Image courtesy Marion/Pixabay, under Creative Commons License.

There may be another, unexpected risk associated with global warming: higher rates of suicide.

For centuries, researchers have noticed that rates of violence and suicide tend to increase in the summer. In a study published in Nature Climate Change, Stanford University professors showed that temperature increases by 2050 could increase suicide rates by 1.4 percent in the United States and 2.3 percent in Mexico. These seemingly small percentages in the suicide rate are actually quite significant—about twice as large in size as the influence of economic recessions, for example—and might explain why the rate of suicide in the United States has risen dramatically over the last 15 years. In real numbers, it means an additional 21,000 suicides in the US and Mexico per year.

Interestingly, the effects in Texas are some of the highest in the country. Even after the introduction of air conditioning—which would be expected to be a counterbalance—suicide rates there have not declined over recent decades. If anything, the researchers say, the effect has grown stronger in Texas over time.

And the effect is even stronger in Mexico, lending credence to the idea of a connection between how hot it is outside and how much people want to kill themselves. The researchers got it down to a mathematical formula: Every 1-degree Celsius increase in average monthly temperature means an additional 0.7 percent increase in suicides in the United States (and an additional 2.1 percent in Mexico).

In their paper, the authors stressed that rising temperature and climate change alone should not be viewed as direct motivations for suicide. Instead, they point out that these factors may contribute to the risk of suicide by affecting the likelihood that an individual makes a suicide attempt.