Hotter weather increases both suicide rates and the use of depressive language on social media, says a new study that analysed half a billion tweets.
The research published in the journal Nature Climate Change suggests that the effects of climate change could be as devastating as the influence of economic recessions when it comes to increasing suicide rates.
Projected temperature rise through 2050 could lead to an additional 21, 000 suicides in the US and Mexico, the findings showed.
"Surprisingly, these effects differ very little based on how rich populations are or if they are used to warm weather, " said lead researcher Marshall Burke, Assistant Professor at Stanford University.
Researchers have recognised for centuries that suicides tend to peak during warmer months.
But, many factors beyond temperature also vary seasonally - such as unemployment rates or the amount of daylight - and up to this point it has been difficult to disentangle the role of temperature from other risk factors.
To tease out the role of temperature from other factors, the researchers compared historical temperature and suicide data across thousands of US counties and Mexican municipalities over several decades.
The team also analysed the language in over half a billion Twitter updates or tweets to further determine whether hotter temperatures affect mental well - being.
They analysed, for example, whether tweets contain language such as "lonely", "trapped" or "suicidal" more often during hot spells.
The researchers found strong evidence linking warmer temperature with higher suicide rates.
To understand how future climate change might affect suicide rates, the team used projections from global climate models.
Temperature rise by 2050 could increase suicide rates by 1. 4 per cent in the US and 2. 3 per cent in Mexico.
"Hotter temperatures are clearly not the only, nor the most important, risk factor for suicide, " Burke emphasised.
"But our findings suggest that warming can have a surprisingly large impact on suicide risk, and this matters for both our understanding of mental health as well as for what we should expect as temperatures continue to warm, " Burke added.