The Limits to Growth Revisited

This book has been a lot of work for me but, finally, it is done. "The Limits to Growth Revisited" has been published by Springer in June of this year.

In some respects, "The Limits to Growth Revisited" is a rather technical book. It goes in some depth in describing the controversy that flared between critics (mainly economists) and supporters of the system dynamics methods used for the 1972 study "The Limits to Growth" (LTG). But "LTG revisited" is not just a technical book. It also tells the whole story of the LTG study: how it was conceived, what were the political reactions to it, how it was demonized and misunderstood, and what is its relevance - also in its more recent versions of 1992 and 2004 - to the present situation of the world.

Writing this book has been a fascinating work. Re-examining the story of LTG opens up a whole new world that urban legends and propaganda had tried to bury under a layer of lies and misinterpretations. We all have heard of the "mistakes" that the authors of LTG, or their sponsors, the Club of Rome, are said to have made. But LTG was not "wrong": nowhere in the 1972 book will you find the mistakes that are commonly attributed to it. LTG never predicted catastrophes to occur soon, never estimated that some specific mineral resources should run out by some specific date, it never contained prophecies of doom. In other words, LTG is not, and never was, "Chicken Little with a computer."

What caused the demonization of the study was, in large part, the fact that it was so new and so advanced for its times that it was widely misunderstood, often by its supporters as well as by its detractors. But the misunderstanding was enhanced by a media campaign very similar to the one that has been recently directed against climate science. The trick of these campaigns is always the same: find a single mistake and use it to demonize the whole concept. It doesn't matter that the mistake is real or an invention, it doesn't count whether it is relevant or not. It is enough to repeat the concept of "mistakes" a large number of times to confuse the public and cloud the issue. In recent times, the method has been used to demonize climate science with the alleged mistake found in the "hockey stick" temperature reconstruction of past climate. For LTG, the "mistake" was found in a few numbers taken from just one of the many tables of the 1972 book. There was nothing wrong in these numbers, but the concept of the "mistakes of the Club of Rome" went viral and it is still widespread, and perhaps prevalent, whenever the LTG study is mentioned today.

Understanding the real message that LTG sent to us in 1972, and that it is still sending, takes a certain effort. First, you have to free your mind from the layers of legends that have accumulated around it over four decades, but that is not enough. You have to free yourself also from the common attitude that prevents us from understanding how complex systems behave. There is no fixed future for systems such as the world's economic system, only trends. But these systems still obey physical laws: the limits of natural resources, the finiteness of the world system, the concentration of greenhouse gases in the atmosphere. And there are the constants of human behavior: mainly our tendency of preferring immediate satisfaction to a future one, a phenomenon known as "discounting the future."

All together, these factors push the world system to follow a well defined path. We cannot determine exactly what the future will be, but we can produce a "fan" of trajectories that show to us where the system is heading to. The original 1972 LTG study had already identified the main factors that have been dominating the behavior of the world's economy. The combined effects of resource depletion and pollution accumulation (seen today mainly in terms of climate change) have been gradually reducing the ability of the industrial system of accumulating capital and of fuelling growth. These factors will, eventually, cause the world's industrial and agricultural systems to start a decline that could be defined as "collapse" which, later on, will involve also the collapse of the world's population.

It is not possible to determine exact dates for these events but, still, the insight that this kind of modelling offers to us is amazing. Just think how the LTG scenarios of 40 years ago can be interpreted as indicating that the worldwide financial crisis that occurred in 2008 may be the first hint of the impending collapse of the world's economy. Note also how these scenarios also anticipate the present debate on whether climate change or "peak resources" is the most important problem that we face. Dynamic modelling is a flexible tool, something that enhances the capability of the human mind to understand the world that surrounds us. The 1972 LTG study was the first to use this tool, but it is not the only possible way. Simpler dynamic models will tend to produce the same final outcome.

If we use this tool, and we use it wisely, we can discover that nothing of the future is written in stone. The future is something that we create every day with our actions. At the same time, we can also discover that the future has a life of its own, that it resents being forced into what we think it should be on the basis of obsolete ideologies. We will have to adapt to the future and that may not be painless but, if we try to understand the future, we may discover that it doesn't need to be our enemy.



