Predict civilization collapse with Python and World3 model

Also, the patterns revealed in their models are useful for understanding patterns in nature and human interaction with it.

The Malthusian model is: more food supply -> more humans -> more food demand -> more food supply -> more humans -> ... A vicious circle. A positive feedback loop. But it's a positive feedback loop operating in machine with negative feedback loops too. It's been over a decade since it's been understood that global human population is going to plateau in just three more decades, then begin declining. Reasons for that are myriad, but if I had to summarize it it would look like this: low child mortality + high life expectancy + high standards of living + high taxes and costs + high retirement costs == low interest in reproduction -- i.e., price signalling works! Who would have thunk it? Not Malthusian modellers, for sure.

The latest check-up is by Gaya Branderhorst in 2020, https://dash.harvard.edu/handle/1/37364868.

Of course, one has to understand that such a model doesn't show you "on the year 2028 the population is size 16.2931 billion". That is not the point. The point is to show how something grows, or shrinks, and the interrelations of the tracked variables. As x goes higher, y starts to diminish and soon after z goes through the roof, that kind of thing.

The collapse of, for example, industrial output levels might be a form of a Seneca cliff. That is, the growth of the industrial output becomes harder and harder to achieve, while the difficulties compound and actually keep on growing long after the growth of industrial output itself has stagnated or started to drop slightly. This will dramatically increase the inhibitory effect, thus creating a growth curve which starts to slow down and then drops fast ("collapse").

Why dismiss the model? The BAU scenario seems to reflect reality for over 50 years now, so is it not rational to try to understand it?

The Limits to Growth is fundamentally a realization that the world has finite resources. It is not illogical to consider this as a truth. At some point there won't be new resources to obtain, and hence growth in systems based on capturing resources will simply slow down (and perhaps even drop fast, "collapse", because difficulties compound). Circular economy and recycling are good but they cannot expand the available resource pool of e.g. raw materials.

Do you have a more specific or substantive criticism of this work? Otherwise, I'd say it's essentially proven itself.

The models cannot predict the future. Too many charlatans have attempted to tell the public that they can, but they can't, and as a result people look for models that can, criteria by which they can trust models based on the credentials of their creators or the granularity of the source data, even reasonable implementation of the source data, but of course, no model can.

But a model can teach you something about the mechanisms behind the interplay between different systems. It can tell you something general about the effects of certain situations. A good example of this can be seen in Lorenz's weather prediction models leading to the formal discipline of chaos theory. Often, algorithmic interaction between different values in models can lead to a discovery of a previously unknown mechanism by which something about the world can be gleaned, even if the model itself is useless at accurately predicting the future.

But you're right, a model can predict nothing, and people need to bear that in mind, because pop science has people convinced that they should live their lives as if existing models can and do predict the future when in fact they do not.

It's where I first heard the term "peak child" or "peak baby" to describe this.

Can you extrapolate on what you mean by this?

From memory I believe one of the ideas in the world model is that over time, as existing stocks of non-renewables are consumed, the remaining stocks of non-renewable resources become more expensive for society to access. E.g. EROI [1] for fossil fuel deposits decreasing. Similarly when mining ore, if the richer ore deposits have all being exhausted, then only lower-grade ore remains, so maybe you need to expend more energy blasting and moving 2x or 3x as much rock as a few decades ago to obtain the same output of metal.

So the idea is that at some point it starts to become more and more expensive -- in terms of the energy input required -- to produce resources that society requires to exist in a steady-state, let alone to continue to fuel growth of the physical economy.

Similarly for pollution -- e.g. for global warming you can regard the atmosphere as a stock where you can store some finite amount of CO_2 pollution before it really starts creating a mess. Once there isn't much stock of cheap CO_2 pollution storage capacity remaining in the atmosphere, you have to start figuring out something else to do, which consumes more energy.

The increasing energy costs of extracting enough non-renewables and dealing with pollution to fuel society leaves less energy for everything else. At some point the energy required for industrial output grows to the extent that there is no longer sufficient energy left for services such as healthcare, education, etc. Therefore the quality of healthcare and education falls off. That has consequences for the human population.

[1] https://en.wikipedia.org/wiki/Energy_return_on_investment