Two separate studies reveal that every day where the average temperature reaches 25 °C or higher is linked to roughly 360 fewer births in France and 192 fewer in Italy nine to ten months later. As Europe faces rapid warming and declining birth rates, researchers suggest that extreme heat may permanently reduce overall fertility rather than just temporarily delay family planning.
When Summer Temperatures Collide with Demographic Decline
The statistical dip arrives nine to ten months after exposure to high temperatures, pointing to fewer conceptions during the hot months. High heat may harm the reproductive health of both men and women, while it may also alter human sexual behavior. While prior investigations in the United States and Hungary documented a rebound effect where missed babies were born later, the French and Italian research found no such sign: some births appear permanently lost.
These findings arrive as both nations confront downward trends in birth rates. Italy dipped below 1.30 children per woman in the early 1990s, leading to rapid population aging. France maintained higher fertility longer, but births dropped by 24 % between 2010 and 2025, according to researchers from the Institut national de la statistique et des études économiques (Insee).
| Country | Estimated Birth Drop per 25°C Day | Historical Context & Trajectory |
|---|---|---|
| France | ~360 fewer births | Births fell 24% from 2010 to 2025. |
| Italy | ~192 fewer births | Fertility below 1.30 since the 1990s. |
A Continent Heating Up Faster Than Models Predicted
Europe is the continent that warms the fastest. Climatologists estimate that some of its regions have become regional heatwave hotspots, with heat arriving faster than climate models predicted. The Mediterranean is particularly exposed. In Italy, average annual temperatures climbed nearly 2 °C over the past sixty years, a rate of warming higher than the global average. Meanwhile, Météo-France indicated that the summer was the hottest in France since measurements began in 1900.
Similar studies conducted in the United States, South Korea, Spain, and at the European level have also found a link between heat and a drop in births. What once looked like a peculiarity of a few countries points to a broader trend. Financial concerns and changing family norms remain the primary explanations for the drop in fertility in Europe, but if heat episodes become more frequent and intense, climate change could play a more important role in the years to come.
What the Data Still Leaves Unanswered
The studies have limits regarding what they can teach us about the effects of heat on birth rates. The studies take into account usual annual cycles of births and temperatures at the regional and national levels. Because they focus on entire populations over time, they allow for less clarity in establishing whether heat itself causes a drop in births than studies comparing people in carefully controlled conditions. Furthermore, the studies rely on data from past decades. With the climate changing rapidly, the link between heat and births could already be different today.
The two new studies estimate that the link is real but fairly weak. As heatwaves stretch longer and repeat with greater frequency, climate change could play a more important role in the years to come.