I have to thank a lot of people for their help and support with this book, but the whole list would be too long here - you can find it in the book. Let me just mention the main ones: Charles Hall, who made this book possible, and Dennis Meadows and Jorgen Randers, two of the authors of the first 1972 LTG study whose contribution was essential for my work. I would also like to mention the help of Jay Forrester, the father of system dynamics, well in his 90s when this book was written but who, nevertheless, provided me with precious insight and information on the story of dynamic modelling. The book is dedicated to the memory of Matt Simmons, who was among the first to re-evaluate the LTG study after it had been demonized in the 1990s.

You can read the introduction to "The Limits to Growth Revisited" on Google Books. Here is the description of the book that you can find on Springer's page.


“The Limits to Growth” (1972) generated unprecedented controversy with its predictions of the eventual collapse of the world's economies. First hailed as a great advance in science, “The Limits to Growth” was subsequently rejected and demonized. However, with many national economies now at risk and global peak oil apparently a reality, the methods, scenarios, and predictions of “The Limits to Growth” are in great need of reappraisal. In The Limits to Growth Revisited, Ugo Bardi examines both the science and the polemics surrounding this work, and in particular the reactions of economists that marginalized its methods and conclusions for more than 30 years. “The Limits to Growth” was a milestone in attempts to model the future of our society, and it is vital today for both scientists and policy makers to understand its scientific basis, current relevance, and the social and political mechanisms that led to its rejection. Bardi also addresses the all-important question of whether the methods and approaches of “The Limits to Growth” can contribute  to an understanding of what happened to the global economy in the Great Recession and where we are headed from there.

• Shows how “The Limits to Growth” is a subject more relevant today than when the book was first published
• Demonstrates how scenario-building using system dynamics models or other methods is an essential tool in understanding possible futures
• Examines the factors that may lead to the rejection of good science when the conclusions are unpleasant
• Separates the reality that the future can never be predicted with certainty from the need to prepare for it

Man vs. Gaia

Image from "deviantart.com"

This cartoon, signed by "humon," shows one aspect of the fight between humans and their environment; also known as "Gaia". The concept is the same as that expressed by George Carlin as, "The planet is fine, the people are fucked".

But even Gaia herself, poor lady, might not emerge unscathed from the fight. She may be robust, but she is not eternal. Look at this graph, from a paper by Franck, Bounama and Von Bloh,

As you see, the earth's biosphere, Gaia, peaked with the start of the Phanerozoic age, about 500 million years ago. Afterwards, it declined. Of course, there is plenty of uncertainty in this kind of studies, but they are based on known facts about planetary homeostasis. We know that the sun's irradiation keeps increasing with time at a rate of around 1% every 100 million years. That should have resulted in the planet warming up, gradually, but the homeostatic mechanisms of the ecosphere have maintained approximately constant temperatures by gradually lowering the concentration of CO2 in the atmosphere. However, there is a limit: the CO2 concentration cannot go below the minimum level that makes photosynthesis possible; otherwise Gaia "dies".

So, at some moment in the future, planetary homeostasis will cease to be able to stabilize temperatures. When we reach that point, temperatures will start rising and, eventually, the earth will be sterilized. According to Franck et al., in about 600 million years from now the earth will have become too hot for multicellular creatures to exist.

Of course, the extinction of the biosphere is not for tomorrow or, at least, the calculations say so. But it is like estimating one's lifespan from statistical data. Theoretically, the homeostatic mechanisms that operate your body could keep you alive until reach a respectable age; sure, but homoeostasis is never perfect. For instance, there are mechanisms in your body designed to reverse the effects of traumas. You may expect these mechanisms to work well if you are young but, if you are hit by a truck at full speed, well, you end up on the wrong side of the life expectancy statistics.

Similar considerations apply to Gaia. Theoretically, the planetary homeostatic mechanisms should keep Gaia alive for hundreds of millions of years, but what about major perturbations, some planetary equivalent of being hit by a truck? Would Gaia be able to recover from a human caused runaway greenhouse catastrophe?

We cannot say for sure. What we can say is that we are living in a period called the "sixth extinction," similar to other major past extinctions. In most cases, these extinctions appear to have been caused by an increase in the concentration of greenhouse gases in the atmosphere. The sixth extinction, too, is taking place in correspondence to a rise of the concentration of carbon dioxide in the atmosphere that may never have happened so fast in the history of the planet. This rapid rise is also taking place under a solar irradiation that has never been so high as it is today. We can't rule out that the sixth extinction will be the last one.

So, in the fight of man vs. Gaia neither one might be left standing. That's just a possibility, of course, but one thing is certain: in this fight, the enemy is us. 



