Does Climate Change Affect Fertility?

Let’s just say: Thank God for air-conditioning

Updated 10/03/18
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Fall may be creeping at our door, but it’s going to take us a while to get over the sweltering heat that’s plagued us the last few months. It was so hot this summer, we hallucinated that fanny packs were back in style. (Oh, wait.)

As these steamy days become more frequent—thanks, climate change—one surprising effect might alter your five-year plan to start a family. According to a new study published in the journal Demography, global warming is making it more difficult for couples to conceive.

For their analysis, the study’s authors looked at birth counts at the state-by-month level and weather data from 1931 through 2010. They discovered a number of interesting things. For example, August and September are two of the busiest months for births in the U.S., thus suggesting that people are most likely to conceive between December and January—aka, cuffing season. Additionally, they found that birth rates are lowest in northeastern states and highest in southern states, but that may be due to other factors outside of rising temperatures, including poverty rates.

Researchers also discovered that make-you-sweat temperatures—that is, 80 degrees and up—were related to a large decline in birth rates 8 to 10 months later. “The effect size,” they wrote in an explainer for The Conversation, “is largest at nine months: on average, each hot day reduces birth rates nine months later by 0.4 percent or about 1,100 births.”

It’s not just that people are turned off at the idea of getting all hot and bothered when it’s, well, hot and bothersome outside. “We find that temperature at the time of conception has no discernible effect on conceptions,” the study states. “However, we find that hot weather does indeed reduce conceptions when exposure occurs two weeks before the estimated time of conception.”

It’s possible, the study’s authors suggest, that fewer people are able to conceive because of the way heat impacts men’s reproductive health. Experimental studies on animals have found that high temperatures can slow sperm production.

Of course, an obvious solution for these fertility issues is to crank up the AC. The study’s authors recognize this, but add: “The costs of increased AC usage include greenhouse gas emissions, underscoring the fundamental dilemma in using energy-intensive technologies to adapt to climate change.” (Not to mention the fact that not all Americans can afford air conditioning.)

Meanwhile, maybe the idea of fewer babies being born into the world sounds great to you. This might particularly hit the spot if you’ve ever had to squeeze into a crowded subway during a particularly humid July morning—yuck. Fewer people, you reason, means fewer bodies doing what they do to make the earth warmer and contribute to climate change, right?

Alan Barreca, an environmental economist at the University of California, Los Angeles and the study’s lead author, disagrees. “There are much more effective ways to reduce the birth rate on the planet,” he said in a statement. “Providing women with economic opportunities and access to birth control have a much bigger effect on the birth rate.”

We like the way he thinks.

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