To write this post, I’ve been back through Limits to Growth, pulling out important parts of the argument. So first, the components of the model. World3 simplifies the world into these main components: population, industrial capital, non-renewable resources, industrial output, pollution, and agricultural production. Because it is a systems dynamics model, there is feedback between different elements, which, when combined with delays, create complexity and non-linear behaviour.
This is my large simplification of the model that sits behind World3 (to be clear, this does not come from Limits to Growth).
In summary, industrial capital and non-renewable resources combine to create industrial output, which in terms creates persistent pollution. This then reduces food production – and so capital is diverted from industrial production to agricultural production, and so, in turn, industrial output declines.
From this, the Limits to Growth team developed 10 scenarios, representing different paths and making different assumptions about rates of population growth and industrial output. The most common outcome, after thousands of runs of the model, is “overshoot and collapse”, with industrial output declining in the 2020s and population declining in the 2030s. As they say, you don’t necessarily need a model to understand this, but a model enables you to be clear about your assumptions about the world.
Collapse is not inevitable
But (and these are important buts) collapse is not inevitable, even though we have now overshot, with the human footprint exceeding the resources of the planet. Growth does not, inevitably, lead to collapse; it depends on how you organise the growth. It is possible, even now, to get to “overshoot and oscillation” at which production and consumption are re-stabilised at a level within the carrying capacity of the planet. But to achieve this, the system needs to retain enough capacity to repair itself. more.