Defying a longstanding tradition of honeymoons in tropical locations, as well as the existence of the entire state of Texas, a new research report out this week from the National Bureau of Economic Research claims there is a link between increasing temperatures and lower “coital frequency.”
Written in dry econometric prose, the report is sprinkled with profound insight into the possible implications of climate change on our sex lives, such as “temperature may affect time use and, in turn, impact mixing rates among potential sexual partners.”
A quick check of U.S. birth rates and temperature by state shows that, overall, there’s probably not cause for alarm:
Also, here’s India, the world’s second most populous country, where it’s usually pretty hot outside:
India's lowest fertility rate is in Tamil Nadu and Kashmir, its hottest and coldest regions. pic.twitter.com/ptExgnYpez— Eric Holthaus (@EricHolthaus) November 5, 2015
To be fair, this isn’t exactly what the researchers looked at. Instead of average temperature, they compared the frequency of unusual “hot days” (defined as warmer than 80 degrees Fahrenheit)—essentially heat waves—and the birth rate about nine months later, using 80 years of weather records and the birthdates of every American since 1931 to show a statistically significant link.
They then extrapolate that finding, using a business-as-usual climate change scenario, to project a 2.6 percent decline in the U.S. birth rate by 2100—equivalent to about 107,000 fewer births per year. But they’re very clear to state that this effect is less pronounced in places where it’s already commonly hot, like the southern United States.
The study was first reported by Bloomberg, quickly promoted by Drudge, and also enthusiastically hot-taked by Cosmopolitan, MTV, and a host of other media that don’t normally cover climate news. Maxim’s amazing headline was: “Mother Nature: Just one Giant Cock Block.” Unbelievably, New York magazine’s blurb was even better: “Global Warming Threatens Boners.”
Though conservative media seemed to (predictably) scoff at the premise that weather can affect human behavior, the study has a ring of truth. In a quick Twitter poll, I was able to replicate the scientists’ findings:
Are you more or less likely to have sex if the temperature outside is above 80°F?— Eric Holthaus (@EricHolthaus) November 3, 2015
It’s been known for decades that humans, like many other animals, have a seasonality in our birth rate that’s consistent across countries and cultures with similar climates. American babies are most likely to be born in August, though the peak is later in the year the further south you go (Washington state peaks in July and Florida peaks in October). That implies Americans have more sex in the fall and winter months. Researchers are still puzzled about exactly why this happens, but we know the effect is real. Public health experts have even proposed taking advantage of the seasonality of births to maximize the effectiveness of vaccination campaigns.
However, there are a lot of problems with thinking about climate change in this way. For one thing, the authors make almost no effort to tease out complex socioeconomic factors that contribute to seasonality in the birth rate, which other studies have found is really important. Other factors, like hormone fluctuations (yes, I’m citing an Elle magazine article as evidence here) and seasonality of sunlight, probably also play a big role.
Also, the effect the authors find is really, really small. Across 80 years of data, a single extra hot day produced a 0.4 percent decrease in the birth rate, though the researchers found a slightly higher birth rate in the 11th, 12th, and 13th month after the hot day that makes up for about one-third of that drop (presumably because couples trying to get pregnant had extra sex in the weeks following the heat wave). An additional one-third of the drop was made up for by the rise of air conditioning since the 1970s. That means the effect of hot days on the birth rate in 2015 is probably only about 0.13 percent—the researchers would probably find a bigger effect each time a new season of a popular show is released on Netflix.
Also, and most importantly, the researchers are clear that the evidence they find isn’t strong enough to prove there’s a link between it being hot outside and not so hot in the bedroom. In the authors’ own words, “this positive relationship cannot be used to infer causal effects.”
So, sleep (or don’t sleep) easy, friends. Yes, climate change will create a nightmare of impacts across vast stretches of our planet, but less sex probably isn’t one of them.