Researchers have warned climate change will lead to extreme weather events, increase human mental health problems and internally displace more than 143 million people.
A recent study from Japan, where temperatures have increased an average of 34.07 Fahrenheit per 100 years, suggests changing temperatures due to global warming could alter the world’s proportion of male and female newborns. The findings, published in the journal Fertility and Sterility and reported on by CNN, follow the scientists’ previous work on how births are affected by extreme environmental events.
To understand the associations, researchers compared Japan’s yearly average temperature differences and extreme events to the proportion of male and female newborn births between 1968 and 2012. They also studied effects on sex ratios of spontaneous fetal deaths after 12 weeks of gestation.
At conception, scientists believe the sex ratio is equal. But during gestation, more than half of all human conceptions die, leaving a sex imbalance at birth. Due to higher female mortality, the global ratio at birth is considered to be 103-106 boys to 100 girls. The world’s sex ratio, according to 2017 data, is 102 males to 100 females.
In recent years, there have been nearly 90,000 newborns, and about 1,000 fetal deaths recorded monthly in Japan. Fetal deaths, according to researchers, involve deaths due to spontaneous abortion or miscarriage after 12 weeks of pregnancy.
Both sex ratios of fetal deaths and temperature differences have been on the rise since the 1970s, whereas the sex ratios of newborn infants have been decreasing.
The conception of boys in particular was deemed especially vulnerable to external stress, such as extreme weather events. In fact, nine months after some of Japan’s most disastrous events — the 1995 Kobe earthquake, 2011 Great East Japan earthquake and Fukushima Daichii power plant nuclear disaster — the proportion of male babies born in affected areas declined by anywhere from 6 percent to 14 percent compared to the previous year. Extreme weather events were also associated with fluctuations in birth weight.
These findings suggest extreme stress can influence gestation and alter the gender ratio of newborns, potentially leading to more boys born in areas with increasing temperatures and fewer boys in areas with more extreme environmental changes, such as drought or wildfire.
Lead researcher Misao Fukuda of the M&K Health Institute told CNN that stress due to “climate events caused by global warming” may also influence the sex ratio.
“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,” the network reported.
University of California, Berkeley professor Ray Catalano added this is because the male infant is “a relatively frail organism.”
“For every society, for every year, the human being most likely to die (prematurely) is male infants. And that’s true for every society that we have data for,” Catalano told CNN.
The National Oceanic and Atmospheric Administration labeled 2010 the hottest year on record since 1880, which rang true for Japan, as well. The summer of 2010 was the country’s hottest since 1898.
