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There’s a scientific reason why summer turns you into a horrible person

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Ah, summer. In theory, it’s a time of sun-kissed leisure and correspondingly sunny moods. How could one fail to be chilled out and cheerful, so this line of thinking goes, when the mornings are so pretty, the evenings are so long, and you’re spending 75% of your out-of-office hours in a pub garden?

But in reality, warm weather can bring out the worst in people. Travelling on public transport when it’s overcrowded and blisteringly hot can reduce even the most unflappable of women to a tantrum-throwing toddler – and if you’ve ever been in the office when the air con breaks on a 26°C day, you’ll know that summer isn’t all sunshine and smiles.

This slightly more sober assessment of the mid-year months is backed up by a new study from a team of US psychologists, which confirms what we’ve long suspected: summer heat can make us really unpleasant to be around.

The research, published in the European Journal of Social Psychology, concludes that we’re less likely to be helpful or “prosocial” when it’s uncomfortably hot, and more likely to be grumpy and uncooperative. In some cases, merely thinking about intense heat can be enough to make us moody.

Read more: Literary quotes to cure a bad mood

The study was led by Liuba Belkin, an associate professor at Lehigh University in Pennsylvania who specialises in organisational behaviour and emotions at work. She says that her team wanted to investigate how temperature influences our emotions.


"It's too hot in here. I'm going to punch someone."

“To our knowledge, this was the first study to establish the connection between ambient temperature and a reduction of prosocial behaviour with data,” Belkin tells Quartz.

The professor and her co-author Maryam Kouchaki, an assistant professor at Northwestern University in Illinois, used data from a large Russian retail chain to investigate how hot weather influenced people’s behaviour.

Read more: How to dress for hot weather if you hate summer clothes

The shops, which sold leather handbags and travel goods, had compiled reports from secret shoppers over the course of two summers in Moscow. In the first summer, from July to August 2010, Moscow was sweltering in a record “mega-heatwave”. In the second, from July to August 2011, the Russian city enjoyed more typical temperatures, with an average temperature of 21°C.

Air conditioning wasn’t a given in Moscow malls in 2010, meaning that many shoppers and retail workers were having to drag themselves around in temperatures of up to 38°C. After analysing the secret shopper reports, Belkin and Kouchaki concluded that shop assistants working in an uncomfortably hot environment were 50% less likely to engage in “prosocial” behaviours such as offering to help customers, listening actively, and making suggestions.

Watch: Summer Expectations vs. Reality

The researchers next conducted a survey in which they asked paid participants to recall or imagine situations where they had felt too hot. After measuring the subjects’ feelings and perceptions and asking them a number of questions, the researchers then asked if they would take part in another survey for free.

Compared to a control group, individuals who had been thinking about being warm were much less likely to volunteer to help in a second survey.

Belkin and Kouchaki concluded that imagining intense heat led people to feel more fatigued, which made them grumpier. Happier moods tend to drive more sociable, friendly behaviour, says Belkin.


Katie Holmes in First Daughter (2004). Researchers found that students were much less likely to volunteer in lectures if the room was too hot.

Finally, Belkin and her co-author asked university students to take part in an experiment to see if a slight fluctuation in temperature was enough to influence behaviour. The students were divided into two lecture theatres, one that was uncomfortably warm and one that was air conditioned. They then asked the students to fill out a survey “for a non-profit organisation that serves children and underprivileged individuals in the local community”.

Even though there was only a 15% difference in the actual temperatures, the students in the hotter room were 31% less likely to volunteer to help. Interestingly, even those individuals who did offer to help still helped much less than the students in the air conditioned room: on average, they answered only six survey questions, compared to 35 in the cooler lecture hall.

“The point of our study is that ambient temperature affects individual states that shape emotional and behavioral reactions,” says Belkin, “so people help less in an uncomfortable environment, whatever the reason they come up with to justify why they cannot do [something]”.

So there you have it: summer = moody and unhelpful. It’s science.

Images: iStock, Rex Features


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