Climate Change Linked to Fewer Male Births in New Scientific Study

Discover how rising temperatures are quietly shifting human birth ratios and how seasons impact male fertility. Learn about the surprising link between climate and reproduction.

A recent scientific study reveals an unforeseen impact of climate change on human life. It shows that increasing global temperatures might affect the number of boys and girls born. Scientists from the University of Oxford examined birth records of over five million children in 33 countries across sub-Saharan Africa and India to investigate how heat influences human reproduction.

The research, led by Dr Abdel Ghany, discovered that when average temperatures exceeded 20°C, there was a slight increase in the birth of girls compared to boys. It is well established that the ratio of male to female births is not exactly equal. Globally, there are typically about 101 to 102 boys born for every 100 girls. The team aimed to determine if climate change could alter this ratio over time.

Stress During Pregnancy Due to Heat

The study found that higher temperatures were associated with a decrease in male births, but the reasons varied by region. In sub-Saharan Africa, extreme heat seemed to raise stress levels during pregnancy, possibly lowering the chances of male foetuses surviving until birth. In India, the impact was observed later in pregnancy, particularly during the second trimester. The effect was most pronounced among older mothers, those who had multiple children, and women in certain northern areas who did not have sons.

Warmer Climates

The researchers explained that sex ratios can be influenced by various factors, such as maternal health, prenatal survival, and social influences. Therefore, changes in temperature might affect both biological processes and family choices, possibly affecting future population trends. The study suggests that warmer climates could slowly influence the balance between genders in some parts of the world, although scientists emphasize that many social and medical factors also play a significant role.

Seasonal Changes

In another study, scientists from the University of Manchester looked into how the seasons affect male fertility. They examined semen samples from over 15,500 men in Denmark and Florida, two regions with very different climates. Despite the differences, both groups showed a similar pattern: sperm quality was highest in summer and lowest in winter.

Professor Allan Pacey, who was part of the team, noted that the seasonal trend was evident even in consistently warm areas, suggesting that temperature alone cannot account for these changes. Instead, biological rhythms related to daylight or seasonal cycles may also play a role in fertility.

These studies demonstrate that environmental factors, including temperature and seasonal changes, might quietly influence human reproduction in ways that scientists are only beginning to understand.