Climate Change May Be Quietly Reducing Male Births, Oxford Study Suggests

Rising global temperatures may be doing more than triggering heatwaves and droughts. They could be influencing who is born.

Researchers at the University of Oxford have found evidence that exposure to high temperatures during pregnancy is associated with a reduction in the number of male babies born.

The study, published in the Proceedings of the National Academy of Sciences, examined how temperature patterns interact with birth outcomes across different regions and social contexts.

In sub-Saharan Africa, the decline in male births was most strongly linked to heat exposure during the first trimester of pregnancy. Researchers suggest that extreme temperatures may increase prenatal stress, potentially affecting fetal survival with male fetuses appearing more vulnerable under such conditions.

The effect was particularly visible among rural women, mothers with multiple children, and women with limited formal education groups often facing reduced access to healthcare and climate protection measures.

India showed a different trend. There, temperature spikes during the second trimester were associated with fewer male births. In a country where son preference has historically shaped reproductive behaviour, researchers believe extreme heat may temporarily disrupt patterns linked to sex selection.

Lead author Dr. Jasmin Abdel Ghany said the findings highlight a lesser-known consequence of climate change.

According to her, extreme heat is not only a public health crisis but also a biological and social force that may influence reproductive outcomes and long-term population trends.

The researchers warn that as climate change intensifies, vulnerable communities could experience widening health inequalities, especially where access to maternal care is already limited.

The study also points to projections showing that the global population exposed to extreme heat could rise from about 23 per cent in 2010 to 41 per cent in the coming decades.

Countries expected to see significant increases in dangerously high temperatures include Nigeria, the Central African Republic, South Sudan, Laos, and Brazil. Some of the largest affected populations are projected in India, Nigeria, Indonesia, Bangladesh, Pakistan, and the Philippines.

Dr. Jesus Lizana, an Associate Professor in Engineering Science at Oxford, said most energy demand changes linked to heating and cooling will occur before global temperatures reach 1.5°C. He stressed the importance of early adaptation strategies and long-term decarbonisation efforts if net-zero targets by 2050 are to be achieved.