Thanks to Antonio Turiel for the link to humon's cartoon and to Weissbach for the link to George Carlin's movie

Italy kills the nuclear demon

The result of the Italian national referendum on nuclear energy are out. As I am writing, the data are not yet official, but it seems certain that the votes against nuclear energy were about 95% of the total (*). A landslide, if ever there was one! It is a disaster for the nuclear industry that is sure to have consequences on nuclear policy even outside Italy.

There will be time for a detailed analysis of the vote, for political considerations, and for thinking of future scenarios. One thing is certain, however: nuclear energy has come a long way from the time, half a century ago, when it was hailed as the solution to all of humankind's problems.

The debate on this referendum was extremely polarized from the beginning. Mostly, detractors presented nuclear energy as dangerous and unreliable and voters seem to have seen the problem in these terms. The choice was seen as black and white, good vs. evil, demons against angels.

But, if the downfall of nuclear energy generates the return of coal as a replacement, then who is the demon and who is the angel is a debatable point.


(*) Final results: Against nukes: 94.1%, for nukes: 5.9%

Peak? What Peak? Greenhouse emissions keep increasing

Recently released emission data from IEA. Reproduced from "Skeptical Science". 

Back in the early 2000s, when I was starting to study peak oil, I used to think that oil depletion was our main problem. Climate change seemed to me a threat for the remote future and, probably, automatically solved by the depletion of fossil fuels. Over the years, however, I saw more and more data accumulating that show that it is not so. I am now convinced that climate change is a much more serious threat to humankind than peak oil.

The most recent data on carbon emissions, published by IEA, are reinforcing my impression. Greenhouse gas emission are NOT going down, despite oil production having probably peaked. The recovery that we are experiencing, weak as it is, has been enough to push emissions to an all-time record high. We are generating more and more CO2, probably, also because depletion is forcing the industry to turn more and more to "dirty" fuels, such as tar sands.

The graph from IEA is especially worrisome because it says nothing about the parallel evolution of methane emissions, another, more powerful, greenhouse gas which is emitted as a result of the extraction and processing of natural gas. Methane emissions are on the rise, too, and the trend toward extraction of shale gas may make the situation worse.


Many times the IPCC has been accused of being too pessimistic and of not having considered depletion in the proposed scenario. But it seems that depletion is not biting on emissions as much as several studies had proposed. Rather, we seem to be following the "worst case" scenario of the several that the IPCC had proposed.

In the future, it may be that the effect of depletion will be felt more strongly but, for the time being, "peak emissions" seem to be far away.

The future is never what it used to be: the last flight of the Space Shuttle

If you have five minutes, you can look at the future as Stanley Kubrik saw it in 1968, in his movie "2001, A Space Odissey." The sequence of the space docking is especially beautiful and especially touching for us, today, with the last Space Shuttle mission programmed for tomorrow, June 8.

It is the end of an age - the age of manned spaceflight. The future is never what it used to be.

Nuclear Fusion: the elusive genie

The recent announcement by two Italian researchers of a new method of attaining energy from nuclear fusion has brought back hopes of an easy and inexpensive way of generating energy. It is almost if the nuclear genie that Walt Disney had created in the 1950s is back with new promises of energy "too cheap to meter." But what exactly do we expect from fusion? Why do we think it could solve our problems? Perhaps, these possibilities have been much overrated.

Maybe it is because of the brightness of the sun. Maybe it is because of the awesome power of the "hydrogen bomb." Or, maybe, it is the abundance of hydrogen in the oceans that makes us think of it as an inexhaustible fuel supply.  Whatever the case, the concept of "nuclear fusion" has a nearly magic ring to it. Touted as the ultimate solution to all of our problems, the dream of nuclear fusion is nicely summarized in the slogan coined in the 1950s: "energy too cheap to meter".

And, yet, dreams have a way of shattering when confronted with the hard reality. Fusing two hydrogen nuclei together, the way used by the Sun to produce energy, turns out to be extremely difficult to do on earth; even though we try to do it along an easier route that uses the isotopes of hydrogen called "deuterium" and "tritium."

