For almost two centuries now, scientists have noticed a place’s suicide rate bears troubling links to the changing of the seasons and the friendliness of its climate.
In 1881, the Italian physician Enrico Morselli noted that suicide rates peak in the summer, deeming the effect “too great for it to be attributed to chance of the human will.” Two decades later, the French sociologist Emile Durkheim noticed the same effect—though he also found the suicide rate was higher in Scandinavian countries.
Even today, CDC data confirms that suicides peak in the United States in the early summer.
Now, scientists have identified one more way that climate shapes suicide—and, worryingly, they have projected that it will only become more pronounced as suicide rates rise in a rapidly warming world.
Unusually hot days cause the suicide rate to rise, according to a study published Monday in Nature Climate Change. If a month is 1 degree Celsius warmer than normal, then its suicide rate will increase by 0.7 percent in the United States and 2.1 percent in Mexico.
“It’s sort of a brutal finding,” says Marshall Burke, a professor of earth science at Stanford University and one of the authors of the paper.
The finding has anxious implications for a world whose climate is rapidly changing. The authors project that roughly 14,000 people—and as many as 26,000—could die by suicide in the United States by 2050 if humanity does not reduce its emissions of greenhouse-gas pollution.