Climate change and optimum population

Overpopulation is often identified as one of the key drivers of climate change. Further, it is often thought that the mechanism behind this is obvious: 'more people means more greenhouse gas emissions'. However, in light of the fact that climate change depends most closely on cumulative emissions rather than on emissions rates, the relationship between population size and climate change is more subtle than this. Reducing the size of instantaneous populations can fruitfully be thought of as spreading out a fixed number of people more thinly over time, and (in light of the significance of cumulative emissions) it is not immediately clear whether or how such a 'spreading' would help with climate change. To bring the point into sharp relief, I first set out a simple model according to which population reduction would not lead to any climate-change-related improvement. I then critically examine the assumptions of the model. If population reduction would lead to a significant climate-change-related improvement, this must be because (i) population reduction would significantly reduce even cumulative emissions, and/or (ii) climate damages are, to a significant extent, driven by the pace of climate change, and not only the eventual extent of the change.