Modeling Unsustainable Growth: A multi-cohort dynamic population model and new formula for two-way coupling with climate models

A realistic projection of greenhouse gas (GHG) emissions and the resulting anthropogenic climate change can only be achieved through the inclusion of human population impacts with feedbacks onto global climate models. The growth of population itself depends on the fertility age and the total fertility rate (TFR), however, detailed distributions of these parameters can make a large impact on the total growth. To investigate these impacts, we have developed a series of multi-cohort dynamic population models with different numbers of fertile cohorts. Census data for various regions can be used as input for these models. These models can eventually be integrated through bidirectional couplings into a climate model such as the Community Earth System Model (CESM), to project future birth rates, total population, and subsequent GHG emissions. We have also developed a new formulation that better demonstrates how total population growth depends on the fertility age, TFR, and average lifetime. We will compare the results of the dynamic model simulations to the predictions from the theoretical equation. Our results show that delaying the age at which a woman gives birth, or spacing out her child-bearing years to accommodate a professional lifestyle, can lead to a sustainable population, and thus slower climate change.