There are good reasons for this task to be so difficult. Two atomic nuclei face a formidable electrostatic barrier that repels each other as they get closer. We tried just about everything possible to overcome that barrier. With the "tokamak" machine, atoms collide inside a plasma that reaches extremely high temperatures. In inertial confinement fusion, pellets of frozen deuterium-tritium mixtures are bombarded with laser beams and electron beams. Exotic particles called muons have been generated expressly to lower the repulsion barrier that keeps nuclei separated. And then, there is piezo-fusion, sono-fusion, bubble-fusion, the "fusor" machine, the fusion of boron with hydrogen in the so called "plasma-focus" technology, the "H-bomb" and, finally, the large number of claims of "cold fusion" (or "LENR" - low energy nuclear reactions).

Many of these devices work; in the sense that they generate observable fusion events that appear as emissions of gamma rays or neutrons. The problem is that we could never manage to attain a flux of fusion events large enough to repay the energy needed to start it. There have been many claims of "anomalous heat" in LENR, but no clear demonstration that fusion reactions were involved.

The only case where fusion is said to produce energy is the "hydrogen bomb" or "H-bomb." But even this device turns out to be overrated in terms of fusion power. There simply doesn't exist a "hydrogen bomb" intended as deriving its explosive power directly from fusion. All existing nuclear bombs are based on the fission of uranium or plutonium, although most are "two-stage" weapons in the sense that they use the fusion of deuterium and tritium as a way to create a neutron flux that increases the fission yield.

So, there is no evidence that we ever came close to obtain useful energy out of nuclear fusion. There remains the example of the Sun. It is up there, so bright; why can't we obtain something similar, here? But, maybe, even the power of the sun has been somewhat overrated. Here are some considerations on this point by the Italian nuclear physicist Luigi Sertorio. He has 50 years of experience in the field and in a recent interview he compared the search for fusion to the search for perpetual motion. To check his numbers, you may go to this link.


Luigi Sertorio on Nuclear Fusion. (translated from Italian)

It is obvious that, as a scientific theme, nuclear fusion on earth is an interesting phenomenon, be it inertial fusion by laser or magnetic confinement fusion. That, then, it can be made to work, is another story. When they say, "fusion is the energy of the sun; man wants to replicate on earth what happens on the sun", it is a hoax; it is due to ignorance. Those who say this should not pass the entrance exam for college. Stars produce a power of one tenth of a thousandth of a watt (10E-4) per kg. Do you realize what this means? A car engine produces something like hundreds of watt per kg. There is a ratio of one million in favor of a car or a scooter in comparison to the sun. So, when we want to make a terrestrial fusion machine that produces power, we are very far away from the way stars work. 

Stars are fusion energy machines that work at extremely low specific power. What happens inside stars is the minimum that exists in nature. And the funny thing is that stars work for billions of years. What we want to do on earth in terms of nuclear fusion is completely different. It is supposed to be one million, ten million times more efficient in terms of energy per kg. Nature said that when she wants to do nuclear fusion she does it in stars. She taught us how it can be done. Man says: "thanks a lot, mother nature, I want to do something completely different." And mother nature says, "All right, big head, now let's see what you can do!" I hope I shall live long enough to see the Lawrence Livermore lab in California shutting down. It has been gobbling up money for 30 or 40 years, maybe half a century, and it makes "boom, boom", these big booms, but no fusion comes out of it.

To finish this story, physics should go on - it must go on. Any idea can be pursued, until the physics community says "enough. It doesn't work, it makes no sense, let's look for another way." Science has always been going on in this way. Some people look for perpetual motion because they haven't understood that there exist some thermodynamic principles that exclude perpetual motion. I can tell you that it happened to me to be the referee for papers proposed to editors, or to journals such as the “Nuovo Cimento.” Someone in his solitude had found the perpetual motion machine. All right, as a physicists who knows of thermodynamics it is my duty to tell to this gentleman "go read papers which are based on physical principles and stop looking for perpetual motion". But it is not stuff that should be forbidden. If someone wants to look at this subject - and he doesn't bother us too much - let him look for perpetual motion. If someone wants to look for inertial fusion; look for it - fine. But don't use up too much money and don't ruin the California budget because you want to look for inertial fusion. But it should not be condemned. Already Cardinal Bellarmino and the Church have condemned research. It is research that, at some point, must say to itself. "Stop, this direction is not the good one. Let's look for another one."


So, what is that we are seeking for, exactly? What miracle do we expect to receive from fusion power? It looks like we are looking for some magical lamp buried in the sand, out of which a magic genie will come out and save us from ourselves. We started looking in the 1950s and it seems that we haven't grown up, yet.