Hot weather is associated with fewer babies being born in France and Italy , according to two new studies. Each day with an average temperature of 25°C or above was linked to about 360 fewer births in France and about 192 fewer in Italy.
Authors
- Raya Muttarak
Professor of Demography, Bocconi University
- Federica Querin
Assistant Professor, Demography and Social Policy, Università di Bologna
- Sophia Noel
PhD Candidate, Sociology, Sciences Po
The drop shows up nine to ten months after exposure to the hot weather. That timing points to fewer conceptions during warm months.
Hot weather can harm reproductive health in both men and women , which could mean fewer pregnancies. It may also change people’s sexual behaviour, and both explanations are possible.
France and Italy are not the first places where researchers have spotted this. Similar studies in the US , South Korea , Spain and across Europe have also found a link between hot weather and fewer births. As the evidence builds, it looks less like the quirk of a couple of countries.
Earlier studies in the US and Hungary found that some of the missing births were “caught up” in the months after the dip, as if couples had simply put off having a baby. But the French and Italian studies see no sign of this, so some births in these two countries may be lost for good instead of moving to another time of year.
A warming climate meets an ageing Europe
Italy and France already have falling birth rates, so each lost birth is consequential. Italy was among the first to drop below 1.30 children per woman , back in the early 1990s. Demographers call this “lowest-low fertility”, and it makes a population grow older rapidly.
France held on to higher fertility than many of its neighbours for longer. But births there fell by 22% between 2010 and 2025, according to researchers at the National Institute of Statistics and Economic Studies , and are now well below the level needed to keep the population stable.
Meanwhile, Europe is the fastest-warming continent . Climate scientists say parts of it have become “regional heat wave hotspots” , with hot weather arriving faster than climate models predicted.
The Mediterranean is especially exposed, and in Italy average annual temperatures have risen by almost 2°C over the past 60 years – a warming rate higher than the global average.
Europe had several long, severe heatwaves this summer, and Météo-France said France’s was its warmest since measurements began in 1900.
If heat does reduce births, the effect would hit hardest in countries where fertility is already low and populations are ageing fast. That gives climate change a place in family and population policy.
What we know – and what we don’t
Still, there are limits to what these studies can tell us about the effects of heat on birth rates.
Both studies account for normal yearly patterns in births and temperatures, at regional and national level. But because they look at whole populations over time, they cannot show as clearly whether heat itself causes fewer births as studies that compare people under carefully controlled conditions.
The studies also rely on data from past decades. With the weather changing fast, the link between heat and births may already look different today, and it could shift again in the future.
Both the new studies estimate that the link is real but fairly small. Changes in family norms and money worries are still the main explanations for falling fertility in Europe. But if hot weather becomes more frequent and more intense, climate change could play a bigger part in the years ahead.
