The effect of heat on fertility rates in France: 1975–2020

The association between heat and fertility is less explored compared to adjacent literature on heat and mortality, despite its potential relevance in shaping age structure and population size within the context of rapid population aging and accelerating climate change. Furthermore, little work has considered this dynamic in the French context, where these demographic and climatic trends are increasingly observable and carry significant policy ramifications. To address this gap, we combine meteorological data and monthly Total Fertility Rates derived from National Institute of Statistics and Economic Studies (INSEE) data and apply fixed-effects regression to estimate the effect of heat on fertility rates in France from 1975 to 2020. We find that daily mean temperatures of ≥ 25 °C are associated with a decline in births of approximately 0.28% both nine and ten months later. Contrary to similar work in other country contexts, we find no short-term rebound in births following this negative shock. We find that this estimate is relatively stable over time, despite changes in policy, childbearing age and adaptive capacity in France over this window. We also do not find consistent differences by regions’ baseline climate. We also consider the role of humidity and consecutive warm days and find suggestive evidence towards the exacerbating role of both these factors, but that meaningful associations between heat and fertility are visible notwithstanding these dynamics as well. Our findings suggest that warm temperatures are a relevant factor in shaping fertility rates over the long term in France and may become increasingly relevant in coming years.