Scientists have found that extreme heat affects people’s emotions across the globe. They studied over a billion social media posts. The research showed that when temperatures climbed above 35°C, negative expressions increased. Low‑income countries showed the strongest emotional decline compared to wealthier ones.
The project, led by MIT and international teams, examined posts from X and Weibo in 157 countries. Each was rated for positivity or negativity and matched to local weather data. Poorer regions showed about three times the emotional impact measured in richer regions.
Heat and Human Behaviour
Evidence from previous decades supports this finding. Drivers are more impatient during hot days, journalists write with greater negativity, and violent crime often rises with heat. Studies in Greece revealed many murders occurred on days warmer than 25°C. Historical research shows uprisings and unrest most often erupted in the summer months. Higher suicide risk has also been noted in hotter periods.
Scientists think heat may alter brain chemicals such as serotonin or influence hormone levels associated with aggression. Yet they caution that outside factors, including poverty and stress, can amplify these effects.
Looking Ahead
Climate forecasts suggest global positivity could drop around 2.3% by 2100 as heat increases. Vulnerable groups rarely present on social media—such as children and elderly people—may face even stronger impacts.
Experts stress that adaptation strategies must address emotions as well as infrastructure. Preparing for the psychological weight of heat will be critical in a warming world.
