A new study published in The Lancet Planetary Health has found that temperatures above or below a “feel-good window” of 12°C to 21°C are linked to a “marked rise” in aggressive online behaviour across the US.

The study, Temperature impacts on hate speech online: evidence from 4 billion geolocated tweets from the USA, adds yet another dimension to the lesser understood and underestimated psychosocial and physiological impacts of climate change. 

The study, which analysed billions of tweets, found hate speech “increasing across climate zones, income groups and belief systems” for temperatures too hot or too cold. This, the authors explain, indicates limits to adaptation to extreme temperatures. 

Using machine learning techniques, the researchers identified 75 million “English-phrased” “hate tweets” in a dataset consisting of more than 4 billion posts on Twitter in the US between 2014 and 2020. They then analysed “how the number of hate tweets changed when local temperatures increased or decreased”.

The study used the United Nations (UN) definition of hate speech – “cases of discriminatory language with reference to a person or a group on the basis of their religion, ethnicity, nationality, race, colour, descent, gender or other identity factor”.

Annika Stechemesser, first author of the study, said in a statement that “detecting hate tweets in more than four billion tweets from US users with our AI algorithm and combining them with weather data, we found that both the absolute number and the share of hate tweets rise outside a climate comfort zone: People tend to show a more aggressive online behaviour when it’s either too cold or too hot outside.” 

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Stechemesser continued: “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.” 

She added: “We see that outside the feel-good window of 12°C to 21°C online hate increases up to 12% for colder temperatures and up to 22% for hotter temperatures across the US.”

Temperatures above 30°C were “consistently linked to strong increases in online hate across all climate zones and socioeconomic differences such as income, religious beliefs or political preferences”.

Co-author Anders Levermann, head of complexity science at the Potsdam Institute for Climate Impact Research and a researcher at Columbia University, said: “Even in high-income areas where people can afford air conditioning and other heat-mitigation options, we observe an increase in hate speech on extremely hot days. In other words: there is a limit to what people can take. Thus, there are likely limits of adaptation to extreme temperatures and these are lower than those set by our mere physiological limits.”  

The study seems to confirm another which found similar results for Europe. That study, Strong increase of racist tweets outside of climate comfort zone in Europe, provided evidence that “the amount of racist and xenophobic content posted to the social media platform Twitter is nonlinearly influenced by temperature”.

Similarly, in China, a study called A 43-Million-Person Investigation into Weather and Expressed Sentiment in a Changing Climate found, among other things, that “extreme weather worsens emotional expressions on social media. Females and individuals in poorer cities are more responsive to unpleasant temperatures.”

What about South Africa?

While a direct line between online hate speech and rising temperatures has not been drawn, the Working Group II contribution to the Intergovernmental Panel on Climate Change’s Sixth Assessment report – described as an “atlas of human suffering” by the UN Secretary-General – is illuminating in showing how increased heat can similarly influence negative social behaviours.

In chapter nine of that report – which focuses on Africa – the authors say studies indicate “high temperatures are strongly associated with poor mental health and suicide in South Africa”.

They indicate that “exposure to extreme heat directly influences emotional control, aggression and violent behaviour, escalating rates of interpersonal violence, with homicides rising by as much as 18% in South Africa when temperatures are above 30℃ compared with temperatures below 20℃”.

In yet another study, Violence in hot weather: Will climate change exacerbate rates of violence in South Africa?, the authors conclude that evidence “increasingly indicates that the propensity for interpersonal violence may increase in uncomfortably hot temperatures”.

Countries like South Africa, “which already have high levels of violence and a rapidly warming climate, may be particularly vulnerable to this underappreciated consequence of climate change”.

The news is concerning given South Africa’s projected warming as the level of global warming increases. South Africa’s Low-Emission Development Strategy 2050, tabled ahead of the COP26 climate negotiations in Glasgow at the end of 2021, said that “in unmitigated greenhouse gas emissions scenarios, warming of up to 8°C is projected over the interior of the country by the end of this century”. OBP/DM

This story first appeared in our weekly Daily Maverick 168 newspaper, which is available countrywide for R25.