Study reveals climate change may reduce male births globally
By Aloys Michael, March 21, 2026For generations, couples have shared beliefs about how to influence the gender of their baby. Many of these ideas are based on tradition rather than science, yet they remain popular in different cultures.
But now, new research suggests that something far more powerful may be at play, climate change.
A study by researchers at the University of Oxford has found that rising temperatures, especially extreme heat, could influence whether more boys or girls are born around the world. The study, titled Temperature and sex ratios at birth, was published on Thursday, March 19, 2026, in the Proceedings of the National Academy of Sciences of the United States of America.
Typically, the number of male and female births is not exactly equal. Globally, there are slightly more boys born than girls, about 101 to 102 males for every 100 females. This balance, known as the sex ratio, is an important measure because it reflects patterns in health, survival during pregnancy, and social factors.
To understand how climate change might affect this balance, researchers analysed more than five million births across 33 countries in Africa and India. They combined detailed temperature records with large-scale population data to see how heat exposure during pregnancy influences birth outcomes.
Sex ratios at birth, the number of boys born relative to girls, are a key demographic indicator. They reflect underlying patterns of maternal health, prenatal survival, and, in some contexts, gender discrimination,” the study states.
“In recent decades, skewed sex ratios have raised concerns in several regions, particularly where son preference and sex-selective abortion are prevalent,” the study reads.
The researchers wanted to explore how rising global temperatures, already a growing concern, might affect these patterns.
Their findings show that in many African countries, high temperatures during the early stages of pregnancy, especially the first trimester, are linked to fewer male births. This suggests that extreme heat may affect the survival of male foetuses.
“This pattern is consistent with increased prenatal mortality driven by maternal heat stress, and is particularly pronounced among women living in rural areas, those with lower levels of education, and those with higher birth orders,” the researchers explained.
In India, the pattern was different. There, the impact of heat appeared later in pregnancy.
“Higher temperatures during the second trimester are associated with fewer male births, especially among older mothers, high-parity births, and women without sons in northern states. The pattern suggests that heat exposure may reduce access to, or use of, sex-selective abortion, temporarily narrowing gender imbalances.”
Regional differences
Despite these regional differences, one trend was clear: temperatures above 20°C were consistently linked to a drop in male births.
“Extreme heat is not only a major public health threat. We show that temperature fundamentally shapes human reproduction by influencing who is born and who is not born,” Lead researcher Abdel Ghany stated.
The findings suggest that climate change does more than affect weather patterns; it may also shape population trends and family outcomes. Heat exposure appears to influence both biological factors, like foetal survival, and social behaviours, such as family planning decisions.
The study also highlights inequality. Women in poorer and rural communities, especially those with fewer resources, were more affected by extreme temperatures. This raises concerns that climate change could widen existing health gaps.
Overall, the research adds to growing evidence that global warming is not just an environmental or economic issue. It is also a public health and demographic challenge, with the potential to reshape societies in unexpected ways.