Warmer Temperatures May Cause More Girl Births

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With the biggest temperature changes ahead of us, it can be hard to predict how climate change will affect the world. Sure, we know it will get hotter, we know the seas will rise and we know to expect more frequent extreme weather events, but nature is so complex that we will never grasp the full consequences until they're right in front of us.

That hasn't stopped scientists from trying to get ahead of the game to minimize damage or at least prepare for it. And now, a new study forewarns an unexpected effect of climate change: more girl births than boy births.

The study was carried out in Japan, where scientists observed birth ratios and set them alongside yearly temperatures from 1968 to 2012. They found that over the years, the number of baby boys born was declining compared to the number of girls.

The also found that extreme weather events, like a very hot summer in 2010 and a very cold winter in 2011, were correlated with increased miscarriages of male fetuses, while female fetuses seemed to be able to withstand the disruption.

“Male conception seems to be especially vulnerable to external stress factors, including climate changes,” reported the study.

This is not the first study to suggest that male females are more susceptible to stress. A Swedish study found that male fetuses were more prone to aborting when temperatures changed.

However, studies in New Zealand and Finland found no link between temperature and male to female birth ratios. The Japanese researchers attributed this to the fact that neither Finland nor New Zealand experience drastic temperature changes from winter to summer, like Japan does.

"The main thing to remember is that [the study in Japan] shows a correlation, which is not the same as causation," said Timothy Mitchell, from Iowa State University, who studies how temperature affects sex determination in reptiles.

Temperature changes will have a much stronger effect on reptiles than it will on humans. Many reptiles depend on temperature to determine what sex their offspring will be. For example, for painted turtles, eggs laid in cooler areas hatch as males while eggs laid in warmer areas are all-female. Warmer global temperatures might make male mates rare for female painted turtles.

But Mitchell reassured us that there may be some feasible solutions for addressing this problem, like creating artificial shade structures in turtle breeding grounds to bring down the temperature in nests. There is also little scientific knowledge about how species will adapt to warming temperatures.

"The jury is still out," added Mitchell. "Turtles went through the same thing that wiped out the dinosaurs and survived."