AI-Based Research Reveals That Extreme Temperatures Fuel Online Hate Speech

Summary: Extreme heat and extreme cold temperatures are associated with a marked rise in aggressive online behaviors, including hate speech, a new AI-based study discovered.

Source: Potsdam Institute for Climate Impact Research

Temperatures above or below a feel-good window of 12–21 degrees Celsius (54–70 °F) are linked to a marked rise in aggressive online behavior across the U.S., a new study finds.

Analyzing billions of tweets posted on the social media platform Twitter in the U.S., researchers from the Potsdam Institute for Climate Impact Research found hate speech increasing across climate zones, income groups and belief systems for temperatures too hot or too cold.

This indicates limits to adaptation to extreme temperatures, and sheds light on a yet underestimated societal impact of climate change: conflict in the digital sphere with implications for both societal cohesion and mental health.

“Detecting hate tweets in more than four billion tweets from U.S. 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 behavior when it’s either too cold or too hot outside,” states PIK scientist Annika Stechemesser, first author of the study to be published in The Lancet Planetary Health.

“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 marginalized groups,” she adds.

“We see that outside the feel-good window of 12–21°C (54–70°F) online hate increases up to 12% for colder temperatures and up to 22% for hotter temperatures across the U.S.”

The well-tempered tweet: Fewest hate tweets at 15–18 °C (59–65°F) across the U.S.

To arrive at these findings, the authors used a machine-learning approach to identify approximately 75 million English-phrased hate tweets in a data set consisting of more than 4 billion tweets posted on Twitter in the U.S. between 2014 and 2020. Subsequently, the authors analyzed how the number of hate tweets changed when local temperatures increased or decreased.

In defining hate speech, the researchers were guided by the official UN definition: Cases of discriminatory language with reference to a person or a group on the basis of their religion, ethnicity, nationality, race, color, descent, gender or other identity factor.

Across the U.S., the authors found low levels of hate tweets in a “feel-good window” of 12–21°C (54–70 °F); the minimum of hate tweets is reached for temperatures between 15 and 18°C (59–65°F).

Temperatures hotter and colder are linked to increases in hate tweets. The precise feel-good temperature window varies a little across climate zones, depending on which temperatures are common.

This shows a thermometer
The consequences of more aggressive online behavior can be severe, as hate speech has been found to have negative impacts on the mental health of online hate’s victims. Image is in the public domain

Temperatures above 30°C (86 degrees Fahrenheit) are, however, consistently linked to strong increases in online hate across all climate zones and socioeconomic differences such as income, religious beliefs or political preferences.

This points to limits of temperature adaptation capability: “Even in high-income areas where people can afford air condition[ing] 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,” says Anders Levermann, head of Complexity Science at the Potsdam Institute, researcher at the Columbia University in the U.S., and co-author of the study.

The hidden climate impact: Mental health

The consequences of more aggressive online behavior can be severe, as hate speech has been found to have negative impacts on the mental health of online hate’s victims. It can also be predictive of hate crimes in the offline world.

“For centuries, researchers have grappled with the question of how climate conditions affect human behavior and societal stability,” Leonie Wenz, working group leader at the Potsdam Institute who led the study, explains.

“Now, with ongoing climate change, it is more important than ever. Our results highlight online hate speech as a new impact channel through which climate change can affect overall societal cohesion and people’s mental health.

“So that means that curbing emissions very rapidly and drastically will not only benefit the outer world. Protecting our climate from excessive global warming is also critical to our mental health.”

About this environment and psychology research news

Author: Press Office
Source: Potsdam Institute for Climate Impact Research
Contact: Press Office – Potsdam Institute for Climate Impact Research
Image: The image is in the public domain

Original Research: Open access.
Temperature impacts on hate speech online: evidence from 4 billion geolocated tweets from the USA” by Annika Stechemesser et al. Lancet Planetary Health


Temperature impacts on hate speech online: evidence from 4 billion geolocated tweets from the USA


A link between weather and aggression in the offline world has been established across a variety of societal settings. Simultaneously, the rapid digitalisation of nearly every aspect of everyday life has led to a high frequency of interpersonal conflicts online. Hate speech online has become a prevalent problem that has been shown to aggravate mental health conditions, especially among young people and marginalised groups. We examine the effect of temperature on the occurrence of hate speech on the social media platform Twitter and interpret the results in the context of the interlinkage between climate change, human behaviour, and mental health.


In this quantitative empirical study, we used a supervised machine learning approach to identify hate speech in a dataset containing around 4 billion geolocated tweets from 773 cities across the USA between May 1, 2014 and May 1, 2020. We statistically evaluated the changes in daily hate tweets against changes in local temperature, isolating the temperature influence from confounding factors using binned panel-regression models.


The prevalence of hate tweets was lowest at moderate temperatures (12 to 21°C) and marked increases in the number of hate tweets were observed at hotter and colder temperatures, reaching up to 12·5% (95% CI 8·0–16·5) for cold temperature extremes (–6 to –3°C) and up to 22·0% (95% CI 20·5–23·5) for hot temperature extremes (42 to 45°C). Outside of the moderate temperature range, the hate tweets also increased as a proportion of total tweeting activity. The quasi-quadratic shape of the temperature–hate tweet curve was robust across varying climate zones, income quartiles, religious and political beliefs, and both city-level and state-level aggregations. However, temperature ranges with the lowest prevalence of hate tweets were centred around the local temperature mean and the magnitude of the increases in hate tweets for hot and cold temperatures varied across the climate zones.


Our results highlight hate speech online as a potential channel through which temperature alters interpersonal conflict and societal aggression. We provide empirical evidence that hot and cold temperatures can aggravate aggressive tendencies online. The prevalence of the results across climatic and socioeconomic subgroups points to limitations in the ability of humans to adapt to temperature extremes.


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