Free Minds & Free Markets

The Limits of The Limits to Growth

Contemplating 1972 predictions of environmental doom, just in time for Earth Day

Forty years ago, The Limits to Growth, a report to the Club of Rome, was released with great fanfare at a conference at the Smithsonian Institution. The study was based on a computer model developed by researchers at the Massachusetts Institute of Technology (MIT) and designed “to investigate five major trends of global concern—accelerating industrial development, rapid population growth, widespread malnutrition, depletion of nonrenewable resources, and a deteriorating environment.” The goal was to use the model to explore the increasingly dire "predicament of mankind." The researchers modestly acknowledged that their model was “like every other model, imperfect, oversimplified, and unfinished.” 

Yet even with this caveat, the MIT researchers concluded, “If present growth trends in world population, industrialization, pollution, food production, and resource depletion continue unchanged, the limits to growth on this planet will be reached sometime within the next one hundred years.” With considerable understatement, they added, “The most probable result will be a rather sudden and uncontrollable decline in both population and industrial capacity.” In other words: a massive population crash in a starving, polluted, depleted world. 

The problem, as the MIT researchers saw it, was exponential growth in all five areas of concern that they investigated. Linear growth is additive—1, 2, 3, 4, 5—whereas exponential growth compounds over time—1, 2, 4, 8, 16.

Earlier this month, Smithsonian magazine ran a short item reporting the findings of a 2008 study [PDF] by Australian physicist Graham Turner. According to Turner, an examination of currently available data reveals that that world economy is right on track to collapse by the middle of this century. Without taking Turner on directly, let’s look at what has happened with each global concern highlighted in the original study since 1972.

Industrial development: World GDP stood in real 2010 dollars at about $19 trillion in 1972 and has tripled to $57 trillion today. Average per capita incomes rose in real dollars from $5,000 to $8,100 today. Just to explore how incomes might evolve between 1972 and 2000, the researchers simply extrapolated the current growth, investment, and population growth rates to calculate GDP per capita for 10 large countries. They stressed these were not "predictions" but added that if one disagreed then one was obligated to specify which factors changed, when and why. A comparison of their extrapolations with actual GDP per capita (in 2010 dollars) finds U.S. GDP per capita $56,000 versus actual $44,000; Japan's per capita GDP was projected to be $120,000 versus actual $46,000; the now defunct USSR would be $33,000 versus Russia's $2,200; and China's per capita income was supposed to grow to $500, but was instead $1,200. 

Population: The Limits researchers noted, “Unless there is a sharp rise in mortality, which mankind will strive mightily to avoid, we can look forward to a world population of around 7 billion persons in 30 more years.” In addition, they suggested that in 60 years there would be “four people in the world for everyone living today.” In fact, average global life expectancy rose from 60 to nearly 70 years. On the other hand, the global fertility rate (the average number of children a woman has during her lifetime) fell from about 6 per woman in 1970 to 2.8 today and continues to fall.

World population stood at 3.8 billion in 1972, which means that a four-fold increase in 60 years would have yielded a total world population of 15 billion by 2030. Even the latest U.N. high fertility population projection foresees about 9 billion by 2030. The U.N.’s low fertility variant yields a maximum world population of about 8 billion around 2050, falling back to 6 billion by the end of the 21st century. It turns out that the invisible hand of population control correlates very nicely with economic freedom.

Food supplies: According to the data from the Food and Agriculture Organization, global food production has more than tripled since 1961, while world population has increased from 3 billion to 7 billion. This means that per capita food has increased by more than a third. The latest figures [PDF] from the United Nations show that as world population increased by a bit over 10 percent between 2000 and 2009, global food production rose by 21 percent.

Arable land was proposed as one possible ultimate limit in the MIT model. In one generous model run, pollution was controlled and nonrenewable resources were essentially unlimited. The MIT researchers assumed that as long as industrial production continued to rise in the 21st century “the yield from each hectare of land continues to rise (up to a maximum of seven times the average yield in 1900) and new land is developed.” Interestingly, since 1900 American corn farmers have already boosted yields nearly seven-fold from 26 bushels per acre to 166 bushels per acre. A 2010 article in Philosophical Transactions of the Royal Society B argued that available technologies could close the yield gap between first world farmers and developing country farmers even as the world warms. If this is done, the article concluded, “There is a good prospect that crop production will increase by approximately 50 percent or more by 2050 without extra land.”

In 1972, the Limits researchers noted that about 1.4 billion hectares of land was being cultivated and projected that if current crop yields did not improve 3 billion hectares would be needed by 2000 to feed a projected population of 7 billion. The Limits analysts did note that if crop yields doubled (which they did not expect) that land devoted to producing crops would only increase marginally—which is what actually happened. The U.N.’s Food and Agricultural Organization reports that since 1960 cropland has expanded from 1.4 billion to 1.5 billion hectares [PDF].

