Social media users get hot under the collar on the warmest days

Hate-filled tweets increase by nearly 60 per cent on hot days, researchers have found, suggesting social media users may want to avoid the platforms during heatwaves.

German researchers found that extreme hot or cold weather triggered outpourings of online aggression, which peaked in Europe when temperatures reached above 30C (86F). Levels of racist tweets were lowest at temperatures between 5C to 11C (41F to 51F), but very cold days saw a 20 per cent increase, and warm days a nearly 60 per cent rise.

In the US, the feel-good window was between 12C and 21C (54F and 70F) but online hate increased up to 12 per cent for colder temperatures and up to 22 per cent when the temperature rose.

The research was based on more than four billion hateful tweets from US Twitter users, and 10million racist tweets in Europe.

Hate speech was defined as discriminatory language with reference to a person or a group on the basis of religion, ethnicity, nationality, race, colour, descent, gender or other identity factor.

“People tend to show a more aggressive online behaviour when it’s either too cold or too hot outside,” said doctoral researcher Annika Stechemesser, of the Potsdam Institute for Climate Impact Research.

“We found that both the absolute number and the share of hate tweets rise outside a climate comfort zone. Being the target of online hate speech is a serious threat to people’s mental health.

“The psychological literature tells us that online hate can aggravate mental health conditions, especially for young people and marginalised groups.”

Throughout history, weather has had a notable influence on human behaviour. The Roman philosopher Cicero observed in the first century BC that: “The minds of men do in the weather share. Dark or serene as the day’s foul or fair.” The researchers said the study showed that extreme weather impacts mood on a wide scale, and even countries with adaptations – such as air conditioning – still saw a large increase.

“There is a limit to what people can take,” said Prof Anders Levermann, head of complexity science at the Potsdam Institute. “There are likely limits of adaptation to extreme temperatures, and these are lower than those set by our mere physiological limits.”

The research was published in The Lancet Planetary Health.