Population driven emissions call for earlier climate mitigation

Econometric studies based on the STIRPAT framework suggest that carbon emissions respond more strongly to population size than to per capita income, yet this relationship has not been explicitly incorporated into the integrated assessment models used for climate policy analysis. We extend one of the most widely known framework, namely the DICE model, to allow population to directly determine emissions beyond its indirect effect through economic activity, calibrating the relevant elasticities on existing empirical estimates. We find that unabated emissions may exceed twice the standard DICE baseline by 2100, requiring substantially earlier and more intensive abatement effort. Full decarbonization appears necessary around mid-century to meet the 2 ᶜⁱʳᶜ C temperature target, and socially optimal by 2070 when mitigation costs and benefits are weighed against each other. These results are primarily driven by a population elasticity above unity which amplifies emissions, combined with a sub-unitary response to per capita income which partly offsets this effect. Our analysis suggests that explicitly accounting for non-proportional effects of population and income on emissions can significantly affect conclusions about the urgency and cost of climate action.