Nonrenewable resources: Probably the most notorious projections from the MIT computer model involved the future of nonrenewable resources. The researchers warned: “Given present resource consumption rates and the projected increase in these rates, the great majority of currently nonrenewable resources will be extremely expensive 100 years from now.” To emphasize the point they pointed out that “those resources with the shortest static reserve indices have already begun to increase.” For example, they noted that the price of mercury had increased 500 percent in the last 20 years and the price of lead was up 300 percent over the past 30 years. The advent of the “oil crises” of the 1970s lent some credibility to these projections.

To highlight how dire the situation with nonrenewable resources was, the MIT researchers calculated how quickly exponential consumption could deplete known reserves of various minerals and fossil fuels. Even if global consumption rates didn’t increase at all, the MIT modelers calculated 40 years ago that known world copper reserves would be entirely depleted in 36 years, lead in 26 years, mercury in 13 years, natural gas in 38 years, petroleum in 31 years, silver in 16 years, tin in 17 years, tungsten in 40 years, and zinc in 23 years. In other words, most of these nonrenewable resources would be entirely used up before the end of the 20th century.

They recognized that it was very likely that undiscovered reserves would be found and that technological improvements at extracting resources would occur, so just to be generous they made the same calculations with known reserves increased five-fold. Again at exponential consumption rates, they expected that after a gratuitous five-fold increase in resources there would now be only 15 years of aluminum left, eight years of copper, one year of mercury, nine years of natural gas, 10 years of petroleum, two years of silver, 21 years of tin, and 10 years of zinc.

Based on current consumption rates, the U.S. Geological Survey (USGS) in its 2012 mineral summaries report [PDF] estimates that the world has 130 years of bauxite reserves, which are used to produce aluminum. Similarly at current consumption rates, known copper reserves will last 43 years. Known lead reserves will last 18 years, although the USGS adds that identified lead resources equal 1.5 billion tons and that would mean a supply lasting somewhat more than 300,000 years. Mercury reserves are enough to another 48 years, but the USGS notes, “The declining consumption of mercury, except for small-scale gold mining, indicates that these resources are sufficient for another century or more of use.” Current silver, tin, tungsten, and zinc reserves will respectively last 22, 19, 43, and 20 years more.

In 1972, the Limits researchers estimated known global oil reserves at 455 billion barrels. Since then the world has produced very nearly 1 trillion barrels [PDF] of oil and current known reserves hover around 1.2 trillion barrels, a 40-year supply at current consumption rates. With regard to natural gas supplies, the International Energy Agency last year issued a report [PDF] asserting, “Conventional recoverable resources are equivalent to more than 120 years of current global consumption, while total recoverable resources could sustain today’s production for over 250 years.”

Why does the horizon of mineral reserves never seem to go out further than a few decades? Basically because miners and technologists do not find it worthwhile to find new sources and develop new production techniques until markets signal that they are needed. How this process evolves is encapsulated by the USGS report which notes that in 1970 known world copper reserves stood at “about 280 million metric tons of copper. Since then, about 400 million metric tons of copper have been produced worldwide, but world copper reserves in 2011 were estimated to be 690 million metric tons of copper, more than double those in 1970, despite the depletion by mining of more than the original estimated reserves.”

Environment: In most of the Limits model runs, the ultimate factor that does humanity in is pollution. In their model pollution directly increases human death rates and also dramatically reduces food production. In fact, as the world economy has grown, global average life expectancy has increased from 52 years in 1960 to 70 years now. It must be acknowledged that globally, pollution [PDF] from industrial and agricultural production continues to rise. But the model assumed that pollution would increase at exponential rates. However, many pollution trends have not increased exponentially in advanced countries.

Consider that since 1970, the U.S. economy has grown by 200 percent, yet the levels of air pollutants [PDF] regulated by the federal government have fallen by nearly 60 percent. For example, in both the U.S. and the European Union [PDF] sulfur dioxide emissions have dropped by nearly 70 percent since 1990. Recent data suggests that sulfur dioxide emissions even from rapidly industrializing China peaked in 2006 [PDF] and have begun declining. Earlier studies cite evidence for a pollution turning point income threshold (purchasing power parity) of around $10,000 [PDF] for demands to reduce this form of air pollution.

Editor's Note: We invite comments and request that they be civil and on-topic. We do not moderate or assume any responsibility for comments, which are owned by the readers who post them. Comments do not represent the views of or Reason Foundation. We reserve the right to delete any comment for any reason at any time. Report abuses.

