A major international study shows that extreme heat strongly affects mood. Scientists analysed more than one billion social media posts worldwide. They observed that once temperatures passed 35°C, negative emotions increased sharply. The effect was greatest in low‑income countries, where sensitivity to climate stress was much higher.
The research team, with MIT involvement, examined posts on X and Weibo. Each message was rated for positivity or negativity, then matched to daily weather data. Results revealed negativity rose 25% in poorer regions compared to 8% in richer ones.
How Heat Shapes Behaviour
For decades, studies have pointed to links between hot weather and irritability. Drivers honk more in traffic during heatwaves, and journalists lean toward harsher wording in the heat. Crime statistics rise as well, with murders in Greece more likely on hot days. Historical uprisings around the world also peaked in summer. Hot weather has even been tied to increased suicide risk.
Scientists believe heat may disrupt serotonin levels or raise hormones connected to aggression. Still, they note that social conditions and stress can amplify these effects.
The Road Into the Future
Climate projections suggest global positivity could fall by about 2.3% by 2100 due to rising heat. Because children and older adults are underrepresented online, the actual impact could be greater.
Experts warn that adaptation must include emotional resilience alongside physical protection. Societies will need to prepare for the psychological costs of living in a hotter world.
