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…