Researchers used artificial intelligence and machine learning to analyze more than 4 billion geolocated tweets over six years and found that, of the tweets containing hate speech, the critical variable was temperatures outside of a 54°F to 70°F comfort zone, according to a study published in The Lancet Planetary Health. On days with temperatures between 21°F to 27°F, hate tweets increased by 12.5% and on hot days between 108°F and 113°F hate tweets rose by 22%.

The findings were consistent across income, including in high-income areas where people can afford air conditioning. The findings mean “hate expressed online could increase under future global warming,” the authors found, and what happens online doesn’t stay there. “Being the target of online hate speech is a serious threat to people’s mental health,” co-author Annika Stechemesser said in a statement. “The psychological literature tells us that online hate can aggravate mental health conditions especially for young people and marginalized groups.” (TIME)