Dive Brief:

• An analysis of decades of historical climate and mental health data indicates that higher temperatures correlate with higher rates of suicide, according to a study in the journal Nature Climate Change.
• Analyzing data from the United States and Mexico, researchers found that suicide rates rise 0.7% in U.S. communities and 2.1% in Mexican communities for a 1-degree Celsius bump in average monthly temperature.
• The researchers project that if climate change continues without interruption at its current rate, the U.S. and Mexico combined could see 9,000 to 40,000 additional suicides by 2050.

Dive Insight:

The association between warm weather and violent crime has been well documented for decades. The correlation even has prompted police departments to alter seasonal tactics — for example, the "summer surge" crime fighting plans enacted in Baltimore and New Orleans — in addition to raising questions about whether global warming could lead to a steady increase in conflicts and violent crimes. 

The new study shows that humans also harm themselves, not just others, in warm weather. Although the correlation between temperature and suicides long has been speculated, this study is notable for its concrete evidence that shows a tie over a long period of time.

Numerous hypotheses exist for why temperature influences crime rates, with many settling on the simple fact that more people head outside of their homes in warmer weather, thus increasing the opportunity to commit crimes. That theory doesn't explain the higher incidence of suicides, though. One research-backed hypothesis that could cover both issues is that heat affects humans' release of internal chemicals, namely serotonin, that affects overall mood and anxiety, in addition to increasing impulsiveness and decreasing inhibition.

The Centers for Disease Control and Prevention (CDC) points out that many factors contribute to suicide, not just mental health conditions. "Mental health conditions are often seen as the cause of suicide, but... many people who die by suicide are not known to have a diagnosed mental health condition at the time of death," its website explains. The new temperature research supports that claim. 

The CDC estimates that 45,000 Americans take their lives annually, making it one of the leading causes of death from 1999 to 2016. Suicide rates increased in every state during that time period, with about half of the states experiencing a 30% increase. 

City governments recently have shown increased interest in tackling problems holistically, meaning taking into account mental and social factors that affect residents' well-being, and thus the well-being of the city's livelihood. For example, loneliness is becoming a more talked about and addressed concern. Many cities already have suicide mitigation programs, but it will be interesting to see if the new heat-suicide study leads additional cities to adopt such programs, or even cities with programs to alter their tactics.