In 1972 the Club of Rome, an informal international group of businessmen, statesmen and scientists, commissioned researchers at MIT to model the Global economic system. The result was a computer model called World3 and the publication of a report called Limits to Growth (LtG). The lead authors were Donella and Dennis Meadows and Jorgen Randers. It was followed up in 1992 with Beyond the Limits and in 2002 with Limits to Growth the 30-year update. I have also drawn on a report in 2008 A comparison of the limits to growth with thirty years of reality by Graham Turner

I will try to summarise what Limits to Growth tells us and clarify what it does and does not do.

The computer programme, World3, takes a number of socio-economic variables and calculates how they might vary until the year 2100. These variables depend on one another in complex and time dependent ways. For example, the population next year will be equal to the population this year plus the number of births minus the number of deaths. The number of births depends on the birth rate some years earlier and mortality in the intervening years. Mortality rates will depend on food supplies and other factors. How much food there is depends on how much land is available and how productive it is, which in turn depends on things like investment and pollution.  The year after that will depend on the results of the calculations for next year and so on. You can see that this calculation becomes very complex and the outcome not at all obvious. An ideal job for a computer.

40 years is a long time in computer technology. In the 1970’s World3 would have been a significant piece of software running on large, expensive computer. Today you can download it from the internet and run it on an ordinary PC (I did this myself and did a few runs but left it at that). However it seems to have stood the test of time. Graham Turner, in his report, looked at how some of the variables have actually changed in the 30 years since it was first run and they track the model reasonably well.

World3 is a relatively simple model. All the parameters are aggregated, that is, they have a single value to represent the whole world. More advanced models could have been developed but haven’t.  As models get bigger, it becomes harder to see why they produce certain outcomes, and there is a view that World3 is a good compromise between over-simplification and unmanageable complexity.

So how was it received? Graham Turner wrote:

“The salient message from the LtG modelling was that continued growth in the global economy would lead to planetary limits being exceeded sometime in the 21st Century,  most likely resulting in collapse of the population and economic system: but also that collapse could be avoided with a combination of early changes in behaviour, policy and technology.

Despite these major contributions, and dire warnings of “overshoot and collapse”, the LtG recommendations on fundamental changes of policy and behaviour for sustainability have not been taken up……From the time of its publication to contemporary times, the LtG has provoked many criticisms which falsely claim that the LtG predicted resources would be depleted and  the world system would collapse by the end of the 20th Century.”

This is just what the programme does not tell us. Not only did none of the runs show collapse until well into this century but, as the authors emphasise, it is not intended to make predictions. It indicates that there is a problem and provides a tool to test the effectiveness of various measures to alleviate the problem. For example, we can see that there are many different resources, some are abundant while others a seem severely limited. We can only guess what reserves are left, how the cost of extraction will increase, what will be technologically important in the future and to what extent one material can be substituted for another. The model represents this as a single variable and allows us to try out the effect of different guesses. It is a way of asking “what if?”

Rather than looking for a forecast we should take the report like we would an accountants report. If you are running a business and your annual report shows you the global indicators, the bottom line. If this tells you that business is heading for trouble, you take note. To rubbish the report and say every thing is fine at the moment, is stupid.

The rubbishing of LtG in the popular mind, probably meant that there were not many votes for politicians and therefore not a lot of action from governments. However Big Business may be amoral but it is not generally stupid. In the 1970’s I was a technology researcher in a large multinational and my colleagues were looking seriously at the potential impact of declining resources and opportunities for renewable energy supplies. Shell started developing solar cell technology and is today one of the largest suppliers. What must be remembered is that any technology takes decades to build up from basic research to a level of production enough to make a global impact.

In Limits to growth, the 30-year update eleven scenarios are discussed in which various assumptions are tested. The first of these scenarios indicate that, without changes in policies, we can expect a collapse in industrial output, food, life expectancy and human welfare, sometime before the end of this century. Which is in the lifetime of my grandchildren.
The next set of runs show the influence of realistic improvements of resource management:
• more accessible non-renewable resources
• pollution control
• land yield enhancement
• land erosion protection
• resource efficiency
These are all a matter of getting the technology right. I am fairly optimistic that this can be done and is being done, but should be no let-up. Big business has a part to play because large scale manufacture is required for some the solutions. For example, a huge area of solar panels will be needed to make a difference. Innovation needs to be encouraged along with acceptance of the inevitable risks.
However the technological fix alone is not enough. The model still indicates a collapse, but delayed by a few decades. To avoid this we also need to limit demand:
• stabilise birthrate
• limit industrial output per person.
As the authors suggest, this means developing a culture of “Enough”. Enough children, enough comfort, enough consumption.
It needs to replace the culture of “Growth”.