Working Paper 33932 DOI 10.3386/w33932 Issue Date June 2025 A smaller human population would emit less carbon, other things equal, but how large is the effect? Here we test the widely-shared view that an important benefit of the ongoing, global decline in fertility will be reductions in long-run temperatures. We contrast a baseline of global depopulation (the most likely future) with a counterfactual in which the world population continues to grow for two more centuries. Although the two populat...