Global warming will have a variety of effects on our planet, yet it may also directly impact our human biology, research suggests. Specifically, climate change could alter the proportion of male and female newborns, with more boys born in places where temperatures rise and fewer boys born in places with other environmental changes, such as drought or wildfire caused by global warming.
A recent study in Japan found a link between temperature fluctuations and a lower male-to-female sex ratio at birth, with conceptions of boys especially vulnerable to external stress factors, wrote Dr. Misao Fukuda, lead study author and founder of the M&K Health Institute in Hyogo.
Last summer, Fukuda and his colleagues published a separate study looking at births in areas hit by environmental events that caused extreme stress. They included Hyogo Prefecture after the Kobe earthquake of 1995; Tohoku after the Great East Japan Earthquake of 2011 (and subsequent nuclear disaster at the Fukushima Daichii power plant); and Kumamoto Prefecture after the 2016 earthquakes. Nine months after these disasters, the proportion of male babies born in these prefectures declined by between 6% and 14% from the previous year.
This data supports the idea that major stress affects gestation, which in turn alters the newborn sex ratio, Fukuda and his co-authors wrote. Stress stemming directly from “climate events caused by global warming” might also affect the sex ratio, Fukuda wrote in an email. Though scientists do not know how stress affects gestation, Fukuda theorizes that the vulnerability of Y-bearing sperm cells, male embryos and/or male fetuses to stress is why “subtle significant changes in sex ratios” occur.