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Extreme heat during pregnancy could one day impact salaries of those fetuses

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There is plenty of research on how the rapid warming of the planet is going to have growing adverse impacts on global economies, health, food supplies and natural disasters.

A new study now suggests that as temperatures continue to rise — particularly with more and more 90-plus-degree days — more fetuses and infants will experience economic loss by age 30.

“There is a growing body of evidence that finds that shocks to the fetus and young child — whether nutritional, environmental, economic or stress-related — have long-term consequences on health, education and economic outcomes throughout the life cycle,” said Maya Rossin-Slater, an assistant professor of health research and policy at Stanford Medicine and a faculty fellow at the Stanford Institute for Economic Policy Research.

Rossin-Slater published her study Dec. 4 in the Proceedings of the National Academy of Sciences, indicating early-life exposure to extreme temperatures is linked to potential losses in human capital. Her co-authors are Adam Isen, an economist with the U.S. Department of Treasury, and Reed Walker, an assistant professor at University of California, Berkeley.

The researchers used data from the U.S. Census Bureau’s Longitudinal Employer Household Dynamic Files, which contain information on adult labor market outcomes linked to county and exact date of birth. They looked at weather in counties in 24 states on any given day, and then measured how many days with average temperatures above 90 degrees a child born on that day in that county would have experienced during gestation and during the first year of life. They then compared the earnings of individuals who were exposed to different numbers of such hot days, but who were of the same race and gender, and born in the same county and on the same day of the year (but in different years).

Each day a fetus or infant experiences 90-plus-degree temperatures, Rossin-Slater and her co-authors found that he made $30 less a year on average, or $430 over the course of his lifetime. While that may not seem like a huge loss of income, the authors point out that their study is best understood from a population-level perspective rather than from an individual one.

“There is a lot of research already showing that extreme heat has immediate effects on labor market productivity and GDP,” she said. “What we are saying is that there is another wrinkle to this — that there can be consequences many years later, on cohorts who are still in the womb.”

Most Americans today only experience one day a year that is 90 degrees or hotter. But the Climate Impact Lab has indicated that if countries continue to take only moderate action on climate change, by the end of this century there will be about 43 such days a year.

So, if you multiple a $30 annual loss a day by 43 days, you come up with an average $1,290 a year — and compounded in large populations of pregnant women in hot climates.

“Prior research shows that exposure to extreme heat in utero leads to lower birth weight and increases infant mortality,” said Rossin-Slater, who is also a core faculty member at Stanford Health Policy. She said poor fetal and infant health could impact adult earnings in three ways: cognitive impairment, poor health that causes people to miss school or work, and less non-cognitive skill development such as self-control.

“With regard to exposure to heat specifically, fetuses and infants are especially sensitive because their thermoregulatory systems are not fully developed and they have less capacity to self-regulate when their bodies are exposed to extreme temperatures,” Rossin-Slater said.

Hot Zones and Air Conditioners

The obvious questions that arise from such research: What happens to the babies of women who already live in very high temperatures? And why not just ensure that all pregnant women have air conditioners, at least in the developed world where it would be more affordable?

Women in warm zones such as parts of Africa and South Asia, as well as U.S. cities like Phoenix and Washington, D.C., shouldn’t worry too much. The loss of income is relatively little and people living in hot climates may actually adapt over time to exposure to extreme heat.

“Our study is not saying that individual people should be doing something differently to avoid exposure to extreme heat,” Rossin-Slater said. “Instead, we think we are providing additional evidence for the possible population-level consequences of climate change and the projected increase in the number of days with extreme temperatures.”

And what about those air conditioners? The cohorts in the study are actually born in the 1970s, during a period of rapid expansion in air conditioning across American households. The researchers found the earning losses went away in areas where most people got air conditioners installed.

“If we think that there is something biological going on as a result of the fetus being overheated, then it makes sense that AC, which prevents the overheating, can mitigate this negative effect,” Rossin-Slater said.

But it’s important to recognize, she said, that air conditioners come with costs, both financial from the perspective of individuals and households who can and can’t afford such systems, and environmental from the perspective of the country or planet as a whole.

“So this is not a `free’ solution and any cost-benefit calculations related to climate change should take into account this adaption response,” Rossin-Slater said. “But we ought to think about what these results imply at the global level — in many countries that are much hotter than the United States and still don’t have AC. So if we are trying to understand global inequality and the impacts of climate change on developing countries, our results suggest that climate change could play a role in perpetuating global inequality across generations.”