  • Tim||

    A 40 year old computer model. PONG was cutting edge 40 years back .

  • Formerly Almanian||

    Pong was the SHIT....when you were, REALLY, REALLY....REALLY stoned.

    Otherwise, "Simon" was the ultimate stoner game. SO intense!

  • Formerly Almanian||


    Fuck Earth Day.

  • ||

    ^This, in spades.

  • Mr. FIFY||

    Fuck Earth Day

    Yeah, that's catchy. I like it.

  • Suki||

    Okay squirrell, trying to quote is not working in Chrome now.
    Comment about massive population crash:

    Ushering in an era of Charlton Heston dystopian movies.

  • Aresen||

    "Charlton Heston dystopian movies."

    That is REAL pollution.

  • T||

    Soylent yellow, on the other hand...

  • JW||

    You know NOTHING of real pollution.

    Those movies are our national treasures, maple sucker.

  • R C Dean||

    "environmentalist garbage in" generating "environmentalist gospel out."

    I'm totally stealing that.

  • db||

    My upcoming earth day activities:
    1. Burn about 20 lb of propane to brew beers (which will release CO2 during fermentation)
    2. Light a fire to keep warm while brewing outdoors.
    3. Use a couple of 500W halogen lamps to light the brewing area
    4. Blast some metal into the forest where I live while brewing.

  • Lost_In_Translation||

    You forgot farting inscessently

  • NeonCat||

    But that's like, you know, natural, man, and you shouldn't harsh on it.

  • Lost_In_Translation||

    What if the whole world farted together?

  • Harvard||

    Earth speeds rotation, increasing angle of axis and earth warms. Seriously man, a European study proves it.

  • db||

    Honestly I was going to write that but thought better.

  • Ska||

    Annual Earth Day Tire Fire.

  • SugarFree||

    Unless there is a sharp rise in mortality, which mankind will strive mightily to avoid, we can look forward to a world population of around 7 billion persons in 30 more years.

    Those ignorant bastards out there putting an end to disease and famine must be stopped at all cost.

  • Lost_In_Translation||

    If you feel the need to increase the rage level against the "eliminationist evnviros", grab the book "Daybreak". It'll make you want to build a furnace that can burn california petrified woods.

  • SugarFree||

    I've read Directive 51, I haven't picked up the other two yet.

  • Lost_In_Translation||

    I don't think the 3rd is out yet. I just finished book two last month. Very enjoyable (and infuriating).

  • Lord Humungus||

    In honor of Earth day, at my "green company" *snicker* which makes *laugh* plastic(!), we were given little seed packets. And we can attend a (voluntary) Earth Day Walk. Yay!

  • JW||

    I hope they were all non-native seeds.

  • Alan Vanneman||

    Ron, I think you need to be writing about food. Maybe a cooking show, "Cookin' with Ron!" Say, did you hear about the Alan Greenspan diet? You eat everything in sight, so the poor will starve to death!

  • T||

    When I am freed from the productive shackles of work, I'm going to write a book called Limits of Modeling. It will consist of all the doom and gloom predictions made by experts with computer models and going back and seeing just how wrong they are.

  • ||

    I will buy a copy.

  • Rasilio||

    Gee with a title like that I thought it was gonna be about the quest to discover just how young a lingeree model has to be before it becomes child porn.

  • Lost_In_Translation||

    As Toddlers with Tiaras shows, there's practically no limit.

  • Sam Grove||

    Little Miss Sunshine

  • k2000k||

    Can we get some sources for were you get your income data came from? I did a quick wiki check for GDP per capita, both nominal and PPP, and IMF, World Bank, or CIA numbers show the US GDP per capita at $ 44,000.

  • Ron Bailey||

    k200k: From the World Bank dataset here. Remember that the figures in the column are for the year 2000 in adjusted 2010 dollars - just to make it extra confusing.

  • hk||

    Pwnage. :]

    The Malthusians are very funny.

  • k2000k||

    *dont show

  • macforreal||

    Come on Ron. 2,4,8,16 is linear (x*c = y (x times c) graphed, x being the independent variable [in this c (constant) is 2)] on x&y axis). Exponential is x raised to the power of c = y. If c is 2 (e.g. squaring), then 1 (1*1),4(2*2), 9 (3*3), 16, etc. The curve is asymtotic.

  • BigT||

    His example was y = 2**x, for x = 1,2,3,4, y = 2,4,8,16. Go back to high school.

  • DonTaylor||

    "helping those who can't help themselves"; can't wait until the police are fully involved domestically. We already have the DEA and prisons helping drug users--if only the could help the fat, the unemployed, the masses yearning to be politically correct!!!

  • دردشه عراقية||


  • Ralfy||

    A new study shows that the forecasts are right:


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