Researchers have linked hotter temperatures to a rise in suicidal thoughts and behavior in young people. The new study adds to existing evidence that rising temperatures are affecting the mental health of adult men and women, too.
There are a number of well-known risk factors linked to suicidality and suicide by young people: a recent or serious loss, such as the death of a parent; stressful life events like bullying; psychiatric illness, particularly a mood disorder like depression; trauma; and issues with substance abuse.
However, new research led by the University of New South Wales (UNSW) Sydney, has added another risk factor. It found a link between an increase in youth suicidal thoughts and behaviors and hotter temperatures.
The researchers examined 55,000 emergency department (ED) presentations for suicidality by people aged 12 to 24 across the state of New South Wales during Australia’s warmer months (November to March) between 2012 and 2019.
When they compared these data to daily mean temperature (DMT) and heatwaves, they found that youth suicidality presentation rates to ED were significantly higher on hotter days. The relationship was linear: for every 1 °C (1.8 °F) rise in DMT ED visits by young people for suicidal thoughts or behavior increased by 1.3%.
“The impact on the very first day where the temperature is hotter than usual is just as bad as each subsequent day, and the effect starts at a more moderate temperature than expected,” said Dr Cybele Dey, a psychiatrist and lecturer at UNSW Sydney and the study’s lead and corresponding author.
For example, on days with a 24-hour mean temperature of 21.9 °C (71.4 °F), which was the average DMT for the study period, there was an average of 45.7 youth suicidality presentations across the state. At that temperature, presentations were 4.7% higher than they ordinarily would’ve been at the state’s spring average DMT of a cooler 18.3 °C (64.9 °F).
When the DMT rose to 25.2 °C (77.4 °F), which is the baseline for a heatwave, presentations were around 9% higher than at the spring DMT. By the time the DMT reached the ‘extreme heat’ temperature of 30 °C (86 °F), presentations were about 15% higher.
“There was an increase in presentations on the first moderate hot day, which tells us it is more likely a biological effect, rather than a flow-on effect from factors like poor sleep,” Dey said. “The heat itself looks to be doing something to increase people’s distress and that is supported by other literature. We know that calls to mental health crisis lines go up with temperature and there are overseas studies showing a link between heat exposure and suicidality presentations, but also increased temperatures and death from suicide.”
In August 2024, research led by Curtin University found that over an almost 20-year period, around 0.5% of suicide deaths in Australia – 264 individuals – correlated with unusually higher temperatures caused by climate change. Suicides associated with heat anomalies were statistically significant among men aged 55 and over. Seasonality was a significant factor, with more deaths during spring (September to the end of November) and summer (December to the end of February).
A few months before, in April, University of Sydney-led research had found a link between higher temperatures and mental health presentations at a Sydney hospital, particularly for women, for whom the risk rose significantly at temperatures at or above 29.2 °C (84.6 °F).
The researchers in the current study said that socioeconomic disadvantage associated with poorer quality housing and air conditioner ownership and usage was a relevant consideration, as was more limited access to green spaces and waterways.
“Independent access to green space, nighttime cooling with sea breezes and your quality of housing are all important factors in determining how people can cope with heat,” said Dr Iain Perkes, psychiatrist and senior lecturer at UNSW’s School of Clinical Medicine and the study’s co-corresponding author. “We’ll need to do more research on these possible mediating factors, but that shouldn’t stop us from getting on and making sensible changes that we know work more broadly to reduce exposure to higher temperatures.”
They said that improved housing quality and giving youths access to cool environments at home and school would help better protect them from the mental health effects of higher temperatures.
“Public health messaging about heat is usually limited to heatwaves and focused on the very young and elderly,” said Dey. “But we need to be doing more to warn and protect the entire population about the impact on both their physical and mental health."
Doctors for the Environment Australia (DEA), a group of medical doctors calling for climate action to reduce health harms, has called for the urgent phasing out of fossil fuels based on the study’s findings.
"Our research shows that young Australians’ mental health suffers in the heat, and we know that climate pollution is contributing to increased extreme weather, including heat,” said DEA spokesperson James Scott, who is a professor of child and adolescent psychiatry and was a co-author on the study. “To reduce heat-related mental health harms for children and young people and reduce ED presentations, we need an urgent and rapid transition from fossil fuels to clean energy.”
Further research is needed on the link between youth mental health and heat to confirm if higher temperatures are causing the increase or simply coincidental to it.
“It’s quite staggering,” said Perkes. “While we haven’t established causality here, the type of pattern … would point to a cause-and-effect response.”
The study was published in the Australia & New Zealand Journal of Psychiatry.
Sources: UNSW Sydney, DEA