Climate change is a public health crisis, from its impacts on air quality to wiping out the healthcare systems we need to stave off sickness. Even the air conditioning we’ll need to beat the heat is likely to make things worse.
A new study published Monday in Nature Climate Change adds to the growing list of climate-related health threats, concluding that rising temperatures are likely to cause more suicides. The study showed that the increased heat could lead to as many as 40,000 additional suicides in the US and Mexico by 2050 if global carbon emissions continue on their current trajectory.
That’s if emissions continue and if heat really causes suicide rates to spike when controlling for other factors, something at least some scientists are sceptical about because, well, suicide is complex and something we still don’t know enough about.
As far back as the 1800s, however, scientists were taking note of an uptick in suicides in the warmer months.
“We were not the first people to come up with this hypothesis,” Marshall Burke, the study’s lead author and assistant earth science professor at Stanford University, told us.
While correlation between heat and suicide is A Thing, the idea that heat directly causes suicide, which is what the authors are claiming, is a new and rather monumental claim. The paper makes this causal link without giving a mechanism for how it happens.
The researchers looked at suicide mortality in the US from 1968 to 2004, a period when there’s enough county-specific data on suicide to compare with temperature and precipitation data. For Mexico, the data includes suicide rates between 1990 and 2010.
The final analysis controlled for other factors that contribute to suicide, including seasonal stresses (such as school), gun ownership rates, regional poverty, and even news of celebrity suicides, among other things.
No matter what else was going on, though, the relationship between heat and suicide remained consistent. When temperatures rose, suicide rates would, too. It didn’t matter whether people in a place were exposed to hot temperatures more often than others. These places were statistically indistinguishable from cooler places.
And it wasn’t that the heat was hastening suicide, either. If that were the case, suicide rates would drop below normal a month after an especially hot month “because the ones who would’ve [committed suicide] in the next month did this month,” Burke explained. The study found suicide rates were average in the month following a hotter month.
He and his team then went on to use this data in 30 global climate models to estimate what suicide could look like in a future where temperatures are even higher than they are today. The number of climate models, along with the uncertainty surrounding the relationship between temperature and suicide, resulted in a wide range of about 9000 to 40,000 deaths.
Despite this solid methodology, some health researchers took issue with the causal link the study claims.
Ans Irfan, a public health professor at George Washington University who’s studied this, acknowledged in an email to us that “this study’s findings are consistent with most of the existing literature, around the globe, insofar as there is a link between increased temperatures and suicide rates”.
Given the study’s design, though, which does not include randomised control trials, Irfan cautions against calling the paper’s findings a “causal link”.
Physician Alexander Trope agrees. He’s a resident physician with the University of California at San Francisco’s Department of Psychiatry and sits on the steering committee of the Climate Psychiatry Alliance, a forum for psychiatrists to talk about the impacts climate change is having on mental health.
For a causal link, he told us he’d prefer to see experimental trials where individuals in a controlled environment can respond to heat and longitudinal studies where individual people’s mental health is tracked alongside biomarkers (such as sweat and body temperature) to see if there’s a biological response pattern.
And, well, Burke gets it. When presented with these criticisms, he said simulating these types of environments would be pretty tricky, especially with suicide.
There are “gold standards” for causal links, he noted, but the variations in weather patterns are random enough that the team feels confident in their research design to claim causation even without identifying the mechanism. And at no point do he or his co-authors suggest climate is the most important or the only factor in causing suicide.
Despite Trope and Irfan’s criticisms, they still applauded this new research as a solid first step in addressing suicide and climate change.
Like climate change, suicide is a global problem. It’s the second leading cause of death in 15- to 29-year-olds worldwide with the grand majority of deaths in medium- to low-income countries, per the World Health Organisation. And these countries did the least to cause climate change.
This study is not the end of the conversation. It’s the start of one.
“Climate change certainly won’t make it easier to live on Earth and enjoy good mental and physical health,” Trope wrote in an email.
“But if we can increase our mental health literacy about the impact that temperature changes, biodiversity decline, and general ecological degradation of our cities, towns, and counties is having on our sense of possibility and richness and ease, then we can begin to come together and can change the arc of the dire predictions this study sets forth for the future.”
If the link between temperature and suicide is physiological, as the authors suggest, that’s a possibility humans need to come to terms with. Acceptance is key when dealing with the realities around climate change, said Laura Schmidt, an environmental advocate who co-founded a grief group around climate change.
“We’ve got to come to terms with the fact that climate change is here and now,” she wrote in an email to us. “We’ve got to face the problems head-on instead of turning away.”
We can feel scared, and we can feel worried. Though not academically trained in psychology, Schmidt said ignoring those feelings can create the environment where despair, depression and eventually suicidal ideation thrive.
A 2014 commentary in Nature points to similar drivers to suicidal behaviour. According to this new study, heat can create that environment, too.
That doesn’t mean there’s no way out or that a person is powerless. Suicide is preventable. So is severe climate change. Addressing both requires change at the policy-level that’ll protect people’s health and save their lives. So will suicides actually increase come 2050 due to rising temperatures?
That is, ultimately, up to us.
If depression is affecting you or someone you know, call Lifeline on 13 11 14.