A study published this week in Nature Climate Change suggests that climate change’s hotter temperatures might have an unintended, unforeseen effect: a veritable spike in suicide rates.
That might seem surprising, given the popular conception that winter’s dreary, perpetually gray, freezing weather is often associated with increases in depression and therefore suicide.
But data indicates that notion is far from the truth. “Even back to the 1800s, suicide rates were higher in late spring and early summer,” Marshall Burke, an assistant professor in the department of earth system science at Stanford University.
That’s odd and counterintuitive, and it inspired Burke and his colleagues to look into searching literature and data for an answer to what might seem like a simple question: Do suicide rates go up in the warmer months?
Burke and his colleagues found that, yes, in fact they do.
“What we wanted to do in this study is isolate the role of temperature from other factors”—socioeconomic, mental health, and other risk factors that could play a role in putting a person at risk of suicide ideation. So Burke and his colleagues looked at mortality data from the U.S. and Mexico dating back a few decades (they chose the U.S. and Mexico because it was the data that was most complete that they had access to).
“We looked at every single mortality event and what happens with death certificate data—where people were when they died and what they died from,” Burke said. The team lined up mortality with exposure to temperature changes, then isolated the effects of temperature on those who had died by suicide.
The results were clear: There was a definite, strong correlation between warmer temperatures and suicide risk, at least in the United States and Mexico. It was powerfully simple, yet brought forth more questions than answers. For example, Burke noted, the temperature-suicide correlation occurred regardless of socioeconomic situation.
“It affects rich and poor people alike,” Burke said. “It doesn’t depend on where you live.”
That goes against the common thinking that climate change’s future effects are going to divide people and affect them differently based on wealth; those who are more well-off can afford the housing, technology, healthcare, and insurance needed to protect oneself from the destructive forces of climate, while those who are poorer are less affected.
But when it comes to suicide and temperature, the economic effects are not so clear-cut. And it’s not just wealth; it seems that, even with adjustments for temperature differences, suicide risks universally go up with temperature increases. “In hot regions, [the thinking goes that] people are more accustomed to heat and less affected by it,” Burke said. “But it doesn’t work like that. The effect on suicide risk is the same no matter if you’re in North Dakota or Texas.
“There’s a widely shared burden of these temperature increases.”
Burke said that climate change-induced suicides are something that researchers are only starting to understand. The farmer suicides of India are an example of the clear correlation between temperature increase and suicide risk, though Burke cautions that the spate of Indian farmer suicides are economically related; in the U.S., only one or two percent of people are in the agriculture industry. “We are seeing a different mechanism here,“ Burke said. “Our data suggests that it’s less likely an economic channel than something else that would affect people.”
But how does temperature affect suicide? Burke said that link is unclear, and that psychiatry and neuroscience don’t present a clear linkage.
But there is a theory that connects temperature to a biological pathway, namely through serotonin, the neurotransmitter often involved with the regulation of human emotion, and which is often manipulated and controlled with antidepressants in those who suffer from depression and suicide ideation. Serotonin, however, is also important in regulating body temperature—which means that figuring out suicides in our climate change future could be nailed down to this single hormone—maybe.
“It’s a plausible link,” Burke said. But there’s no association in a causal pathway, and there’s definitely a need for future research before such a connection can be made.
One thing that Burke repeatedly emphasized is that the study purely looked at how temperature itself—without socioeconomics and various health determinants—could play a role in suicide rates. “None of our results suggest that other factors aren’t important; they are, in fact, quite important [in predicting suicide],” he said.
Their estimate is that, between the United States and Mexico and given the estimated range of temperature increases of 1.1 and 2.9 degrees Celsius by 2100, Burke estimated that there would be “tens of thousands of suicides.”
“By 2050, there could be 20,000 excess suicides, or suicides that would not have happened otherwise,” he said.
Burke said that the way forward is clear: looking at different countries and regions and seeing if the correlation holds, and how temperature is causing these suicide spikes. “The climate change model we talk about generates winners and losers,” he said. “Our results show that it will generate more losers than winners, unfortunately.”