search for the data you are looking for. Of course you can also go to UN or World Bank web sites but Google is a convenient aggregator. Crude birthrate peaked in 1965 at 34 and was 19 in 2011 (per 1000). The death rate is slowly declining and was 8, which makes for a growth rate of 1.1%. The death rate will increase when the age structure shifts higher up. As explained, total fertility rate has declined rapidly but even at replacement level, population inertia will cause population growth to persist for several decades.

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