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The Limits to Growth book is an interesting read. To quote Box, "All models are wrong, but some are useful". I wouldn't take the dates-ranges estimated from the modelling that seriously, but the modelling assumptions are worth reading about and reflecting on. The overall modelling and dynamics seem pretty plausible to me. From memory, the rough argument was that society depends upon input flows of energy, resources (metals etc) and food. Society needs to allocate resources and energy to extract these inputs. Energy sources such as fossil fuel reserves are finite stocks, some are cheap to extract (high energy return on energy invested). Over time we consume and deplete the high EROEI reserves and have to move on to consuming the lower EROEI reserves. This means that the fraction of energy society needs to allocate for energy extraction increases over time, so there's less energy for other uses. Similarly, we deplete the cheap to extract stocks of metal required to build and maintain industry, leaving stocks that require higher inputs of metal and energy to extract. Similarly for agricultural yields, as we mine and deplete accumulated stocks of nutrients out of the soil. The business as usual scenario leading to "overshoot and collapse" behaviour is that we have increasing population, increasing industrial capital and increasing demands for energy, food and resource inputs, while the fraction of energy and resources that need to be allocated to energy, resource and food production grows over time. The fraction of remaining surplus energy and resources that can be allocated to things like education, healthcare, research, art decreases over time. At some point the growing fraction of energy and resources that needs to be allocated to energy and resource extraction becomes so large vs the existing population and industrial base that there simply isn't enough surplus to maintain healthcare, education, research, etc at the same level. The "Overshoot and collapse" dynamic describes stocks of population, industry etc growing to peaks well beyond sustainable levels before the above dynamics catch up and cause them to rapidly decline. The researchers did a bunch of modelling of alternative scenarios, exploring how to avoid these "Overshoot and collapse" dynamics. |