Limits to Growth

I read this book after reading Factfullness, from Hans Rosling. It was a lucky coincidence. In Factfullness, Rosling argues that our model of the world is often wrong and imprecise. In Limits to Growth (LTG), the authors work out, step by step, such a model.

The model that the authors present is aimed at understanding how growth will continue up to 2100. The authors do not argue that the model captures every possible aspects impacting growth. They are well aware that it’s a model, with some simplification in it. What they tried to do, is to make it usefull for their goal. In this regard, the model is well argumented and realistic. The limits of the model are also disclosed transparently – for instance, the model has no notion of geography or politics.

The situation now in the world is already unsustainable – we are facing overshoot. The formidable challenge up to 2100 is to solve overshoot for the current population, but also to improve the system to accommodate 4 billions people more.

At its core, the model is based on a few key abstractions, which are presented linearly in the book.

  • The first abstraction is the world population. Population growth is controlled by income level and global health measures that reduce death (here you see the link with Factfulness very clearly).
  • The second and third abstractions are sources and sinks. Sources provide natural resources that we can transform into capital to sustain the economy, and sinks absorb the waste or pollution produced by the system. Elements in the system can act as sources and sink – for instance, tree produce wood and do absorb some CO2.
  • The fourth abstraction is that of limits. Sources and sinks have limits, which constrain how much can be provided or absorbed. A limit can be absolute, constraining the finite amount in the world, or a rate, constraining how much can be produced or absorded in a certain time.

You can tune various parameter in the model to compute scenarios about the future. And that’s what they do in the book.

The first scenario is the utopia scenario without limits. In this scenario, growth continue indefinitively and the civilization prosper beyond 2100. The other scenarios are scenario with limits in place and various assumptions about the rate of progress and global policies.

And here is the bad news. In these scenarios, growth tend to stop in the second half of the century and lead to a collapse with population decline. These scenario are no forecast. The only oultine possible trajectories and trends. Unfortunately, no matter how we tune the model, as soon as we re-introduce limits, the collapse trend is clear.

This is also the case for ecomodernism scenarios. There’s a whole chapter in the book explaining why technological progress and market alone, even with ideal parameters, won’t suffice.

Several such scenario lead to collapse due the lag time between reaction and problem. We are dealing with cycles that happen over decades. It takes decades for pollution to disseminate from production site to environment; it takes decades to engineer new technologies; it takes decades to renew or replace existing infrastructure. When the reaction comes, it’s too late. The most optimist scenario (scenario 6) of this category seem to almost achieve sustainability, but ultimately collapse too due to pressure on the system and the cost of technology required for it.

This book is a fascinating analysis, even if the perspective is grim.

In all the scenarios, the same model is used as well as the same limits (except for the scenario without limit). We could of course explore a lot more scenarios, with modifications in the model or of the limits. I’m sure the authors did. But the model and these limits reflect what the authors think approximates best reality. Finding solutions for an alternate reality doesn’t help. But it’s a model after all, so there’s room for critique of the results. And for hope.

What I would have found interesting but isn’t in the book, is a “backward” analysis of how much rate of progress assuming these limits would be needed to achieve true sustainablility. If 2020 told us anything with the pandemic, it’s that if pressure is there, progress can sometimes happen fast.

The story of the ozone hole acts in the book as a case study of a real-world feedback loop with long delay. This story is hopeful, even if unclear how we could replicate such success for other areas. In the last chapter, the authors make a call for a next revolution after the industrial revolution – the sustainability revolution. I like the idea, but wished that the learnings of the ozone story would have been transformed in more concrete inputs in this chapter.

This book left me a better understanding of:

  • Delays in feedback loops
  • The risk of ecomodernism
  • The role of land/food in growth
  • Systems thinking
  • The ozone hole

On top if all that, I’m very impressed that the first version of the book was written in the 70s. 50 years later we only start to believe what they were saying because we start to see it for real (seeing is believing), not because we’ve become more clever.


The scientific message of LtGgot lost in the turmoil of the pop-ular debate. Global society is likely to overshoot, said LtG,andthen be forced to decline or collapse – because of significant re-action delays in the global economy. These are the lags in the per -ception and localization of global limits, the significant institu-tional delays involved in (democratic) decision making, and thebiophysical lags between implementation of remedial action andthe improvement of the ecosystem. The real message was appar -ently never picked up by anyone, neither critic or fan.

But as con-traction does not occur in the model system until around 2020,historical comparison up to 2010 does not give much guidanceabout the veracity of the contraction part of the LtGbusiness asusual scenario. By 2030, we will have a much clearer answer tothat question.