This paper addresses the contribution of changes in population size and structures to greenhouse gas emissions and to the capacity to adapt to climate change. The paper goes beyond the conventional focus on the changing composition by age and sex. It does so by addressing explicitly the changing composition of the population by level of educational attainment, taking into account new evidence about the effect of educational attainment in reducing significantly the vulnerability of populations to climatic challenges. This evidence, which has inspired a new generation of socio-economic climate change scenarios, is summarized. While the earlier IPCC-SRES (Intergovernmental Panel on Climate Change—Special Report on Emissions Scenarios) scenarios only included alternative trajectories for total population size (treating population essentially as a scaling parameter), the Shared Socio-economic Pathways (SSPs) in the new scenarios were designed to capture the socio-economic challenges to climate change mitigation and adaptation, and include full age, sex, and education details for all countries.