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It’s been a hot summer for the Northern Hemisphere. Heat waves have been felt across the United States, the United Kingdom, Mexico and parts of Europe.

Now research from Stanford University has found that as the earth’s temperature increases, so will suicide rates. They have projected that by 2050, increases in temperature could lead to a further 21 thousand suicides in Mexico and the United States.  

It has long been recognized that suicide rates typically peak during the warmer months of the year. But the role of temperature in this has been hard to distinguish from other factors that may be at play such as unemployment rates and amount of daylight during warmer months.

To try and determine how significant a role temperature played in suicide rates, the researchers, led by Stanford economist Marshall Burke, examined historical data of temperature and suicides in thousands of counties and municipalities in both the United States and Mexico. The data spanned several decades.

The researchers also turned to social media to determine whether people have tendency towards suicidal thoughts or actions in warmer months. They examined the language in more than half a billion Twitter posts (tweets) during hot periods of weather to see whether they contained words like “suicide”, “lonely” or “trapped”.

They found compelling evidence that suggests an increase in hot weather leads to an increase not only in suicide rates, but also in depressive phrases and language being used on Twitter.

They found that the impacts of hot weather didn’t vary much when comparing socio economic status or whether a population was “used to” warm weather. In Texas, where it can get very hot, the researchers found the impact of temperature on suicide rates were some of the highest in the United States. Although in recent decades many homes in Texas have installed air conditioning, suicide rates have not declined. On the contrary, researchers say the impact of weather on suicide rates appear to has grown stronger as they years have gone on.

According to the Centers for Disease Control and Prevention, suicide is the tenth leading cause of death in the United States, with almost 45 thousand people dying by suicide annually. In individuals between the age of 10 and 34 suicide is the second leading cause of death and in those aged 35 to 54 it is the fourth leading cause of death.

In 2016, there were more than twice the number of suicides as homicides in the United States. The Stanford researchers say suicide rates in the United States have increased dramatically in the past 15 years.

To see how these suicide rates may change over time under the impact of climate change, the researchers used climate change projection models. They estimated that temperature increases between now and 2050 might increase suicide rates by 1.4 per cent in the United States and 2.3 per cent in Mexico.

The projected impact of temperature increases are as significant in influence on suicide rates as economic recessions (which have been found to increase the rate of suicides) and of suicide prevention programs or gun restriction laws (which have been found to decrease the rate of suicides).

The impact of a warming climate and its impact on conflict and violence has long been a subject of study. Researchers have consistently found that people are more inclined to fighting and violence when it’s hot. The researchers say these latest findings on climate suggest that heat can profoundly impact the human mind and influence how a person decides to inflict harm whether on others or on themselves as in suicide or self harm.

The researches emphasise that climate change and rising temperatures across the world should not necessarily be viewed as a direct motivator for people to commit suicide. They argue that climate change and increased temperatures could increase suicide risk by influencing the likelihood of a situation that leads to self-harm.

"Hotter temperatures are clearly not the only, nor the most important, risk factor for suicide," Burke said. "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."