Claim: Hot Days Permanently Damage Babies

Guest essay by Eric Worrall

A new study claims exposure during early childhood to temperatures above 90F (32C) permanently damages the child’s earning potential.

Climate Change Might Lower Salaries

The more 90-degree days a fetus or infant endured, the lower his or her earnings in adulthood.

OLGA KHAZAN

Even if countries take moderate action on climate change, by the end of this century, Phoenix is expected to have an extra month of days above 95 degrees Fahrenheit, while Washington, D.C., is expected to have another three weeks of these sweltering days, as the Climate Impact Lab and New York Times reported.

A new study suggests that even days that are an average of 90 degrees Fahrenheit, or 32 Celsius, might have long-term, negative impacts on developing fetuses. The stress of the hot weather might show up as reduced human capital once those fetuses reach adulthood.

Maya Rossin-Slater, a health-policy professor at Stanford University, said she and her team wanted to understand the long-term consequences of climate change on people. For the study, published today in the Proceedings of the National Academy of Sciences, she and other researchers looked at data on births, weather, and earnings in half the states in the United States. For a given county, on a given day, they measured how many days above 90 degrees a child born that day would have experienced during gestation and during their first year of life. They then compared that person’s salary as an adult to someone born in that same county on that same day in other years.

It turned out fetuses and infants exposed to a single extra 90-plus degree day made $30 less a year, on average, or $430 less over the course of their entire lifetimes. Right now, the average American only experiences one such day a year. (This study looked at the average temperature throughout the entire day, not the highest temperature that day.) By the end of the century, there will be about 43 such days a year.

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Read more: https://www.theatlantic.com/science/archive/2017/12/hot-weather-fetuses/547406/

The abstract of the study;

Relationship between season of birth, temperature exposure, and later life wellbeing

Adam Isena, Maya Rossin-Slaterb, and Reed Walker

We study how exposure to extreme temperatures in early periods of child development is related to adult economic outcomes measured 30 y later. Our analysis uses administrative earnings records for over 12 million individuals born in the United States between 1969 and 1977, linked to fine-scale, daily weather data and location and date of birth. We calculate the length of time each individual is exposed to different temperatures in utero and in early childhood, and we estimate flexible regression models that allow for nonlinearities in the relationship between temperature and long-run outcomes. We find that an extra day with mean temperatures above 32 °C in utero and in the first year after birth is associated with a 0.1% reduction in adult annual earnings at age 30. Temperature sensitivity is evident in multiple periods of early development, ranging from the first trimester of gestation to age 6–12 mo. We observe that household air-conditioning adoption, which increased dramatically over the time period studied, mitigates nearly all of the estimated temperature sensitivity.

Read more: http://www.pnas.org/content/early/2017/11/28/1702436114.abstract

Unfortunately the full study is paywalled, but I’m concerned about the small scale of the effect the authors claim to have separated from what must be a great deal of noise.

Different states and countries at the same tropical latitude clearly have very different income levels. Singapore has a GDP per capita of $52,000 per annum. Kenya, also on the equator, has an income per capita of $1400 / annum. Ethiopia, slightly further from the equator than Kenya, has a GDP per capita of $700 / annum. Clearly birth temperature is not the only factor affecting income.

Even in the USA which is where the study authors focus their data analysis, there are significant income disparities between states with similar climates. According to Wikipedia, in 2016 California had an income of $58,619 per capita per annum. Oregon, to the North of California has an income of $50,582 – a substantial difference. Washington State, even further North, has an income of $64,454 per capita per annum. A true climate effect – going North causes both a decrease and an increase in income levels.

You wouldn’t have much of a mistake with these disparities to introduce a substantial bias into the results.

There are other more subtle biases which may have been overlooked. Cost of living tends to be substantially higher in cold climates. My personal observation is the need to pay expensive heating bills forces people in cold climates to work harder – I certainly had to work harder to cover the bills in cold months, when I lived in England.

Overheating can damage babies, you have to be very careful with babies in hot weather. But given the noisy impact of other factors on income levels, its difficult to see how that single factor could be reliably extracted from population data.

Update (EW): Tom Judd points out that all babies have already been exposed to 270 days or more of continuous 37C temperatures by the time they are born – well in excess of the 32C cited by the study authors as being the minimum temperature at which their claimed effect is detectable.