Rising Temperatures and Suicide

Suicide deaths have received a lot of public and professional attention recently after the Centers for Disease Control and Prevention reported a 30 percent increase in the number of suicides in the United States between 2000 and 2016. Coincidentally, information about the link between heat and suicide was published in the July Nature Climate Change. This is information that all psychiatrists should note.

The authors of this study report that a 1 degree Celsius increase in average monthly temperature increased suicide rates 0.7 percent in the United States and 2.1 percent in Mexico. In a separate interview, the lead author—Marshall Burke of Stanford University—acknowledged the multifaceted contributions to suicide; however, this new study is remarkable and stands out from previous studies reporting linkage between heat and suicide by controlling for a multitude of confounding variables. These include gender, time of year, rural or urban residence, regional poverty and income levels, location effects such as daylight exposure, gun availability, and access to air-conditioning.

The study by Burke and colleagues is the first to look at rates in North America; other reports linking climate change and suicide have had more limited scope and have looked at rural farmers in India and in Australia.

The effects described in the Burke study hold true whether in cooler or hotter climates, and over decades, indicating that there is no adaptation to warming temperatures over time. The authors highlight the contribution of improved general health to economic development (lessened environmental exposures, greater access to air-conditioning) but find no such adaptation for the relationship between increased temperature and suicide. “Even once you control for income, you still don’t see air-conditioner use come through as a factor. Suicide is a fundamentally different animal from these other types of mortality, like cardiac mortality, that you see in the literature” said Burke in the July 23 Atlantic.

In addition to reviewing suicide data, the authors analyzed over 600 million social media communications and found an increase in depressive language and suicidal ideation correlated with increased temperatures.

Given their results, the authors made a startling projection about the future impacts of climate change and global warming. They estimated that by 2050, assuming no reduction in greenhouse gas emissions, there will be 14,020 excess suicides in the United States and 7,460 excess suicides in Mexico. These rates are comparable to the effects on suicide incidence due to economic recessions and unemployment, celebrity suicides, gun restriction laws, and suicide prevention programs, according to the report.

Although the underlying biological and physiological mechanisms remain to be elucidated, there is some speculation on the role of serotonin. Additional research is clearly needed. The authors end their article with a final call for implementing “policies to mitigate future temperature rise.”

The urgency to control climate change is clear: we must use our leverage to limit global warming and advocate for policies that protect our communities and promote mental well-being. ■