If scorching temperatures have you losing your cool, you’re not alone. New research suggests that our warming world could be behind your bad mood.
Using social media, scientists from MIT and institutions across the world tracked people’s emotions and mapped them in relation to days of extreme heat.
They analysed more than 1 billion social media posts from more than 150 countries. Their findings? Heat doesn’t just make us sweat, it makes us sour.
The study, published in the journal One Earth, revealed that when temperatures soar above 35°C, our collective mood takes a dive – especially in lower-income countries.
An ‘unprecedented window’ into human emotions
Researchers examined 1.2 billion social media posts on X (formerly known as Twitter) and Weibo from 157 countries over the span of a year. Each post was given a sentiment rating from 0.0 for very negative posts to 1.0 for very positive posts.
They then pinned each one to 2,988 locations across the globe to correlate them with the weather when they were posted.
They found that when temperatures rise over 35°C, sentiments expressed in these posts became around 25 per cent more negative in lower-income countries and 8 per cent more negative in higher-income countries.
“Social media provides us with an unprecedented window into human emotions across cultures and continents,” co-author Jianghao Wang from the Chinese Academy of Sciences said in a statement.
“This approach allows us to measure emotional impacts of climate change at a scale that traditional surveys cannot achieve, giving us real-time insights into how temperature affects human sentiment worldwide.”
The effects of heat on mood in low-income countries were triple those found in more economically robust settings. The researchers say it underscores the importance of incorporating adaptations into future climate impact projections.
Is hot weather making us angry?
This is far from the first study to link high temperatures to bad moods. Research from the 1980s found that the higher the temperature, the more likely drivers are to honk their horns. Drivers with their windows down, and presumably with no air conditioning, were even more likely to express their road rage.
Even journalists are more prone to using negative language when it’s hot, according to one study of coverage of the 2008 Beijing Olympics.
The impact on people’s mood can be much more serious than feeling grumpy in the heat, however. Swathes of research over the last 50 years have demonstrated the link between violent crime and heat.
One 2019 study revealed that more than 30 per cent of the 137 murders reported in Central and Northern Greece between 1995 and 2004 happened on days with average temperatures over 25°C.
Another paper from the 1980s saw scientists track uprisings around the world from 1791 to 1880. They found that an overwhelming majority happened in the summer months, regardless of which hemisphere they looked at. In Europe, uprisings were significantly more likely to occur in July, whereas in South America, they were more likely to happen in January.
People are also more likely to turn their anger and negative mood on themselves, with one 2018 study finding that there was a higher risk of suicide on hotter days.
As to why, there are a multitude of different theories. Some suggest that the weather may alter our brain’s biology, with Finnish scientists correlating high temperatures with levels of serotonin – an important brain chemical which regulates happiness, anxiety and our overall mood. Others suggest hot weather increases our testosterone levels, making us more aggressive.
It is important to remember, however, that most studies show a correlation between hot weather and bad moods or behaviour. This doesn’t necessarily mean these factors are directly influencing one another – numerous other factors could be involved.
Will our moods be worse in the future?
Looking to the future, researchers used long-term global climate models to estimate how rising temperatures could impact our emotional well-being by the end of the century. Even assuming that societies gradually adapt to the heat, their projections suggest a 2.3 per cent decline in global sentiment by 2100, driven by high temperatures.
“It’s clear now, with our present study adding to findings from prior studies, that weather alters sentiment on a global scale,” said co-author of the most recent study Nick Obradovich, from MIT’s Sustainable Urbanisation Lab and the Laureate Institute for Brain Research in Tulsa.
“And as weather and climates change, helping individuals become more resilient to shocks to their emotional states will be an important component of overall societal adaptation.”
The researchers acknowledge that there’s still a lot to unpack. For one, social media users don’t reflect the full population. Young children and the elderly, groups that are especially vulnerable to extreme heat, are underrepresented on platforms like X and Weibo. That means the actual emotional toll could be even higher than the study suggests.
While infrastructure can help us adapt to the physical effects of heat, the research shows that understanding and preparing for its emotional impact could be just as critical.